energy saving in pumps, fans & compressors - petrofed.winwinho...

ENERGY SAVING IN PUMPS,
FANS & COMPRESSORS
P. K. MUKHOPADHYAY
New Delhi
December, 2008
1

Energy – Pumps
Pumping – 25-50% Energy in plants
– 20% World Electric Energy
9%
27%
64%
Energy
Repair
Cost
Life Cycle Cost Analysis
2

Energy Saving in Pumps
Pumping System
-Line Size
-Fittings
- Valves
- Pumps
-Motors
- Drives
Line Size
- Velocity Limits
High – Errosion, NPSHA, Noise, Standards
Low – Sedimentation
--- Minimise Life cycle cost
3

Energy Saving in Pumps
P in Control Valves for same size & flow rate
4

Life Cycle Cost – Pumping System
COST
LINE DIAMETER
5

Pump System Interaction
Pump Curve
Operating Point
HEAD, FT
System Curve
Capacity, GPM
6

Typical Pump Curves
Pump Curve
Operating Point
Head
Efficiency
Efficiency
System Curve
BEP
NPSHR
BHP NPSHR
BHP
Capacity
7

Pump Overdesign
‣ Overdesign resulting actual
operation away from BEP
BID evaluation-efficiency
difference of ½ to 1%
System clearance
}
Lighter shaft To Check 8

Handling Pump Overdesign
& Part-Load with Time
Approaches
Methods
– Shift Pump Curve
– Shift System Curve
– Shift Both
– Throttling by Control Valves
– Bypassing Pump
– Two pumps in series
– Start-Stop Operation
– Variable Speed Operation
– 2-Speed Motor
9

Part Load Operation
Throttling by Control Valve
Conventional Method
High Energy
Valve Wear
10

Part Load Operation
Bypassing Pump
High Energy
Temperature Rise
Valve Wear
11

Part Load Operation
Affinity Laws
Change
Constant
Casing`
RPM N
IMP D
Q 1 D 2
2
Q 2 Q 1 N 2
H 2 H 1 N 2
2
H 1 D 2
N 1
D 1
BHP BHP 1
N
3
2 2 BHP 1
D 2
3
N 1
D1
N 1
Assumes Constant Efficiency
IMP. D
RPM N
SAME
D 1
Two Pumps in parallel
Start-Stop operation
By changing N at
constant D, efficiency is
constant if system is
mainly friction load. If
system contains static
head efficiency loss will
occur.
For changing D efficiency
is constant if D change is
less than 5%. For 25%
change efficiency drop
can be 2% or more
depending on N s .
12

Effect of RPM Change of Efficiency
Pump Curve
13

Matching pump & system curves
By Variable speed drive
Head, %
Power, %
Capacity, %
14

Part Load Operation
Energy efficiency is best with RPM change and for
system with mainly frictional loss.
Typical energy saving
Full Load
Part Load
Power for part Load
Throttling
Variable speed drive
% saving VSD
GPM
3600
2400
FT
180
152
HP
165
118
28
2 – Speed Motor
If part-loads are in two regions 2-speed motor is effective.
Typical speeds, RPM
1750/1150, 1750/850, 1150/850, 3500/1750
Cheaper than VSD
15

Part–Load Operation
2-SPEED MOTOR AND THROTTLING
16

Pump Selection
Specific Speed N s = N√Q
(g∆H) ³⁄
For Simplicity g is dropped N s
= N√Q
(∆H) ³⁄
Based on Anderson’s Work
Efficiency η =0.94 – 0.08955 Q(gpm) . X
N(rpm)
– 0.29 Log º 2286
Ns
-0.21333
2
X = 140
ξ(µ - in ) ≈ 1
17

BEP of Centrifugal pumps as function
of NS,Q/N & Shape
18

BEP of Pumps – Flowserve corp
19

Change of Pump Efficiency on Part-Load
20

Effects of Viscous Fluid on Pump Curve
21

Achieving High BEP
Avoid N s < 1000
N s Too High
BEP Highest N s 2500
How to achieve higher BEP?
N s = N√Q
(∆H) ³⁄
N up to 3600
NPSHR
∆H is large, use Multistage pump
22

Vendor Offer Evaluation
Compare offer BEP with calculated values. If large mismatch to
investigate impeller type, clearance, surface roughness, etc.
Initial Test Run
Design & Actual – Operating points, efficiency. Need for
throttling. Consider
Change rotor dia
Trim Rotor
Change Rotor Width
Different no of blades
Blade discharge Angles
Orifice in discharge
Impeller with angle trim at periphery
23

Change Rotor Dia
24

Rotor Trim Correction
25

Efficiency %
60
40
20
0
26
80
X 10
Change Rotor Width
Capacity GPM X 100
100
Head feet

