Innovative Revamping of Ammonia plants for Capacity up and Energy Efficiency - Ammonia Know How

10/25/2017 Innovative Revamping of Ammonia plants for Capacity up and Energy Efficiency - Ammonia Know How
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Innovative Revamping of
Ammonia plants for Capacity up
and Energy E iciency
Author: Harshad P Pandya, Independent Consultant; harshadppandya@gmail.com
Ammonia and methanol manufacturing have been one of the most energy intensive chemical production. High consumption and cost of
energy, limited availability and need for minimizing emission of GHG gas and other pollutants has led to major technological changes in last
30-40 years. Ammonia and methanol are produced largely from Natural Gas with Steam reforming and resultant raw synthesis gas is treated
di erently to produce pure synthesis gas as per need of both processes. Broad comparision of synthesis gas quality required for ammonia
and methanol is presented This study paper highlights benefits and ways of revamping vintage ammonia and methanol plants for
capacity increase and e iciency improvement. The paper brings innovative revamp for substantial capacity increase and energy reduction in
a gas based ammonia plant through use of proven process modules like oxygen fired reformer, inert free ammonia loop, ASU for pure
nitrogen and oxygen, cryogenic purification/nitrogen wash etc which have been successfully used in di erent flow sheet of ammonia plants
based on di erent feed stock and with higher capacities .
Ammonia has remained important building block for production of Fertilizers and chemicals. About 80% of ammonia produced is used as
nitrogen source in fertilizers like urea, DAP, MAP, NPK ,Ammonium sulfate/phosphates, ammonium nitrate ,etc , while other 20 % is used in
several industrial application such as plastics, fibre, explosives, hydrazine, amines, nitriles, dyes and intermediates .Ammonia is also used for
environment protection measures in removal of NOX from flue gases. Liquid ammonia is an important solvent and refrigerant .
Ammonia plants and world capacity
Global Annual ammonia production capacity was more than 160 million tons in year 2015.Major of the ammonia production facility based
on production data of 2015 are located in China, Russia, India, USA ,Indonesia, Trinidad, Ukarine, Canada .,Saudi Arabia and middle East.
There are several other plants in di erent countries. There are more than 400 ammonia plants of size ranging from 100 mtpd to 3300 mtpd
.Ammonia plants built in eighties and a er are in the capacity range of 1000 to 2200 mtpd. Modern plants are being designed in the range of
2200 to 3300 mtpd.
Ammonia production and Energy requirement
Ammonia production plants are based on energy feed stock such as Natural Gas, Naphtha, fuel oil, coal and other hydrocarbons. More than
80 % capacity is based on natural gas while several small ammonia plants based on coal as a feed stock are working in China. Many naphtha
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10/25/2017 Innovative Revamping of Ammonia plants for Capacity up and Energy Efficiency - Ammonia Know How
based ammonia plants are either switched over or in the process of switch over to Natural Gas. Few ammonia plants based on fuel oil are
switched over to natural gas. Flow sheet of conventional NG based ammonia plant is shown on diagram I
Diagram I: Flow sheet of conventional Ammonia plant
Source :Industrial E iciency Technology Database Ammonia ietd.iipnetwork.org
Ammonia production technology has been one of the most energy intensive technology and it has matured over the years due to
development of newer catalyst and CO2 absorption solvents, improved metallurgy for high temperature and pressure requirement, improved
separation systems mainly cryogenic purifications, intensive process integration , development of e icient compression and drive systems etc
. Modern Ammonia technology available from reputed technology suppliers are quite competitive in terms of reliability, operating cost,
energy e iciency. Excellent review of these technology is presented by R K Aggarwal, S Banerjee, R M Maliya
(reference 1,2)
As per IFA 2008-2009 summary report on energy e iciency and CO2 emissions in ammonia production, energy use for best available
technology (BAT ) for natural gas based plant is 28GJ per t ammonia and energy use by best practice technology (BPT) is 32 GJ per t ammonia.
