Simulation and comparative exergy analyses of oxy-steam combustion and O2/CO2 recycled combustion pulverized-coal-fired power plants

Oxy-steam combustion is proposed as an alternative for the next generation oxy-fuel combustion technology. In order to justify the economic feasibility of this novel oxy-fuel combustion, a conventional 600 MWe pulverized-coal-fired power plant in China is selected to be retrofitted to oxy-steam combustion and O2/CO2 recycled combustion separately, whilst the O2/CO2 recycled combustion system serves as the base case for comparisons. The modeling and simulation of these two systems are carried out with Aspen Plus version 11.1. Simulation results indicate that on the same boundary conditions, the mass flow of the main steam and reheated steam in the oxy-steam combustion system must be reduced by 0.84%, which makes the net energy efficiency of the oxy-steam combustion system decrease by 0.15%. The comparative exergy analyses reveal that the net exergy efficiency of the oxy-steam combustion system is 0.153% lower than that of the O2/CO2 recycled combustion system. The marked increase of the exergy destruction happening in the oxy-steam combustion furnace is the fundamental cause of the decrease of the exergy efficiency.