Abstract
The British Coal Corporation and the University of Surrey, England, are collaborating to develop a model to describe the bubbling behaviour of a fluidised bed combustor. The model is based on the Clift and Grace model of bubble interaction and coalescence, but is being extended to incorporate the effect of heat transfer tubes in the bed. As in any such model, a necessary boundary condition is the size, frequency and sequence of bubbles forming at the distributor. Relatively little data on bubble formation is reported in the literature, especially under conditions such as those obtaining in a combustor where a cold gas stream enters a hot bed. This paper reports an experimental investigation of bubble formation in a 0.3m square atmospheric pressure coal-fired combustor. The distributor comprised nine vertical 'standpipes', ie capped tubes with horizontal radial holes. A 150mm diameter silica window was mounted in the bed wall to enable high-speed video tape recording of the formation of bubbles at one of the standpipes. Transient gas flow and pressure in three of the standpipes were measured and related to bubble formation. The work was undertaken to provide some elucidation of the mechanisms of bubble formation from standpipe distributors and also some of the information necessary for algorithms to simulate the air distributor in the model.