Theoretical study on coal gasification behavior in CO2 atmosphere driven by slag waste heat

Blast furnace slag, a main by-product of ironmaking process, contained high-quality sensible heat, accounting for almost 30 % of total energy consumption in iron and steel industry. This paper proposed CO2 coal gasification method aimed at recovering waste heat from blast furnace slag. Based on Gibbs free energy minimization, influence of temperature, CO2/C, pressure and steam were investigated. Under optimal operating conditions at 1023-1198 K, CO2/C of 1.5-2.0 and atmospheric pressure, total amount of syngas was 2.78 kmol, with 67.1 % CO and 8.79 % H2. Addition of steam could adjust compositions of syngas. H2/CO of syngas reached 1.0, 1.5 and 2.0 when H2O(g)/CO2 were 1.45/0.55, 1.73/0.27 and 1.95/0.05, which could be used as organic raw materials for chemical industry. Meanwhile, energy and exergy efficiencies of coal gasification were found to be 63.84 % and 62.58 %, respectively, under optimal operating conditions. For different syngas products, when H2O(g)/CO2 was 1.95/0.05, exergy loss was the lowest, with internal and external exergy loss amounting to 31.80 % and 2.16 % respectively. These works provided theoretical guidance on use of the coal gasification reaction for recovering waste heat from blast furnace slag and contributed to the achievement of the strategic goal of CO2 energy saving and emission reduction.