Page 312 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Packed Towers 301

eter. Even though the column diameter may show a dif- Capat35 Cmrelatwn [83]
ference between the requirements at the top, bottom
and/or middle of the column, do not be too quick to try Figures 9-21G and 9-211 present the proprietary esti-
to create a column design with diameter variations as the mating capacity charts for the various sizes of the Intalox@
results vary up the column. Sometimes for vacuum packing for a non-foaming system. The system base HETP
columns the calculations show that a larger diameter in of a packing is the flat HETP value produced by uniform
the upper section would perform better, so check out distribution, see Figure 9-22.
using the same diameter throughout the column, because The terminology for the chart referenced to Norton's
this is the least expensive, and somewhat easier to fit all [83] Intalox@ random packing of various sizes designated as:
the parts together. Even though the pressure drop or
D'
HETP may not be the same throughout [154, 156, 1571, Size No. Imensions..
adjustments can be made, if warranted, to even changing 15
the packing size or style/type in various segments of the 25 1
column. This requires some careful calculations for the 40
effective HETP and the total height of the individual sec- 50 2
tions and then the total column/tower. But, it is often 70
worth the effort, particularly for tall towers, say above Design information used by permission of Norton Chemical Process
20-30 ft of packing. For low pressures as well as other Products Go.
columns, determine the pressure drop for each packed
,
section of the column, plus the pressure drop through the low parameter, X- L/ G 2/pG /PI, chart (9 - 32)
internal components.
capacity parameter, C, = v Jpc / (PL - PG 1,
fi/sec or m /sec (9- 33)
Proprietary Random Packing Design Guides
Capacity rating, C,, = feet/sec., or m /sec, from chart
~Vwton Intalox Metal Tower Packing (IMP@')
Norton offers a new high performance system centered EfEcient capacity, C, = C,
around an improved Intalox@ metal tower packing,
-
including effective internals to provide the distribution ft./ sec/ or meters / sec. (9 34)
and pressure drop consistent with the higher perfor- This is the greatest vapor rate at which the packing still
mance of the packing itself. maintains the system base HETP [83].
Figures 9-6J and -6U illustrate the IMTP packing. The
manufacturer's key performance descriptions are [83] : Capacity rating - [C,/C,,] (100) = o/o capacity [83]

1. Greater capacity and efficiency than fractionation Pressure drop equation: For IMTP packing, non-foam-
trays and other dumped packings. ing system, use: Figure 9-21G or I.
2. Pressure drop approximately 40% lower than equiva- where flow parameter, X = as previously noted, Equation 9-32.
lent size Pall rings.
3. Low liquid hold-up. Capacity parameter, Y = F C? vo.]
4. Structural strength allows packing depths to 50 ft or
more Value for F coefficient (used by permission Norton [83])
5. Easy to use in distillation, from deep vacuum where
low pressure drop is beneficial, to high pressure IMTP size ,Yo. 15 No. 25 No.40 No.50 No. 70
where capacity surpasses many trays. FwhenC,inm/sec 349 441 238 194 129
6. HETP values nearly independent of flow rate. F when C, in ft/sec 51 41 24 18 12
7. Packing properties related to a performance curve:
(a) The system base HEW of a packing, which is the where v = liquid kinematic Viscosity, centistokes
flat HETP value produced by uniform distribution. = p/(sp.gr) centistokes
= liquid viscosity, centipoise
(b) The efficient capacity (not the same as hydraulic (3 = surface tension, dynes/cm
capacity or flood point) of a packing, which is the L = liquid mass rate, lb/hr
greatest vapor rate at which the packing still G = gas mass rate, lb hr
maintains the system base HETP. Norton [96] p~ = liquid density, Ib/@
rates packings by percent of efficient capacity PG - gas density, Ib/f$
rather than percent of flood. Vg = V = superficial gas velocity, ft/sec or m/sec