Carbon Migration And Sulfur,Nitrogen Conversion Characteristics In A Pressurized Oxy-fuel Coal Combustion Process

Pressurized oxy-fuel combustion technology can achieve the enrichment of CO₂ in flue gas,which is conducive to the efficient capture of CO₂.It is a promising carbon capture technology.Compared with atmospheric oxy-fuel combustion technology,pressurized oxy-fuel combustion technology is more economical with the advantages of oxy-fuel combustion technology fully exerted.However,the elevated pressure results in the change of the coal combustion characteristics.In order to investigate the effects of combustion pressure,combustion atmosphere,combustion temperature,coal particle size and coal type on the migration and transformation characteristics of carbon,sulfur and nitrogen in the pressurized oxy-fuel coal combustion process,experiments were carried out on the self-built pressurized horizontal tube furnace oxy-fuel combustion test system.This study is aimed at obtaining the law of migration and transformation of carbon and the generation and emission of pollutants during the process of pressurized oxy-fuel coal combustion,which can provide theoretical reference for the practical application of pressurized oxy-fuel combustion technology.The carbon migration law and coal ash formation characteristics of pressurized oxy-fuel combustion process were studied.Under the same combustion temperature and atmosphere conditions,with the increase of combustion pressure,the conversion of carbon in coal to CO₂ increases and residual carbon ratio in coal ash is also reduced.Under the same combustion pressure and temperature conditions,the CO₂ generation rate in the21%O₂/79%CO₂ atmosphere is lower than that in the air atmosphere,while the CO emission is significantly increased.With the increase of the oxygen concentration in the O₂/CO₂ atmosphere,the CO₂ generation rate increases and CO production is reduced.Increasing the combustion temperature or reducing the coal particle size can promote the conversion of carbon in coal to CO₂.However,with the increase of combustion pressure,the influence of combustion temperature on the CO₂ generation rate is weakened and the effect of coal particle size on the CO₂ generation rate is enhanced.Besides,with the increase of combustion pressure,the particle size of coal ash first decreases and then increases,the pore structure of coal ash first increases and then weakens,the high temperature mineral in ash decreases and the low temperature mineral increases.The conversion characteristics of sulfur in coal to SO₂ during pressurized oxy-fuel combustion process were investigated and the in-furnace lime-based desulfurization test was carried out to investigate the desulfurization characteristics of limestone.Under the same combustion temperature and atmospheric conditions,increasing the combustion pressure can enhance the sulfur fixation capacity of coal ash and reduce the emission of SO₂.Under the same combustion temperature and pressure conditions,the SO₂ emission in the21%O₂/79%CO₂ atmosphere is lower than that in the air atmosphere,and increasing the oxygen concentration in the O₂/CO₂ atmosphere can promote the SO₂ emissions.Increasing the combustion temperature or reducing the coal particle size will increase the SO₂ emission.But as the combustion pressure increases,the combustion temperature has an enhanced effect on SO₂ emissions,while the effect of coal particle size on SO₂ emissions is weakened.The incorporation of limestone can effectively reduce the emission of SO₂,and the increase of combustion pressure,oxygen concentration,combustion temperature and molar ratio of Ca/S are beneficial to improve the efficiency of the in-furnace lime-based desulfurization.The conversion characteristics of nitrogen in coal to NO_x during pressurized oxy-fuel combustion process are revealed and the nitrogen conversion behavior of pressurized oxy-fuel coal combustion process is simulated.Under the same combustion temperature and atmosphere conditions,increasing the combustion pressure can effectively reduce NO_x emissions.Under the same combustion pressure and temperature conditions,the NO_x emissions in the 21%O₂/79%CO₂ atmosphere are lower than that in the air atmosphere,and increasing the oxygen concentration in the O₂/CO₂ atmosphere enhances the NO_x emissions.Increasing the combustion temperature or reducing the coal particle size can increase the NO_x emission.However,as the combustion pressure increases,the effect of combustion temperature on NO_x emissions increases,and the effect of coal particle size on NO_x emissions is weakened.Based on the experimental results,a numerical simulation experiment on the nitrogen conversion behavior of pressurized oxy-fuel coal combustion was carried out on CHEMKIN software.The formation behaviors of the main nitrogenous products N₂,NO,NO₂ and N₂O in the flue gas were investigated considering the effects of combustion pressure,combustion temperature and oxygen concentration.The main reaction path of nitrogen conversion in pressurized oxy-fuel coal combustion process was clarified.