Oxidation of molten impurities in converters by means of combustion flames: Thermodynamic principles. 1. Thermodynamic analysis of processes in natural-gas combustion

In the production of steel, as the productivity rises and the resource and energy consumption declines, improvements in converter design are required to ensure preliminary scrap and batch heating and to intensify redox processes in the liquid bath and exhaust-gas combustion above the bath, without impairing the durability of the injection systems and the converter lining. The use of fuel–oxygen combustion flames in the converter resolves numerous technological problems. The hydrodynamics in the reaction zones and in the liquid bath may be greatly changed by fuel combustion in the converter’s working space with jet formation or by means of submersible combustion flames. In the present work, thermodynamic methods are used to analyze the dynamics of gaseous-fuel combustion and the oxidation of elements in the converter bath on interaction with high-temperature combustion products. The interaction of the combustion flame and chemical elements in the converter bath is calculated for equilibrium conditions. The use of the combustion flames is found to change the composition of the gas phase in the converter’s working space (above the bath), which contains H₂ and H₂O in addition to the traditional components associated with oxygen injection: O₂, CO, CO₂. The presence of H₂ and H₂O changes the thermal conditions and oxidative properties of the gas phase. In the combustion of gas–oxygen fuel, the optimal composition of the initial gas mixture (natural gas + oxygen) must correspond to the ratio 100% CH₄ + 69% O₂. The oxidation product is gaseous phase consisting of 40% CO₂ + 60% H₂O. The total enthalpy of combustion of the gas–oxygen fuel at converter temperatures, with an oxygen excess greater than 1.0 (up to 2.0), is about 200 kJ per mole of the initial reagents. In the oxidation of methane by carbon dioxide, the total enthalpy of combustion is between–7 and–14.5 kJ/mol of initial reagents at 1800 K. The process becomes endothermal at temperatures above 2000 K: ΔH₂₂₀₀ = 7.7–15.4 kJ/mol. In the oxidation of natural gas by water vapor, ΔH₁₈₀₀–2200 = 19.5–70 kJ/mol. Thus, flame temperatures above 1800 K may only be attained in the oxidation of methane by oxygen. The use of air, carbon dioxide, or water vapor as the oxidant does not yield the required thermal effect.