Pilot plant air-steam gasification of nut shells for syngas production

Autothermal gasification of hazelnut and almond was carried out and the performances of a pilot plant with a feeding rate of 20-30 kg/h were evaluated. Air, mixes of air with steam and oxygen with steam were used as gasification medium; the gas flows corresponded to different equivalence ratios of combustion, ER(O2), and water reaction, ER(H2O). The recording of the thermal profile inside the reactive bed during the runs made it possible to highlight a sequence of exothermic and endothermic reactions. In the plant tests, the residues were completely converted in gaseous and liquid energy carriers with a cold gas efficiency (CGE) ranging from 61% to 75% while the production of biooil ranged from 90-250 g/kg of fed nutshell (dry basis). The molar ratio H2/CO in syngas increased by using steam as co-gasification agent. Steam was necessary to stabilize the process in the case of using oxygen as main gasification agent. Oxy-steam gasification also provided the best results in terms of syngas heating value and thermal power output of the plant. The tar yield was inversely correlated to the residence time of the gas in the bed, in according with a zero order reaction for tar cracking into incondensable hydrocarbons. © 2017, ETA-Florence Renewable Energies. All rights reserved.