Because gas pressure loss increases rapidly with the approach of flooding, it has been suggested that the coke layers may fluidize before the liquid starts to flood, since the liquid density is much higher than the coke density. Fundamentally, fluidization occurs when the downward force of the burden is exceeded by the upward force of the gas stream. The latter is expressed as the pressure drop of the gas per unit height of the furnace. The force of the gas stream is proportional to the gas velocity and inversely proportional to the coke particle diameter and bed voidage. The bed voidage decreases if the liquid flow rate increases.
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