Actual average energy consumption in various countries across the globe is in the range of 34 to 43.6 GJ per t ammonia. Such variation is
due to capacity, plant age, technology and feed stock. This brings out immense energy saving opportunity by way of plant
revamp/technology modernization. Use of BAT would result into 25 % energy saving and reduction in green house gases by 30 %. For plants
already in operation energy e iciency optimization can be achieved through integrated infusion of newer technology concepts in existing
plant (Reference 1, 3 )
E orts to improve energy e iciency: As mentioned earlier several improvements in the technology has resulted into incremental
improvement in energy consumption per unit ton of ammonia produced .These are :
Development of catalyst, improved material/metallurgy, improved absorption solvents, equipment design, e icient rotating equipment
Reduction in Primary Reformer Duty, Part of reforming at lower temperature in Pre-Reformer
Utilizing Secondary Reformer outlet gas heat for reforming.
Increasing Conversion share of Secondary Reformer by excess air and recovery of excess Nitrogen downstream.
More e icient Burner tips to reduce excess air, Insulation / refractory for Furnaces, equipment and piping. More Heat recovery from flue
gases.
Superior Primary Reformer Tube Material with lower thickness and higher catalyst volume
Steam superheating by Process gas in place of using other furnace.
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10/25/2017 Innovative Revamping of Ammonia plants for Capacity up and Energy Efficiency - Ammonia Know How
Supply Compression Energy directly by Gas Turbine and exhaust to HRSG or Reformer Furnace.
Use of Vapor Absorption for cooling GT / Compressor suction. Reducing Loop Pressure Drop.
Power Recovery Unit for High pressure gases let down, Hydraulic Turbine for liquid let down.
More e icient machinery and Advance Instrumentation and control
Lower Process Steam (requires improved catalyst and lower heat requirement for CO2 Removal System).
Use of Energy for Process Condensate treatment for generating Process Steam.
Feed Gas Saturation with Process Condensate to reduce treatment and process steam requirement.
Lower Energy for CO2 removal. Improved solution activators and e icient packing
More steam export makes available additional DM water and BFW water more better Heat recovery.
2 stage Ammonia synthesis
Improved ammonia refrigeration system
Isothermal single stage CO shi reactor
CO shi and ammonia synthesis reactor with axial-radial design to reduce pressure drop
Additional and improved Catalyst at various steps.
Reduce steam to carbon ration in PR . Such reduction in S/C ratio and oxygen firing will reduce pressure drop between primary reformer
and CO2 removal
Modify present CO2 removal to MDEA for energy e iciency, low CO2 leakage and any environmental issues
It is pertinent to note the positive e ect of these changes on specific energy consumption for ammonia during last 40 years as shown diagram
II.
Diagram II: Energy Learning Curve for Ammonia
Source: Chaudhary 2001,PSI 2004
Several of above changes are proprietary in nature and require careful integration with existing process flow sheet . Implementation of any of
above specific improvements for capacity up/energy reduction can be thought of as per site study , present performance, cost of natural gas,
alternative supply etc Revamp invest is detailed out in FEMA 2005 by Rafiqual et al(3 ) ,which is summarized as follows
Retrofit measure
Average improvement
GJ/T
Range GJ/T
Uncertainty
parameter %
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Cost

10/25/2017 Innovative Revamping of Ammonia plants for Capacity up and Energy Efficiency - Ammonia Know How
€per t/year
Reformer large improvement 4.0 ±1.0 17 24
Reformer moderate improvement 1.4 ±0.4 20 5
Improvement CO2removal 0.9 ±0.5 33 15
Low pressure synthesis 0.5 ±0.5 67 6
Hydrogen recovery 0.8 ±0.5 50 2
Improved process control 0.72 ±0.5 50 6
Process integration 3.0 ±1.0 23 3
Drivers for Ammonia plant Revamp for capacity and energy e
iciency
1. Need for improving energy e iciency :Vintage plants built in years1970- 1990 were in capacity range 400 to 1350 MTPD. However they
are energy in e icient and consumes 8 to 9.5 Gcal per MT ammonia as compared to modern plants in capacity range of 1350 to 3300
MTPD with energy consumption 6.5 to 7.5 Gcal/mt
2. High energy cost in India, SEA Countries and other Asian AND European countries provides opportunity to replace/modernize ine icient
old compressors for reliability
4 Strict pollution norms and need for reduction in GHG emission
5 Additional ammonia capacity at incremental cost
