Study On The Interaction Of Pulverized Coal Particles In The Combustion Process

The pulverized coal combustion is a complex physicochemical process.It is necessary to have an in-depth understanding of the combustion characteristics of pulverized coal particles and the interaction between pulverized coal particles for improving the fuel energy utilizaiotn and reducing the pollutants generated during the combustion process.A mathematical model for the unsteady combustion process of pulverized coal particles was built by the combined UDF program based on FLUENT software.The variatioin of particle temperature and the distribution of components concentration were obtained when the combustion characteristics of single pulverized coal and interacting particles at different interspaces are clarified,which reveals the interacting mechanism of pulverized coal particles combustion.The phenomenon of “Carmen Vortex Street” appearing in the combustion of pulverized coal particles were also studied in this work.The combustion characteristics of single coal particle under low flow rate conditions were carried out at different gas flow rates and initial gas temperatures.The results show that,due to the influence of hot gas flow,the homogeneous combustion of volatile matter is mainly experienced at downstream of coal particle,while the heterogeneous reaction of char occurs on the surface of the coal particle.Increasing the gas flow rate,the devolatilization rate,volatile flame size,particle burning rate and oxygen consumptioin rate are all increased.The inlet gas temperature rises,the temperature of volatile flame and char particle increase.A preliminary study on the “Kamen Vortex Street” phenomenon in the combustion process of sinle pulverized coal particle was carried out.The results show that the temperature and gas species distribution in the downstream region of the particles are symmetrically and smoothly under low Reynolds number.When the inlet flow velocity reaches a certain value,that is,when the Reynolds number exceeds a certain value,the karman vortex street appears in the tail region of the combusting coal particle,accompanied by the vortex shedding in the temperature,velocity and gas species of the downsteam region of the particle.Increasing the Reynolds number causes the frequency of vortex shedding to increase.The combustion characteristics of upstream particle and downstream particle at different interspaces were investigated,and the interaction between two particles was analyzed by getting the history of particle temperature,devolatilization,ignition temperature,and product distribution during in pulverized coal particle combustion.It is obtained that the upstream coal particles has a higher burning rate than the downstream particle.Increasing the particle interspaces within a certain interval,the temperature history of upstream particle is advanced,which means that the temperature versus thime vurve is close to that of the single particle.The particle hearing and mass loss is delayed for the downstream particle due to the effect of the lower initial temperature of the upstream particels,and its temperature history shifts to the right direction.For the combusting pulverized coal particles arranged in the direction of the air flow,there is a maximum particle interspace.When it is less than this distance,increasing the particle interspace causes the temperature history of upstream paticle move to the left and that of downsteam particle move to the right direaction.When it is greater than this distance,increasing the particle interspace will accelerate the burning rate of downsteam particle,and the temperature and mass fraction history will move to the left.Inceasing the particle interspace will always accelerate the burning rate of upsteam particle,which is close to the combustion of a single pulverized coal particle.