Effect of two methods for flue gas energy extraction over the entire temperature range on the tri-compression sCO<sub>2</sub> coal-fired power plant

Abstract

<p indent="0mm">For the supercritical CO₂ cycle (sCO₂), the tri-compression (TC) cycle significantly improves thermal efficiency compared to the recompression cycle (RC). Then it is necessary to construct a TC coal-fired power plant for further efficiency improvement. Flue gas energy extraction across the entire temperature range is a serious challenge for indirect sCO₂ coal-fired power plants. A flue gas cooler (FGC) installed in the boiler tail flue and a combined cycle based on overlap energy utilization (OEU) are designed to address this issue. The basic cycle is tri-compression plus reheating (TC+RH). Two thermodynamic models of OEU and FGC are constructed in conjunction with the boiler’s thermal-hydraulic characteristics. Due to a lack of flue gas heat load cooler and a pinch temperature difference limit of 30°C, the boiler exhaust flue gas temperature (<italic>T</italic>_fg,ex) for the FGC system is as high as 172.6°C, lowering boiler efficiency to 90.64%. However, for the OEU system, <italic>T</italic>_fg,ex can be cooled to 126.0°C, which corresponds to a boiler efficiency of 92.85%. Additionally, the FGC system’s energy destruction in the moderate- and low-temperature flue gas regions is greater than that of the OEU system, indicating that the OEU system’s energy quality of flue gas and working medium in the above-flue gas region is more closely matched.