A high-speed video system has been used to study the flow in the vicinity and inside half-cut models of gas distributor nozzles as they are used in circulating fludized bed combustors. From these measurements mechanisms for erosion and for the backflow of solids could be deduced. Nozzles with a bubble cap type design with a duct where gas is flowing downwards to the gas outlet and with low exit gasvelocities seem to be necessary to avoid solids backflow and erosion.
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