Flow and Pressure Drop in Catalyst Beds

Pressure drop in catalyst beds is governed by the same principles as in any flow system. Consequently, at very low flow, pressure drop is directly proportional to velocity, and at very high flow, to the square of velocity. These conditions correspond to the laminar and turbulent regimes of the flow. 

Leva et al (1949) and Ergun (1952) developed similar useful equations. Later, these were refined and modified by Handley and Heggs (1968 ) and by MacDonald et al (1979). All these equations try to handle the transient regime between laminar and turbulent flow somewhat differently but are based on the same principles. 

Leva s correlation (Leva 1949) is the easiest to use in manual calculation, especially when the particle diameter-based Reynolds number is high, i.e., above Rep l,000. A changing exponent n in the Leva expression, shown below, accounts for the transient region as turbulence of flow increases. The dependence of n on Rep was specified by Leva graphically (1949) as n growing with the Rep between 1.0 and 2.0. The value reaches n = 1.95 at Rep =1,000 thus approximating 2.0 closely. 

This correlation was used earlier as can be seen in the 1974 paper because, at that time, interest was focused mostly on high flows with high Rep. 

For the full range of flow, including the smaller flows and on smaller size catalysts, a more useful correlation for pressure drop is the Ergun 

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