Integrating flue gas into membrane-based oxygen-enriched gasification of municipal solid wastes for enhancing waste-to-energy conversion

The waste-to-energy (WTE) gasification process converts municipal solid wastes (MSWs) into electrical energy, offering a sustainable solution for solid waste management. Oxygen-enriched gas (OEG) has demonstrated potential to enhance WTE conversion. However, the elevated oxygen content can result in localized overheating, posing damage to the gasifier. The integration of CO₂-containing gases, such as through flue gas recirculation (FGR), regulates gasification temperatures and improves operational stability. Despite that, flue gas contains nitrogen, and its impact on OEG gasification efficiency—especially the lower heating value (LHV) of syngas and carbon conversion efficiency (CCE)—remains elusive to date. Hence, this study aims to examine the effects of nitrogen in flue gas and FGR rate on syngas quality and carbon conversion. OEG gasification experiments were conducted using refuse-derived fuel (RDF) as MSW feedstock. As a baseline, membrane-based OEG with 45 % oxygen purity for gasification was employed, owing to the energy- and cost-efficiency of membrane air separation. Flue gas of two different concentrations was then introduced at varying recirculation rates to evaluate its impact on the OEG gasification process. Albeit a dilution effect caused by the non-combustible nitrogen gas, our findings suggest that flue gas with a 35 % CO₂ concentration and 10 % recirculation rate is technically viable. Under these conditions, syngas LHV reached 7.74 MJ/m³, while CCE improved by 6 %, as compared to OEG gasification without FGR. These results provide critical insights into the role of flue gas in optimizing OEG gasification for enhanced WTE conversion of MSWs.