Soot Formation Model Based On PBM And Simulation Of Pulverized Coal Combustion

Coal is one of the major energy sources in the world today,and more than 40% of the world’s electricity coms from coal-fired power plants.Soot is the product of the conversion of gaseous volatiles produced by coal during incomplete combustion or pyrolysis,and is one of the important constituents of ash produced by coal combustion.Most soot particles are on the order of micrometers and belong to the category of PM10.Therefore,soot emitted into the atmosphere has a large negative impact on air quality and human health.In the internal of coal-fired boilers,soot has a strong influence on temperature due to its strong radiation absorption and emission capability.Therefore,it is of great significance to study the formation mechanism of soot.The early soot generation models mainly include the one-step reaction model by Khan and Greeves and the two-step reaction model by Tesner.Based on these two soot generation models,researchers have established multiple models based on different combustion conditions.In this thesis,based on the Moss–Brookes semi-empirical model,a new mathematical model is obtained by modifying the influence factors affecting the agglomeration of soot.Compared with the one-step reaction model and the two-step reaction model,the new model pays more attention to the influence of chemical reaction rate and collisional agglomeration on soot formation.When correcting the collision factor,considering that the turbulence effect and the Brownian motion play a major role in the agglomeration and are independent of each other,the vector addition is performed to obtain the agglomeration function.After determining the soot generation model,the UDS function in Fluent was used to customize the correction factor function,and the new model was used to simulate the pulverized coal combustion experiment of the Japan Central Electric Power Research Institute(CRIEPI).The results show that the numerical simulation predicts that the temperature and experimental temperature error are within a reasonable range,and the pulverized coal particle moving speed agrees well with the experimental trend.The parameters such as the volume fraction of soot particles and the growth trend of the particle size along the combustion direction are maintained with the experimental values.Next,this thesis simulates the CRIEPI experiment using a one-step model and a two-step model,and compares them with the new model and experimental data.The results show that the one-step model and the two-step model have lower prediction values for soot production,and the temperature is higher than the experimental value.The new model has the least error in the prediction of soot and temperature field and experimental values.The soot particle size growth trend and the cross-section soot mass fraction in the direction along the increase of HAB,thepredicted value of the new model is also better than the first two models.Since soot has the function of absorbing and emitting radiation,it will affect the temperature of the pulverized coal combustion flame,which in turn affects the formation of soot itself.Therefore,this paper also calculates the prediction results of soot production under the conditions of three models considering whether or not to consider radiation.The results show that the difference between the two groups of volume fractions calculated by the one-step reaction model is the largest when using the same model to calculate the two sets of results considering and not considering the radiation;the two-step reaction model is second;the new model difference is the smallest.Finally,the reasons for the different gaps generated by the three models are analyzed and explained,The results show that there is a great correlation between the concentration of soot and the absorption rate of mixed fluid.