Biomass Gasification in a Fast Internal Circulating Fluidised Bed (FICFB) Gasifier

At the University of Canterbury a 100 kW FICFB gasification system has been built, commissioned and operated to characterize the product gas under a range of conditions. This system was chosen for advantages over fixed bed types and was based on the successful design originally developed by the Vienna University of Technology. It incorporates two closely coupled fluid bed stages, a bubbling bed for gasification and a fast circulating bed for combustion. This duality provides a medium calorific value producer gas suitable for use as a fuel in a heat engine. Steam gasification is used in the bubbling fluid bed at 800 C to form a product gas rich in hydrogen and low in nitrogen with some residual char. The char is transferred with bed material to the circulating fluid bed, where it is combusted along with LPG to heat the bed material. The hot bed material is circulated back to the gasification stage providing heat for the endothermic gasification reactions. Currently the gas is being directly burnt in an afterburner but will require cleaning and removal of tars before it can be burnt in an engine generating set. The results will be used to select suitable gas cleaning and tar removal technology and provide a database for scale up and computer modelling in support of the wider program. Variable conditions include, the biomass to steam ratio, circulation rate and bubbling bed temperature. Characteristics of the product gas measured include the gas composition and tar composition.