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Overlap energy utilization reaches maximum efficiency for S-CO2 coal fired power plant: a new principle

Sun, Enhui, Xu, Jinliang, Hu, Han, Li, Mingjia, Miao, Zheng, Yang, Yongping, Liu, Jizhen
Energy conversion and management 2019
absorption, air, carbon dioxide, coal, energy, flue gas, heat, power plants, temperature, vapors
For a coal fired power plant, a combined supercritical CO2 cycle (S-CO2) absorbs flue gas energy over entire temperature range. Because top/bottom cycles absorb high and moderate temperature flue gas energy respectively, there is an efficiency gap between the two cycles. To fill the efficiency gap, the overlap absorption of flue gas energy is proposed, using top cycle to absorb high temperature flue gas heat, but bottom cycle to absorb not only moderate temperature flue gas heat, but also a part of high temperature flue gas heat. The overlap energy absorption in a high temperature regime increases CO2 heat absorption temperature to improve bottom cycle efficiency. A four steps roadmap guides us to construct a combined cycle with RC+DRH as top cycle and RC+DRH+EAP as bottom cycle to reach the maximum efficiency limit, where RC, DRH and EAP represent the cycles of recompression, double-reheating and external air preheater, respectively. The components sharing among top/bottom cycles ensures simple system layout, and EAP recycles extra heat of bottom cycle to the system, keeping a smallest heat dissipation to environment. The net power efficiency reaches 47.99% at the main vapor parameters of 620 oC/30 MPa. The overlap energy utilization can be extended for other systems.