LAB REPORT SKKC 4761
SEPARATION PROCESSES LABORATORY II
2019/2020 – 04
EXPERIMENT 6
TITLE
Double Effect Evaporation
LAB INSTRUCTOR
Dr Hashim Hassan
SECTION
04
GROUP NO.
5
GROUP MEMBERS
No.
Name
1.
SHAHIRAH BINTI SHAMSUDDIN
A16KT0384
2.
ZAHARATUL JANNAH BINTI SHAHARI
A16KT0470
3.
KAVILASHINI A/P MANIKAM
A16KT0130
4
WONG JIA MIN
A16KT0454
5
TWU LE YING
A16KT0442
DATE OF
EXPERIMENT
: 01/10/2019
DATE OF
SUBMISSION
: 08/10/2019
GRADING SECTION
Criteria
Technical Aspects
Matric
Score
/ 5%
Abstract
/ 10%
Introduction
Literature Review
/ 10%
/ 10%
Methodology
/ 10%
Results & Discussion
Conclusion
/ 40%
/ 10%
References
/ 5%
Comment
Overall Marks
/ 100%
ABSTRACT
Evaporation is a type of vaporization of a liquid that occurs from the surface of liquid
into its gaseous phase at its saturation temperature. Boiling is another type of vaporization
which is characterized by bubbles of saturated vapor forming in the liquid phase. Besides,
evaporation is a kind of separation technique where it removes a liquid by boiling or
vaporizing off some of the liquid in the feed. In this experiment, climbing film evaporator
was used to separate the sugar and water from the sugar solution under single-effect
evaporation. The two objectives in this experiment are to study the effect of operating
temperature on the concentration profile of sugar solution and also the effect of feed flow rate
on the final concentration of sugar solution. The sugar solution was prepared by dissolving 1
kg of sugar in 10 litres of water and served as the feed in the evaporator to undergo
evaporation. Valves were closed every 5 minutes to collect the products at each different
operating temperature, while every 5 minutes for 30 minutes for each feed flow rate to
determine the refractive indices of the solutions. The results were then compared to the
theoretical values from references to obtain the concentration profile of the sugar solution
product. Based on the result obtained, when feed flow rate increased (6.48 L/hr, 9.72 L/hr
and 12.96 L/hr) and the operating temperature was remained constant at 100ᵒC, the
concentration of sugar solution decreased, which are 68.51%, 44.74% and 28.59%
respectively. A higher volume of sugar solution and a lower volume of water were also
obtained. The results were tabulated and graphs were plotted. Meanwhile, the discussion is
also included in this report to support the results obtained. Some experimental errors and
precaution steps were also mentioned in this report.
2
TABLE OF CONTENT
TOPIC
PAGE
Abstract
2
Table of Content
3
1.0
2.0
3.0
Introduction
1.1
Background of Experiment
4
1.2
Problem Statement
5
1.3
Objectives of Experiment
5
Literature Review
2.1
Introductions
2.2
Basic Concept of Evaporation
2.3
Factors Affecting an Evaporation
Process
Methodology
3.1
Apparatus and Materials
9
3.2
Procedure
9
4.0
Results and Discussion
10
5.0
Conclusion
12
6.0
References
13
7.0
Appendices
14
3
1.0
INTRODUCTION
1.1
Background of Experiment
Evaporation is a separation process used to concentrate aqueous solutions which
involves removal of volatile solvent from an aqueous solution consisting of non-volatile
solute by vaporization, in a vessel known as evaporator. Evaporation process begins with a
liquid product and ends up with a more concentrated liquid as the main product. In some
special cases, the evaporated, volatile component is the main product, for example in water
desalination the vapors obtained by the evaporation process are condensed and used for
drinking purposes. Similarly, the water that contains minerals is evaporated to obtain solid
free water which can then be used in boilers.
Air coil and liquid coolers are two main categories of evaporators used in industrial
refrigeration. In the air coil, refrigerant passes through the pipes and air passes outside the
tube. For efficient heat transfer fins attached to the external surface of pipes and air currents
between the ribs. Besides, for natural circulation evaporators, forced circulation evaporators,
rising film tubular evaporators and falling film tubular evaporators feed enters the bottom of
the heating tubes and vaporization begins at that height within the tubes where the liquor
temperature exceeds the boiling temperature at the existing pressure. As the liquor moves up
inside the tubes, the liquor starts rapid boiling and additional vapor is produced and the
velocity of the liquid vapor mixture increases. The vapor-liquid mixture then enters to the
cyclone separator where they are separated.
