Numerical Simulation Of Gas-Solids Flow And Reaction Characteristics In HDCFB

HDCFB has higher solids holdup and particle circulation rates,which increases the processing capacity of the reactor,and has good heat and mass transfer characteristics.Therefore,the HDCFB has a good application prospect in the process industry.On the basis of experimental research of the HDCFB,the purpose of this paper is to recognize the stability of HDCFB system operating conditions,investigate the gas-solids flow behaviors in HDCFB riser and downer reactor by adopting the numerical simulation method.This paper provides the theory basis for the design,amplification and optimizing operation,which is beneficial to explore the industrial application of HDCFB reactor.Firstly,we analyze the stability operating conditions of HDCFB system by establishing the uncertainty analysis method based on the Bayesian theory.The Sobol index is used to characterize the influence of each operable variable on the high-density stability operation of CFB.Different from LDCFB,it is found that the key to realize highdensity operation is the driving force of particle phase.Further investigation on the influence of fluctuation of operable variables on stability operation of the HDCFB is carried out.It is found that the key to realize the stability operation of the HDCFB is to control the fluctuation of the pile height of companion bed or to maintain the stability of the pile height of companion bed.The numerical model of the HDCFB riser reactor was carried out by considering the influence of cluster.The gas-solids flow structure in the HDCFB riser reactor was decomposed,the equation was closed by the directly numerical simulation results.The multi-zone drag model was established to realize the simulation results of the gas-solids flow in the HDCFB riser reactor.Based on the simulation results,we established the calculation method of particle diffusion coefficient and the self-adaptive particle clustering judgment-tracking algorithm to analyze the particle back-mixing bahaviors and cluster characteristics.The industrial riser reactor under the condition of high density operation has low temperature and large catalyst-oil ratio.In order to handle with inferior oil,it is necessary to increase the cracking capacity of heavy oil.Inhibiting the thermal cracking reaction and promoting the catalytic cracking reaction can improve the product selectivity,improve the yields of gasoline and liquefied gas,and reduce the yields of dry gas and coke.The gas-solids flow model of HDCFB downer reactor was established by considering the influence of the cluster.The dynamic equilibrium equation of the number of particles in and off the cluster was solved by means of the dynamic equilibrium model of cluster in the downer,and then the diameter of the cluster was calculated.In addition,the reaction model based on the cluster was established.A comprehensive gas-solids flow and reaction model was established.The established model was applied to simulate the coal pyrolysis reactor.The gas-solids flow,heat transfer and mixing behaviors of the binary particles,including the coal particles and heat carrier particles,and the coal pyrolysis reaction process in downer was accurately simulated.