Influence of biomass materials and gas flow rate on downdraft gasifier performance

In this article, the performance of a 20 kWe open top downdraft biomass gasifier has been modeled using EQB computer code. EQB program, consists of six modules (i.e., fluid flow, heat transfer, drying, pyrolysis, and oxidation and reduction reactions), has been used to describe physical and chemical processes of downdraft biomass gasifier. A brief description of EQB, its strength and limitations are also highlighted. Model predictions fitted well with measurements. The influence of gas flow rate and type of biomass materials (i.e., soft-wood, ordinary-wood and hard-wood) on dry gas composition, calorific value, conversion efficiency, temperature profile, and gasifier power output has been investigated. Although, results for gasifier operated on different biomass materials give relatively low fluctuations, even though, hardwood is identified better class of wood material.

I. Introduction

The degrading environmental and energy crisis have been a matter of serious concern, the world over. In tropical countries like India, biomass resources are abundant. It is identified as an ideal solid fuel for the decentralized power production systems. Thus, volarization of waste and biomass to produce green energy is badly needed for its more productive utilization. The agricultural wastes and woody biomass can be transformed into combustible gaseous mixture via gasification (i.e., thermal route). It is an efficient and environmentally benign route with neutral CO₂ production. The gasification process takes place in well designed gasifiers, where solid biomass undergoes drying (moisture removal), thermal-degradation, oxidation and reduction to generate producer gas. It is a mixture of combustibles viz. CO, H₂ and CH₄; and diluents viz., CO₂ and N₂. The gas also contains tar and ash. Among the available designs for fixed bed gasifiers, downdraft configurations have high potential to generate relatively clean gas. Thus, presently, it is the best choice to decentralized systems in low power range (i.e., gasifier system) to cater the power needs of rural and urban society.