Page 73 - Applied Process Design For Chemical And Petrochemical Plants Volume II

62 Applied Process Design for Chemical and Petrochemical Plants

Xylene: Sensible heat Example 8-20: Open Steam Stripping of Heavy Absorber
(106) (33.33) [0.40 x 1.81 (80”-20”) = 153,000 Rich Oil of Light Hydrocarbon Content (used by
Latent heat permission following the method of R W. Ellerbee,
(106) (33.33) (82.87 x 1.8) = 525,000 ChensiCaZ Engineering [ 1271)
Total heat load 1,872,400 Btu A gas processing plant selectively extracts ethylene and

1,872,400 Btu / 100 mols I ethane from an incoming natural gas mixture stream.
Lbs steam required for heat load =
970 Btu/lb at 212°F These two light hydrocarbons are absorbed in a heavy gas*
line type absorber “oil,” and then stripped with open steam
= 1,932 lbs steam/lOO mols in an open tower. The system data are (see Figure 841):
volatile
Rich oil rate to tower: 8,500 mol/hr
1,932
Mols steam required for heat load = - Overhead product of ethylene and ethane: 775 mol/hr
18 Overhead product from
= 107.2 mols steam / 100 mols volatile material accumulator: 55% vapor and 45% liquid
Accumulator conditions: 48 psia and 133.F
Reflux hydrocarbon in top vapor @ 175°F: 850 mol/hr
Total mols steam/lOO mols volatile feed = 153.7 + 107.2 Steam (superheated) enter bottoms
= 262.9 below tray: 14,000 lb/hr
Water partial pressure in the mixed vapor
Total pressure of system: at bottoms: 20 psi
Hydrocarbons mix partial pressure: 50 psi - 20 psi = 30 psi
Ng + LOT
n=
Ii/pi Neglect pressure drops through the system.
igs Determine: How much water is removed from the over-
LT = Total mols volatile material at start = 100 head accumulator and the intermediate dehydrator or
water removal tray? No water is removed from the bottoms
x= 155*7 ’ loo = 580 mm Hg abs due to the use of superheated steam.
0.4397

Hydrocarbon 775 rnolslhr Hydrocarbon 450 rnolslhr
50 Dsia 140°F
Total rnolalhr 48 psia 8 135°F vapr
- Condenser Accurnmulator
(HC + Water) 1,893
Dehydrator tray
\
Water 243 molslhr
-
Rich Oil 8 500 rnolalhr ! - - - - - . Reflux 850 HC rnolslhr 45% Liquid Hydrocarbon
509 rnolshr Water
L-
50 psia

Stripping
solurnn

p,=20 psi
300°F
Steam 14,000 Ib/h 777.77 mols/hr
4 Figure 6-41. Open steam stripping
+ light hydrocarbons from a rich oil.
Modified for ExarnDle 8-20 and
Lean Oil 8,500 rnolslhr
L- used by permission, Ellerbee, R. W.,
Chem. Eng. Mar. 4 (1974), p. 108.