Benchmarking of power cycles with CO 2 capture The impact of the chosen framework 4 th Trondheim Conference on CO 2 Capture, Transport and Storage Kristin Jordal, 1
The benchmarking activity at SINTEF/NTNU within BIG CO2 Nine different power cycles with CO 2 capture evaluated Fuel is natural gas Reference case is a gas turbine combined cycle of 386 MW and a thermal efficiency of 56.7% The work has been presented at GHGT-7 and in Energy Amine absorption (post combustion) Oxyfuel CC Efficiency 70.0% 65.0% 60.0% 55.0% 50.0% 57 % Near term concepts Oxy-fuel with cryogenic oxygen production 48 % 47 % 47 % 45 % 49 % Membranebased + CLC 51 % 50 % 50 % 53 % 67 % Pre-combustion capture with ATR 45.0% 40.0% 35.0% CC base case Amine ATR Oxyfuel CC WC Graz CLC MSR-H2 AZEP100% AZEP85% SOFC/GT Kvamsdal et. al. 2007 2
About quantitative benchmarking The methodology for general thermodynamic studies of different power cycles is well established - it is known what process conditions give a high thermal efficiency CO 2 capture and compression is a new element to be included in power cycles Benchmarking of different power cycles with CO 2 capture against a reference case without capture has become an acknowledged method to evaluate the impact of CO 2 capture on power cycle efficiency (and cost) The boundary for a power plant with CO 2 capture is more complex than that of a standard power plant 3
My power plant boundary 10 years ago Ambient boundary Fuel: (Danish) natural gas Exhaust to atmosphere Air at GT standard ambient conditions 15 C, 1.013 bar a 60% humidity ~ Electric power to the grid Power plant boundary Picture of Västhamnsverket in Helsingborg, Sweden Cooling water η th = Power output Fuel input 4
The power plant boundary with CO 2 capture Ambient boundary Fuel: Natural gas, LNG Exhaust to atmosphere (except oxyfuel) Purge gas Recovered purge gas CO 2 transport and storage Fuel: coal CO 2 processing water Air ASU oxygen nitrogen ~ Electric power to the grid Power plant boundary oxygen nitrogen Cooling water η th = Power output Fuel input 5
Framework selection Standard boundary conditions or site specific? Standard boundary conditions, as far as possible, make the results more of general interest Site-specific boundary conditions give a more true picture for a selected site or geographic area Ambient temperature Cooling water temerature Natural gas delivery conditions (LNG or gas?) CO 2 final pressure Oxygen production on site? }Norwegian conditions favourable! What technology level do we want to reflect? Current (known) technology status previous SINTEF benchmarking Estimated future technology, when CO 2 capture is likely to be generally adopted for new power plants topic in this presentation Purpose is to present an idea of what could be the development potential of some different capture technologies 6
Site-specific conditions: impact of cooling water temperature (=condenser pressure) 0,06 0,05 0,04 Condenser outlet pressure [bar] Continental Europe Benchmarking 12 10 8 6 Relative difference in specific turbine work [%] 0,03 0,02 0,01 0 Avedøre 2 design value (Denmark) 5 10 15 20 25 4 2 0-2 -4-6 5 10 15 20 25 Continental Europe Benchmarking Assumed pinch point 10 C in condenser Relative gain from reduced cooling water temperature (right picture) based on LP turbine in combined cycle only. Value reduced when considering the entire turbine train with multiple steam extractions. 7
Example of framework selection: Future technology levels Parameter GT combustor outlet temperature [ C] GT max blade temperature (rough estimate) Max steam temperature [ C] HP/IP steam turbine inlet pressure [bar] Previous benchmarking ~5-10 years (?) 1328 1428 1528 900 940 980 560 600 (done today already) 111/27 Result of optimisation ~15-20 years(?) 700 (goal of R&D programs), 656 max in this work Result of optimisation (HP supercritical?) Amine re-boiler steam requirement [kj/kg CO 2 ] 3.4 (low figure!) 2.8 1.5 (unrealistic for temp-swing only) Each new technology level requires a new reference case without CO 2 capture! 8
Establishing new reference cases (1): Gas turbine modelling, future technology A realistic generic gas turbine required when increasing the combustion temperature Temperature increase possible due to increased materials temperature and better blade cooling Pressure ratio adapted for anticipated exhaust temperature 9
