Downflow of solids in standpipes

General two-phase theory is applied to the flow of gas-solid mixtures in standpipes. It is shown that at a fixed flow rate both fluidized bed flow and packed bed flow can coexist in the same standpipe. Matsen's analysis of standpipe flow is extended and a general method for determining flow pattern and gas entrainment rate in standpipe flow is described. Data from a commercial standpipe in a fluid bed catalytic cracking unit are analysed. The analysis shows that fluidized bed flow occurs in the standpipe in support of Matsen's work on standpipe flow in another fluid bed catalytic cracking system.Flow instability, in standpipe is discussed in the light of this work and a mechanism of flow instability based on transition in flow pattern is postulated.