The roadmap towards the efficiency limit for supercritical carbon dioxide coal fired power plant

Abstract

The Chinese Government has issued a series of documents to explain China’s control over the carbon dioxide (CO2) emission. One of the major tasks is to develop higher efficiency coal fired power plant, compared with current running power plant. In this paper, we aim to explore the roadmap to reach the efficiency limit for coal fired power plant using supercritical carbon dioxide cycle (sCO2 cycle). Referenced to Carnot cycle, the proposed roadmap is to increase the cycle efficiency by elevating average heat absorption temperature (Tave,h) and lowering average heat release temperature (Tave,l). In contrast to recompression cycle (RC), tri-compression cycle (TC) is introduced. Due to the increased Tave,h, TC achieves the second largest contribution for efficiency increment, followed by the reheating technique. Then, TC, double reheating (DRH) and intercooling (IC) are integrated as TC + DRH + IC in the power plant. To completely absorb flue gas energy over entire temperature range of (1500 ∼ 120) °C. A top cycle and a bottom cycle are connected for cascade utilization of flue gas energy. Overlap energy utilization is further utilized to fill the efficiency gap between top and bottom cycles. The proposed cycle also integrates the module boiler design to suppress the pressure drop penalty, and the flue gas recirculation to keep the heater surface temperature in an accepted level. A numerical model is developed for the comprehensive sCO2 cycle. At the main vapor parameters of 35 MPa/630 °C, the sCO2 coal fired power plant reaches the net power generation efficiency of 51.03%, which is higher than 48.12% for a supercritical water-steam power plant at the same capacity. Such efficiency improvement saves 175.2 kilotons of coal and reduces 396.4 kilotons of CO2 emission for 1000 MW capacity in a fascial year. Our work provides the guideline for the design and operation of large scale sCO2 coal fired power plant.