6 Lower time for implementation and cost e ective revival of old/idle plants
7 Lot many successful examples of revamp across the globe ( more than 150)
This review paper will examine few important concepts for increasing capacity and energy e iciency in vintage ammonia plant
Case study 1 :Use of Chilling to improve ammonia production
For incremental improvement and energy e iciency, chilling provide option that avoids expensive upgrades of compressor system which are
in many cases limiting both capacity and energy e iciency. This concept has been applied in several ammonia plants for multiple benefits of
higher production, reduced power consumption and in some cases saving of costly steam which otherwise is required for vaporizing
ammonia by a consumer downstream fertilizer production unit. Few examples are
1. Addition of synthesis gas chillier at suction of synthesis gas compressor of 450 & 500 MTPD ammonia plants of GSFC Vadodara originally
built in years 1967 &1969 respectively. It helped in increasing synthesis gas compressor capacity by @8 %.These chillers were generating
about 4 mt/hr of vapour ammonia which was sent to DAP/AS plants about 1 km away by a pipe line thus avoiding steam consumption of
about 2 mt/hr otherwise required . Later on, this vapour ammonia network was connected with other ammonia vapour generator units ,
thus avoiding compression of vapour ammonia generated in the ammonia and other plants . This is one of the earliest chilling measure
in fertilizer industry to increase ammonia plant compressor capacity (1,5 )
2. Indo Gulf Fertilizers debottlenecked the process air compressor of their 1520 mtpd ammonia plant by proving suction chilling. IGFC
utilized Vapour Absorption Machine VAM to cool atmospheric air to 15©.( 6 )
3. Concept of Multistage Integrated Chilling MIC to increase ammonia production is presented by Kinetics Process Improvements MIC
process modification is a staged thermal coupling of ammonia compression system with the process air compressor. It is reported that
the MIC scheme along with other measures provides the potential to achieve incremental increase in ammonia capacity and energy
e iciency improvements up to 15 % with no modifications in process air compressor, synthesis gas compressor and ammonia
compressor(7)
To summarize , following chilling sources can be explored within ammonia complex
1. Use of generated vapour ammonia in the complex itself in any ammonia consuming plant/section
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2. Use of VAM using heat energy from flue gases (in temperature range of 125 to 180 ). It could be hot flue gas in convection section of
primary reformer or in HRSG if GT is installed in the complex
3. Low pressure steam otherwise getting vented in the complex or low level heat up stream of CO2 removal unit
4. Use of existing ammonia refrigeration capacity
Case study 2 :Use of Gas Turbine for process air compressor/power generation;
Several old ammonia plants have been designed with either electric driven process air ,ammonia refrigeration compressors and in few cases
the synthesis gas compressor also electric driven. Such plants are designed with import of power and excess steam is exported .The plants
which are designed with steam driven process air and synthesis gas compressors usually import power and steam from typical o site
boiler/power house or state electricity grid . Such plants using steam for power production or import power , do have very low energy
e iciency as more than 50 % of energy contained in steam is transferred to cooling water through condensation and losses. Such cases where
both steam and power is required , use of Gas Turbine provide an energy e icient solution. This concept is practiced in new plants in several
ways such as (a) provide a gas turbine to run process air compressor and utilize exhaust gases (at around 500 ©)as combustion air in primary
reformer. With this arrangement it is possible to achieve high e iciency of the order of 90 %. However this concept can be considered at
design stage itself. In revamp situation this would call for several major modifications . (b) Alternatively exhaust gases can be sent to Heat
Recovery Steam Boiler (HRSG ) to generate high/medium pressure steam to meet steam requirement of ammonia-urea plant and excess
steam can be used to produce power . This can be applied to new design as well as existing plants
As ammonia plant is considered to be power house producing large steam/power, it is essential to optimize the steam and power balance and
driver selection for optimum energy consumption. For a typical 2500 MTPD Ammonia and 3850 MTPD urea project , developmental work was
