Flow of particulate materials in a vertical standpipe



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Standpipes are mechanical devices used to convey particulate solids downwards, usually from a region at lower pressure co a region at higher pressure, with tne aid of gravity. A well known application is the flow of a gas- solid mixture down from a fluidized bed in refinary processes, such as fluid catalytic cracking, fluid hydroforming and fluid coking. Tney are also used in the SASOL synthetic gasoline process and solid fuel processes of coal gasification and liquefaction. Despite the importance of the present applications and the potential of much wider use in the future, the mechanics of standpipe operation is still poorly understood. As a result, most industrial standpipes are still being designed empirically based on past experience. Inis is particularly unfortunate since standpipes are well known to devolop an instability under certain circumstances, causing a transition to a state with inadequate pressure build-up in the pipe. This may lead to operational problems such as loss of circulation and reversed gas flow which have resulted in a reduction of plant throughput or even complete shut-down of the plant. [...]