Ion transport membrane (ITM) reactors have been suggested as a novel technology for fuel reforming and oxy-fuel combustion, integrating air separation and fuel conversion, in order to reduce plant complexity and the associated energy penalty (Hong et al., 2012). The presence of a fuel on the permeate side helps increasing oxygen chemical potential gradient across the membrane and oxygen permeation rates.
This paper addresses the field of fluidized bed biomass gasification: a globally endothermic process, requiring oxygen input to the reactor to assure autothermal behaviour. It is proposed to incorporate ITM in a biomass gasifier and a model is developed to study partial combustion of char as a means to provide thermal energy to the gasification reactions. Reference is made to a lab scale gasification rig: the gasifier temperature is imposed, and conservation equations are integrated across the fluidized bed close to the membrane. Char concentration is considered uniform everywhere, so that the reaction rate depends on local temperature and oxygen concentration. A pseudo-homogeneous reaction model is considered. The approach of interpenetrating continua is utilized to schematize the gas/solid fluidized bed properties.
The numerical evaluations show that oxygen transfer fluxes of the order of those exhibited experimentally by perovskite membranes, in the temperature range typical for fluidized bed gasifiers, can assure process feasibility and autothermal behaviour, without diluting the product gas with nitrogen, compressing air streams or adopting complex reactor schemes.