A climbing film evaporator is a specialized type of evaporator in which a thin film of
liquid is passed over a rising and falling plate to allow the evaporation process to occur. It is
an extension of the falling film evaporator and has application in any field where the liquid to
be evaporated cannot withstand extended exposure to high temperatures, such as the
concentration of fruit juices. The basic design of the climbing film evaporator consists of two
phases. In the climbing phase, the liquid feed is heated by a flow of steam as it rises through a
corrugated plate. In the subsequent falling phase, the liquid flows downward at high velocity
under gravitational force. Evaporation and cooling occur rapidly in the falling phase.
4
The main advantage of climbing film evaporator is its short residence time. Since the
liquid feed does not remain in the evaporator for long, this evaporator is suitable for heat or
temperature sensitive material. Thus, this evaporator is used widely in food, beverages and
pharmaceutical industries. Besides that, the colour, texture, nutritional content and taste of the
liquid feed can be preserved too. Despite its functionality, this evaporator has a few
drawbacks such as large energy consumption.
1.2
Objective of Experiment
The objective of this experiment is:
●
To study the effect of operating temperature on the concentration profile of sugar
solution.
●
1.3
To study the effect of feed flowrate to the final concentration of sugar solution.
Scopes of Experiment
This experiment is conducted using is climbing film evaporator. 9.1wt% of sugar
solution is fed into the evaporator to carry out the evaporation of water from the sugar
solution to concentrate the sugar solution. The experiment is carried out at different feed
flowrate and temperature to study effect of feed flowrate on the final concentration of sugar
solution obtained. The volume and refractive index of product samples of water and sugar
solution are measured at interval of 5 minutes for half an hour. The outcome of the result is
discussed by the data collected.
5
2.0
LITERATURE REVIEW
2.1
Introduction
Generally, evaporator is used widely in various process, including pharmaceuticals,
food and beverages, chemicals, pulp and paper, polymers and resins, inorganic salts, acids,
bases and a variety of other material. Evaporation is one of the process that can be used in
order to concentrate the solution. According to Miyawaki et al. (2005), there are three
methods always used in concentrating the solution which are reverse osmosis
(RO),evaporation and freeze concentration. Based on these three methods, evaporation is the
leading and earliest technology been used widely in various industry. There are various types
and variations of evaporators, and the best for its application based on the product
characteristics and desired results.
The main advantage of climbing film evaporator is its short residence time. Since the
liquid feed does not remain in the evaporator for long, this evaporator is suitable for heat or
temperature sensitive material. Thus, this evaporator is used widely in food, beverages and
pharmaceutical industries. Besides that, the colour, texture, nutritional content and taste of the
liquid feed can be preserved too. Despite its functionality, this evaporator has a few
drawbacks such as large energy consumption.
2.2
Basic Concept of Evaporation
In evaporation, the vapour from a boiling point solution is removed and a more
concentrated solution remains. In most of the cases, evaporation can be refers to the removal
of water from an aqueous solution. According to Monceaux and Kuehner (2009), evaporation
can be described as a process which involve the thermal energy in order to separate the
substances, which the concentration of targeted solution is increased which caused by the
separation of volatile component such as water in the original solution. Based on the
difference in vapour pressure between the components, the volatile phase (water) is removed.
6
Evaporator is the device used in the evaporation process. The basic principle of
evaporator is simple, which remove water from a solution or slurry through evaporation
process. Evaporator is different from dryer because the concentrate discharge from
evaporator is always in liquid phase. While, the discharge from a dryer is in solid form,
usually a flowable powder or meal. The feed to an evaporator is always in liquid phase and
still in liquid form even after the water is evaporated.
The physical process of evaporation need the input of energy in form of heat in order
to convert a liquid into vapour. Since most of the evaporators use the method of evaporation
to remove water, so it is must for the evaporators have a source of heat to operate its system.
The heat source for most of the evaporators is water vapour, either in the form of boiler steam
or waste vapour from other processes. Besides that, evaporators require a means to transfer
heat energy from the heat source into the evaporator liquid. Most of the evaporators use a
tubular heater known as shell and tube heat exchanger for this purpose. In the shell part,
water vapour is condensed on the outside of the tube which giving up its heat energy. The
evaporator liquid, which is inside the tubes, absorbs the heat given up by the water vapour.
