Estimation of Carbon Dioxide Emissions in Rotary Hearth Furnace Using a Thermodynamic Model

A thermodynamic model has been developed for the estimation of carbon dioxide (CO2) emissions from rotary hearth furnace (RHF) using different reductant coals and external fuel gases for the production of sponge iron. The model developed incorporates coal pyrolysis and ore reduction. Output predictions including coal and fuel gas additions are computed under no heat loss condition and the stoichiometric addition of the reductant carbon. Validation with available data from literature has been carried out. The external fuel gas quantity is determined by calculating adiabatic flame temperature (AFT) and heat requirement in the reduction zone using software FactSage 6.4. Total iron present in the sponge is variable depending on the reductant coal and sponge metallization. Combustion products of producer gas and syn gas may be oxidizing to the metallic iron in the reduction zone unless extra coal is added. The CO2 emission potential is computed based on complete combustion of the exit gas from RHF. The emission is estimated to vary from 1.29 to 1.34 ton CO2/ton of sponge for a high VM and low ash coal, depending on external fuel. The optimum post-combustion inside the reduction zone is found to be 20% under conditions of stoichiometric coal rate.