An assessment of the gasification characteristics of some agricultural and forest industry residues using a laboratory gasifier

Abstract

Gasification means here the reaction of solid fuels with air to yield a low calorific value gas, suitable as a fuel. The solid fuels considered are agricultural and forest industry residues, biomass fuels. Biomass-derived gas is an alternative to natural gas.

A laboratory-scale downdraft gasifier was used to study the gasification properties of certain biomass fuels. The grate is the most critical part of the gasifier. Two designs were tested: a rotating eccentric grate and a perforated steel basket. The latter was specifically designed for use with granular fuels such as mulled walnut shells.

Batch tests were performed with different biomass fuels and at varying fuel consumption rates. Biomass fuel consumption rate was determined by mounting the gasifier on a platform scale and weighing it before and after a run. The composition of the generated gas and the mass and heat balances were determined. Substantial closure errors are reported. These are considered to be the result of tars in the gas which were not accounted for.

Yields varied from 75.5% in the case of walnut shells to 46% for rice hulls. With a biomass fuel consisting of a mixture of two sizes of walnut shells, yields in excess of 80% were recorded at high fuel consumption rates.

Some practical aspects concerning the gasification of biomass fuels and problems associated with cotton gin trash, rice hulls, and wood residues are discussed.