CFD-DEM Simulation of Raceway Formation in a Blast Furnace

Abstract

Blast furnace is one of the most significant technologies in ironmaking industry. Particularly, in the lower part of blast furnace, the raceway is considered to be one of the most important zones where complex chemistry and physical reactions occur. In order to achieve higher efficient and stable operating situation, investigations on raceway region have become a useful and critical method to achieve a deeper understanding of blast furnace, since the stability and shape of raceway influence the total production. In this thesis, a 2-D slot model on the basis of combined discrete element method (DEM) and computational fluid dynamics (CFD) (DEM-CFD) model has been used to carry out numerical study of complex particle and gas two phase flows in blast furnace raceway region. In the DEM-CFD coupling approach, the motions of single particles are modeled by DEM approach as discrete phase, and the gas flow field is considered as continuum phase, modeled by CFD approach. By using DEM-CFD approach, the effect of some variables on raceway such as bed weight, gas velocity and coke combustion can be achieved. In addition, with the development of computational technology, this method can be used to simulate the blast furnace in actual size and generate rich microscopic information such as flow structure and force structure. Thus, the DEM-CFD approach is used in this thesis to investigate the effect of some parameters on raceway size and shape. The calculated results indicate that these parameters have obvious effects on raceway size and shape. Three kinds of typical raceways are witnessed from calculated results: anti-clockwise raceway, clockwise raceway and plumelike raceway. This phenomenon is examined by investigating the particle flow pattern, particle velocity, porosity, normal contact force and gas flow at raceway region. The observation of two contrary circulating gas vortexes located upon and below tuyere during raceway formation has a good agreement with experiments carried out in cold models. If the simulation condition has a positive effect on the increment of one of the two gas vortexes, this gas vortex will become the main circulating gas flow and determine the circulating direction. The plumelike raceway is always generated for the cases with loaded packed bed which is formed by increasing the density of particles.