Change Blade Number
27
Capacity, %
Head and Efficiency., %

Effect of No of Vanes & Discharge Angle
Head & Efficiency, %
Capacity, %
28

Impeller With Angle-Trim at Peripheral
29

Pump Performance with Orific in Discharge
¼ORIF
Head, Ft
Capacity, GPM
30

Performance Change with Orifice
Head, %
B.H.P., %
Capacity, %
31

Increasing Pump Capacity
Underfiling vane tips
Removing metal from volute
tongue
Performance after underfiling vane tips
Underfiling vane tips
32

Removing Metal from Volute Tongue
33

Performance after metal removal
from volute tongue
Head and Efficiency, %
Q = Capacity Normal
Q1 = Capacity after volute chipping
A =Projected volute inlet area normal
A1 = Projected volute inlet area after chipping
34

Different Variable Speed Drives
Permanent magnet adjustable speed drive
Single unit adjustable speed drive
AC adjustable voltage drive
Wound-Rotor induction motors
• Liquid rheostat controls
• Tirastat II secondary controls
• Contact secondary controls
Adjustable frequency drives
• Pulse width modulation frequency inverters
• Solid state frequency inverters
• Flux vector drives
Modified Kraemer drives
DC motor with SCR power supply drives
Variable speed fluid drives
35

Variable Speed Drives
Permanent magnet adjustable speed drives
• Number of units up to 400HP in use
• Problems of dissipating heat losses
Adjustable frequency drives
• Widely used in units below 1000 HP
• Used over 10,000 HP units
• Sophisticated electronic system
Variable speed fluid drives
• Used for 400 – over 40,000 HP units
36

Pump test at frequent intervals
Performance deterioration with time
Need for repair or change of components
including impellers
37

Efficiency of variable-speed drives
Efficiency, %
Design Speed, %
38

Efficiency of Electric Motors (Four-Pole)
Premium Efficiency Motor
Efficiency, %
EPAct Motor
Typical Older Motor
Horsepower
39

Energy Consumption in Fans
System Design
Choice of type
• Efficiency
• Reliability
• Noise
Centrifugal Type
Airfoil BEP > 80%
Backward inclined / Curved BEP > 75%
Axial
Vane Axial BEP >75%
40

Handling Fan Over design & Part Load
Throttling by dampers
Orifice in discharge
Inlet vane control
Speed control
• Variable Speed Motor
• 2 Speed Motor
Variable Pitch
• Vane Axial Fan
41

Outlet Damper & Variable Speed Control
42

Inlet Vane Control on Backward
Curved Centrifugal Fan
43

Blade Pitch Change on Vaneaxial Fan
44

Power Consumption for Part-Load
Conditions
45

Power Consumption for Part-Load
Conditions …..
46

Power Consumption for Part-Load by
Different Methods
47

Compressor
System Design
Choice of Type
In FCC Service
• Since 1950 Centrifugal Compressors
• Presently axial compressors turndown 75% with
little efficiency loss
• Efficiency 12% higher
48

Handling Overdesign & Part Load
Inlet damper control
Bypass valve control
Inlet vane control
Variable speed control
Diffuser vane control
49

Types of System Curves
50

Control of a Gas Compressor
Suction Volume V o 5.5 M ³ /S @ 3.63 BAR & 37°C
Pressure Ratio (P d /P s ) o 9.73
No of Stages 7
Power P io
51

Part Load Operation
Constant Pressure Ratio
P d /P s =9.73
Flow (V/V o
) – 0.75
Regulation
Power
P i
/P io
REL
Power
Surge
V s /V o
Speed
Variation
0.78
100
0.67
Suction
Throttling
0.83
107
0.65
Adjustable Inlet
Vane
0.80
103
0.60
By Passing
1.00
128
52

Part Load Operation
Parabolic System Resistance Curve
P d /P s -9.73
Flow (V/V o ) – 0.85
Regulation
Speed Variation
Suction
Throttling
Adjustable Inlet
Vane
By Passing
Power
P i /P io
0.62
0.75
0.73
0.90
Relative
Power
100
121
118
145
53

Power Input in Refrigeration
Compressors at Part-Load
GAS COMPRESSION POWER INPUT, %
SPEED CONTROL
VANE CONTROL
SYSTEM VOLUMETRIC FLOW, %
54

Part Load Operation Comparison of
Power Consumption
At constant P d / P s speed variation is only slightly
better than adjustable vane & suction throttling
With parabolic system resistance curve speed
variation is superior to adj. inlet vane & suction
throttling
For refrigeration compressor speed control & adj. inlet
vane are superior in different ranges.
55

Summary of Energy Saving
56