Page 290 - Applied Process Design For Chemical And Petrochemical Plants Volume II
P. 290
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