Tar removal from the producer gas of a small scale downdraft gasifier using a fatty acid based,wet packed-bed scrubber

Small scale gasification combined heat and power (CHP) systems offer an alternative to diesel fuelled generators for power generation in remote communities and industrial sites. Tar and particulates in the producer-gas can damage the internal combustion engine generator and increase operation and maintenance costs. In this work, we present a novel trickle-bed scrubber using filtered waste cooking oil as a cost effective and easy-to-operate gas clean-up method for a small CHP system. The performance of the trickle-bed scrubber was compared against a packed-bed filter utilizing woodchips in a 20 kW_th downdraft gasifier. Used-cooking oil was selected as the solvent and woodchips as the bed-material as these are readily available, inexpensive, and can be recycled in the gasifier as fuel. A woodchip packed-bed filter reduced the tar and particulate matter (PM) in the producer gas from gasification of spruce chips (11% moisture) from 1.6 to 1.4 g/Nm³ and from 0.16 to 0.087 g/Nm³ respectively. The trickle-bed scrubber was able to reduce the tar and PM in the producer gas from gasification of pinewood (8% moisture) from 1.38 to 0.28 g/Nm³, and 0.209 to 0.082 g/Nm³, respectively. Tar and PM removal efficiency improved by 60% and 29% respectively. Components such as benzene, toluene, naphthalene, and biphenylene were the major tar components. After passing the trickle-bed, most tar was removed, with a preference for removal of multi-ringed aromatics and gravimetric tars. Parameters such as the tar and particulate concentration, feedstock moisture content, and feedstock source affect the performance of the gas clean-up system.