Increasing in heat cause the water in the evaporator liquid to boil and produce bubbles of
water vapour in the liquid. When these bubbles reach the surface of the evaporator and burst,
the escaping water vapour carries some of the evaporator liquid with it.
Some examples of evaporation are concentration of aqueous solution of sugar, sodium
chloride, sodium hydroxide, glycerol, glue, milk and orange juice. For these cases, the
concentrated solution is the desired product and the evaporated water is usually neglected.
2.3
Factors Affecting an Evaporation Process
The physical and chemical properties of the solution being concentrated and the
vapour being removed depends mainly on the type of evaporator used besides the pressure
and temperature of the process. Several properties which affect the evaporation process is
describe below.
7
1.
Concentration in the Liquid
The liquid feed to an evaporator is usually dilute, means low in viscosity, similar to that
of water and relatively high heat-transfer coefficient are achieved. As evaporation proceeds,
the solution may become very concentrated and quite viscous which lead to the mark drop in
the heat-transfer coefficient.
2.
Solubility
When the solutions are heated and the concentration of solute increases, the solubility
limit of the material in solution may be exceeded and crystals may form. This can limit the
maximum concentration in solution which can be obtained by evaporation. Most of the time
the solubility of the salt increases with temperature. So, during hot temperature, concentrated
solution from an evaporator is cooled to room temperature and this can cause crystallization.
3.
Pressure and Temperature
The boiling point of the solution is related to the pressure of the system. The higher
the operating pressure of the evaporator, the higher the temperature at boiling. Furthermore,
as the concentration of the dissolved material in solution increases by evaporation, the
temperature would rise. In order to keep the temperatures low in heat-sensitive materials, it is
must to operate under 1 atm pressure which is under vacuum.
8
3.0
Methodology
3.1
Apparatus and Materials
Climbing film evaporator, 250mL measuring cylinders, collecting jars, refractometer, 2kg of
sugar, 20L of water
3.2
Procedures
1. Sugar solution was prepared using 2kg of sugar and 20L of deionized water.
2. The steam boiler was turned on.
3. The capacity of feeding pump was adjusted to 60% to manipulate the feed flowrate at
6.48 L/hr and the operating temperature was set at 115°C.
4. The feeding pump was turned on and the vacuum pump was switched on in order to
speed up the evaporation process.
5. The product sugar solution and water condensed were collected separately by
adjusting the position of the valves.
6. For collecting the product sugar solution sample, V7 was closed and V8 was opened
simultaneously. At the same time, V9 was closed and V10 was opened simultaneously
to collect the condensed water sample.
7. Then, the volume and refractive index of the collected product were measured.
8. The valve controlling steps (V7, V8, V9 and V10) were repeated every 5 minutes and
the data collected was recorded. The same steps were repeated for 80% and 100%
feeding pump capacity.
9
4.0 RESULTS AND DISCUSSION
4.1 Experimental Data
Feed
Flowrate
(L/hr)
Time
(min)
6.48
5
10
15
20
25
30
5
10
15
20
25
30
5
10
15
20
25
30
9.72
12.96
Volume of
Sugar
Solution
Obtained
(mL)
170
100
130
130
130
130
350
270
230
230
230
230
460
450
450
400
430
440
Volume of
Water
Obtained
(mL)
650
730
650
660
660
650
750
780
810
790
810
810
810
840
900
840
860
850
Refractive
Index of
Water
Obtained,
%
1.3337
1.3337
1.3334
1.3334
1.3334
1.3334
1.3336
1.3330
1.3337
1.3337
1.3332
1.3337
1.3337
1.3336
1.3337
1.3337
1.3338
1.3337
Sugar Solution Obtained
Refractive Concentration
Index, %
,%
1.3908
1.4135
1.4226
1.4301
1.4321
1.4403
1.4230
1.4076
1.4045
1.4031
1.4016
1.4029
1.3941
1.3812
1.3785
1.3785
1.3780
1.3775
Figure 4.1 Graph of sugar solution concentration versus feed flowrates
10
37.05
51.48
57.26
62.03
63.30
68.51
57.52
47.73
45.76
44.87
43.91
44.74
39.15
30.95
29.23
29.23
28.91
28.59
11
From the mass balance perspective, the volume of sugar solution and volume of
water collected are inversely proportional to each other. When more water is being
evaporated, less sugar solution is produced, resulted more concentrated sugar solution. This
follows the material balance equation for an evaporator which is F= L + V, where
F = Liquid feed flow rate
L = Sugar solution flow rate
V = Steam (water) flow rate
Thus, the higher the operating temperature of the evaporator, the greater the
volume of water being evaporated. Consequently, higher concentration of sugar solution is
collected.
