Multiphysics Field Simulation Of Unsteady Calcination Process In Double-Chamber Lime Shaft Kiln

The double-chamber co-current regenerative lime shaft kiln has become the main kiln type for lime production due to its high lime activity and low energy consumption.This study intends to focus on the problems of unstable lime quality and excessive NO_x emission peak concentration in the production process of coal-fired double-chamber lime shaft kiln.Carrying out numerical simulation research provides a theoretical basis for the fine control of the lime shaft kiln production process,which is of great significance and engineering guiding value for promoting the large-scale and clean lime shaft kiln.This study takes the 600t/d double-chamber lime shaft kiln as the research object.Based on the FLUENT software,the secondary development of limestone decomposition reaction,gas-solid heat transfer and other models is carried out,and the numerical simulation of the unsteady calcination process of the double-chamber lime shaft kiln is carried out.Research.Its main work and conclusions are as follows:（1）The three-dimensional geometric model of the single-chamber one-eighth area in the double-chamber lime kiln shaft kiln was established,the porous media model was used to describe the limestone material layer structure,and the DPM model was used to describe the movement process of pulverized coal particles and its combustion process was numerically simulated.The results show that the smaller the porosity of limestone and the smaller the particle size of coal powder,the more favorable the diffusion of coal powder in limestone is;During the combustion of pulverized coal,the temperature of the airflow increases,which is conducive to the diffusion of pulverized coal in the cross section,and its concentration distribution is relatively uniform..（2）In view of the difference in temperature between limestone and gas,and the fact that the decomposition reaction of limestone gradually advances from the surface to the center of the particle,the secondary development of the models of limestone energy equation,downward velocity and shrinkage nucleation reaction has been carried out to realize the combustion of pulverized coal and limestone.The coupled numerical simulation of the decomposition reaction has obtained the multi-physics distribution characteristics of the steady-state calcination process of limestone.（3）Aiming at the characteristic that the two chambers of the double-chamber lime shaft kiln are in the alternate switching state of calcination and heat storage,a multi-physics unsteady numerical simulation of the lime shaft kiln during the calcination period,the burnout period and the heat storage period is established.Method,taking the above-mentioned steady-state multi-physics field of lime shaft kiln as the initial value,the unsteady calcination process of limestone was numerically simulated,and the change of the multi-physic field in the kiln with time was obtained.The maximum value is reached during 40～60s,the temperature of the flue gas entering the connecting channel is 780℃,and the mass fraction of CO₂is 26.5%.（4）Based on the results of the unsteady calculation of the temperature field of limestone,the time-dependent changes of fuel-type NO_x and thermal-type NO_x during the unsteady calcination of limestone were simulated.The results show that the variation of thermal NO_x with time is the reason for the peak of NO_x concentration in flue gas.52 pictures,5 tables,61 references...