DRIVER SELECTION FOR LNG COMPRESSORS 14th December 2004 Dr Sib Akhtar MSE (Consultants) Ltd Carshalton, Surrey SM5 2HW
[email protected] http://www.mse.co.uk Tel: 020 8773 4500
Driver Selection for LNG Compressors Introduction Drivers Used in Past & Present Projects Factors Influencing Driver Selection Potential Future Applications Pros & Cons of: Steam Turbines Industrial Gas Turbines Aero-derivative Gas Turbines Electric Motors
Conclusions and Observations © MSE 2004
Introduction History Early LNG Trains Steam Driven Development of Gas Turbines The LNG Growth Pause US & UK became self sufficient in Gas Japan and later Korea needed secure energy-LNG Japan remains the biggest importer of LNG
Re-emergence of LNG Demand New Markets Gas Shortages in US Re-opening of LNG terminals Expansion of LNG in Europe UK to become net importer of Gas
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Common LNG Process Systems Phillips Cascade Process Three Pure Components Propane Ethylene Methane
APCI (Air Products) Two Components Propane Mixed Component Refrigerant
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New Emerging LNG Process Systems Linde Process Three Mixed Refrigerants
Axens Liquefin Process Dual Mixed Refrigerant
Shell Process Dual Mixed Refrigerant
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Factors Influencing Compressor Driver Selection Plant Capacity Process Used – Choice and Number of Refrigerant Streams Compressor Configuration Plant Location; Ambient Conditions Plant Availability Operational Flexibility Economic Factors - CAPEX & OPEX © MSE 2004
Gas Trade Flows
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Source: Energy Information Administration – The Global LNG Market Status & Outlook
LNG Import Capacity
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Source: Energy Information Administration – The Global LNG Market Status & Outlook
LNG Export Capacity
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Source: Energy Information Administration – The Global LNG Market Status & Outlook
LNG Processes Phillips Optimised Cascade and Air Products (APCI) processes dominate the LNG plants currently under design, construction & operation New processes include: Axens (DMR) Linde (Statoil) Turbo-Expander (BHP)
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Phillips Cascade Process Many plant still being designed and built using the cascade process – simple and reliable Three pure components used for refrigeration: Propane pre-cooling Ethylene Methane
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Phillips Cascade Process Propane pre-cooling Centrifugal compressors Typically 2 x ~30 MW Gas Turbines (e.g. Frame 5)
Ethylene and Methane cycles Centrifugal compressors Typically 2 x ~30 MW Gas Turbines (e.g. Frame 5) for each cycle
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Phillips Cascade Process ALNG – Trinidad Propane pre-cooling Centrifugal compressors 2 x Frame 5 C – upgraded to D
Ethylene and Methane cycles Centrifugal compressors 2 x Frame 5 C upgraded to D for each cycle
Plant Capacity 3 MTPA – Raised to 3.3 MTPA High Availability 95-96%
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Phillips Cascade Process ALNG – Optimised Design Phillips Cascade Process
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Phillips Cascade Process Simple to design and operate Simple cycle Frame 5 gas turbines mechanical drive No helper turbine or large motor needed for start-up Increased size with two gas turbine trains for each refrigerant process Parallel compressor trains avoids capacity limits Increased CAPEX due to more (six) trains offset by increased availability 95-96% with parallel train operation Loss of one train does not cause plant shut down Production carries on with reduced capacity Refrigerant and exchangers temperature not affected by one train trip enabling quick restart © MSE 2004
