Design, construction and operation of a low-tar biomass (LTB) gasifier for power applications

Abstract

A low-tar biomass (LTB) gasifier with internal recirculation of pyrolysis gas and a separate combustor installed in the partial oxidation zone has been designed, developed and operated. The gasifier mixes the pyrolysis gases with gasifying air and burns the mixture in a combustor while maintaining a very low tar content in the producer gas. The resulting tar content is much lower than those obtained in previous studies for the same type of downdraft moving bed gasifier considering the heating value of the producer gas. The use of wood chips with a moisture content of 11–34 wt% as a fuel resulted in a very low tar content of 10.6 mg/Nm3 with a lower heating value of 4.56–4.96 MJ/Nm3. The operation of the LTB gasifier achieved a cold gas efficiency of approximately 82.7% on average, while maximum value was 91.9%. The temperature profile of the LTB Gasifier observed is relatively low compare to the typical downdraft moving bed gasifier. The obtained producer gas used directly in an internal combustion engine without observing deposits in the engine after operation. The behavior of the LTB gasifier can be described using a thermodynamic equilibrium model that has a good agreement with the model parameters.