Upsets Caused by Too Good an Underflow Seal

It is possible to avoid such solids bridging by modifying the flapper valve assembly so that a small amount of gas can leak into the valve and maintain some fluidization of the dipleg solids. This can be achieved by suitable modification of the flapper valve assembly. Once the flapper valve assembly has been in service for some time, normal erosive wear of the mating surfaces will automatically permit sufficient leakage to prevent solids compaction. 

Active aeration of diplegs is normally undesirable since the aeration piping will generally not hold up over an extended period in the rather severe operating environment in which they normally operate. 

rotating gas flow with the solids concentrated at the wall ( inlet region ) 

dilute solids-gas flow with an overall solids volume fraction of 0.05-0.1. Here, the solids travel in strands , having a slip velocity with the gas an order of magnitude higher than the terminal velocity of an individual 

dense particle-gas flow low in the dipleg wherein the solids volume fraction is about 1/3, and the solids are in a fluidized state 

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