Fixed beds friction factor

Pressure Drop. The prediction of pressure drop in fixed beds of adsorbent particles is important. When the pressure loss is too high, cosdy compression may be increased, adsorbent may be fluidized and subject to attrition, or the excessive force may cmsh the particles. As discussed previously, RPSA rehes on pressure drop for separation. Because of the cychc nature of adsorption processes, pressure drop must be calculated for each of the steps of the cycle. The most commonly used pressure drop equations for fixed beds of adsorbent are those of Ergun (143), Leva (144), and Brownell and co-workers (145). Each of these correlations uses a particle Reynolds number (Re = G///) and friction factor (f) to calculate the pressure drop (AP) per... 

While the particle diameter of fixed bed reactors is on the order of 1-5 mm, the particle size used in another type of reactor—fluidized bed reactors—is on the order of 50-200 p,m. Because of the small diameters, the effectiveness factor is close to 1 in most cases. The Ergun equation characterizes the pressure drop across a bed of solids—at low gas velocities (relative to the particle terminal velocity). When the drag force of the upward moving fluid exceeds the weight of the particles, the particles become fluidized—they begin to move up and down and the solids bed itself behaves like a fluid objects that are denser than the bed will fall through the bed while objects that are less dense will be remain at the top. Based on a force balance, the pressure drop across the bed, AF/L, will be equal to the head of solids (neglecting frictional forces) ... 

Numerous correlations are given in the literature for the friction factor of a fixed bed,, and for the friction factor of a single particle,, of various shape (e.g., Jakubith, 1998). Both factors may also be linked for example, fb can be calculated as follows (Broetz and Schoenbucher, 1982) ... 

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