THE CIRCUMFERENTIAL DISTRIBUTION OF WASTAGE ON IN-BED TUBES IN FLUIDIZED-BED COMBUSTORS

The circumferential distribution of metal loss about heat exchanger tubes within fluidized bed combustors usually shows one of two distinct patterns. In one case, flats are formed on either side of the tube bottom and there is little or no loss at the bottom (Type A); in the other case, the wastage is concentrated at the bottom and falls off to either side (Type B). Previous explanations for this difference in behaviour have mostly relied on an assumption of a difference in the actual damage process or material response. In this paper, a simple computer simulation shows that Type A behaviour can result from a high degree of constraint on the flow conditions around tubes, and that the introduction of a small degree of flow variability into such a system will lead to Type B behaviour.