APCI Process Most of existing plant are using the APCI process with 3 – 3.3 MTPA Fr 6 / Fr 7 combination Train capacities up to 4.7 MTPA built or under construction using Fr 7 / Fr 7 combination Higher Capacities to 7.9 MTPA being announced with Frame 9 GT Two main refrigeration cycles: Propane pre-cooling Mixed refrigerant liquefaction and sub-cooling © MSE 2004
APCI Process Propane pre-cooling Centrifugal compressor (to 15 – 25 bar) Side-streams at 3 pressure levels Typically requires a ~40 MW Gas Turbine (e.g. Frame 6) plus Helper Motor or Steam Turbine Compressor sizes reaching maximum capacity limits Added aerodynamic constraint; high blade Mach numbers due to high mole weight of propane (44) Prevents utilisation of full power from larger gas turbines (Frame 7) © MSE 2004
APCI Process Mixed refrigerant liquefaction and sub-cooling Axial LP for Shell Advised Plant Centrifugal HP compressor (45 – 48 bar) Typically requires ~70 MW Gas Turbine (e.g. Frame 7) plus Helper Motor or Steam Turbine
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ELLIOTT IN LNG A HISTORY OF FIRSTS
World’s first large-scale liquefaction plant (CAMEL – Arzew, Algeria)
World’s first baseload refrigeration plant (Phillips - Kenai, Alaska)
World’s first gas turbine driven LNG compressors (Phillips, Alaska)
World’s first single-mixed refrigerant (APCI) process compression (Esso (Exxon) – Marsa el-Brega, Libya)
World’s first dual-shaft (GE Frame 5) gas turbine driven compressor strings (P.T. Arun (Mobil) – Indonesia)
World’s first C3-MR (APCI) process compression (P.T.Arun – Indonesia)
World’s first GE Frame 7 driven Propane MR compressor (Ras Gas 1&2 – Ras Laffan, Qatar)
World’s largest four-section Propane MR compressor (Ras Gas 3 – Ras Laffan, Qatar - UNDER CONSTRUCTION)
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Partial List - ELLIOTT LNG Plants End User
Process
Capacity MM T/Yr
# of Units
Service
C.A.M.E.L. Arzew, Algeria
Cascade
1.3
3 3 3 3 3
Propane Ethylene Methane 1 Methane 2 Vapor
Phillips Petroleum Kenai, Alaska
Cascade
1.1
2 2 1
Propane Methane 1 Methane 2
Esso Libya Marsa El Brega, Libya
Mixed Refrigerant
3.2
4 4
MR-1 MR-2
Sonatrach Arzew, Algeria
Mixed Refrigerant & Propane
16.4
6 6 6
MR-1 MR-2 Propane
Abu Dhabi Liquefaction Co. Das Island, Abu Dhabi
Mixed Refrigerant & Propane
3.0
2 2 2 2
Feed Gas Feed Gas Feed Gas Propane
P. T. Arun Liquefaction Co. Lhokseumawe, Indonesia
Mixed Refrigerant & Propane
9.0
6 6 6
MR-1 MR-2 Propane
Ras Laffan Liquefaction Co. Qatar
Mixed Refrigerant & Propane
6.0
2 2 2
MR-1 MR-2 Propane
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APCI Process Mixed refrigerant liquefaction and sub-cooling Large volumetric flows Two casing arrangements (LP and an HP) Axial LP / centrifugal HP compressor (45 – 48 bar) Typically requires ~70 MW Gas Turbine (e.g. Frame 7) plus Helper Motor or Steam Turbine LP and HP compressor speeds compromised LP axial compressor (higher efficiency) HP centrifugal compressor © MSE 2004
APCI Process APCI
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Example of APCI Process Evolution Petronas MLNG, located in Bintulu, Sarawak First trains designed in the ’70s: 3 x Centrifugal compressors 3 x Steam Turbine drivers ~ 37 MW each
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Example of APCI Process Evolution Extension trains designed in the ’90s: Propane pre-cooling: Centrifugal compressor 30 MW Gas Turbine & 7 MW Steam Turbine
Mixed component refrigeration (MCR): LP axial compressor & HP centrifugal compressor 64 MW Gas Turbine & 7 MW Steam Turbine
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RAS GAS I & II – RAS LAFFAN, QATAR
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RAS GAS III (&IV), RAS LAFFAN, QATAR UNDER UNDER CONSTRUCTION CONSTRUCTION
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Axens Liquefin Process Mixed refrigerants for pre-cooling, liquefaction and sub-cooling duties Liquefin development studies presently oriented towards increasing capacity to 6 MTPA with: 2 x Frame 7 Gas Turbines for main compression 2 x Frame 5 Gas Turbines for power generation
