Gasification of hazelnut shells in a downdraft gasifier

The potential offered by biomass to reduce greenhouse gas production is now being more widely recognised. The energy in biomass may be realised either by direct combustion use, or by upgrading into more valuable and useable products such as gas, fuel oil and higher value products for utilisation in the chemical industry or for clean power generation. Up till now, gasification work has concentrated on woody biomass but recently sources of other biomass with large energy production potential have been identified, namely hazelnut shells. Therefore, a pilot scale downdraft gasifier is used to investigate gasification potential of hazelnut shells. A full mass balance is reported including the tar production rate as well as the composition of the produced gas as a function of feed rate. Additionally, the effect of feed rate on the CV/composition of the product gas and the associated variations of gasifier zone temperatures are determined with temperatures recorded throughout the main zones of the gasifier and also at the gasifier outlet and gas cleaning zones. Pressure drops are also measured across the gasifier and gas cleaning system because the produced gas may be used in conjunction with a power production engine when it is important to have low pressure drop in the system. The quality of the product gas is found to be dependent on the smooth flow of the fuel and the uniformity of the pyrolysis, and so the difficulties, encountered during the experiments are detailed. The optimum operation of the gasifier is found to be between 1.44 and 1.47Nm3/kg of air fuel ratios at the values of 4.06 and 4.48kg/h of wet feed rate which produces the producer gas with a good GCV of about 5MJ/m3 at a volumetric flow of 8–9Nm3/h product gas. It was concluded that hazelnut shells could be easily gasified in a downdraft gasifier to produce good quality gas with minimum polluting by-products. It is suggested that, in view of ease of operation, small-scale gasifiers can make an important contribution to the economy of rural areas where the residues of nuts are abundant. It is also suggested that gasification of shell waste products is a clean alternative to fossil fuels and the product gas can be directly used in internal gas combustion engines, thus warranting further investment/encouragement by authorities to exploit this valuable resource.