Thermodynamic analysis of synergistic coal gasification using blast furnace slag as heat carrier

In this paper, a thermodynamic analysis of the synergistic coal/CO2/H2O gasification process with BFS (blast furnace slag) as heat carrier was performed using the Gibbs free energy minimization approach through Lagrange multiplier method. The effect of temperature, pressure and C/CO2/H2O were investigated. Carbon, CO2 and H2O conversion, H2 and CO yield, and H2/CO ratio were used to characterize the synergistic gasification performance. The results showed that the atmospheric pressure was preferable for coal gasification and the increasing of temperature caused the increase in carbon conversion and syngas production. The optimal temperature of the synergistic gasification was 800-900 °C. Not only did it ensure the coal gasification reaction completely, but also it recovered the BFS waste heat effectively. The results clearly showed that the addition of H2O and CO2 could lead to the reduction of the carbon residue and increase of the production of H2 and CO, respectively. Meanwhile, it was beneficial to reduce the waste heat using to heating extra steam and enhance the coal/CO2 gasification reaction rate by controlling the addition of CO2 and H2O reasonably. Moreover, the production syngas application was also investigated by changing the relative CO2/C ratio and H2O/C ratio in the feed to modify the H2/CO ratio.