Analysis of effect of biochar injection in blast furnace on smelting parameters as well as economic and environmental benefits

The steel industry faces an extremely urgent task of decarbonization. Biochar, as a renewable fuel with carbon neutral properties, can promote deep decarbonization in blast furnace ironmaking. To investigate the effectiveness and economic benefits of biochar injection in blast furnaces, this study developed a full furnace energy and mass balance model that considered the physicochemical properties of different fuels and the distribution of reactions within the furnace. The model compared and analyzed the changes in smelting parameters, carbon emission reduction, and economic performance when injecting wood chip biochar （Biochar A） and corn stalk biochar （Biochar B） at injection ratios ranging from 0 to 40%. Industrial trials were also conducted at injection ratios of 0 to 20%. The model results indicate that the physicochemical properties of biochar affect the thermal state of the blast furnace and fuel performance. As the injection ratio increases to 40%, injecting Biochar A reduces the fuel rate from 509 kg/t to 504 kg/t, increases the theoretical combustion temperature from 2 172 ℃ to 2 208 ℃, decreases the proportion of total furnace heat loss from 5.92% to 4.79%, and improves the gas utilization rate. Injecting Biochar B raises the theoretical combustion temperature to 2 186 ℃ but increases the fuel rate to 516 kg/t and causes a slight decrease in the gas utilization rate. The industrial trial results show that under short term operation with a injection of 10% to 20%, the blast furnace operating parameters remain within an acceptable range. The fuel rate is maintained between 509 kg/t and 511 kg/t, and parameters such as top temperature, permeability index, hot metal temperature, and the gas flow distribution in furnace （W）, furnace condition stability （Z）, and gas flow uniformity （K） values all fluctuate within normal ranges. In terms of carbon emission reduction and economic performance, based on the model boundaries and the carbon neutral assumption for biochar, at the injection ratio of 40%, fossil derived CO₂ emissions are reduced from 1 318 kg/t to 1 252 kg/t, achieving a net reduction of 66 kg/t. The fuel cost （excluding carbon tax） increases from 839.11 yuan/t to 881.26 yuan/t. A scenario analysis incorporating a carbon tax reveals that when the price of biochar is 1.5 yuan/kg, a minimum carbon tax of 173.31 yuan/t （CO₂） can ensure economic viability. When the carbon tax is 0 yuan/t （CO₂）, a maximum biochar purchase price of 1.326 yuan/kg can ensure economic viability.