Effect of Ca/Fe additives on solution loss reactions of cokes in H₂O+CO₂ atmosphere

To examine the solution loss reaction properties of cokes with Ca/Fe additives in a hydrogen-rich blast furnace, the solution loss reactions of cokes were performed using a CO₂ (N₂) carrier gas with various percentages (0–30%) of H₂O vapor, and the effect of Ca/Fe additives on the Boudouard reaction (C + CO₂ = 2CO) and water–gas reaction (C + H₂O = CO + H₂) of cokes in a H₂O + CO₂ atmosphere was studied by examining the content of CO and H₂ in the off-gas. The results demonstrate that the coke reactivity has a positive linear relationship with the percentages of H₂O vapor in H₂O + CO₂ and H₂O + N₂ atmospheres, and the fitting slope k could be used to characterize the rate constant for the solution loss reaction of cokes in H₂O + CO₂ and H₂O + N₂ atmospheres. The k value for the solution loss reaction of the coke in the H₂O + CO₂ atmosphere is smaller than that of the coke in the H₂O + N₂ atmosphere, which shows that there is a competition between the reactions of H₂O and CO₂ with cokes in the H₂O + CO₂ atmosphere. Furthermore, the experimental reactivities of coke are smaller than their theoretical reactivities in the H₂O + CO₂ atmosphere, and the difference between the experimental and theoretical reactivities of the basic coke (BC) is less than those of the cokes with Ca/Fe additives (BC + Ca, BC + Fe), which shows that the Ca/Fe additives affect the competitive relationship of the reactions of CO₂ and H₂O with coke. Two inhibition factors, \alpha_\rmCO_2/\rmH_2\rmO and \alpha_\rmH_2\rmO/\rmCO_2 , are proposed to measure the degree of inhibition based on the difference in the k value for the cokes in H₂O + CO₂ and H₂O + N₂ atmospheres. The inhibition factor \alpha_\rmCO_2/\rmH_2\rmO could quantitatively characterize the inhibition degree of CO₂ on C + H₂O reaction in the H₂O + CO₂ atmosphere, and the inhibition factor \alpha_\rmH_2\rmO/\rmCO_2 could quantitatively characterize the inhibition degree of H₂O on the C + CO₂ reaction in the H₂O + CO₂ atmosphere. The \alpha_\rmCO_2/\rmH_2\rmO factors of BC, BC + Fe, and BC + Ca cokes are 0.260, 0.251, and 0.170, respectively, and the \alpha_\rmH_2\rmO/\rmCO_2 factors of BC, BC + Fe, and BC + Ca are 0.121, 0.217, and 0.263, respectively. The Ca/Fe additives in cokes reduce the \alpha_\rmCO_2/\rmH_2\rmO factor and increase the \alpha_\rmH_2\rmO/\rmCO_2 factor, showing that Ca/Fe additives can attenuate the inhibition degree of CO₂ on the C + H₂O reaction and improve the activity of the C + H₂O reaction, and the Ca additive has a greater impact on the competitive relationship between the reactions of CO₂ and H₂O with coke than the Fe additive. The catalytically active substances in Ca/Fe additives in cokes could be CaFe₂O₄ and Ca₂Al₂SiO₇, and the difference in the existing states of Ca/Fe elements in cokes causes the difference in the catalytic effect of Ca/Fe additives on the solution loss reactions of cokes.