Assessing the impact of downdraft gasifier geometry on syngas characteristics

This study investigated the effect of downdraft gasifier throat design on syngas quality. Parameters examined during investigation include throat inclination, biomass type as well as moisture, and equivalence ratio. Corn cobs and carpenter waste wood at 5% moisture level using an inlet airflow rate ranged between 10–15 ms −1 were processed in downdraft gasifier. The oxidation chamber was provided with seven nozzles each having diameter 12 mm. Trials were conducted using single throat (having inclination 30°,40° and 50°) and dual throat configuration (fixed at 50° for second throat). The maximum syngas energy values using air as oxidizing medium for corn cobs and waste wood in single throat gasifier design was found to be 6.39 and 6.51 MJ/Nm 3 . In contrast, the dual throat configuration yields energy values of 7.14 and 7.20 MJ/m 3 for the same feed stock. The experiment in dual throat gasifier recorded increased in syn gas yield to 2.94 m 3 for corn cobs and 2.62 m 3 for waste wood as compared to 2.91 m 3 and 2.48 m 3 in the single-throated setup. Moreover, an average tar production of 2.2 and 1.8 g/Nm 3 was observed in dual throat design using corncob and waste wood that was less than single throated set up. The observed superficial gas residence time inside the reactor reduction zone during experimentation ranging 2.3–3.5 ms for the single-throat design and 3.3–4.9 ms for the dual-throat configuration. The dual-throat geometry increases residence time by approximately 40%. The results concluded that dual throat increases thermal cracking during the gasification processes, leading to an improved syngas quality and better biomass conversion efficiency. The results also confirm that downdraft gasifiers having dual throat geometry offer a sustainable solution in meeting the thermal and power needs of the rural community using local available biomass resources.