Energy efficiency analysis of pressurized oxy-coal combustion system utilizing circulating fluidized bed

Abstract

Oxy-fuel combustion with circulating fluidized bed (CFB) is one of the most important technology for carbon dioxide capture and sequestration. However, its development and application are seriously hindered by the low net efficiency mainly resulting from the use of air separation unit (ASU) and carbon dioxide compression and purification unit (CPU). In this work, a pressurized oxy-coal CFB combustion cycle was established mainly including ASU, CFB combustion unit, heat exchangers, power island and CPU. Based on the material and energy conservation, the detailed energy penalties of ASU, CPU, and recirculating compressor were investigated under the varying combustion pressures from 0.105 MPa to 3 MPa. Results revealed that with the increase of combustion pressure, the energy consumption of ASU increases while that of CPU decreases. Compared with PC boiler, the influence of the recirculating compression work on CFB system is negligible in lower pressures. Overall, Higher combustion pressure is favorable to the oxy-coal CFB combustion. By minimizing the penalties and recover more latent heat, the net efficiency rises up from 27.2% to 30.5% in this work while the optimum pressure being about 1.1 MPa. Meanwhile the mole fraction of carbon dioxide can reach 92% which is satisfied with the demands.