| The steel industry is a typical intensive energy consumption and greenhouse gas emission industry.The development of new blast furnace ironmaking technology for significantly reducing energy consumption and carbon emissions represents a new trend in the context of global low-carbon economic development and the tide of decarbonization.The cohesive zone is a very important physical area inside the blast furnace.The iron ore in this area is softened and melted by heating,and phase transition occurs to generate liquid phase(slag,molten iron),when the upward airflow at the bottom passes through the cohesive zone.Especially,complicated and intense heat and mass transfer,phase transition,and gas redistribution all occur in this region.The morphology and location of the cohesive zone are closely related to the stable operation of a blast furnace and its efficient smelting of iron ore,however the study on the complex thermochemical behaviors of the cohesive zone has not been comprehensively studied.In fact,understanding complex transfer process of softening melting and phase transition of iron ore particles in the cohesive zone is the basis and key to optimally control the cohesive zone.Therefore,this study establishes a method,the combining Computational Fluid Dynamics with Discrete Element Method(CFD-DEM),for investigating the heat transfer and melting process of particles in the cohesive zone.which would provide fundamental insights into the phase change melting phenomena in the cohesive zone for a better understanding and optimization in operations.The main text of the research is as follows:The numerical study of heat transfer process of iron ore particle-scale phase transition is conducted.Firstly,the heating and melting process of single particle iron ore is analyzed,based on the validated one-dimensional transient heat transfer model particle level,and then the effects of particle diameters,gas velocity and inlet gas flow temperature on the internal thermal state of iron ore particles are discussed.Finally,In addition,the influences of different working conditions on the temperature distribution inside the particle are compared.The results show that the internal thermal resistance of the particles increases with the increase of particle size,resulting in a slower moving speed of the phase interface and a longer melting time of the particles.It is noted that,the diameter has the most significant effect on heat transfer caused by the phase transition of the particles.The numerical research on the heating and melting process of iron ore particles in a packed bed is investigated based on CFD-DEM.The effect of particle sizes on the internal heat transfer of iron ore particles and the gas-solid flow heat transfer in the particle packed bed were analyzed.In addition,the effect of particle packed distribution type on the temperature distribution is discussed.The results show that the particle heat transfer capacity as the particle diameter decreases,however,the heat transfer efficiency of the packed bed decreases.It shows that the alternate filling distribution of large and small particles will improve heat exchange efficiency and speed up particle melting time.The numerical simulation of the softening process of iron ore particles in packed bed is conducted.Firstly,a mathematical model for the softening of iron ore particles is established,and then the iron ore particles softening in process is analyzed.The results show that,the iron ore particles are gradually soften as the temperature increases,which leads to continuous decrease of the bed height and packed bed permeability,thus affecting the gas flow direction.This numerical model is beneficial for investigating the softening behaviors of iron ore particles in cohesive zone and its effects on blast furnace operations. |
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