Modeling on the blast furnace with CO2-enriched hot blast

Abstract

Ironmaking and steelmaking are resource- and energy-intensive industries and major sources of CO2 emissions. We investigated the use of recycled CO2 gas to replace some of the air in the hot blast under smelting conditions in a blast furnace. CO2 reacts with carbon in the raceway zone; hence, a kinetic model of the CO2-enriched hot blast reaction with coke in the raceway zone was established. At the end of the raceway and its influence area, newly added CO2 gas reacts with carbon to form CO gas. A blast furnace mass and energy balance calculation model was established by assuming that all CO2 gas reacted to produce CO gas in the raceway zone based on the above conclusion. These CO molecules were oxidized into CO2 gas by the indirect reduction of iron ore in the middle and upper parts of the blast furnace; the conversion ratio from newly added CO2 to CO at the top of the blast furnace was approximately 50%. The conversion of CO2 to CO gas absorbed physical heat, which cooled the furnace; this may affect the normal operation of the blast furnace. Therefore, before using CO2 gas to replace part of the air in the blast furnace, it is necessary to evaluate the heat conditions of the blast furnace. To partially offset this heat loss, three heat supplementation methods were compared. For every 1% increase in the CO2 enrichment rate, the coke ratio needs to be increased by approximately 5 kg/THM, the hot blast temperature needs to be increased by approximately 65 °C, or the coal ratio needs to be increased by approximately 5.5 kg/THM.