Design and development of a small-scale biomass downdraft gasifier

Abstract

This study focused on the design and testing of a downdraft gasifier. The gasifier design was based on a combination of the Imbert and stratified models with some modifications. Sizing of the gasifier was done using empirical relations and some experimental data relating to specific gas generation rate, biomass flow rate, throat diameter and reduction zone diameter etc. The thermal capacity of the gasifier was set at 5 kW. A cyclone separator, an air-cooling unit and a filter unit (containing wood shavings) were coupled to the gasifier’s reactor to purify the produced syngas. The gasifier system was tested in a forced draught mode using air as the gasifying medium. The feedstock conversion rate of the gasifier was 1.25kg/hr for wood chunks (10-70mm) and 2.1kg/hr for wood shavings (2-5mm). The syngas produced for both types of wood residues burnt with stable blue flames, indicating minimal tar percentage in the syngas. This signifies that the produced syngas can be safely utilized not only for cooking but also in internal combustion engines to generate electricity.

Keywords: Bioenergy, Biomass, Downdraft gasifier, Gasification, Renewable energy, Synthesis gas, Wood waste