Numerical Simulation Of Flow And Reaction In Alumina Fluidized Bed Calciner

Alumina is an important industrial raw material,and the alumina industry is related to the national lifeline.The alumina roaster is the main equipment for alumina roasting in the alumina preparation process.The fluidized bed alumina roaster has the advantages of high thermal efficiency,high automation and small footprint compared with other furnace types.As far as the fluidized bed alumina roaster itself is concerned,the fuel used is mostly heavy oil.The heavy oil combustion has low thermal efficiency and large pollution,which has not met the requirements of industrial development.With the development of gas fuels and the reduction of transportation costs,fuel selection has also shifted from liquid fuels to cleaner and more efficient high-burning gaseous fuels.In the fluidized bed alumina roaster,complex multiphase flow,heat transfer and chemical reaction processes are simultaneously carried out.These processes are coupled to each other.It is difficult to restore the flow field in the furnace by conventional techniques,analyze the roasting process,and improve the design of the roaster.Increased the difficulty.Therefore,for the fluidized bed alumina roaster,the furnace roasting situation of diesel fuel and natural gas fuel was explored by numerical simulation.Taking the circulating fluidized bed alumina roaster of a plant in Inner Mongolia as the research object,a geometric model was established.Based on the Euler-Euler two-fluid model,the multiphase flow in the furnace was simulated,and the gas-solid phase heat transfer and radiation heat transfer were considered.A model of pyrolysis reaction and combustion reaction in the furnace was established.In the simulation process,the calcined raw materials,crystalline aluminum chloride and product alumina,are respectively reduced to a single particle size,and the combustion of diesel and natural gas is simplified to the combustion of a single gas component,and the particle concentration distribution in the furnace under different fuel conditions is obtained.Data such as particle velocity distribution,gas composition distribution,temperature distribution and chemical reaction rate distribution were analyzed,and the characteristics of each distribution and the causes were analyzed.During the roasting process,the heat released by the combustion of the fuel is divided into two parts and fed into the furnace.A part of the burner is burned in the under-bed burner below the fluidized bed air distribution plate to heat the fluidized air in the fluidized air chamber,and the heat is sent to the furnace by the high-temperature fluidized wind,and the other part of the fuel is placed on the bed of the furnace side wall.The burner is directly fed into the furnace,and a combustion reaction is carried outin the furnace to release heat.Aiming at the roasting process using diesel fuel,the effects of fuel distribution and cycle rate on the temperature distribution in the bed and the pyrolysis rate distribution of crystalline aluminum chloride were investigated.The roasting process using natural gas as fuel was simulated,and the characteristics of particle concentration distribution,particle velocity distribution,gas composition distribution,temperature distribution and chemical reaction rate distribution in the furnace were obtained and the causes were analyzed.Two burner layout schemes were set up,one was fed from one side of the side wall of the furnace,and the other was fed from both sides of the side wall of the furnace.The effects of the two schemes on the roasting process were investigated,and the simulation results were carried out.