Page 290 - Applied Process Design For Chemical And Petrochemical Plants Volume II
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Packed Towers                                           279

                                                      Table 9-2 1 (Continued)
                               Relative Performance Characteristics of Tower Packing and Column Trays1
            .......   ....   ... .~   ......            .  __  -                                 .        .. .-    ..
                                                    Material   Relative   Mass   Pressure
            Company               Configuration    of Const2   Cost?   Transfe8   Drop    Capacity  Comments
                               ..
            ..        ..     -    .-                                 .              ..         --
            Random Packing
            R’utter Rings         Crimped, curved     M      Mod/Lo      Hi       V.Lo      Hi     Superior liquid
                                  slotted strips                                                   spreading F.R.I.
                                                                                                   tested efficiency
            Structured Packing
            SNAP-GIUDT~I          Slotted, snaplock   M         Hi       Med      E.Lo     E.Hi    “I” beam
                                 shape                                                             configuration
                                                                                                   High capacity, non-
                                                                                                   fouling
            Montz A3TM           Wire-weave corrugated   M     V.Hi     V.Hi       Lo       Hi     Highest efficiency
            Montz BIT’”          Embossed sheet metal   M       Hi      V.Hi      V.Lo      Hi     Sinusoidal
                                                                                                   corrugations
                                                                                                   Maximum surface
                                                                                                   utilized
                                   .      .                 ~                                              .__-
            GENERAL COMMENTS
            1. Comparisons of relative cost and performance are applicable only within same manufacturer.
            2. M = Metal (Generally 304 SS. Other alloys available); P = Plastic (Wide selection); C = Ceramic
            3. Costs: .Mod  = Moderate or = conventional packing; Lo = conventional packing; Hi = conventional packing
            4. Mass Transfer efficiency
            5. Structured packings frequently used for high Wcuum service
            6. Carbon steel and other metals sometimes available.
            7. Wide range of plastics generally available
            8. Packing efficiency and capacity vary with specific application. Contact vendor for assistance in making final decision.
            9. There is no intention to reflect negatively on any manufacturer’s packing or trays (author note).
            Used by permission; W.P.  Stadig, ChemicaZProcessing@, Feb. (1989), Ritman Publishing Co.


                                Table 9-22                        of HETP has been to determine the number of theoretical
              Typical Performance Characteristics Comparison of   stages (plates) required for a given separation by the usual
                         Tower Packings and Trays                discrete tray-by-tray method (stepwise) and then using the
                                                       .~        height of packing equivalent to one theoretical plate, mul-
                                         Type of Internal
                                      .               .           tiply to obtain  the total height of packing. This requires
                                            Random   Structured   the  use  of  experimentally  or  industrially  determined
           Characteristic           Trays   Packing   Packing    HETP values for the  same system or one quite  close in
            ..........      .. ~.                      .
           Capacity                                              terms of pressure, types, or families of fluids and packing
             F-factor, (ft/s)  (lb/ft3) l/*  0.23-2.0   0.25-2.4   0.1-3.6   size and family type  (see Figure 9-18 and Table 9-22 and
             C-factor, ft/s       0.03-0.25   0.03-0.3   0.01-0.45   later  discussion).  Table  9-23  [ 1331  compares  several
           Pressure drop, mm Hg/                                 process systems and the corresponding average HETP for
             theoretical stage       3-8     0.9-1.8   0.01-0.8   2-in. diameter slotted packing rings.
           Mass transfer efficiency,
             HETP, in.              24-48    18-60      430      Packing Size
            .                         . ~             ..  .~
           Reproduced by  permission: Chen, G. K, Chem. Eng., Mar. 5 (1984) p. 40,
             all rights reserved.                                  This affects contact efficiency; usually, the smaller pack-
                                                                 ing is more efficient; however, pressure drop increases.
                                                                   As a general guide, use:
           efficiency for other systems and apply judgement to select
           a value.                                                      Random Packing Size,        Column
             The HETP  (Height Equivalent to  a Theoretical  Plate           Nominal, in.           Diam., in.
           (stage or plate))  is the  tray spacing divided by  the frac-         %-54                 6-1 2
           tional overall tray efficiency [82]. The transfer unit con-           5h1                  12-18
           cept  has  been  useful  for  generalized  correlations  [89].       1-1%                  18-24
           Because packed towers operate with  continuously chang-              1%-2                  2448
           ing compositions through the packed height, the concept               2-3                36-larger
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