Higher capacities possible using: Frame 9 GTs Electric motors Steam turbines etc. © MSE 2004
Axens Liquefin Process Similar to APCI with Propane compressor replaced with Mixed Refrigerant for pre-cooling Allows more balanced flows, refrigeration loads and power between the two compressors Avoids the process design limits associated with Propane compressors
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Axens Liquefin Process Axens
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Shell DMR Process Ref Ref O OG G JJ July July 16 16 2001 2001
Similar to Axens but with twin parallel compressor trains for each process stream Use of aero-derivative or VSD motors Shell claim 4.5 - 5.5 MTPA and lower cost
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Linde Process Mixed refrigerants for pre-cooling, liquefaction and sub-cooling duties Minimum of Three Gas Turbine or electric motors needed for compressor driver 4.3 MTPA plant under construction with VSD motor drivers and onsite power generation with aero-derivative gas turbines
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Linde Process
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Process Design, Driver Ratings & Compressor Configuration APCI process uses larger and larger gas turbines to reduce CAPEX in a single train configuration; bigger gas turbine have lower $/kW Frame 7EA used for Mixed Refrigerant Frame 6 being replaced by Frame 7 for Propane for larger plants The plants are “single train” i.e. each machine is designed for 100% capacity and arranged in series © MSE 2004
Process Design, Driver Ratings & Compressor Configuration Phillips Optimised Cascade process have used 2x50% compressor configuration and achieved cost savings and high availability Shell DMR process appears to favour twin train configuration and achieves 4.5 - 5.5 MTPA with larger aero-derivative
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Gas Turbines Used in LNG Plant Heavy Duty Gas Turbines: Mechanical drive shown in blue Power generation shown in yellow
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Aero -Derivative Gas Turbines Aero-Derivative for LNG Plant – Potential Aero-derivative Gas Turbines:
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Combined Cycles and LNG Plant – Potential Combined Cycles: LM1600PE LM2500PE LM2500+ 6STG LM6000PC LM6000PD Sprint RB211-24GT RT62 Trent 50 Trent 60
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ISO Pow er (kW ) Heat Rate (kJ/kW h) Efficiency (%) 18591 7605 45 31048 7186 50 40912 6981 52 55007 6764 53 59142 6876 52 39760 7005 51.4 64458 6780 53.1 72268 7189 50.1
Economies of Scale
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Source: Gower and Howard, “Changing Economics of Gas Transportation”
Economies of Scale
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Source: Introduction to LNG, University of Houston Institute for Energy, Law and Enterprise
Steam Turbines - Pros Several established Vendors Size; may be built to exact process specification Mechanical drive up to 130 MW not a problem Constant speed power generation 600–1100 MW High reliability; 30 years life is achievable High availability; compressors & steam turbines may both achieve 3 years non-stop operation, no need for inspection Steam is often required elsewhere in process Mixed fuel; boilers can utilise varying fuel mix whereas gas turbines require fuel specification to be maintained Higher thermodynamic efficiency than simple cycle GT (but lower efficiency than GT-steam combined cycle) Power output relatively unaffected by ambient conditions © MSE 2004
Steam Turbines - Cons Perceived as old “Victorian” technology Physically very large; boilers, condensers, desalination plant (for make-up water), water polishing plant etc. CAPEX of steam turbine plant is higher than simple cycle GT (but similar cost to combined cycle) Overhaul of steam turbine similar to large frame GT (but interval between overhauls is twice as long!) Added complexity in steam auxiliaries, including feed heating, boiler feed pumps etc.
