Systematic approach to determination of optimum gas-phase mass transfer rate for high-gravity carbonation process of steelmaking slags in a rotating packed bed

In order to reduce CO2 emissions and waste generation from the steelmaking industry; a high-gravity carbonation process via rotating packed bed (RPB) was developed using cold-rolling mill wastewater (CRW) and basic oxygen furnace slag (BOFS). Since mass transfer among phases is believed to be a key to effective carbonation for CO2 fixation, in this study, a mass transfer model for the high-gravity carbonation process was developed based on two-film theory. The mass transfer characteristics including overall gas-phase mass transfer coefficient (K(G)a) and height of a transfer unit (HTU) were determined accordingly. The results indicated that the mass transfer resistance of carbonation using BOFS/CRW in an RPB was mainly lay on the liquid side. In addition, the effect of key operating variables such as rotating speed, slurry flow rate, gas flow rate, and liquid-to-solid (L/S) ratio on mass transfer characteristics was evaluated. The developed model was validated with the experimental data, where the experimental K(G)a values lay within +/- 20% of the values estimated. Based on the obtained results, empirical models of K(G)a and HTU values were established. Furthermore, response surface methodology (RSM) was applied to optimize the high-gravity carbonation process from the viewpoint of mass transfer characteristics. The obtained RSM results were in fairly good agreement with the results of the developed model based on the two-film theory. Based on the theoretical models and statistical analyses, the optimum gas-phase mass transfer rate for high-gravity carbonation process of steelmaking slags in an RPB was graphically determined. (C) 2015 Elsevier Ltd. All rights reserved.