Gasification enhancement and tar reduction using air fogging system in a double walled downdraft biomass gasifier

Abstract

Air-blown gasifier suffers from lower heating value of producer gas (PG) compared to steam gasification, but at the expense of the addition of steam boiler for the latter. The performance of an air-blown double walled downdraft biomass gasifier was characterized experimentally. Air fogging unit was added to the annulus of the gasifier allowing for superheated steam to be generated as additional oxidizer. Steam-to-biomass (S/B) ratio has been introduced to investigate the optimum amount of injected water needed to produce the optimum quality of PG. Comparisons were made on the composition and heating value of PG with and without water injection which were analysed and calculated with the aid of gas chromatograph. Highest heating value of PG was 4.72 MJ/Nm3 at S/B ratio of 0.2 which corresponded to about 10% increment. Various S/B ratios were investigated in this study in the range of 0.1–0.3. However, as S/B ratio exceeded 0.25, it resulted adversely to the quality of PG. The effect of water injection on tar contamination in PG was also investigated. Tar reduction was proportional to the amount of the injected water resulting in about 8% reduction at maximum S/B ratio corresponding to 0.65 g/m3 tar yield.