A preliminary evaluation of different residual biomass potential for energy conversion in a micro-scale downdraft gasifier

•Six different biomasses were tested in a lab-scale downdraft gasifier.•Elemental and ash analyses were performed on biomass and char.•The contaminant amount in the gas and the gasification efficiency were measured.•Pistachio shell, hemp and driftwood performed acceptably in terms of efficiency. Residual biomass can be a promising alternative to replace fossil fuels for energy production. Through small-scale gasification systems it is possible to obtain a fuel gas from solid biomass that can be used for electrical and thermal energy generation. In this work, six different biomasses (five agro-industrial residues and A1 ENplus pellets) were tested in a lab-scale prototype. For each tested feedstock, elemental and ash analyses were carried out. The contaminant amount in the produced gas was measured as well as the mass and energy fluxes to calculate the gasification efficiency. The ratio between the pressure drop across the reactor and the gas flow raised to the square was introduced to compare the gasifier behavior at different power outputs. The results showed that with the exclusion of the tests run with cork, the other tested agro-industrial residues (pistachio shell, hemp and driftwood) performed acceptably in terms of efficiency, providing also a char with a carbon content over 70% as by-product.