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interheater stages as feed stages with heat transferred out as negative and heat transferred in as
positive:
Partial condenser and Top pressure = 250 psia
No condenser or stage pressure drop. Therefore, bottom pressure also = 250 psia
Number of stages = 17 (includes partial condenser and partial reboiler)
Feed stage one = 5 from the top for the intercooler
Feed stage two = 9 from the top for the feed to the column
Feed stage three = 13 from the top for the interheater
At the top, reflux rate = 150 lbmol/h
At the bottom, bottoms rate = B = F  D = 100  23 = 77 lbmol/h
Estimated distillate rate = 23 lbmol/h (actual rate)
Estimated reflux rate = 150 lbmol/h (actual rate)
Estimated temperature of stage 1 = 120oF
Estimated temperature of bottom stage = 300oF
Estimated temperature of stage 2 = 140oF
Although the feed is given as a bubblepoint liquid at 250 psia and 213.9oF, the SRK equation of
state gave a bubblepoint temperature of 210.7oF, which was the value used. Based on the feed
composition below, the distillate rate of 23 lbmol/h corresponded to a desired split between
propane and nbutane. The calculations converged rapidly in 3 outerloop iterations with results
given below and on the following pages:
Condenser duty = 856,200 Btu/h
Reboiler duty = 1,014,000 Btu/h
o
Top temperature = 115 F compared to assumed value of 120oF
Bottom temperature = 264.4oF compared to assumed value of 300oF
Stage 2 temperature = 123.7oF compared to assumed value of 140oF Exercise 10.23 (continued) Analysis: (continued) Analysis: (continued) Exercise 10.23 (continued) Exercise 10.24
Subject:
Determination of optimal feed locations for two feeds of light normal paraffin
hydrocarbon mixtures by a rigorous equilibriumstage method.
Given: Feeds of compositions below as a bubblepoint liquids at a constant column pressure of
250 psia. Column has a partial condenser, partial reboiler, and 30 equilibrium stages in the
column. Distillate rate = 36.0 lbmol/h and reflux rate = 150.0 lbmol/h. PengRobinson equation
of state for Kvalues and enthalpies. Suggested feed locations are stage 15 (stage 17 from the top
counting the partial condenser), and stage 6 (stage 26 from the top counting the partial
condenser) from the bottom for the heaviest feed, F2. PengRobinson equation of state for Kvalues and enthalpies.
Find: Optimal feedstage locations.
Analysis: The calculations were made with the TOWER model (Insideout method) of the
Chemcad program, with the following specifications:
Partial condenser
Top pressure = 250 psia
No condenser or stage pressure drop. Therefore, bottom pressure also = 250 psia
Number of stages = 32 (includes partial condenser and partial reboiler)
Feed one initially to stage = 17 from the top
Feed two initially to stage = 26 from the top
At the top, reflux rate = 150 lbmol/h
At the bottom, bottoms rate = B = F  D = 100  36 = 64 lbmol/h
Estimated distillate rate = 36 lbmol/h (actual rate)
Estimated reflux rate = 150 lbmol/h (actual rate)
Estimated temperature of stage 1 = 120oF
Estimated temperature of bottom stage = 250oF
Estimated temperature of stage 2...
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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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