Discrete Simulation of Gas-solid Flow and Softening-melting Behaviour in a Blast Furnace

摘要

The blast furnace is a complicated multiphase flow reactor with hazardous working conditions, and its understanding is still a challenge in research community. In the recent decades, the discrete element modelling is becoming a popular tool to study this process, especially for the particle related phenomena, such as gas-solid flow, particle softening-melting behaviour and gas-solid heat transfer. This work aims to develop some new and better methods to describe this process based on the discrete model.The discrete model shows some unique advantages in describing particle motion; however the high computing cost limits its application in the study of blast furnace. A sector model is successfully developed to represent the full 3D cylinder vessel, which can effectively reduce the number of particles and hence the computational cost. Its validity is first examined through two common industrial processes; hopper flow and pile formation. The results generated by the sector model are exactly the same as the full 3D model, but saved 90% computing time. Then, the sector model is applied to study the gas-solid flow in a blast furnace, and the comparison between the sector model and the slot model are given in detail. Understanding the particle softening and melting behavior in the cohesive zone is the basis to describe the gas/liquid distribution and thermal-chemical behavior in this zone, which is critical to understanding the complex physical and chemical phenomena in a blast furnace. The CFD-DEM method accompanying with the gas-particle heat transfer is one powerful tool to carry out this study. The softening and melting behaviour of wax particles is successfully captured, by implementing the correlation between Young’s modulus and temperature of wax. And the multi-layer behaviour is also studied and then a parametric study. Further, in order to study the heat transfer in the raceway of blast furnace, the gas-solid heat transfer based on the discrete model is first used in a moving bed. The simulation is quantitatively consistent with the previous experimental data, that demonstrating the capability to accurately describe the thermal phenomenon in the raceway.