Increased Use of Natural Gas in Blast Furnace Ironmaking: Mass and Energy Balance Calculations

In blast furnace ironmaking, coke can be partially replaced by injected natural gas. Tuyère injection of cold natural gas is commonly practiced in North America. In this work, limits to the tuyère injection rate have been quantified with mass and energy balances. The fundamental origin of the limits is the endothermicity of methane injection. In principle, shaft injection of preheated and partially combusted methane would obviate the endothermic effect. However, the thermal and chemical energy parameter indicates that the energy requirement in the lower part of the furnace—to melt hot metal and slag—might not be met in the case of shaft injection. Tuyère injection of preheated methane might be a feasible alternative. Calculated combustion kinetics support the feasibility of partial combustion of preheated methane (with sub-stoichiometric oxygen) before injection.