Establishing new reference cases (2): Combined cycle modelling For each new gas turbine, a new reference combined cycle must be established NG HRSG Exhaust We cannot compare a CO 2 capture cycle based on advanced power plant data against a reference cycle reflecting older technology Air GT Steam turbine Generator Efficiency optimisation in this case was done in GTPRO T g [ C] P el [MW] Efficiency [%] Steam data [bar/ C/ C] 1328 386 56.7 111/560/560 1428 411 57.9 111/560/560 1428 414 58.2 140/580/580 1528 436 58.8 111/560/560 1528 440 59.4 180/600/600 10
Post combustion capture development possibilities 60 58 56 Theoretical improvements in post combustion capture (90% capture rate) Combined cycle + capture development N.B.! Upper limit values are extremely optimistic! Cycle efficiency [%] 54 52 50 48 46 Combined cycle development No capture 100 mbar 1.5 kj/kg CO2 2.8 kj/kg CO2 3.4 kj/kg CO2 Should be regarded as an extreme limit for the potential for this thechnology 44 42 40 1328 1428 1528 Gas turbine combustor outlet temperature [ C] 11
Oxyfuel CC development possibilities Cycle efficiency [%] 60 58 56 54 52 50 48 46 44 42 40 Oxyfuel improvements through improved gas turbine and bottoming cycle Gas turbine temp.increase 1328 1428 1528 Gas Turbine Combustor outlet temperature [ C] Potential for applying supercritical steam data? No capture pr=45, DT=20 PR=45 pr=35 pr=29.2 Gas turbine temp.increase, pressure ratio increase and steam cycle pinch point decrease Capture is more integrated in the oxyfuel CC than in the post combustion cycle. More difficult to push performance parameters towards the extreme in a computational exercise Oxyfuel CC penalised by consistent framework for steam bottoming cycle??? 12
Pre-combustion with ATR Cycle efficiency [%] 70 60 50 40 30 20 10 0 Increased combustor outlet temperature for ATR case No capture ATR 1328 1428 1528 Gas turbine combustor outlet temperature [ C] CO 2 capture in precombustion with ATR even further integrated than in oxyfuel CC No benefit (in current process layout) from increasing GT pressure ratio Not possible (in current process layout) to use improved steam data from reference CC Only technology improvement with positive impact on performance is increased combustor outlet temperature 13
Chemical Looping potential Potential for combined cycle CLC plant options Plant efficiency 56,0 % 54,0 % 52,0 % 50,0 % 48,0 % 46,0 % 44,0 % 100% fuel conversion 99% fuel conversion 42,0 % 40,0 % combined cycle CLC, reactor temp 900 C combined cycle CLC, reactor temp 1000 C combined cycle CLC, reactor temp 1100 C Single reheat combined cycle CLC, reactor temp 1000 C Double reheat combined cycle CLC, reactor temp 1000 C Single reheat combined cycle CLC, reactor temp 1100 C Double reheat combined cycle CLC, reactor temp 1200 C Source: Naqvi R., 2006, Analysis of Natural Gas-Fired Power Cycles with Chemical Looping Combustion for CO2 capture, Doctoral Theses at NTNU, 2006:138. 14
Summary, future development potential 60 58 56 54 52 50 48 46 44 42 40 15 No Capture 1328 Amine 1328 Oxyfuel 1328 ATR 1328 CC-CLC, 900 C No capture 1428 Amine 1428 Oxyfuel 1428 ATR 1428 Single reheat CC-CLC, 1000 C No capture 1528 Amine 1528 Oxyfuel 1528 ATR 1528 Double reheat CC-CLC, 1200 C
Conclding remarks, future development potential When considering future development potential, the same boundary conditions were applied as in previous benchmarking New reference combined cycles were established to reflect the anticipated technology development Post combustion capture has a low degree of integration with the power plant, and it is easy to produce theoretical results with increased cycle efficiency, beyond a realistic limit It appears from this work that the more integrated the CO 2 capture into the cycle, the more difficult it could actually be to improve cycle efficiency beyond combustor outlet temperature improvements The development potential with evolving technology should be useful to consider for a manufacturer before deciding to pursue the development of a certain technology 16
Concluding remark: impact of chosen framework for CO 2 capture studies Main issue: be careful when presenting results and/or when interpreting results that are presented to you! Is the framework for the study consistent? What is included in the efficiency calculation? What are the boundary conditions? (site specific? ISO standard?) What is the technology level? Is it realistic? Outdated? What is the reference case without CO 2 capture? Does it have the same framework as the case(s) with CO 2 capture? 17
