THERMO-ECONOMIC ANALYSES AND COMPARISONS OF TWO S-CO_2-BRAYTON-CYCLE-BASED COMBINED POWER CYCLES FOR CONCENTRATED SOLAR POWER PLANTS

摘要

In order to pursue superior cycle efficiency and lower power generation cost for the CSP plants, two S-CO_2-Brayton-cycle-based power cycles with different utilization methods of the residual heat recover of the top S-CO_2 Brayton cycle (SCBC) are investigated to seek alternatives to the stand-alone S-CO_2 cycle as the power block of concentrated solar power plants. The residual heat released by the top S-CO_2 cycle are either utilized to drive a LiBr absorption chiller (AC) for further chilling of the CO_2 fluids exiting the precooler before entering the main compressor inlet temperature or recovered by an organic rankine cycle (ORC) for generating electricity. Thermo-economic analysis and optimization are performed for the SCBC-AC and SCBC-ORC, respectively. The results show that the thermal and exergetic efficiencies of the SCBC-AC are comparable with those of the SCBC-ORC in low pressure ratio conditions (PR<2.7) but are apparently lower than SCBC-ORC when PR is over 2.7. The LCOE of the CSP plant integrated with SCBC-AC is more sensitive to the change of PR. The optimal PR to maximum the cycle efficiency or minimize the plant LCOE for the SCBC-ORC is higher than that for the SCBC-AC, while the optimal recuperator effectiveness to minimize the LCOE of CSP plant integrated with SCBC-ORC is lower than that of SCBC-AC. The optimization results show that the thermo-economic performance of the SCBC-AC is comparable to that of the SCBC-ORC. Significant η_(ex) improvement and LCOE reduction can be obtained by both the two combined cycles relative to the stand-alone S-CO_2 cycle. The maximal η_(ex) improvements obtained by the SCBC-ORC and SCBC-AC are 6.83% and 4.12%, respectively. The maximal LCOE reduction obtained by the SCBC-ORC and SCBC-AC are 0.70￠/(kW·h) and 0.60￠/(kW·h), respectively.