Abstract:
Gasification, the important and promising technologies for biomass conversion, can provide a high overall thermal efficiency. Conventional gasification typically employs a partial oxidation process using air. However, the calorific value of product gas is relatively low because of the dilution of product gas by nitrogen in air. The aim of this study is to develop a new gasifier based on a concept of separation of combustion zone and gasification zone to increase the calorific value of the product gas. The new gasifier, dual-bed gasifier (DBG), consists of bubbling fluidized bed and a two-stage moving bed reactor. The former served as a combustor to provide the energy for endothermic gasification reactions in gasification zone while the latter served as a gasifier to produce syngas. Sawdust was used as feedstock in this study. The hydrogen content of 31.14 vol %, carbon monoxide content of 23.79 vol % and the nitrogen content of 2.87 vol % could be obtained by using S/C ratio of 1 at 700°C without using catalyst. The high hydrogen yield and extremely low nitrogen yield lead to considerably high heating value (12.52 MJ/N cb.m.) of product gas. Carbon conversion into gas is 64.51% and cold gas efficiency is 56.66%. The result verifies that this new gasifier, DBG, can produce high quality of product gas that can be use as direct fuel or be subjected to gas to liquid processes for synthesis of liquid fuels.