Page 356 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Packed Towers 345

Table 9-39 For Concentrated Solutions and More General Application
System Film Control*
............ -- .. The following equation applies for diffusion in one
Gas Film direction (e.g., absorption, extraction, desorption) [74]:
. . .- .. .-
1. Absorption of ammonia in water I1
2. Absorption of ammonia in aqueous ammonia NOG = s (l-Y)MdY (9 - 82)
3. Stripping of ammonia from aqueous ammonia (1 - Y ) (Y - Y *)
4. Absorption of water vapor in strong acids y2
3. Absorption of sulfur trioxide in strong sulfuric acid
6. Absorption of hydrogen chloride in water
7. Absorption of hydrogen chloride in weak hydrochloric acid (9 - 83)
8. Absorption of 5 vol. percent ammonia in acids
9. Absorption of sulfur dioxide in alkali solutions
10. Absorption of sulfur dioxide in ammonia solutions or
11. Absorption of hydrogen sulfide in weak caustic
12. Evaporation of liquids Y1
13. Condensation of liquids dY 1/21n- 1+Y1 (9 - 84)
. . -. . ~. 1+Y2
Liquid Film y2
... . -. .. . .-
1. Absorption of carbon dioxide in water or
2. Absorption of oxygen in water
3. Absorption of hydrogen in water
4. Absorption of carbon dioxide in weak alkali
3. Absorption of chlorine in water (9 - 8.3)
. .... . .
Both Gas and Liquid Film
.. where (1 - Y)M = log mean average of concentration at the
1. Absorption of sulfur dioxide in water opposite ends of the diffusion process, (1 - y)
2. Absorption of acetone in water in main gas body, and (1 - y*) at the inter-
3. Absorption of nitrogen oxide in strong sulfuric acid
. , face [74]
*From: M. Leva, Tower Packings and Pachd Tower Design, 2nd Ed. p. 91, y = Concentration of solute in gas, mol fraction
U.S. Stoneware Go. (1933), by permission, now, Norton Chemical y* = Concentration of solute in gas in equilibrium
Process Products Corp. with liquid, mol fraction
Y = Concentration of solute in gas, lb mol
If the system has more than two components, the calcu- solute/lb mol solvent gas
lations may be based on the component which varies the P Concentration of solute in gas in equilibrium
=
most in passing through the unit, or the component for with liquid, lb mol solute/lb mol solvent gas
which good data are available.
A large majority of the systems have operating lines and If the liquid film controls:
equilibrium curves which can be assumed as straight over
the range covered by the design problem. For the condi- (9 - 86)
tions of a straight line equilibrium curve, y* = mx, Col-
burn [lo, 111 has integrated the relation above to obtain:
x1 l+X,
--I
2.3 log [ (1 - P") M + P"] dX 1/21n- (9- 87)
N= (9- 81) l+X,
1 - P"
x2
where N may be NOG or NOL depending on operation. where x = concentration of solute in liquid, mol fraction
x* = concentration of solute in liquid in equilibrium
Table 9-40 identifies several important conditions that with gas, mol fraction
affect the values of P" and M. These are extracted from X = concentration of solute in liquid, lb mol solute/lb
mol solvent
Colburn's larger summary [ 111. X* = concentration of solute in liquid in equilibrium
Figure 9-70 is a plot to aid in solving the equation for N with the gas, lb mol solute/lb mol solvent
(or NOG or NOL) .
For constant temperature absorption, with no solute in It is usually necessary to graphically integrate the first
the inlet liquid, x2 = 0, and the abscissa becomes y1/y2. terms of the above equations, although some problems do
allow for mathematical treatment.