Simulation of Biomass Gasification in Fluidized Bed Using Aspen Plus

Gasification is a thermo-chemical process to convert carbon-based compounds such as biomass and coal into a gaseous fuel. Among the various types of gasification methods, fluidized bed gasification is one which is considered as more efficient method than others as biomass is fluidized in a mixture of air/oxygen and steam. In the present study, a comprehensive steady state process model has been developed for biomass gasification in atmospheric fluidized beds using Advanced System for Process Engineering (ASPEN PLUS) simulator. Three ASPEN PLUS reactor models namely, RYIELD for drying and decomposition of biomass into its elements, RGIBBS for achieving both chemical and phase equilibrium of volatile matter available in biomass and RCSTR for carrying out char gasification have been used. The fluidized bed reactor has been divided into finite small elements because there exists change in number of moles, change in partial pressures of all the components along the height of the reactor as the reactions take place inside the reactor. To consider the change in superficial velocity which results from change in number of moles along the height of the reactor, each of these elements has been simulated by one RCSTR. Finally, the effects of steam to biomass ratio, equivalence ratio and temperature on the composition and lower heating value of product gas have been studied. Using optimization tool available in Aspen Plus, the optimum values of steam to biomass ratio and equivalence ratio have been found out. Keywords— Biomass, gasification, Aspen Plus, gas composition, heating value, optimization, steam to biomass ratio and equivalence