MEEBAL Exam 1
October 2013
Show all work in your blue book. Points will be deducted if steps leading to answers are not
shown. No work outside blue books (such as writing on the flow sheets) will be considered. No
outgoing text messages are allowed during the exam. You must use given stream numbering in
the problems (no points given if different numbering system is used). Report all answers with
three significant digits. All pressures are absolute unless otherwise specified. You are allowed to
use one page of notes and a calculator (no textbooks, computers or tablets such as iPads are
allowed). You must pass in your test sheet with your blue book for your exam to be graded (put
your name on the exam sheet).
1. (25 points)
1
Compressor
2
3
Reactor
4
Stream 1 (100 mol/h) contains a mixture of 70 mol% C3H8 and 30 mol% H2, and enters a compressor at 298 K
and 23 atm. After passing through the compressor, the stream (Stream 2) is at 298 K and 32 atm. It enters a
reactor, where it is burned with 20% excess air (Stream 3) to form CO2 and H2O in the following reactions
(unbalanced):
__C3H8 + __O2 → __CO2 + __H2O
(Reaction 1)
__H2 + __O2 → __H2O
(Reaction 2)
Some of the C3H8 is also consumed in the following side reaction (unbalanced):
__C3H8 + __O2 → __CO + __H2O
(Reaction 3)
The conversions of C3H8 and H2 are 85% and 80%, respectively. Of the C3H8 that reacts, 90% reacts to form
CO2, and remainder reacts to form CO.
Assume all streams obey the ideal gas equation of state.
Calculate:
a.
b.
c.
d.
e.
(5 pts) Volumetric flow rate (L/h) of Stream 2
(5 pts) Molar flow rate (mol/h) of O2 in Stream 3
(5 pts) Molar flow rate (mol/h) of CO2 and CO in Stream 4
(5 pts) Molar flow rate (mol/h) of H2O in Stream 4
(5 pts) Mole fraction of O2 in Stream 4
MEEBAL Exam 1
October 2013
2. (25 points)
5
Separator 2
7
4
1
2
Reactor
3
Separator 1
6
Methanol (CH3OH) is produced in the following two reactions:
CO + 2H2 → CH3OH
CO2 + 3H2 → CH3OH + H2O
A fresh feed of CO, H2, CO2 and N2 (Stream 1) combines with a recycle stream (Stream 5) and enters a reactor
(Stream 2) with a flow rate of 100 mol/h at 100 K and 43 atm. The composition of Stream 2 is 25 mol% CO, 65
mol% H2, 2 mol% N2, and 8 mol% CO2. The single-pass conversions of CO and CO2 in the reactor are 75% and
60%, respectively. The reactor effluent (Stream 3) enters Separator 1, which removes all CH3OH and H2O as
Stream 6 (there is only CH3OH and H2O in Stream 6). Stream 4 then enters Separator 2, which removes all N2
and 75% of the H2 as Stream 7. Stream 5 is then recycled and combined with Stream 1.
Assume that the gases are non-ideal and obey the compressibility factor equation of state.
Critical constant data:
CO: Pc = 34.5 atm; Tc = 133 K
H2: Pc = 12.8 atm; Tc = 33.3 K (Note: for H2, you need to apply Newton’s corrections, which state that
8 atm and 8 K need to be added to Pc and Tc, respectively, prior to calculating PR and TR)
N2: Pc = 33.5 atm; Tc = 126.2 K
CO2: Pc = 72.9 atm; Tc = 304.2 K
The molecular weight of CH3OH is 32 g/mol.
Calculate:
a.
b.
c.
d.
e.
(5 pts) Volumetric flow rate (L/h) of Stream 2
(5 pts) Molar flow rate (mol/h) of each component in Stream 3
(5 pts) Molar flow rate (mol/h) of each component in Stream 5
(5 pts) Molar flow rate (mol/h) of each component in Stream 1
(5 pts) Total molar flow rate (mol/h) of Stream 1 to scale this process to achieve a CH3OH
production rate of 10,000 g/h
MEEBAL Exam 1
October 2013
3. (25 points)
A mixture of C3H8 and C4H10 (Stream 1) is burned with pure O2 (Stream 2) in a furnace. The combustion
products (Stream 3) leave the reactor at 100 kmol/h and contain 48 mol% H2O. Stream 3 is passed through a
condenser where all the water condenses and flows out as Stream 5 (there is only water in Stream 5). Residual
gases (Stream 4) contain 70 mol% CO2 and 30 mol% O2.
Calculate:
a.
b.
c.
d.
e.
(5 pts) Molar flow rate of O2 in Stream 4 (kmol/h)
(5 pts) Molar flow rate of Stream 1 (kmol/h)
(5 pts) Mole fraction of C3H8 in Stream 1
(5 pts) Molar flow rate of Stream 2 (kmol/h)
(5 pts) Percent excess O2 in Stream 2 (%)
MEEBAL Exam 1
October 2013
4. (25 points)
N2 + 3H2 à 2NH3
100 kmol/h of fresh feed (Stream 1) to an ammonia (NH3) production reactor contains N2 and H2 in
stoichiometric molar ratio and 20 mol% inert gas (I). The feed is combined with a recycle stream (Stream 7) and
enters the reactor as Stream 2 (N2, H2 and I). The single-pass conversion in the reactor is 50% for both N2 and
H2. The reactor effluent flows to a condenser (Stream 3). The liquid stream (Stream 4) contains all the NH3
formed (there is only NH3 in Stream 4). The gas stream (Stream 5) is split into recycle (Stream 7) and purge
(Stream 6) streams in molar ratio of 4 moles in Stream 7 for every mole in Stream 6. In every stream containing
N2 and H2, the two species are in stoichiometric molar proportion. It is helpful to use component molar flows for
each stream because the molar ratio of N2 to H2 is constant.
Calculate:
a.
b.
c.
d.
e.
(5 pts) Molar flow rate of inert gas in Stream 2 (kmol/h)
(5 pts) Mole fraction of H2 in Stream 3
(5 pts) Extent of reaction across the reactor (kmol/h)
(5 pts) Molar flow rate of Stream 6 (kmol/h)
(5 pts) Overall conversion of N2
Grading rubric:
5 pts – correct answer (or answer is off due to a carryover error from previous
part), all work clearly shown
3.5 pts – one minor mistake, all work is shown and an answer is reported
2 pts – one major mistake or multiple minor mistakes with answer reported; or
mostly correct work but didn’t finish and didn’t provide an answer
1 pt – multiple errors but some logical/pertinent work is shown
0 pts – no attempt or nothing pertinent