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

Abstract

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 CO2 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 tHM/h oxygen blast furnace that produces 1154 kgCO2/tHM, we can reduce the CO2 emissions between 6.1% and 7.4% by coupling a 150 MW Power to Gas plant. This produces 21.8 kg/tHM of synthetic methane that replaces 22.8 kg/tHM of coke or 30.2 kg/tHM of coal. The gross energy penalization of the CO2 avoidance is 27.1 MJ/kgCO2 when coke is replaced and 22.4 MJ/kgCO2 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 O2 coming from the electrolyzer, the net energy penalizations are 23.1 MJ/kgCO2 and 17.9 MJ/kgCO2, respectively. Discussion: The proposed integration has energy penalizations greater than conventional amine carbon capture (typically 3.7 – 4.8 MJ/kgCO2), 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.

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

“…( 41)). The derivation of these equations is similar to the conventional methodology, 19) but adapted to the frame of reference of the extended operating line. The meaning and units of the different variables is specified in the nomenclature section.…”

“…The operating line of a blast furnace is the graphical representation of the mass and energy balances concerning the formation of the reducing gas (range 0 < X < 1 in a Cartesian plot) and its utilization to reduce the iron ore (range 1 < X < 2 of the plot). This methodology was firstly proposed by Rist et al, 18) and recently revisited by Bailera et al 19) to account for multiple injections in the tuyeres. However, two restrictive conditions must be assumed: (i) a constant ratio along the blast furnace between the moles of reducing gas and the moles of Fe produced, and (ii) the absence of oxidized gases at the beginning of the indirect reduction process.…”

“…A more detailed description of all these reactions can be found in conventional operating diagram methodologies. 19) x The similar mole balance can be performed per unit of mole of Fe produced in the blast furnace, where the units of each addend in the ordinate axis are given by Eq. (9).…”

“…The mathematical derivation of these coordinates, as well as the calculation of the individual terms of the energy balance, follows the same procedure as for the conventional operating diagram (see the work of Bailera et al 19,24) for more details). The only new terms in the energy balance are those related to the injection of CO 2 and H 2 O through the tuyeres, and to the sensible heat of the gas injected in the middle zone.…”

“…This value combines the individual Chaudron diagrams of the Fe-O-C and Fe-O-H systems (Eqs. ( 30) and (31)) 19) by using the ratio of H 2 moles in the gas, x h (Eq. ( 32)).…”