Study On Pressurized Oxy-coal Combustion Characteristics And System Energy Consumption Analysis

Oxy-coal combustion has obvious advantages in the field of CO₂ separation,capture and storage,due to the huge energy consumption of the air separation system and the CO₂ purification and compression system,the economy of system is not very good.The pressurized oxy-coal combustion technology is developed based on oxy-coal combustion.The combustion characteristics of the pulverized coal at 0.1-5 MPa and the energy consumption of the pressurized oxy-coal system are analyzed in this paper.The pressurized oxy-coal near-zero emission power generation system was studied.The process of air separation,coal combustion and CO₂ compression was carried out under the condition of high pressure.High pressure flue gas condenser was used to recover the vaporization latent heat of water vapor in the flue gas and the efficiency of power generation system was improved,at the same time,CO₂ was liquefied by multi-stage compression system.The combustion characteristics of pulverized coal are more different between nomal pressure and pressurized atmosphere.Pressurized TGA were used to study the bituminous coal and lignite coal combustion characteristics under different pressure（0.1 MPa,1 MPa,2 MPa,3 MPa,4 MPa,5 MPa）and different atmosphere（21%O2/79%CO₂,30%O2/70%CO₂,40%02/60%CO₂）,the kinetic parameters were aslo be calculated.The results show that compared with normal pressure oxy-coal atmosphere,pulverized coal ignition temperature is lower and the comprehensive combustion performance is better under pressurized oxy-coal atmosphere,at the same O2/CO₂ ratio,the ignition temperature of the pulverized coal decreases first and then increases with the increasing pressure,and the ignition point is the lowest at 3 MPa.The comprehensive combustion performance is the best.The TG curve and DTG curve of bituminous coal and lignite have the same performance.However,due to the difference of volatiles content between the two coals,the reaction speed of lignite combustion is faster under the same pressure condition.The random nucleation and subsequent growth function of index 1 can better characterize the power of pulverized coal combustion under pressurized oxy-coal condition.The activation energy,the pre-exponential factor and other kinetic parameters can be obtained by calculation.The flue gas composition of pulverized coal combustion is different under different pressure conditions.This paper analyzes the change of pulverized coal combustion flue gas under different pressure conditions by using pressurized oxy-coal fixed bed.The results show that the ignition time of pulverized coal is lower than that of normal pressure under the condition of pressurized,and the burnout time is generally higher than atmospheric pressure.For lignite coal and bituminous coal,the mean combustion temperature is higher than atmospheric pressure,indicating that the lifting pressure,the coal burning intensity is improved.Regardless of bituminous coal or lignite,the oxygen concentration under various pressure conditions change in the same law.As the volatile content of bituminous coal was lower,the O2 concentration in the initial stage did not change obviously.When the reaction pressure is increased（<2 MPa）,the CH4 content in the flue gas will increase,and when the pressure is further increased,the CH4 production will be reduced.The formation of CO and CO₂ in the flue gas is opposite.Under the low pressure condition,the flue gas velocity is high,which is not conducive to the combustion of the pulverized coal and oxygen,resulting in high concentration of CO in the flue gas under low pressure,Because the flue gas velocity is slow,is conducive to complete combustion of coal,CO₂ concentration is high,in this experiment the maximum volume concentration of CO₂ close to 90%.A 300 MW pulverized coal-fired boiler was used.The model of pulverized oxy-coal combustion power generation system was established by using ASPEN PLUS software,and the energy consumption of the system under different pressure conditions was studied.When the pressure is from 0.1 MPa to 5 MPa,the energy consumption of air separation unit rises from 64.862 MW to 115.025 MW,and the energy consumption per unit of oxygen increases from 0.309 kWh/m3 to 0.548 kWh/m3.The energy consumption of the flue gas compression system decreases with the increase of the pressure.When the pressure is 0.1 MPa,the energy consumption of the flue gas compression system is the highest,which is 41.325 MW.With the increase of the pressure,the vaporization latent heat of water vapor partially counteracts the energy consumption of the air separation system;the pressurized oxy-coal combustion system is more efficient than the atmospheric oxy-coal combustion system.When the pressure is raised from 0.1 MPa to 2 MPa,the net efficiency of the power generation system increases from 27.73%to 29.28%,and the net efficiency of the power plant is the highest under the condition of 2 MPa.