Effect of reactant types (steam, CO₂ and steam + CO₂) on the gasification performance of coal using entrained flow gasifier

This study investigates the gasification behaviour of bituminous coal using different reactants of CO₂, steam and a mixture of CO₂ and steam under entrained flow gasification conditions at temperatures of 1000°C and 1200°C with atmospheric pressure. The major gas constituents of the syngas were measured using online micro-GC with a model number Varian 490, whereas the minor pollutant gases were analysed using Kitagawa gas detection tubes. A maximum carbon conversion of 86% was achieved under steam gasification at a temperature of 1200°C compared to 74% from CO₂ gasification. The higher carbon conversion from steam gasification is due to the higher gasification reactivity than CO₂ gasification. At 1000°C, the lower heating value (LHV) from steam gasification was determined to be 60%, 70% and 80% higher than that of CO₂ gasification using the reactant concentrations of 10, 20 and 40 vol.%, respectively. Using a stoichiometric 50/50 ratio of CO₂ and steam, the yield of H₂, CO and CH₄ were increased by 56%, 106% and 35% compared to that of pure CO₂ gasification. At 1000°C, the LHV under mixed reactant condition is close to the LHV from the pure steam gasification at 1200°C. In steam gasification, increasing the temperature by 200°C from 1000°C decreases the LHV by 17 and 10% using 10 and 20 vol.% steam. The higher heating value from steam gasification is due to the H₂ and CH₄-rich syngas compared to CO-rich syngas in CO₂ gasification. The BET surface area of the solid char from steam gasification is about 17 and two times higher than that of CO₂ gasification at 1000°C and 1200°C, respectively.