Flow of fluidized solids and bubbles in standpipes and risers

Equations are presented for the densities of fluidized solid-bubble mixtures in downward and upward vertical flow. Data from a large commercial standpipe are in close agreement with calculations. Flow instability is predicted when downward solid flow is sufficient to hold a gas bubble stationary in a standpipe. Commercial experience of such instability is presented indicating the existence of slugs in a 45-in.-diam. standpipe.