mass transfer unit operation project in adigrat university was done.

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ADIGRAT UNIVERSITY
COLLEGE OF ENGINEERING AND TECHNOLOGY
DEPARTMET OF CHEMICAL ENGINEERING
COURSE TITLE MASS TRANSFER UNIT OPERATION
COURSE CODE Cheg3114
PROJECT MASS TRANSFER UNIT OPERATION
NETWORK -SIX
NAME OF STUDENT ID NO SECTION 1
1. LETBRHAN BAHTA………………………….0963/06
2. LETU DESALEGN………………………………0969/06
3. MEKONEN G/WAHID………………………. .1064/06
4. MIHRET G/MESKEL………………………….1121/06
5. MULUBRHAN G/MESKEL…………………….0893/05
6. TEKLAY GODEFA ……………………………..1429/06
7. TEMESGEN ABRAHALEY……………………..1464/06
Submitted to instructor H.T submission date 01/09/08 E.C

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Table content
Topic page
Introduction………………………………………………………………… 3
Chapter one
1. Drying of solid ………………………………………………………………………………4
2. Method of drying………………………………………………………………………….4
3 .mechanism of dryer………………………………………………………………………..5
4. Objective drying………………………………………………………………………………5
5. Application of drying………………………………………………………………………….5
6. Gas vapor mixture………………………………………………………………………….6
7. psychometric term…………………………………………………………………………..7
8. psychometric chart……………………………………………………………………………8
Chapter two
9. Crystallization………………………………………………………………………………10
10. Types of crystallizers………………………………………………………………………10
11, objective of crystallization…………………………………………………………………10
Chapter three
12. Extraction…………………………………………………………………………………12
13. Types extractor……………………………………………………………………………13
14. Objective extraction…………………………………………………………………………14
15. Application of extraction……………………………………………………………….15
16 .Advantage of extraction………………………………………………………………….15

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INTRODUCTION
In ancient time was used to separate two or more phase a different types of unit operation. These
unit operations are in traditional method and requires high amount of energy, poor quality
product and less economical profit. These unit operation was used by
 Mineral to separate from its ore
 In industry such as food processing, pharmaceutical,
Nowadays, these unit operations were used in modernized method in different corner of world in
industry. These unit operation include
 Drying
 crystallization
 extraction
These unit operation backbone in industry to produce a given raw material in to required product.
The separation of drying convert solid, semisolid or liquid feedstock into solid product by
evaporation of the liquid into vapor phase due heat. drying various feedstock for the following
reason;
 for preservation
 reduction in cost transportation
 easy handling etc.
is a science dealing with the physical law of air –water vapor mixture.it is a field of engineering
concerned with determination of physical and thermodynamic properties of gas
mixture.psychrometric chart it is representation of gas –vapor mixture use a chart to analyze
processing involving moist air and to determine moist air properties.
crystallization is a processes of formation solid precipitate from melt deposited directly from
gas.it also a chemical solid liquid separation technique in which mass transfer of solute from
liquid solution to form pure solid. Crystallization have a several importance.
Extraction the withdrawing of active agent or west substance from solid or liquid mixture with
a liquid solvent. The solvent is not or only partial miscible solid or liquid.
Depending on the phase following types of extraction.
1. Solid-liquid extraction
2. Liquid- liquid extraction
3. Gas-liquid extraction (absorption)

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The main area of extraction is for hydro metallic, for petroleum and pharmaceutical industry.
CHAPTER ONE
Drying of solid
Drying is unit operation in which liquid is separated from solid other than mechanical method.
In other word, the word dry refers to generally removal of moisture from substance.
This process is often used as final production step before packing product.
Dry is often necessary in various industrial operation particularly in chemical processes industry
to remove moisture from wet solid a solution or gas to make it dry and choice of dry medium
depend the chemical nature of the material.
Dryer are used in variety industries such as
 Food processing technology
 Pharmaceutical
 Paper, etc.
1.1method of dryer
Dryer can be divided in to two main type based on heating mode
 Convective (direct dryer)
 Conductive (indirect dryer)
 Radiant(radiation)
A, direct dryer (adiabatic)
Unit uses sensible heat of the fluid that contact the solid to provide the heat vaporization of the
liquid.
When, air heating increases the driving force for heat transfer accelerate drying. It is also reduce
relative humidity.
Direct dryer convectively heat a product through direct contact with heated air ,gas or combusted
gas product.
It is direct contact between the material and the drying air to dry material. More than 85%
industrial dryer use convective is convective type.
B, Indirect dryer (none adiabatic)

