Revisiting the Rist diagram for predicting operating conditions in blast furnaces with multiple injections

Background: The Rist diagram is useful for predicting changes in blast furnaces when the operating conditions are modified. In this paper, we revisit this methodology to provide a general model with additions and corrections. The reason for this is to study a new concept proposal that combines oxygen blast furnaces with Power to Gas technology. The latter produces synthetic methane by using renewable electricity and CO (2) to partly replace the fossil input in the blast furnace. Carbon is thus continuously recycled in a closed loop and geological storage is avoided. Methods: The new model is validated with three data sets corresponding to (1) an air-blown blast furnace without auxiliary injections, (2) an air-blown blast furnace with pulverized coal injection and (3) an oxygen blast furnace with top gas recycling and pulverized coal injection. The error is below 8% in all cases. Results: Assuming a 280 t (HM)/h oxygen blast furnace that produces 1154 kg (CO2)/t (HM), we can reduce the CO (2) emissions between 6.1% and 7.4% by coupling a 150 MW Power to Gas plant. This produces 21.8 kg/t (HM) of synthetic methane that replaces 22.8 kg/t (HM) of coke or 30.2 kg/t (HM) of coal. The gross energy penalization of the CO (2) avoidance is 27.1 MJ/kg (CO2) when coke is replaced and 22.4 MJ/kg (CO2) when coal is replaced. Considering the energy content of the saved fossil fuel, and the electricity no longer consumed in the air separation unit thanks to the O (2) coming from the electrolyzer, the net energy penalizations are 23.1 MJ/kg (CO2) and 17.9 MJ/kg (CO2), respectively. Discussion: The proposed integration has energy penalizations greater than conventional amine carbon capture (typically 3.7 – 4.8 MJ/kg (CO2)), but in return it could reduce the economic costs thanks to diminishing the coke/coal consumption, reducing the electricity consumption in the air separation unit, and eliminating the requirement of geological storage.