Allothermal Fluidized Bed Reactor for Steam Gasification of Biomass

Abstract

This article evaluates a hybrid multi-compartment cyclic fluidized-bed reactor for the allothermal steam gasification of biomass. The concept combines space and time delocalization to approach an ideal allothermal gasifier. Thermochemical conversion of biomass in time and space sequences of steam biomass gasification and char/biomass combustion is envisioned in which the exothermic combustion compartments provide heat into an array of interspersed endothermic steam gasification compartments. This concept may enhance unit heat integration and thermal efficiency while procuring nitrogen-free synthesis gas without requiring addition of oxygen (or air) to the steam gasification compartment nor contact between the flue gas and the synthesis gas. The strengths and weaknesses of existing autothermal and allothermal gasification technologies are analyzed and a new allothermal reactor concept is introduced. Elements of gasification chemistry, fluidization hydrodynamics, and heat transfer requirements are described that are relevant for the design of the multi-compartment fluidized-bed gasifier/combustor. A preliminary design of the experimental hot mock-up is presented, including a discussion of process diagrams and mass balance.