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Is method of removal of the liquid phase from solid material through the application of heat such
as the heat transfer medium is separated from product to be dried by metal well.
Heat a product through contact with heated well.
It is avoid the direct contact between the material and drying air.
C .radiant dryer this cause duo to radiation heat transfer method sunlight
1.1.2 Mechanism of drying
Drying is complex operation involving transient transfer of heat and mass along with several rate
processes such as chemical transformation or physical transformation which may cause change
product quality as well as mechanism heat and mass transfer.
In some products having relatively high initial moisture content an initial linear reduction of the
average product moisture content as function of time may be observed for limited time.
The drying rate during this period is mostly depend on the rate of heat transfer to material being
dried. Therefore, the maximum achievable drying considered on to be heat transfer limited.
Migration of moisture from the interior of an individual grain to surface .evaporation of moisture
from surface to surrounding.
In money processes improper drying may lead to irreversible damage to product quality and
hence non salable product.
1.1.3 Objective of dryer
Dryers are used for money purpose to decrease the product moisture in order to control the
quality product.
 To avoid or eliminate moisture which may lead to corrosion and decrease product
stability.
 To make material easy or more suitable for handling.
 To reduce the cost of transportation of large volume material.
 To improve or keep the good properties of material.e.g flow ability , compressibility
 To control the porosity of material
 To increase rate crystalize
1.1.4 Application of dryer
Is an energy intensive unit operation in chemical, food, and allied industries. It is always desired
to have low cost.

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 Realizing high durability by using brush motor
 Increase porosity material
Their application areas are
 Cement production
 Alcohols and beverage production
 Pharmaceutical production,etc
1.2 Gas vapor mixtures (hygrometry)
Is science dealing with the physical laws of air water vapor mixtures.
It is engineering field used to determination of physical and a thermodynamic property of gas
mixture. Atmospheric air normally contains some water vapors. When designing an air condition
system the temperature and moisture content of air to be conditioned. And the same properties of
the air needed to produce the desire air conditioned effect.
The most common system of interest is the mixture water vapor and air. Because of its
application
 Heating
 Ventilating
 Air condition
Properties of gas vapor mixtures are
1) Relative humidity
2) Humidity ratio
3) Absolute humidity
4) Psychromaitic ratio
1. Relative humidity
is properties gas vapor mixture the ratio amount that given amount of air is holding to amount
of moisture that given amount of air can hold.
2. Humidity ratio; is actual weight of water in air water vapor mixture.
That means amount of moisture per unit of dry air.
W= ……………………….1
Where
W=the ratio moisture per dry

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G=the amount weight of dry air
3. Absolute humidity the mass water vapor per unit volume of air containing the water
vapor. That mean, the same as the water vapor density.
4, psychometric ratio ; is the ratio of the heat transfer coefficient to product of mass
transfer coefficient and humid heat at wetted surface.
It may expressed r= hc/ycs…………….(2)
Where r=psychometric ratio, hc=convective heat transfer coefficient,
y=convective mass transfer coefficient
Cs=humid heat
1.3 psychometric term; there so money psychometric term some of these
1. Adiabatic saturation temperature; equilibrium gas temperature reached by unsaturated
vaporizing liquid under adiabatic condition.
N.B for air/water system only it is equal to with wet bulb temperature.
2. Bound moisture; liquid physically/chemically bound solid matrix so as exert a vapor
pressure lower than that of pure liquid at the same temperature.
3.Dew point temperature at which a given unsaturated air vapor mixture becomes saturated.
4. Dry bulb temperature; temperature measured by a dry thermometer immersed in the vapor gas
mixture.
5. Equilibrium moisture content (x*); at a given temperature and pressure ,the moisture content
of moist solid in equilibrium with gas vapor mixture.
6. critical moisture content (XC) ;moisture content at which the drying rate first begin to drop
under constant drying condition.
7. wet bulb temperature ; liquid temperature attained when the large amount of air vapor mixture
is contacted with the surface.
8,Falling rate period ;Drying period (under constant drying conditions) during
which the rate falls continuously in time.
9.Water activity, aw Ratio of vapor pressure exerted by water in solid to that of pure water at the
same temperature.
1oWet bulb temperature, Liquid temperature attained when large amounts of air-vapor mixture
is contacted with the surface. In purely convective drying, drying surface reaches wet bulb
temperature during the constant rat period.

