GAS-LIQUID SOLIDS FLUIDISED BEDS

The hydrodynamics of three-phase fluidised systems is complex and reference should be made to specialised publications for a detailed treatment(87 91). Only a brief summary of their characteristics is given here. 

If a gas is introduced at the bottom of a bed of solids fluidised by a liquid, the expansion of the bed may either decrease or increase, depending on the nature of the solids and particularly their inertia. It is generally found that the minimum fluidising velocity of the liquid is usually reduced by the presence of the gas stream. Measurements are difficult to make accurately, however, because of the fluctuating flow pattern which develops. 

At very high gas rates, even large particles do not break down the large gas bubbles and the amount of liquid dragged up in their wake can be so great that some regions 

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