RO eBook Part 15 Control Philosophy

Chapter 58 : Controls 

Here is the list of controls subject that will be addressed in this Chapter and in the following Chapters: 

Control Type Description 

Control Philosophy in the Wheastone Project 

Control philosophy for filters 

Control philosophy for UF 

Control philosophy of SWRO with Turbocharger 

Control philosophy of SWRO with PX 

Control philosophy of BWRO with VFD for RO HP pump 

Control philosophy of EDI 

Control philosophy of Calcite Bed Contactors 

Control philosophy of Carbon Filters (in Series) 

Control philosophy of Calcium Hypochlorite system 

Control philosophy of CO 2 system 

Control philosophy for Potable Water system 

General Control Philosophy 

Chapters & Appendices 

This is general discussion onn the control philosophy 

adopted in this plant. 

Refer to Chapter 59. The control philosophy is based on a 

desalination project in Mexico. 

Refer to Chapter 60. The control philosophy is based on 

the Wheatstone project in Australia. 




the above SWRO assuming we are using PX instead of 

Turbocharger. 




the Wheatstone project in Australia using CEDI from 

Ionpure/Evoqua. 











Refer to Appendix 15. This is a brief discussion 

describing PID controls, lead/lag strategy for pumps, and 

various other subjects 

Here is a description of the controls associated with the Wheatstone desalination project. Since this is a full-blown 

desalination plant that incorporates almost everything except for sludge system, it is a good example to be used to 

explain the various types of controls associated with each equipment. The plant is built mostly by Xylem in the USA 

and Xylem Australia, the engineer is BECHTEL who are also responsible for installation and commissioning, and the 

owner is Chevron. 

Links to references for the PFD and PID are shown on the website (Wheastone PID). These PFD/PID were simple 

versions done in Visio. The actual PFD/PID done in ACAD are proprietary information and will not be used in this 

document. 

Additional references are flowcharts attached to each associated chapter, and alarm list which is attached to the end 

of the documents. 

Chapter 58 Control Philosophy - General Page 1

Control Philosophy in the Wheastone Project 

The plant operates in AUTO or MANUAL mode. In MANUAL mode, operators in the centralized control room can start 

or stop any unit in the plant thru the plant’s HMI. In this mode, operators will have the flexibility to start and stop any 

unit and to alternate the operation of duty/standby units. However, if there are critical alarm conditions that inhibit 

the start of a certain unit, that unit will not start. 

In AUTO mode, the plant will be controlled by the PLC. In this mode, the start and stop cycles are normally controlled 

by liquid levels in the following tanks: 

1. UF Filtrate Tank 0T-3613A & 0T-3613B 

2. SWRO Product Tank T-3608 

3. BWRO Product Tank T-3618 

4. DEMIN Product Storage Tank T-3603 

5. Potable Water Storage Tank T-3605 

6. Utility Water Distribution Tank 

7. IAH (Inlet Air Humidifier) Storage Tank 

The entire plant is divided into separate plants that operate independently. 

1. The pretreatment plant which consist of the UF 

2. The Desalination plant which consist of the SWRO only 

3. The DEMIN plant which consists of the BWRO & EDI 

4. The potable water treatment plant 

5. The utility water treatment plant 

The set of general rules that govern the control of the equipment are: 

1. Any piece of component in any equipment must be in AUTO when operating the unit (i.e., pumps, valves, 

etc.…). Otherwise, an alarm is initiated followed by abnormal shutdown. 

2. All pump stations with Duty/Standby pumps will not alternate automatically if there is FAULT from the duty 

pump. Isolation valves for the standby pumps are normally closed. If there is FAULT from the duty pump, an 

alarm is initiated and operator must investigate the problem & clear the FAULT. If the duty pump is not able 

to operate, the standby pump will become the lead pump until the duty pump is back in service. 

3. UF trains will alternate ON & OFF at CEB which is set to be every 8 hours. Each UF train must have equal runtime 

to the maximum extent possible. For example, when the CEB cycle begins for a train A1, the PLC will 

start the train in the next order in the hierarchy table. 


Bank A1 Bank A2 Bank A3 Bank B1 Bank B2 Bank B3 

Position 1 Position 2 Position 3 Position 4 Position 5 Position 6 

Filtration 

Standby 

CEB 

Filtration 

Standby 

Filtration Span = 

1-hour 

Standby CEB Filtration 

CEBSP = 8-hours 

(Span between two CEB) 

4. SWRO trains must alternate daily. Since there are two trains, the lead and lag trains will switch based on 24- 

hour timer. 

5. The DEMIN system will not operate continuously, so the BWRO and EDI trains will alternate or switch the 

lead/lag status at every start-up & shutdown. For example, if the EDI train A ran for 6 hours in one day, EDI 

train 2 becomes the lead train and will start next when there is call for DEMIN water. 

6. Backwash of all carbon filters (De-chlorination of 1 st pass RO permeate) and IAH must be performed on a 

weekly basis (7-day timer) unless P rises above setpoint. Differential pressure increase that will trigger an 

alarm and override the timer. When the units are backwashed by differential pressure, the BW Frequency 

timer will be rest to zero. The lead unit will be backwashed first followed by the lag unit. If the differential 

pressure alarm is ON in filter A and the filter B is in backwash, the PLC will delay the BW initiation until filter B 

BW cycle is complete. 

7. Backwash of all calcite filters (Utility & Potable) must be performed on a weekly basis (7-day timer) unless P 

rises above setpoint. Differential pressure increase that will trigger an alarm and override the timer. When 

the units are backwashed by differential pressure, the BW Frequency timer will be rest to zero. Please note 

that whenever the filter requires replenishment of the calcite, the unit must be backwashed manually. 

8. For BWRO with low-TDS water, shutdown is followed by flushing of the RO unit with feedwater while the RO 

HP Pump is OFF. Typically, this is done by the LP (Low-Pressure) RO feed water pump. This cycle is called 

post-flush. In this case here, the pre-flush and the post-flush cycles are the same. The shutdown sequence 

begins with opening the Auto-Flush valve, followed by shutting down the RO HP pump, followed by closing 

the feed isolation valve after the preset time of Auto-Flush is complete, and last closing the autoflush valve. 

The flush period should be set during commissioning of the RO train. 

9. Some specifications require the BWRO to be flushed with permeate water. This is usually recommended 

when the feedwater conductivity is high or when TDS is possibly greater than 5000ppm. In this case, 

shutdown is followed by flushing of the RO unit with permeate water using a dedicated flushing pump while 

the RO HP Pump is OFF. In this case, a flushing inlet valve on the BWRO is required, a dedicated flushing 

pump is required, but flushing tank is not required. The storage tank will be used to post-flush the RO. 


10. In SWRO, the flushing system is integral to the SWRO unit. If you have one train or two trains, it is preferable 

that each RO is equipped with its own flushing tank and flushing pump. If you have multiple train, typically 

these trains will share one flushing system. When a RO train starts, it is flushed 

11. When there is no call for water, the PLC shuts-down the RO trains one at a time as the level drops in the 

storage tank (depending on how many trains are operating). 

Alarm conditions associated with equipment malfunction, or pumps and automated valves not in AUTO will not be 

discussed further in this document. In general, all these conditions will generate an alarm when units are in AUTO and 

operating under normal conditions: 

a) ON/OFF or modulating valves not in AUTO 

b) Pumps not in AUTO and not READY or RUNNING when commanded to start 

c) Any FAULT or TRIP from a pump 

d) Any feedback from limit switches indicating that valve is not in correct status 

Any alarm condition will cause the following: 

a) All alarms will be displayed on the HMI which requires action by the operator. The operator must 

ACKNOWLEDGE and RESET the alarm after investigating the problem. 

b) After any type of shutdown (abnormal or normal) on the SWRO, the SWRO train is flushed immediately. 

c) After any type of shutdown (abnormal or normal) on the BWRO, the BWRO train is flushed immediately. 


Chapter 59 : Control Philosophy – Filters 

Dual Media Filters (Small System with air Scour) 

Here is an example of filters used in a desalination project for a plant in Mexico. These sketches are for roughing filter 

followed by polishing filter (two filters in series). The Service, air scour, BW, and rinse cycle is applicable to all types of 

filters except for large filters. 

Please note that most systems do not have two filters in series which is commonly referred to as dual filtration- they 

have only one, and most small filters do not have air scour step especially in brackish water application. 

Flow Path through Dual Media Filters 

The duplex dual media filter consists of two tanks operating in series each contains two layers of media & support 

media. Seawater enters the first dual media filter (00GDB01AT101) where particulate is removed. Filtered from the 

1 st filter water enters the 2 nd dual media filter (00GDB01AT102) where escaped particle is further removed. 

Typically, dual media filters remove particles 20 µm (microns) in size or larger from the feed water. The media layers 

are arranged with the largest, least dense granules on top and the smallest, most dense media on the bottom. From 

top to bottom the two active filtration layers consist of a top layer of # 1 anthracite, and a second layer of sand. The 

last layer is simply a gravel support. 

Seawater is injected with coagulation enters the first filter 00GDB01AT101. Filtered water from 00GDB01AT101 goes 

into 2 nd filter 00GDB01AT102. The filtered water exits 00GDB01AT102 where it is injected with antiscalant & sodium 

bisulfite (Sodium Metabisulfite) chemicals. The pretreated water flows into the desalination system, which consists 

primarily of cartridge filter housings skid & SWRO, skid. 

Seawater 

Dual Media 

Filter 

00GDB01AT101 

Dual Media 

Filter 

00GDB01AT102 

To Seawater RO 

(Desalination System) 

Coagulation 

Pump 

Antiscalant 

Pump 

Sodium Bisulfite 

Pump 

Coagulation 

Seawater is injected with coagulant such as Ferric Chloride prior of entering the dual media filters. Coagulation 

typically removes suspended solids such as colloidal Silica & Colloidal Iron. The coagulant neutralizes the charges of 

colloidal materials where they eventually collapsed in the dual media filter. 

Chapter 59 Control Philosophy - Filters Page 5

Suspended 

Solids 

- 

- 

- - 

- 

- 

Particle 

- 

As you can see from the above sketch, the difference between suspended solids and particles is the following: 

• Suspended solids do not settle to the bottom of the container - particles do. 

• Suspended solids are electrically charged (typically negatively charged) – particles are neutral. 

Flow Path during Service 

During normal operation, water flows from top to bottom through each 

dual media filter. As water moves downward through the bed, particulate 

is left behind amongst the media granules. As dirt accumulates on top and 

between the sand particles, the sand is clumped together, in other words, 

dirt binds the media together. As dirt accumulates the pressure drop 

increases and the dual media filter must be backwashed to remove 

trapped particles. In this project, we provided air blower to air scour the 

filter prior to backwash. 

Sand Clumps 

Anthracite 

Sand 

Gravel 

Filter in Service 


Flow Path during Air Scour 

Air scour breaks down the clumps or dirt that binds the sand particles together. In this step, 

the water is drained to a level slightly covering the media. Afterward, the blower is turnedon 

pumping air upward through the filter. 

Air Scour 

Flow Path during Backwash 

During backwashing, the water flow is reversed. Water is forced up through the media layers, 

flowing from bottom to top. This causes the media layers to expand upwards, allowing 

particles to be swept away to drain. Because of their differing specific gravity, the layers will 

re-settle in their original configuration. 

A backwash pump is turned on pumping water from backwash tank. The makeup water for 

the backwash tank consist of concentrated seawater from SWRO reject and reject from 

brackish water RO. 

Filter in Backwash 

Flow Path during Fast Rinse 

After backwashing, a down-flow fast rinse phase compacts the media layers. During fast rinse, water flows from top 

to bottom as in service with the rinse valve open. The fast rinse purpose is the compact the bed and to re-establish 

the original bed level. In this mode, which lasts 2 – 4 minutes, all water is diverted to drain (rinse valve open). 

Most of the particles in the water are trapped in the 1 st filter. Any remaining particles will be captured in the 2 nd filter. 

Backwash initiation is accomplished by time basis only in Automatic mode or manually by operator via the PC. The 

time cycle of the service operation is preset for a period of 48 hours for the 1 st filter & 96 hours for the 2 nd filter. 


Pressure Vessel Construction 

Code: ASME Section VIII Div. 1 

18" x 14" 

Manway 

Material of Construction 

4" Flange 

Item Material Specification 

Shell: CS SA-516 Gr 70 [1] 

Heads: “ SA-516 Gr 70 

Inlet Nozzle: “ SA-106 Gr B 

Outlet Nozzle “ SA-516 Gr 70 

Manway “ SA-516 Gr 70 

External Coating: Epoxy 

Internal Lining: Rubber 

Carbon Steel 

1/4" Thick 

54" OD 

4" Flange 

2" Blind Flange 

For Media Removal 

Notes: (1) ASTM designation for Carbon Steel (CS) 

4" PVC Header with 

3/4" internals 

Design Parameters 

Parameter English Unit Metric Unit 

Design Pressure: 100 psi 6.9 bars 

Design Temperature: 120 °F 35 °C 

Accessories 

Item 

Description 

MAWP [1]: 113.13 psi 7.8 bars 

Manway 14” x 18” 

Shell Length: 60” 152.4 cm 

Lifting Lugs 

(2) per code 

Outside Diameter: 54” 137.2 cm 

Corrosion Allowance: 

None 

Type of Heads: 

Ellipsoidal 

Shell Thickness: ¼” 6.35 mm 

Head Thickness: ¼” 6.35 mm 

Overall Length: 8’- 4¼” 254.6 cm 

Dry Weight: 1,336.3 lbs. 606 kg 

Legs 

Front: Extended for face piping 

support 

Nozzle Schedule 

Baseplate 

Size 

4” x 4” x ⅝” thick plate with 1” holes 

Qty Rating Type Description 

A 4” 1 150# FFSO Service Inlet 

B 4” 1 150# Pad Service Outlet 

C 2” 1 150# Pad Media Removal 

D 2” 1 150# FFSO Vent 

Flooded Weight: 7,987 lbs. 3,622 kg 

Total Volume: 804.4 gal 3 m³ 

Filtration Surface Area: 15.4 ft² 1.43 m² 

English Unit 

Metric Unit 


SV-208 

BW Pump 235 gym @ 72’ (31 psi) 52 m³/hr @ 21.9 m (2.2 bar) 

Blower 53 SCFM @ 7 psi 90 Nm³/hr @ 483 mbar 

Feed Flowrate: 70 gpm 16 m³/hr 

Superficial Velocity: 4.5 gpm/ft² 11.2 m/hr 

BW Rate: 15.3 gpm/ft² 36.4 m/hr 

Air Scour Rate: 3.44 SCFM/ft² 63 m/hr 

Design basis for BW Pump & Blower: 

Typical BW rate: 15 to 20 gpm/ft²; Typical Air Scour rate: 3 – 4 SCFM/ft² 

00GDB01 

AA101 

00GDB01 

AA108 

00GDB01 

AA901 

00GDB01 

AA906 

00GDB01 

AT101 

00GDB01 

F-102 

AT102 

00GDB01 

AA104 

00GDB01 

AA902 

00GDB01 

AA109 

00GDB01 

AA907 

00GDB01 

AA106 

00GDB01 

AA105 

00GDB01 

AA111 

00GDB01 

AA110 

00GDB01 

AA107 

00GDB01 

AA903 

00GDB01 

AA112 

00GDB01 

AA908 

00GDB01 

AP101 

00GDB01 

AN101 

Figure 59-1: Dual Media Filters Service Cycle Sketch 

PC Screen Status: 

Operation 

Valves, AA104/AA105/AA112 /AA110 are Open 

AA912 open 

Color Status 

Red 

Red 


SV-208 

Service Cycle 

This sketch illustrates what happens when the 2 nd filter is in backwash. In this case, the 1 st filter remains in service and 

the bypass valve on the 2 nd filter opens and remain open until the backwash cycle of that filter is complete. 

00GDB01 

AA101 

00GDB01 

AA108 

00GDB01 

AA901 

00GDB01 

AA906 

00GDB01 

AT101 

00GDB01 

F-102 AT102 

00GDB01 

AA104 

00GDB01 

AA902 

00GDB01 

AA109 

00GDB01 

AA907 

00GDB01 

AA106 

00GDB01 

AA105 

00GDB01 

AA111 

00GDB01 

AA110 

00GDB01 

AA107 

00GDB01 

AA903 

00GDB01 

AA112 

00GDB01 

AA908 

00GDB01 

AP101 

00GDB01 

AN101 

Figure 59-2: Dual Media Filter AT101 Service Cycle Sketch 

PC Screen Status 

Operation 

Valve AA104 & AA105 remain open 

AA109 & AA110 close 

AA108 open 

AA912 remain open 

Color Status 

Red 

Changes to Green 

Changes to Red 

Red 


SV-208 

Drain Cycle 

Drain cycle prepares the filter for air scour. Water is drained to just about the top of the media. In this cycle, air 

enters the tank from the vent valve pushing water down where it exits from the rinse outlet valve. The time cycle is 

preset at 5 minutes, but should be adjusted by visual observation of the level in the tank during start-up. 

In the sketch below, the 1 st filter is isolated until the BW cycle is complete. Divert valve A101 diverts flow to 2 nd filter. 

00GDB01 

AA101 

00GDB01 

AA108 

00GDB01 

AA901 

00GDB01 

AA906 

00GDB01 

AT101 

F-102 

00GDB01 

AA104 

00GDB01 

AA902 

00GDB01 

AA109 

00GDB01 

AA907 

00GDB01 

AA106 

00GDB01 

AA105 

00GDB01 

AA111 

00GDB01 

AA110 

00GDB01 

AA107 

00GDB01 

AA903 

00GDB01 

AA112 

00GDB01 

AA908 

00GDB01 

AP101 

00GDB01 

AN101 

Figure 59-3: Dual Media Filter AT101 Drain Cycle Sketch 


Operation 

00GDB01AA104 & 00GDB01AA105 Closes 

00GDB01AA101/00GDB01AA109/00GDB01AA110 remain open 

00GDB01AA903 & 00GDB01AA113 open 

00GDB01AA912 remain open 

Color Status 




Red 


SV-208 

Air Scour Cycle 

During air scour, the blower turns on and the solenoid valve on the discharge line of the blower closes. Air help 

loosen up the clogged media for easier backwash. The time cycle of the air scour operation should be preset for a 

period of 5 minutes. 

00GDB01 

AA101 

00GDB01 

AA108 

00GDB01 

AA901 

00GDB01 

AA906 

00GDB01 

AT101 

00GDB01 F-102 

AT102 

00GDB01 

AA104 

00GDB01 

AA902 

00GDB01 

AA109 

00GDB01 

AA907 

00GDB01 

AA106 

00GDB01 

AA105 

00GDB01 

AA111 

00GDB01 

AA110 

00GDB01 

AA107 

00GDB01 

AA903 

00GDB01 

AA112 

00GDB01 

AA908 

00GDB01 

AP101 

00GDB01 

AN101 

Figure 59-4: Dual Media Filter AT101 Air Scour Cycle Sketch 


Operation 

Valves AA107 & AA901 open 

Valves AA101, AA109 & AA110 are open 

Blower AN101 is ON 

Solenoid Valve AA912 closes 

Color Status 


Red 




SV-208 

Fill Cycle 

Fill cycle prepares the filter for backwash. The BW inlet & BW outlet valves open filling water in the tank all the way 

up. 

00GDB01 

AA101 

00GDB01 

AA108 

00GDB01 

AA901 

00GDB01 

AA906 

00GDB01 

AT101 

00GDB01 F-102 

AT102 

00GDB01 

AA104 

00GDB01 

AA902 

00GDB01 

AA109 

00GDB01 

AA907 

00GDB01 

AA106 

00GDB01 

AA105 

00GDB01 

AA111 

00GDB01 

AA110 

00GDB01 

AA107 

00GDB01 

AA903 

00GDB01 

AA112 

00GDB01 

AA908 

00GDB01 

AP101 

00GDB01 

AN101 

Figure 59-5: Dual Media Filter AT101 Fill Cycle Sketch 


Operation 

Valves AA903 & AA901 close 


Valves AA101, AA109 & AA110 remain open 

Blower AN101 is off 

BW Pump AP101 is on 

Valve AA912 opens 

Color Status 



Red 





SV-208 

Backwash Cycle 

Backwash cycle is flow of water from bottom to top (reverse of service flow). During backwash, the media expands 

upward as water travels in this direction allowing particles that are trapped between sand media to be washed out. 

The backwash pump turns on during this cycle to provide the backwash water, which is stored in the backwash tank. 

The timing for the backwash cycle is at 10 minutes. During this cycle, it is estimated the wastewater volume to be 8.7 

m³, and the backwash pump flowrate set at 52 m³/hr. 

00GDB01 

AA101 

00GDB01 

AA108 

00GDB01 

AA901 

00GDB01 

AA906 

00GDB01 

AT101 

00GDB01 F-102 

AT102 

00GDB01 

AA104 

00GDB01 

AA902 

00GDB01 

AA109 

00GDB01 

AA907 

00GDB01 

AA106 

00GDB01 

AA105 

00GDB01 

AA111 

00GDB01 

AA110 

00GDB01 

AA107 

00GDB01 

AA903 

00GDB01 

AA112 

00GDB01 

AA908 

00GDB01 

AP101 

00GDB01 

AN101 

Figure 59-6: Dual Media Filter AT101 Backwash Cycle Sketch 


Operation 

Valves AA106 & AA902 remain open 


BW Pump AP101 is still running 

Valve AA912 remain open 

Color Status 

Red 

Red 

Red 

Red 


Rinse Cycle 

In the rinse cycle, the bed is compacted to its original position. During this cycle, the service inlet and rinse outlet 

valves open allowing water to flow from top to bottom. Unlike service mode, the water is discharged directly into the 

trenches where eventually ends up in the neutralization pit. Depending on how many trains are on-line, the flowrate 

may vary depending on pressure. The rinse cycle timer is preset at 4 minutes. The rinse wastewater is discharged 

into the trenches. 

00GDB01 

AA101 

00GDB01 

AA108 

00GDB01 

AA901 

00GDB01 

AA906 

00GDB01 

AT101 

00GDB01 F-102 

AT102 

00GDB01 

AA104 

00GDB01 

AA902 

00GDB01 

AA109 

00GDB01 

AA907 

00GDB01 

AA106 

00GDB01 

AA105 

00GDB01 

AA111 

00GDB01 

AA110 

00GDB01 

AA107 

00GDB01 

AA903 

00GDB01 

AA112 

00GDB01 

AA908 

SV-208 

00GDB01 

AP101 

00GDB01 

AN101 

Figure 59-7: Dual Media Filter AT101 Rinse Cycle Sketch 


Operation 

Valves AA106 & AA902 closes 



BW Pump AP101 stops (off) 


Color Status 



Red 

Changes to green 

Red 

Chapter 58 Control Philosophy - General Page 15

SV-208 

Service Cycle 

This sketch illustrates what happens when the 1 st filter is not in service, and the 2 nd filter is in service. In this case, the 

1 st filter is isolated and the bypass valve on the 2 nd filter opens and rem 

00GDB01 

AA101 

00GDB01 

AA108 

00GDB01 

AA901 

00GDB01 

AA906 

00GDB01 

AT101 

00GDB01 

F-102 AT102 

00GDB01 

AA104 

00GDB01 

AA902 

00GDB01 

AA109 

00GDB01 

AA907 

00GDB01 

AA106 

00GDB01 

AA105 

00GDB01 

AA111 

00GDB01 

AA110 

00GDB01 

AA107 

00GDB01 

AA903 

00GDB01 

AA112 

00GDB01 

AA908 

00GDB01 

AP101 

00GDB01 

AN101 

Figure 59-8: Dual Media Filter AT101 Service Cycle Sketch 


Operation 

Valves AA104 & AA105 close 


Valve AA108 close 


Color Status 

Green 

Red 

Green 

Red 


Backwash Cycle for the 1 st Filter 

Here is a summary of the status of each valve in the various phases of BW operation of filter 00GBD01AT101 when the 

two trains are running together. 

Cycle Duration Maximum 

Flowrate 

Volume AP101 

(BW Pump) 

AN101 

(Blower) 

SV-208 

(Solenoid Valve) 

Service 48 hrs 15.9 m³/hr OFF OFF ON 

Pause 30 sec. --- --- OFF OFF OFF 

Drain 150 sec. TBD OFF OFF ON 


Air Scour 5 min. OFF ON OFF 


Fill 150 sec. ON OFF ON 

BW 10 min. 52 m³/hr 8.7 m³ ON OFF ON 


Rinse 4 min. 15.9 m³/hr 1 m³ OFF OFF ON 


Cycle AA101 AA108 AA104 AA105 AA106 AA902 AA903 AA107 AA901 

Service X X O O X X X X X 

Pause O X X X X X X X X 

Drain O X X O X X O X O 


Air Scour O X X X X X X O O 


Fill O X X X O O X X X 

BW O X X X O O X X X 


Rinse O X O X X X O X X 


Notes: 

1. X = Closed; O = Open; BW = Backwash; TBD = To be determined 

2. The Pause cycle is inserted between each cycle to allow time for open valves to close. It is preferable that the 

valves close slowly to prevent fluid hammer. 

3. During filter 00GDB01AT101 backwash, the service inlet (00GDB01AA109) & outlet (00GDB01AA110) valves 

for 00GDB01AT102 remains open. All other valves on 00GDB01AT102 will be closed. 


Dual-Media Filters (Horizontal CS large Vessels) 

Here is the actual Backwash (BW) Sequence for large horizontal CS vessel for a project in the Middle East. BW 

initiation is set for 24-hours for example. Each filter will start when the elapsed filter timer zeroes out: When the filter 

is in filtration mode, the filtration timer start counting down from 24 hours until it reaches zero. When the BW cycle 

is complete, the filtration timer reset itself back to 24-hours. 

BW cycle must also be initiated manually or whenever the differential pressure increases above its setpoint. If the BW 

is initiated by a high differential pressure alarm or manually (thru HMI), the filtration will be rest automatically to zero. 

Each sequence in the BW cycle will have its own timer as well. Refer to the various cycles below. The BW cycle is 

aborted if there is a Fault from the BW pump or blower, or when one the valve is commanded to open or close and 

limit switch’s feedback is not received by the PLC. 

Step 0: Filter In-Service 

The backwash sequence code will remain in this step until one of the treatment unit’s backwash interlock flags goes 

true. The influent and effluent valves are open. 

Step 1: Transition 

Close influent valve. Override the In-Service filter level signal Apply the Drain Down 

Flow Rate Setpoint. Allow 60 seconds for valve travel. 

Step 2: Drain Down 

The filter is drained down through the effluent valve. The effluent valve will open if the air scour has not been 

selected as “Disabled”. Typical time duration is 1800-seconds maximum and is user adjustable. If drain down level 

has been achieved before the drain down timer expires, then the sequence advances to step 3. If the filter level does 

not drop down to drain down level within the user entered drain down time, or air scour is selected to be “Disabled” 

at the HMI, then the air scour step will be skipped and the sequence will advance to step 7. 

Step 3: Transition to Air Scour 

Close the effluent valve. 

Step 4: Air Scour 

Turn on the blower. When sufficient air pressure has been developed such that, the pressure has exceeded the 

operating setpoint, open the air scour valve. Typical time duration is 180 seconds. 

Step 5: Concurrent Air Scour /Backwash 

Open the backwash inlet valve. Set backwash flow rate to low flow rate. Modulate backwash control valve to achieve 

low flow rate. Continue with air scour. Typical time duration is 60 seconds and is operator adjustable. This time 

setting will be set such that before backwash water enters the waste troughs, air scour has ended and remaining air 

bubbles have escaped the filter to not wash media into the troughs. 

Step 6: Stopping Blower 

Close the air supply valve and keep the blower running. When the blower pressure has exceeded the high pressure 

setpoint for more than the service personnel adjustable time, turn the blower off. 

Step 7: Pre-Backwash Low Flow 


Continue with low flow rate. Typical time duration is 240 seconds and is user adjustable. 


Moving to high flow. Set backwash flow rate to high flow rate. Modulate backwash control valve to achieve high flow 

rate. Allow time for rate ramp up. Typically, 30 seconds. 

Step 9: Backwash High Flow 

Filter is backwashed at high rate. Typical time duration is 300 seconds and is user adjustable. 

Step 10: Post Backwash Low Flow 

Set backwash flow rate back to low flow rate. Modulate backwash control valve to achieve low flow rate. Typical time 

duration is 60-120 seconds and is user adjustable. 

Step 11: Bed Settle 

Close backwash modulating and inlet valve. Close waste valve. After a short delay, stop the backwash pump. Typical 

time duration is 60 seconds and is user adjustable. 

Step 12: Filter Refill 

Open influent valve. 

Refill filter to operating level. Typical time duration is 120 seconds and will be adjusted on site by service personnel. 

Step 13: Filter to Waste Time 

Open filter to waste valve. Typical time duration is 35-45 minutes. Effluent turbidity level is not examined. When the 

timer expires, advance to step 14. 


Not used, skip to step 15. 

Step 15: Return to Service 

Close filter to waste valve. Open effluent isolation valve. Unit is now In-Service 


Rapid Sand Filters 

The control scheme for Rapid Sand filter is the same as the above. If you have a dedicated turbidity instrument for 

each filter, BW cycle should be programmed to start the BW when filtration timer elapsed, or there is high differential 

pressure alarm, or there is high turbidity alarm, or manually. 

