To clarify the gasification and consumption behavior of unburnt char ascending in the coke packed bed in the lower part of the blast furnace, char reaction-consumption model has been newly developed considering the average residence time and co-gasification with coke particles. The chemical reaction rate constant has been determined based on the high temperature experiments on the char injection into the coke packed bed.
From the analyses using this model, the following results were obtained.
( 1 ) The mean ascending velocity of char particles with the diameter of 20 μm was approximately 0.3 m/s, and it was smaller than the actual gas velocity by one order of magnitude, suggesting the char particles had fairly long residence time in the blast furnace.
( 2 ) The consumption rate of char became lower with the increase in the solid-gas loading ratio. This was considered to be caused by the higher ascending velocity which resulted from the successive renewal of stagnant particles in the packed bed by supplied char particles.
( 3 ) According to the examination of char consumption behavior along the blast furnace height, char discharge rate from the top of the thermal reserve zone could be reduced considerably by decreasing char exhaust rate from the raceway. This phenomenon resulted from the increase in the consumption rate throughout the height, due to the decrease in the solid-gas loading ratio. Therefore, to suppress the char exhaustion from the top, it was necessary to improve the combustion efficiency in the raceway at higher injection rate of pulverized coal.
