FLUIDIZATION OF A MULTI-SIZED GROUP-B SAND AT REDUCED PRESSURE

The fluidized bed pyrolysis of oil sand produces a spent sand which contains 1-2 wt.% carbonaceous residue. The rapid bitumen pyrolysis reactions indicate that the fluidized bed inventory is essentially spent sand. This spent sand has been shown to be a Group B sand according to the classification scheme of Geldart. A multi-sized Group B sand was smoothly fluidized with air by reducing the pressure above the surface of the bed to less than the pressure at the inlet of the distributor. Beds of sand with heights up to four times the reactor diameter were taken from the slugging regime to smooth fluidization by changing the effective distributor pressure drop while the reactor was operating at reduced pressure above the bed. The characteristics of reactor pressure drop versus superficial gas velocity were determined for the multi-sized particles under reduced pressure and compared to the fluidization behavior of multi-sized particles in the more common positive gas pressure systems. The shapes of fluidizing and defluidizing curves caused by pulling air from the reactor top were similar but not the same as curves obtained at atmospheric pressure by pushing air through the distributor. An 'interpreted' minimum fluidization velocity definition for multi-sized particles fluidized at reduced pressures is proposed and shown to be consistent with predictive correlations.