Level XMTR 

LIT 

Clarifier 

M 

Influent Valve 

Trough 

BW 

Underdrain 

Differential Head 

XMTR 

PIT 

Anthracite, 24" Depth 

Sand, 18" Depth 

Gravel 

Underdrain, 12" Depth 

Venturi 

Flowmeter 

Effluent Valve 

Modulating 

M 

AIT 

AE 

Turbidity 

Clearwell 

Air Scour 

Inlet Valve 

M 

Rinse Valve 

M 

Drain 

M 

BW Outlet 

Valve 

Drain 

Next Filter 

Blowers 

M 

Clearwell 

BW Pumps 

Venturi 

Flowmeter 

M 

Main BW 

Modulating Valve 

BW Inlet 

Valve 

Next Filter 


Chapter 60 : Control Philosophy - UF 

List of Equipment & References 

This control philosophy is based on the Wheatstone LNG plant project. In this desalination project, here are the list of 

equipment and the associated tag number: 

1. There are two filtrate tanks (FRP), each 75 m³ in capacity, connected by a DN400 pipe without any valve, 

essentially operating as one tank, 0T-3613A/B. Each tank is equipped with DP level transmitter, LIT-36700A/B. 

This tank will be chlorinated and will be subject to shock chlorination. 

2. There is UF feedwater tank provided by customer, T-3602 

3. There are (2) duty/standby UF Feed pumps, 0P-3628A/B, operating by VFD 

4. There are (2) duty/standby UF BW pumps, 0P-3629A/B, operating by VFD 

5. There are (6) UF trains, 0PK-3603-F06A (1)/F-06A (2)/F-06A (3)/F-06B (1)/F-06B (2)/F-06B (3). 

6. There are (2) duty/standby metering pumps (MP) for ferric chloride, 0P-3641A/B. Ferric chloride tank is a tote 

without any level switch. 

7. There are one MP of for each of the chemicals used for CEB: 

a. Sodium Hypochlorite MP, 0P-3645. 

b. Caustic MP, 0P-3642. 

c. Hydrochloric Acid MP, 0P-3644. 

d. All chemical tanks are a chemical tote without any level switches. 

8. Instrumentation consist of the following: 

a. Pressure transmitter located at the common feed to the UF, PIT-36656 

b. Turbidity monitors located at the inlet of the UF, AIT-36658, and another one located at the common 

effluent of UF trains, AIT-36675. 

c. There is DP level transmitter in each of the filtrate tank, LIT-36660A/B 

d. There is feed flowmeter and modulating valve on each of the UF trains 

Permissive Conditions 

In the normal operating cycle (AUTO), starting the UF pretreatment plant will be dictated by the level in the filtrate 

tanks 0T-3613A/B. When there is call for water in the filtrate tank (LAL), the Seawater UF pump 0P-3628A will start 

pumping water thru the UF trains into the tanks 0T-3613A/B. The permissive condition for starting the pumps is the 

following: 

1. Level in the UF feedwater tank T-3602. If there is enough water above the centerline of the discharge piping 

of the UF feed pumps skid, these pumps will start automatically (there is no low-level alarm). 

2. SWRO/UF Feed pumps, both 0P-3628A/B must be in AUTO and READY 

3. UF BW pumps, both 0P-3629A/B must be in AUTO and READY 

4. All UF trains must be in AUTO 

5. All metering pumps for CEB (Sodium Hypochlorite, Caustic and Acid) must be in AUTO and READY 

6. Metering pumps for ferric Chloride, must be in AUTO and READY 

7. All ON/OFF valves in each UF train are in AUTO, etc. 

Please note that all pumps have HOA selector switch in local panels which we are going to refer to as hard signal. HMI 

also HOA selector switch which we are going to refer to it as soft signal. The hard signal override the soft signal. The 

only way you can have full control of the pump on the HMI, it is when the actual selector switch in the local control 

panel is in AUTO. 

Chapter 60 Control Philosophy - UF Page 21

General Control Strategy 

When there is no demand for water in the filtrate tanks 0T-3613A/B, a high-level alarm will terminate the run signal 

for the operating UF trains. The permissive condition for starting the UF BW pumps is the level in the filtrate tank 0T- 

3613A. 

Turbidity monitors will constantly monitor the feed & filtrate quality. If feed turbidity from AIT-36658 exceeds 50 

NTU, a warning on the HMI will alarm operator to investigate the water quality problem. This will be a warning only – 

not an alarm. It is up to the operator to shut down the entire plant if the problem is not resolved within reasonable 

amount of time. These spikes may occur if there is accidental oil spill from ships or if there is red tide event. If there 

is red tide, the operator must shut down the plant. 

Effluent turbidity is typically 0.1 to 0.2 NTU Maximum. The RO should not operate at water turbidity that exceeds 1 

NTU. An alarm will shut down the plant if effluent turbidity from AIT-36675 > 1 NTU for more than 10 minutes (all 

time delays will be adjusted on the HMI). Plant operator must take notice if turbidity starts climbing above 0.5 NTU 

and take immediate action to investigate the problem. 

TMP (Trans-Membrane Pressure) must not exceed 800mbar during normal operation. Typical operating conditions 

averages between 300 to 500mbar. If TMP of any train exceeds 800mbar, the PLC will shut down the corresponding 

bank, and operator must investigate the problem. At this high TMP, the train will most likely require CIP. At the 

request of BECHTEL, we added a TMP alarm which will be set at 700mbar (Hi alarm). The 800mbar setting will be 

called Hi-Hi TMP alarm. 

The Coagulant (ferric chloride) metering pump is equipped with electronic stroke controller which receives 4-20mA 

signal in proportion to the feed flowrate to all UF. Since there is no feed flowmeter on that line, the totalized 

flowrates from the flowmeters located on each of the UF train will be used to control the ferric chloride stroke 

positioner. The metering pumps will not start until the VFD accelerate the UF feed pumps to its maximum setpoint 

(until flow is established). 

The mechanical strainers will both be operating during normal operation. When P across each strainer is greater 

than 414mbarg (6 psi), the drain valve open for 10 seconds and flushes the units at the rate of 22.7m³/hr (100 gpm). 

Hierarchy Table 

When the UF trains are in AUTO and there is a call for water, only (3) UF trains will be starting. Which UF train will 

start and which one will be on standby follows a hierarchy table. The purpose of this table is to maintain as much as 

possible equal filtration time between all (6) trains and to minimize the impact of volume losses in the filtrate tanks 

when a CEB is performed for one UF train. 

When a CEB 1 is performed, the level in the filtrate tanks will drop significantly and the time required to recover must 

be spread out to allow fast recovery of water losses. Calculations shows that the least impact will occur if the CEB 

cycles for the UF trains are spread out every 8-hours (24 hours per day/3 times a day). So, for example when train “3” 

starts CEB, train “4” (the next train in the hierarchy table) will receive a call from the PLC to start. 

The following chart illustrates the time synchronization between individual banks. This table starts at time 0 after 

commissioning of the UF plant. When there is no call for water and the UF trains stop, the position of each UF train in 

this table is saved so that when the plant re-start, the position of each UF train will continue from the last position. 




Filtration 

Standby 

CEB 

Filtration 

Standby 


1-hour 


Figure 60-1: UF Hierarchy Table 

Operating Cycles 



The following is a description of operating cycles that will be used in this project for UF the system: 

1. Filtration Cycle: each UF train will operate for 82 minutes before initiating BW (Backwash) 

2. BW Cycle: each UF train will be backwashed for 60 seconds 

3. CEB 1 Cycle: each CEB 1 will be performed every 8-hours. CEB 1 is a combination of Caustic & Sodium 

Hypochlorite. The BW counter will advance by 1 every time a BW is complete. When the counter is between 

5 & 6, and filtration time is approximately 8-hours, CEB 1 starts. CEB 1 counter will advance by one each time 

a CEB 1 is complete, and BW counter is reset to zero. Incidentally, CEB is short for Chemically Enhanced 

Backwash. 

4. CEB 2 Cycle: CEB 2 is injection of Caustic & Sodium Hypochlorite first, followed by acid. CEB 2 starts when 

counter CEB 1 is roughly 24 which correspond to once very week. When CEB 2 is complete, the CEB 1 counter 

is reset to zero. 


Filtration Cycle 

The UF modules are inside-out configuration operating in dead-end mode. Filtration time duration is set at 82 

minutes in this project. Refer Figure 60-2: UF Filtration Cycle. In this figure, valves highlighted in green color are open 

and valves highlighted in red are closed. Color scheme used throughout is the same as the one used in the HMI 

screens. 

Filtration 

(Filtration Bottom, FB) 

From UF BW 

Pumps 

XV-36674 

P 

BW 

Filtrate/BW Line 

PIT 

36671 

XV-36668 

P 

To CIP Tank 

PIT 

36672 

DN20 

AIT 

XV-36669 

P 

To CIP Tank 

Q-3605 

From UF 

Feed Pumps 

XV-36665 

P 

FV-36666 

FIT 

36666 

M 

PIT 

36673 

XV-36670 

P 

From CIP Tank 

DN50 

Drain 

Valve 

Figure 60-2: UF Filtration Cycle 

BW Cycle 

This is reversal of the filtration cycle where filtrate water using the UF BW pump is pushed from the outside of the 

fibers to the inside. This process requires a lot of water. This manufacturer uses minimum 230 LMH (230 liters/hr per 

m² of surface are of modules) as the basis for BW flowrate. Each UF bank has [32] 60-m² modules. The minimum 

flowrate required is 230 x 32 x 60 = 441,600 liter per hour or 441.6 m³/hr (1 m³ = 1,000 liters). 

BW starts after 82 minutes of filtration cycle for 40 seconds “excluding the ramp time for the UF BW pumps and 

opening/closing of valves”. 

The BW sequence of events starts by isolating the bank (closing all filtrate valves), open BW valves XV-36667 & XV- 

36669, start the BW pump, ramp the BW pump to full speed or the speed at which the flowrate is 441.6 m³/hr, stay at 

this position for 27 seconds (BWT= Backwash Top). The 2 nd step is called BWB (=Backwash Bottom), where XV-36670 

open simultaneously while XV-36669 closes. BWB cycle’s period is 13 sec. When this cycle ends, the BW pump start 

ramping down until no flow is detected, close all BW valves, and open all filtrate valves (XV-36665 & XV-36668). Refer 

to Figure 60-3: UF Backwash Top Cycle and Figure 60-4: BW Bottom Cycle. 


Backwash (BW) 

(Backwash Top, BT) 

From UF BW 

Pumps 

XV-36674 

P 

BW 


PIT 

36671 

XV-36668 

P 

To CIP Tank 

PIT 

36672 

DN20 

AIT 

XV-36669 

P 

To CIP Tank 

Q-3605 

From UF 

Feed Pumps 

XV-36665 

P 

FV-36666 

FIT 

36666 

M 

PIT 

36673 

XV-36670 

P 

From CIP Tank 

DN50 

Drain 

Valve 

Figure 60-3: UF Backwash Top Cycle 


Backwash (BW) 

(Backwash Bottom, BB) 

From UF BW 

Pumps 

XV-36674 

P 

BW 


PIT 

36671 

XV-36668 

P 

To CIP Tank 

PIT 

36672 

DN20 

AIT 

XV-36669 

P 

To CIP Tank 

Q-3605 

From UF 

Feed Pumps 

XV-36665 

P 

FV-36666 

FIT 

36666 

M 

PIT 

36673 

XV-36670 

P 

From CIP Tank 

DN50 

Drain 

Valve 

Figure 60-4: BW Bottom Cycle 

Backwash (BW) 

0T-3613A 

UF BW 

Pumps 

0P-3629A 

PIT 

36662A 

PIT 

36662B 

FIT 

36666 

M 

441.6m³/hr 

To one UF 

Train 

0P-3629B 

0P-3645 

Sodium 

Hypochlorite 

Caustic 

0P-3642 

Figure 60-5: BW System in BW Cycle 

0P-3644 

Hydrochloric 

Acid 


Note in Figure 60-5: BW System in BW Cycle above, pumps highlighted in green are ON, and pump highlighted in red 

are Ready and OFF. As mentioned before regarding the color scheme for valves, we are following the same color 

scheme as the HMI screen for pumps. 

Since each BW requires these detailed steps, we will not repeat these steps in subsequent cycles. We will simply refer 

to this step as BW @ 230LMH. The BW steps are illustrated in Figure 60-6: UF BW Steps. 

Figure 60-6: UF BW Steps 

In this multi-train UF system, there is only one backwash station and priorities must be arranged based on overall 

system demands. Signal to backwash from the individual UF trains are given at the end of each filtration cycle. 

Backwash request can be – at times – in a very close time frame, so the backwash pump may not be able to serve 

each train immediately. However, if we set the filtration span between UF trains at say half-hour to one hour, the 

cycle of BW pumps during filtration cycles will be spread out, and conflict between various requests can be minimized. 

Generally, the PLC will be programmed to implement the following rules: 

a) If there is a call for BW and the level in the tank is 2100mm, the BW is delayed until level in tank is above 

2100mm. 

b) Backwash pump will act on a first come first serve basis 

c) Filtration sequence will be extended until availability of backwash pump 

d) Soaking time CEB will be extended until availability of backwash pump 

e) Each BW requires minimum 4.9 m³ when pump operating at full speed for 40 seconds. The volume does not 

account for the volume required for acceleration time when pump is ramping up & deceleration time when 

pump is shutting down. It is extremely important that UF BW pump start/stop minimize water hammer to the 

maximum extent possible. 


CEB Cycle 

This is Chemical Enhanced Backwash where chemicals are injected using filtrate water and the UF BW pump. The CEB 

requires half of the flow of standard BW (230.4 m³/hr @ 120 LMH). In the charts published by the manufacturer, this 

is referred to as “BW @ 120LMH”. 

In CEB, chemicals are injected in the first step at reduced flowrate, followed by soaking, followed by rinse at the same 

rate as backwash (flowrate = 441.6 m³/hr). There are two (2) types of CEB: 

1) The daily CEB program that will be implemented is injection of Caustic + Sodium Hypochlorite which we are 

going to refer to it as CEB 1. After injecting & soaking of chemicals, a rinse/BW must be followed to make 

sure all chemicals are out the system. The intent of this chemical soaking is to minimize & manage the 

potential growth of biological activities within the fibers of the modules. 

2) The weekly CEB program that will be implemented is injection of Caustic + Sodium Hypochlorite followed by 

acid which we are going to refer to it as CEB 2. The intent of this weekly CEB is to remove organic matters 

first, and then remove any inorganic scale deposits such as Calcium Carbonate, Calcium Sulfate, etc. that may 

have deposited on the inside surfaces of the UF fibers. Acid cleaning alone is not as effective as the injection 

of caustic & sodium hypo first followed by acid. 

Figure 60-7: CEB 1 Cycle 


CEB 1.1 (B) & CEB 1.2 (see Figure 60-8: CEB 1 and CEB 2 Cycle below) will be set to occur once a week or twice a week. 

Figure 60-8: CEB 1 and CEB 2 Cycle 

The next figures show the actual pumps & valves status in the BW system and the UF train during CEB 1 & CEB 2. Here 

is the guide for the figures 

1) Injection of chemicals in CEB 1: Refer to Figure 60-9: BW System in CEB 1 Cycle 

2) Soaking: Refer to Figure 60-10: UF Train in Soaking Cycle 

3) Rinse: This is the same as BW. Refer to Figure 60-5: BW System in BW Cycle, Figure 60-3: UF Backwash Top 

Cycle, and 

4) Figure 60-4: BW Bottom Cycle 


CEB 1 

0T-3613A 

UF BW 

Pumps 

0P-3629A 

PIT 

36662A 

PIT 

36662B 

FIT 

36666 

M 

230.4m³/hr 

To one UF 

Train 

0P-3629B 

0P-3645 

Sodium 

Hypochlorite 

Caustic 

0P-3642 

Figure 60-9: BW System in CEB 1 Cycle 

0P-3644 

Hydrochloric 

Acid 

Soaking during CEB 

From UF BW 

Pumps 

XV-36674 

P 

BW 


PIT 

36671 

XV-36668 

P 

To CIP Tank 

PIT 

36672 

DN20 

AIT 

XV-36669 

P 

To CIP Tank 

Q-3605 

From UF 

Feed Pumps 

XV-36665 

P 

FV-36666 

FIT 

36666 

M 

PIT 

36673 

XV-36670 

P 

From CIP Tank 

DN50 

Drain 

Valve 

Figure 60-10: UF Train in Soaking Cycle 


In the soaking cycle, all valves in & out of the UF trains will be closed. 

CEB 2 

0T-3613A 

UF BW 

Pumps 

0P-3629A 

PIT 

36662A 

PIT 

36662B 

FIT 

36666 

M 

230.4m³/hr 

To one UF 

Train 

0P-3629B 

0P-3645 

Sodium 

Hypochlorite 

Caustic 

0P-3642 

Figure 60-11: UF BW System in CEB 2 Cycle 

0P-3644 

Hydrochloric 

Acid 


Here are the facts about the parameters settings and the equipment provided in this project: 

a) The SWRO requires three (3) banks to supply feedwater to the SWRO 

b) Each UF train will be producing approximately on average 107 to 110 m³/hr of filtrate. 

c) The two tanks 0T-3613A & B have total effective capacity of 134.4 m³. This is equivalent to 11 m³/m of height. 

d) The volume of waste water required for weekly CEB (CEB 2) is approximately 12 m³ of filtrate water. This will 

drop the level in the filtrate tanks by more than 1 meter. 

e) The volume of waste water required for daily CEB (CEB 1) is approximately 18 m³ of filtrate water. This will 

drop the level in the filtrate tanks by 1.6 meter. 

f) The CEB will isolate a train for at least 30 minutes - no filtrate production occurs during this time. 

g) The CEB must be performed on a specific UF train approximately every 8 hours 

h) The setting for the metering pumps for the Caustic & Sodium Hypochlorite will be set manually during 

commissioning. Manufacturer recommends that the effluent from the UF BW pump must have a target pH of 

9.8 and concentration of chlorine at 20ppm. 

i) The setting for the metering pumps for the Hydrochloric Acid will be set manually during commissioning. 

Manufacturer recommends that the effluent from the UF BW pump must have a target pH of 2.5. 

j) When CEB 1 starts on a specific train, the next train in the hierarchy table will be placed in service 

immediately. 

k) Each CEB program must be provided with an individual counter in the control program to keep track of the 

completed operating cycles. This enables the operator to define the CEB schedule by using the settings in the 

user interface to stipulate that the CEB should be performed after the completion of a certain number of 

operating cycles (freely adjustable set point value). Once the CEB has been initiated, the corresponding 

counter is set back to zero. 

l) If the level in the tank is at setpoint or anywhere between 4500 & 4750mm, and there is a call for CEB on any 

train, a complete CEB will be performed. 

m) If at any moment, a UF train is taking off-line for maintenance, the position of that train will be moved to the 

last position in the hierarchy table above 


PLC Controls 

Each UF train will have the following major controls: 

1. PLC AUTO: The PLC is controlling the UF trains per the hierarchy table. 

2. PLC MANUAL: When the train is in manual, the following controls will be available to advance each cycle in 

the UF train: 

a. PLC FILTRATE: The train will be placed in filtrate. 

b. PLC STANDBY: The train will be taking off line. 

c. PLC BW: The train will be backwashed. 

d. PLC CEB1: A CEB 1 is performed on the unit. During commissioning when you are filling the tank, you 

can adjust the time of CEB 1 to 18-hours after filtration. 

e. PLC CEB2: A CEB 2 is performed on the unit. During commissioning when you are filling the tank, you 

can adjust the time of CEB 2 to once or twice a week. 

3. PLC OFF: Same as PLC STANDBY. 

4. ACK/ALARM: Acknowledge an alarm if it occurs. 

In AUTO mode, the UF trains will be controlled by the level in the storage tank 0T-3613A. The PLC will control the 

operation of each UF train (Filtration, BW, CEB) per the hierarchy table. The following conditions must be met: 

1. All SWRO/UF feed pumps and UF BW Pumps must be in AUTO & READY. 

2. All valves on the UF banks must be in AUTO and in the correct position. 

3. All permissive conditions to operate SWRO/UF feed pumps and UF BW Pumps must be met 

4. The PLC will adjust speed of the SWRO/UF Feed pumps to maintain level within different level set points in 

the filtrate tank 0T-3613A using proportional control and if needs be integral control as well. 

5. The PLC will adjust speed SWRO/UF Feed pumps to maintain constant pressure (PIT-36656) in the main feed 

header to all UF banks. A constant pressure will eliminate the continuous hunting for the right position of 

feed control valve FT-36666 in each bank. It will also allow better equal distribution of flow into each bank. 

In MANUAL or HAND, the plant operator can control each bank manually. In MANUAL mode, the bank will operate 

regardless of the level in the filtrate tank level downstream. UF banks however will not start in any mode, MANUAL 

or AUTO, under the following conditions: 

1. If there is Fault or Trip alarm from SWRO UF Feed & UF BW pump 

2. If there is low-level alarm in tank T-3602 

3. If there is not enough pressure in the feed header to all UF Trains (< 0.5 barg), PIT-36656 

4. If there is excessive pressure in the feed header to all UF Trains (> 5 barg), PIT-36656 

In OFF, the UF train is isolated. OFF is mainly provided to allow maintenance on the UF unit. 

Please note that CIP is only done when the UF bank is in OFF cycle. CIP requires filling the CIP tank with unchlorinated 

permeate water, starting the heater only if water is cold (< 20ºC), mixing the chemicals to the right pH, 

and recirculating the solution thru the CIP tank until the right pH and temperature is achieved. Temperature of CIP 

chemicals is not critical for UF in comparison with RO. 


Alarm Conditions 

The most important two alarm points in the UF are the effluent turbidity & the TMP. Since the UF is feeding the 

SWRO, turbidity of water must meet RO membranes turbidity constraints, specifically, turbidity should be less than 1 

NTU. 

It is important to indicate that SDI is much better parameter to measure than turbidity. The UF in general will 

produce water between 0.1 & 0.2 NTU. 

If this turbidity increases to 0.5 NTU for example, operator must take measures to check the turbidity instrument 

calibration and verify that reading with portable unit, and must check if SDI value have changed from previous values. 

The 2 nd most important alarm point is high TMP. High trans-membrane pressure up to 800mbarg means that the BW 

scheduled as part of the regular cleaning and the daily CEB that followed are not able to restore the modules back to 

previous performance. 

Although this may never occur, in the events of a Red Tide event or there is an oil spill from shipping lanes, the feed 

turbidity will increase abruptly & the PLC will initiate a warning to operator to stop the UF process entirely. The UF 

modules are rated for maximum feed turbidity of 50 NTU. 

Level alarm points are simply process alarm points and are not listed in this section. 

Table 60-1: UF Standard Operating Cycles 

Process Frequency Duration 

Flowrate 

(m³/hr) 

Comments 

Filtration 82 minutes 82 min. ≈ 330 Average is 105 m³/hr per bank 

BW Every 82 minutes 40 sec. 441.6 

CEB 1 See below Consists of CEB 1.1 (B) 

Chemical Injection 60 sec. 230.4 Caustic + Sodium Hypo 

CEB 1.1 (B) Soaking 10 min. 0 

Rinse 60 sec. 441.6 

CEB 2 

Consists of CEB 1.1 (B) above + 

CEB 1.2 (see below) 

Chemical Injection 60 sec. 230.4 Hydrochloric Acid 

CEB 1.2 

Soaking 15 min. 0 

Rinse 60 sec. 441.6 

~29 min 


UF System 

Control Philosophy Charts 

BECHTEL P.O. No.: 

Project Name: 

Wheastone LNG Plant 

Onslow, Australia 

25657-540-POA-MWRO-00001 

DESCRIPTION 

Control Philosophy 

UF System 

DRAWN By: 

APPROVED BY: 

REV: 

Sam Shaheen 

REVISED 

PAGE 

3/8/2016 

1 OF 4

Automatic Normal START/STOP of UF Trains 

Operator push 

MANUAL/START 

button 

Low-Level alarms in 

0T-3613A or B 

Operator push 

MANUAL/STOP 

button 

High-Level alarms in 

0T-3613A or B 

Check if all UF 

Trains are in 

AUTO? 

Step 1 

No 

Show Alarm on 

HMI/PCS 

Stop UF Feed Pump 0P- 

3628A, and Stop Ferric 

Chloride MP 0P-3641A 

Yes 

Close Inlet Valves 

XV-36654 

Check if duty UF 

Feed Pump 0P- 

3628A in AUTO? 

Step 2 

No 

Abort Start-Up 

Close Outlet Valves 

XV-36668 

Yes 

Is duty Ferric 

Chloride pump in 

AUTO? 

Step 3 

No 


Yes 

Is there Low Level 

alarm in T-3602? 

Step 4 

Yes 


No 

Position valves on 

the UF Trains for 

Service 

Step 5 

Start UF Feed Pump 

0P-3628A 

Step 6 

Start Ferric Chloride 

Pump 0P-3641A 

Step 7 


Project Name: 




DESCRIPTION 


Automatic Start-up & Shutdown 

of UF Trains 

DRAWN By: 


REV: 

Sam Shaheen 

REVISED 

PAGE 

3/8/2016 

2 OF 4


Description of Steps 1 & 5: 

- Check if UF trains are in AUTO and all corresponding valves on each train are in AUTO 

- Each UF train will start according to its last position in the hierarchy table shown below (Figure 1) 

- Figure 1 shows the hierarchy table and the position of each UF train at time 0 (during commissioning). 

- Only (3) Trains will be running at all times. 

- Only one train will be backwashed at any time. If there is call for Backwash for any other train while the BW 

pump is running, BW will be delayed until BW of the 1 st train is complete. 

FIGURE 1 



Filtration 

Standby 

CEB 

Filtration 

Standby 


1-hour 




SETTING: 

Filtration Cycle between BW: 82 minutes 

BW: 1 minute approximately after filtration cycle 

CEB1 is set every approximately 8 hours 

CEB1 = CEB 1.1(B) as designated by UF manufacturer, Caustic + Sodium Hypo 

CEB2 = CEB 1.2 as designated by UF manufacturer, Hydrochloric Acid 

CEB1.2 will be conducted after so many CEB1.1 (possibly every week). The counter that tracks the No. of CEB1 {CEB1.1(B)} 

after which CEB1.2 should be conducted, will be adjustable in the field during commissioning. When CEB1.2 is applied, it will 

be applied in conjunction with CEB1.1(B). 

CEB1 will be reset to Zero when CEB2 is completed. 


Project Name: 




DESCRIPTION 



UF Trains 

DRAWN By: 


REV: 

Sam Shaheen 

REVISED 

PAGE 

3/8/2016 

3 OF 4

Filtration Cycle for one Train Only 

Service Cycle 

Followed by 

BW Cycle 

Cycle# 1 

CEB1 

Counter = 1 

Service Cycle 

Followed by 

BW Cycle 

Cycle# ? 

Service Cycle 

Duration = 82 min. 

Service Cycle 

Followed by 

BW Cycle 

Cycle# 2 

BW Cycle 

Duration = 1 min. 

CEB1 

Counter = 2 

Service Cycle 

Followed by 

BW Cycle 

Cycle# 3 

CEB1 

Counter = 3 

Service Cycle 

Followed by 

BW Cycle 

Cycle# 4 

Place this train on 

Stanby 

CEB1 

Counter = 4 

Service Cycle 

Followed by 

BW Cycle 

Cycle# 5 

Start the next train 

in the hierarchy 

table 

CEB1 

Counter = 5 

Service Cycle 

No BW 

Cycle# 6 

CEB1 

Counter = 6 

CEB 1.1 (B) 

(NaOH + NaOCl) 

Soaking/Rinse 

CEB 1.2 (Acid) 

Every Week Only 

Soaking/Rinse 


Project Name: 




DESCRIPTION 


Filtration Cycle 

UF System 

DRAWN By: 


REV: 

Sam Shaheen 

REVISED 

PAGE 

3/8/2016 

4 OF 4

Chapter 61 : Control Philosophy of SWRO with Turbocharger 




1. There are two filtrate tanks (FRP), each 75 m³ in capacity, connected by a DN400 pipe without any valve, 

essentially operating as one tank, 0T-3613A/B. Each tank is equipped with DP level transmitter, LIT-36700A/B. 

This tank will be chlorinated and will be subject to shock chlorination. 

2. There is SWRO permeate water tank, T-3608 

3. There are (2) duty/standby SWRO LP pumps, 0P-3631A/B, operating by VFD 

4. There are (2) duty/standby Cartridge Filter Housings 

5. There are (2) duty/standby SWRO trains, 0PK-3603-F02A/F02B. Each SWRO train has a dedicated SWRO HP 

Pump, 0P-3630A or B, which are not mounted on the skid. These pumps have 500KW medium voltage (MV) 

6.6kVA motors driven by MV VFDs. Each SWRO train is also equipped with a Turbocharger equipped with 

modulating AUX valve. 

6. There are (2) sets of duty/standby MP (Metering Pumps) for each of the following chemicals: 

a. Antiscalant MP, 0P-3618A/B. 

b. Hydrochloric Acid MP, 0P-3616A/B. 

c. Biocide MP, 0P-3619A/B. 

d. Sodium Bisulfite MP, 0P-3617A/B. 

e. All chemical tanks are a chemical tote without any level switches. 

