Mass Transfer Design question paper

7/21/2019 Mass Transfer Design question paper

1/11

UNIVERSITI

TEKNOLOG

P

ETRONAS

FINAL

EXAMINATION

SEPTEM

BER

2012

SEM

ESTER

COURSE

:

CCB2053

MASS

TRANSFER

DESIGN

DATE

: 29th DECEMBER

2012

(SATURDAY)

TIME

:

9.00 AM

-

12.00

NOON

(3

HOURS)

INSTRUCTIONS

TO

CANDIDATES

1.

Answer

ALL

questions from the Questions

Booklet.

2. Begin

EACH

answer

on a new

page

in the Answer

Booklet.

3.

lndicate

clearly answers

that are

cancelled,

if any.

4. Where applicable,

show clearly steps

taken in arriving at the

solutions and indicate

ALL assumptions.

5. Do not

open

this

Question

Booklet

until instructed.

6.

Engineering

Data Formulae

Booklet

is

provided.

Note

:

There

are

ELEVEN

(11)

pages

in this

Question

Booklet

including

the

cover

page

and

Appendix.

Universiti

Teknologi

PETRONAS


2/11

1.

CCB 2053

a.

Explain

TWO

(2')

types of

mass transfer

and

gives

TWO

(2)

examples

for each

type of

mass

transfer.

[4

marks]

b.

Ammonia

(NHs)

gas

is diffused

through a layer

of nitrogen

(N2) gas

at

298

K and 1 atm

pressure.

The

partial pressure

of ammonia

at

one

point

is 0.133

atm

and

at the

other

point

20

mm

away

it

is

0.066 atm. The

diffusivity

of the

mixture

is

2.30

x 10-5

m2ls.

.

Calculate

the flux

of

NH3

in

kgmol/s,m2

with

non-diffusing

Nz

at

one boundary.

[4

marks]

ii.

Repeat

part

(i)

assuming

Nz

also diffuses

and the

flux

is

eq uimolar

cou

nterdiffusion.

[3

marks]

iii.

Based

on the mass flux

obtained

in

part

(i)

and

(ii),

which

conditions

give

the

highest

flux? Explain

your

answer.

[3

marks]


3/11

c.

CCB

2053

flash separator

which

IGURE

Q1

shows

an

adiabatic

equilibrium

indicates

all

variables

in

each stream.

F

zi

TF

Pf

L

xi

il

TL

P,

FIGURE

Q1:

Adibatic

Equilibrium

Flash

Separator

Compute

the degrees

of

freedom

using

the Gibbs

phase

rule.

[3

marks]

might

be

specified

to

solve

the

above

[3

marks]

What

variables

problem?


4/11

ccB2053

a.

Give

THREE

(3)

reasons

why

an

economic

tradeoff

exists

between the

number

of trays

and

the reflux

ratio.

[3

marks]

b.

A continuous

distillation

column

operating

at

1

atm

is

to be

designed

for

separating

an ethanol-water

mixture.

The feed

is 20

mol%

ethanol

and

the

feed

flow

rate

is

1000

kgmol/h

of

saturated liquid.

A

distillate

composition

of

80

mol% ethanol

and

bottoms

composition

of not

more

than

2

mol%

ethanol

is desired.

The

reflux ratio

is

5/3. Equilibrium

data for ethanol-

water

system

at

1

atm are

given

in

TABLE

e3.

TABLE

Q3:

Equilibrium

data

of

ethanol

in

ethanol-water

system

Temperature

("c)

Molpercent

of

ethanol

in the liquid

phase,

x

Molpercent

of

ethanol

in

the

gas

phase,

y

100.0

0.00

0,00

95,5

1.90

17.00

89.0

7.21

38,91

86.7

9.66

43.75

84 1

16.6't

50.89

82.7

23.37

54.45

82.3

26.08

55.80

80.7

39.65

61.22

79.7

51.98

65.99

78.7

67.63

73.85

78.1

89.43 89.43

78.3

100.00

100.00


5/11

ccB2053

i.

calculate

the amount

of

distillate

and bottom

products

in

kgmol/h.

[4

marks]

ii.

By

using

the

graphical

McCab-e-Thiele

method,

determinethe

number

of

theoretical

stages

required.

[6

marks]

iii. Estimate

the

minimum

reflux

ratio.

[3

marks]

iv.

lf the

feed

condition changes

to saturated vapour

condition, discuss

the differences

in

the

number

of theoretical

stages.

[4

marks]


6/11

a.

b.

CCB

2053

Using

a

suitable diagram,

show

the

operating line for

minimum

liquid

flow

of absorption

process

and

the operating line

for minimum

gas

flow of a stripping process.

Justify

your

answers.

[4

marks]

A

packed

tower 4,0

m

tall

is

used

to

absorb

ethyl

alcohol

from

an

inert

gas

by

90 kgmol/h

of

pure

water

at

303K

and 101.3 kPa.

The

total

gas

stream

flowrate

of

100

kgmol/h

contains 2.a

moP/o

alcohot

and the

exit

concentration

is 0.20

mol%.

The

equilibrium

relation is

y

:

mx

:

0.68x for this dilute

stream.

i. Calculate

the mol

fraction

of

ethyl

alcohol in

the ext liquid.

