In-Situ Optical Investigations On Ignition And Combustion Characteristics Of Single Coal Particle Under Pressurized Oxy-Fuel Environment

Pressurized oxygen-fuel combustion is a second generation of oxy-fuel combustion technology,which has the characteristics of low energy loss and low cost.Compared with atmospheric oxy-fuel combustion,the ignition characteristics of pulverized coal under pressurized oxygen-enriched conditions are significantly different.But until now,research on pressurized oxy-fuel combustion are still lacking.Therefore,it has important value of theoretical and engineering application to conduct in-situ optical basic experimental research on the pressurized oxy-fuel combustion of pulverized coal.The pressurized optical accessible flat-flame reaction system was designed.A microscopic optical diagnosis method based on high-speed camera and long exposure camera,including particle tracking velocity method,colorimetric thermometry method and reconstruction method for volatile flame,was developed.Combining with the experimental system and data processing method developed above,the ignition and combustion characteristics of single coal particle under ambient temperature of 1400 K,oxygen concentration of 20%,and pressure range of 0.1-10 bar were investigated.Firstly,the pressurized oxy-fuel ignition combustion characteristics of Shenhua bituminous coal were investigated experimentally.The results indicated that as the ambient pressure rises,the oxygen partial pressure increases significantly,which accelerates ignition and oxidation reaction,but at the same time the particle heating rate decreases,and the release and diffusion of volatiles are reduced.As a result,with the increase of pressure,the ignition delay time of Shenhua bituminous coal and the average soot concentration of volatile flame increases first and then decreases,while the size of volatile flame decreased monotonously,while the duration of combustion increased monotonously.On this basis,effect of coal rank on the ignition and combustion characteristics of pulverized coal under high pressure were investigated.The research shows that under all pressures,the ignition methods of sub-bituminous coal and bituminous coal are homogeneous,and there is a typical volatile combustion stage,while the ignition method of anthracite is heterogeneous.And the pyrolysis rate of bituminous coal is higher than that of sub-bituminous coal,and methane and other light gases account for a larger proportion of bituminous coal pyrolysis components,which results in the duration time and peak soot concentration of volatiles flame greater than that of bituminous coal,while the average flame temperature of bituminous coal is higher than that of sub-bituminous coal.As the coal rank increases,the difficulty of pyrolysis increases,and the ignition delay time increases under atmosphere.However,as the pressure rises,the pyrolysis temperature of bituminous coal decreases more than that of sub-bituminous coal,resulting in a smaller ignition delay time of bituminous coal under high pressure.