7. SWRO Flushing system to consist of flushing pump 0P-3615 and flushing tank 0T-3624. 

8. There are a lot of instrumentation and valves, but we are going to mention only the ORP instrument and the 

feed dump valve that will dump the feed flow to the SWRO in case there is high ORP alarm 


In the normal operating cycle (AUTO), starting one SWRO train plant will be dictated by the level in the SWRO 

permeate storage tank T-3608. When there is call for water in this tank (LAL), the SWRO LP pump 0P-3631A will start 

pumping water thru the cartridge Filter Housings, and SWRO train (pre-flushing). The permissive condition for 

starting the pump is the following: 

1. Level in the UF Filtrate tanks 0T-3613A/B. If there is enough water above the centerline of the discharge 

piping of the SWRO LP pump skid, the duty pump will start automatically (there is no low-level alarm). 

2. SWRO LP pump, 0P-3631A/B must be in AUTO and READY 

3. SWRO HP Pumps, both 0P-3630A/B must be in AUTO and READY 

4. In this project, there is no intention of pumping acid or antiscalant, so a provision is made in the HMI so that 

these pumps will be interlocked with the SWRO HP Pump if it is deemed necessary. 

5. Sodium Bisulfite MP must be in AUTO and READY 

6. Flushing pump must be in AUTO and READY 

7. All ON/OFF valves in each UF train are in AUTO 

8. Turbo modulating valve is in AUTO and READY 





Chapter 61 Control Philosophy of SWRO w/ Turbo Page 35


Here is a summary of the most important control strategies that are incorporated in the control of the SWRO are the 

following: 

In PLC AUTO mode, the RO train will be controlled by the rise or fall of water level in the storage tank T-3608. START 

and STOP of the RO train is controlled specifically by the DP type level transmitter in this storage tank. 

In HAND, the RO start-up is initiated by the plant operator manually regardless of the level in the permeate water 

storage tank downstream. Once you switched the SYSTEM to HAND, you must start every pump manually by 

switching the corresponding soft HOA selector switches to HAND. RO train however will not start in any mode, HAND 


1. If there is Fault or Trip alarm from SWRO HP pump 

2. If there is low-level alarm in the filtrate storage tank 0T-3613B 

3. If there is low-pressure alarm due to low-pressure in the suction line of the SWRO HP pump 

4. If ORP alarm is present 

In PLC OFF, the SWRO HP pump shuts down and the RO is isolated. OFF is mainly reserved to allow maintenance on 

the RO unit. Please note that CIP is only done when the SWRO is in OFF cycle. CIP requires filling the CIP tank with 

un-chlorinated permeate water, start the heater, mixing the chemicals to the right pH, and recirculating warm 

solution thru the CIP tank until the right pH and temperature is achieved. 

There are two types of Shutdown: Normal and Abnormal. Any type of shutdown (normal or abnormal caused by 

alarm condition) will be followed immediately by flushing cycle. When a unit shut down, all chemical metering pumps 

associated with SWRO will stop (Scale Inhibitor, Sodium Bisulfite, Calcium Hypochlorite for permeate, etc.). 

Flushing system is an integral part of the SWRO equipment. It is critical that SWRO will be flushed immediately after 

shut-down (Normal or Abnormal) – This will be referred to as Post-Flush. The post-flush’s cycle will flush out the 

highly-concentrated seawater from the piping which can cause severe corrosion due to the extremely high chloride 

content. This seawater is 1.7 times more concentrated than the raw seawater coming in to the SWRO. 

The SWRO will also be flushed on Start-up – This will be referred to as Pre-Flush. The pre-flush’s cycle will flush out 

standing water in the pipe. Still (non-moving) seawater is always subjected to attack by micro-algae’s and other 

species that may have escaped pre-treatment. The pre-flush’s cycle is approximately 5-minutes. 

Flushing tank must always be full. When there is flush and the lagging SWRO starts, it will fill the flush tank 0T-3614 

first by opening valve XV-36889, before diverting back to the permeate line or before opening valve XV-36884. 

Upon start-up, the VFD will ramp up the speed of the RO HP Pump at a rate of 1 barg per second to avoid slamming 

the membranes against the reject end of the housing. 

The SWRO HP Pump is controlled by the PLC to maintain constant permeate flowrate. The VFD controls the speed of 

the pump in proportion to permeate flowrate. Changes in flowrate occurs because either the temperature have 

changed, the feedwater quality have changed (usually seasonal), and because of fouling (with time). 

The sodium bisulfite is injected continuously to maintain ORP below the Hi-limit set-point which will be determined in 

the field. This is usually anywhere between 240 to 300mV (milli-Volt). If the sodium bisulfite will not drop the ORP 

value to less than the Hi set-point, an alarm is initiated and the feed dump valve (XV-36871) open to divert the entire 

feed back to 0T-3613A. 

Cartridge filter housing differential pressure alarm will not shutdown the plant. If this value is above 1 barg, a warning 

will be shown on the HMI to alarm operator to schedule a time to change the cartridges. The plant should not rely on 


this instrument however. After start-up, operators should establish a period for changing out cartridges every “x” 

months to prevent build-up of high P. We cannot emphasis the importance of cartridges in the operation of 

desalination plant. These cartridges are the final protection for the RO especially when overdosing ferric chloride or 

the reaction of ferric chloride with antiscalants if they are used. 

The Energy Recovery Device is equipped with modulating valve (FV-36888). This valve will operate based on brine 

flow. With time, the membranes start to foul and thus require more pressure to produce the same amount of water 

of 122 m³/hr. This valve will increase brine flow to provide more boost pressure. 

Before the SWRO start producing permeate water, it must fill the flushing 0T-3624 tank first. Whenever the PLC 

detects level below high-level setting (1480mm), it will open valve XV-36889 until high-level in flushing tank is 

detected. The permeate isolation valve XV-36884 will open and XV-36889 will close after the tank is full of water. 

Flushing time will reset during start-up. The first time the unit is flushed, it will be monitored to check how long it will 

take for the conductivity of the reject to reach the same as the conductivity of the incoming flushing water. Volume 

of flushing water requirement is dependent on the size of the RO or the volume required filling all components within 

the unit (piping, pressure vessels, pumps, etc.…). 

Permeate Dump 

Valve 

(Open) 

Flushing Water 

Flushing Inlet 

Valve 

(Open) 

150 m³/hr 

RO HP 

Pump 

Turbo Bypass 

Valve 

Permeate 

Isolation 

Valve 

(Closed) 

Filtered Water 

Feed Isolation 

Valve 

(Closed) 

Turbocharger 


Operational Modes 

Table 61-1: Summary of Operational Conditions for the SWRO 

Condition/Alarm 

SWRO Automatic Start 

SWRO Automatic Stop 

Alternation of SWRO train 

SWRO Operational modes 

Types of Shutdown 

Flushing 

POST-FLUSHING Cycle 

PRE-FLUSHING Cycle 

Description 

When there is call for water in tank T-3608 (or when level is below “Lo” preset alarm 

setting), the duty SWRO train will start. 

When there is no call for water in tank T-3608 and the level has reached the Hi level 

setting, the SWRO train will stop. 

The SWRO train duty/standby will alternate every 24-hours If SWRO train A has 

been running for example for 20-hours the previous day, SWRO train B will become 

the duty train & train A becomes the standby train. 

SERVICE 

STANDBY 

PRE-FLUSH 

POST-FLUSH 

Type I Shutdown: This is an emergency shutdown due to process alarms which would 

cause significant damage to the membrane system if the process could shutdown 

normally. 

Type II Shutdown: This is a normal shutdown initiated by the operator or caused by 

alarms that would not cause damage to the process if the normal shutdown steps 

could occur. 

When SWRO starts, it will go into PRE-FLUSH cycle before it is placed in SERVICE. 

When SWRO shuts down, it will go into POST-FLUSH cycle before it is placed in 

STANDBY. 

This is SWRO permeate water flushing using flushing pump 0P-3615 while SWRO HP 

Pump 0P-3630 is OFF. 

This is filtrate water flush using SWRO LP pump 0P-3631 to flush the RO while the 

SWRO HP Pump 0P-3630 is OFF. 

The flushing pump will push SWRO permeate water thru the RO. The PLC commands the following pumps & valves 

per the steps below: 

1. SWRO HP Pump shuts down 

2. SWRO LP Pump shuts down 

3. Flushing inlet valve open, XV-36876 

4. Feed isolation valve closes, XV-36875 

5. Turbo bypass valve on the reject line open, XV-36887 

6. Permeate dump valve opens, XV-36883 

7. Permeate isolation valve closes, XV-36884 


Alarms 

Here is the list of major alarms related to the SWRO: 

Table 61-2: List of Alarms 


FAL-36886 

SWRO Reject Low Flow 

Alarm 

PY-36886 

Low Pressure Alarm 

PAH-36813 

High Membrane Feed 

Pressure Alarm 

AAH-36870 High ORP 

Alarm 

AAH-36882 

SWRO High Permeate 

Conductivity Alarm 

SWRO High Recovery Alarm 

FAH-36880 

SWRO High Permeate Flow 

Alarm 

PDAH-36867A 

High P Alarm, 0F-3603A 

PDAH-36867B 

High P Alarm, 0F-3603B 

LAL-36700 

Low level alarm in Flushing 

tank 0T-3624 

XA-36876 

XA-36949 

Description 

If reject flow drops to 76 m³/hr while SWRO is in SERVICE (i.e., operator closing a 

valve on the reject line, the SWRO will shut down immediately, and an alarm is 

initiated. This condition will damage the membranes. THIS IS A CRITICAL ALARM. 

This is calculated value (PI36681 – PDI368867) which monitors the suction pressure 

for the SWRO HP Pump 0P-3630. If pressure is less than 2 barg, stop SWRO train 

after time delay (3-5 sec.). Starving the pump will cause cavitation. THIS IS A 

CRITICAL ALARM. 

If the pressure on this line exceeds 82 barg (1200psi), shut down SWRO unit 

immediately. This condition is related to safety of personnel. THIS IS A VERY 

CRITICAL ALARM DUE TO HIGH PRESSURE. 

If the monitor detects any residual chlorine in water, the SWRO HP Pump stops, the 

feed dump valve XV-36871 will open, and feed isolation valve to the duty SWRO train 

will close 36875. This condition will damage the membranes. THIS IS A CRITICAL 

ALARM. 

If permeate conductivity > 1000 S/cm, stop the SWRO after a time delay (10 

minutes). This is an indication of possible o-ring problem or one or more membranes 

are damaged. 

If FIT-36880 DIVIDED BY (FIT-36880 + FIT-36886) is HH (> 50%) for 30mins stop SWRO 

& initiates an alarm. 

If permeate flow increases above 176 m³/hr with time, that is an indication that 

membranes have been oxidized (i.e., exposed to chlorinated water). Typically, this 

condition occurs simultaneously with higher than usual conductivity rise. A warning – 

not an alarm will be initiated to investigate the problem. 

If P > 1 bar, isolate train & change cartridges on train 1 in the cartridge filter 

housings skid 


housings skid. Since both trains are running simultaneously, most likely both 

readings will be the same. 

When there is a low-level alarm in the tank and the duty SWRO is in service, the fill 

valve XV-36889A or B will open to fill the tank until the tank is full and high level 

alarm is ON (LAH-36700). If the duty SWRO is not in service, the tank will be filled 

first when the SWRO goes back in service (XV-36889 opens) while permeate isolation 

valve XV-36884 remains closed until the tank is full. When the tank is full, XV-36889 

closes & XV-36884 opens simultaneously. 

MV VFD FAULT or NOT READY. This VFD drives the SWRO HP Pump 0P-3630 motor. 

Fault maybe caused by various alarms such as SWRO HP Pump 0P-3630’s motor High 

Winding Temp., possibly vibration, or Fault from the VFD itself, etc. 

VFD NOT READY (this VFD drives the SWRO LP Pump 0P-3631 motor) 

Please note that alarms that are related to Medium Voltage VFD (i.e., VFD Fault), SWRO HP Pump 0P-3630 (i.e., high 

winding temperature), valves stock (can’t open or close), valves or pumps not in AUTO, Fault from SWRO LP Pump, 

etc. are not process related alarms. 


If there is EMERGENCY SHUTDOWN or there are any alarms that will cause the RO train to shut down, the unit will go 

in flush cycle only if the following permissible conditions are met: 

1. There is water in the flushing tank (high level alarm ON) 

2. SWRO flushing pump is in AUTO and is not @ FAULT 

During the process of POST-Flushing, if any of the valves are stock and the PLC do not receive confirmation of open or 

close status, the unit will go immediately into standby. 

1. Feed isolation valve is in AUTO & open the valve should close when POST-Flushing cycle begins 

2. Inlet flushing valve is in AUTO & closed the valve should open when POST-Flushing cycle begins 

3. Permeate isolation valve is in AUTO & open the valve should close when POST-Flushing cycle begins 

4. Permeate dump valve is in AUTO & closed the valve should open when POST-Flushing cycle begins 

5. Turbo bypass valve is in AUTO & closed the valve should open when POST-Flushing cycle begins 

The HMI will show alarm which must be acknowledged by the operator. When the cause of the alarm is fixed, the 

alarm is reset and the unit is re-flushed automatically. 

Types of SWRO Shutdown 

There are two types shutdown: 

a) Type I Shutdown: This is an emergency shutdown due to process alarms which would cause significant 

damage to the membrane system if the process could shutdown normally. 

b) Type II Shutdown: This is a normal shutdown initiated by the operator or caused by alarms that would not 

cause damage to the process if the normal shutdown steps could occur. 

After any type of Shutdown, the SWRO is flushed immediately with SWRO permeate water – This is referred to as Post- 

Flush. Flushing pump will introduce permeate water stored in the flushing tank. All the Flushing water is usually flows 

thru the concentrate line to waste basin. 

On start-up of the RO train, the SWRO train is flushed with filtered seawater from tank 0T-3613B – This is referred to it 

as Pre-Flush. During this cycle, the SWRO LP pump pushes seawater thru RO train while the SWRO HP Pump is off. 

Type I Shutdown Sequence 

STEP 

No. 

Time 

Min/Sec 

1 00:00 

1.1 00:60 

1.2 00:60 

Operator Action and PLC Sequence 

OPERATOR switches SYSTEM to OFF or 

pulling the EMERGENCY pushbutton or 

Type I alarm condition exists 

PLC to shut down all pumps: 

SWRO HP Pump 0P-3630 shuts down 

SWRO LP Pump 0P-3631shuts down 

PLC to shut down all chemical pumps: 

Scale inhibitor pump 0P-3618 shutsdown 

Sodium Bisulfite pump 0P-3617 shutsdown 

if it is running 

2 PLACE SWRO TRAIN IN STANDBY 

2.1 00:90 

PLC commands all valve to STANDBY 

positions: 

Process and Control System Alarm Conditions 

Reaction 

Indicate “EMERGENCY SHUTDOWN” on HMI 

display 

VFD decelerates both pumps 

from operating speed to zero 

RPM. 

Verify valve positions: 

When valves positions 

are confirmed, 


STEP 

No. 

Time 

Min/Sec 

3 00:90 RO POST-FLUSH 

3.1 00:90 


Feed isolation valve XV-36785 closes 

Permeate dump valve XV-36883 opens 

Permeate isolation valve XV-36884 

closes 

PLC checks water level in Flushing 

Tank, 0T-3624 

3.2 01:10 

PLC commands SWRO to permeate 

flush position: 

ERD bypass valve XV-36887 open 

Inlet Flushing iso. valve XV-36876 

open 

3.3 01:10 Start Post-Flush Timer 

3.4 01:10 Start Flushing Pump 0P-3615 

3.5 

06:10 

or 

LAL- 

36700 is 

ON 

End of Permeate Flush Timer or lowlow 

level alarm in 0T-3624 is ON. 

Stop Flushing Pump, 0P-3615 

4 06:10 SWRO TRAIN STANDBY 

4.1 06:30 

PLC sets RO to STANDBY position: 

ERD bypass valve XV-36887 closes 

Inlet Flushing iso. valve XV-36876 

closes 

Feed isolation valve XV-36785 remain 

closed 

Permeate dump valve XV-36883 

remain open 


remain closed 

4.2 06:30 

PLC place RO train in “STANDBY” 

mode 

Process and Control System 

Reaction 

ZSC-36875 contact is closed 

ZSO-36883 contact is closed 


Indicate “Post-Flush” cycle on 

the HMI 

If tank is full (high level alarm 

is not ON) proceed to the 

next step. If not, abort flush 

& alarm on HMI. 

Verify the following Valve 

Positions: 



Check 0P-3615 Run 

Feedback. 

Verify valves position: 



Indicate Train “STANDBY” 

status at HMI 


indicated “STANDBY” 

status of RO train. If 

not confirmed within 

60 seconds of starting 

step 1, indicate FAULT 

condition, display 

alarm on HMI. RESET 

will be required to clear 

the FAULT. 

If not confirmed within 

30 seconds, abort Type 

II shutdown and show 

alarm on HMI. 

If feedback is not 

receivedalarm. 

RESET will be 

required to clear 

the fault. 


Type II Shutdown Sequence 

STEP 

No. 

Time 

Min/Sec 

Operator Action and PLC Sequence Process and Control System 

Reaction 

1 00:00 SHUT-DOWN INITIATION 

During RO system running, an 

operator switch the “SWRO” to OFF 

1.1 

or HAND” or High level alarm in the T- 

3608 water tank or a type II Alarm 

was active. 

2 00:00 

PLC PREPARES SWRO FOR POST- 

FLUSH 

PLC Commands SWRO train to shut 

down: 

00:30 

SWRO HP Pump 0P-3630 reduces PLC confirms pump speed 

operating speed to 25-30% 

feedback 

00:40 ERD bypass valve XV-36887 open ZSO-36887 contact is closed 

00:50 Permeate dump valve XV-36883 open ZSO-36883 contact is closed 

00:60 Permeate iso. valve XV-36884 closes ZSC-36884 contact is closed 

Alarm 

Conditions 

RO Train shut-down is initiated. 

Run condition for the train is removed. 

Terminate Alarm Monitoring for RO Train 

00:90 

SWRO LP Pump 0P-3631 shuts-down: PLC confirms pump speed 

VFD reduces operating speed to 0. feedback 

Scale inhibitor pump stops, 0P-3618A 

or B 

PLC confirm pump stop 

feedback 

If Sodium Bisulfite pump is running, 

shuts down the pump 0P-3617A or B 

“ 

01:00 SWRO HP Pump 0P-3630 shuts down 

completely. 

PLC confirms pump speed 

feedback 

01:10 Feed Isolation Valve, XV-36785 closes ZSC-36785 contact is closed 

3 RO POST-FLUSH 

If tank is full (high level 

3.1 

alarm is not ON) proceed to 

PLC checks water level in Flushing 

the next step. If not, abort 

Tank, 0T-3624 

flush & alarm on HMI. 

3.2 01:20 

3.3 

01:20 

3.4 01:20 

PLC commands SWRO to permeate 

flush position: 

Inlet Flushing isolation valve, XV- 

36876 open 

ERD bypass valve, XV-36887 open 

Permeate dump valve XV-36883 open 

Permeate iso. valve XV-36884 closes 

Feed Isolation Valve, XV-36785 closes 

Start Post-Flush Timer – Timer to be 

set initially at 5-minutes 

Start Flushing Pump 0P-3615 for 5 

minutes 

PLC to verify the following 

valve positions: 






Check 0P-3615 Run 

Feedback 



step 1, indicate Fault 

Condition and identify 

problem on HMI 

display. RESET will be 

required to clear the 

fault. 

Permeate flush timer is 

indicated in the HMI 

and can be changed by 

operator 


STEP 

No. 

Time 

Min/Sec 


Reaction 

06:20 or 

LAL- End of Permeate Flush Timer or lowlow 

Timer expired, or level low 

36700 is 

level alarm in 0T-3624 is ON. alarm is ON 

ON 

3.5 06:20 Stop Flushing Pump, 0P-3615 PLC to confirm pump stop 

4 06:20 RO TRAIN OFF-LINE 

PLC sets RO to Off-Line position: PLC to verify valve positions: 

Inlet flushing valve XV-36876 closes ZSC-36786 contact is closed 

ERD bypass valve XV-36887 closes ZSC-36887 contact is closed 

4.1 06:40 Permeate dump valve XV-36883 ZSO-36883 contact is closed 

remains open 


Permeate iso. valve XV-36884 remain 

closed 

4.2 06:40 

PLC place RO train in “STANDBY” 

mode 


status at HMI 

Alarm 

Conditions 



RESET will be 


the fault. 


Start-Up Sequence 

Table 61-3: SWRO Train Start-Up Sequence 

STEP Time 

Process and Control System Alarm 


No. Min/Sec 

Reaction 

Conditions 

1 00:00 SYSTEM START-UP INITIATION 

1.1 00:00 

System will start because at Low 

Indicate “RO Train Start 

Level alarm in the T-3608 water 

Initiation” on HMI. 

Tank. 

2 00:10 CHECKING PERMISSIVE CONDITION (Refer to Error! Reference source not found.) 

2.1 00:10 

Check if all valves and pumps are in 

AUTO 

Check if there is no FAULT signal 

from any pump (0P-3631 or 0P- 

3630) 

3 00:10 START PRE-FLUSH 

3.1 00:10 

Position valves for Pre-Flush: 

Open feed isolation valve, XV-36875 

(Permeate dump valve XV-36883 

remains open) 

3.2 00:40 Start Pre-Flush timer 

3.3 00:40 

Start SWRO LP pump 0P-3631(at the 

normal service flowrate of 305 

m³/hr) 

3.4 00:70 Pre-Flush begins 

3.5 05:70 Pre-Flush is complete 

4 05:70 RO START 

4.1 05:70 

Check if there is Low Pressure alarm 

(PIT36681 – PDT36867) 

4.2 05:70 Start SWRO HP Pump 0P-3630 

4.3 07:20 

4.4 07:20 

PID control takes over & start 

modulating pump speed based on 

permeate flowrate setpoint 

Open permeate isolation valve XV- 

36884 

Close Permeate dump valve XV- 

36883 

Confirm the following: 



VFD accelerate pump speed to 

previous speed in 30 seconds 

The VFD accelerate pump 

speed to “95% of the normal 

operating speed of the pump” 

at an approximate acceleration 

rate of 10psi/sec 

Check if permeate flowrate 

have reached setpoint of 122 

m³/hr within 5% 

Confirm the following 

positions: 



If one of the valves is 

not in the right 

position, show an 


will be required to 

clear the fault. 

Confirm 

RUNNING 

feedback from 

VFD 

If suction pressure is 

below 2 barg for more 

than 30 sec., abort 

start-up. 

Check RUNNING 

feedback from 

VFD 

4.5 07:50 

Check if there is high-pressure 

alarm, PAH-36878 

4.6 07:50 Check if PY-36886 > 5 psi [1] 

4.7 07:50 HYDRAULIC CHECK 

If pressure is > 80 barg 

for more than 30 sec., 

abort start-up. 

Abort start-up 

immediately (no 

delay) 


STEP 

No. 

Time 

Min/Sec 

4.8 07:50 


Check if concentrate flowrate is 

within 5% of setpoint (183 m³/hr) 

4.8 07:50 

Check if recovery is within 12.5% 

of setpoint, 40% [2] 

5 07:50 QUALITY CHECK 


Reaction 

Alarm 

Conditions 

If Concentrate 

flowrate is < 

76.3 m³/hr for 

more than 3- 

sec, abort startup 


immediately after 10 

minutes delay 

5.1 

Check permeate conductivity, AIT- 

36882 

If conductivity > 1000 

S/cm, indicate an 

alarm on HMI after 5- 

minutes delay. If 

conductivity remains 

greater than setpoint 

after 10 minutes, 


6 07:50 RUN 

6.1 07:50 RO Train confirmed in Run Condition 

All requirements for RO train 

operation have been met 

Indicate Train is 

in “SERVICE” 

status at HMI 

Note: 

1. PY-36886, SWRO HP Pump suction pressure, is the difference pressure of {PIT-36881-PIT-36878} or {PIT- 

36881-PIT-36879} 

2. Maximum allowable operating recovery is 45%. The high alarm setting is 50%. 


UF Trains 

PDIT 

36867A 

XV-36871 

Feed Dump 

Valve, F.O. 

0T-3613A 

Filrate tank 

75 m³ 

0T-3613B 

Filrate tank 

75 m³ 

PIT 

36681A 

Cartridge Filter Housings 

Train 1, Qty 9 

Torroidal 

Conductivity/Temp. 

AIT 

36869 

AE 

36869 

AE 

36866 

pH 

AIT 

36870 

AE 

36870 

ORP 

SWRO Trains 

0P-3651A/B 

Sodium 

Hypochlorite 

Metering Pumps 

The two filtrate tanks are connected by DN400 pipe. 

The two tanks are essentially one tank with 150 m³. 

0P-3631A/B 

SWRO LP Pumps 

75KW Motors 

PIT 

36681B 

PDIT 

36867B 

Cartridge Filter Housings 

Train 2, Qty 9 

305 m 3 /hr 

1342 gpm 

0P-3617A/B 

Sodium Bisulfite 

Metering Pumps 

This is type of cartridge filter housings used because the Specs calls for 

ASME pressure vessel. 

SWRO LP Pumps 0P-3631A/B 

SWRO Cartridge Filter Housings 0F-3603A/B 

SIZE FSCM NO DWG NO REV 

SCALE 1 : 1 SHEET 11 OF 12

150 m 3 /hr 

660 gpm 

P 

P 

CIP Feed 

218 m 3 /hr 

(960 gpm) 

Medium Voltage VFD 

operating @ 6.6kVA 

VFD 

8" 

Class 600# 

Valve 

P 

XV-36889 

Flushing 

Tank 

Feedwater 

305 m 3 /hr 

(1342 gpm) 

Feed Isolation 

Valve, 10" 

P 

XV-36875 

0P-3630 

RO HP Pump 

DSS Construction 

500KW IP55 Motor 

400VAC/3F/50Hz 

0-60 barg 

(0-870 psi) 

PI 

36877 

0-137.9 barg 

(0-2000 psi) 

PIT 

HP Brine Inlet 

(24) 1200 psi Housings 

(7) Membranes/Housing 

(168) Membranes 

36878 PIT 

0-137.9 barg 

(0-2000psi) 

PIT 

36879 

0-2.5 barg 

(0-36 psi) 

36881 

FIT 

36880 

AIT 

36882 

Cond. 

6" 

Reject Recirculating Line 

P 

XV-36883 

P 

XV-36884 

2" 

Permeate Recirculating Line 

Permeate 

Dump 

Permeate 

122 m 3 /hr 

(537 gpm) 

Class 600# 

Valve 

Flushing Inlet 

Isolation Valve 

XV-36876 

LP Brine Inlet 

Turbo Bypass 

valve 

XV-36887 

FIT 

36886 

0-2 bars 

(0-30psi) 

PI 

36885 

8" 

8" 

M 

Brine 

M 

Modulating Valve 

FV-36888 

183 m 3 /hr 

(805 gpm) 

Turbocharger 

DSS Construction (SAF 2507) 

w/ Built-in AUX Valve 

> 75% Efficiency 

LIT 

36700 

0T-3624 

Flushing Tank 

HDPE, 10 m³ 

PIT 

36703 

0P-3615 

Flushing Pump 

316SS 

22KW IP55 Motor 

400VAC/3F/50Hz 

CIP Tank 

0T-3619 

SWRO Train + Flushing System 

SWRO Train 1 has Suffix A for Instrument 

SWRO Train 2 has Suffix B for Instrument 

SIZE FSCM NO DWG NO REV 

SCALE 1 : 1 SHEET 12 OF 12

SWRO System 



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SWRO 

REVISED 

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Normal Start 

Operator push 

MANUAL/START 

button 

Low-Level alarm in 

T-3608 

Step 1 

(I 36-61) 

Note: I 36-XX is a reference for interlock # on the PID 

A 

Yes 

Is SWRO in AUTO? 

Yes 

Is there Low Level 

alarm in 0T-3613B 

or A? 

Step 2 

No 

Step 3 

(I 36-15C/16C) 

The SWRO will 

not Start 

Yes 

No 


Show Alarm on 

HMI/PCS 

No 

Is the Turbo 

bypass valve XV- 

36887 in AUTO & 

open? 

Yes 

Is SWRO LP Pump 

in AUTO & not @ 

FAULT? 

Step 8 

Step 9 

No 

Yes 

Is the flush inlet 

valve XV-36876 in 

AUTO and closed? 

Step 4 

Yes 

No 


No 

If there is FAULT, abort start-up 

No 

Is SWRO HP Pump 

in AUTO & not @ 

FAULT? 

Step 10 

Yes 

Is the Turbo 

Bypass valve XV- 

36887 in AUTO 

and open? 

Step 5 

No 


Start Pre-Flush 

Timer 

Step 11 

Yes 

If there is no confirmation of OPEN status from limit 

switch, abort start-up 

Open feed isolation 

valve XV-36875 

Step 12 

Is the permeate 

dump valve XV- 

36883 in AUTO 

and open? 

Step 6 

No 


No 

Valve Opens 

Yes 

Step 13 

Start SWRO LP Pump 

0P-3631 

Is the feed 

isolation valve XV- 

36875 in AUTO 

and closed? 

Step 7 

No 


If there is FAULT, 

abort start-up 

(I 36-39) 

No 

Step 14 

(I 36-110) 

Pump Confirmed ON 

Start Sodium 

Bisulfite Pump 0P- 

3617 

Yes 

A 

No 




Pre-Flush Timer 

Zeroes out (Elapsed) 

Yes 

Go to the next page 


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Normal Start 

From previous 

page... 

