Hydrodynamics of gas‐liquid‐solid annular fluidization

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Abstract
In a strict sense, operation of the three‐phase ebullated bed reactor used in the H‐Oil process is not characterized by conventional three‐phase fluidization, but by annular three‐phase fluidization. In annular three‐phase fluidized beds differences in the hydrodynamic behavior over that found in conventional beds occur through changes in the bubble behavior. The addition of a concentrically located inner column in a gas‐liquid‐solid fluidized bed promotes bubble coalescence. This increase in coalescence can be observed either through changes in the liquid velocity of transition from the coalesced bubble regime to the dispersed bubble flow regime or through changes in holdup behavior. A hydraulic diameter defined for the annulus region proves suitable when comparing different annular systems having the same outside column diameter, but unsuitable when comparing systems having different outside column diameters.