Pressure drop, packings correlations

The most commonly used design procedure is based on the Sherwood-Leva-Eckert packing correlation curve, commonly referred to as the general pressure drop (GPD) correlation curve. Multiple versions of the curve and associated correlations have been developed. They differ in the correlation parameters used in... 

Fig. 23. Pressure drop and flooding correlation for various random packings (95). ip = p- o IP-l (standard acceleration of free fall) = 9.81 m/s, p, = liquid viscosity ia mPa-s numbers on lines represent pressure drop, mm H2O /m of packed height to convert to ia. H2O /ft multiply by 0.012. Packing...

When two phases are present the situation is quite complex, especially in beds of fine soHds where interfacial forces can be significant. In coarse beds, eg, packed towers, the effects are often correlated empirically in terms of pressure drops for the single phases taken individually. 

Porous Media Packed beds of granular solids are one type of the general class referred to as porous media, which include geological formations such as petroleum reservoirs and aquifers, manufactured materials such as sintered metals and porous catalysts, burning coal or char particles, and textile fabrics, to name a few. Pressure drop for incompressible flow across a porous medium has the same quahtative behavior as that given by Leva s correlation in the preceding. At low Reynolds numbers, viscous forces dominate and pressure drop is proportional to fluid viscosity and superficial velocity, and at high Reynolds numbers, pressure drop is proportional to fluid density and to the square of superficial velocity. 

The iC values (vapor-liquid equihbrium ratios) in Equation (13-123) are estimated from the same equation-of-state or aclivity-coefficient models that are used with equilibrium-stage models. Tray or packed-section pressure drops are estimated from suitable correlations of the type discussed by Kister (op. cit.). 

FIG. 14-50 Pressure drop correlation for random packings, as presented hy Robbins. [Cbem. Eng. Progr., 87(1), 19 (1990). Reproduced with peimission of the Ameiican Institute of Chemical Engineers. Copytight 1990 AlChE. All fights reseroed. ] To convert inches H20/ft to mm H20/m, multiply by 83.31. 

Determination of pressure drop through the column (for packed columns, correlations dependent of packing type, column-operating data, and physical properties of the constituents involved are available to estimate the pressure drop through the packing for plate columns, the pressure drop per plate is obtained and multiplied by the number of plates)... 

The packing factor (F) is an important design variable in determining the capacity of any packing design from a flooding, or pressure drop standpoint. This-factor was first described by Sherwood in 1938. The empirical correlation is ... 

Figure 9-21F. Strigle s latest generalized pressure drop correlation. Note G = gas mass velocity, Ib/ft -sec. Used by permission of Strigle, R. F. Jr., Packed Tower Design and Applications Random and Structured Packings, 2nd ed. Gulf Publishing Co., (1994) p. 19.

Figure 9-21G. Generalized pressure drop correlation for non-foaming systems for IMTP metal random packing. Parameter of curves is pressure drop in inches of water/foot packed height. Numbers in parentheses are mm of water/meter of packed height. Used by permission of Norton Chemical Process Products Corp., Bull-IHP-1, 12/91 (1987).

Pressure drop data for several styles and arrangements of drip point grid tile are given in Figures 9-25A-9-25E. These are not included in the general GPDC correlations for random packings. 

Figures 9-21F and 21G (for Norton s IMTP packing only) can be up to 20% higher than industrial experience for the same Cj values at a flow parameter (FP) of 0.01 [82]. At an absolute colunrn pressure of 10 mm Hg or less, the pressure drop actual can be up to 30% lower than that read from the Figure 9-21F at the FP of 0.01 and the same Cg value [82]. The conclusion is that the generalized correlation, Figures 9-2IF and -21G always give a conservative design AP at operating pressures less than 70 mm Hg abs. Several other factors must be considered, such as variability of gas and liquid rates and densities or specific volumes.

Figures 9-32A and B [98] illustrate the correlation of wet pressure drop and system vapor rate at various liquid rates for No. 2 Nutter rings however, other available data indicate that other sizes of Nutter rings, Pall rings, and selected other packing shapes correlate in the same manner.

Revised Packed Tower Pressure Drop Correlation Constants for Towers Operating Below Flooding Region... 

Useful correlated information on pressure drop across packing supports and redistribution plates is practically not available. Some order of magnitude guide data is given in Figures 9-37-41. 

Leva, M., "Reconsider Packed-Tower Pressure-Drop Correlations, Chem. Eng. Progress, V. 88, No. 1 (1992), p. 65. 

However, on die basis of the relation between pressure drop and die minimum fluidisation velocity of particles, the point of transition between a packed bed and a fluidised bed has been correlated by Ergun41 using (17.7.2.3). This is obtained by summing the pressure drop terms for laminar and turbulent flow regions. 

Figure 11.44 correlates the liquid and vapour flow rates, system physical properties and packing characteristics, with the gas mass flow-rate per unit cross-sectional area with lines of constant pressure drop as a parameter. 

A new generalised correlation for pressure drop in packed columns, similar to Figure 11.44, has been published by Leva (1992), (1995). The new correlations gives a better prediction for systems where the density of the irrigating fluid is appreciably greater than that of water. It can also be used to predict the pressure drop over dry packing. 

Correlation was found between domain size and attainable column efficiency. Column efficiency increases with the decrease in domain size, just like the efficiency of a particle-packed column is determined by particle size. Chromolith columns having ca. 2 pm through-pores and ca. 1pm skeletons show H= 10 (N= 10,000 for 10 cm column) at around optimum linear velocity of 1 mm/s, whereas a 15-cm column packed with 5 pm particles commonly shows 10,GOO-15,000 theoretical plates (7 = 10—15) (Ikegami et al., 2004). The pressure drop of a Chromolith column is typically half of the column packed with 5 pm particles. The performance of a Chromolith column was described to be similar to 7-15 pm particles in terms of pressure drop and to 3.5 1 pm particles in terms of column efficiency (Leinweber and Tallarek, 2003 Miyabe et al., 2003). Figure 7.4 shows the pressure drop and column efficiency of monolithic silica columns. A short column produces 500 (1cm column) to 2500 plates (5 cm) at high linear velocity of 10 mm/s. Small columns, especially capillary type, are sensitive to extra-column band... 

The pressure drop through packed columns, and the flooding conditions, can be estimated from the generalized correlation of Leva (1992), shown in Fig. 13-5. The pressure gradient in millimeters of water per meter of packed height is the parameter on the curves, and interpolation is usually necessary to determine the pressure drop (note that the pressure... 

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