Step 15 

(I 36-46) 

Check if PY-36886 

is < 2 barg? 

Yes 


Step 16 

No 

Start SWRO HP 

Pump 

Pump Start 

VFD ramps up the speed of the pump to a 

preset point (i.e., 95%). A separate PID 

loop will take over controlling the pump 

speed until permeate flow reaches 

setpoint. 

Interlock 36-51 

Step 17 

Check if there is 

no high level 

alarm in 

Flushing tank 

0T-3624? 

Yes 

Open Flushing Fill 

Tank Valve 

XV-36889 

Yes 

Tank is full and high 

level alarm is ON 

LAH-36700 

No 

Step 18 

Open Permeate 


XV-36884 

If there is no confirmation of OPEN status from limit switch, abort 

start-up 


(I 36-53) 

Valve Open 

Step 19 

Close Permeate 

Dump Valve 

XV-36883 

If there is no confirmation of CLOSED status from limit switch, abort 

start-up 


(I 36-53) 

Valve Closes 

Step 20 

Close Turbo Bypass 


If there is no confirmation of CLOSED status from limit switch, abort 

start-up 


(I 36-53) 

Valve Closes 

Step 21 

( I 36-43) 

Check if PI-36878 

is > 82 barg? 

Yes 


(I 36-53) 

No 

Step 21 

( I 36-44) 

Check if Reject 

flowrate is below 

set-point (185 

m³/hr) 

If the flow drops to < 65 m³/hr stop RO 

Yes 


(I 36-53) 

No 



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Normal Start 

From Previous Page 

No 

Check Recovery if 

below or above 

set-point (40%) 

If Recovery is less than or greater than 40%, abort after time delay. 

Recovery in the range of 35 to 45% is acceptable. 


No 

Check if permeate 

conductivity > 

high setpoint? 

> 1,000 mS/cm Open Permeate Dump 

Valve XV-36883 

Conductivity remain at > 1000 mS/ 

cm for more than 5-minutes 


No 

RO in SERVICE 


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Abnormal Shutdown 

In this chart, all pumps are assumed READY and all valves are assumed in AUTO 

Operator Push 

Emergency 

Shutdown 

Alarm Condition 

Indicate Emergency Stop on HMI 

OR 


Stop RO HP Pump 

0P-3630 

If there is any type FAULT... 

Abort Flush 

Alarm on HMI 

Stop RO LP Pump 

0P-3631 


Abort Flush 

Alarm on HMI 

Open flush inlet 


XV-36876 OPEN 

Confirmed? 

No 

Abort Flush 

Alarm on HMI 

Open Permeate 

Dump Valve 

XV-36883 

XV-36883 OPEN 

Confirmed? 

No 

Abort Flush 

Alarm on HMI 

Close feed isolation 


XV-36875 CLOSE 

Confirmed? 

No 

Abort Flush 

Alarm on HMI 


Isolation Valve XV- 

36884 


Confirmed? 

No 

Abort Flush 

Alarm on HMI 

Open Turbo Bypass 


XV-36887 OPEN 

Confirmed? 

No 

Abort Flush 

Alarm on HMI 


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ORP Alarm – Abnormal Shutdown 

(Interlock 36-41) 

ORP Alarm 

from AIT- 

36870 

VFD to decrease pump s speed to the 

lowest possible (i.e., < 25%) where 

the flow stops 

Start Standby 

Sodium Bisulfite MP 

0P-3617B @ 100% 

Stroke 

Yes 

Open Feed Dump 


Stop Duty SWRO LP 

Pump 0P-3631A 

Stop Duty SWRO HP 

Pump 0P-3630 

Valve Open 

Close Feed Isolation 


After confirmation that Pump is OFF 

Valve did 

not Open 

Valve Closed 

If ORP Alarm 

AAH-36870 stays 

ON? 

No 

Simultaneously close feed dump 

valve XV-36871 and open feed 

isolation valve XV-36875 

Valves are in correct position 

Yes 

Start sequence of shutting down of duty 

train & prohibit starting of standby train 

Re-Start Duty SWRO LP Pump 0P- 

3631A 


Pump not 

confirmed ON 

Show Alarm on 

both HMI & 

PCS 

Re-Start Duty SWRO HP Pump 0P- 

3630 

Pump not confirmed ON 

Show Alarm on 

both HMI & 

PCS 

Stop Standby 

Sodium Bisulfite MP 

0P-3617B 

Note: 

Feedwater is assumed to have residual chlorine all the time up to the filtrate tanks 0T-3613A/B. Sodium 

Bisulfite pump is continuously controlled by the ORP monitor AIT-36870. 


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Normal Shutdown 

In this chart, all pumps are assumed READY and all valves are assumed in AUTO 

Operator push 

MANUAL/STOP 

button 

High-Level alarm in 

T-3608 

Step 1 


0P-3630 


Abort Flush 

Alarm on HMI 

Step 2 

Stop RO LP Pump 

0P-3631 & Sodium 

Bisulfite Injection 


Abort Flush 

Alarm on HMI 

Step 3 

Open flush inlet 


XV-36876 OPEN 

Confirmed? 

No 

Abort Flush 

Alarm on HMI 

Step 4 

Open Permeate 

Dump Valve 

XV-36883 

XV-36883 OPEN 

Confirmed? 

No 

Abort Flush 

Alarm on HMI 

Step 5 

Close feed isolation 



Confirmed? 

No 

Abort Flush 

Alarm on HMI 

Step 6 



36884 


Confirmed? 

No 

Abort Flush 

Alarm on HMI 

Next Page 


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Step 7 

Open Turbo Bypass 


XV-36887 OPEN 

Confirmed? 

No 

Abort Flush 

Alarm on HMI 

Step 8 

Check level in 

flushing tank? 

If there is lowlevel 

alarm? 

Yes 

Abort Flush 

Alarm on HMI 

Step 9 

Start Flush Cycle 

Timer 

Flush Pump 0P-3615 

Start 

Confirm Start of 

Pump? 

No 

Abort Flush 

Alarm on HMI 

Yes 

Step 10 

Flush Cycle Timer 

Ends 


Stop 

Confirm Stop of 

Pump? 

No 

Abort Flush 

Alarm on HMI 

Yes 

Step 11 

Close Flush inlet 



Confirmed? 

No 

Abort Flush 

Alarm on HMI 

Yes 

Step 12 

Place SWRO in 

STANDBY Mode 

Step 13 


LAG Position 


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Check level in 

flushing tank? 

If there is lowlevel 

alarm? 

Yes 

Abort Flush 

Alarm on HMI 


Timer 


Start 

Confirm Start of 

Pump? 

No 

Abort Flush 

Alarm on HMI 

Flush Cycle Timer 

Ends 


Stop 

Confirm Stop of 

Pump? 

No 

Abort Flush 

Alarm on HMI 

Close Flush inlet 



Confirmed? 

No 

Abort Flush 

Alarm on HMI 


OFF Mode 

Show Alarm on 

HMI 


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Alarm HMI Screen Setpoint 

Alarm 

AAH-36870 

SA-36949A/B 

Description 

High ORP Alarm 

0P-3631A FAULT 

Setpoint 

> + 300mV 

LAL-36660A/B Low-Level Alarm in 0T-3613B or A TBD 

PAL-36681A/B Low Press. Alarm 0P-3631A/B TBD 

PAH-36681A/B 

PDAH-36681A/B 

High Diff. Press. Alarm across 0F- 

3603A/B 

> 1.0 barg 

TAH-36869 High SWRO feedwater Temp. alarm > 40 ºC 

XA-36876A/B 

AAH-36882A/B 

FAL-36886A/B 

FAH-36880A/B 

PAH-36878A/B 

PAL-36886A/B 

High Press. Alarm 0P-3631A/B 

0P-3630A/B FAULT 

High SWRO Permeate Conductivity 

Alarm 

Low Flow Alarm on the reject line 

High Flow Alarm on the permeate line 

High Press. Alarm on the membrane 

feed line 

Low Press. Alarm on the suction line of 

0P-3630A/B (Calc. value) 

> 1000 mS/cm 

> 172 m³/hr 

> 82 barg 

Time Delay 

3 sec. 

None 

24-hrs 

10 min. 

None 

600 sec. 

< 76 m³/hr 3 sec. 

3 sec. 

3 sec. 

Critical 

Alarm? 

Yes 

No 

Yes 

No 

< 2.0 barg 3 sec. Yes 

Remarks 

Shut-Off head of pump is only 61.47m ( 

6 barg). See note 3. 

Notes: 

1) Critical alarms will not be ignored by PLC when unit is operating in MANUAL Mode. 

2) Alarms will show Alarm|Active on the corresponding SWRO train. Operator must acknowledge the alarm on the PCS and rest 

the alarm after investigating the problem. 


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Chapter 62 : Control Philosophy of SWRO with PX 


Let’s assume that the SWRO for the Wheatstone project is equipped with PX instead of Turbocharger. The list of 

equipment will be: 

1. There are two filtrate tanks (FRP), and SWRO permeate water tank T-3608, same as previous chapter. 

2. There are (2) duty/standby SWRO LP pumps, 0P-3631A/B, operating by VFD 

3. There are (2) duty/standby Cartridge Filter Housings 

4. There are (2) duty/standby SWRO trains, 0PK-3603-F02A/F02B. 

a. Each SWRO train is equipped with a PX rack [(3) PX-300]. Refer to Figure 62-3: PX Projection. 

b. Each SWRO train has a dedicated SWRO HP Pump, 0P-3630A or B, which are not mounted on the skid. 

These pumps now are rated for 124 m³/hr @ minimum of 67 barg driven by VFD. 

c. Each SWRO train is equipped with PX booster pump rated at 181 m³/hr @ 3 barg driven by VFD. 

5. Chemical Feed systems: Same as in previous chapter. 

6. SWRO Flushing system to consist of flushing pump 0P-3615 and flushing tank 0T-3624. 

7. Instrumentation and valves: In a PX system, there are more additional instruments and valves. 

For reference on the difference between the two systems, please refer to this sketch done in Microsoft Visio. 

Flow path thru Pressure Exchanger 

The flow path thru pressure exchanger is complicated. It is best to visit the company’s website at 

www.energyrecovery.com or go to google and check this old video posted by the manufacturer which is now posted 

on YouTube at http://www.youtube.com/watch?v=udffed4Pq3g. 

A PX system consists of the following: 

1. Pressure Exchanger(s) which consists of the following: 

a. Pressure Housing same as RO pressure housing 

b. Ceramic Rotor – This is the heart of the PX system. The rotor allows the HP (High-Pressure) brine 

stream to push the LP (Low-Pressure) feed stream directly. The rotor rotates at approximately 1200 

RPM when RO HP pump starts pressurizing the system. 

c. Ceramic Rotor’s housing 

d. End plates 

2. PX Circulation Pump: This pump is always driven by VFD and its function is to re-pressurize the HP (High- 

Pressure) feed because the HP brine is lower in pressure than the RO HP pump pressure stream C. 

End Plate 

Chapter 62 Control Philosophy of SWRO w/ PX Page 46

+ 

Ceramic Rotor 

Ceramic Rotor’s 

housing 

Ceramic Rotor 

Figure 62-1: Schematic Diagram of a PX Device 

In Figure 1 shows the various paths of all streams. The purpose of the PX system is to pressurize portion of the 

seawater feed which is equal to reject or brine flow by the PX unit, and to pressurize the remainder of the feed which 

is equal to permeate flow by the RO HP Pump. We will use LP & HP for all streams as abbreviations for Low-Pressure 

& High-Pressure. 

Stream A is the LP Feed stream which splits into streams: Stream B flowing into the PX LP feed side, and stream C 

which flows into the RO HP pump and is pressurized by the RO HP pump. Stream C is combined with stream E as it 

enters the RO housings. 

Stream C is the portion of the LP feed which is pressurized by the RO HP pump to the reverse osmosis required per RO 

projection. A check valve at the discharge of the RO HP pump will isolate that stream from stream E. 

Stream G is the HP brine which is the main source of pressure for the LP feed stream (Stream B). Pressure transfers 

from the high-pressure concentrate stream [G] to a feed stream [B]. The rotor spins freely, driven by the flow at a 

rotation rate proportional to the flow rate and lubricated by high-pressure process water. Unlimited capacity is 

achieved by arraying multiple PX devices in parallel. 

Stream D is the HP feed stream which is pressurized by Stream G. Since the reject or brine stream’s pressure (Stream 

G) is usually 1 to 2 bars less than Stream C, the circulation pump is provided to add that pressure as it mixes with 

Stream C. The flow from the circulation pump is combined with Stream A to become Stream E. 


Stream H is the LP brine exiting the PX system. The pressure of this stream should be no less than 1 bar (14.5 psi). 

This is the same stream G which has lost its pressure to Stream B and lost a little bit of water for lubrication of the 

rotor. 

In a reverse osmosis system equipped with PX Pressure Exchanger® energy recovery devices, the membrane reject is 

directed to the membrane feed as illustrated in Figure 1. A rotor, moving between the high-pressure and low lowpressure 

streams, removes the reject concentrate and replaces it with feed water. 

The PX devices and the check valve at the discharge of the high-pressure pump seal the high-pressure portion of the 

RO process. During RO-process operation, water is introduced to the high-pressure loop [D-E-G] by the high-pressure 

pump as stream C. Almost all this water exits as permeate and the rest flows through narrow gaps that surround the 

PX device rotor, creating a nearly frictionless hydrodynamic bearing. Lubrication flow is typically about 0.5% of the 

total flow from the high-pressure pump and is measurable as the difference between the high-pressure pump flow 

rate [C] and the permeate flow rate [F]. 

The flow delivered by the high-pressure pump and the resistance to permeate and lubrication flows provided by the 

membrane elements and the PX devices, respectively, pressurize the high-pressure loop. Although water is also 

introduced to the high-pressure loop by the PX devices at process location D, an equal flow rate of water is removed 

by the PX devices at process location G. The PX system is divided into two loops: High-Pressure (HP) and Low- 

Pressure (LP). The HP loop and the LP loop are completely independent. The flow in the HP loop is almost constant 

and the only way to increase recovery is to increase the flowrate of the RO HP Pump. 

High-Pressure Loop 

RO HP 

Feed 

Pump 

PX 

Booster 

Pump 

Low-Pressure Loop 

LP Feed-In, 2 bars 

P=1bar 

LP Feed 

Pump 

Figure 62-2: ERI Operation 


The manufacturer, ERI, prefers to see a pressure not exceeding 2-bar for the low feed-in line (Stream B). Per ERI, the 

expected pressure drop is 1 bar across the unit. The low-pressure-Brine-Out line (Stream H) should be equipped with 

a valve to keep a backpressure to ensure constant lubrication inside the rotor - this is equivalent to maintain constant 

NPSH in case of pump. 

RO Process Startup 

A reverse-osmosis process equipped with PX technology is started up with the following sequence: 

1. Start the feed water supply pump (the SWRO LP Pump, 0P-3629A) 

2. Start the PX booster pump 

3. Thoroughly vent air from the process 

4. Start the high-pressure pump, 0P-3630A or B 

The RO system is not pressurized before the high-pressure pump is started. 

RO Process Shutdown 

A normal shutdown sequence is as follows: 

1. Shutdown the high-pressure pump, 0P-3630A or B 

2. Wait until the concentrate has been displaced from the SWRO system by the PX booster pump and the PX 

rack 

3. Shutdown the PX booster pump 

4. Shutdown the feed water supply pump, 0P-3629A 

The system remains pressurized at the osmotic pressure of the feed water by osmotic or “suck-back” flow. After the 

high-pressure and PX booster pumps stop, system pressure decreases very slowly as lubrication water is pushed 

through the PX device lubrication channels and into the low- pressure piping. Osmotic pressure decreases as suckback 

permeate accumulates in the membranes. If more rapid depressurization is necessary, a vent valve in the highpressure 

loop must be opened. 

Flushing 

RO membranes require occasional flushing to limit biological fouling. Biological fouling can increase RO process 

energy consumption and cause malfunctions. There are two types of flush: Feed Water Flush (Pre-Flush) during startup 

and Permeate Flush (Post-Flush) before shut-down. Regardless of the flush water used, all parts of the PX device 

must be flushed, i.e. low-pressure flow channels, high- pressure flow channels, and lubrication channels. Refer to 

ERI’s Installation, Operation and Maintenance Manuals for specific information about flushing requirements. 

Step (2) of a normal shutdown sequence is a Feed Water Flush. Both permeate and concentrate production have 

ceased and high-pressure and low-pressure bulk flows through the PX devices continue. The flow path of the Feed 

Water Flush per Figure 1, is B-D-E-G-H driven by the feed water pump and the circulation pump. A Feed Water Flush 

is typically continued until conductivity measurements at process locations G and H are satisfactory. 

A Permeate Flush is performed on a partially- or fully-depressurized system. This is accomplished by introducing 

permeate simultaneously to the PX device low-pressure inlet [B] and either to the high-pressure pump inlet [A] or 

through some other injection point such as a CIP connection. Permeate may be produced during this flushing process. 

If so, it may be necessary to block permeate flow to divert lubrication flow through the PX devices. 


PX Rotor Lubrication 

Both process flow and lubrication flow are required for the PX rotor to spin. The process flows include the feed flow 

from the supply system introduced to the PX devices at process location B in Figure 62-1 and the concentrate flow 

driven by the circulation pump. Lubrication flow is normally provided by the high-pressure pump as described 

above. The lubrication flow rate is typically less than 1% of the high-pressure pump flow rate or less than 0.5m³/hr 

(2.2 gpm) per PX device. 

Without lubrication flow, the PX device rotors may stop rotating. If this occurs, the concentrate-feed water exchange 

will cease. Flush water introduced at process location B will exit at process location H without flowing through the 

membrane array. With insufficient lubrication flow, rotor rotation can result in damage to the PX device’s ceramic 

components. A grinding sound may be heard as the ceramic components rub together without lubrication. 

If the high-pressure pump is not on, such as during flushing, the lubrication flow necessary to keep the PX rotors 

spinning can be provided by osmotic (suck-back) flow through the membranes. However, if the RO process is fully 

depressurized, the lubrication flow necessary to keep the rotors spinning must be either pushed through the highpressure 

pump by the supply pump or injected through some other point in the high-pressure loop such as a clean-inplace 

(CIP) inlet. If the flush water has very low salinity, the lubrication flow may exit the process through the 

membranes under low trans-membrane pressure. It may be necessary to block permeate flow to divert lubrication 

flow through the PX devices. 

The following conditions apply: 

1. Allowable flow ranges for individual PX Units are listed in the company’s website. PX units are not designed to 

operate outside of these ranges. 

2. Seawater feed to PX units must be filtered to 5 microns or less and should be subjected to the same 

pretreatment as seawater being fed to the SWRO membranes. 

3. Piping connections to PX units must be designed to minimize stress on the fittings and vessel. 

4. The PX unit must be vessel bearing plates (end caps) incorporate interlocking restraining devices which must 

be kept dry and free of corrosion. Deterioration of these devices could lead to catastrophic mechanical failure 

of the PX side. 

5. The PX unit must not be exposed to temperatures less than 1ºC (33ºF) or greater than 45ºC (113ºF). 

6. Under no circumstances shall be brine inlet pressure (HP IN) exceed 82.7 barg (1200psig). 

7. The Seawater feed inlet shall not exceed 10.3 barg (150psig). The minimum discharge pressure from the PX 

unit shall be 1 barg (15psig). 

8. The PX unit(s) must be removed from the SWRO system when performing hydrostatic testing on piping or 

other SWRO system components. Never attempt to hydrostatic test a PX device. 

9. Some chemical additives are known to be the cause of operational failure of PX unit(s). These chemicals 

include, but are not limited to polyacrylates, occasionally used for scaling prevention. These chemicals can 

cause PX device failure by forming a sticky substance which physically jams the PX unit(s). 

10. Install piping and fittings so that the PX unit(s) can be isolated from membrane reject flow during membrane 

cleaning. Failure to do so may introduce debris that may damage the PX unit. 


In the normal operating cycle (AUTO), starting one SWRO train plant will be dictated by the level in the SWRO 

permeate storage tank T-3608. When there is call for water in this tank (LAL), the SWRO LP pump 0P-3631A will start 

pumping water thru the cartridge Filter Housings, and SWRO train (pre-flushing). The permissive condition for 

starting the pump is the following: 


1. Level in the UF Filtrate tanks 0T-3613A/B. If there is enough water above the centerline of the discharge 

piping of the SWRO LP pump skid, the duty pump will start automatically (there is no low-level alarm). 

2. SWRO LP pump, 0P-3631A/B must be in AUTO and READY 

3. SWRO HP Pumps, both 0P-3630A/B must be in AUTO and READY 

4. PX booster pump must be in AUTO and READY 

5. In this project, there is no intention of pumping acid or antiscalant, so a provision is made in the HMI so that 

these pumps will be interlocked with the SWRO HP Pump if it is deemed necessary. 

6. Sodium Bisulfite MP must be in AUTO and READY 

7. Flushing pump must be in AUTO and READY 







Here is a summary of the most important control strategies that are incorporated in the control of the SWRO are the 

following: 

In PLC AUTO mode, the RO train will be controlled by the rise or fall of water level in the storage tank T-3608. START 






5. If there is Fault or Trip alarm from SWRO HP pump 

6. If there is low-level alarm in the filtrate storage tank 0T-3613B 

7. If there is low-pressure alarm due to low-pressure in the suction line of the SWRO HP pump 

8. If ORP alarm is present in the feedwater 

In PLC OFF, the SWRO HP pump shuts down and the RO is isolated. OFF is mainly reserved to allow maintenance on 

the RO unit. Please note that CIP is only done when the SWRO is in OFF cycle. CIP requires filling the CIP tank with 

un-chlorinated permeate water, start the heater, mixing the chemicals to the right pH, and recirculating warm 

solution thru the CIP tank until the right pH and temperature is achieved. 


alarm condition) will be followed immediately by flushing cycle. When a unit shut down, all chemical metering pumps 

associated with SWRO will stop (Scale Inhibitor, Sodium Bisulfite, Calcium Hypochlorite for permeate, etc.). 

Flushing system is an integral part of the SWRO equipment. It is critical that SWRO will be flushed immediately after 

shut-down (Normal or Abnormal) – This will be referred to as Post-Flush. The post-flush’s cycle will flush out the 

highly-concentrated seawater from the piping which can cause severe corrosion due to the extremely high chloride 

content. This seawater is 1.7 times more concentrated than the raw seawater coming in to the SWRO. 

The SWRO will also be flushed on Start-up – This will be referred to as Pre-Flush. The pre-flush’s cycle will flush out 

standing water in the pipe. Still (non-moving) seawater is always subjected to attack by micro-algae’s and other 

species that may have escaped pre-treatment. The pre-flush’s cycle is approximately 5-minutes. 


Flushing tank must always be full. When there is flush and the lagging SWRO starts, it will fill the flush tank 0T-3614 

first by opening valve XV-36889, before diverting back to the permeate line or before opening valve XV-36884. 

Upon start-up, the VFD will ramp up the speed of the RO HP Pump at a rate of 1 barg per second to avoid slamming 

the membranes against the reject end of the housing. 

The SWRO HP Pump is controlled by the PLC to maintain constant permeate flowrate. The VFD controls the speed of 

the pump in proportion to permeate flowrate. Changes in flowrate occurs because either the temperature have 

changed, the feedwater quality have changed (usually seasonal), and because of fouling (with time). 

The sodium bisulfite is injected continuously to maintain ORP below the Hi-limit set-point which will be determined in 

the field. This is usually anywhere between 240 to 300mV (milli-Volt). If the sodium bisulfite will not drop the ORP 

value to less than the Hi set-point, an alarm is initiated and the feed dump valve (XV-36871) open to divert the entire 

feed back to 0T-3613A. 

Cartridge filter housing differential pressure alarm will not shutdown the plant. If this value is above 1 barg, a warning 

will be shown on the HMI to alarm operator to schedule a time to change the cartridges. The plant should not rely on 

this instrument however. After start-up, operators should establish a period for changing out cartridges every “x” 

months to prevent build-up of high P. We cannot emphasis the importance of cartridges in the operation of 

desalination plant. These cartridges are the final protection for the RO especially when overdosing ferric chloride or 

the reaction of ferric chloride with antiscalants if they are used. 

Before the SWRO start producing permeate water, it must fill the flushing 0T-3624 tank first. Whenever the PLC 

detects level below high-level setting (1480mm), it will open valve XV-36889 until high-level in flushing tank is 

detected. The permeate isolation valve XV-36884 will open and XV-36889 will close after the tank is full of water. 

Flushing time will reset during start-up. The first time the unit is flushed, it will be monitored to check how long it will 

take for the conductivity of the reject to reach the same as the conductivity of the incoming flushing water. Volume 

of flushing water requirement is dependent on the size of the RO or the volume required filling all components within 

the unit (piping, pressure vessels, pumps, etc.…). 


Table 62-1: Summary of Operational Conditions for the SWRO 


SWRO Automatic Start 

SWRO Automatic Stop 

Alternation of SWRO train 

SWRO Operational modes 


Description 

When there is call for water in tank T-3608 (or when level is below “Lo” preset alarm 

setting), the duty SWRO train will start. 

When there is no call for water in tank T-3608 and the level has reached the Hi level 

setting, the SWRO train will stop. 

The SWRO train duty/standby will alternate every 24-hours If SWRO train A has 

been running for example for 20-hours the previous day, SWRO train B will become 


SERVICE 

STANDBY 

PRE-FLUSH 

POST-FLUSH 

Type I Shutdown: This is an emergency shutdown due to process alarms which would 

cause significant damage to the membrane system if the process could shutdown 

normally. 



Flushing 

POST-FLUSHING Cycle 

PRE-FLUSHING Cycle 

Description 

Type II Shutdown: This is a normal shutdown initiated by the operator or caused by 

alarms that would not cause damage to the process if the normal shutdown steps 

could occur. 

When SWRO starts, it will go into PRE-FLUSH cycle before it is placed in SERVICE. 

When SWRO shuts down, it will go into POST-FLUSH cycle before it is placed in 

STANDBY. 

This is SWRO permeate water flushing using flushing pump 0P-3615 while SWRO HP 

Pump 0P-3630 is OFF. 

This is filtrate water flush using SWRO LP pump 0P-3631 to flush the RO while the 

SWRO HP Pump 0P-3630 is OFF. 

The flushing pump will push SWRO permeate water thru the RO. The PLC commands the following pumps & valves 

per the steps below: 

1. SWRO HP Pump shuts down 

2. SWRO LP Pump shuts down 

3. Flushing inlet valve open, XV-36876 

4. Feed isolation valve closes, XV-36875 

5. Turbo bypass valve on the reject line open, XV-36887 

6. Permeate dump valve opens, XV-36883 

7. Permeate isolation valve closes, XV-36884 

Alarms 

Here is the list of major alarms related to the SWRO: 

Table 62-2: List of Alarms 


FAL-36886 

SWRO Reject Low Flow 

Alarm 

PY-36886 


PAH-36813 



AAH-36870 High ORP 

Alarm 

AAH-36882 

SWRO High Permeate 

Conductivity Alarm 

SWRO High Recovery Alarm 

Description 

If reject flow drops to 76 m³/hr while SWRO is in SERVICE (i.e., operator closing a 

valve on the reject line, the SWRO will shut down immediately, and an alarm is 

initiated. This condition will damage the membranes. THIS IS A CRITICAL ALARM. 

This is calculated value (PI36681 – PDI368867) which monitors the suction pressure 

for the SWRO HP Pump 0P-3630. If pressure is less than 2 barg, stop SWRO train 

after time delay (3-5 sec.). Starving the pump will cause cavitation. THIS IS A 

CRITICAL ALARM. 

If the pressure on this line exceeds 82 barg (1200psi), shut down SWRO unit 

immediately. This condition is related to safety of personnel. THIS IS A VERY 

CRITICAL ALARM DUE TO HIGH PRESSURE. 

If the monitor detects any residual chlorine in water, the SWRO HP Pump stops, the 

feed dump valve XV-36871 will open, and feed isolation valve to the duty SWRO train 

will close 36875. This condition will damage the membranes. THIS IS A CRITICAL 

ALARM. 

If permeate conductivity > 1000 S/cm, stop the SWRO after a time delay (10 

minutes). This is an indication of possible O-ring problem or one or more membranes 

are damaged. 

If FIT-36880 DIVIDED BY (FIT-36880 + FIT-36886) is HH (> 50%) for 30mins stop SWRO 

& initiates an alarm. 



FAH-36880 

SWRO High Permeate Flow 

Alarm 

PDAH-36867A 

High P Alarm, 0F-3603A 

PDAH-36867B 

High P Alarm, 0F-3603B 

LAL-36700 

Low level alarm in Flushing 

tank 0T-3624 

XA-36876 

XA-36949 

Description 

If permeate flow increases above 176 m³/hr with time, that is an indication that 





housings skid 


housings skid. Since both trains are running simultaneously, most likely both 

readings will be the same. 

When there is a low-level alarm in the tank and the duty SWRO is in service, the fill 

valve XV-36889A or B will open to fill the tank until the tank is full and high level 

alarm is ON (LAH-36700). If the duty SWRO is not in service, the tank will be filled 

first when the SWRO goes back in service (XV-36889 opens) while permeate isolation 

valve XV-36884 remains closed until the tank is full. When the tank is full, XV-36889 

closes & XV-36884 opens simultaneously. 

