CHE343 Exam 1 October 2018
Name:_____________________ Uniqname:___________________
Show all work. Points will be deducted if steps leading to answers are not shown. Clearly state all assumptions
and approximations. No outgoing messages/information of any kind are allowed during the exam. You must
use the given stream numbering and notations in the problems (no points given if different
numbering/notations are used). Report all answers with three significant digits. You are allowed to use one
page of notes and a calculator (no textbooks, computers or tablets such as iPads are allowed).
1. (20 points)
**No work in this exam packet will be graded – only work in the workbook packet will be graded**
A distillation column (1 atm) receives a two-phase feed at 89 ºC that is 30 wt% ethanol and 70 wt% water. The
feed flow rate is 1000 kg/h. The external reflux ratio L0/D = 3. The distillate is 90 wt% ethanol. A total condenser
produces a subcooled liquid (reflux and distillate) at 40 ºC. Bottoms from the partial reboiler is 96 wt% water
(saturated liquid). Use the enthalpy composition diagram provided in the workbook packet at the end of Problem 1,
as needed.
Find:
a. (5 pts) Recovery of ethanol in the distillate (%)
b. (5 pts) Temperature of the vapor entering the total condenser (ºC)
c. (5 pts) QC (kcal/h)
d. (5 pts) QR (kcal/h)
1
, CHE343 Exam 1 October 2018
Name:_____________________ Uniqname:___________________
2. (20 points)
**No work in this exam packet will be graded – only work in the workbook packet will be graded**
D=?
()# =?
F=100
kmol/h
!"# = 0.5 /.
B=?
-. (+# = 0.15
A distillation column operating with a partial reboiler and without the condenser turned on. A saturated liquid of
methanol and water (zF,M=0.5) is fed with a flowrate (F) of 100 kmol/h. The boilup ratio is 3.2, and the bottoms
product (xB,M) of 0.15 (mole fraction of methanol). Assume CMO is valid.
Find:
a) (5 pts) Mole fraction of methanol in the distillate, xD (use flow diagram above)
V
D=?
()# = 0.90
F=100
kmol/h -0
!"# = 0.5 /.
-. B=?
(+# = 0.15
b. (5 pts) Minimum reflux ratio if the total condenser is now turned on and xD is now 90 mol% methanol
(q=1, feed is the same as in part a, VLE graph is provided in the workbook packet)
c. (5 pts) Number of stages (including partial reboiler) if the reflux ratio is three times the minimum
reflux ratio (use flow diagram in part B, total condenser is on, VLE graph is given in the workbook
packet)
d. (5 pts) Boilup ratio for the column with the total condenser (use flow diagram in part B, total
condenser is on)
2
Name:_____________________ Uniqname:___________________
Show all work. Points will be deducted if steps leading to answers are not shown. Clearly state all assumptions
and approximations. No outgoing messages/information of any kind are allowed during the exam. You must
use the given stream numbering and notations in the problems (no points given if different
numbering/notations are used). Report all answers with three significant digits. You are allowed to use one
page of notes and a calculator (no textbooks, computers or tablets such as iPads are allowed).
1. (20 points)
**No work in this exam packet will be graded – only work in the workbook packet will be graded**
A distillation column (1 atm) receives a two-phase feed at 89 ºC that is 30 wt% ethanol and 70 wt% water. The
feed flow rate is 1000 kg/h. The external reflux ratio L0/D = 3. The distillate is 90 wt% ethanol. A total condenser
produces a subcooled liquid (reflux and distillate) at 40 ºC. Bottoms from the partial reboiler is 96 wt% water
(saturated liquid). Use the enthalpy composition diagram provided in the workbook packet at the end of Problem 1,
as needed.
Find:
a. (5 pts) Recovery of ethanol in the distillate (%)
b. (5 pts) Temperature of the vapor entering the total condenser (ºC)
c. (5 pts) QC (kcal/h)
d. (5 pts) QR (kcal/h)
1
, CHE343 Exam 1 October 2018
Name:_____________________ Uniqname:___________________
2. (20 points)
**No work in this exam packet will be graded – only work in the workbook packet will be graded**
D=?
()# =?
F=100
kmol/h
!"# = 0.5 /.
B=?
-. (+# = 0.15
A distillation column operating with a partial reboiler and without the condenser turned on. A saturated liquid of
methanol and water (zF,M=0.5) is fed with a flowrate (F) of 100 kmol/h. The boilup ratio is 3.2, and the bottoms
product (xB,M) of 0.15 (mole fraction of methanol). Assume CMO is valid.
Find:
a) (5 pts) Mole fraction of methanol in the distillate, xD (use flow diagram above)
V
D=?
()# = 0.90
F=100
kmol/h -0
!"# = 0.5 /.
-. B=?
(+# = 0.15
b. (5 pts) Minimum reflux ratio if the total condenser is now turned on and xD is now 90 mol% methanol
(q=1, feed is the same as in part a, VLE graph is provided in the workbook packet)
c. (5 pts) Number of stages (including partial reboiler) if the reflux ratio is three times the minimum
reflux ratio (use flow diagram in part B, total condenser is on, VLE graph is given in the workbook
packet)
d. (5 pts) Boilup ratio for the column with the total condenser (use flow diagram in part B, total
condenser is on)
2