carried out to estimate energy reduction with di erent drive system ,which is summarized on diagram IV
Diagram IV
E ect of Energy consumption with di erent Drives
Serial Number
Driver concept
Energy reduction Gcal/mt urea
1 Gas fired boiler and all machines steam turbine driven Base case
2
Air compressor by gas turbine and rest all steam turbine
driven
-0.26
3 All power and steam from GT+HRSG+Steam Turbine -0.45
For 500 MTPD Ammonia and 800 MTPD Urea plant based on conventional technology, potential for energy saving with GTR+HRSG was
evaluated as shown on diagram V
Diagram V
Power Generation :Conventional vs GT+HRSG
Particulars Present Design With GT +HRSG
Type of drive and source of power conventional power plant power and steam from GT+HRSG
Net power MW 23 23
Net steam for urea mt/hr 50 50
Fuel consumption for steam and power NM3/HR 13190 10567
Reduction in energy use mmkcal per mt urea base -0.65
Savings $ per year @NG cost 5 $ per mmbtu base 3.9
Estimated cost of GT+HRSG million $ base 18
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Many ammonia-urea plants operating with import of power are in the process of implementing this concept. RCF-Trombay is implementing
GT+ HRSG concept .At present they are importing 40.7 MW power from state distribution and 184 mt/hr of steam is generated in gas fired
boiler. Implementation of this concept of GT +HRSG is expected to result into energy saving of 86.5 Gcal/hr for Trombay complex .(8 ).IFFCO
Phulpur is also planning to implement GT +HRSG for energy e iciency .
Case study 4 :Application of Pinch Analysis
Pinch analysis initially developed to optimize energy usage in a new design can equally be applied to analyse and improve the process in a
retrofit situation. It is focused on improving the manner in which way hot and cold utilities (flue gas, steam, process/steam condensate,
cooling water , refrigeration, etc ) are utilized to serve needs of the process .In retrofit situations, constraints by existing equipment to achieve
optimum use of energy can be overcome through improvement in process –utility interface. Major steps of pinch study are obtain relevant
data on existing process configuration, generate targets for each relevant utility, identify in e iciency in existing heat exchanger network,
identify possible process modifications to reduce energy use and decide viability of modification for implementation. To illustrate ,detail
pinch analysis of an ammonia plant of about 1000 tpd has been presented and documented by Natural Resources Canada (9). This study
brought out several process improvements with primary benefits of energy use reduction by 2 GJ/T Total steam demand reduction of 30
t/hr, shut down of package boilers and about 11 % reduction in NOx and CO2 emissions. Simple pay- back period of required modification
was 1.5 years at a gas price of 6 can$ per GJ. The study also brought out other retrofit opportunity for cost and energy savings .
Case study 5 : Innovative revamp using proven process modules
While increasing production capacity in existing ammonia plant, major hurdles/bottlenecks faced vary from plant to plant and it is also
dependent on type of technology put to use, design margins applied during installation, maturity of technology, site specific changes such as
raw material specification ,etc. Major limitations encountered by operating group are
Limitation of primary reformer viz highest operating temperature, catalyst volume and limiting pressure drop
Limitation of process air/synthesis gas compressor
High pressure drop between reformer and synthesis
Limitation of ammonia synthesis unit
Several successful capacity revamp have been reported with application of technological improvement such as pre-reformer, use of heat
exchanger type reformer, cryogenic purification ,up-gradation of ammonia synthesis . This case study describes the concept of revamping a
vintage ammonia plant through use of modular technology applied in several ammonia and methanol plants. This concept for revamping of
conventional ammonia plant is based on following changes in the flow sheet through add on “ process modules “
1. Convert existing secondary reformer to oxygen firing. This requires new oxygen burner and refractory rework of SR vessel
2. Optimize oxygen addition to modified SR to match required additional capacity and minimize loading of primary reformer
3. Add dedicated ASU for pure oxygen and nitrogen.
4. Modify present CO2 removal to MDEA for energy e iciency, low CO2 leakage and eliminate environmental issues
5. By pass existing Methanation section to avoid hydrogen loss and extra methane generation
6. Add cryogenic purification /Liquid Nitrogen wash for drying and purifying synthesis gas and hydrogen/nitrogen ratio control .