MV VFD FAULT or NOT READY. This VFD drives the SWRO HP Pump 0P-3630 motor. 

Fault maybe caused by various alarms such as SWRO HP Pump 0P-3630’s motor High 

Winding Temp., possibly vibration, or Fault from the VFD itself, etc. 

VFD NOT READY (this VFD drives the SWRO LP Pump 0P-3631 motor) 

Please note that alarms that are related to Medium Voltage VFD (i.e., VFD Fault), SWRO HP Pump 0P-3630 (i.e., high 

winding temperature), valves stock (can’t open or close), valves or pumps not in AUTO, Fault from SWRO LP Pump, 

etc. are not process related alarms. 

If there is EMERGENCY SHUTDOWN or there are any alarms that will cause the RO train to shut down, the unit will go 

in flush cycle only if the following permissible conditions are met: 

1. There is water in the flushing tank (high level alarm ON) 

2. SWRO flushing pump is in AUTO and is not @ FAULT 

During the process of POST-Flushing, if any of the valves are stock and the PLC do not receive confirmation of open or 

close status, the unit will go immediately into standby. 

3. Feed isolation valve is in AUTO & open the valve should close when POST-Flushing cycle begins 

4. Inlet flushing valve is in AUTO & closed the valve should open when POST-Flushing cycle begins 

5. Permeate isolation valve is in AUTO & open the valve should close when POST-Flushing cycle begins 

6. Permeate dump valve is in AUTO & closed the valve should open when POST-Flushing cycle begins 

The HMI will show alarm which must be acknowledged by the operator. When the cause of the alarm is fixed, the 

alarm is reset and the unit is re-flushed automatically. 

Types of SWRO Shutdown 

There are two types shutdown: 

c) Type I Shutdown: This is an emergency shutdown due to process alarms which would cause significant 

damage to the membrane system if the process could shutdown normally. 

d) Type II Shutdown: This is a normal shutdown initiated by the operator or caused by alarms that would not 

cause damage to the process if the normal shutdown steps could occur. 


After any type of Shutdown, the SWRO is flushed immediately with SWRO permeate water – This is referred to as Post- 

Flush. Flushing pump will introduce permeate water stored in the flushing tank. All the Flushing water is usually flows 

thru the concentrate line to waste basin. 

On start-up of the RO train, the SWRO train is flushed with filtered seawater from tank 0T-3613B – This is referred to it 

as Pre-Flush. During this cycle, the SWRO LP pump pushes seawater thru RO train while the SWRO HP Pump is off. 


Type I Shutdown Sequence 

STEP 

No. 

Time 

Min/Sec 

1 00:00 

1.1 00:60 

1.2 00:60 


OPERATOR switches SYSTEM to OFF or 

pulling the EMERGENCY pushbutton or 


PLC to shut down all pumps: 

SWRO HP Pump 0P-3630 shuts down 

SWRO LP Pump 0P-3631shuts down 

PLC to shut down all chemical pumps: 

Scale inhibitor pump 0P-3618 shutsdown 

Sodium Bisulfite pump 0P-3617 shutsdown 

if it is running 

2 PLACE SWRO TRAIN IN STANDBY 

2.1 00:90 


3.1 00:90 

PLC commands all valve to STANDBY 

positions: 

Feed isolation valve XV-36785 closes 

Permeate dump valve XV-36883 opens 


closes 

PLC checks water level in Flushing Tank, 

0T-3624 

3.2 01:10 

PLC commands SWRO to permeate flush 

position: 

ERD bypass valve XV-36887 open 

Inlet Flushing iso. valve XV-36876 open 


Process and Control System Alarm Conditions 

Reaction 

Indicate “EMERGENCY SHUTDOWN” on HMI display 

VFD decelerates both pumps 

from operating speed to zero 

RPM. 

Verify valve positions: 




Indicate “Post-Flush” cycle on 

the HMI 

If tank is full (high level alarm is 

not ON) proceed to the next 

step. If not, abort flush & 

alarm on HMI. 


Positions: 



3.4 01:10 Start Flushing Pump 0P-3615 Check 0P-3615 Run Feedback. 

3.5 

06:10 

or 

LAL- 

36700 is 

ON 

End of Permeate Flush Timer or low-low 


Stop Flushing Pump, 0P-3615 

4 06:10 SWRO TRAIN STANDBY 

4.1 06:30 

PLC sets RO to STANDBY position: 


Inlet Flushing iso. valve XV-36876 closes 

Feed isolation valve XV-36785 remain 

closed 

Verify valves position: 



When valves positions 

are confirmed, indicated 

“STANDBY” status of RO 

train. If not confirmed 

within 60 seconds of 

starting step 1, indicate 

FAULT condition, display 


will be required to clear 

the FAULT. 


30 seconds, abort Type II 

shutdown and show 

alarm on HMI. 



RESET will be 


the fault. 


STEP 

No. 

Time 

Min/Sec 


Permeate dump valve XV-36883 remain 

open 


remain closed 

4.2 06:30 PLC place RO train in “STANDBY” mode 


Reaction 


status at HMI 


Type II Shutdown Sequence 

STEP 

No. 

Time 

Min/Sec 


Reaction 


During RO system running, an operator 

1.1 

switch the “SWRO” to OFF or HAND” or 

High level alarm in the T-3608 water 

tank or a type II Alarm was active. 

2 00:00 PLC PREPARES SWRO FOR POST-FLUSH 

PLC Commands SWRO train to shut 

down: 

00:30 

SWRO HP Pump 0P-3630 reduces PLC confirms pump speed 

operating speed to 25-30% 

feedback 

00:40 ERD bypass valve XV-36887 open ZSO-36887 contact is closed 

00:50 Permeate dump valve XV-36883 open ZSO-36883 contact is closed 

00:60 Permeate iso. valve XV-36884 closes ZSC-36884 contact is closed 

Alarm 

Conditions 

RO Train shut-down is initiated. 

Run condition for the train is removed. 

Terminate Alarm Monitoring for RO Train 

00:90 

SWRO LP Pump 0P-3631 shuts-down: PLC confirms pump speed 

VFD reduces operating speed to 0. feedback 

Scale inhibitor pump stops, 0P-3618A or 

B 

PLC confirm pump stop 

feedback 

If Sodium Bisulfite pump is running, 

shuts down the pump 0P-3617A or B 

“ 

01:00 SWRO HP Pump 0P-3630 shuts down 

completely. 

PLC confirms pump speed 

feedback 

01:10 Feed Isolation Valve, XV-36785 closes ZSC-36785 contact is closed 

3 RO POST-FLUSH 

If tank is full (high level alarm 

3.1 

is not ON) proceed to the next 

PLC checks water level in Flushing Tank, 

step. If not, abort flush & 

0T-3624 

alarm on HMI. 

3.2 01:20 

PLC commands SWRO to permeate flush 

position: 

Inlet Flushing isolation valve, XV-36876 

open 

ERD bypass valve, XV-36887 open 

Permeate dump valve XV-36883 open 



PLC to verify the following 

valve positions: 










problem on HMI display. 

RESET will be required to 



STEP 

No. 

3.3 

Time 

Min/Sec 

01:20 

3.4 01:20 


Start Post-Flush Timer – Timer to be set 

initially at 5-minutes 

Start Flushing Pump 0P-3615 for 5 

minutes 


Reaction 

Check 0P-3615 Run Feedback 

Alarm 

Conditions 

Permeate flush timer is 

indicated in the HMI and 

can be changed by 

operator 

06:20 or 

LAL- 

36700 is 

ON 

End of Permeate Flush Timer or low-low 



alarm is ON 

3.5 06:20 Stop Flushing Pump, 0P-3615 PLC to confirm pump stop 


4.1 06:40 

PLC sets RO to Off-Line position: 

Inlet flushing valve XV-36876 closes 


Permeate dump valve XV-36883 

remains open 

Permeate iso. valve XV-36884 remain 

closed 

PLC to verify valve positions: 







status at HMI 



RESET will be 


the fault. 

Start-Up Sequence 

Table 62-3: SWRO Train Start-Up Sequence 

STEP Time 

Process and Control System Alarm 


No. Min/Sec 

Reaction 

Conditions 

1 00:00 SYSTEM START-UP INITIATION 

1.1 00:00 

System will start because at Low 


Level alarm in the T-3608 water 

Initiation” on HMI. 

Tank. 

2 00:10 CHECKING PERMISSIVE CONDITION (Refer to Error! Reference source not found.) 

2.1 00:10 

Check if all valves and pumps are in 

AUTO 

Check if there is no FAULT signal 

from any pump (0P-3631 or 0P- 

3630) 

3 00:10 START PRE-FLUSH 

3.1 00:10 

Position valves for Pre-Flush: 

Open feed isolation valve, XV-36875 

(Permeate dump valve XV-36883 

remains open) 

3.2 00:40 Start Pre-Flush timer 

3.3 00:40 

Start SWRO LP pump 0P-3631(at the 

normal service flowrate of 305 

m³/hr) 

Confirm the following: 



VFD accelerate pump speed to 

previous speed in 30 seconds 

If one of the valves is 

not in the right 

position, show an 


will be required to 


Confirm 

RUNNING 

feedback from 

VFD 


STEP Time 

No. Min/Sec 


3.4 00:70 Pre-Flush begins 

3.5 05:70 Pre-Flush is complete 

4 05:70 RO START 

4.1 05:70 

Check if there is Low Pressure alarm 

(PIT36681 – PDT36867) 

4.2 05:70 Start SWRO HP Pump 0P-3630 

4.3 07:20 

4.4 07:20 

4.5 07:50 

PID control takes over & start 

modulating pump speed based on 

permeate flowrate setpoint 

Open permeate isolation valve XV- 

36884 

Close Permeate dump valve XV- 

36883 

Check if there is high-pressure 

alarm, PAH-36878 

4.6 07:50 Check if PY-36886 > 5 psi [1] 

4.7 07:50 HYDRAULIC CHECK 

4.8 07:50 

Check if concentrate flowrate is 

within 5% of setpoint (183 m³/hr) 

4.8 07:50 

Check if recovery is within 12.5% 

of setpoint, 40% [2] 



Reaction 

The VFD accelerate pump 

speed to “95% of the normal 

operating speed of the pump” 

at an approximate acceleration 

rate of 10psi/sec 

Check if permeate flowrate 

have reached setpoint of 122 

m³/hr within 5% 

Confirm the following 

positions: 



Alarm 

Conditions 

If suction pressure is 

below 2 barg for more 

than 30 sec., abort 

start-up. 

Check RUNNING 

feedback from 

VFD 

If pressure is > 80 barg 

for more than 30 sec., 



immediately (no 

delay) 

If Concentrate 

flowrate is < 

76.3 m³/hr for 

more than 3- 

sec, abort startup 


immediately after 10- 

minutes delay 

5.1 

Check permeate conductivity, AIT- 

36882 

If conductivity > 1000 

S/cm, indicate an 

alarm on HMI after 5- 

minutes delay. If 

conductivity remains 

greater than setpoint 

after 10 minutes, 


6 07:50 RUN 

6.1 07:50 RO Train confirmed in Run Condition 


operation have been met 

Indicate Train is 

in “SERVICE” 

status at HMI 

Note: 


3. PY-36886, SWRO HP Pump suction pressure, is the difference pressure of {PIT-36881-PIT-36878} or {PIT- 

36881-PIT-36879} 

4. Maximum allowable operating recovery is 45%. The high alarm setting is 50%. 


PX Projection 

Figure 62-3: PX Projection 


Chapter 63 : Control Philosophy of BWRO 




The BWRO water system, isolated between tanks T-3608 & tank 0T-3618, consists of the following equipment: 

1. There is SWRO permeate water tank, T-3608, which supplies feedwater to the BWRO trains 

2. BWRO LP pumps 0P-3614A/B which draw chlorinated water from SWRO product water tank T-3608 

3. There are (2) carbon filters, F-3611A/B, in series to de-chlorinate the water ahead of the BWRO trains. The 

activated carbon filters (GAC) to remove the chlorine from feedwater to BWRO. 

4. Common pH instrument, retractable type, located at the common effluent line from GAC filters, AIT-36997 

5. ORP instrumentation located at the effluent line from each GAC filter, AIT-36996A or B 

6. There are (2) duty/standby BWRO trains, 0PK-3603-F04A/F02B. Each BWRO train has a dedicated BWRO HP 

Pump, 0P-3643A or B, which are mounted on the skid. 

7. There is one Caustic Metering Pump, 0P-3621, to raise the BWRO feedwater to pH between 8 to 10. 

8. There is a tank downstream of the BWRO trains, 0T-3618, to store the permeate water (this tank is between 

the BWRO trains and EDI trains). 


In the normal operating cycle (AUTO), starting one BWRO train plant will be dictated by the level in the BWRO 

permeate storage tank 0T-3618. When there is call for water in this tank (LAL), the BWRO LP pump 0P-3614A will 

start pumping water thru the activated carbon filter housings, and BWRO train (pre-flushing). The permissive 

condition for starting the pump is the following: 

1. Level in the SWRO permeate water tank T-3608. If there is enough water above the centerline of the 

discharge piping of the BWRO LP pump skid, the duty pump will start automatically (there is no low-level 

alarm). 

2. BWRO LP pump, 0P-3614A/B must be in AUTO and READY 

3. BWRO trains are in AUTO and READY 







Here is a summary of the most important control strategies that are incorporated in the control of the BWRO are the 

following: 

In PLC AUTO mode, the RO train will be controlled by the rise or fall of water level in the storage tank 0T-3618. START 






Chapter 63 Control Philosophy - BWRO Page 62

1. If there is Fault or Trip alarm from BWRO LP Pumps 0P-3614A/B or BWRO HP pumps 0P-3643A/B 

2. If there is low-level alarm in the storage tank T-3608 

3. If there is low-pressure alarm on the suction line of the BWRO HP pump 

4. If there is ORP alarm from the lagging GAC filters 0F-3611A/B or none of the GAC filters are in service 

In PLC OFF, the BWRO HP pump shuts down and the RO is isolated. OFF is mainly reserved to allow maintenance on 

the RO unit. Please note that CIP is only done when the BWRO is in OFF cycle. 


alarm condition) will be followed immediately by flushing cycle. When a unit shut down, the caustic metering pump 

will stop. 

The 2 nd Pass BWRO Trains which is part of the DEMIN water sub-system will operate when there is demand for DEMIN 

water. However, the BWRO is isolated from the EDI system by the BWRO product water tank 0T-3618, so start & stop 

of the RO is controlled by the level in storage tank 0T-3618. 

In normal operation, the BWRO HP Pump is controlled by the PLC to maintain constant permeate flowrate. The VFD 

controls the speed of the pump in proportion to permeate flowrate. 

The BWRO Permeate conductivity is continuously monitored via a conductivity instrument and in the event the quality 

goes above the preset level, the off-spec product will be diverted back to SWRO Product Tank T-3608, by opening the 

Permeate Bypass Valve and closing the Permeate isolation valve. If the product quality does not improve within the 

preset time the BWRO Unit will shut down with an alarm indication. 

Upon any type of shutdown (normal or abnormal), the unit will go into post-flush cycle. 

Upon any type of startup, the unit will go into pre-flush cycle. 

The GAC Filters are arranged in series, once the lead filter is exhausted or requires backwashing, it will be bypassed 

and the second filter takes over. Backwashing is estimated to be required once every 7 days to ‘fluff’ the media and 

prevent clogging. 

The BWRO LP Pumps 0P-3614A/B pushes water thru two GAC (activated carbon filters) 0F-3611A/B. At the effluent 

from each GAC (Granular Activated carbon), there is an ORP monitor. When the plant starts, filter 0F-3611A is the 

lead filter & filter 0F-3611B is the lag filter. These filters will continue to remove chlorine until the 1 st filter is 

exhausted and chlorine breakthrough is detected by the ORP instrument AIT-36996A. When this occurs, filter A 

should be isolated, the carbon media is replaced, and this filter is put back into the service as the lagging filter. 

However, if there is elapsed time between replacing the media in filter A and the process continue as is, it is going to 

take a long time before filter B is exhausted. So, the ORP alarm that is critical to BWRO is always generated by the 

lagging filter or if one filter is operating. 

It is anticipated that the DEMIN system (BWRO & EDI) will not run continuously (few hours per day). The BWRO & EDI 

trains are programmed to alternate these units between lead & lag at each start. 



Table 63-1: Operational Modes 


BWRO Automatic Start 

BWRO Automatic Stop 

Alternation of BWRO train 

BWRO Operational modes 


Flushing 

Post-Flushing 

Pre-Flushing 

Description 

When there is call for water in tank 0T-3618 (or when level is below “Lo” preset 

alarm setting), the duty BWRO train will start. 

When there is no call for water in tank 0T-3618 and the level has reached the Hi 

level setting, the BWRO train will stop. 

The BWRO train duty/standby will alternate every 24-hours If BWRO train A has 

been running for example for 8-hours the previous day, BWRO train B will become 


SERVICE 

STANDBY 

PRE-FLUSH 

POST-FLUSH 

Type I Shutdown: This is an emergency shutdown due to process alarms which 

would cause significant damage to the membrane system if the process could 

shutdown normally. 

Type II Shutdown: This is a normal shutdown initiated by the operator or caused 

by alarms that would not cause damage to the process if the normal shutdown 

steps could occur. 

Each START & STOP will be preceded by at least 5-minutes flush. Flushing time 

will re-set during start-up (i.e., 2 – 5 minutes). The BWRO LP Pump will be used to 

flush water from tank T-3608 while the RO HP Pump is off. Flushing for BWRO is 

different from SWRO. The 2 nd pass does not have dedicated flushing system as in 

the SWRO. Pre-Flush and Post-Flush are the same. 

When BWRO shuts down, it will go into POST-FLUSH cycle before it is placed in 

STANDBY. Unlike SWRO, PRE-Flush & POST-Flush for the BWRO are the same. See 

description below. 

When BWRO starts, it will go into PRE-FLUSH cycle before it is placed in SERVICE. 

See description below. 

Post-Flush 

When BWRO shuts down, the following sequence occurs: 

1. Permeate dump valve XV-36818 opens 

2. Permeate isolation valve XV-36817 closes 

3. BWRO HP Pump Shuts down 

4. Modulating reject control valve FV-36821 opens to 100%. 

5. Flushing begin: BWRO LP Pump remain ON, permeate dump valve XV-36818 remain open after, feed isolation 

valve XV-36810 remain open 

6. Flushing timer zeroes out 

7. BWRO LP Pump Stops 

8. Feed isolation valve XV-36810 closes 

9. All other valves remain in their position 

Pre-Flush 

When BWRO Starts, the following sequence occurs: 


1. Permeate dump valve XV-36818 is open & remain open 

2. Permeate isolation valve XV-36817 is closed & remain closed 

3. BWRO HP Pump is OFF & remain OFF 

4. Modulating reject control valve FV-36821 is opens @ 100% 

5. Feed isolation valve XV-36810 open 

6. Flushing begin: BWRO LP Pump Starts after confirmation of all status of valves 

7. Flushing timer zeroes out 

8. BWRO HP Pump Starts 

9. Permeate isolation valve XV-36817 open 

10. Permeate dump valve XV-36818 closes 

11. Modulating reject control valve will go back to its previous position (95%), and PID control takes over & start 

modulating the valve 


Alarms 

Table 63-2: Summary of Alarms 


FAL-36821 

BWRO Reject Low Flow 

Alarm 

PY-36887 


PAH-36813 



AAH-36816 

BWRO Permeate 

Conductivity 

FAH-36821 

BWRO Reject High Flow 

Alarm 

BWRO High Recovery Alarm 

FAH-36814 

High Permeate Flow Alarm 

All other alarms & 

permissive conditions 

Description 

If reject flow drops to 0 m³/hr while BWRO is in SERVICE (i.e., operator closing a valve 

on the reject line, the BWRO will shut down immediately, and an alarm is initiated. 

This condition will damage the membranes. THIS IS A CRITICAL ALARM. 

This is calculated value (PI36711 – PDI36806) which monitors the suction pressure for 

the BWRO HP Pump 0P_3643. If pressure is less than 1 barg, stop BWRO train after 

time delay (3-5 sec.). Starving the pump will cause cavitation. THIS IS A CRITICAL 

ALARM. 

If the pressure on this line exceeds 31 barg (450psi), shut down BWRO unit 

immediately. This condition is related to safety of personnel. THIS IS A CRITICAL 

ALARM. 

If permeate conductivity > 40 S/cm, stop the BWRO after a time delay (10 minutes). 

This is the maximum conductivity limit for operation of the EDI. Please note that tank 

0T-3618 is 46.4 m³ (It will take at least 2-hours for the entire tank to reach that 

conductivity level). 

If reject flow > 17 m³/hr while BWRO is in PRE-FLUSH or POST-FLUSH due to 

malfunction of the reject flow valve FV-36821, the BWRO will abort the flushing cycle, 

and alarm is initiated. 

If FIT-36814 DIVIDED BY (FIT-36814 + FIT-36821) is HH (> 80%) for 30mins stop BWRO 

& initiates an alarm. Please note that it is common to operate a 2 nd pass RO up to 

90% recovery. 

If permeate flow increases above 22.2 m³/hr with time, that is an indication that 




Please refers to PID & associated interlocks. 


Types of BWRO Shutdown 

In general, there are two types shutdown: 

a) Emergency Shutdown: This shutdown is due to process alarms which would cause significant damage to the 

membrane system. 

b) Normal Shutdown: This shutdown initiated by high level in downstream storage tank, or manually initiated by 

operator. 

After any type of Shutdown, the BWRO is flushed with feedwater. 

Table 63-3: BWRO Train Emergency Shutdown Sequence 

STEP Time Operator Action and PLC Sequence 

No. Min/Sec 


1.1 00:00 

OPERATOR selects EMERGENCY 

SHUTDOWN from the HMI by selecting 

the Emergency Shutdown pushbutton 

OR 



Reaction 

RO Train shut-down is 

initiated. 

Run condition for the train is 

removed. 

Terminate Alarm Monitoring 

for RO Train. 

2 BWRO SHUTDOWN 

2.1 00:30 Stop BWRO HP Pump 0P-3643 completely PLC to confirm pump speed 

2.2 00:30 Stop Caustic dosing pump 0P-3621A or B Confirm dosing pump is OFF 

2.4 00:30 Close feed isolation valve XV-36810 Confirm ZSC-36810 is closed 

2.5 00:30 

2.6 00:60 

PLC will check the following permissive 

conditions to flush: 

Is there a low-level alarm ON in tank T- 

3608? 

Is there a FAULT from BWRO LP pump 0P- 

3614? 

Is there any ORP alarm (AAH-36996A or 

B)? 

Is there any FAULT from the following 

valves: 

Permeate dump valve, XV-36818 

Permeate iso. valve XV-36817 

Reject Control Valve FV-36821 

PLC commands RO valves to “Post-Flush” 

position as follows: 

Permeate dump valve, XV-36818 opens 


Reject Control Valve FV-36821open to 

100% 

2.7 If there is only ORP alarm (AAH-36996A 

or B), refer to note 1 


3.1 01:30 Start Flush Timer 

3.2 00:00 

BWRO LP Pump, 0P-3614A starts for the 

duration of flush 

If there is no Fault, proceed 

to step 2.6. 


Positions: 



Position feedback of FV- 

36821 

PLC to verify if feed 

Alarm 

Conditions 

If there is fault from any 

condition, abort Flush, 

alarm operator to clear 

the Fault & RESET the 

system 






RESET will be required 

to clear the fault. 


STEP 

No. 

Time 

Min/Sec 


3.3 06:30 End of Permeate Flush Timer 


4.1 06:30 


BWRO LP Pump, 0P-3614 shuts down 



4.3 Start the lag BWRO 


Reaction 


alarm in T-3608 is ON 

PLC to verify the following: 

BWRO LP Pump Stop 

feedback 



status at HMI 

Alarm 

Conditions 



RESET will be 


the fault. 

Notes 

1. If there is ORP alarm (AAH-36996A or B) from the lagging filter or from the only filter running, the PLC will 

command the system as followed: 

a. Stop BWRO HP Pump 0P-3643 completely (BWRO LP pump 0P-3614 remains ON) 

b. Open feed flush valve XV-36807 

c. Close feed isolation valve XV-36810 

d. Keep dumping water until all the steps below are completed: 

i. Activated carbon vessels 0F-3611 have been switched off from A to B or from B to A 

ii. ORP value start decreasing until is stabilized 

iii. ORP value have not changed for minimum of 5-minutes 

e. If ORP alarm remains ON and have not changed, the PLC will shut down BWRO LP Pump 0P-3614, and 

show an alarm on the HMI. Operator must put the system in manual mode, start BWRO LP pump 

while feed flush valve is open until all chlorinated water is flushed from the piping from the tank T- 

3608 to inlet of the BWRO skid. 


Table 63-4: BWRO Train Normal Shutdown Sequence 

STEP 

No. 

Time 

Min/Sec 


Reaction 


During RO system is running, an operator RO Train shut-down is 

selects the “System STOP” push button initiated. 

on the HMI Display. 

Run condition for the train is 

1.1 00:00 

OR 

removed. 

LAH-36802 level is ON (High level in 0T- Terminate Alarm Monitoring 

3618). 

for RO Train. 

OR 

A type II Alarm is active. 

2 BWRO SHUTDOWN 

Stop BWRO HP Pump 0P-3643: 

PLC to confirm pump speed 

2.1 00:30 Reduce speed of BWRO pump to 30% 

(adjustable) 

2.2 00:00 Stop Caustic dosing pump, 0P-3621A or B Confirm dosing pump is OFF 

PLC commands RO valves to “Post-Flush” Verify the following Valve 

position as follows: 

Positions: 

2.3 00:60 

Permeate dump valve, XV-36818 opens ZSO-36818 contact is closed 

Permeate iso. valve XV-36817 closes ZSC-36817 contact is closed 

Reject Control Valve FV-36821open to Position feedback of FV- 

100% 

36821 



3.2 00:00 

BWRO LP Pump, 0P-3614A remain ON for 

the duration of flush 

3.3 06:30 End of Permeate Flush Timer 


4.1 06:30 


BWRO HP Pump 0P-3643 shuts down 

completely 

BWRO LP Pump, 0P-3614 shuts down 




alarm in T-3608 is ON 

PLC to verify the following: 

BWRO HP Pump Speed 

BWRO LP Pump Stop 

feedback 



status at HMI 

Alarm 

Conditions 






RESET will be required 

to clear the fault. 



RESET will be 


the fault. 


Table 63-5: BWRO Train Start-Up Sequence 

STEP Time 

No. Min/Sec 


1 00:00 START-UP INITIATION 

System will start by pressing the Start 

1.1 00:00 

button on the HMI or by Low Level alarm 

in the Product Water Tank, 0T-3618 (LAL- 

36802 is ON) 

2 00:00 START PERMISSIVE CONDITIONS 

2.1 

2.2 

2.3 

0P-3614A or B must be in “Ready and in 

AUTO” 

BWRO High Pressure Pump 0P-3643 must 

be “Ready and in AUTO” 

Caustic Dosing Pump 0P-3621A or B must 

be “Ready and in AUTO” 

2.4 

There is no ORP Alarm from the lag unit 

of BWRO GAC (0F-3611A/B) 

PLC commands BWRO Train valves to 

Pre-Flush/start-up position: 

Feed isolation valve XV-36810 opens 

2.5 00:00 Reject Control Valve FV-36821 opens to 

100% 

Verify that Permeate dump valve, XV- 

36818 is still open 

3 PRE-FLUSH 

3.1 00:00 Start Pre-Flush Timer 

3.1 00:30 

PLC commands pumps to start: 

BWRO LP Pump 0P-3614 start 


Reaction 


Initiation” on HMI & PLC until 

the conclusion of Step 3. 

BWRO LP Pumps Ready. 

“Ready” signal from the VFD 

for BWRO HP Pump control 

Confirm “Ready” signal from 

Chemical Dosing Pump. 

System valves are driven to 

start-up position. 

PLC confirmed that all valves 

selected position is in correct 

position. 

Set @ 5 minutes for now (to 

be adjustable in the field) 

PLC will verify the following: 

BWRO LP pump RUNNING 

feedback 

3.2 05:30 Pre-Flush Timer zeros out 

4 START RO ON-LINE 

4.1 05:45 

BWRO HP Pump 0P-3643 starts: PLC will 

increase speed of the pump until the flow 

reaches 95% of its setpoint of 22.2 m³/hr. 

At this point, control of the VFD is 

handed over to the PID loop that controls 

the analog signal to the VFD based on 

permeate flow setpoint which is the loop 

variable. 

4.2 05:45 

PLC checks BWRO HP Pump suction 

pressure and flow conditions: 

Suction Pressure is > 1 bar (See note 1) Check PY-36887 [1] 

Concentrate Flow is 5.6 m³/hr ( 5%) 

High Permeate Press. PAH-36815 See note 2 

Reference speed feedback 

from of BWRO HP Pump 

Alarm 

Conditions 

If either pump is not in 

auto, then alarm. 

If both not in auto, 

abort startup. 

If any Chemical Dosing 

Pump Selector switch is 

not in “Auto”, abort 

system start-up and 

indicate fault at the HMI 

& PLC. 

Abort start-up if there is 

an ORP alarm (time 

delay = 3 sec.) 

