| Summary: | Heat recirculation in combustion enables low grade fuels to be burnt, raises the thermodynamic efficiency and burning rate above normally burning mixtures, and minimises high temperature pollutants. Spouted beds have been used as heat recirculating burners by Khoshnoodi et al. (1978) and Arbib et al. (1981). Scaling-up the bed for the utilisation of liquid and solid fuels raises two problems; the high bed pressure drop at start-up and the flaring of the reactant gas above the descending particles in the annulus. Initial work on a multiple spout bed confirmed the limitations due to these difficulties. Its characteristics were studied, including particle-gas interactions between the spouts. The installation of a solid "draft-tube" above each spout as a means of reducing these problems substantially was considered and a large bed with a mobile draft-tube, capable of operation under high temperatures, was designed. A series of cold experiments involving variations of tube-length, bed depth, particle recirculation gap and particle size were performed to characterise the bed. Combustion experiments followed with methane-air mixtures over a wide range of flow. It was found that a prolonged bed preheat period was necessary prior to burning at slightly above two-thirds of the normal lean flammability limit, compared to shorter times experienced in smaller spouted bed combustors. Heat transfer coefficients in the spout and the flame fountain regions were predicted, using a heat balance model and available data. A design for the ultimate burner for the combustion of low grade liquid and solid fuels based on this work is presented.
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