Countercurrent fixed-bed gasification of biomass at laboratory scale

A laboratory-scale countercurrent fixed-bed gasification plant has been des igned and constructed to produce data for process modeling and to compare t he gasification characteristics of several biomasses (beechwood, nutshells, olive husks, and grape residues). The composition of producer gas and spat ial temperature profiles have been measured for biomass gasification at dif ferent air flow rates. The gas-heating value always attains a maximum as a function of this operating variable, associated with a decrease of the air- to-fuel ratio. Optimal gasification conditions of wood and agricultural res idues give rise to comparable gas-heating values, comprised in the range 5- 5.5 MJ/Nm(3) with 28-30% CO, 5-7% CO2, 6-8% Hz, 1-2% CH4, and small amounts of C-2- hydrocarbons (apart from nitrogen). However, gasification of agric ultural residues is more difficult because of bed transport, partial ash si ntering, nonuniform flow distribution, and the presence of a muddy phase in the effluents, so that proper pretreatments are needed for large-scale app lications.