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Unformatted text preview: number of stages, absorbent flow rate, and absorbent temperature on the
absorption of a paraffin hydrocarbon gas.
Given: 2,000 lbmol/h of a gas mixture containing in mole fractions, 0.830 C1, 0.084 C2, 0.048
C3, 0.026 nC4, and 0.012 nC5, at 75 psia and 60oF. Absorbent oil of MW = 161.
Assumptions: SRK for Kvalues and enthalpies.
Find: For the following four cases, compute product flow rates and compositions, and interstage
vapor and liquid flowrates and compositions:
Case No. of Stages (a)
(b)
(c)
(d) 6
12
6
6 Absorbent rate,
lbmol/h
500
500
1,000
500 Absorbent
temperature, oF
90
90
90
60 Analysis: Chose nC11 , MW = 156, for the absorbent oil The calculations were made with the
Tower model (Insideout method) of Chemcad. For Case (a), the specs are:
No condenser with top pressure = 75 psia
Column pressure drop = 0 psi.
Number of stages = 6
Feed gas to stage 6
Absorbent to stage 1
At the top, no condenser
At the bottom, no reboiler
Estimated distillate rate = 2,000 lbmol/h
Estimated reflux rate = 500 lbmol/h
Estimated temperature of stage 1 = 100oF
Estimated temperature of bottom stage = 100oF
Estimated temperature of stage 2 = 100oF
Specifications for the other 3 cases differed only in the number of equilibrium stages and the
flow and temperature of the absorbent oil, plus changes in the estimates. Convergence of each
case was achieved in 3 or 4 iterations.
The results for each case are given on the following
s, where it is observed that
1. Doubling the number of stages, only increases the absorption of nC5. It is the only feed gas
component with an absorption factor, A = L/KV, > 1.
2. Doubling the absorbent rate almost doubles the amount absorbed of each feed gas component.
3. Lowering the absorbent temperature increases somewhat the absorption of lighter components Analysis: (a) (continued) Exercise 10.36 (continued) Exercise 10.36 (continued)
Analysis: (a) (continued) Exercise 10.36 (continued)
Analysis: (b) (continued) Exercise 10.36 (continued)
Analysis: (b) (continued) Exercise 10.36 (continued)
Analysis: (c) (continued) Exercise 10.36 (continued)
Analysis: (c) (continued) Exercise 10.36 (continued)
Analysis: (d) (continued) Exercise 10.37
Subject: Absorption of a hydrocarbon gas with ndecane.
Given: 1000 lbmol/h of a paraffin hydrocarbon gas, of composition below, at 90oF and 75 psia.
1000 lbmol/h of nC10 absorbent at the same temperature and pressure. Absorber has 4
equilibrium stages and operates at 75 psia.
Assumptions: SRK for Kvalues and enthalpies.
Find: Product rates and compositions, stage temperatures, and interstage vapor and liquid flow
rates and compositions.
Analysis: As shown below, when the gas feed was flashed, it was found to contain 7.2 mol%
liquid. The calculations were made with the Tower model (Insideout method) of Chemcad, with
the following specifications:
No condenser
Column pressure drop = 0 psi.
Number of stages = 4
Feed gas to stage 4
Absorbent to stage 1
At the top, no condenser
At the bottom, no reboiler
Estimated distillate rate...
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This document was uploaded on 02/24/2014 for the course CBE 2124 at NYU Poly.
 Spring '11
 Levicky
 The Land

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