Preloading regime

The Engel, Stichlmair, and Geipel correlation applies only in the preloading regime. The packing geometry is represented in the... 

FIG. 14-73 Liquid holdup, air-water data by Billet ( Packed Column Design and Analysis, Ruhr University, Bochum, Germany), preloading regime. (From Kister H. Z., Distillation Design, copyright by McGraw-Hill reprinted with permission.)... 

Equation (8.13) states that pressure drop is the sum of two terms. The first term describes the friction loss through the packing, and is the only important term in the preloading regime and when Lf is below 20,000, Under these conditions, the pressure drop is proportional to the square of the gas rato. The second term describes the increase in the slope of the pressure drop with gas rate in the loading regime. 

The effect of liquid and vapor rates on the operating holdup is shown in Fig. 8.21. In the preloading regime holdup is essentially independent of vapor flow (100,101), but is a strong function of liquid flow rate and packing size. Smaller-size packings and high liquid rates tend to have more holdup. 

Vapor and liquid loads (Fig. 8.18). For constant LfV operation in the preloading regime, generally... 

Summary. In the preloading regime, packing size, type, and distribution affect HETP. With aqueous-organic systems, HETP may be sensitive to underwetting and composition. HETP of structured packings may also be affected by pressure (at high pressure), and vapor and liquid loads. 

Figure 12 Continued) Random versus structured pacbiTie (d) Liquid holdup, air water data b(y Billet (3), preloading regime.

The preloading regime (regions A-B and A -B in Figs. 8.15 and 8.16a) Most packed towers etre designed to operate in this region. Column efficiency is independent of flow rate and column pressure drop uniformly increases with vapor flow rate. An exception is wire-mesh structured packing, where column efficiency declines with an increase in loads (Fig. 8.16c). 

The pressure drop per unit bed height in the preloading regime can be found from Ref. [19] ... 

Westerterp and Kuczynski [9] considered the flow of solids as a flow of rivulets (trickles) rather than of individual particles. They assumed that in the preloading regime, the solids phase flows almost exclusively in the form of trickles. It was further assumed that some gas is dragged along by the trickles flowing downward. The trickles release the gas when they collide with the walls of fixed bed elements. The released gas flows upward together with the main stream, and in... 

The dynamic holdup in the preloading regime was successfully predicted using this approach [9], but the empirical parameter str had to be determined from the same experimental data. Westerterp and Kuczynski [9] did not derive a relation for rehable prediction of dynamic holdup in the loading range. Instead, for rough estimation, the use of Equation (22.7) and Equation (22.9) was suggested. 

The result of Equation (22.30) is, under this assumption, the constant value of average solids velocity in the preloading regime. Comparison of the values calculated using a very simple Equation (22.30) and the values obtained by Roes and van Swaaij [4] for their experimental systems yields excellent agreement. Detailed discussion of this issue will be the subject of a future publication. 

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