CFD And DEM Simulation Of Gas-based Shaft Furnace

With the advantages of low energy consumption,low environmental load and high product quality,gas-based shaft furnace direct reduction process has become the largest direct reduction process in the world.Depending on the abundant coal resources in our country,the development of coal gasification-shaft furnace-electric furnace technology will be one of the leading directions of low-carbon and sustainable development of China's iron and steel industry.As the key of the whole process,the efficient production of gas-based shaft furnace is affected by many factors,such as furnace type parameters,temperature distribution in the furnace,flow field,motion of burden,etc.In this paper,CFD and DEM numerical simulation are used to study the reduction process,cooling process,distribution and motion of burden in gas-based shaft furnace.The main contents are as follows:(1)The mathematical model of gas-based shaft furnace is established based on CFD,and the reduction process of iron oxide in reduction section is simulated.The effects of reducing temperature and atmosphere on the distribution of solid mass fraction,gas phase and temperature were investigated.Meanwhile,the effects of top pressure on the distribution of pressure and density of reducing gas were also studied.The results show that when the reduction temperature is 900?,with the increase of H2 content in the reducing gas,the utilization ratio of reducing gas increases,the reduction rate accelerates and the output increases.However,the reduction gas volume needs to be increased appropriately.In addition,with the increase of the top pressure of the furnace,the overall gas pressure in the furnace increases,and the reducing gas tightness increases.The decrease of the pressure gradient is not only conducive to the smooth operation of the shaft furnace,but also to the corresponding increase of the residence time of the raw gas.(2)In this study,natural gas is used to cool the DRI to 80?.Based on the principle of equal volume,the cooling section models under different furnace body angles are established.The cooling conditions of the axial and radial of the cooling section are studied.The results show that the cooling effect is better when the shaft angle of the cooling section ranges from 76-80? with a certain amount of cooling gas.When the angles is large than 80°,the cooling effect decreases obviously.However,the smaller the angle is,the higher the cooling section height is.(3)Two charging models of pipe distributor and chute distributor were established,and the distribution process,the growth and shape of pile were observed.The characteristics of the mass circumferential distribution,the volume fraction of large particles and the void ratio were investigated from the particle size.The results show that the pipe distributor is more suitable for gas-based shaft furnace.(4)In order to understand the motion of the burden in the furnace,DEM is used to simulate the burden motion at different discharging speeds.The flow pattern and residence time of the burden were investigated,and the motion rate of the burden and the voidage distribution were also quantitatively studied.The results show that the burden doesn't motion in piston flow,the motion rate of the burden in the center is about 10%?20%faster than the average rate,and the residence time is less than other part.In the design of furnace,the height of reduction section should be calculated in combination with the motion rate of the burden in the center and the necessary residence time.