Numerical simulation of blast furnace raceway depth and height, and effect of wall cohesive matter on gas and coke particle flows

We have presented the calculated results of the particle and the gas flows in the raceway region in an actual blast furnace of which dimension is the same as that of the commercial blast furnace. We used Distinct Element Method for the computation of the multi-body interaction among coke particles and Finite Difference Method for the numerical analysis of Navier-Stokes equations with the interaction terms between gas and particles for the gas flows. The calculated results show a typical raceway pattern and typical distributions of gas and particle velocities and void fraction in an actual blast furnace. The results present the size and the shape of raceway. These change as the time and show the unstable and unsteady motion. Both of the depth and the height of raceway periodically change and have roughly two different periods. The calculated mean values of the depth and the height of raceway are fairly in good agreement with the measured data by Matsui et al. (ISIJ Int., 45 (2005)) Thus our calculated values present the rough but the proper estimation of raceway characteristics in an actual blast furnace. The unsteady change of the calculated pressure at the nozzle outlet also indicates two different periods of which values agree with those of the raceway. The short period would indicate the usual fluctuation of the raceway and the long period would do the large scale change of the flow. These results show that the raceway grows and shrinks during the short period and greatly changes its shape and size during the long period. Calculated results present an unusual phenomenon example in the blast furnace, namely the unusual high air velocity wide region touched to the furnace wall is formed due to the air flow penetrated the powder particle wall formed around the outside of the raceway, the effect of the softening melting zones and the size reduction of coke particles in the furnace center region. We calculated the gas and particle instantaneous velocity vectors, and the instantaneous iso-contour of void fraction with the cohesive matter on the furnace wall in the actual blast furnace. The cohesive matter considerably changes the gas and the particle flows, particularly dose the flows near the furnace wall.