Quantitative evaluation of CO₂ emission reduction and energy conservation in iron making process by using in-plant CO recycling system

Japanese iron and steel manufacturing industries import a significant amount expensive coking coal (coke); reduction of coke consumption is a great challenge for the industry. In this paper, we propose an in-plant CO recycling system which supplements coke with gaseous CO as a reducing agent in the blast furnace. Process flow diagrams including a blast furnace with CO recycling, coke oven, and hot blast stove were built in Aspen Plus and the effect of CO recycling on coal conservation, exergy efficiency, and CO₂ emission were quantitatively evaluated. In the blast furnace the input exergy, effective exergy ratio, overall CO₂ emissions, and the input coke decreased as the degree of CO circulation was increased. The recirculated CO gas was separated from the Blast Furnace Gas (BFG), the coke oven gas, and the converter gas. The separation and recycling of CO into the blast furnace resulted in the decrease of input coke, and input exergy by 13.0% and 10.3%, respectively. On the other hand, overall CO₂ emissions increased by 2.6%.