Page 346 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Packed Towers 335

(text cmtinucdfiom page 331) Note: The HETP's noted are valid only €or 0-/p
xylene at the test conditions. Nevertheless, the ratio
2. Calculate the liquid load of HETP's should remain approximately constant.
gpm = (381,000)/(8.33) (60) (.68) = 1,120
gpm/ft2 - (1,120)/(176.713) = 6.3 Crid Packing: Nutter Engineering (Figure 6-PP)
3. Select the Gempak size: For applications and design details refer to the manu-
On plot of Gfactor vs. liquid load as shown in Fig- facturer concerning these types of packings.
ure 9-57A mark the operating point (A) using 6.3 Figure 9-58 illustrates performance of No, 3 Snap-
gpm/€t2 and Gfactor = 0.28. The point on the figure GridTM. For mass transfer for distillation HE", use:
is above the Gempak AS (0.25-in. crimp height) pack-
ing flooding line. AU other packing sizes would be HETP Hog (lnh)/(h - 1) (9-70)
operating below flooding. For example, if Gempak
AS (0.375-h. crimp height) is to be used, the percent where h = m (Gm/&) (9-71)
flooding at design loads will be: HEW = height equivalent to a theoretical plate, inches

At constant L/V ratio-(OwOD) x 100 = 75.2% Hog = height of an overall gas phase transfer unit,
. ,4t constant liquid rate-(100) (BA/BE) = 70.0% inches
U, = volumetric overall heat transfer coefficient,
Kormally in distillation, flooding at constant L/V Btu/(hr) (fts) (OF)
ratio is more representative of actual plant operations m = slope of equilibrium line expressed in mole
(constant liquid loads may also be representative in fraction
cases like absorbers), In general, percent flooding up G,, L, = gas, liquid molar rate based on superficial
to 7330% is acceptable for continuous operation. tower area, mol/(hr) (ftz)
Gempak AS (0.375-in. crimp height) would be a good H,, Hi = height of gas, liquid phase transfer unit, inches
selection for this example. Gempak AS (0.5-in. crimp Re = Reynolds number of gas phase
height) would also be a good selection, with flooding
of 70% at constant L/V ratio and 65% at constant liq- Koch F%# Packing: Koch. Engineering Co.
uid rate. Gempak AS (0.25-in. crimp height) would
not be a good selection in this case since flooding Koch Flexigrid@ packing bulletin [lo61 states that the
would be over 100%. packing (Figures MSS, -IT) has a fixed, ordered orien-
4. Pressure Drop tation and is supplied as layers that stack in a prescribed
On pressure drop plots, mark a Ghctor of 0.28 fashion within the bed. Features include [106]:
and 6.3 gpm/ft2 as shown in Figures 9-57B and 9-57C.

For Gempak AS (O..i-in. crimp height), AP = 0.31 in. liq/ft 1. High capacity; constructed in 60 in. x 16 in. x 2% in.
For Gempak AS (0.3754~ crimp height), AP = 0.55 in. high modules.
liq/ft 2. High efficiency: constructed in 60 in. x 16 in. x 2% in.
high modules.
For a bed of 6.5 ft, the pressure drop for the bed is:
3. Each successive layer of the grid is rotated 45" during
For Gempak AS (0.5-in. crimp height) = 0.31 x 6.3 = 2.0 installation.
inches of liquid 4. Lower pressure drop.
For Gempak AS (0.375411. crimp height) = 0.35 x 6.3 = 3.6
inches of liquid 5. Tendency to coke or foul far less than other grids,
due to elimination of horizontal planes where liquids
Pressure drop for both AS (0.5-in. crimp height) or solids can stagnate.
and AS (0.375-in. crimp height) packings is accept- 6. Low liquid holdup.
able for the crude tower operation. 7. Fabricated of most metals, such as carbon steel, stain-
5. Efficiency, Figure 957D less steel, aluminum and others as required.
On efficiency plot, mark GEactor at 0.28.

For Gempak AS (0.5-in. crimp height): HEW = 13.5 in. Capacity comparison at flooding is shown on Figure
(0.89 hTS/ft) 9-59 as a function of the vapor and liquid capacity factors
For Gempak AS (0.375-in. crimp height): HETP = 10.2 in. C, and CL. Koch developed correlations, used by permis-
(1.18 NTS/ft) sion [106]: