Refining Contribution at Hotspot and Emulsion Zones of Argon Oxygen Decarburization: Fundamental Analysis Based upon the FactSage-Macro Program Approach

Abstract

Examining the kinetics involved in the Argon Oxygen Decarburization (AOD) process, especially in the hotspot and emulsion zones within distinct reactors, can offer a deeper understanding of the refining mechanism in stainless-steelmaking. A predictive dynamic model has been formulated to estimate the effects of different refining processes, encompassing decarburization, desiliconization, demanganization, and chromium removal. The model includes a sub-model for heat loss calculation. The FactSage™ software, along with its macro programming capability, was utilized to incorporate thermochemical and kinetic information into the model. The model forecasts that the predominant chromium removal occurs within the hotspot zone, while carbon, silicon, and manganese removals occur in both the hotspot and emulsion zones. The predictions regarding the transient compositions of steel and slag, as well as the temperature of the steel bath, align with the plant data (Average of five heats), showcasing consistency.

Appendices

Appendix 1

Initial, A = B = C = 1

$$\alpha ={\text{A}} {\left(\frac{{E}_{{\text{total}}}^{{\text{O}}}}{8000}\right)}^{0.5}$$

(A1)

$${\beta =\text{ B}\left(\frac{{E}_{{\text{total}}}^{{\text{O}}}}{8000}\right)}^{0.5}$$

(A2)

$${\delta =\text{ C}\left(\frac{{E}_{{\text{total}}}^{{\text{O}}}}{8000}\right)}^{0.5}$$

(A3)

Now model was run according to Figure 2, corresponding to the input parameters outlined in Table I.

The convergence criteria obtained from plant trials are applied both before and at the end of the reduction stage of the process

Now, to meet converge criteria A, B, and C values changes

Best fitted with plant data when A = 0.09, B = 0.3, and C = 0.6 only. I.e., we finally got the Eqs. [24–26]

Appendix 2

Heat Loss Model

The heat of dissolution of C, Si, Mn, Cr, and Ni is 2.11, − 4.67, 0, 0.40, and 0 KJ/kg

The specific heat of Fe, C, Si, Mn, and Cr is 0.945, 2.278,3.064,1.258, and 1.687 KJ/kg

The heat of the formation (1600 °C) of SiO₂, MnO, Cr₂O₃ and FeO are 37.5, 7.1, 11.6 and 6.05 MJ/kg

The sensible heat of steel, CO, CO_2, and slag is 1.413, 1.86. 1.86 and 2.915 MJ/kg

Heat of formation of CaO–SiO₂ is 4.5 MJ/kg of Si

$$ \begin{aligned} {\text{Heat input}} = & {\text{Sensible heat of hot metal + heat of reaction }} \\ & ={\text{ enthalpy of hot metal + decarburization + heat of combustion of CO gas to C}}{{\text{O}}_{2}} \\ &+{\text{oxidation of silicon, manganese, and chromium + formation of FeO }} \\ & + {\text{formation of CaO}}{\text{.Si}}{{\text{O}}_{2}} \\ \end{aligned} $$

(A4)

$$ \begin{aligned} {\text{Heat output = }} & {\text{ enthalpy of steel + enthalpy of CO gas }} \\ & \,{\text{ + enthalpy of C}}{{\text{O}}_{2}}{\text{gas + enthalpy of slag}} \\ \end{aligned} $$

(A5)

By solving the above two Eqs. [A4] and [A5], we get heat input = 2207.3 MJ and heat output = 1891.7 MJ.

Therefore, heat losses = 315.6 MJ/THM

Total heat losses of the system = 142 × 227.89 = 44815.2 MJ

Heat loss per time step of process = 1120.38 MJ