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exam question with bounce question
CLSE 201 Chemical Engineering Fundamentals: Material Balances FALL 2014
EXAM #2.
You may use your book but not your notes. Ther
e are no trick questions. Use one side of engineering
paper, begin each numbered problem on a new page, number the pages in order, show all your work, and
box
your answers
. Make sure you write legibly. Partial credit will
be given if you show all
your work cl
early. When
done, put the pages in order, put this test page on top, stapl
e together at the top left corner, and put your name on
the top right of the test page. Do NOT fold.
1.
The flowchart attached is part of an overall process that is used to dispose of solvent wastes
generated in the paint and coating industry. The primary solvents that need to be disposed are
Ethyl Acetate (ETA) and Isopropyl alcohol (IPA). In
this process, three streams of differing
compositions are mixed and the resulting stream is
fed into an incinerator, where the solvents are
burned. Stream #1 contains pure ETA, Stream #2 contains pure IPA, while Stream #3 contains both
ETA and IPA.
The incinerator is not too effective to complete
ly oxidize all of the solvents and CO thus appears
in the exhaust gases. When this happens, 2% of the entering IPA and 5% of the entering ETA
remain unburned. The unburned IPA and ETA are recycled back to form a new stream into the
mixer. Of the IPA that is burned, 80% is completely oxidized to CO
2
and 20% is only partially
oxidized to CO. Similarly, 90% of the burned ET
A is completely oxidized and 10% is partially
oxidized.
NOTE
: All % are in mol%
a. There are four variables that still need to
be labeled on this flowchart. The four variables are
needed to correctly label the flowchart. These have nothing to do with the conversion data above so
there is no need to label the given information. Find the four missing variables, label them and
please
circle them
so that I can find the answers easily¦..(
10
points)
b. Complete the DOF analyses on the flowchart page. (There may be more lines in the DOFA boxes
than you need). For each piece of given information
that you cite as a degree of freedom, use the
justification side to explain either 1) which flow
chart variables that information will allow you to
determine or 2) which variables will be related by using that information (i.e., which variables will
appear in an expression you will write using the info
rmation). Your justification phrases should take
the forms: find variable1 or find variable1 and variable2 or relate variable1 to variable2,
variable3¦¦(
20
points)
c. Complete
an analysis of the flowchart by systematically developing the equations required to
determine all of the variables on the flowchart. Do
no
numeric calculations. Number your
equations and be sure to include a short phrase next to each equation telling me what that equation
is about. For example, phrases such as water bal
ance or conversion relationship will suffice as
explanations¦..(
35
points)
d. Using the variables on the flowchart, develop the auxiliary equations needed to calculate
a. The fraction of water in the exhaust gas due to combustion of the ETA only
b. Mole fraction of carbon dioxide in the exhaust gas on a dry gas basis.
c. Yield of carbon monoxide based on the combined flow of both fuels¦..(
20
points)
e. For the reactions involving only ETA, derive expr
essions for the output stream components from the
incinerator in terms of the extents of reaction. Do
no
numeric calculations¦..(
15
points)
NOTE
: ALL
Å
‘s are in kmol/hr
DOF ANALYSES
On the mixer Justification On the Incinerator Justification
BONUS QUESTION:
Fuels for motor vehicles other than gasoline are being ev
aluated as they generate lower
levels of pollutants than
does gasoline. Compressed propane has been suggested as
a source of power for vehicles. Suppose that in a
test, 20 kg of C
3
H
8
is burned with 400 kg of air to produce 44 kg of CO
2
and 12 kg of CO. What was the percent
excess air? ¦¦.(
10
points).
