Reduction of specific coke consumption in blast furnace by impact on thermal reverse zone

Abstract

At the blast furnace of PJSC “Magnitogorsk Metallurgical Plant” (MMK), the specific consumption of coke was reduced by impact on thermal reverse zone (TRZ) by increasing the consumption of natural gas above 120 m3/t of cast iron under conditions of increased reactivity and reduced hot strength of coke. In the first pair of periods, an increase in CRI from 38.4 to 39.3 % with a decrease in CSR from 36.3 to 34.6 % was accompanied by an increase in the ratio of natural gas consumption and total oxygen entering the furnace from 0.43 to 0.45 by increasing the specific gas consumption from 123.2 to 133.5 m3/t of cast iron. The set of actions increased the TRZ length towards the blast-furnace mouth by 1.9 % with its unchanged location along the lower part. Reducing the heat consumption in the TRZ increased the temperature difference between gas and materials there by an average of 36 °С. In the second pair of periods, the consumption of natural gas was 143.9 m3/t of cast iron with a decrease in the oxygen content in the blast from 27.6 to 27.0. They were accompanied by the following changes in the processes under consideration: an increase in the length of the TRZ towards the blast-furnace mouth by 2.6 % and the distance from the tuyere hearth by 3.4 %, an increase in the degree of carbon reduction from 32.0 to 33.3 %, an insignificant (on average 0.3 °С) increase in the temperature difference of gas and materials in the TRZ. In the first pair of periods, reduction in the coke specific consumption was 4.7 kg/t of cast iron with an increase in furnace productivity by 27 t/day. Conditions and course of the processes of the second pair ensured a decrease in the coke specific consumption by 1.6 kg/t of cast iron and led to a decrease in cast iron production by 41 t/day.