Heat balance of fluidized bed gasifier with triple-beds and dual circulation

A new type of circulating fluidized bed gasifier has been proposed. The main features of this proposed gasifier are the adoption of a triple-beds structure (comprising pyrolyzer, gasifier, and combustor), and a circulation path for tar-absorbing material that is separate from the circulation path for the fuel and silica sand. Independent circulation systems are employed for the fuel system and for the tar-absorbing particles, and the pyrolyzer and gasifier each have a two-stage fluidized bed. This new gasifier is called “a fluidized bed gasifier with triple-beds and dual circulation”. As the second stage towards development of the proposed new type gasifier, based on the data of the fundamental experiments obtained in our previous study, the parameters for obtaining higher cold gas efficiency as well as the particle circulation rates capable of sustaining desired temperatures in each furnace were clarified by the heat balance. As a result, in the proposed circulating fluidized bed gasifier with a capacity of 5 t/d, a particle circulation rate of 3.1 t/h in the upper stage, and that of 5.8 t/h in the lower stage respectively was required to maintain temperatures of 973 K in the pyrolyzer, 1073 K in the gasifier, and 1173 K in the combustor. Under these conditions, obtaining a cold gas efficiency of more than 70% was possible.