Landfill gas upgrading with pilot-scale water scrubber: Performance assessment with absorption water recycling

A pilot-scale counter current absorption process for upgrading municipal solid waste (MSW) landfill gas to produce vehicle fuel was studied using absorption, desorption and drying units and water as an absorbent. Continuous water recycling was used without adding new water to the system. The process parameters were defined by a previous study made with this pilot system. The effect of pressure (20–25 bar), temperature (10–25 °C) and water flow speed (5.5–11 l/min) on the upgrading performance, trace compounds (siloxanes, halogenated compounds) and water quality were investigated. Raw landfill gas flow was kept constant at 7.41 Nm3/h. Methane (CH4) and carbon dioxide (CO2) contents in the product gas were 86–90% and 4.5–8.0% with all studied pressures and temperatures. The remaining fraction in product gas was nitrogen (N2) (from 1% to 7%). Organic silicon compounds (siloxanes) were reduced by 16.6% and halogenated compounds similarly by 90.1% by water absorption. From studied process parameters, only water flow speed affected the removal of siloxanes and halogen compounds. The absorbent water pH was between 4.4–4.9, sulphide concentration between 0.1–1.0 mg/l and carbonate concentration between 500–1000 mg/l. The product gas drying system reduced the siloxane concentration by 99.1% and halogenated compounds by 99.9% compared to the raw landfill gas. In conclusion, the pilot-scale gas upgrading process studied appears to be able to produce gas with high energy content (approx 86–90% methane) using a closed water circulation system. When using a standard gas drying system, all trace compounds can be removed by over 99% compared to raw landfill gas.

► Water can be recycled completely when an effective under pressure desorption system and water cooler are used.
► The highest average CH4 concentration achieved was 90.2% by volume. The highest CO2 removal efficiency was 88.9%.
► Water absorption with water recycling removes siloxanes on average 16.6% from the studied landfill gas.
► High degree of removal of TMS and D5 and significant enrichment of L2 and L3 was observed.
► Commercial gas drying system can remove most siloxanes from upgraded landfill gas (approx. 99.1%).