Extending the Operating Line Methodology to Consider Shaft and Preheating Injections in Blast Furnaces

In the last years, the injection of reducing gases in the shaft and preparation zone of the blast furnace has been proposed as a decarbonization option, mainly associated to oxyfuel blast furnaces and top gas recycling configurations. However, the Rist diagram, which is one of the preferred methodologies to characterize the operation of blast furnaces, is not valid to evaluate these new decarbonization options. In this article we propose a generalization of the operating line methodology to extend its applicability to scenarios of variable molar flows along the blast furnace (i.e., shaft and preheating injections) and noncontinuous oxidation profiles (presence of CO2 and H2O in the injected gases). The extended operating line methodology was implemented in an Aspen Plus simulation, which provides a detailed modelling of the preparation zone, the thermal reserve zone, the lower zone and the raceways. The simulation was used to validate the generalized operating line methodology through three different data sets: (i) an airblown blast furnace with pulverized coal injection and O2 enrichment, (ii) an oxyfuel blast furnace with shaft gas injection, and (iii) an oxyfuel blast furnace with preheating gas injection in the preparation zone. In general, the discrepancy between the reference data and the simulation results is well below 3.5%, so the extended operating line methodology is considered validated.