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

?

’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).