Process engineering

1. MP5040: PROCESS ENGINEERING
Lecturer: Miss. J Sajeeva
Lecture Number 11

2. QUESTION
A solute A is to be recovered from an inert carrier gas B by absorption into a solvent. The gas entering into the
absorber flows at a rate of 500 kmol/h with 𝑦𝐴 = 0.3 and leaving the absorber with 𝑦𝐴 = 0.01. Solvent enters the
absorber at the rate of 1500 kmol/h with 𝑥𝐴 =0.001.
The equilibrium relationship is 𝑦𝐴 = 2.8 𝑥𝐴 . The carrier gas may be considered insoluble in the solvent and the
solvent may be considered nonvolatile.
1. Determine the ത
𝐿 and ത
𝑉
2. Find out the operation line
3. Construct the x-y plots for the equilibrium and operating lines using both mole fraction and solute-free
coordinates
ഥ
𝒀𝑨 =
ത
𝑳
ഥ
𝑽
ഥ
𝑿𝑨 + (ഥ
𝒀𝑨𝒃 −
ത
𝑳
ഥ
𝑽
ഥ
𝑿𝑨𝒃)

3. ANSWER
Data
𝐿𝑡 =
1500𝑘𝑚𝑜𝑙
ℎ
, 𝑦𝐴𝑏 = 0.3, 𝑉𝑏 =
500𝑘𝑚𝑜𝑙
ℎ
, 𝑥𝐴𝑡 = 0.001, 𝑦𝐴𝑡 = 0.01
𝑦𝐴 = 2.8 𝑥𝐴 (equilibrium curve)
The carrier gas may be considered insoluble in the solvent and the solvent may be considered nonvolatile. So, we
can neglect the flow rate of the solvent in the entrance and exit of the solvent in liquid and vapor respectively.
ത
𝐿 = 𝐿𝑡 (1 - 𝑥𝐴𝑡) = 1500(1 − 0.001) = 1498.5 kmol/h
ത
𝑉 = 𝑉𝑏 (1 - 𝑦𝐴𝑏) = 500(1 − 0.3) = 350 kmol/h
ഥ
𝒀𝑨 =
ത
𝑳
ഥ
𝑽
ഥ
𝑿𝑨 + (ഥ
𝒀𝑨𝒃 −
ത
𝑳
ഥ
𝑽
ഥ
𝑿𝑨𝒃)

4. ANSWER
𝐿𝑡 =
1500𝑘𝑚𝑜𝑙
ℎ
, 𝑦𝐴𝑏 = 0.3, 𝑉𝑏 =
500𝑘𝑚𝑜𝑙
ℎ
, 𝑥𝐴𝑡 = 0.001, 𝑦𝐴𝑡 = 0.01
ത
𝐿 = 1498.5 kmol/h
ത
𝑉 = 350 kmol/h
The concentration of A in the solvent stream leaving the absorber can be determined from the following expressions:
𝑥𝐴𝑏 =
𝐹𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑜𝑓 𝐴 𝑖𝑛 𝐿𝑏
𝐹𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑜𝑓 𝐴 𝑖𝑛 𝐿𝑏+ത
𝐿
𝐹𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑜𝑓 𝐴 𝑖𝑛 𝐿𝑏 (𝐿𝑏𝑥𝐴𝑏) = Flow rate of A in 𝐿𝑡 + Flow rate of A in 𝑉𝑏 - Flow rate of A in 𝑉𝑡
𝐹𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑜𝑓 𝐴 𝑖𝑛 𝐿𝑏 (𝐿𝑏𝑥𝐴𝑏) = 𝐿𝑡 𝑥𝐴𝑡 + 𝑉𝑏𝑦𝐴𝑏- Flow rate of A in 𝑽𝒕(𝑉𝑡𝑦𝐴𝑡)
ത
𝑋𝐴𝑏 =
𝑥𝐴𝑏
(1 − 𝑥𝐴𝑏)
ത
𝑌
𝐴𝑏 =
𝑦𝐴𝑏
(1 − 𝑦𝐴𝑏)
ത
𝑌
𝐴 =
ത
𝐿
ത
𝑉
ത
𝑋𝐴 + (ത
𝑌
𝐴𝑏 −
ത
𝐿
ത
𝑉
ത
𝑋𝐴𝑏)
𝐿𝑏𝑥𝐴𝑏 + 𝑉𝑡𝑦𝐴𝑡 = 𝐿𝑡𝑥𝐴𝑡 + 𝑉𝑏𝑦𝐴𝑏