If any valve did not 

provide correct 

feedback, abort system 

Start and indicate fault 

at HMI & PLC. 

If these conditions are 

not met, abort start-up 

and indicate fault at 

HMI & PLC. If met, 

continue with program. 


STEP 

No. 

Time 

Min/Sec 

4.3 05:45 


5.1 


Start duty Caustic Dosing Pump 0P-3621A 

or B when permeate flowrate reaches its 

setpoint 

Check if AIT-36809 (feed conductivity) is 

< 40S/cm. If not 

Open permeate isolation valve XV-36817 

Close permeate dump valve XV-36818 

PLC scans all parameter if no alarm is 

present. 

6 06:00 All checks are complete 

6.1 RO Train confirmed in Run Condition 


Reaction 

Check RUNNING feedback 

If conductivity > 40S/cm: 

Keep permeate dump valve 

open XV-36818 while 

permeate isolation valve 

remain closed 


operation have been met. 

Alarm 

Conditions 

If alarm is ON for 

more than 10 

minutes, abort 

start-up 

Indicate Train “RUN” 

status at HMI and PLC. 

Notes: 

1. Suction pressure is calculated by subtracting PIT-36711 – PDIT36806 

2. High Permeate pressure PY-36887 is {PIT-36815 - PDIT-36813} or {PIT-36815 - PDIT-36820}. For example, if 

BWRO LP Pump 0P-3614A is the duty pump, and BWRO train A is the duty RO, suction pressure is equal to 

PIT36711A - PDIT36806A. If the pressure > 5 psi, abort start-up & shut down unit without any delay. 


BWRO System 



Project Name: 




DESCRIPTION 



DRAWN By: 


REV: 

Sam Shaheen 

BWRO 

REVISED 

PAGE 

3/21/2016 

1 OF 7

Automatic Normal START of BWRO 

(page 1 of 3) 

Operator push 

START button 


0T-3618 

I 36-33 

A 

Step 1 

Is there Lo-Lo 

Level alarm in 

T-3608? 

(I 36-33) 


No 



36817 in AUTO 

and closed? 

Step 8 

Yes 

Step 2 

Is the duty BWRO 

train in AUTO? 

No 

The BWRO will 

not Start 

Show an alarm 

on the HMI & 

PCS 



36818 in AUTO 

and OPEN? 

Step 9 

Yes 

No 

Yes 

Step 3 

Is the BWRO 

Activated Carbon 

Filters in AUTO? 

No 


No 

Is the feed 


36810 in AUTO 

and closed? 

Step 10 

Yes 

Yes 

Step 4 

Is BWRO LP Pump 

0P-3614A Ready? 

No 


Refer to Interlocks I-36165 & I-36166 

on BWRO PID 

No 

Is the feed dump 

valve XV-36807 in 

AUTO & closed? 

Step 11 

Yes 

Yes 

Step 5 

Is BWRO HP Pump 

0P-3643 Ready? 

No 


Yes 

Is there ORP 

alarm from GAC? 

Step 12 

Yes 

No 

Step 6 

Is Caustic Pump 

0P-3621A Ready? 

No 


Start Pre-Flush 

Timer 

Step 13 

Yes 

No 

If there is no confirmation of OPEN status from 

limit switch, abort start-up 



Step 14 

(I 36-65/66) 

Step 7 

Is the Reject 

Control Valve FV- 

36821 in AUTO 

and 100% open? 

No 




No 

Valve Open 

Start BWRO LP 

Pump 0P-3614 


Yes 

A 



Project Name: 




DESCRIPTION 


Automatic Start 


DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 

3/21/2016 

2 OF 7


(page 2 of 3) 

From previous 

page... 

B 

Step 16 


high pressure 

alarm PAH- 

36813? 

Yes 


If the flow is below 5.6 m³/hr stop RO 

after time delay. 

Check if Reject 

flowrate is below 

set-point 

No 

No 

Step 17 

(I 36-68) 


high flow alarm 

FAH-36821? 

If the flow > 17 m³/hr, abort flushing & start-up 


If Recovery is less than or greater than 80% 

(±5%), abort after time delay (i.e., 10 minutes) 


below or above 

set-point 

No 

Pre-Flush Timer 

Elapsed 

Yes 

Check if PI-36813 

is > 31 barg? 

Check if PY-36887 

is < 2 barg? 

Yes 


No 


No 

Start BWRO HP 

Pump 0P-3643 



Pump Start 

VFD ramps up the speed of the 

pump to a preset point (i.e., 95%). 

A separate PID loop will take over 

controlling the pump speed until 

permeate flow reaches setpoint. 

Open Permeate 


XV-36817 

If there is no confirmation of OPEN status from limit switch, abort start-up 


Valve Open 


Dump Valve 

XV-36818 

If there is no confirmation of CLOSED status from limit switch, abort start-up 


Valve Closes 

Partially close reject 

control valve FV- 

36821 

If there is no confirmation of CLOSED status from limit switch, abort start-up 


B 


Project Name: 




DESCRIPTION 




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REVISED 

PAGE 

3/21/2016 

3 OF 7


(page 3 of 3) 

From previous 

page... 

No 

Check if permeate 

conductivity > 

high setpoint? 

> 40 mS/cm 

10-minutes 

delay 

Open 

Permeate 

Dump Valve 

XV-36818 

Is permeate dump 

valve open 

confirm? 

Conductivity remain at 40 mS/cm for more 

than 10-minutes 


Yes 

Abort start-up if OPEN feedback is not received 


Start Caustic 

injection 

RO in SERVICE 


Project Name: 




DESCRIPTION 




DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 

3/21/2016 

4 OF 7

Normal Shutdown of BWRO 

(page 1 of 2) 

Push STOP button 

High Level Alarm in 

0T-3618 

Is BWRO in 

AUTO? 

No 

Shut down unit 

manually 

Yes 


0P-3643 

Step 1 

If there is no confirmation of STOP status, abort Flushing cycle 

Abort Flush 

Alarm on HMI 

Pump OFF 

Stop Caustic 

Injection 

Step 2 


Show Warning 

on the HMI 

Pump OFF 

Open Permeate 

Dump Valve 

XV-36818 

Valve Open 

Step 3 

If there is no confirmation of OPEN status, abort Flushing cycle 

Abort Flush 

Alarm on HMI 



36817 

Step 4 

If there is no confirmation of CLOSED status, abort Flushing cycle 

Abort Flush 

Alarm on HMI 

Valve Close 

Open reject control 

valve FV-36821 to 

100% 

Step 5 

If the valve do not open to 100% & remain in its position, abort Flushing cycle 

Abort Flush 

Alarm on HMI 

Valve Confirmed 100% OPEN 


Timer 

Step 6 



Project Name: 




DESCRIPTION 




DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 

3/21/2016 

5 OF 7

Normal Shutdown of BWRO 

(page 2 of 2) 

From previous 

page... 

Stop BWRO LP Pump 

0P-3614 after Flush 

cycle ends 

Step 7 


Abort Flush 

Alarm on HMI 

Pump OFF 

Close feed inlet 


Step 8 


Abort Flush 

Alarm on HMI 

Valve Closed 

Place BWRO in 

STANDBY Mode 


Project Name: 




DESCRIPTION 




DRAWN By: 


REV: 

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REVISED 

PAGE 

3/21/2016 

6 OF 7

Abnormal Shutdown of BWRO 

(page 1 of 1) 

Operator Push 

Emergency 

Shutdown 



OR 



0P-3643 


Abort Flush 

Alarm on HMI 

Pump OFF 

Stop Caustic 

Injection 


Show Warning 

on the HMI 

Pump OFF 

Open Permeate 

Dump Valve 

XV-36818 

Valve Open 

If there is no confirmation of OPEN status, abort Flushing cycle 

Abort Flush 

Alarm on HMI 



36817 


Abort Flush 

Alarm on HMI 

Valve Closed 

Open reject control 

valve FV-36821 to 

100% 

If the valve do not open to 100% & remain in its position, abort Flushing cycle 

Abort Flush 

Alarm on HMI 

Valve Confirmed 100% OPEN 


Timer 

Stop BWRO LP Pump 

0P-3614 after Flush 

cycle ends 


Abort Flush 

Alarm on HMI 

Pump OFF 




Abort Flush 

Alarm on HMI 

Valve Closed 

Place BWRO in Out 

of Service Mode 


Project Name: 




DESCRIPTION 




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REV: 

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REVISED 

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7 OF 7

Chapter 64 : Control Philosophy of EDI 




1. There is feedwater tank between the 2 nd pass RO and EDI, 10 m³ capacity, 0T-3618. The tank is equipped with 

DP level transmitter, LIT-36802. 

2. There is a set of (2) duty/standby EDI feed pumps, 0P-3622A/B with a throttling valve on the discharge line of 

the pumps. 

3. There is a set of two duty/standby EDI skids, each equipped with a control panel. The OEM have supplied an 

HOA selector switch, an Emergency pushbutton, and a RESET button. There is no dedicated PLC provided by 

Agape, all instruments are wired to a junction box. All electrical connections are connected to a centralized 

PLC. 

4. This system uses Ionpure CEDI VNX30-2 and is assembled by Agape Water Solutions (the OEM). 

5. DEMIN storage tank, T-3603, built by the owner (Chevron) 

The EDI Trains are controlled by the level in DEMIN Storage Tank T-3603. When there is call for water (or when level 

is below “Lo” preset alarm setting), the EDI train will start. When there is no call for water and the level has reached 

the Hi level setting, the EDI train will stop. 


In the normal operating cycle (AUTO), starting one EDI train plant will be dictated by the level in the DEMIN storage 

tank T-3603. When there is call for water in this tank (LAL), the duty EDI feed pump 0P-3622A will start pumping 

water thru the EDI. The permissive condition for starting the EDI feed pump and EDI is the following: 

1. Level in the EDI feedwater tank 0T-3618. If there is enough water above the centerline of the discharge piping 

of the EDI feed pumps skid, the duty pump will start automatically (there is no low-level alarm). 

2. EDI feed pumps, 0P-3622A/B must be in AUTO and READY 

3. EDI systems, 0R-3602A/B must be in AUTO and READY 

4. Feedwater conductivity cannot exceed 40µS/cm. This is the 2 nd pass permeate water stored in the tank. The 

conductivity in the tank may be higher than the actual conductivity reading on the BWRO permeate line due 

to possible intrusion of CO 2 into the tank. 

Please note that EDI feed pumps and EDI skids have HOA selector switch in local panels which we are going to refer to 

as hard signal. HMI also HOA selector switch which we are going to refer to it as soft signal. The hard signal override 

the soft signal. The only way you can have full control of the pump and the EDI system on the HMI, it is when the 

actual selector switch in the local control panel is in AUTO. 


When there is no demand for water in the DEMIN water tank T-3603, a high-level alarm will terminate the run signal 

for the operating EDI train. When there is demand for water (when there is low level alarm in the tank), the lead EDI 

train will start. 

It is anticipated that the EDI will not run continuously (few hours per day). The EDI trains are programmed to 

alternate the EDI train between lead & lag at each start. 

Chapter 64 Control Philosophy - EDI Page 72

Operating Procedures 

The control system is comprised of one nonprogrammable EDI power supply control panel per skid with all 

instrumentation wired to terminals in the centralized Xylem’s PLC control panel. Any operation outside the design 

requirements as outlined in the manual can cause permanent damage to the EDI modules. 

Each EDI train has its own free standing panel with DC power supplies inside the panel to power up the modules. The 

face of the panel has voltage/current monitor, Resistivity/Temp. monitor, E-Stop pushbutton, RESET pushbutton, HOA 

Selector Switch, Power ON light. 

Please note: The Feed water to the EDI must always be of acceptable quality. The 

specifications call for water less than 40 S/cm from the BWRO permeate. 

Table 64-1: Operational Modes 

Operation 

EDI Automatic 

Operation 

Alternation 

(Lead/Lag) 

Automatic 

Flushing 

Modes of 

Operation 

Standby 

Start-Up 

EDI-DIVERT 

Operation Description 

The EDI Trains are controlled by the level in DEMIN Storage Tank T-3603. When there is call for 

water (or when level is below “Lo” preset alarm setting), the EDI train will start. When there is no 

call for water and the level has reached the Hi level setting, the EDI train will stop. 

It is anticipated that one EDI train will operate few hours every day to fill the DEMIN water tank. 

Therefore, the Lead/Lag alternation of each train will be set at 24 hours. In other words, each 

train will alternate from lead to lag and vice versa every time an EDI train starts or stops. 

For optimal performance and to prevent biofouling, EDI is programmed to power on and rinse to 

drain at least once every 24 hours of idle. 

List of specific of specific operating modes: 

1. STANDBY 

2. EDI-RINSE 

3. EDI OPERATE 

4. AUTO-SHUTDOWN 

In standby mode, the EDI valves are all closed and the system awaits the call for water. For more 

detailed on the position of each valve, refer to DWG 3452-2EDI-DWG-4. 

All feed water to the EDI must enter slowly. Water Hammer is not acceptable and will cause 

permanent damage to the EDI. Slowly open all valves and size interconnecting piping with 

acceptable flow velocities. Wait at least 5 seconds before one valve is completely open before 

closing another valve. Always ensure flow path is present. 

The Feed water to the EDI must always be of acceptable quality. Allow the RO system to flush to 

drain for an acceptable period before feeding the EDI system, and return the RO to divert mode if 

RO permeate conductivity exceeds acceptable level 

When the EDI system first starts, the water is diverted to drain. 

1. Confirm EDI product valve XV36774 is closed. 

2. Open EDI product-divert valve XV36775. 

3. Open Feed valve XV34680 

4. Establish RO product water flow thru the EDI module. Read the flows from FIT-36769 & 

FIT-36771. If acceptable, turn on EDI power. 

5. If flow rates drop out of specifications, immediately shutdown EDI power and divert flow 

back to 0T-3618. 

6. If the readings are within the specifications, then Divert EDI product water to 0T-3618 for 

1 minute. 


Operation 

Operation Description 

7. Run the EDI for 1 minute in “RINSE” mode where EDI product water is diverted back to 

the above tank. After time elapses: 

8. Check AIT36772. If product water is acceptable, begin “EDI Operation” mode. 

9. If AIT36772 is not acceptable, run system in “EDI Divert” mode for 2 minutes and return 

to step 1. 

NOTE: EDI Divert should not occur for longer than 1 hour. Divert time is a customer preference. 

Sometimes additional run time allows resin to regenerate, but if power is not sufficient it could 

exhaust resin. 

See EDI alarm schedule shutdown & delay. 

EDI-OPERATE 

Emergency 

Stop (E-Stop) 

Auto- 

Shutdown 

EDI Operate Mode fills Demin water storage tank. 

1. Confirm no alarm from the BWRO unit (permeate conductivity > 40S/cm) 

2. Confirm no EDI alarms. 

3. Open EDI product water valve XV36774, wait 5 seconds 

4. Close EDI drain valve XV36775. 

5. If the quality of the solution (AIT36772) goes bad, return EDI system to “EDI Rinse” mode 

and alarm. 

6. After Call for Demin water is present, start Auto shut down. 

Activation of system E-Stop will stop all EDI module power, close all valves and place the system 

in Standby-Mode until the E-STOP is cleared. 

When Demin water storage tank is full, return to standby mode. 

1. Power off EDI Modules 

2. Close Feed valve XV34680, wait 5 seconds 

3. Close EDI product water valve XV36774, wait 5 seconds 

4. Close EDI product-divert valve XV36775. 

Auto shut down returns unit to standby for short term module storage. 


Alarms and Interlocks 

Here is a list of alarms and interlocks associated with this unit: 

Table 64-2: Summary of Operational Conditions for the EDI 


Description 

If EDI power Supply is commanded ON and ON feedback is not received, the 

Power Supply Fault 

system immediately goes into standby. 

FIT-36769 EDI Product Flow If FIT-36769 is below 6.8 m³/hr for more than 20 seconds and the system is in EDI OPERATE 

mode, an auto-shutdown is performed and the system is placed into standby. If the 

system is not in RO-EDI mode, then the system will go immediately into standby mode. 

An alarm is sent to the HMI. 

FIT-36771 

If FIT-36771 is below 1.36 m³/hr for 20 seconds and the system is in EDI- OPERATE, 

EDI Concentrate Flow auto-shutdown is performed and the system is placed into standby. If the system is not 

in RO-EDI mode, then the system will go immediately into standby mode. An alarm is 

sent to the HMI. 

EDI Recovery 

If FIT-36769 DIVIDED BY (FIT-36769 + FIT-36771) is HH (> 90%) for 30mins and the 

system is in EDI operation mode an auto-shutdown is performed and the system is 

placed into standby. If the system is not in RO-EDI mode, then the system will go 

immediately into standby mode. An alarm is sent to the HMI. 

AIT-36772 

If AIT-36772 is below 10 mΩ-cm, then move sequence back to EDI-Rinse and resume 

EDI product Resistivity process from that step. Alarm to HMI. 

TIT-36773 

HH alarm: 43.3ºC (Shutdown) 

Product Temperature H alarm: 37.8 ºC (Warning) 

L alarm: 10ºC (Warning) 

LL alarm: 1.67ºC (Shutdown) 

Inlet Conductivity, AIT- If conductivity is > 40 µS/cm & EDI train is in EDI OPERATE, the unit will shut down. 

36712 (From BWRO) Operator must act to flush tank 0T-3618 tank. 

Inlet Pressure, PI-36841 See note 1 

LT-36802 Tank 0T-3618 HH alarm: 1900mm; H alarm: 1600mm; LL alarm: 211mm 

L alarm: 794mm Shut down EDI feed pumps & EDI trains 

Notes: 

1. There are no pressure transmitters on these units and there is no scenario where pressure can get that high 

(i.e., shutoff head of EDI pumps is lower than 6 barg). Operator must visually inspect pressure gauges & shut 

down unit if the pressure in the range of 6.2 to 6.9 barg. 

The table below shows alarm conditions for all analog I/O. All alarm set points are Low (L) or High (H) and all interlock 

set points are High-High (HH) or Low-Low (LL). All Set-Points are entered from screens located at the local HMI. 

Table 64-3: EDI Alarm Conditions 

Instrument Unit LL L H HH 

LT-36802 

Feed Tank 0T-3618 

mm 

DEMIN Water Tank T-3603 

mm 

AIT-36772 

(Product Resistivity) 

mΩ-cm 

10 minimum 

TIT-36773 ºC 1.67 10 37.8 43.3 


Instrument Unit LL L H HH 

(Product Temperature) (ºF) (35) (50) (100) (110) 

FIT-36769 

(Product Flow) 

m³/hr 

(gpm) 

6.8 

(30) 

FIT-36771 

(Concentrate Flow) 

m³/hr 

(gpm) 

1.36 

(6.0) 

Recovery % 90 

Inlet Pressure, PI-36841 

(From RO) 

barg 

(psi) 

6.2 

(90) 

6.9 

(100) 

Inlet Conductivity, AIT-36712 

(From BWRO) 

µS/cm 40 

Table 64-4: EDI Operation Modes 

Device Tag Standby Mode EDI Rinse Mode EDI Operate 

XV-36840 (EDI Feed) Closed Open Open 

XV-36774 (EDI Product) Closed Closed Open 

XV-36775 (EDI Product Divert) Closed Open Closed 

EDI Power Supply OFF ON ON 

Start-Up 

All feed water to the EDI must enter slowly. Water Hammer is not acceptable and will cause permanent damage to 

the EDI. Slowly open all valves and size interconnecting piping with acceptable flow velocities. Wait at least 5 

seconds before one valve is completely open before closing another valve. Always ensure flow path is present. 

The Feed water to the EDI must always be of acceptable quality. Allow the RO system to flush to drain for an 

acceptable period before feeding the EDI system, and return the RO to divert mode if RO permeate conductivity 

exceeds acceptable level 

EDI Divert 

1. When the EDI system first starts, the water is diverted to drain. 

2. Second Pass RO rinse cycle is complete and RO is in operation mode. 

3. Confirm EDI product valve XV-36774 is closed. 

4. Open EDI product divert valve XV-36775. 

5. Open Feed valve XV-36840 

6. Establish RO product water flow thru the EDI module. Read the flow FIT-36769 & FIT-36771. 

7. If acceptable, turn on EDI power. 

8. If flow rates drop out of specifications, immediately shutdown EDI power and return RO to “2 nd Pass RO Divert 

Mode”. 

9. If the readings are within the specifications, then Divert EDI product water to drain for 1 minute. 

Run the EDI for 1 minute in “RINSE” mode where EDI product water is diverted to drain. After time elapses: 


a) Check AIT-36772. If product water is acceptable, begin “EDI Operation” mode. 

b) If AIT-36772 is not acceptable, run system in “EDI Divert” mode for 2 minutes and return to step a. 

NOTE: EDI Divert should not occur for longer than 1 hour. Divert time is a customer preference. Sometimes additional 

run time allows resin to regenerate, but if power is not sufficient it could exhaust resin. 


EDI Operation Mode 

EDI Operate Mode fills Demin water storage tank. 

1. Confirm no RO alarms. 

2. Confirm no EDI alarms. 

3. Open EDI product water valve XV-36774, Wait 5 seconds 

4. Close EDI drain valve XV-36775. 

5. If the quality of the solution (AIT-36772) goes bad, return EDI system to “EDI Rinse” mode and alarm. 

6. After Call for Demin water is present, start Auto shut down. 


System Safety Requirements 

There is a system E-Stop. Activation of system E-Stop will stop all EDI module power, close all valves and place 

the system in Standby-Mode until the E-STOP is cleared. Emergency stop is an emergency condition which 

immediately shuts down all components and places the system in standby mode until the E-STOP fault is cleared. E- 

STOP is SET when healthy and RESET when unhealthy. 


Alarms 

Alarm 

Power Supply Fault 

FIT-36769 EDI 

Product Flow 

FIT-36771 

EDI Concentrate 

Flow 

EDI Recovery 

AIT-36772 

EDI product 

Resistivity 

Description 

If EDI power Supply is commanded ON and ON feedback is not received, the system 

immediately goes into standby. 

If FIT-36769 is HH or LL for 20 seconds and the system is in EDI-RO operates mode an autoshutdown 

is performed and the system is placed into standby. If the system is not in RO-EDI 

mode, then the system will go immediately into standby mode. An alarm is sent to the HMI. 

If FIT-36771 is LL for 20 seconds and the system is in EDI- RO operation mode an autoshutdown 

is performed and the system is placed into standby. If the system is not in RO-EDI 

mode, then the system will go immediately into standby mode. An alarm is sent to the HMI. 

If FIT-36769 DIVIDED BY (FIT-36769 + FIT-36771) is HH for 30mins and the system is in EDI 

operation mode an auto-shutdown is performed and the system is placed into standby. If the 

system is not in RO-EDI mode, then the system will go immediately into standby mode. HMI 

will display an alarm. 

If AIT-36772 initiates a Low-Low resistivity alarm, then move sequence back to EDI-Rinse and 

resume process from that step. HMI will display an alarm. 


EDI System 



Project Name: 




DESCRIPTION 


EDI System 

DRAWN By: 


REV: 

Sam Shaheen 

EDI 

REVISED 

PAGE 

3/22/2016 

1 OF 5

Automatic Normal START of EDI 

(page 1 of 2) 

Operator push 

START button 


T-3603 

Step 1 

(I 36-80) 

A 

Is there LoLo level 

alarm in 0T-3618? 

Step 2 

(I 36-82) 


No 

Is the feed 


36840 in AUTO 

and closed? 

Step 8 

Yes 

If there is no confirmation of OPEN, abort 

start-up 



Step 9 

Step 3 

PLC sends a 

Remote ON signal 

Valve Open 

Start duty EDI feed 

pump 0P-3622 

Step 10 

Step 4 

Is EDI in AUTO 

Yes 

No 


(I 36-86) 


If the flow < 20 m³/hr, 


No 

Step 11 

(I 36-92) 

Check product 

flow from FIT- 

36769? 

If the flow = 20 m³/hr, 

go to next step 

Step 5 

Is the EDI Feed 

Pump 0P-3622A 

Ready? 


If the flow < 1.38 m³/hr, abort 

start-up 

Step 12 

(I 36-93) 

Check 

concentrate flow 

from FIT-36771? 

Yes 

If the flow = 2.2 m³/hr, 

go to next step 

Step 6 

Is product valve 

XV-36774 in 

AUTO and closed? 

No 


Step 13 

(I 36-97) 


it is @ set-point 

Yes 

Step 7 


divert valve XV- 

36775 in AUTO 

and open? 

No 


Product & concentrate 

flows did change 

Yes 

Turn ON EDI power 

Step 14 

Yes 

Product & 

concentrate flows 

did not change 

A 



Project Name: 




DESCRIPTION 



EDI Trains 

DRAWN By: 


REV: 

Sam Shaheen 

EDI 

REVISED 

PAGE 

3/22/2016 

2 OF 5

If product resistivity 

> 10 mW /cm 

From previous 

page... 

Automatic Normal START of EDI 

(page 2 of 2) 

Continue EDI 

RINSE Cycle for 

max. of 30 

minutes 

Check product & 

concentrate 

flowrates? 


If product resistivity 

remains less than 10 

mW /cm 

Stop EDI power 

Remote ON disabled 

Start EDI RINSE cycle 

for 1 minute 

Step 17 

Shut Down EDI feed 

Pump 

EDI operating & producing 

water. Product water is 

diverted to drain. 

Step 18 

Stop EDI RINSE cycle 

after 1 minute 

If Recovery is less than or greater than 

90% (±2%), abort after time delay 


Pump OFF 

Switch duty EDI 

Train to Standby 

No 

Start Lagging EDI 

Train 

Step 19 

(I 36-90) 

Check Product 

Resistivity? 

If product resistivity < 10 mW /cm 

Start EDI RINSE 

Cycle for 2 

minutes 

Step 20 

(I 36-96) 

Check Product 

Temperature? 

Notes: 

If at any point there is a loss of power from any of the power module, the 

EDI train goes into shutdown (Interlock 36-95) 

Abort 

Start-Up 

No 

Open Product 


36774 

If product resistivity improved & now > 

10 mW /cm 

Valve Open 

Close Product dump 


No 

Abort 

Start-Up 

Valve Closed 

Switch to EDI 

OPERATE Mode 


Project Name: 




DESCRIPTION 



EDI Trains 

DRAWN By: 


REV: 

Sam Shaheen 

EDI 

REVISED 

PAGE 

3/22/2016 

3 OF 5

Normal Shutdown of EDI Train 

(page 1 of 1) 

Push STOP button 

High Level Alarm in 

T-3603 

PLC remove the 


Is EDI in AUTO? 

No 

EDI will Not 

Start 

Alarm on HMI 

Alarm on HMI 

and PCS 

Power-off EDI 

If there is no confirmation from Remote Start Status 

Alarm on HMI 

Stop duty EDI feed 

pump 

If there is no confirmation of STOP Status 

Alarm on HMI 

Pump OFF 



If there is no confirmation of CLOSED Status 

Alarm on HMI 

Valve Closed 


isolation valve 

XV-36774 

Wait 5 seconds after confirmation of CLOSED Status 

If there is no confirmation of OPEN Status 

Alarm on HMI 

Valve Closed 




36775 


Alarm on HMI 

Valve Closed 

EDI Train is placed in 

LAG mode 


Project Name: 




DESCRIPTION 



EDI Trains 

DRAWN By: 


REV: 

Sam Shaheen 

EDI 

REVISED 

PAGE 

3/22/2016 

4 OF 5

Abnormal Shutdown of EDI Train 

(page 1 of 1) 

Operator Push 

Emergency 

Shutdown 



OR 


PLC remove the 


Power-off EDI 

If there is no confirmation from Remo te Start Status 

Alarm on HMI 

Stop duty EDI feed 

pump 

If there is no confirmation of STOP Status 

Alarm on HMI 

Pump OFF 




Alarm on HMI 

Valve Closed 


isolation valve 

XV-36774 


If there is no confirmation of OPEN Status 

Alarm on HMI 

Valve Closed 




36775 


Alarm on HMI 

Valve Closed 

EDI Train is placed in 

Out of Service 


Project Name: 




DESCRIPTION 



EDI Trains 

DRAWN By: 


REV: 

Sam Shaheen 

EDI 

REVISED 

PAGE 

3/22/2016 

5 OF 5

Chapter 65 : Control Philosophy of Calcite Bed Contactors 

In the Wheatstone project, there two REMIN systems: One for UW (Utility Water), and one for PW (Potable Water). A 

common CO 2 storage tank with two different panels (one for UW & one for PW), will inject CO 2 as gas to the inlet of 

both streams. The intent of this unit is to add alkalinity & calcium to the water by dissolving the calcite media as it 

travels thru the calcite bed. The injection of CO 2 in the feed stream to the calcite filters will drop the pH of the 

incoming water allowing the calcite media to dissolve more quickly. 

Each Remin system (potable or utility) consists of two vessels operating in parallel. Calcite filters are loaded with 

calcite media to adjust the pH of the SWRO product water to make it suitable for potable water (PW) & utility water 

(UW). The water entering the calcite filters flows from top to bottom. In both cases, the two vessels operate as 

duty/standby. 

The BW is initiated manually by totalized flowrate. The flowmeter is located at the common effluent from both 

vessels. When the totalized flow reaches a setpoint, the operator must check visually the level of calcite in the tank, 

and if the level drops to the recharge level, the lagging unit is placed in duty and the leading unit is placed in standby. 

