System Analysis on Supercritical CO2 Power Cycle with Circulating Fluidized Bed Oxy-Coal Combustion

Abstract

Supercritical carbon dioxide (S-CO2) Brayton power cycle is a competitive technology to achieve high efficiency in a variety of applications. However, in coal power applications, the CO2 generated from coal combustion still discharges into the atmosphere causing a series of environment problems. In this work, an 300 MWe S-CO2 power cycle with circulating fluidized bed (CFB) oxy-coal combustion was established including air separation unit (ASU), CFB boiler, recuperator system and carbon dioxide compression and purification unit (CPU). Based on the material and energy conservation, the cycle efficiency of S-CO2 (620°C, 25 MPa) Brayton power cycle with CFB oxy-coal combustion is evaluated compared to the oxy-coal combustion steam Rankine cycle and S-CO2 Brayton power cycle with the 31.65 kg/s coal supply. After that, the influence of several factors, e.g., exhaust flue gas temperature, split ratio in recuperator system and the oxygen supply on the cycle efficiency was investigated and analyzed. The results show that the net efficiency of S-CO2 power cycle with CFB oxy-coal combustion (32.67%) is much higher than the steam Rankine cycle utilizing CFB with 17.5 Mpa, 540°C steam (27.3%), and 25 Mpa, 620°C steam (30.15%) under the same exhaust flue gas temperature. In addition, lower exhaust flue gas temperature and higher split ratio are preferred to achieve higher cycle efficiency. Lower oxygen supply can reduce the energy consumption of ASU and CPU, further increasing the system net efficiency. However, the energy losses of ASU and CPU are still very large in oxy-coal combustion and need to be improved in further work.