Packed height

Design Procedure. The packed height of the tower required to reduce the concentration of the solute in the gas stream from to acceptable residual level ofjy 2 may be calculated by combining point values of the mass transfer rate and a differential material balance for the absorbed component. Referring to a sHce dh of the absorber (Fig. 5),... 

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...

In order to determine the packed height it is necessary to obtain a value of the overall number of transfer units methods for doing this are available for binary systems in any standard text covering distillation (73) and, in a more complex way, for multicomponent systems (81). However, it is simpler to calculate the number of required theoretical stages and make the conversion ... 

An alternative to determining packed height is through the use of an empirical term, height equivalent to a theoretical plate (HETP). This term can be measured in a fashion similar to that used for the overall plate efficiency of a column (eq. 44) ... 

E] Z = packed height, m of each section with its own liquid distribution. The original work is reported in English units. Cornell et al. (Ref. 81) review early literature. Improved fit of Cornell s ( ) values given by Belles and Fair (Refs. 74 and 75) and in Fig. 5-29. 

Design data for separation of the particular or similar mixture in a packea column are not available. Design procedures are better estabhshed for tray-type columns than for packed columns. This is particularly so with respect to separation efficiency since tray efficiency can be estimated more accurately than packed height equivalent to a theoretical stage (HETP). 

Design method used Woe Packed height, m Design safety factor... 

Once packing heights are determined in other sections from HETP (distillation) or Koa (absorption), the height allowances for the internals (from Figure 1) can be added to determine the overall column height. Column diameter is determined in sections on capacity and pressure drop for the selected packing (random dumped or structured). 

As a general rule packing heights per su V]vort plate should not exceed 12 It lot Raschig rings or l,a-20 It Idr most other packing shapes. Othei tvpes fit within these limits. The mechanical, vibrational and thermal shock loads become important md sometimes affect the tower operation beyond these limits. 

To allow for the vertical height required for packed tower distributors and redistributors—and in tray towers the vertical height used by additional trays—typically using 10%-20% of the vertical packed height (10% for 2-in. random packing and 20% for structured packing) [136] the analysis indicated ... 

The HETP (Height Equivalent to a Theoretical Plate (stage or plate)) is the tray spacing divided by the fractional overall tray efficiency [82]. The transfer unit concept has been useful for generalized correlations [89]. Because packed towers operate with continuously changing compositions through the packed height, the concept... 

Parameter of Curves is Pressure Drop m Inches of Water/Foot of Packed Height... 

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).

Low to medium pressure column operation, select design pressure drop of 0.40 to 0.60 in. water/ft of packing height, although some towers will operate... 

Figure 9-26. SLE Data Chart for 1-in. metal Pall rings, aqueous systems, pressure drop only. Data from 15-84 in. dia. test columns with packed heights of 2-10 ft. Reproduced with permission of the American Institute of Chemical Engineers, Kister, H. Z. and Gill, D. R., Chemical Engineering Progress, V. 87, No. 2 (1991) p. 32 all rights reserved.

Redistribute the liquid every 10 ft and allow 2 ft additional for redistribution = 36 ft. Then use 4-10 ft sections of packing. For 20 theoretical plates, total performance packed height 20 (18 in./12 in.) = 30 ft. Allow for loss of equilibrium at (1) reflux entrance = 1 HETP and (2) feed entrance = 2 HETP and (3) redistribution (2) = 2 HETP totals 5 HETP. 

Estimated pressure drop of loading from Figure 9-21C = 0.40 in water/ft of packing. For total packed height, AP s (0.40) (16.5 + 24) = 16.2 in. water total (packing only). Preliminary evaluation of condenser requirements Condense 97,300 lb/day... 

The static hold-up is independent of liquid and gas rates, since it represents the liquid held in the packing after a period of drainage time, usually until constant weight of material is received. This requires approximately 1 hour for a 10-in. dia. x 36-in. packed height tower. Table 9-34 adequately summarizes the data. 

Figure 9-50. HETP and pressure drop data for a typical distillation system. Packing equivalent to X-200 (8 strands), stainless steel. System methylcyclohexane and toluene. Reflux Ratio 100%. Column Diameter 18 inches. Packed Height 5 feet. Used by permission ACS Industries, Inc., Separation Technology Division, Bull. B-129 (1992).

Considering the reboiler as a theoretical tray, for 3 theoretical trays the packing height for an HETP of 7 in. is 7 (3)/12 = 1.75 ft. This requires 4 standard elements which are 6.7 in. deep, or 80 ft of packing. 

Reynolds number for gas S = length of corrugation side Uge = effective velocity of gas Ug = superficial velocity of gas Ui = superficial velocity of liquid Ap = pressure drop per unit packed height e = packing void fraction 0 = angle of flow channel (from horizontal) fi = viscosity p = density... 

Pressure drop Range usually 0.3-0.5 in. water/ft, or, 30-40 mm water/m of packed height [116]. 

Estimate required packing height from Bravo, et al. 

Process packed height = 5.4 ft Distribution packed height = 2.00 Total 7.4 ft... 

Pressure drop is approximately 0.5 in./ft packing height. Figure 9-2 ID. 

Tower Packing Height for Amnwnia-Hydrogen-Nitrogen Mixture... 

Tower Diameter = 12 Packing =3/4" Roschig Rings Packed Height = 16 ... 

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