GAS-SOLIDS TWO-PHASE FLOW IN STANDPIPE UNDER NEGATIVE PRESSURE GRADIENT
This paper presents an experimental study on the axial pressure, voidage and gas flow of gas solids two phase flow in a  150 mm×11500 mm standpipe under negative pressure gradient.The outlet of standpipe is submerged in a dense fluidized bed and the maximum mass flux of solids is about 1200 kg·m -2 ·s -1 .The axial pressures, voidage and gas flow in the standpipe are affected by mass flux of solids, inlet velocity of cyclone, fluidizing velocity, mainly determined by mass flux of solids.When mass flux of solids is less than 200～250 kg·m -2 ·s -1 , there are two fluidization regimes coexisting in the standpipe,a dilute phase flow and a bottom dense phase flow The pressure is low and changes little in the dilute regime.Gas flows upward, which is fluidizing gas from the standpipe bottom.When mass flux of solids is more than 200～250 kg·m -2 ·s -1 , there is only one dense phase conveying regime in the standpipe.The pressure increases progressively from top to bottom and pressure profiles are smooth Gas flows downward, and is carried by particles The axial voidage distribution in the standpipe changes from Z shaped profile to S shaped as mass flux of solids increases.