Page 339 - Applied Process Design For Chemical And Petrochemical Plants Volume II
P. 339
328 Applied Process Design for Chemical and Petrochemical Plants
From Figure 9-51 the pressure drop is 0.38 mm Hg/ft or The Flexipac@ structural packing have better efficiency
0.85 mm Hg total. than available random packing, particularly at low liquid
rates, per Reference 101.
Top Section
Intalox High Perfmmance Metal Structured Packing [I 0.21
The top vapor load at an L/D of 0.8 is 8,620 lb/hr. The
total pressure drop for 7 theoretical trays is slightly less According to the manufacturer’s literature [ 1021, this
than 2 mm Hg and pv is 0.002 lb/ft3 at 8 mm Hg top pres- packing surpasses the best of other sheet-metal structured
sure. Duplicating the calculations made for the bottom packings in terms of efficiency and capacity. See Figure
section results in 9-611. The unique surface-texturing feature provides for
greater use of the packing surkce to achieve enhanced
D = 5 ft 9 in. levels of mass transfer, and the overall geometry allows
Packing height = 2.8 ft greater capacities and efficiencies to be obtained. Tests
Pressure drop = 1.06 mm Hg have been conducted on this and other packings at the
Therefore, use column diameter = 6 ft 9 in.
University of Texas at Austin’s “Separation Research Pro-
gram, Center for Energy Studies” for distillation capacity
Nomenclature
and efficiency, and published in Reference 103.
For good and uniform performance of any structured
A = cross-sectional area, ft2
D = diameter, ft packing it is essential to have uniform, consistent vapor
F, = V, (&) ‘I2 and liquid distribution; therefore, much care must be
G = vapor rate, lb/sec-ftZ given to the design details. See earlier discussion in this
g, = 32.2 (Ib mass) (ft)/(lb force) (sec)2 chapter.
L = liquid rate, lb/sec-ftZ For specific final performance sizing of a distillation col-
L/D = reflux ratio umn using Norton’s Intalox@ structured packing the
Pf = packing factor designer is referred to the manufacturer’s technical rep-
Qc = condenser duty, Btu/hr resentatives, and should not assume the preliminary
Q = reboiler duty, Btu/hr results obtained from any manufacturer’s bulletin includ-
V, = reboiler vapor rate, lb/hr ed here will necessarily serve as a final design. As a pre-
V, = superficial vapor velocity, ft/sec liminary examination of a design problem (used by per-
p1 = liquid density, lb/ft3 mission of Norton Chemical Process Products) :
pv = vapor density, lb/ft3
1\, = latent heat of vaporization, Btu/lb
1. Calculate flow parameter, X
Koch l%xipac@ Structured Packing
This type comes in four sizes, Types 1 through 4, and is
L = liquid mass rate, lb/sec
constructed of corrugated metal sheets (See Figure 9- G = vapor or gas mass rate, lb/sec
6GG). The types vary by corrugation size; the larger the pg = gas density, Ib/ft? at conditions
type number, the greater is the depth of corrugation. The p~ = liquid density, lb/ft3 at conditions
deeper corrugations give higher capacity and lower pres- A = area, ft2 tower cross-section area
sure drop. According to Koch reference [ 1011, at the same
efficiency, in countercurrent gas-liquid operation, this 2. Read chart, Figure 9-55, and obtain C,, ft/sec, at
packing has a higher capacity and lower pressure drop packing type shown.
than any available dumped or structured packing. The ter- 3. Calculate efficient capacity, CSC:
minology for Figure 9-54 is:
F, = V& = [G/3,600 @, 1 (A)](&), Wsec (9 - 67) (5 = surface tension, dynes/cm
p = liquid viscosity, cp
where G = vapor rate, lb/hr 4. Calculate:
V = vapor rate, ft/sec
pv = vapor density, lb/ft3
A = cross-sectional area, ft2
AP = pressure drop, in. water/ft height V = superficial gas velocity, ft/sec, or m/sec depending on
the units used
Chart parameter lines are gpm/ft* cross-section. V = G/ (pd), ft/sec