Simulation Study of an 800 MW_e Oxy-combustion Pulverized-Coal- Fired Power Plant

摘要

Oxy-combustion technology has been considered as a feasible choice to reduce the CO, emissions from the coal-fired power plants through adding a cryogenic air separation unit (ASU) process and a flue gas treatment unit (FGU) process to a conventional combustion process. This technology is capable of enriching the CO_2 concentration and then allowing CO_2 sequestration in an efficient and energy-saving way. To study the operation characteristics of the oxy-combustion process, an 800 MW_e oxy-combustion pulverized-coal-fired power plant was simulated and analyzed using the commercial flowsheet software Aspen Plus. The base simulation result indicates that Aspen Plus is a proper tool to research the oxy-combustion system. The net efficiency of the oxy-combustion system is 10.36% [lower heating value (LHV)] lower because of the ASU and FGU processes; the unit power consumption for the oxygen production in the ASU is 0.247 kW h (kg of O_2)~(-1). Many important parameters and different cases were also studied in this paper. The results show that a recycle ratio range of 0.705-0.726 is proposed for cold recycle cases, whereas 0.617 is recommended for the hot recycle case. The CO_2 concentrations of flue gases from the oxy-combustion boiler range from 84 to 92 mol % for cold recycle cases and from 57 to 58 mol % for hot recycle cases because of the high H_2O content, respectively. However, the CO_2 purity from the FGU for each case can reach 99 mol %. In addition, in comparison to the air-combustion case, oxy-combustion cases have higher SO_x fractions but a similar unit of the SO_x production rate (0.78 mol/kg of coal) and much lower NO_x fractions in the flue gas. Moreover, a sensitivity analysis about the concentration of the oxygen product from the ASU and an optimization of the distillation column in the ASU were also performed. The optimal value of the total stage number, the reflux ratio, and the number of feed stage for the distillation column in the 95 mol % oxygen case are 28,1.04, and 15th, respectively. All of these results will be helpful to the oxy-combustion system design and operation.