Doctor Thesis (Mechanical Engineering)
A novel study on biomass-air gasification using a horizontal entrained-flow gasifier and catalytic processing of the product gas has been conducted. The study was designed to investigate the effect of catalyst loading on the product gas. The use of a horizontal entrained-flow gasifier reactor was used toassess the effect of the gasifier reactor orientation on the gasification process. Both experimental and computational fluid dynamics (CFD) approaches were employed. The gasification tests were conducted at 800oC and equivalence ratio of 0.23 while the product gas was catalysed at 350-400oC and a gas hourly space velocity (GHSV) of 8000h-1. Preparation and characterisation of wood powder and catalysts were performed using classical methods. Moreover, the syngas and tar composition were analysed using a gas chromatograph (GC) and GC-mass spectrometer (GC-MS) respectively. The research findings showed that maximum fuel conversion and cold gas efficiency using a horizontal entrained-flow gasifier were 99% and 70%respectively. The gasifier length can also be reduced from the common 1000-2000 mm to 500 mm. The catalysis study showedthat pumice and kaolin have limited catalytic effect on the product gas.However,doping with CeO2, ZrO2, CuO and NiO improved the syngas heating value, coking resistance and tar conversion. A notable increase in syngas LHVwas achievedusing ceria doped pumice (8.97MJ/Nm3) and copper doped pumice (8.66MJ/Nm3) compared to6.67 MJ/Nm3of non-catalytic test. For the tested catalysts, CeO2doped pumice exhibited highest coking resistance. Furthermore, catalytic tar conversion was mainly through cracking and partial oxidation reactions. The lowesttar yield was found to be 3.55g/Nm3using kaolin-ceria-zirconia catalystcompared to 14.92 g/Nm3of non-catalytic gasification. Tar reduction usinguntreated pumice was through adsorption and ranged4-6 g/Nm3.In general, the results of this study suggest that there exist a sensitivity to the gasifier orientation on the overall gasification process. It has also shown that metal oxides have both beneficial and detrimental effects of syngas composition. Although syngas heating value increased with increasing catalyst loading, H2showed a decreasing trend highlighting that further catalyst modification is required. Furthermore, pumice and kaolin can be utilised as catalyst support in the gasification technology. However, further experimental investigation on doping various catalytic metals and testing at different operating conditions are hereby proposed.