SELECTIVE EXHAUST GAS RECIRCULATION IN COMBINED CYCLE GAS TURBINE POWER PLANTS WITH POST-­‐COMBUSTION CARBON CAPTURE Erika Palfi, Laura Herraiz, Eva Sánchez Fernández, Mathieu Lucquiaud The University of Edinburgh, School of Engineering, The Kings Buildings, Edinburgh EH9 3JL, United Kingdom Contact details: E.Palfi@ed.ac.uk +44 (0) 7476681902 1. INTRODUCTION AND MOTIVATION •  Commercial scale deployment of Post-­‐combusGon Carbon Capture (PCC) technologies in •  Previous work has shown the minimum requirements for the operaMon of CCGT + PCC with S-­‐EGR and invesGgated the effects on the gas turbine performance and steam cycle, and Combined Cycle Gas Turbine (CCGT) power plants requires the cost and the energy penalty to evaluates the reducMon in volume of packing and energy consumpMon in the post-­‐
be considerably reduced. Increasing the CO2 parGal pressure enhances the driving force for CO2 combusGon capture unit with amine-­‐based chemical absorpGon. separaGon. •  SelecMve exhaust gas recirculaMon (S-­‐EGR) appears as an alternaGve to convenMonal exhaust •  This work focuses on the detail concept of SEGR to provide the knowledge for pilot scale development in the UK with water management opGons in the recycling loop and heat gas recirculaMon (EGR) to further increase the CO2 concentraGon (> 6.5%mol) in the flue gas at integraGon and expanding relevant learnings to other plant configuraMons. It will require the the inlet of the post-­‐combusGon capture unit, without compromising the O2 level in the development of novel engineering opMons, for instance for the cooling of large volumes of combustor (> 16%mol). flue gas, advanced process integraGon and balance of plant consideraGons around the recycling loop. 2. PREVIOUS WORK 60 Gas Turbine power (x2) Steam Turbine power (x1) Power variaMon (MW) 50 CCGT net power (2-­‐in-­‐1) 40 CCGT net thermal efficiency (LHV) 30 5 4 3 20 2 10 1 0 0 7 70 6 60 5 50 4 40 3 30 2 20 -­‐10 -­‐1 1 10 -­‐20 -­‐2 0 EGR B. SERIES 2.3 Effect on the Post-­‐CombusMon Capture Unit 6 S-­‐EGR Parallel S-­‐EGR Series 97/96.7 95/32 S-­‐EGR Series 90/48 S-­‐EGR Series 85/58 •  A higher CO2 concentraGon in the working fluid results in a small deviaMon of compressor and turbine performance from the design operaGon condiGons. •  At high selecGve CO2 transfer efficiency, the overall increase in CO2-­‐enriched air density results in a higher mass flow rate which leads to an increase in gas turbine power output. •  The higher flue gas mass flow rate and temperature entering the heat recovery steam generaGon results in a larger high pressure steam flow and thus higher steam turbine power output. •  CCGT net power output accounts for the penalty due to steam extracGon. •  An increase in the fuel consumpGon to keep the turbine inlet temperature (TIT) at the design value increases the thermal input, limiGng the increase in the thermal efficiency. Packing volume reducMon (%) 2.2 Effect on the Power Output and Thermal Efficiency Specific Reboiler Duty reducMon (%) A. PARALLEL Efficiency variaMon (% points) 2.1 ConfiguraMons 0 EGR 35% S-­‐EGR Series S-­‐EGR Series S-­‐EGR Series S-­‐EGR parallel 85/58 90/48 95/31 97/96 S-­‐EGR parallel: SelecGve recirculaGon raGo 70%, post-­‐combusGon capture efficiency 96.7%, selecGve CO2 transfer efficiency 97%. S-­‐EGR series 85/58: post-­‐combusGon capture efficiency 58%, and selecGve CO2 transfer efficiency 85%. S-­‐EGR series 90/48: post-­‐combusGon capture efficiency 48%, and selecGve CO2 transfer efficiency 90%. S-­‐EGR series 95/31 post-­‐combusGon capture efficiency 31%, and selecGve CO2 transfer efficiency 95%. •  A higher CO2 concentraGon in the flue gas at the bonom of the absorber enhances the solvent capacity (higher CO2 loading in the rich solvent). OpGmising the lean solvent CO2 loading and solvent flow rate, this results in a reducMon of the specific reboiler duty. •  The reducGon in the packing volume is also due to the smaller flue gas flow rate that is treated in the PCC unit, in the configuraGon in parallel, and the lower absorber CO2 capture efficiency required for an overall capture level of 90%, in the configuraGon in series. 3. CURRENT AND FUTURE WORK •  Comparison of different technologies, designs and concepts of separaGon units for S-­‐EGR. •  Expansion of preliminary Gas Turbine Combined Cycle model with S-­‐EGR unit. •  Establishing combusMon limits and flame stability operaGng. •  Developing CO2 transfer device models, from first principles to advanced model incorporaGng kineGcs, heat transfer and water balance. •  Part-­‐load operaMon and low-­‐load factor cycles. •  Obtaining limitaMons for S-­‐EGR. •  The designed and validated models will allow idenMfying key operaMng parameters, gas turbine system modificaMons, recycling raMo opMmisaMon and operaMng limits for two to three promising CO2 transfer technologies.
•  Developing a top-­‐down methodology for further material research and technology selecGon for SEGR, updaGng the current understanding by developed model, obtained results as well as technical and economic evaluaGons. •  The part-­‐load operaGon and low-­‐load factor cycles will allow to make suggesGons for design and operaMon of power plants that are opGmal or near opMmal. •  Develop guidelines for new-­‐build CCGTs, including engineering opGons for an effecGve implementaMon strategy. •  ExaminaGon of engineering challenges to retrofit exisMng CCGTs with S-­‐EGR. •  InvesGgaGon of coal plant with S-­‐EGR opGons and its limitaGon. •  Expanding relevant learnings to retrofit exisMng CCGT with S-­‐EGR. •  Predict the performance and opMmise the integraGon of S-­‐EGR in coal fired power staMons. KEY REFERENCES: [1] Merkel, T.C. et al., 2013. SelecGve Exhaust Gas Recycle with Membranes for CO 2 Capture from Natural Gas Combined Cycle Power Plants. Industrial & Engineering Chemistry Research, 52, pp.1150–1159 [2] Jonshagen, K., Sipöcz, N. & Genrup, M., 2011. A Novel Approach of Retroficng a Combined Cycle With Post CombusGon CO2 Capture. Journal of Engineering for Gas Turbines and Power, 133(1), pp.011703–1–7 [3] Zhang, X. et al., 2013. Post-­‐combusGon Carbon Capture with a Gas SeparaGon Membrane: ParameGc Study, Capture Cost, and Exergy Analysis. Energy&Fuels, pp.
130308131947001 ACKNOWLEDGEMENTS: