Page 361 - Applied Process Design For Chemical And Petrochemical Plants Volume II

350 Applied Process Design for Chemical and Petrochemical Plants

This has been shown to correlate for a wide variety of 3. Determine by:
tower packings, various operating conditions, and physical
1
-
properties of the solute and inert gases. The calculated -- -- 1 +-=- 1 1 (9 94)
must be used in conjunction with the effective interfacial KGa kGa H’kLa H’KLa
areas determined by Shulman [65] Figure 947, to establish
a reliable value for kGa. Figure 947 should be used with the Height of a Traasfer Unit, HOG, HOL, HTU
abscissa as G/$/0.075 for inert gas other than air [67]:
An earlier concept of height equivalent to a theoretical
kGa = k(a) plate (HETP) for relating the height of packing to a unit
of transfer known as the theoretical stage or plate has gen-
HTU (WPhase) = G’/~@IMPBM (9-89) erally been dropped in favor of the “height of a transfer
unit“ €€TU, and designated as HOG or HOL depending on
where 4, = diffiuivity of solute in gas, ft2/hr
kG = *phase mass transfer coefficient lb mol/hr (ft2) whether it was determined from gas or liquid film data.
(am) HETP data for absorption and distillation is given in the
MM = mean molecular weight of gas, lb/lb mol section under packed tower distillation.
PBM = mean partial pressure of inert gas in the gas
phase, atm
p~~ = gas viscosity, lb/(hr) (ft)
p~ = gas density, lb/ft3
G = superficial gas rate, lb/ (hr) / (ft2) Height of Overall Transfm Unit
1 1 1 l m 1 For small changes in concentration and total number
-=- +-=- +-=- (9 - 90)
KGa kGa H’kLa kGa kLa H‘KLa mols of gas and liquid remain essentially constant; applic-
able to all but very concentrated solutions. For the latter
1 1 H ’ l 1 case see References 18 and ’74.
-=- +-=- +- (9 - 91)
KLa k,a kGa KLa mkGa
GM -
HOG=K aP (9 95A)
H‘ = Henry’s law constant, lb mols/(ft3) (atm) G ave
kL = liquid-phase mass transfer coefficient, lb
mols/(hr) (ft2) (lb mols/ft3) (9 - 95B)
The relation
(9 - 96)
vaporization (kGa), h
-
0.85
= - -L (9 92)
I
absorption (kGa), ho
is reported to correlate *8% based on data tested, and
appears to be founded on a sound investigative program. Height of Individual Transjier Unit
For the liquid phase based on Raschig ring and Berl sad-
dle data [65] : For same conditions as (1.) Some data are reported as
individual gas or liquid film coefficients or transfer unit
heights. However, it is often possible to use it as overall
-
(9 93) data if the conditions are understood.

HG = Gm (9 - 98)
k~a
Pave,
use of kG and kL
r,
1. From physical properties of system, determine and HL =- (9 - 99)
kL. If system is known or can be assumed to be essen- kLa PL
tially all gas or all liquid film controlling, then only the
controlling k need be calculated. For greater accura-
cy, both values are recommended, because very few
systems are more than 80% controlled by only one k.
2. Combine effective interfacial area to calculate kGa or
kLa.