Effect of Coke Oxidation Kinetics on Mineral Wool Cupola Performance

Abstract

In order to evaluate the effect of impact of the nature of solid fuel on performance indicators of a shaft melting furnace of the cupola type with an internal diameter of 2200 mm and a layer height of 4.5 m, and conditions for its oxidation, the real range of change in the properties of industrial coke batches of various manufacturers is determined (8 varieties) under conditions of non-oxidation heating of coke samples in an argon atmosphere at the rate of 5 deg/min to a temperature of 1000°C and isothermal exposure in an air atmosphere. Operating conditions of the mine unit on these cokes are evaluated with respect to values of specific coke consumption, mineral melt yield, thermal efficiency and changes in conditions for development of heat transfer from gases to materials based upon the ratio of heat capacities of their flows obtained from industrial tests. It is shown that an increase in the complete coke oxidation interval from 7 to 12.5 – 13.0 min will provide a decrease in specific coke consumption from 265 to 225 kg/ton of melt, i.e., by 15.9%, an increase in yield of mineral melt from 25.3 to 30.02%, i.e., by 18.66%, with a decrease in cupola total thermal efficiency from 61.7 to 60.2%, i.e., by 1,5%. For this it is advisable to use coke with maximum heat of combustion. Use of coke mineral raw material during melting, which has a rate of change of sample weight from 5.0 up to 8.0 – 8.5%/min (more active coke), provides a coke minimum specific consumption at the level of 224 kg/ton of melt with a maximum yield of molten smelting product of at least 29.8% of the weight of the initial components with unit thermal efficiency at 61.7%. For this it is necessary to use more active coke with respect to blast oxygen. Heat transfer process conditions from gases to materials during smelting are characterized by low intensity with the lowest ratio of heat capacities of material and gas flows not lower than 0.827 in the range of complete coke oxidation 12.5 – 13.0 min and an average rate of change in sample weight of about 6.0%/min.