Efficient utilization of high CO2 landfill-gas for syngas generation: Ultra-rich combustion pathways study in porous media reactor via CFD simulation

Abstract

The current investigation explores the possibility of extracting syngas from low-calorific value landfill-gas rich-combustion with pure O₂, which contains a considerable amount of CO₂ in its composition as an effective strategy in CO₂ utilization. The results illustrate that enhancement in mixture velocity leads to a notable increment in syngas energy conversion efficiency from 36.9 % to 44.14 %. Furthermore, it was observed that the maximum rate of H₂ production occurs at an equivalence ratio of 2.2, followed by a subsequent decrease until the end of the studied interval. At a mixture velocity of 25 cm/s, CH₄ and CO₂ conversion ratios reach a maximum of 89.02 % and 42.85 %, respectively, alongside the highest syngas production efficiency. Moreover, with an equivalence ratio of 1.6 and a fuel mixture containing 70 % CH₄, the highest achievable syngas composition was found to be 0.3277 for CO, 0.2841 for H₂, 0.0676 for CH₄, and 0.2534 for CO₂, indicating useful conditions for syngas production. Eventually, reaction pathways analyses revealed that the hydrogen abstraction reactions of hydrocarbon species by H radical which majorly progress through direct CH₄ to H₂ conversion route, and hydrocarbon recombination routes have a key role in H₂ production from landfill gas. Moreover, for landfill gas with high CO₂ content, direct CO₂ to the CO reduction route is determinative. Conversely, when the CH₄ content of landfill gas is high, hydrocarbon recombination followed by ketenyl radical formation and decomposition to CO is the primary pathway in different mixture equivalence ratios.