The rational mode of nut coke charging into the blast furnace by compact trough-type charging device

Abstract

The laboratory research on the 1:5 scale physical model of a trough-type bell-less charging device (BLCD) resulted in the rational mode of nut coke charging into the BLCD hopper together with sinter and pellets. This rational mode provides the highest uniformity coefficient of its entering the furnace throat area. The amount of nut coke in the BLCD hopper was at rates of 100, 550 and 1000 kg per 16 tons batch for an actual furnace. In this study, a three-factor Box-Behnken experimental design was used. The following factors have been considered: the sequence of nut coke charging into the hopper, the degree of charge gate opening, and nut coke consumption per feeding. The mathematical description of the output parameter is given by a second-degree polynomial. The significance of each coefficient of the equation resulted from experimental data processing was determined by Student’s t test. The position of nut coke in the centre of the raw material mass in the BLCD hopper resulted in the highest uniformity coefficient and reached 0.85. We investigated the influence of the charging sequence of sinter, quartzite, ore, pellets and nuts into the BLCD hopper on the furnace performance and blast furnace processing during three periods of experienced heats lasting 8–9 days in one of the blast furnaces with a compact trough-type BLCD at Magnitogorsk Iron and Steel Works OJSC (MMK). We evaluated the drainage ability of the hearth on several factors: the amount of slag remaining in the furnace after discharging, the time interval from the start of discharging until the slag occurrence and slag viscosity. In the first period, when nut coke was positioned on the bottom of the BLCD hopper, the amount of slag, remaining in the furnace, was 0.38 of the ladle. When nut coke was charged into the BLCD hopper last (period 2), the amount of slag increased to 0.44 showing the deterioration in the drainage property of the hearth. In the third period, when nut coke was positioned in the centre of the raw material mass, the amount of slag decreased to 0.31 of the ladle that resulted in the improved filtration of melting liquid products through the coke packed bed. The deterioration in the filtering ability of the coke packing in the second period, compared to the first one, was followed by decreased coefficient of the replacement rate of coke by nut coke from 0.64 to 0.59 kg/kg. In the third period, improved penetrability of the coke packing was followed by an increased coefficient of the replacement of coke by nut coke to 0.85 kg/kg. Indicators of the furnace performance intensity according to their types, the drag coefficient of charge by zones and the reduction degree with reducing agents corresponded to the results obtained.