Air gasification of biogas-derived digestate in a downdraft fixed bed gasifier

The results showed that no ash slagging was observed and therefore it is feasible to operate digestate gasification under 800 °C and ER ranging from 0.25 to 0.30. High temperature favored gas production, 800 °C is proposed for digestate gasification in the present study. ER with a medium value improved gas quality and cold gas efficiency (CGE), and the optimal LHV of 4.78 MJ/N m3 and CGE of 67.01% were obtained with ER of 0.28. High ER favored the increase of gas yield and decrease of tar concentration, and the optimal gas yield of 2.15 N m3/kg and tar concentration of 1.61 g/N m3 were achieved with ER of 0.30. Improved molar ratio of H2/CO varying from 1.03 to 1.08 was obtained at 800 °C, indicating gaseous product has the potential for chemical synthesis processes (1 < H2/CO < 2). The byproducts biochar and ash could be applied on land as fertilizer.