Computational Modeling Of The Ignition Characteristics Of Single Coal Particle Under Different Combustion Atmospheres

The ignition of pulverized coal is extremely important to the safety and economy of pulverized coalboilers in the power station. Only have a profound understanding of the ignition characteristics ofpulverized coal particles, in order to ensure stable ignition and burningof pulverized coal in the furnace.O₂/CO₂combustion technology is a new-friendly combustion method, suggested as one of the easiest toimplement large-scale CO2enrichment and emission reduction technology from power plants coalcombustion. However, due to its low efficiency of the thermal cycle, in recent years, the combustionmode that using H₂O to reduce the high temperature of pure oxygen combustion and the correspondingthermal cycle caused particular concern.Earlier studies haven’t recognized pulverized coal ignitionmechanism clearly under O₂/CO₂atmosphere.For the effect of H₂O,the basic research is not yet carriedout.This paper studies the ignition characteristics of single coal particles under different combustionmodes, mainly include the following three parts:Firstly, the paper details computational model of the ignition of the single particle.This modelconsider the coal surface absorb the radiate heat, and consider the heterogeneous&homogeneousreactions and the heat&mass transfer in the air, thus the model can precisely predict the ignitionbehavior and combustion characteristics of coal particles.Secondly, we make some modifications to the model, so that the model can accurately simulate theignition characteristics of pulverized coal under O₂/CO₂combustion, and compare with the experimentalresults in the literature. Detailed study of the effect factors of CO2for pulverized coal ignition are made,and found that the thermal conductivity is the main reason for the differences of ignition delay underO₂/CO₂and O2/N2combustion mode. We also study the effect of ambient temperature, oxygenconcentration and particle size for the ignition characteristics of coal particles, and found that under theconditions that in the low oxygen concentration and a small particle size, coal particles occur easierhomogeneous ignition, while when under the conditions that in a high oxygen concentration and thelarge particle diameter pulverized coal experienced heterogeneous ignition.Thirdly, through the study of the ignition characteristics of pulverized coal under O₂/H₂Ocombustion mode, we found that the gas phase reaction of H₂O will greatly affect the pulverized coalignition characteristics. Under low oxygen concentration, the ignition delay of pulverized coal underO₂/H₂O atmosphere is less than O₂/CO₂atmosphere, while when under the high oxygen concentration,the ignition delay under O₂/H₂O atmosphere is greater than under O₂/CO₂atmosphere. But whetherthe oxygen concentration is low or high, the ignition temperature of pulverized under O₂/H₂O atmosphere must be higher than the combustion process applying O₂/CO₂. Under O₂/CO₂atmosphere,the ignition delay and the ignition temperature of pulverized coal and show different trends in lowoxygen concentration and high oxygen concentrations with the addition of H₂O.