With above modification/addition the revamp flow sheet will have features as shown in the diagram VI and Table VII
Diagram VI
Ammonia Revamp using proven process modules
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Table VII
Major impact of Process changes
Section Changes Benefits Remark
Primary reformer
Lower steam /carbon ratio
Lower pressure drop, higher
throughput
Can be implemented independently
a er process simulation and steam
balance
Secondary reformer
Oxygen firing in place of air
firing
Increase in throughput,
flexibility to add NG directly to
Secondary Reformer for extra
capacity
Existing SR Vessel can be used with
new refractory and oxygen burner
HT shi reactor & LT shi
reactor
No changes
check adequacy of catalyst
volume/life
CO2 Removal
Revamping for lower CO2
Leakage and energy
consumption
Less consumption of steam
Utilize excess low level heat for
chilling, DMW heating
Methanation
Bypassing
Saving of hydrogen and reduced
methane generation
Reduces pressure drop
Cryogenic
purification/nitrogen wash
New section to remove all
impurities from synthesis gas
and ratio control
Generation of inert free
synthesis gas
Purge gas from this section can be
used as fuel
Ammonia Synthesis
As per capacity requirement
Loop working with pure
hydrogen: nitrogen will result
higher capacity thus avoiding
major modifications
Inert free ammonia loop
Introduction of above modular changes in the flow sheet along with all feasible changes like reduction in steam to carbon ration in primary
reformer, heat recovery measures will help in creating positive impact for capacity rise of the order of 15 to 20 % with significant reduction in
energy consumption .It may be mentioned here that so far no such revamp with all the above features has been implemented. However each
of the modules such as oxygen fired reformer(or Auto Thermal Reactor ), cryogenic purification, improved CO2removal , Air Separation Unit
for pure oxygen and nitrogen, inert free ammonia loop are operating successfully in di erent ammonia plants based on natural gas, fuel oil,
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coal and Natural Gas based methanol plants of higher capacity .With good design and process integration of newer process modules,
these benefits can be obtained from a revamped ammonia plant .
Concluding Observations
High cost of natural gas, need of additional production requirement and environmental issues are prompting ammonia operators to
continuously strive for newer improvements in the process. Various case study such as chilling for increasing compressor capacity, use of gas
turbine , process simulation for heat integration and use of innovative proven process modules such as conversion from air to oxygen firing,
ASU for pure nitrogen and oxygen, cryogenic purification/nitrogen wash , inert free ammonia loop will help in substantial improvement in
capacity and energy e iciency of old ammonia plant. This can be achieved by better understanding of the process by owners themselves
and process intervention with suppliers of such process modules to develop integrated revamp .
References and literature cited
1. A Modern Intervention for Ammonia Plants : Harshad P Pandya,” World Fertilizer Magazine” May-June 2017 ,p 34-38(edited version on
innovative improvements in Ammonia plants)
2. Ammonia Plant Technology options and KRIBHCO’s operating experience on KBR Technology : R K Aggarwal, S Banerjee, R M Maliya
Indian Journal of Fertilizers 72-87 ,December 2015
3. Industrial E iciency database, Ammonia: Technology Resource and Benchmark ; ietd.iipnetwork.org
4. Rafiqul , I. , C. Weber , B. Lehmann , and A. Voss , 2005 : Energy e iciency improvements in ammonia production – perspectives and
uncertainties. Energy ,30 : 2487 – 2504.
5. TERI Report on GSFC Energy conservation E orts
6. Debottlenecking of process air compressor of Ammonia plant by suction chilling : CK Datta , Anand K Gupta ; Indian Journal of Fertilizers
23-24 ,July 2007
7. Use Multistage integrated chilling to increase ammonia production V K Arora .Hydrocarbon Processing 39-46, April 2015
8. Reports from www.rcfltd.com and public domain on energy conservation measures in RCF Thal plants
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