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Industrial Gas Turbines - Pros Simple cycle GT is uncomplicated in its design Low CAPEX Economies of scale when using large frame GTs Extensive operational experience with mechanical drive applications Large population; perceived as low risk technology Skid mounted; easier to install than a steam system Smaller plant footprint; less extensive civil works Lower NOX than Aero-derivative GT Range of sizes available: Frame 5
~ 30 MW
Frame 6
~ 40 MW
Frame 7
~ 75 MW
Frame 9
~ 110 MW
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Industrial Gas Turbines - Cons Paucity of Vendors! Low thermal efficiency, high CO2 emissions Maintenance is intensive, involving prolonged on-site work which reduces plant availability Fixed sizes and fixed optimal speeds Process and compressors must be designed around the GT (unlike steam turbines) Process may not make full use of the GT power Power output highly sensitive to ambient conditions e.g. typical large GT: 100% power At 15 °C
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~95% power
At 20 °C
~88% power
At 30 °C
~82% power
At 40 °C
Aero -Derivative Gas Turbines - Pros Aero-Derivative Higher thermal efficiency than Industrial GT; 38-42% compared to 28-32% for similar size Industrial GTs in simple cycle Smaller footprint area than Industrial GT because of aero design Shorter maintenance period; modular design allows gas engine and power turbine sections to be swapped out Off-site maintenance (in factory) Thus, higher plant availability Most engines have free power turbines for variable speed operation (within a range) Large helper motors or steam turbines may not be needed for start-up Range of sizes available: RB211
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~ 30 MW
LM6000
~ 40 MW
Trent
~ 55 MW
Aero -Derivative Gas Turbines - Cons Aero-Derivative Paucity of Vendors (essentially only 2)! Higher NOX than Industrial GTs Engines need more care and maintenance due to higher operating pressures and temperatures and design complexity Fixed sizes and fixed optimal speeds Process and compressors must be designed around the GT (unlike steam turbines) Process may not make full use of the GT power Power output highly sensitive to ambient conditions Fuel quality is critical – even more than in Industrials! Limited operating experience for LNG, although extensive for offshore mechanical drive and power generation Powers greater than 60 MW not available in simple cycle Dry Low Emissions (NOX) technology adds complexity Higher risk technology than Industrial GTs © MSE 2004
Combined Cycles - Pros Mitigates some of the cons of Industrial GTs Adds some of the pros of Steam Turbines Essentially, 50% extra power / 50% extra thermal efficiency / 50% lower CO2 emissions Allows optimisation of process and compressors Steam turbine can be used for start-up and additional power Steam may be required elsewhere in the process
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Combined Cycles - Cons High CAPEX, increased complexity, more extensive civil works… same as for Steam Turbine Combined cycles are not presently favoured by LNG plant designers, but may be considered when CO2 is taxed!
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Variable Speed Electric Motors - Pros Can be made to suit, allowing optimisation of process and compressors Higher availability of LNG plant than if using GTs or Steam Turbines Reduced manning levels May avoid gearboxes for 3000-3600 rpm compressor speeds (large flow capacity compressors) Power generation may be off-site Lower CAPEX if power is bought from the grid Simple layout, reduced civil works © MSE 2004
Variable Speed Electric Motors - Cons Most LNG plant are in remote locations; off-site power generation of 400-500 MW not available! Very high CAPEX if power generation is built alongside LNG High OPEX (although savings may be possible) Limited experience with high power VSDs; 45-55 MW is achievable, 65 MW is the maximum Electrical issues at compressor start-up; grid peak current and fault levels Power generation using GTs must happen somewhere; CO2, NOX and sensitivity to ambient conditions is similar to a GT (unless power generation is using a combined cycle)
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Conclusions and Observations LNG drivers are predominately Industrial Heavy Duty Gas Turbines e.g. GE Frames 5, 6, 7 … even 9! Frame 5s generally used on older LNG plant, although ALNG in Trinidad was recently fitted with Frame 5Ds; these are demonstrating high overall availability at low CAPEX… 3.3 MTPA with 6 x Fr 5 Fr 6 / Fr 7 combinations replaced Steam Turbines at MLNG Now Fr 6 / Fr 7 commonly used at NLNG, Oman LNG, Qatar LNG… 3.3 – 3.5 MTPA Fr 7 / Fr 7 combinations used at Qatar LNG, but with poor use of GT power because of non-optimal process, process had to be redesigned… ~4 MTPA Larger and larger trains are pushing the limits of compressor technology i.e. Axials for Mixed Refrigerant and largest centrifugals for Propane © MSE 2004
Conclusions and Observations When parallel trains are used (instead of series) e.g. ALNG: Smaller driver sizes can be used e.g. Frame 5s Compressor capacities are halved, so centrifugals may be used instead of axials Plant availability is enhanced Improved operability, re-starting after a train failure is simpler and quicker Plant costs are surprisingly lower
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