5. ANSWER
But
𝑦𝐴𝑡 =
𝑭𝒍𝒐𝒘 𝒓𝒂𝒕𝒆 𝒐𝒇 𝑨 𝒊𝒏 𝑽𝒕
𝑭𝒍𝒐𝒘 𝒓𝒂𝒕𝒆 𝒐𝒇 𝑨 𝒊𝒏 𝑽𝒕+ഥ
𝑉
= 0.01
𝑭𝒍𝒐𝒘 𝒓𝒂𝒕𝒆 𝒐𝒇 𝑨 𝒊𝒏 𝑽𝒕 = 3.5354 kmol/h

6. ANSWER
Determine
1. ഥ
𝒀𝑨𝒃
2. ഥ
𝑿𝑨𝒃
ത
𝑋𝐴 =
𝑥𝐴
(1−𝑥𝐴)
=
𝑚𝑜𝑙𝑒 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝐴 𝑖𝑛 𝑡ℎ𝑒 𝑙𝑖𝑞𝑢𝑖𝑑
𝑚𝑜𝑙𝑒 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑛𝑜𝑛 𝐴 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡𝑠 𝑖𝑛 𝑡ℎ𝑒 𝑙𝑖𝑞𝑢𝑖𝑑
ത
𝑌
𝐴 =
𝑦𝐴
(1−𝑦𝐴)
=
𝑚𝑜𝑙𝑒 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝐴 𝑖𝑛 𝑡ℎ𝑒 𝑣𝑎𝑝𝑜𝑟
𝑚𝑜𝑙𝑒 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑛𝑜𝑛 𝐴 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡𝑠 𝑖𝑛 𝑡ℎ𝑒 𝑣𝑎𝑝𝑜𝑟
ത
𝑌
𝐴 =
ത
𝐿
ത
𝑉
ത
𝑋𝐴 + (ത
𝑌
𝐴𝑏 −
ത
𝐿
ത
𝑉
ത
𝑋𝐴𝑏)
0.4286,0.0987

7. EQUILIBRIUM CURVE
The equilibrium curves in both mole fraction and solute-free coordinates are calculated from the following
procedures:
1. 𝐶ℎ𝑜𝑜𝑠𝑒 𝑎 𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑥𝐴 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 0.001 𝑎𝑛𝑑 0.10
2. 𝐸𝑣𝑎𝑙𝑢𝑎𝑡𝑒 𝑡ℎ𝑒 𝑐𝑜𝑟𝑟𝑒𝑠𝑝𝑜𝑛𝑑𝑖𝑛𝑔 ത
𝑋𝐴 =
𝑥𝐴
(1−𝑥𝐴)
3. 𝐸𝑣𝑎𝑙𝑢𝑎𝑡𝑒 𝑦𝐴 = 2.8 𝑥𝐴
4. 𝐸𝑣𝑎𝑙𝑢𝑎𝑡𝑒 𝑡ℎ𝑒 𝑐𝑜𝑟𝑟𝑒𝑠𝑝𝑜𝑛𝑑𝑖𝑛𝑔 ത
𝑌
𝐴 =
𝑦𝐴
(1−𝑦𝐴)
𝑥𝐴
ത
𝑋𝐴 𝑦𝐴
ത
𝑌
𝐴

8. OPERATING LINES
The operating lines in both mole fraction and solute-free coordinates are calculated from the
following procedures:
1. 𝐶ℎ𝑜𝑜𝑠𝑒 𝑎 𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑥𝐴 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 0.001 and 0.0898
2. 𝐸𝑣𝑎𝑙𝑢𝑎𝑡𝑒 𝑡ℎ𝑒 𝑐𝑜𝑟𝑟𝑒𝑠𝑝𝑜𝑛𝑑𝑖𝑛𝑔 ത
𝑋𝐴 =
𝑥𝐴
(1−𝑥𝐴)
3. 𝐸𝑣𝑎𝑙𝑢𝑎𝑡𝑒 ത
𝑌
𝐴 =
ത
𝐿
ഥ
𝑉
ത
𝑋𝐴 + (ത
𝑌
𝐴𝑏 −
ത
𝐿
ഥ
𝑉
ത
𝑋𝐴𝑏)
4. 𝐸𝑣𝑎𝑙𝑢𝑎𝑡𝑒 𝑡ℎ𝑒 𝑐𝑜𝑟𝑟𝑒𝑠𝑝𝑜𝑛𝑑𝑖𝑛𝑔 ത
𝑦𝐴 =
𝑌𝐴
(1+𝑌𝐴)
𝑥𝐴
ത
𝑋𝐴 𝑦𝐴
ത
𝑌
𝐴

