Thermodynamic Integration And Optimization Of Pressurized Oxy-Fuel Combustion Power Plants

Oxy-fuel combustion technology is one of the most promising carbon capture technologies for coal-based power plants.The concentration of CO₂ in flue gas is enriched in O₂/CO₂environment,which is helpful to inhibit the formation of NO_x.Oxy-steam combustion is considered as an alternative option of oxy-fuel combustion technology.Condensed water from flue gas is recirculated to control the temperature in the furnace,avoiding the enrichment of impurities in flue gas.Also,oxy-steam combustion is simple and compact since recycled flue gas is replaced by smaller amount of condensed water.Pressurized oxy-fuel combustion systems have been proposed recently,with the objective of improving the energy efficiency by recovering the latent heat of steam in the flue gas on the basis of atmospheric oxy-fuel combustion.It is necessary to make a preliminary comparison between pressurized and atmospheric combustion to demonstrate the application prospect of the pressurized oxy-fuel combustion.Thermodynamic analysis of O₂/CO₂ and O₂/H₂O oxy-fuel combustion under different operating pressures is performed for research and evaluation.In this paper,a 600 MW supercritical oxy-fuel combustion power plant is established from the traditional pulverized-coal-fired power plant.Both O₂/CO₂ and O₂/H₂O oxy-fuel combustion power plants integrated with an air separation unit?ASU?and a flue gas compression and purification unit?CPU?are modeled using Aspen Plus.The sensitivity analysis of furnace combustion temperature,operating pressure,air ingress,flue gas recirculation mode and boost of the circulating equipment are performed with the same boundary conditions.The heat recovery from the ASU,CPU,and acid condenser can be integrated to improve the overall power plant performance,acting as the ASU heater,CPU heater,and acid condenser.The ASU,CPU and acid condenser substitute the low-pressure feedwater heaters and optimized the plants.The optimization is affected by the layout of three heat exchangers.Different layout modes are simulated and compared to find the optimal scheme.Four oxy-fuel combustion power plants,i.e.atmospheric O₂/CO₂,atmospheric O₂/H₂O,pressurized O₂/CO₂ and pressurized O₂/H₂O,are analyzed under the same boundary conditions.The results show that the net power efficiency of each base case is positively correlated with the furnace combustion temperature and negatively correlated with the air ingress and the boost of the circulating equipment.For the O₂/CO₂ oxy-fuel combustion power plant,the net power efficiency of flue gas recirculation with wet mode is slightly higher than that of the dry mode.For the pressurized oxy-fuel combustion power plant,the operating pressure is varied in the range of 1-80 bar.The net power efficiency increases with the rise of pressure and then decreases.The maximum net power efficiency is achieved at around 10 bar.After heat integration,the net power efficiency of wet-mode pressurized O₂/CO₂ oxy-fuel combustion power plant is 35.93%the highest among four oxy-fuel combustion power plants.The net power efficiency of pressurized O₂/H₂O oxy-fuel combustion power plant is 34.44%.O₂/H₂O power plants will have larger optimization space and broad application prospects due to compact layout and low economic cost.