Numerical Simulation Of Multiphase Reaction Process In Reduction Furnace Of Gas Sulfur Pre-reduction Phosphogypsum System

Gas sulfur reduction of phosphogypsum for acid co-production of sulfo-aluminate cement clinker is a new process technology for treating industrial solid waste phosphogypsum,and the reaction of calcium sulfate in the suspension reduction furnace is the key to this process technology.In this paper,based on the pilot system of dilute phase fluidized gas sulfur reduction of phosphogypsum,the gas-solid two-phase reaction process in the reduction furnace is used as the research object,and a combination of numerical simulation and experiment is used to explore the multi-phase reaction of calcium sulfate decomposition in the suspension reduction furnace,to obtain the specific process of flow,heat exchange and decomposition in the furnace,and to provide a basic theoretical reference for the development of key equipment of this technology.Finally,the influence of different process parameters on the performance of the reduction furnace is analysed,and the optimal process parameters for the reduction furnace are obtained through response surface optimisation.The main conclusions are as follows:Combined with the pilot test,the monitoring and sampling points are reasonably arranged to obtain the relevant process parameters under actual working conditions,providing a basis for determining the accuracy of the simulation results.The SST k-ωturbulence model,the DPM discrete phase model and the P1 radiation model were selected using Fluent software.The chemical reaction model was selected as a generic finite rate model based on the gas-solid reaction nucleation model,and the overall chemical reaction rate was obtained by calculating the chemical reaction resistance in the reaction rate equation to further accurately describe the gas-solid reaction process.The temperature error between the simulation results and the pilot test data was only2.23%and the CaSO₄ decomposition rate error was 8.07%,proving the reliability of the model and simulation results.The simulations under pilot conditions show that the multiphase flow in the reduction furnace has a spiral upward trend and is accompanied by multiple backflow vortices,and the maximum residence time of the raw meal particles in the furnace reaches 7.08 s.The location of the intense chemical reaction in the reduction furnace is accompanied by a change in temperature.The lower end of the reduction furnace is heated by the combustion of gaseous sulphur with O₂ in the kiln tail flue gas,and the heat absorption effect of the chemical reaction between the gaseous sulphur and CaSO₄particles in the lower section of the reduction furnace forms a low temperature zone in the incident area of the raw meal particles.When n（CaSO₄）/n（S₂）is high,it can stabilize the flow field and temperature field of gas-solid phase in the furnace;the increase of particle residence time makes the flow field in the upper part of the furnace more and more stable,and the decomposition rate of CaSO₄ gradually increases,and the change of flue gas temperature at the end of the kiln mainly affects the ambient temperature and the decomposition rate of CaSO₄ in the reduction furnace,meanwhile,the increase of flue gas temperature can improve the problem of uneven temperature distribution in the upper part of the reduction furnace.The optimization results showed that n（CaSO₄）/n（S₂）had the most significant effect on the decomposition rate of CaSO₄,followed by the particle residence time.The optimal combination of process parameters was n（CaSO₄）/n（S₂）=3.04,raw material particle residence time 8.90 s,and kiln tail flue gas temperature 1265.39 K.