The unit in standby should be loaded with calcite, and backwashed manually. In this project, they did not include a 

rinse valve like typical filter (Australian design). 

Differential 

Level 

LIT 

Calcite Filters 

The flow of the effluent water is monitored by a magnetic flow transmitter located on the common effluent line from 

both vessels. The flow transmitter will totalize the flow and will initiate a warning when the totalized flow reached its 

setpoint, and automatically switch over from filter A to filter B or vice versa. The warning will appear on the HMI 

screens until operator recharge the vessel with calcite media. 

Level of calcite in the tank is monitored by differential pressure transmitter which measures the difference of pressure 

between the top of the vessel & bottom of the vessel and translates that to difference in level. If the level drops to 

the low-level alarm before the totalized flow warning, the PLC will automatically switch over from tank A to B or vice 

versa, and indicate an alarm on the HMI screens until operator recharge the empty vessel. 

After loading the media, the filters are backwashed for few minutes to remove any dirt & debris, and put back to 

service. 

Chapter 65 Control Philosophy - Calcite Bed Contactors Page 79

Service 

Inlet 

BW 

Outlet 

Service Water 

Service 

Outlet 

BW Water 

BW 

Inlet 

Drain 

Effluent 

Calcite Filter in Service 

Figure 65-1: Calcite Filters in Service Cycle 


Service 

Inlet 

BW 

Outlet 

Service Water 

Service 

Outlet 

BW Water 

BW 

Inlet 

Drain 

Effluent 

Calcite Filter in Backwash 

Figure 65-2: Calcite Filters in BW Cycle 

We will describe the UW system only in this section. The feed pumps supplying water from tank T-3608 to the filters 

are 0P-3604A/B, and the backwash pump 0P-3635 will be used to BW the calcite filters 0F-3610A/B. 

In automatic mode, flowmeter FIT-36035 on the utility line will totalize the flow. Once the total flow reaches a 

setpoint of 68,000 m³ (to be adjustable after start-up & commissioning), the PLC will switch operation to the lagging 

tank, and initiate a warning to instruct operator to go and inspect the level of calcite in the exhausted vessel. 

In this system, CO 2 is injected at the inlet of the skid at the static mixer SP-36230, and Soda Ash is injected at the 

outlet of the skid at the static mixer SP-36164. 


The calcite filters for UW has the following instrumentation: 

Instrument Description Alarm Setpoint 

PDIT-36889A/B Diff. Press. XMTR on each vessel 0F- ½ bar above clean water P 

3610A/B 

AE/AIT-36916 

FIT-36035 

FIT-36983 

PI-36982 

pH sensor/monitor @ the common 

effluent from calcite filters 

This is a signal (analog input) provided by 

BECHTEL’s DCS. It is the responsibility of 

Xylem to totalize the flow & initiate BW. 

The instrument is located on equipment 

provided by BECHTEL. 

Magnetic flowmeter to monitor the BW 

flowrate (discharge of 0P-3635) 

Pressure gauge at the discharge of the BW 

Pump 0P-3635 

If pH > 8.5, stop Soda Ash pumps 0P- 

3648A/B 

Totalized flow setpoint: 68,000 m³ (FY- 

36460) 

FAH-36460 is high flow alarm that will 

shut down the unit if the peak flow 

exceeds 126.7 m³/hr 

If low flow alarm is initiated, the PLC will 

abort the BW cycle & stop the BW pump 

0P 0P-3635 

The filters will be backwashed automatically based on timer or if there is a differential pressure increase between 

inlet & outlet. If the BW is initiated based on differential pressure, the BW Frequency timer will be reset to zero. The 

valve tag numbers associated with each vessel is shown below. 

Valve 

Vessel 

0F-3610A 

0F-3610B 

Service Inlet Valve XV-36732A XV-36732B 

Service Outlet Valve XV-36891A XV-36891B 

BW Inlet Valve XV-36890A XV-36890B 

BW Outlet Valve XV-36924A XV-36924B 


Figure 65-3: Calcite Filters for UW 

Soda Ash 

CO2 Gas 

Xylem’s Scope 

(Skid Mounted) 

PK-3611 


0F-3609A/B 

PDIT 

36849 Xylem’s Scope (Skid Mounted Unit) 

Chlorine 

Analyzer 

Vent 

Tank T-3608 

FIT 

36050 

AIT 

36523 

Cartridge 

Filter 

Housing 

316SS 

Chlorine 

Analyzer 

AIT 

36851 

Sample 

Sample 

0P-3608A/B 

0T-3605 

Potable Water Tank 

317 m³ 

Drain 

Drain 

Vent 

0P-3634 

BW Pump 

Refer to DWG # 

WS1-*-00014 

0P-3605A/B 

Cartridge 

Filter 

Housing 

316SS 

Sample 

Sample 

Drain 

From Calcium Hypo 

Tank T-3623 

0P-3646A/B 

Xylem’s Scope (Skid Mounted Unit) 

Cart. Housings 

0PK-3606 

0F-3606A/B 

Duty/Standby 

Drain 

UV Sterilizers 

0PK-3605-R01A/1B 

Duty/Standby 

Figure 65-4: Calcite Filters for PW (Potable Water) 

Chapter 65 Control Philosophy of Calcite Bed Contactors Page 83

UW & PW Calcite Filters 



Project Name: 




DESCRIPTION 



0F-3609A/B, 0F-3610A/B 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 

3/8/2016 

1 OF 6

Service 

Inlet 

BW 

Outlet 

CO 2 

BW 

Inlet 

Calcite Filter 

UW/PW 

PDIT 

SWRO Permeate 

Storage Tank 

Service 

Outlet 

Soda Ash 

T-3608 

AIT 

pH 

Feed Pump 

BW Pump 

Calcite Filter 

UW/PW 

PDIT 

Drain 

Equip. 

UW 

PW 

Tag No. Tag No. 

Feed Pump 

BW Pump 

0P-3604A/B 

0P-3635 

0P-3608A/B 

0P-3634 

Service Inlet Valves XV-36732A/B XV-36928A/B 

Service Outlet Valves XV-36891A/B XV-36931A/B 

BW Inlet Valves 

BW Outlet Valves 

XV-36890A/B 

XV-36924A/B 

XV-36932A/B 

XV-36933A/B 

Diff. Press. Transmitters PDT-36889A/B PDT-36930A/B 

pH Transmitter 

AIT-36916 AIT-36917 


0F-3610A/B 0F-3609A/B 

Package 

0PK-3612 0PK-3611 

Avg./Peak Flowrate (m³/hr) 90/127 10/10 

Provided by BECHTEL 

UW: 263 m³/hr @ 20m, 22KW motor 

PW: 29 m³/hr @ 20m, 4KW motor 

BW should be conducted every time you refill the vessels with 

media 

Frequent BW between refill will be set by a timer (once a week, 

or twice a week, etc ) – only for duty vessel. 

Target pH: 7.0 to 8.5 max. 

UW: 2017mm ID x 3384mm H 

PW: 950mm ID x 2084mm H 


Project Name: 




DESCRIPTION 


Sketch of Calcite Filters 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 

3/8/2016 

2 OF 6

Automatic Normal STARTUP of Calcite Filters 

Operator push 

MANUAL/START 

button 

Signal from UW or 

PW (Call for water) 

The Calcite 

Filters will not 

Start 

No 

Show Alarm 

on HMI/PCS 

Is the System in 

AUTO? 

Step 1 

No 

A 

Yes 

Yes 

Is there Low 


0T-3608? 

Step 2 

Yes 

Abort Start- 

Up 


No 

Are the Feed 

pumps in AUTO 

& Ready? 

Step 7 

No 

Yes 

Is the Service 

inlet valves in 

AUTO and 

closed? 

Step 3 

No 

Abort Start- 

Up 

If there is no confirmation of OPEN 

status from limit switch, abort start-up 

No 

Open Service Inlet 

& Outlet Valves 

Step 8 

Yes 

Yes 

Is the Service 

Outlet valves in 

AUTO and 

closed? 

Step 4 

No 

Abort Start- 

Up 

No 

Start Duty Feed 

Pump 

Step 9 

Yes 

Is the BW Inlet 

valves in AUTO 

and closed? 

Yes 

Step 5 

No 

Abort Start- 

Up 

NOTES: 

Call for Water Signal: This is 

discrete signal from BECHTEL s 

PCS. 

Is the BW Outlet 

Valves in AUTO 

and closed? 

Step 6 

Yes 

A 

No 

Abort Start- 

Up 

Step 1: System in AUTO 

The two unit will operate either in 

parallel or duty/standby. Disabling 

or enabling the duty/standby or 

duty/duty will be built into the 

parameter setpoint screen. 


Project Name: 




DESCRIPTION 


Calcite Filters Automatic 

Start-up 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 

3/8/2016 

3 OF 6

There are two levels in calcite filters: The refill level which is the minimum level required for the unit to operate, and the 

maximum level. When the calcite level reaches the refill level, operator must isolate the vessel, and refill the tank with calcite 

to the maximum level and backwash the media before placing the unit in service. In the case of the UW REMIN, the setpoint 

to check the level is set at 68,000 m³ totalized flow thru the unit. For the PW REMIN, the setpoint is 6,000 m³. 

Maximum level 

Differential 

Level 

Refill level 

LIT 

UW REMIN: 

FT 

36035 

FQI 

36460 

FQI 

36460 

Totalized Flow > 

68,000m³ 

Show Warning on PCS to alarm 

operator to check calcite level 

PW REMIN: 

FT 

36050 

FQI 

36460 

FQI 

36460 

Totalized Flow > 

6,000m³ 

Show Warning on PCS to alarm 

operator to check calcite level 

P.S.: 

1) There is a conflict in the tag No. for both systems to be corrected. 

2) It is not clear if BECHTEL is sending an analog signal for flow or discrete. To be finalized. 


Project Name: 




DESCRIPTION 


Calcite Filters Refill 

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Sam Shaheen 


REVISED 

PAGE 

3/8/2016 

4 OF 6

Calcite Filter in Service 

Service Water 

Service Inlet 

BW Outlet 

BW Water 

BW Inlet 

Service Outlet 

Effluent 

Drain 

Service Water 

Service Inlet 

Calcite Filter in Backwash 

BW Outlet 

BW Water 

BW Inlet 


Effluent 

Drain 


Project Name: 




DESCRIPTION 


Calcite Filter BW (Backwash) 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 

3/8/2016 

5 OF 6

Operator push 

MANUAL button 

for Vessel A 

Service Timer 

expires 

Operator push BW 

button for Vessel A 

Is there Low 


0T-3608? 

BW Time Expired 

Stop BW Pump 

Abort BW 

No 

Is the BWPump 

in AUTO & 

Ready? 

Open Service Inlet 

& Outlet valves 

Abort BW 

No 

Are the valves in 

AUTO? 

Close BW Inlet & 

Outlet valves 

Open BW inlet & 

Outlet valves 

No 

Is the vessel in 

AUTO mode? 

No 

Place Vessel in 

Standby 

Close Service inlet 

& Outlet valves 

Place Vessel back 

in Service (Service 

Timer begins... 

Start BW Pump 

Start the Feed 

Pump 

Abort BW 

Yes 

Is there any low- 

Flow alarm 


Project Name: 




DESCRIPTION 


Calcite Filter BW (Backwash) 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 

3/8/2016 

6 OF 6

Chapter 66 : Control Philosophy for Carbon Filters 

The activated carbon filters remove chlorine from water. The two filters 0F-3611A & 0F-3611B operate in series. 

Filter 0F-3611A is the lead filter and filter 0F-3611B is the lag filter. 

With time, as chlorine is removed within the carbon media bed, filter A is exhausted first. When this filter is 

exhausted & chlorine breakthrough occurs, the ORP instrument AIT-36996A should detect the chlorine residual. 

When ORP alarm is initiated, filter 0F-3611A is isolated and the flow is diverted to filter 0F-3611B. 

The following is the sequence of events that will be programmed in the PLC: 

Stages 

Stage 1 

Stage 2 

Stage 3 

Stage 4 

Action 

Filter 0F-3611A is the lead filter, and filter 0F-3611B is the lag filter 

Filter 0F-3611A is exhausted & isolated. Only 0F-3611B is operational. 

The media in Filter 0F-311A is replaced, and 0F-3611A becomes operational. Filter 0F-3611B will 

remain the lead filter until its media is exhausted while filter 0F-3611A becomes the lag filter. 

Filter 0F-3611B is exhausted & isolated. Only 0F-3611A is operational. 

When filter-A is exhausted, operator should take all necessary steps to replace the exhausted media & re-start filter 

0F-3611A. The operating cycles of all GAC filters consists of the following: 

a) SERVICE 

b) OFF (Time required to close & open valves) 

c) BACKWASH (6 minutes) 

d) OFF (Time required to close & open valves) 

e) RINSE (4 minutes) 

f) SERVICE 

Filters are backwashed automatically based on the following logic: 

1. AUTO 

2. MANUAL 

Normal filter backwash sequence will be automatic. When in AUTO, the BW cycle is initiated based on timer or rise in 

differential pressure. Backwash frequency should be set once a week (to be adjustable) when the BWRO train is OFF 

(the DEMIN water system works intermittently). The duty BWRO LP Pump 0P-3614A (or B) will be used to BW each 

filter sequentially. 

Manual mode is reserved for start-up & commissioning, and for maintenance. In this mode, the operator will be able 

to advance thru all the BW cycles, or select any specific cycle while skipping other cycles. 

The valves tag numbers for each filter and their functions are shown in the Table below. 

Chapter 66 Control Philosophy – Carbon Filters Page 84

Table 66-1: Valve Tag Numbers for Dechlorination GAC Vessels 

Valve 0F-3611A 0F-3611B Common 

Service Inlet Valve (Service Inlet A or B) XV-36988A XV-36988B [1] 

Service Outlet Valve (Service Outlet A or B) XV-36988B [1] XV-36991B 

BW Inlet Valve (BW Inlet A or B) XV-36989A XV-36989B 

BW Outlet Valve (BW Outlet A or B) XV-36990A XV-36990B 

Rinse Valve (Rinse A or B) XV-36909A XV-36910B 

Vessel 2 Lead – Vessel 1 Lag – Inlet (Divert Valve A - 

Top) 

XV-36991A 

Vessel 2 Bypass (Divert Valve A - Bottom) 

XV-36437 

Vessel 2 Lead – Vessel 1 Lag Effluent (Divert Valve B) 

XV-36436 

Isolation valve to BWRO Feed (Common Effluent) 

XV-36438A 

Off-Spec Dump Valve (Off-Spec Dump) 

XV-36438B 

Notes: 

1. XV-36988B is service effluent from 0F-3614A, and acts as service inlet to 0F-3614B when the two vessels are 

operating in series where 0F-3614A is the leading vessel 

2. The designation for the valves in GREEN, are the one used in Figures 66-1 to 66-8. 


The position of valves during various cycles is shown in the Table below. 

Table 66-2: BW Cycle Operation for 0F-3611A/B 

Cycle No. 1 2 3 4 5 6 

Backwash Cycle SERVICE OFF Position Backwash OFF Position RINSE SERVICE 

Service Inlet Valve • • • 

Service Outlet Valve • • • • 

BW Inlet Valve • • • • • 

BW Outlet Valve • • • • • 

Rinse Valve • • • • • • 

Vessel 2 Lead • • • • • • 

Vessel 2 Bypass • • • • • • 

BWRO LP Pump ◦ • ◦ • ◦ ◦ 

BW Pump N/A N/A N/A N/A N/A N/A 

Duration (Sec.) 30 360 30 240 

 

Notes: 

◦: Open for valve, ON for pump 

•: Closed for valve, OFF for pump 

During the rinse cycle, the service outlet valve open, followed by closing the rinse valve. 


Divert Valve B 

BW Outlet A 

Divert Valve A 

BW Outlet B 

Service 

Inlet A 

BWRO LP Pump 

0P-3614 

Dechlorination 

Activated carbon 

Filter 

0P-3611A 



Filter 

0P-3611B 

Service Outlet A 

Service Inlet B 

BWRO Trains 

Service Outlet B 

Common 

Effluent 


Rinse A 

Off-Spec 

Dump 

Off-Spec Dump 

to T-3608 

Waste to Q-3605 

BW 

Inlet A 

BW 

Inlet B 

Rinse A 

Figure 66-1: De-chlorination Activated Carbon Filters Service Cycle (Stage 1) 

The normal service cycle is defined as the SWRO permeate water being processed thru activated carbon filter 0F- 

3611A (lead filter) and then thru filter 0F-3611B (lag filter). The two units operate in series. The green line shows the 

flow path thru both filters. 


NOTES: 

• The two BWRO LP Pumps 0P-3614A & B will be 

running simultaneously during BW of any filter 

• Service flow will be diverted from lead filter 0F-3611A 

to 0F-3611B 


BW Outlet A 


BW Outlet B 

Service 

Inlet A 


0P-3614 



Filter 

0P-3611A 



Filter 

0P-3611B 





Common 

Effluent 


Rinse A 

Off-Spec 

Dump 

Off-Spec Dump 

to T-3608 


BW 

Inlet A 

BW 

Inlet B 

Rinse B 

Figure 66-2: De-chlorination Activated Carbon Filter A BW Cycle 

Backwash cycle for both trains start by backwashing the first filter followed by backwashing the 2 nd filter. Backwash 

cycle period is 6 to 10 minutes (to be adjustable). Backwash frequency is once every week or if the differential 

pressure rises 0.35 barg above clean water pressure drop (to be finalized during start-up). Note that the BWRO LP 

Pump is used for backwashing the filter. 



NOTES: 

• The two BWRO LP Pumps 0P-3614A & B will be 

running simultaneously during Rinse of any filter 

• Service flow will be diverted from lead filter 0F-3611A 

to 0F-3611B 

BW Outlet A 


BW Outlet B 

Service 

Inlet A 


0P-3614 



Filter 

0P-3611A 



Filter 

0P-3611B 





Common 

Effluent 


Rinse A 

Off-Spec 

Dump 

Off-Spec Dump 

to T-3608 


BW 

Inlet A 

BW 

Inlet B 

Rinse B 

Figure 66-3: De-chlorination Activated Carbon Filter A Rinse Cycle 

Rinse cycle is the same as the service cycle except the rinse valve is open to drain. The rinse cycle allows the bed to 

drop and to compact as it was during the service cycle. Typical duration of this cycle is 2 to 4 minutes to be adjustable 

in the field. Rinse flowrate is the same as the service flowrate. 



BW Outlet A 


BW Outlet B 

Service 

Inlet A 


0P-3614 



Filter 

0P-3611A 



Filter 

0P-3611B 





Common 

Effluent 


Rinse A 

Off-Spec 

Dump 

Off-Spec Dump 

to T-3608 


BW 

Inlet A 

BW 

Inlet B 

Rinse B 

Figure 66-4: De-chlorination Activated Carbon Filter B BW Cycle 



BW Outlet A 


BW Outlet B 

Service 

Inlet A 


0P-3614 



Filter 

0P-3611A 



Filter 

0P-3611B 





Common 

Effluent 


Rinse A 

Off-Spec 

Dump 

Off-Spec Dump 

to T-3608 


BW 

Inlet A 

BW 

Inlet B 

Rinse B 

Figure 66-5: De-chlorination Activated Carbon Filter B Rinse Cycle 



BW Outlet A 


BW Outlet B 

Service 

Inlet A 


0P-3614 



Filter 

0P-3611A 



Filter 

0P-3611B 





Common 

Effluent 


Rinse A 

Off-Spec 

Dump 

Off-Spec Dump 

to T-3608 


BW 

Inlet A 

BW 

Inlet B 

Rinse A 

Figure 66-6: De-chlorination Activated Carbon, Stage 2 

This is the flow path when 0F-3611A is bypassed and the service flow is processed thru 0F-3611B (Stage 2). This is the 

case when Filter A is exhausted and requires replacement of Carbon media. During stage 2, isolation of 0F-3611A will 

occur per the following sequence of valves operation: 

1. Service inlet valves XV-36988A (Service Inlet A) and XV-36988B (Service Inlet B) closes 

2. Divert valve XV-36991A (Divert Valve A) open diverting the service flow to 0F-3611B 



BW Outlet A 


BW Outlet B 

Service 

Inlet A 


0P-3614 



Filter 

0P-3611A 



Filter 

0P-3611B 





Common 

Effluent 


Rinse A 

Off-Spec 

Dump 

Off-Spec Dump 

to T-3608 


BW 

Inlet A 

BW 

Inlet B 

Rinse A 

Figure 66-7: De-chlorination Activated Carbon Filter Stage 3 

When media is replaced in filter 0F-3611A, filter 0F-3611B becomes the lead filter, and filter 0F-3611A becomes the 

lagging filter. The operation will continue until media in filter B is exhausted and the process is reversed. 



BW Outlet A 


BW Outlet B 

Service 

Inlet A 


0P-3614 



Filter 

0P-3611A 



Filter 

0P-3611B 





Common 

Effluent 


Rinse A 

Off-Spec 

Dump 

Off-Spec Dump 

to T-3608 


BW 

Inlet A 

BW 

Inlet B 

Rinse A 

Figure 66-8: De-chlorination Activated Carbon Filter Stage 4 

If there is an alarm from the ORP monitor from the effluent of any of the lagging filter, this implies that either the ORP 

sensor or monitor is malfunctioning or both filters require replacement of the carbon media. The following sequence 

of events will follow: 

1. The dump valve XV-36438B open returning water back to SWRO product water tank T-3608 

2. The common effluent valve XV-36438A closes 

3. The feed dump valve on the duty BWRO train XV-36807A or B will open for 3 seconds. 

If the alarm remains after the 3-sec delay, the duty BWRO LP pump stops & the duty BWRO train stops 

simultaneously. 

Please refer to the following drawings: 

• Xylem PID 574_30009 or Chevron DWG # WS1-3600-PRO-PID-BEC-WRO-00045 

• Interlocks I-36 165 & I-36 166 in the above drawing 

• Xylem’s USA 3452-2BWRO-DWG-2 & 3 or Chevron DWG # WS1-3600-PRO-PID-BEC-WRO-00005 & 24 


Figure 66-6 shows the flow path when filter 0F-3611A is the lagging filter. This scenario can occur when the 1 st filter’s 

media have exhausted and became the lagging filter instead of the lead filter, the carbon media has not been replaced 

and the operation continued until the 2 nd filter carbon media is exhausted. 


BWRO GAC Modes of 

Operation 


Project Name: 




DESCRIPTION 

Logic Diagram 

Lead/Lag 

DRAWN By: 


REV: 

Sam Shaheen 

BWRO Activated Carbon 

REVISED 

PAGE 

7/15/2016 

1 OF 13

Drain 

Drain 

GAC in Service 

Service Water 

Service Inlet 

BW Outlet 


BW Water 

BW Inlet 

Effluent 

Rinse 

GAC in Backwash 

Service Water 

Service Inlet 

BW Outlet 


BW Water 

BW Inlet 

Effluent 

Rinse 


Project Name: 




DESCRIPTION 

Logic Diagram 

GAC BW Cycle 

Service & BW 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 


2 OF 13

Drain 

GAC in Rinse 

Service Water 

Service Inlet 

BW Outlet 


BW Water 

BW Inlet 

Effluent 

Rinse 


Project Name: 




DESCRIPTION 

Logic Diagram 

GAC BW Cycle 

Rinse Cycle 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 


3 OF 13

T-3608 


Activated carbon filters for BWRO operates in series (lead/lag). Vessel A can be either in Service as the Lead vessel, or the Lag vessel, or OFF (i.e., waiting for media to be replaced), or in BW. Same applies for 

Vessel B. However, If vessel A is Lead, vessel B must be the lag unit & vice versa. In MANUAL mode, operator can select any of the (3) modes of operation of the Activated Carbon Filters. 

Divert Valve 

From B to A 

XV-36436 

Service 

Inlet A 

Divert Valve 

From A to B 

XV-36991A 

AIT ORP 

36996A 

BW Outlet A 

AIT ORP 

36996B 

BW Outlet B 

Caustic 

XV-36988A 

XV-36990A 

XV-36990B 

BWRO LP 

Pumps 

GAC 

0F-3611A 

PDIT 

36993A 

Service 

Outlet 

XV-36988B 

GAC 

0F-3611B 

PDIT 

36993B 

Service 

Outlet B 

XV-36991B 

Common 

Outlet 

XV-36438A 

AIT 

36997 

pH 

Divert Valve 

From A to BWRO 

XV-36989A 

BW 

Inlet A 

XV-36437 

XV-36989B 

BW 

Inlet B 

Dump 

XV-36438B 

Rinse Valve A 

XV-36909A 

Rinse Valve B 

XV-36909B 

Drain 


Project Name: 




DESCRIPTION 

Logic Diagram 

Vessel A is Lead 

Vessel B is lag 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 


4 OF 13

T-3608 


T-3608 



Vessel B is Lag 

Divert Valve 

From B to A 

XV-36436 

Service 

Inlet A 

Divert Valve 

From A to B 

XV-36991A 

AIT ORP 

36996A 

BW Outlet A 

AIT ORP 

36996B 

BW Outlet B 

Caustic 

XV-36988A 

XV-36990A 

XV-36990B 


Pumps 

GAC 

0F-3611A 

Service 

Outlet 

XV-36988B 

GAC 

0F-3611B 

Service 

Outlet B 

XV-36991B 

Common 

Outlet 

XV-36438A 

AIT 

36997 

pH 

Divert Valve 


XV-36989A 

BW 

Inlet A 

XV-36437 

XV-36989B 

BW 

Inlet B 

Dump 

XV-36438B 

Rinse Valve A 

XV-36909A 

Rinse Valve B 

XV-36909B 

Drain 

Vessel A is Lag 

Vessel B is Lead 

Divert Valve 

From B to A 

Service 

Inlet A 

Divert Valve 

From A to B 

AIT ORP 

36996A 

BW Outlet A 

AIT ORP 

36996B 

BW Outlet B 

Caustic 


Pumps 

GAC 

0F-3611A 

Service 

Outlet 

GAC 

0F-3611B 

Service 

Outlet B 

Common 

Outlet 

AIT 

36997 

pH 

Divert Valve 


BW 

Inlet A 

BW 

Inlet B 

Dump 

Rinse Valve A 

Rinse Valve B 

Drain 


Project Name: 




DESCRIPTION 

Logic Diagram 

Lead/Lag 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 


5 OF 13

T-3608 


T-3608 



Vessel B is Lag and ORP Alarm AAH-36996B is ON 

Divert Valve 

From B to A 

XV-36436 

AAH 

36996B 

Service 

Inlet A 

Divert Valve 

From A to B 

XV-36991A 

AIT ORP 

36996A 

BW Outlet A 

ORP 

AIT 

36996B 

BW Outlet B 

Caustic 

XV-36988A 

XV-36990A 

XV-36990B 


Pumps 

GAC 

0F-3611A 

Service 

Outlet 

XV-36988B 

GAC 

0F-3611B 

Service 

Outlet B 

XV-36991B 

Common 

Outlet 

XV-36438A 

AIT 

36997 

pH 

Divert Valve 


XV-36989A 

BW 

Inlet A 

XV-36437 

XV-36989B 

BW 

Inlet B 

Dump 

XV-36438B 

Rinse Valve A 

XV-36909A 

Rinse Valve B 

XV-36909B 

Drain 

Vessel A is Lag and ORP Alarm AAH-36996A is ON 


Divert Valve 

From B to A 

Service 

Inlet A 

Divert Valve 

From A to B 

AAH 

AIT ORP 

36996A 

36996A 

BW Outlet A 

AIT ORP 

36996B 

BW Outlet B 

Caustic 


Pumps 

GAC 

0F-3611A 

Service 

Outlet 

GAC 

0F-3611B 

Service 

Outlet B 

Common 

Outlet 

AIT 

36997 

pH 

Divert Valve 


BW 

Inlet A 

BW 

Inlet B 

Dump 

Rinse Valve A 

Rinse Valve B 

Drain 


Project Name: 




DESCRIPTION 

Logic Diagram 

ORP Alarm on Lagging Vessels 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 


6 OF 13

T-3608 


Vessel A is Isolated 


Divert Valve 

From B to A 

XV-36436 

Service 

Inlet A 

Divert Valve 

From A to B 

XV-36991A 

AAH 

36996A 

AIT ORP 

36996A 

BW Outlet A 

AIT ORP 

36996B 

BW Outlet B 

Caustic 

XV-36988A 

XV-36990A 

XV-36990B 


Pumps 

GAC 

0F-3611A 

Service 

Outlet 

XV-36988B 

GAC 

0F-3611B 

Service 

Outlet B 

XV-36991B 

Common 

Outlet 

XV-36438A 

AIT 

36997 

pH 

Divert Valve 


XV-36989A 

BW 

Inlet A 

XV-36437 

XV-36989B 

BW 

Inlet B 

Dump 

XV-36438B 

Rinse Valve A 

XV-36909A 

Rinse Valve B 

XV-36909B 

Drain 

This will occur when Vessel A s media is exhausted and ORP alarm is ON. Vessel A will be isolated until 

operator change the carbon media. Once media is replaced, Vessel A goes back on-line as the lagging vessel. 


