Page 132 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Distillation 121

Mols component absorbed/mol lean oil = 0.’72/64.8 = 0.0111 To = Lean oil temperature, “F
U = Overall heat transfer coefficient between absorber
Mols of component in off gas out top of absorber: outside surface and atmosphere, Btu/(ft2) (“F) (hr);
usual value = 3.0
= 500.0 - 0.72 = 499.28 VI = Mols/hr lean gas leaving absorber
Vi = Gas leaving tray i, mols/hr
These results do notjustify recalculation for greater Vi + 1 = Gas leaving tray, i + 1, mols/hr
accuracy. Note that 98% of the C3H4 is absorbed VN = Vapor leaving bottom absorber tray, mols/hr
instead of 96.5% as initially specified. This could be Vx + 1 = Mols/hr rich gas entering absorber
revised by reassuming a lower (slightly) oil rate, but Vo = Mols/hr stripping medium (steam or gas) entering
stripper
this is not considered necessary. vli = Molar gas flowate of component “i” leaving plate 1 in
The off gas analysis Y1 represents mols gas out per absorber
mol entering rich gas. v, + li = Molar gas flowrate of component “i” in entering gas
For a new design a study should be made of num- to absorber
ber of trays against required lean oil for a given W = Rate of flow, thousand Ib/day
X = Number mols absorbed component or stripped per
absorption. mol lean oil entering column
X1 = Number mols liquid phase component in equilibrium
Nomenclature For Part 2, Absorption and Stripping with Y1
= Mols of a component in liquid absorbed per mol of
X~R
(Special notations, all others same as for Distillation lean oil entering column
Performance Nomenclature, Part 1) ZXi = Total mols of all liquid phase Components absorbed
per mol of lean oil (omitting lean oil present in
liquid phase, considered = 1.0)
A’ = Edmister’s effective absorption factor
A“ = Outside surface area of absorber, ft2 XM + 1 = Number liquid phase mols of component entering
stripper per mol of lean oil
A = Absorption factor, average
A, = EfYective absorptive factor Gi = Number liquid phase mols of component entering
absorber with iean oil per mol of lean oil
AB^ = Absorption factor for each component at conditions Y1= Number vapor phase mols of component leaving top
of bottom tray
plate of absorber per mol rich gas entering absorber
AT^ = Absorption factor for each component at conditions Yi = Mols component in vapor phase from tray “i”/mol
of‘ top tray
Cp = cp = Specific heat, Btu/lb (“F) rich gas entering absorber
E, = Kosorption Efficiency, or fraction absorbed XYi = Total mols of all vapor phase components stripped
per mol of stripping medium
E, = Overall tray efficiency, fraction YN + 1 = Number vapor phase mols of component entering
E, = Stripping efficiency, or fraction stripped
fai = Fraction of v, + li absorbed by the liquid absorber per mol rich gas entering
fsi = Fraction of l0i stripped out of the liquid Yo* = Number vapor phase mols of component in
G,i = Mols individual components stripped per hour equilibrium with lean oil per mol of rich gas entering
AH = Total heat of absorption of absorbed components,
thousand Btu/day Subscripts
K = Equilibrium constant, equals y/x, at average tower
conditions 1, 2, etc. = Components in a system
L~I = Mols/hour rich oil entering stripper Arnb = Ambient
+ 1
A,
LN = Liquid leaving bottom absorber tray, mols/hr bg, = Arithmetic average
L,, = Mols/hr lean oil entering absorber, or leaving DG = Discharge gas
stripper e = Effective
loi = Molar flow of component “i” in entering liquid to i = Individual components in mixture
absorber IG = Intake gas
M = Number theoretical stages in stripper Key = Key component
m = M (see above) L = Lean concentration end of column
N = Number theoretical stages in absorber LO = Lean oil
n = N (see above) Min = Minimum condition
S, S, = Stripping factor, average and effective, respectively o = Operating condition
S’ = Edmister’s effective stripping factor R = Rich concentration end of column
Ti = Tray i, temperature, “F RO = Rich oil
TN = Bottom tray temperature, “F S = Absorbed components
TN + 1 = Inlet rich gas temperature, “F