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1.4 PSYCHROMETRIC CHART
Psychometric chart is a graphical representation of psychometric processes of air. And also used
to determine the physical and thermodynamic properties of moist air.
1, Sensible heat; psychometric processes that involves the increase or decrease in the
temperature of air without changing its humidity ratio.
2, heating and humidifying; a psychometrics processes that involves the simultaneous
increase in both dry bulb temperature and humidity ratio of the air.
3, cooling and dehumidifying ; a psychometric processes that involves the removal of water
from the air the air temperature falls below the dew point temperature.
Fig 1.1 psychometric chart
4, Adiabatic(evaporative cooling) a psychometrics process that involves the cooling of air
without heat loss. Sensible heat lost by the air is converted to latent heat in the added water
vapor

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SUMMERY
Drying is one of separation unit operation that remove the moisture of solid, semisolid and
liquid feedstock by helping of heat .drying perhaps the oldest most common and most diverse of
chemical unit operation .why is drying needed?
 Easy to handling
 Free flowing
 To minimize transportation cost
Transport of moisture within solid may occur by the following mechanism of mass transfer
 Liquid diffusion; if the wet solid is at a temperature below the boiling point of the liquid.
 Vapor diffusion; if the liquid vaporize with in material.
 Surface diffusion
Psychometric is a science that studies the physical and thermodynamic properties of gas vapor
mixture.
Psychometrics chart it is graphically representation of psychometrics processes of gas vapor
mixture.
Transport of moisture within the solid may occur by any one or more of the following
mechanisms of mass transfer:
• Liquid diffusion, if the wet solid is at a temperature below the boiling point of the liquid
• Vapor diffusion, if the liquid vaporizes within material
• Surface diffusion (possible although not proven)
• Hydrostatic pressure differences, when internal vaporization rates exceed the rate of vapor
transport through the solid to the surroundings
Psychometric term; there so money psychometric term some of these
 Adiabatic saturation temperature,
 Bound moisture
 Constant rate drying period
 Dew point Temperature
 Dry bulb temperature
Psychometric chart is a graphical representation of psychometric processes of air. And also used
to determine the physical and thermodynamic properties of moist air.

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CHAPTER TWO
CRYSTALLIZATION
Crystallization is a process of formation of solid precipitate from a solution melt or rarely
deposited directly from gas.
Crystallization is separation and purification technique employed to produce wide variety
materials. Solution is mixture of two or more species that form a homogeneous single phase.
Solution is combination solvent and solute.
The solution to be ready to crystallize must to be supersaturated.
A solution in the solute concentration exceeds equilibrium (saturated) solute concentration at
given temperature known as a supersaturated solution.
There are four main method to generate super saturation are
 Temperature change (mainly cooling)
 Evaporation of solvent
 Chemical reaction and
 Change solvent composition
Crystallization from solution can be thought two steps.
 Crystal growth (birth)
 Nucleation
The birth of new crystal which is called nucleation refers the beginning of the phase separation.
The solute of molecule has formed the smallest sized particle possible under the conditions
present. The next stage of the crystallization processes is for the nuclei to grow large by
addition of solute molecule from the supersaturated solution. This part crystallization processes
is known as crystal growth. Crystal growth along with nucleation control the final particle size
distribution obtained in a system.
In addition the condition rate of crystal growth has significant impact on the product purity
2.1 step of crystallization
Modeling of crystal growth in solution crystallization is often done by two step model. The
The overall growth can expressed
RG=Kd(Cb-Ci)…………………….(diffusion step)
RG=Kr(Ci-C*)r
…...…………………………………………(integration step)

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The two step method is totally ignoring by the effect heat transfer on the crystal growth kinetics.
RG=(Cb-C*)g…………………..overall
Where (Cb-C*) is supersaturation
RG=Kd(Cb-Ci) =kd⌈ ⌉ ( ) _(Ci*- )
RG=Kd⌊ – ( ) ⌋
where Ci* and Cb* are the saturation concentrations evaluated at the interface and bulk
temperatures, respectively.
2.2 TYPES OF CRYSTALIZER
There are crystallizers of batch and continuous operation. Crystallizers depending on the system
of cooling classified in to two.
1. Air cooled crystallizers
2. Water cooled crystallizers
1. Air cooled crystallizers; the massecuite is cooled by circulation of air from the wall of
crystallizer and the surface of the massecuite.
The cooling effect is slow. Nowadays the air cooled crystallizers are commonly used for storing
high massecuite is not favored.
2. Water cooled crystallizers; is type of crystallizer can be classified in two
 Water jacketed
 Cooling coil of rotating type
2.3 OBJECTIVE OF CRYSTALLIZATION
Crystallization is used for various purposes.
 To form solid crystal
 To eliminate unwanted material
 Forcing further exhaustion of mother liquor
SUMMERY
Crystallization is a process of separation and purification technique employed to produce wide
variety material. Crystallization may be defined as a phase change crystalline product is obtained
from a solution
There are four main methods to generate super saturation that are the following
• Temperature change (mainly cooling),

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• Evaporation of solvent,
• Changing the solvent composition
Crystallization from solution has two steps.
 Crystal growth
 Nucleation
The birth of new crystal which is called nucleation refers the beginning of the phase separation.
The solute of molecule has formed the smallest sized particle possible under the conditio
Application to ant insolvent crystallization. Concentration feedback control has been applied to
ant solvent batch crystallization processes
There are crystallizers of batch and continuous operation. Crystallizers depending on the system
of cooling classified in to two.
 Air cooled crystallizers
 Water cooled crystallizers
Crystallization is used for various purposes.
 To form solid crystal
 To eliminate unwanted material
 Forcing further exhaustion of mother liquor