Project Name: 




DESCRIPTION 

Logic Diagram 

Vessel A out of Service 


DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 


7 OF 13

T-3608 


Vessel A is Isolated 

Vessel B is Lead and ORP Alarm AAH-36996B is ON 

Divert Valve 

From B to A 

XV-36436 

AAH 

36996B 

Service 

Inlet A 

Divert Valve 

From A to B 

XV-36991A 

AIT ORP 

36996A 

BW Outlet A 

ORP 

AIT 

36996B 

BW Outlet B 

Caustic 

XV-36988A 

XV-36990A 

XV-36990B 


Pumps 

GAC 

0F-3611A 

Service 

Outlet 

XV-36988B 

GAC 

0F-3611B 

Service 

Outlet B 

XV-36991B 

Common 

Outlet 

XV-36438A 

AIT 

36997 

pH 

Divert Valve 


XV-36989A 

BW 

Inlet A 

XV-36437 

XV-36989B 

BW 

Inlet B 

Dump 

XV-36438B 

Rinse Valve A 

XV-36909A 

Rinse Valve B 

XV-36909B 

Drain 

This will occur when Vessel B is the lead vessel, vessel A is out of service, and ORP alarm AAH-36996B is 

ON. When this occurs, the dump valve XV-36438B will open diverting flow to drain, and the PLC will shut 

down the duty BWRO train and BWRO LP Pump. 


Project Name: 




DESCRIPTION 

Logic Diagram 

Vessel A out of Service 

Vessel B is Lead + ORP Alarm is ON 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 


8 OF 13

T-3608 


Vessel A is Lead and ORP alarm AAH-36996A is ON 

Vessel B is Isolated 

Divert Valve 

From B to A 

XV-36436 

Service 

Inlet A 

Divert Valve 

From A to B 

XV-36991A 

AAH 

AIT ORP 

36996A 

36996A 

BW Outlet A 

AIT ORP 

36996B 

BW Outlet B 

Caustic 

XV-36988A 

XV-36990A 

XV-36990B 


Pumps 

GAC 

0F-3611A 

Service 

Outlet 

XV-36988B 

GAC 

0F-3611B 

Service 

Outlet B 

XV-36991B 

Common 

Outlet 

XV-36438A 

AIT 

36997 

pH 

Divert Valve 


XV-36989A 

BW 

Inlet A 

XV-36437 

XV-36989B 

BW 

Inlet B 

Dump 

XV-36438B 

Rinse Valve A 

XV-36909A 

Rinse Valve B 

XV-36909B 

Drain 

This will occur when Vessel B s media is exhausted and ORP alarm is ON. Vessel B will be isolated until 

operator change the carbon media. Once media is replaced, Vessel B goes back on-line as the lagging vessel. 


Project Name: 




DESCRIPTION 

Logic Diagram 

Vessel B out of Service 


DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 


9 OF 13

T-3608 


T-3608 


Vessel A in BW (Backwash) 

Divert Valve 

From B to A 

XV-36436 

Service 

Inlet A 

Divert Valve 

From A to B 

XV-36991A 

AIT ORP 

36996A 

BW Outlet A 

AIT ORP 

36996B 

BW Outlet B 

Caustic 

XV-36988A 

XV-36990A 

XV-36990B 


Pumps 

GAC 

0F-3611A 

Service 

Outlet 

XV-36988B 

GAC 

0F-3611B 

Service 

Outlet B 

XV-36991B 

Common 

Outlet 

XV-36438A 

AIT 

36997 

pH 

Divert Valve 


XV-36989A 

BW 

Inlet A 

XV-36437 

BW 

Inlet B 

Dump 

XV-36438B 

XV-36989B 

Rinse Valve A 

XV-36909A 

Rinse Valve B 

XV-36909B 

Drain 

Vessel A is in Rinse 

Divert Valve 

From B to A 

Service 

Inlet A 

Divert Valve 

From A to B 

AIT ORP 

36996A 

BW Outlet A 

AIT ORP 

36996B 

BW Outlet B 

Caustic 


Pumps 

GAC 

0F-3611A 

Service 

Outlet 

GAC 

0F-3611B 

Service 

Outlet B 

Common 

Outlet 

AIT 

36997 

pH 

Divert Valve 


BW 

Inlet A 

BW 

Inlet B 

Dump 

Rinse Valve A 

Rinse Valve B 

Drain 


Project Name: 




DESCRIPTION 

Logic Diagram 

Lead/Lag 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 


10 OF 13

T-3608 


T-3608 


Vessel B in BW (Backwash) 

Divert Valve 

From B to A 

XV-36436 

Service 

Inlet A 

Divert Valve 

From A to B 

XV-36991A 

AIT ORP 

36996A 

BW Outlet A 

AIT ORP 

36996B 

BW Outlet B 

Caustic 

XV-36988A 

XV-36990A 

XV-36990B 


Pumps 

GAC 

0F-3611A 

Service 

Outlet 

XV-36988B 

GAC 

0F-3611B 

Service 

Outlet B 

XV-36991B 

Common 

Outlet 

XV-36438A 

AIT 

36997 

pH 

Divert Valve 


XV-36989A 

BW 

Inlet A 

XV-36437 

BW 

Inlet B 

Dump 

XV-36438B 

XV-36989B 

Rinse Valve A 

XV-36909A 

Rinse Valve B 

XV-36909B 

Drain 

Vessel B is in Rinse 

Divert Valve 

From B to A 

Service 

Inlet A 

Divert Valve 

From A to B 

AIT ORP 

36996A 

BW Outlet A 

AIT ORP 

36996B 

BW Outlet B 

Caustic 


Pumps 

GAC 

0F-3611A 

Service 

Outlet 

GAC 

0F-3611B 

Service 

Outlet B 

Common 

Outlet 

AIT 

36997 

pH 

Divert Valve 


BW 

Inlet A 

BW 

Inlet B 

Dump 

Rinse Valve A 

Rinse Valve B 

Drain 


Project Name: 




DESCRIPTION 

Logic Diagram 

Lead/Lag 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 


11 OF 13

Starting BWRO GAC 

Low-Level Alarm 

in 0T-3618 

Is the duty 

BWRO train in 

AUTO? 

Step 1 

No 

The BWRO 

System will 

not Start 

Switch the Vessel 

from lead to lag 

At start-up, the lead vessel A will 

run until media is exhausted (ORP 

value exceeds setpoint). When this 

occurs, the vessels switch lead & 

lag position. Operator must make 

arrangement to schedule time to 

replace the media in the previous 

lead vessel. 

Yes 

Show Alarm 

on HMI/PCS 

Is there ORP 

Alarm from the 

effluent of the 

lag Vessel? 

Yes 

Open Dump valve 

XV-36438B to 

divert flow to drain 


Activated 

Carbon Filters in 

AUTO? 

Step 2 

No 

No 

Stop BWRO train if 

it is runing 

Yes 

Abort Start- 

Up 

Both Vessels will operate per 

new lead/lag arrangement 

Position Valves 

per Lead/Lag 

Arrangement 

Show Alarm 

on PCS 

Start BWRO LP 

Pump 0P-3614A 

Yes 

BWRO GAC is in 

SERVICE 

Is there ORP 


effluent of the 

lead Vessel? 

No 

Is there high pH 


common 

effluent? 

pH > 11 

Yes 

Show Warning on 

the HMI Screen 

for 1-hour 

Yes 

Operator to check 

the pH sensor 

If alarm is not 

acknowledged 

within 1-hour 

Show Alarm on 

PCS, 

Shutdown the 

BWRO Train 

No 

Is there low pH 


common 

effluent? 

pH < 8 

Yes 

Show Warning on 

the HMI Screen 

Yes 

Operator to check the pH 

sensor or the caustic pump 

stroke setting 


Project Name: 




DESCRIPTION 

Logic Diagram 

Calcite Filters Automatic 

Start-up 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 


12 OF 13

Service Timer 

expires 

Start BW Cycle for 

Vessel A until it 

expires 

A 

Delay BW 

until level 

alarm clears 

Yes 

Is there Low- 

Low Level alarm 

in 0T-3608? 

Start Rinse Cycle 


Outlet valves for 

Vessel B 

Delay BW 

until BWRO 

Train Stops 

Yes 


train Running? 

Open Service inlet 

valve & Rinse 

valve on Vessel A 

Position 

valves for 

Rinse... 

Open Service inlet 

valve & Rinse 

valve on Vessel B 

No 


Outlet Valves 

Rinse Cycle Ends 

Abort BW 

No 

Is the Pump 0P- 

3614A in AUTO 

& Ready? 

Rinse Cycle Ends 

Close all 

remaining valves 

on Vessel B 

Abort BW 

No 

Are the valves in 

AUTO? 

Yes 

Start BW Cycle 

For Vessel B 

Place both vessels 

on Standby 

Position valves for BW... 

Open BW inlet & 


Vessel A 

Close all 

remaining valves 

on Vessel A 

Position 

valves for 

BW... 

Close Service inlet 

& Outlet valves for 

Vessel A 

Open BW Inlet & 


Vessel B 

Start Pump 0P- 

3614A 

BW Cycle ends 

Rinse Cycle begins 

A 

NOTES: 

Each vessel will operate in (3) cycles: Service, OFF and Backwash (BW). During backwash, the final set is a rinse cycle. The vessels will be programmed to 

BW automatically every 7-days when the BWRO Train is OFF (Service Cycle timer to be set @ 7 days). When the BW sequence is initiated, BWRO LP Pump 

0P-3614A will start the BW of vessel A followed by BW of vessel B. Duration of BW of each vessel is 6 minutes. Duration of Rinse is 2 minutes. All of the 

above parameters will be adjustable in the corresponding setpoint screen. Operator will also be able to start BW & Rinse cycle thru pushbutton on the HMI 

screen when the unit is in PCS MANUAL. 


Project Name: 




DESCRIPTION 

Logic Diagram 

Automatic BW (Backwash) 

DRAWN By: 


REV: 

Sam Shaheen 


REVISED 

PAGE 


13 OF 13

Chapter 67 : Control Philosophy – Calcium Hypochlorite System 

Calcium Hypochlorite system consists of the following: 

1. Tank (0T-3623) to prepare a batch solution of 2-3% chlorine solution using calcium hypochlorite pellets 

2. Recirculation pumps 0P-36XX to recirculate water when chlorine concentration in the recirculation drops 

below setpoint. There are complicated set of valves that will open to fill the tank with water when level drops 

to Low level setting, and close the valve when tank is filled. 

3. Chlorine monitor and flow transmitter on the recirculation line 

4. One set of duplex metering pumps 0P-3651A/B dedicated to chlorinate the 1 st pass RO (SWRO) permeate 

flowing into tank T-3608 

5. One set of chlorine metering pumps 0P-3632A/B for UW distribution line 

6. One set of chlorine metering pumps 0P-3646A/B for PW. 

7. One set of Soda Ash metering pumps 0P-3648A/B for UW. 

8. One set of Soda Ash metering pumps 0P-3647A/B for PW. 

All metering pumps are equipped with automatic stroke adjustment controller. 

Soda Ash storage tank is a chemical tote that is replaced by chemical supplier when there is no chemical left in the 

tank. 

Commercial Calcium Hypochlorite Storage Tank 

Preparation of solution starts when there is low level alarm in the storage tank. There are two redundant short wave 

radar level transmitters (LIT-36904A & 36904B). If the low-level alarm is ON, the redundant fill valves XV-36964 or XV- 

36965 open to fill the tank with water until the high-level alarm is ON. These valves are normally closed. Once the 

CLOSE feedback from these valves is received by the PLC, the recirculation pumps 0P-3633A or B start recirculating 

the water thru the tank. The tank is equipped with a basket strainer filled with calcium hypochlorite pellets where 

flow of water goes upward thru the basket and exits from the perforated section on the top zone of the basket (Refer 

to Figure 67-1: Calcium Hypochlorite Basket). 

Two recirculation pumps (0P-3633A/B) will start recirculating water up through a mesh basket which contains the 

Calcium Hypochlorite pellets until water is concentrated between 2 to 3% of hypochlorite. The re-circulation time will 

be determined in the field during commissioning of the plant. 

Once the re-circulation timer expires, the fill valves XV-36964 or 36965 will close and the circulation pump 0P- 

3633A/B shuts down. 

After preparation of solution in the tanks, the downstream calcium hypochlorite metering pumps resume operation. 

When the level in the tank 0T-3623 drops & low-level alarm is ON, the tank is refilled with water and recirculation 

back & forth thru the tank is resumed as described in the above section. 

Chapter 67 Control Philosophy – Calcium Hypo Page 96

Figure 67-1: Calcium Hypochlorite Basket 


Metering Pumps, 0P-3651A/B 

These pumps will inject chlorine at the inlet of T-3608 to chlorinate the SWRO permeate water storage tank. 

The injection of chlorine will be done proportionally with flow of SWRO Permeate water (FIT-36880A or B) depending 

on which train is on duty. The setpoint for the desired applied chlorine will fine-tuned by the Chlorine analyzer AC- 

36032 located at the inlet to the tank T-3608. 

Chlorine Analyzer 

(BECHTEL’s Scope) 

Injection Point 

Please note that these pumps will be interlocked with the duty SWRO train. If the RO HP Pump 0P-3630A or B is 

operating, the duty chemical pump 0P-3651A will be ON. If the RO HP Pump 0P-3630A or B is not operating, the duty 

chemical pump 0P-3651A will be OFF. 


These pumps will inject chlorine into the UW (Utility Water) distribution line. The injection of chlorine will be done 

proportionally to totalized flow of FIT-36035 (effluent from UW Calcite Filters 0F-3610A/B) and FIT-36030 (inlet to IAH 

Activated Carbon Filters). The setpoint for the desired applied chlorine will fine-tuned by the Chlorine analyzer AC- 

36456 located at the inlet to the tank T-3608. 


Soda Ash 


Tank T-3623 

FIT 

36460 



PK-3612 


0F-3610A/B 

FIT 

36035 

Chlorine 

Analyzer 

AIT 

36456 

UW from T-3608 

0P-3604A/B 

Refer to 

DWG # 

WS1-*-00013 

FIT 

36030 

F 



PK-3612 

IAH Activated 

carbon Filters 

0F-3614A/B 

UW To Distribution 


Refer to 

DWG # 

WS1-*-00046 

IAH Tank 


Tank T-3623 

0P-3632A/B 

Figure 67-2: UW System 

Please note that these pumps will be interlocked with the duty pump 0P-3604A (or B). If the duty pump 0P-3604A, 

the duty chemical pump 0P-3632A will be ON. If the duty pump 0P-3604A is not operating, the duty chemical pump 

0P-3632A will be OFF. 



These pumps will inject chlorine into the PW (Potable Water) distribution line. Below is a simplified sketch of this 

system. The inlet to tank T-3605 is equipped with Flow Transmitter FIT-36050, and chlorine analyzer AIT-36523. The 

injection of chlorine will be done proportionally with flow of FIT-36050 (flow of effluent from calcite filter), and will be 

will fine-tuned by the Chlorine analyzer AIT-36851 located at the discharge from the cartridge filter housings 0F- 

3606A/B to maintain a residual between 0.2 to 0.4. 


Chlorine 

Analyzer 

AIT 

PDIT 

36849 

36851 

Vent 

Potable Water 

Distribution 

Cartridge 

Filter 

Housing 

316SS 

Sample 

Sample 



CO2 Gas 

Potable Water from 

0P-3608A/B 

PK-3611 


0F-3609A/B 

Refer to 

DWG # 

WS1-*-00014 

Drain 

Cart. Housings 

0PK-3606 

0F-3606A/B 

Duty/Standby 

Chlorine 

Analyzer 

Drain 

UV Sterilizers 

0PK-3605-R01A/1B 

Duty/Standby 

BECHTEL’s Scope 

AIT 

FIT 

36523 

Soda Ash 

36050 

0T-3605 

Potable Water Tank 

317 m³ 


Tank T-3623 

0P-3646A/B 


0P-3605A/B 

Figure 67-3: PW System 

Please note that these pumps will be interlocked with the duty pump 0P-3608A (or B). If the duty pump 0P-3608A, 

the duty chemical pump 0P-3646A will be ON. If the duty pump 0P-3608A is not operating, the duty chemical pump 

0P-3646A will be OFF. 

Control Philosophy - Soda Ash 

Soda Ash systems pumps chemicals into the UW Calcite filters common effluent line and PW Calcite filters common 

effluent line. The purpose of the Soda Ash is to raise the pH to 8.5 maximum before is being distributed to the UW 

and PW distribution lines. 


In the UW system, the metering pumps are controlled proportionally based on flow FIT-36035 and fine-tuned with the 

pH instrument AIT-36916 (Integral control). 

Same applies for the PW system where FIT-36050 and AIT-36917 controls the stroke % of the pumps. 

Interlocks 

Here is a list of interlocks shown on the P&ID drawings WS1-3600-PRO-PID-BEC-WRO-00015-001, 002 & 003. 

Interlock # Action 

36149 High level alarm LAH-36904A closes fill valve XV-36965 

36152 Low level alarm LAL-36904A open fill valve XV-36965 

36195 High level alarm LAH-36904B closes fill valve XV-36964 

36197 Low level alarm LAL-36904B open fill valve XV-36964 

36150 Low-Low level alarm LALL-36904A will stop all metering pumps, 0P-3651A/B, 0P-3632A/B, 0P- 

3646A/B, and recirculation pumps 0P-3633A/B 

36196 Low-Low level alarm LALL-36904B will stop all metering pumps, 0P-3651A/B, 0P-3632A/B, 0P- 

3646A/B, and recirculation pumps 0P-3633A/B 

Signals Required from OWNER 

This system requires a lot of interface with OWNER’s DCS. 

1. FAULT from pumps 0P-3604A/B: Discrete Input 

2. RUNNING from pumps 0P-3604A/B: Discrete Input 

3. FAULT from pumps 0P-3608A/B: Discrete Input 

4. RUNNING from pumps 0P-3608A/B: Discrete Input 

5. AIT-36032: Analog Input 

6. FT-36030: Analog Input 

7. FIT-36050: Analog Input 

The HMI shall indicate/provide the following parameters for each pump: 

1. Auto/Manual selection 

2. Start/Stop command 

3. Metering pump in duty 

4. Metering Pump Ready 

5. Metering Pump Fault 

The same applies to all other chemical pumps. 


Chapter 68 : Control Philosophy - CO 2 System 

The CO2 tank and panels are provided by BOC in this plant. The CO2 tank provides gas to two panels: one fully 

automatic panel to the large system UW (Utility water), and small panel where all instruments and valves are manual 

for the small system PW (Potable Water). 

Utility Water 

The Utility Water Carbon Dioxide (CO 2) dosing system operates in automatic mode. 

1. The CO 2 flow is automatically adjusted by the modulating valve FV-36944 

2. CO 2 flowrate is not monitored by any physical instrument. FC-36944 in drawing WS1-*-00022 is a signal sent 

from BECHTEL’s DCS that represents a ratio of CO 2 Flow to main flow which is monitored by FIT-36035. FIT- 

36035 is a flowmeter in BECHTEL’s scope that monitors the inlet to UW Calcite filters 0F-3611A/B. Pressure in 

the gas line is monitored by PIT-36945. 

3. Start/Stop of the Gas flow is controlled by the ON/OFF ball valves XV-36946 & XV-36947. When the flow is 

commanded to start, XV-36946 opens first followed by XV-36947. When the flow is commanded to stop, XV- 

36947 closes first followed by XV-36946. 

4. The permissible condition to start the CO 2 gas flow is a Remote signal from BECHTEL’s DCS to start or stop the 

CO 2 flow. 

UW CO2 Panel 

The ultimate objective for calcite addition is to raise alkalinity and calcium to increase the LSI. The CO 2 addition is to 

lower the pH of the SWRO permeate to increase the dissolution rate of calcite. The more CO 2 is added (or pH is 

lowered), the higher is the alkalinity and LSI. 

For the UW, the system data are: 

• Normal/Peak Flowrate: 83.8/127 m³/hr 

• Tank OD: 3000mm OD 

• Superficial Velocity thru the vessel (Normal/Peak): 12.0/18.3 m/hr [4.9/7.5 gpm/ft²] 

The limestone bed contactor program by Schott Engineering, shows that 45ppm of CO 2 is required to maintain slightly 

positive LSI based on the RO projection for 23 °C for 3-Years old membranes (refer to Figure 36). At 83.8 m³/hr, the 

average consumption of CO 2 is 3.771 kg/hr (=83.8 x 45/1000) and the daily average is 91 kg/day. The full output is 

attached in this document. Refer to the complete CO 2 projection “schotts_limestone_program_v1.02”. 

To estimate the flowrate of CO 2, assume the gas behaves as ideal gas and you can apply the ideal gas law PV = nRT 

where: 

1. P = Pressure in atmosphere 

2. V = Volume in liter or liter/hr or liter/min (depending on the unit of No. of moles) 

3. n = Number of moles or moles/hr or moles/min 

4. R = Gas constant = 0.0821 (liter x atm) /(mole x ºK) 

5. T = Temperature in ºK (kelvin) 

Since molecular weight of CO 2 gas is 44.01 gram/mole 

Chapter 68 Control Philosophy – CO 2 Page 102

Number of moles = 3.771 kg/hr x 1000 gram/kg / 44.01 gram/mole = 85.7 moles/hr 

Assume temperature to be ambient temperature 21.1ºC ºK = 21.1 + 273.15 = 294.1 

Assume Pressure is equal to 100psi 100psi/14.696 = 6.8 atm 

Solving for volume where V = nRT/P = 85.7 x 0.0821x294.1/6.8 = 304 liter/hr = 5.07 liter/min 

The ratio of the main flowrate 83.8 m³/hr to the CO 2 flow of 5.07 liters/min is 16.5, and the opposite – ratio of CO 2 

flow to main flowrate is 0.061 or 6.1%. Please note that we are using liters/min because the CO 2 gas flowmeter 

default unit is liters/min. 

CO 2 Flow Control in PW 

Ratio Controller 

FI36944/FI36035 

Range:0 – 100% 

Service 

Inlet 

P 

Backwah 

Outlet 

P 

P 

P 

Backwash 

Inlet 

Service 

Outlet 


Water 

Diff. Press. 

PDIT 

FIT 

36035 

Feed Pumps 

P 

P 

M 

Effluent 

P 

P 

FC 

36944 

CO 2 

F 


Wastewater 

Backwash Pump 

Figure 68-1: UW System CO2 Flow Control Scheme 


Here is what you need to know about the mass flowmeter in the UW panel: 

1. The Mass Flowmeter (FC-36944) is a combination of flowmeter and a control valve. The unit is also equipped 

with its own built-in PID loop. 

2. The flowmeter is equipped with analog input for the setpoint, and analog out for the measured value (value 

of the CO 2 flowrate). The setpoint is the ratio of the main flowrate entering the calcite filter to the flow of CO 2 

gas. The analog output for the CO 2 flow (in liters/min). 

3. The mass flowmeter default unit uses liters/min for the gas flow 

4. The BECHTEL feed pumps to calcite filters do not have VFD (they run on DOL) 

Potable Water Panel 

The Potable Water Carbon Dioxide (CO 2) dosing system operates in manual mode only. The CO 2 flow is manually 

adjusted by the ball valve 0VV-361855. The flowrate is constant as long as the Potable Water Storage Tank (0T-3605) 

does not have a high-level alarm active (HLL-36510) and there is enough pressure in the gas line which is monitored 

by PIT-36985. The CO 2 flow is stopped/started by two solenoid valves in series: XV-36959 within the CO 2 Panel and 

XV-36960 at the injection point. 

When there is demand for CO 2, first the panel valve XV-36959 opens and then XV-36960 opens to ensure that the CO 2 

line is pressurized and PAL-36058 is not active. If HHL-36510 or PAL-36058 becomes active the injection point valve 

XV-36960 closes first followed by XV-36959 until both alarms are no longer active and then the system restarts by 

opening XV-36959 then XV-36960. 


Chapter 69 : Control Philosophy – Potable Water (PW) Skid 

The PW package 0PK-3605/3606 consist a set of two cartridge filter housings (0F-3606), and a set of two UV Sterilizers 

(0PK-3605-R01A/B). 

The potable water is pumped thru the cartridge filter housings to remove any particles and the UV to remove viruses 

& bacteria. 

Cartridge Filter Housings (0PK-3606) 

The Cartridge Filter Housings operate in parallel (both units will be running at the same time). 

The cartridge filter housings pressure drop is monitored by a common differential pressure transmitter PDIT-36849. 

When P reaches 1 bar, one unit will be isolated by closing inlet & outlet valves and cartridges are replaced. This unit 

will be placed back in duty (re-open inlet & outlet valves), and the 2 nd unit is isolated and cartridges are replaced. 

Once replacement of these cartridges is complete, re-open the inlet & outlet valves. 

UV System (0PK-3605) 

The UV Sterilizers operate as duty/standby. 

The two UV units by Wedeco are small units rated for 10m³/hr and consist of 316SS Chamber with one UV light inside 

the chamber. Each UV unit is equipped with a dedicated panel or cabinet. This cabinet is equipped with controller 

with displays to show status of the UV lamp (i.e., UV Intensity in W/m², running hours, status of UV such as NORMAL 

OPERATION, etc…). On this skid, there is another control panel with chlorine monitor (OLPV-OPK3605-01) provided by 

Xylem. All interconnecting wiring (230VAC) will be connected to the OLPV-OPK3605-1 panel. Xylem has wired the UV 

panels to the OLPV-OPK3605-1 panel. 

Xylem’s panel 

Wedeco panel 

Facts about These UV Units 

In general, avoid dry running. Do not allow the UV lamp to turn ON if there is no flow. 

It takes time for the UV lamp to warm up to the minimum intensity required. Manufacturer DEFAULT setting is 

approximately 2 minutes. 


There are (3) alarms & warnings regarding UV intensity and lamp status: 

1. Low dose 

2. Very low dose 

3. Lamp failure 

Temperature cut-off is 50ºC on these units. If temperature inside the chamber reaches this level, the UV will shut 

down. 

The face panel of the UV is equipped with 3-position selector switch “Test/O/Normal” which is the equivalent to 

H/O/A: Test = HAND, O = OFF, and Normal = AUTO or REMOTE. 

The following is the list of signals and their description: 

Signal I/O Signal Description 

Run AUTO DO The “Run AUTO” Signal activates as soon as the run command is received from 

the PLC (If the HOA switch is in Remote or Normal). This signal deactivates if 

either the HOA switch is turned off or the “Run Signal Disappears”. 

System Running DI The “System Running” Signal activates when the UV reactor has warmed up and 

is running (warm up is currently 120 seconds as mentioned above). The signal 

is activated regardless whether the unit is in Test mode, or Normal mode. This 

signal deactivates after the unit has gone through the shutdown sequence 

(currently set @ 180 seconds). Therefore, if the “System Running” signal is 

received while the system is meant to be off, it means that someone has 

switched the unit on locally. 

Run Signal Confirmation DI This signal confirms that the UV unit is in Normal (AUTO) mode (ready to be 

controlled by PLC) 

Pre-Alert DI This signal activates when UV intensity have reached 80% of the setpoint value. 

The setpoint value of lamp intensity is an alarm indicating that the UV lamp’s 

intensity is very low and requires replacement of the UV lamp. 

FAULT DI This is an alarm from over temperature or lamp’s low-intensity or any other 

alarm that may exist that prevents the UV from operating properly. 

The start-up sequence for the UV is: 

1. PLC sends a “Run AUTO” signal to start the UV 

2. The UV sends feedback confirming “Running In Remote” Signal is received 

3. The UV lamp warm up sequence starts (requires at least 1 to 3 minutes’ warm-up time) 

4. When warm up period ends, “Run Signal Confirmation” signal is sent back to the PLC. If it is not received after 

two minutes’ delay (+120s), system goes into Fault 

5. After “System Running Signal Received”, the Potable Water Feed Pumps (0P-3605A or B) can start. 


Wiring between UV and its Panel 

Contact 

Remote ON/OFF by a no voltfree 

-contact or 230VAC signal. 

Signaling “NORMAL ON” 

Signaling “system running” 

Signaling “pre-alert” 

Signaling “system failure” 

Interlocking the control circuit 

of a pump or valve 

Signaling “Cabinet 

Over-temperature” 

“Analog output 0/4-20 mA“ 

Description 

To protect the UV lamps against high frequencies of switching ON & OFF- it may 

be useful to install an additional off-delay timer (< 30 minutes) for the UV system. 

This contact leaves rest position when the system is switched on with selector 

switch in position “NORMAL”. It may be combined with other contacts to avoid 

alarm signaling when the UV system is switched OFF. 

If all UV lamps are in operation, this contact leaves rest position ~ 6 minutes after 

switching ON, this means ≈ 3 minutes after the UV intensity is higher than the 

alarm threshold value. 

This contact leaves rest position when the UV intensity is lower than the pre-alert 

threshold value but higher than the alarm threshold value. 

This contact is in rest position when a UV lamp fails or when the UV intensity is 

lower than the alarm threshold value*. It is recommended to combine this 

contact with terminals “NORMAL ON”. 

By this contact the control circuit of a pump or shut-off valve can be interlocked. 

This contact is closed ≈ 6 minutes after switching ON, this means after UV lamp is 

in operation and the UV intensity is higher than the alarm threshold value* (the 

delay time allows “stabilization” of UV intensity)-+ see also chapter IV. 

“OPERATION“. 

This contact leaves rest position when the internal temperature is lower than 50 

ºC. With “high temperature” the UV lamps will be not allowed to start switching 

on. 

This is for the UV Intensity. The load for external signal processing must not 

exceed 500 Ohm. Factory setting = 0-20mA.

RO eBook Part 15 Control Philosophy

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