Thank you for your attention! 18
BIG CO2 benchmarking: Stream input data (boundary conditions) Fuel feed stream Composition N2 [mole%] 0,9 CO2 [mole%] 0,7 C1 [mole%] 82 C2 [mole%] 9,4 C3 [mole%] 4,7 C4 [mole%] 1,6 C5+ [mole%] 0,7 Properties Pressure [bar a] 50 Temperature [ C] 15 Molecular weight [g/mol] 20,05 Density [kg/sm3] 0,851 Conditions lower heating value [kj/sm3] 40448 lower heating value [kj/kg] 47594 Air feed streem Composition N2 [mole%] 77,3 CO2 [mole%] 0,03 H2O [mole%] 1,01 Ar [mole%] 0,92 O2 [mole%] 20,74 Properties Pressure [bar a] 1,013 Temperature [ C] 15 Oxygen feed streem Composition O2 [mole%] 95 N2 [mole%] 2 Ar [mole%] 3 Properties Pressure [bar a] 2,38 Temperature [ C] 15 Conditions Energy production requirement kj/kg O2 812 CO2 outlet Composition CO2 concentration [mole%] 88,6-99,8 Properties Pressure [bar a] 200 Temperature [ C] 30 19
BIG CO2 benchmarking: Computational assumptions (inside the power plant) Heat exchangers Pressure drop [%] 3 T min gas/gas [ C] 30 T min gas/liquid [ C] 20 HRSG T steam out/exhaust in [ C] 20 HRSG pinch point [ C] 10 CO2 compression intercooler temeprature [ C] 30 Gas side pressure drop through HRSG [mbar] 40 Reactors GT Combustor and reactor pressure drop [%] 5 Duct burner pressure drop [%] 1 Combustor outlet temperature (max) [ C] 1328 Reactor outlet temperature, CLC and AZEP [ C] 1200 Turbomachinery efficiencies Main GT Compressor polytropic efficiency [%] 91 Main GT Uncooled turbine polytropic efficiency [%] 91 Small compressor polytropic efficiency [%] 87 Small turbine polytropic efficiency [%] 87 CO2 compression isentropic efficiency stage 1 [%] 85 CO2 compression isentropic efficiency stage 2 [%] 80 CO2 compression isentropic efficiency stage 3 [%] 75 CO2 compression isentropic efficiency stage 4 [%] 75 SOFC/GT cycle compressor polytropic efficiency [%] 87,5 SOFC/GT cycle turbine polytropic efficiency [%] 87,5 AZEP and SOFC/GT recirc compressor polytropic efficiency [%] 50 HP steam turbine isentropic efficiency [%] 92 IP steam turbine isentropic efficiency [%] 92 LP steam turbine isentropic efficiency [%] 89 Pump efficiency (incl. motor drive) [%] 75 Note: Small compressor/turbine refers to H2O/CO2 recircualtion compressor, ATR and MSR-H2 fuel compressors, MSR-H2, CLC and AZEP CO2/steam turbines Steam power cycle Max steam temperature, pure steam cycle [ C] 560 HP steam turbine inlet pressure [bar a] 111 IP steam turbine inlet pressure [bar a] 27 LP steam turbine inlet pressure [bar a] 4 Max temperature WC HP turbine [ C] 900 Deaerator pressure [bar a] 1,2 Condenser pressure, pure steam cycle [bar a] 0,04 Condenser pressure, Water Cycle [bar a] 0,045 Condenser pressure, Graz cycle [bar a] 0,046 Condenser pressure, Oxyfuel CC [bar a] 1,01 Cooling water inlet temperature [ C] 8 Cooling water outlet temperature [ C] 18 CO2-capture-specific cycle units CO2 absorption recovery rate, ATR and post combustion [%] 90 CO2 stripper outlet pressure, ATR and post combustion [bar a] 1,01 Amine re-boiler steam requirement [MJ/kg CO2] 3,4 Pressure drop in absorption column [mbar] 150 Methane conversion MSR-H2 [%] 99,8 Shift reaction conversion MSR-H2 [%] 99 H2 separation MSR-H2 [%] 99,6 CLC degree of carrier oxidation [%] 100 CLC degree of carrier reduction [%] 70 CLC degree of fuel utilisation [%] 100 Auxiliaries Generator mechanical efficiency [%] 98 O2 and CO2 compression mechanical drive efficiency [%] 95 Auxiliary power requirements (of net plant output) [%] 1 20
Konsept 1a: Eksosgassrensing med amin Condenser NG HRSG Exhaust: CO 2,N 2, O 2,H 2 O Pre-cooler N 2, O 2, H 2 O Amine absorption H 2 O Amine stripper CO 2 to compression Energy CO 2 -rich amine Air GT Steamturbine Generator LP steam (4 bar, 140 C) Amine 21
Oxy-fuel CC NG Pressurized oxygen Condenser HRSG 83 % CO 15 % H 2 O 1328 C 1.8 % O 2 H 2 O CO 2 to compression ST GT Generator 96 % CO 2 2 % H 2 O 2.1 % O 2 90 % recycle 22
Konsept 2a: Reformering av hydrokarboner vha autotermisk reaktor (ATR) CO 2 to compression FC ABS H2 H1 ATR HTS LTS Condenser 55 % H 2 45 % N 2 PRE Steam H 2 O C 1328 C HRSG ST Exhaust Model assumptions: 15 bar in ATR steam-carbon ratio = 2 Tout ATR = 900 C H1 and H2 are boilers Steam cycle: 3 pressure levels (4, 27 og 111 bar) and reheat Condenser heat used in the absorption stripper Air GT Generator 90 % CO 2 is removed by absorption NG 23