Experimental Study On Ignition Characteristics Of Pulverized Coal Particles On Optical Measurement

The study of ignition characteristics of pulverized coal particles plays a crucial role in the efficient utilization of coal and the stable operation of the burner.In particular,the research on the change of ignition mode,ignition delay and ignition temperature of pulverized coal particles under different conditions is very important to guide the industrial practice and establish the ignition model of pulverized coal.Based on summarizing previous research methods and research conclusions about the ignition of pulverized coal particles,a flat-flame assisted entrained flow reactor was designed and manufactured.The system has the advantages of high heating temperature,high heating rate,quick and effective adjustment of experimental conditions,and easy optical measurement.In this paper,an optical measurement system consisting of a high-speed camera and a continuous laser was established,and the particle image processing method,the particle tracking velocimetry method,the particle ignition judgment method,the two-color temperature measurement method were created.Using the experiment system and the optical measurement system,an experimental study was conducted on the ignition characteristics of pulverized coal particles.The influences of the coal rank on ignition mode,ignition delay and ignition temperature at the particle level were investigated using the flat-flame assisted entrained flow reactor.The results indicated that anthracite coal particles ignite heterogeneously while bituminous and lignitec coal particles ignite homogeneously in the gas phase.The lignite particles break up during devolatilization.Because of high rank coals has a lower volatile content which is more difficult to ignite,ignition delay times and ignition temperatures decrease with decreasing coal rank.In the combustion stage of coal char,the char oxidation start to ignition from the local to the whole.And the temperature of char oxidation increase with increasing coal rank.Then,the experimental study on the ignition characteristics of bituminous coal in O₂/CO₂ atmosphere and O₂/N₂ atmosphere was conducted.The particle size,shape,intensity of the apparent flame emission,ignition delay times and temperature were compared in different atmospheres during the ignition of pulverized coal particles.Under the O₂/CO₂atmosphere,the pulverized coal particles will have a longer ignition delay times and devolatilization times,smaller size,lower char oxidation temperature than the O₂/N₂atmosphere.Increasing oxygen concentration accelerates particle ignition,increase particle combustion temperature and decrease particle size.The effect of O₂ can be explained by its effect on mixture reactivity.