Influence of Potassic Additives on Sludge Gasification Under Model Flue Gas Atmosphere

In this study, the influence of potassic additives (K2CO3 and biomass ash (BA)) on sludge gasification under model flue gases was investigated. Two model gases consisting of O2/CO2/N2 and O2/CO2/H2O/N2 were used as gasifying agents. Under O2/CO2/N2 atmosphere, the lower heating values (LHV) of produced gas were in a range of 3.07–3.79 MJ/Nm3, and cold gas efficiency (CGE) were in a range of 47–66%. When steam was introduced into the gasification atmosphere, the efficiency of the process significantly improved. LHV of the produced gas under O2/CO2/H2O/N2 atmosphere was in a range of 6.48–7.18 MJ/Nm3, and CGE was in a range of 73–88%. K2CO3 had an obvious catalytic effect on sludge gasification process. Additionally, K2CO3 had stronger catalytic effect under steam-free atmosphere and it was better in promoting CO generation when compared with BA. BA exhibited the ability to increase gas yield under steam-free atmosphere, while it only had a slight effect under steam-containing atmosphere. Based on continuous monitoring of gas during gasification process, LHV of the produced gas could be increased by nearly twofold, possibly up to 11.96 MJ/Nm3, by controlling the proper reaction time (10–12 min) to prevent the dilution effect from excessive gasifying agents.