Study On The Direct Reduction Simulation Of Iron-bearing Dust In The Thick-layer Rotary Hearth Furnace

Iron and steel production process will produce a large number of iron-bearing dust.China’s crude steel output is estimated to be 1 billion tons,and the iron dust sludge output will reach 80-120 million tons.Iron-bearing dust contains a lot of iron,carbon,zinc,lead,magnesium and other elements,which has a high recovery value.However,at present,the utilization rate of iron-bearing dust in China is low,which not only causes the waste of resources but also causes serious environmental pollution.Therefore,reasonable recovery and treatment of iron-bearing dust is of great significance to the sustainable and healthy development of China’s iron and steel industry.At present,the methods of treating metallurgical dust and sludge mainly include landfill method,physical method,wet process,fire process and so on.The fire process is more suitable for the process production of iron and steel enterprises.There are a variety of process types,among which the rotary hearth furnace process is one of the most promising treatment methods.Compared with other processes,the rotary hearth furnace process has better adaptability,high reliability,easy operation and maintenance,and relatively small environmental pollution.However,at present,the rotary hearth furnace process uses pellets laid at the bottom to deal with iron-bearing dust.Only 1-2 layers of pellets can be laid,and the thickness of the material layer is only 10-15mm,which greatly restricts the continuous improvement of the working efficiency of the rotary hearth furnace process.The research on rotary hearth furnace mainly focuses on the reduction mechanism of pellets and the direct reduction process of traditional thin layer.There are few studies on the problem that the thickness of rotary hearth furnace is thin and the production efficiency is limited.In this paper,a three-dimensional direct reduction mathematical model of thick-layer rotary hearth furnace was established considering the turbulence model,component transport model,radiation model and dynamic grid model to explore the technological characteristics of thick-layer rotary hearth furnace.The influence of different working parameters such as excess air coefficient and C/O ratio on metallization rate and dezincification rate of thick-layer rotary hearth furnace was studied.The simulation results of different operating conditions were analyzed to explore the most favorable operating parameters for the thick-layer rotary hearth furnace process.The results show that there is no obvious vortex in the main working area of the thicklayer rotary hearth furnace,but the flow velocity at the outlet is large,so measures should be taken to reduce the velocity according to the situation.The bottom pure pulverized coal can play the role of rapid heating layer,can ensure the reducing atmosphere in the process of work,to prevent the reduced metal element from being oxidized again.The overall metallization rate is higher when the material is released,which can meet the needs of producing sponge iron.The zinc oxide in the layer is basically completely reduced to achieve a better effect of zinc removal,can continue to be used in the subsequent production process,indicating that the thicklayer rotary hearth furnace process is in line with the production practice.The situation of different C/O ratios and excess air coefficient were analyzed.When the material C/O ratio is 1.2,1.3,1.4,the metallization rate of the material is 94.83%,94.62%,94.84%,and the dezincification rate is 99.01%,99.03%,98.85%,respectively.The C/O ratio has little effect on the dezincification rate and metallization rate.The increase of C/O ratio will lead to the decrease of production efficiency of thick-layer rotary hearth furnace and increase production cost at the same time,which is harmful to the actual production.When the excess air coefficient is 0.9,0.95,1.0,the metallization rate of the material is 94.83%,95.39%,96.94%,and the production energy consumption is 0.5227,0.5196,0.5113 t anthracite powder/t sponge iron,respectively.The dezincification rates were 99.01%,99.39%and 99.56%,respectively.Excess air coefficient increases from 0.9 to 1.0,metallization rate increases by 2.11%,energy consumption per ton of sponge iron decreases by 2.18%,and dezincification rate increases by 0.55%.To sum up,the thick-layer rotary hearth furnace process can effectively improve the thickness of the material layer and improve the treatment efficiency,to meet the requirements required in the actual production.When the ratio of carbon to oxygen is 1.2 and the excess air coefficient is 1.0,it is more suitable for the current working state of the thick-layer rotary hearth furnace.In the actual production process,the dezincification rate can reach 99.56%,the metallization rate is 96.94%,and the coal consumption per ton of cast iron is 0.5113t anthracite powder/t sponge iron.