According to Figure 4.1, the graph of sugar solution concentration versus feed flow rates
shows that the sugar solution concentration is inversely proportional to the feed flow rate of
the liquid sugar solution entering the evaporator. The concentration of sugar solution
decreased when the feed flow rates increased. At faster feed flow rate, the residence time of
the liquid sugar solution in the evaporator reduced. As a result, the heat transfer from the
evaporator to the sugar feed solution become incomplete. In this context, incomplete heat
transfer between the evaporator and the sugar feed solution greatly reduced the kinetic
energy provided for the water molecules to break free from the hydrogen bonds, causing
less water being evaporated and producing less concentrated sugar solution. Thus, at faster
feed flow rate, the concentration of sugar solution become lower.
As observed, the refractive index data for the water distillate are within the range of
1.3330 to 1.3337 which correspond to the theoretical water refractive index value, 1.333.
This shows that the water distillate collected is comparably pure and does not contain any
sugar. This confirmed no mistake is made while measuring the refractive index of the
solutions.
There are several precaution steps that should be taken into consideration to
improve the accuracy of the experimental results obtained. Firstly, the time to turn off the
valve before collecting the samples should be more constant and precise. This ensures
12
accurate amounts of samples are taken for the next measurement. Meanwhile, the sugar
stock solution need to be prepared well before starting the experiment to prevent any
insoluble sugar is found during the experiment. Lastly, the eyesight of observer should be
perpendicular to the scale of the measuring cylinder when taking readings to minimize
parallax error.
13
5.0 CONCLUSION
Evaporation technique was used to separate both sugar and water in this experiment
and the apparatus used was the climbing film evaporator. The objectives of this experiment
are to study the effect of operating temperature on the concentration profile of sugar
solution and the effect of feed flow rate on the final concentration of sugar solution. Based
on the result obtained, when feed flow rate increased (6.48 L/hr, 9.72 L/hr and 12.96 L/hr)
and the operating temperature was remained constant at 100ᵒC, the concentration of sugar
solution decreased, which are 68.51%, 44.74% and 28.59% respectively. A higher volume of
sugar solution and a lower volume of water were also obtained. The objectives of this
experiment are achieved at the end of the experiment.
14
6.0 REFERENCES
Badger, L. W., & Banchero J. T. (1955). Introduction to Chemical Engineering, McGrawHill,
New York.
Perry, R. H., & Green, D. (1988). Perry’s Chemical Engineers’ Handbook, 6th edition,
McGraw-Hill.
Geankoplis, C. J. (2014). Transport Processes & Unit Operations, 4th edition, Pearson
Education Limited.
Miyawaki, O., Liu, L., Shirai, Y., Sakashita, S., & Kagitani, K. (2005). Tubular ice system for
scale-up of progressive freeze-concentration. J. Food Eng. 69(1): 107–113.
15
7.0 APPENDICES
Appendix A: Concentration of sugar solution with respect to the refractive index
Table A1 Refractive index for sugar concentration
Sugar Concentration (%)
Refractive Index (nD)
0
1.3330
5
1.3403
10
1.3479
15
1.3557
20
1.3639
25
1.3723
16
Figure A2 Graph of sugar concentration versus refractive index
17
Sample calculation:
The linear equation of the graph plotted for sugar concentration versus refractive index
obtained is:
y = 635.69x - 847.07
For flow rate at 6.48 L/hr, the refractive index of sugar solution product is 1.4403nD. The
sugar concentration corresponding to 1.4403nD is calculated by substituting the value into
the equation obtained above.
y = 635.69 (1.4403) – 847.07
y = 68.51 %
Thus, the concentration of sugar solution is 68.51 %. Same calculation applied for the rest
sugar solution concentration.
18
19