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

• S-CO 2 coal fired power plant was investigated. • The overlap energy utilization (OEU) principle was proposed. • OEU increases the average heat absorption temperature for bottom cycle. • An external air preheater (EAP) recycles extra heat to the system for bottom cycle. • OEU and EAP reaches identical efficiencies for top and bottom cycles. For a coal fired power plant, a combined supercritical CO 2 cycle (S-CO 2) 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 CO 2 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 °C/30 MPa. The overlap energy utilization can be extended for other systems. [ABSTRACT FROM AUTHOR]