Numerical analysis of carrier gas characteristic effects on flow dynamics and combustion efficiency in natural gas and pulverized coal injection

The mixing injection of natural gas and pulverized coal into the blast furnaces shows a promising technological approach in the context of global carbon reduction initiatives. Carrier gas and coal pass through the air inlet of coal lance, and the characteristics of carrier gas affect the flow in the air inlet and the combustion efficiency of coal, so it is very important to study the change of carrier gas characteristics in the lower part of blast furnace. By means of numerical simulation, the influence of carrier gas characteristics (injection rate, composition, and temperature) on the mixed combustion of natural gas (NG) and pulverized coal in the tuyere raceway of Russian blast furnace was analyzed. When N₂ is used as carrier gas, the injection rate of carrier gas is reduced from 4000 to 2000 m³/h, the average tuyere temperature is increased (1947.42 to 1963.30 K), the mole fractions of CO and H₂ are increased, and the burnout rate of pulverized coal is decreased. Increasing the carrier gas temperature is helpful to improve the burnout of pulverized coal. For every 20 K increase of carrier gas temperature, the average temperature in the raceway increases by 20.6 K, which promotes the release and combustion of volatiles, but the increase of carrier gas temperature from 373 to 393 K only leads to 1.16% burnout change. Considering the transportation characteristics of pulverized coal, it is suggested that the carrier gas temperature should be kept at about 373 K to obtain the best performance. It is worth noting that when air is used as carrier gas, the burnout rate of pulverized coal is increased by 2.69% compared with N₂.