Modelling the performance of a laboratory-scale fluidised-bed gasifier

Abstract

The long term supply of relatively low-cost electricity within South-eastern Australia is favoured by the efficient utilisation of low-rank coal reserves within this region. A number of advanced technologies have been considered by the Cooperative Research Centre (CRC) for Clean Power from Lignite, and its predecessor, with the most promising of these options all relying on the high-pressure, gasification of lignite. An ongoing focus of the Centre’s Advanced Gasification program is its mathematical model of a bubbling fluidised bed gasifier (FBG). This model has been developed previously, and partially validated, using literature data obtained for mainly high-rank coals. While the model has been successfully applied to gain further insight into experimental observations in some limited instances, it has not yet been rigorously validated for Australian brown coals. The Centre has recently commissioned, and is now operating, a 200-mm laboratory-scale, atmospheric-pressure bubbling fluidised bed gasifier with the specific intention of collecting in-bed and process data for validation of the FBG model. An air-dried mixture of low-ash Victorian lignite is gasified using air and steam. Gases are sampled using water-cooled probes at various locations within the bubbling bed and in the freeboard. Gas samples are analysed for major products (CO, H2 and CO2), minor products (CH4 and higher hydrocarbons) and pollutant species (e.g. H2S, SO2, COS, etc) using a suite of analysers that includes a Fourier transform infrared (FTIR) spectrometer and a micro-gas chromatograph (GC). The product syngas is also sampled and analysed after exiting the gasifier. Other data necessary for the model validation, such as pressure, temperature, and feed flow rates, are also collected. This paper reports on the first phase of this validation program and discusses deficiencies of the existing theoretical model when describing the performance of a real bubbling, fluidised-bed gasifier.