9. EQUILIBRIUM CURVE
The equilibrium curves in both mole fraction and solute-free coordinates are calculated from the following
procedures:
1. 𝐶ℎ𝑜𝑜𝑠𝑒 𝑎 𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑥𝐴 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 0.001 𝑎𝑛𝑑 0.10
2. 𝐸𝑣𝑎𝑙𝑢𝑎𝑡𝑒 𝑡ℎ𝑒 𝑐𝑜𝑟𝑟𝑒𝑠𝑝𝑜𝑛𝑑𝑖𝑛𝑔 ത
𝑋𝐴 =
𝑥𝐴
(1−𝑥𝐴)
3. 𝐸𝑣𝑎𝑙𝑢𝑎𝑡𝑒 𝑦𝐴 = 2.8 𝑥𝐴
4. 𝐸𝑣𝑎𝑙𝑢𝑎𝑡𝑒 𝑡ℎ𝑒 𝑐𝑜𝑟𝑟𝑒𝑠𝑝𝑜𝑛𝑑𝑖𝑛𝑔 ത
𝑌
𝐴 =
𝑦𝐴
(1−𝑦𝐴)
𝑥𝐴
ത
𝑋𝐴 𝑦𝐴
ത
𝑌
𝐴

10. OPERATING LINES
The operating lines in both mole fraction and solute-free coordinates are calculated from the
following procedures:
1. 𝐶ℎ𝑜𝑜𝑠𝑒 𝑎 𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 𝑥𝐴 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 0.001 and 0.0898
2. 𝐸𝑣𝑎𝑙𝑢𝑎𝑡𝑒 𝑡ℎ𝑒 𝑐𝑜𝑟𝑟𝑒𝑠𝑝𝑜𝑛𝑑𝑖𝑛𝑔 ത
𝑋𝐴 =
𝑥𝐴
(1−𝑥𝐴)
3. 𝐸𝑣𝑎𝑙𝑢𝑎𝑡𝑒 ത
𝑌
𝐴 =
ത
𝐿
ഥ
𝑉
ത
𝑋𝐴 + (ത
𝑌
𝐴𝑏 −
ത
𝐿
ഥ
𝑉
ത
𝑋𝐴𝑏)
4. 𝐸𝑣𝑎𝑙𝑢𝑎𝑡𝑒 𝑡ℎ𝑒 𝑐𝑜𝑟𝑟𝑒𝑠𝑝𝑜𝑛𝑑𝑖𝑛𝑔 ത
𝑦𝐴 =
𝑌𝐴
(1+𝑌𝐴)
𝑥𝐴
ത
𝑋𝐴 𝑦𝐴
ത
𝑌
𝐴

11. PLOT THE GRAPHS

12.  The driving force for mass transfer becomes zero whenever the operating line intersects or touches the
equilibrium curve.
 This limiting condition represents the minimum solvent rate to recover a specified quantity of solute or
the solvent rate required to remove the maximum amount of solute.
LIMITING CONDITIONS FOR ABSORPTION PROCESS.

13.  In Figure A, the intersection of the equilibrium and operating lines
occurs at the bottom of the absorber.
 This condition defines the minimum solvent rate to recover a
specified quantity of solute.
 This minimum solvent rate can be calculated from the following
expression:
LIMITING CONDITIONS FOR ABSORPTION PROCESS.

14.  In Figure B, the intersection of the equilibrium and operating lines
occurs at the top of the absorber.
 This condition represents the solvent rate required to remove the
maximum amount of solute.
 This solvent rate can be calculated from the following expression:
LIMITING CONDITIONS FOR ABSORPTION PROCESS.

15. BASIC PROCESS OPERATIONS
DISTILLATION PROCESS

16. WHAT IS DISTILLATION?

17. INTRODUCTION
1. Distillation is the process of separating the components or
substances from a liquid mixture by using selective boiling and
condensation.
2. A "distillation column" is an essential equipment item to do
"distillation" of liquid mixture on the basis of the differences in
component volatilities.
3. “Distillation" is a physical separation process not a chemical reaction.
4. Distillation may result in
1. complete separation
2. nearly pure components are obtained
3. partial separation
4. increases the concentration of selected components in the mixture

18. SUGGEST ANY DAILY
ACTIVITIES THAT ARE
USING DISTILLATION
PROCESS

19. APPLICATION
1. The earliest known evidence of "distillation“ comes from a
"terracotta distillation" apparatus dating to 3000 bc in the
"Indus valley civilization"
2. Initially "distillation" is believed to have been used to make
perfumes / distillation of alcoholic beverages occurred.
3. As far as industrial application is concerned distillation is
used for many commercial processes such as the production
of gasoline, distilled water, xylene, alcohol, paraffin,
kerosene and many other liquids
4. Gas may be liquefied and separated it is called as "cryogenic
distillation“ For example: nitrogen, oxygen and argon are
distilled from air.

