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ABSTRACT
CaL technology is a promising means for post-combustion CO2 capture in already existing power plants, and heat integration is an effective way to lower the efficiency penalty caused by CO2 capture. Three cases with different heat integration degree were investigated in the manuscript to predict the efficiency penalty and the specific energy consumption for CO2 capture, aiming to find the optimum scheme of integrating capture unit into coal-fired power plant. The sensitivity analysis was also conducted to compare the impacts of key parameters. The simulation results show that the Case 3, which employs a variety of measures to improve the internal heat integration within CaL and reclaims the surplus released heat via an additional steam cycle, has the lowest efficiency penalty, 5.75%. It also indicates that heat integration in Case 3 results in a 14.4% of decrease in coal consumption, a 5.8% of reduction in power consumed by CO2 compression process, a 13.6% of drop in power consumption in ASU, and a 31.5% of decrease in specific energy consumption for CO2 capture. The sensitivity analysis shows that the efficiency penalty may be reduced by 0.011 percentage points for each degree decrease in temperature difference of MH-1. As the compression efficiency increases from 70% to 85%, the efficiency penalty decreases from 6.51% to 5.47%, and the specific energy consumption reduces from 2.21 MJ/kg CO2 to 1.80 MJ/kg CO2.
Abbreviations: APH: Air Preheater; ASUL: Air Separation Unit; BFPT: Boiler Feedwater Pump Turbine; CaL: Calcium Looping; CCS: Carbon Capture and Sequestration; CFPP: Coal-Fired Power Plant; GSS: Gas-Solid Separator; HPC: High Pressure Column; HPEC: High Pressure Economizer; HPSH: High Pressure Super-Heater; HPST: High Pressure Steam Turbine; HRSG: Heat Recovery Steam Generator; IPEC: Intermediate Pressure Economizer; IPEV: Intermediate Pressure Evaporator; IPSH: Intermediate Pressure Super-Heater; LPST: Low Pressure Steam Turbine; LHV: Low Heat Value; LPC: Low Pressure Column; LPEC: Low Pressure Economizer; LPEV: Low Pressure Evaporator; ORC: Organic Rankine Cycle; RH: Reheater.
Nomenclature
| ECCO2 | = | Specific energy consumption coefficient (MJ/kg CO2) |
| ER | = | CO2 emission rate (kg CO2/kW∙h) |
| F0 | = | Molar flow rate of fresh sorbent (kmol/s) |
| = | Molar flow rate of CO2 stream (kmol/s) | |
| = | Molar flow rate of SO2 stream (kmol/s) | |
| FR | = | Molar flow rate of recycled sorbent excluding fresh makeup (kmol/s) |
| p | = | Pressure (bar) |
| PASU | = | Power consumption in ASU (MW) |
| Paddit | = | Net electric power of additional steam cycle (MW) |
| Pbase | = | Net electric power of baseline plant (MW) |
| Pcomp | = | Power consumption in CO2 compression (MW) |
| Pnet | = | Net electric power of overall system (MW) |
| Qboiler | = | Heat consumption of boiler in baseline plant (MW) |
| Qcal | = | Heat consumption in calciner (MW) |
| Qhr | = | Heat recovered in additional steam cycle (MW) |
| RCa:C | = | Molar ratio of CaO to CO2 |
| T | = | Temperature (C) |
| ηaddit | = | Net thermal efficiency of additional steam cycle |
| ηbase | = | Net thermal efficiency of baseline plant |
| ηcapt | = | CO2 capture efficiency |
| ηhr | = | Heat recovery efficiency |
| ηoverall | = | Overall thermal efficiency with CCS |
| ηGSS-1 | = | Separation efficiency of GSS-1 (%) |
| ηGSS-2 | = | Separation efficiency of GSS-2 (%) |
| Xave | = | Average carbonation conversion |
| x | = | Dryness |
Acknowledgments
This work was supported by the National Key Research and Development Program of China (2018YFB0604302-02); the Fundamental Research Funds for the Central Universities (No. 2015MS116); and the National Natural Science Foundation (No.51606066).