Technical assessment of the functional and operational performance of a fixed bed biomass gasifier using agricultural residues

Abstract: Currently, there is a general concern about the effects of CO2 emissions onthe atmosphere that are the major cause of the global warming phenomenon.This situation has necessitated a trend towards the reduction on thedependency on fossil fuels, a challenge facing the present generation. Biomass gasification is the thermal chemical conversion of biomass into acombustible gaseous product (producer gas) by the supply of a gasificationagent which can be air, oxygen or steam. Biomass gasification has thepotential of contributing to the growing energy needs of the world particularlyas a renewable energy technology. The potential sustainable global suppliesof biomass encompassing sustainable recoverable residues including cropresidues, forest residues and biomass plantations is 293.3 EJ/year. This research, therefore, has investigated the performance of a fixed bedgasifier using various agricultural residues as the feedstock. The atmosphericgasifier was operated in downdraft mode. The agricultural residuesconsidered in this research include groundnut shells, coffee husks, rice husks,bagasse and maize cobs. The proximate analyses to determine the physicalcharacteristics of the agricultural residues such as the moisture content, ashcontent, bulk density and particle size were carried out. Also, the temperaturevariations in different regions of the gasifier were investigated. Gascomposition was determined at different sampling intervals. Finally, thegasification parameters such as gas flow rate, gasification rate, turn downratio; equivalence ratio and cold gas efficiency were calculated. The highest gasification rates were obtained in the ranges of 5.9 – 17.9 kg/hrwhile the average gas lower heating values were in the range of 3.2 –4.7MJ/Nm3. The analysis of the functional and operational performance was done for onlydowndraft mode of operation because of the non technical limitation of theflexible tube making the connection from downdraft to updraft mode ofoperation becoming rigid due to the effect of thermal stresses over the yearsand it has no replacement.