20. SUB COMPONENTS OF DISTILLATION COLUMN
1. A "bubble cap" tray has riser or chimney fitted over each hole and a
cap that covers the riser. The "cap" is mounted so that there is a
space between riser and cap to allow the passage of vapor. Vapor
rises through the chimney and is directed downwards by the cap.
Finally discharging through slots in the cap finally bubbling through
the liquid on the tray
2. "Sieve trays" are simply metal perforated plates with holes in them
vapor passes straight upward through the liquid on the plate. The
arrangement, number and size of the holes are design parameters
3. Valve trays - In valve trays perforations are covered by liftable caps.
The lifting gap directs the vapor to flow horizontally into the liquid,
thus providing better mixing than is possible in "sieved trays"

21. SUB COMPONENTS OF DISTILLATION COLUMN
1. A "bubble cap" tray has riser or chimney fitted over each
hole and a cap that covers the riser.
2. The "cap" is mounted so that there is a space between
riser and cap to allow the passage of vapor.
3. Vapor rises through the chimney and is directed
downwards by the cap. Finally discharging through slots
in the cap finally bubbling through the liquid on the tray

22. SUB COMPONENTS OF DISTILLATION COLUMN
1. Sieve trays are simply metal perforated plates with holes in them
vapor passes straight upward through the liquid on the plate.
The arrangement, number and size of the holes are design
parameters
2. Valve trays - In valve trays perforations are covered by liftable
caps. The lifting gap directs the vapor to flow horizontally into
the liquid, thus providing better mixing than is possible in "sieved
trays"

23. MAIN COMPONENTS OF DISTILLATION COLUMN
1. Distillation columns are made up of several components. Each of which is used either to
1. transfer heat energy
2. enhance material transfer
2. A schematic of a typical distillation unit with a single feed and two product streams is
shown.
3. A vertical shell where the separation of liquid components is carried out.
4. Column internal such as trays, plates and packings which are used to enhance component
separations.
5. A reboiler to provide the necessary vaporization for the distillation process
6. A condenser to cool and condense the vapor leaving the top of the column
7. A reflux drum to hold the condensed vapor from the top of the column, so that liquid
reflux can be recycled back to the column.
8. Receivers are used to store the outputs from top and bottom of the column

24. A SIMPLE DISTILLATION PROCESS
1. Liquid mixture that is to be processed is known as the feed
and this is introduced usually somewhere near the middle of
the column to a tray known as the "feed tray“.
2. The feed tray divides the column into a top enriching our
rectification section and a bottom that is "stripping section“.
3. The feed flows down the column where it is collected at the
bottom in the reboiler heat is supplied to the reboiler to
generate vapor. The source of heat input can be any suitable
fluid Although in most chemical plants this is normally steam.
4. The vapor raised in the reboiler is reintroduced into the unit at
the bottom of the column. The liquid removed from the
reboiler is known as the bottoms product.

25. A SIMPLE DISTILLATION PROCESS
5. The vapor moves up the column and as it exits the top
of the unit it is cooled by a condenser.
6. The condensed liquid is stored in a holding vessel
known as the reflux drum.
7. Some of this liquid is recycled back to the top of the
column and this is called the reflux.
8. The condensed liquid that is removed from the system
is known as the "distillate or top product".

26. A SIMPLE DISTILLATION PROCESS
❑ Each tray has 2 conduits, one on each side, called
DOWNCOMER
❑ Liquid falls through the downcomers by gravity from one tray
to the one below it.
❑ A WEIR on the tray ensures that there is always some liquid
(HOLDUP) on the tray and is designed such that the holdup is at
a suitable height, e.g. such that the bubble caps are covered by
liquid.
❑ Vapor flows up the column and is forced to pass through the
liquid, via the openings on each tray.
❑ The area allowed for the passage of vapor on each tray is called
the "active tray area"