[4

marks]

I

ill

Using

the

analytical

equations,

calculate

the

theoretical

trays,

y'/.

tv.

Determine

the HETP

for

the

above absorption

proess.

[4

marks]

Show

the

relationship

between

the number

of

theoretical

trays

obtained

n

part

(ii)

and

the number

of

transfer unit

obtained

in

part

(iii)

by

using suitable

graphical

explanation.

[4

marks]


7/11

a

.

CCB 2053

distillation

for

certain

n

general,

extraction

applications.

I

0

0.69

1.41

2.89

6.42

13.30

25.50

36.70

45.30

46.40

s

preferred

over

Define

the

liquid-liquid

extraction

process

and

over

distillation,

b.

i.

state

TWo

(2)

requirements

for liquid-liquid

extraction

to

be

feasible.

[2 marks]

An

aqueous

feed

of

200

kg/h

containing

25

wt% acetic

acid is

being

extracted

by

pure

isopropyl

ether

at

the

rate of

600 kg/h

in a

counter-current

multistage

system.

The

exit

acid concentration

in

the

aqueous

phase

is to

contain

3 wt%

acetic acid.

The

riquid-riquid

equilibrium

data at 25oC

and

1 atm

are

presented

in TABLE

e4.

TABLE

Q4: Liquid-liquid equilibrium

data

for

acetic

acid

(A)-

water

(W)-

isoproppyl

ether

(E)

system

at2SoC

and

1

atm.

Water

layer

lsopropyl

ether layer

wt%(A)

wt%(W)

wt%(E)

wt%(A)

wt%(W)

wt%(E)

0

0.6

99.4

0.18

0.5

99.3

0.37

its

importance

[2

marks]

98.9

98.4

97.1

84.7

71.5

98.9

98.1

97.1

95.5

91.7

84.4

71.1

58.9

45.1

37.1

1.2

1.2

1.5

1.6

1,9

2.3

3.4

4.4

9.6

16.5

0.7

0.79

0.8

1.93

1.0

11.40

3.9

21.60

6.9

4.82

1.9

93.3

31.10

10.8

58.1

36.20

15.1

48.7


8/11

&


9/11

5.

CCB 2053

A

continuous

countercurrent

multistage

system

is

to be

used

to leach

oil

from

a

meal

by

benzene

solvent.

The

process

is

to

treat

2000 kg/h

of

an

inert

solid meal (B)

containing

800

kg

oil (A) and

also

50

kg

benzene

(c),

The

inert flow

per

hour

in

the fresh

solvent

mixture

contains

1310

kg

benzene

and 20

kg

oil. The

leached

solids

are

to contain

ea

kg oil.

The

leaching

process

is in

the

condition

of constant

underflow

of

N

=

1.85

kg

solid/kg

solution.

a.

Plot

the

equilibrium

data on

a Ponchon-savarit

diagram

using

the

graph paper

provided.

[4

marks]

b.

usng

the

graph

in

part

(a),

determine

the

weight

fraction

of or,

yy

leaving

the

stream.

[4

marks]

c.

calculate

the

amount

of

underflow

slurry,

L,

trd in

the ovelow,

v,

leaving

the

stream.

d.

Determine

the number

of

stages

required

for

the

process.

-END

OF

PAPER-

I


10/11

Constants

Gas

constants,

R;

=

8314

m3Pa /kg

'K'mol

=

83.145 cm3

barlK.mol

=

82.055 cm3

atm/K.mol

CCB

2053

Conversion

factors

T(K)

=

tf

C)

+

Zts

1

atm

=

760

torr

=

101325

Pa

l

bar

=

1OsPa

=

0.9869 atm

1 liter

=

1

dm3=

1O0O cm3

APPENDIX

Equatons:

1.

General

diffusion

and convection

No:

-cD*+.9o(*^+trr)

azc

J

o

=

D

ulP

n' -

p

'l)

Flux

for

equimolarcounter

diffusion

"

RT(r,

-

,,)

2.

Stagnant,

non-diffusing

B

(total

pressure

constant)

:

r

DnuP

tY

.,

-

--ln

RT(2,-Zt)

P-p,qt

3. Rectifying

operating

line:

.R

xD

l'-_-r+_

'

R+l

R+l

5. Absorption

material

balance:

(constant

molar

flow)

{

+-)*

v

(

-z'):

t(

-.,-l

.'

l+,-l

f

l-

r,0, (l- o,)

-

[l-r,,J lt-

y,,)

6. KremserEquation

:

nl

lt

t-

"?u--)r-

)lwhere

ris

Absorption

ractor

i

A,

:

:t-

:

I

Y,

-

ntr,

-'re

ls

ADSorPIlon

ffi

V

r,,

InA

4. Rayleigh:

'idL:

ln

L'

-

f'

d*

Jr

r

J,

,-_t-

L2

^=y-x

10


11/11

CCB 2053

^/

_

ln{l(t

-l)

t

All0,,,

-

kx,,y(y,,,,

-

kxi,)l+

(t

l)}

t'oc

-

7. Extraction:

Fraction

of a solute,

i,

absorb

"O:

ffi

8.

Fuller

equation:

/r

_

lo'r'trs(l

lMrrllM)'')

u..18-ffi

11

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Mass Transfer Design question paper