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CHAPTER 3
EXTRACTION
Extraction is withdrawing of active agent or west substances from solid or liquid mixture with
liquid solvent.by intensive contact active agent transfer from solid or liquid mixture into solvent.
After the mixing the two phases are separated which happen either gravity or centrifugal force.
3.1 Types extraction; there are three types extraction method depend on the phase.
These are
 Solid –liquid extraction
 Liquid-liquid extraction
 Gas-liquid extraction (absorption)
3.2 selection of solvent
the solvent for extraction has to withdraw the active agent from mixture in order to enhance the
rate extraction.
 Selectivity; only the active agent has to be extracted no further substances which mean
that high selectivity required.
 Capacity to reduce the amount necessary solvent capacity of solvent has to be high.
 Miscibility; to achieve simple regeneration of the solvent the miscibility of solvent and
primary solvent has to be law.
 Recovery solvent; the has to be separated from extract phase easily to produce solvent
free active agent.
 Low price
 No toxic or less
 Corrosion; if the solvent is corrosive price for construction increase.
3.3 Type of extractor; extractor is anequipment used to separate the same or different
phase.
There is several type of extractor.
Such as
1. Single step mixer-separator
2. Mixer-settler-cascade
3. Centrifugal extractor

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1. Single step mixer –separator; it is simplest extraction equipment which operated
continuous or discontinuous. The transfer of the agent from one phase in to other phase take
place in the mixer the separation of the two phases is done in the separator by gravity force.
Advantage
-High efficiency per step - low apparatus height
-High operating area - insensible for suspended substances
Limitation
-High ground area necessary -high energy required and regulating effort
-high solvent cost
2. Mixer –settler-cascade; adding more mixer-settler unit cascade is obtained. This unit can
operate in counter current.
3 .centrifugal extractor; this exist of rotating drum where the heavier phase is transported to
the periphery and the lighter phase to the center.
This means centrifugal force is responsible the counter current flow of the phase.
Advantage
 High through put
 Short residence time by fasting of equilibrium
Disadvantage
 High cost for investment
3.4 Mechanism of extraction
The extraction material is no homogenous substances but exist of a lot of capillary. At the
beginning the solvent enter the capillaries and solute extract. A solution with high concentration
is produced. Because of diffusion a concentration change between the solution in extraction
material and solution surrounding the solid particle take places.at the end of extraction processes
still a certain amount of solution consist of solvent and extracted substance is retained in the
solid amount of particle because of adhesive forces.
3.5 Objective of extraction
Extractions have been used for different purpose.

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 To separate active agent from solvent
 To eliminate the undesired product from required one
 To control quality product
Requirement of extraction; to transfer high amount agent from the starting phase into the extract
the extraction equipment has fulfill the following point.
 High mass transfer coefficient which is achieved in most case by high relative velocities
between the two phases.
 No axial remixing
 Fast and complete phase separation
3.6 Application of extraction; extraction have being a lot of application area.
The main area of extraction
 For hydro metallic processes
 For pharmaceutical industry
 For petroleum industry and for cleaning west water to separate solved compound. When
we see the application extraction in pharmaceutical industry.
Typical applications of extraction in bioprocessing include:
1. Purification of antibiotics
2. Purification of alkaloids
3. Protein purification using aqueous two-phase systems
4. Purification of peptides and small proteins
5. Purification of lipids
6. Purification of DNA
The photonics processes is used to for extraction in biotechnology.(e.g. for production
antibiotics) in the herbal drug industry, in the food ,essential oil and so.
3.7Advantage of extraction
The main advantages of extractions are
 It is less threating to the environment
 It require minimum electrical energy
 The solvent are completely recycled within the system.

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SUMMERY
Extraction is withdrawing of active agent or west substances from solid or liquid mixture with
liquid solvent.by intensive contact active agent transfer from solid or liquid mixture into solvent.
An extraction process makes use of the partitioning of a solute between two immiscible or
partially miscible phases. When the extraction takes place from one liquid medium to another,
the process is referred to as liquid-liquid extraction. There are three types extraction method
depends on the phase. These are
 Solid –liquid extraction
 Liquid-liquid extraction
 Gas-liquid extraction (absorption)
There is several type of extractor.
Such as
A.Single step mixer-separator
B. Mixer-settler-cascade
Centrifugal extractor
D. column without energy
Typical applications of extraction in bioprocessing include:
 Purification of antibiotics
 Purification of alkaloids
 Protein purification using aqueous two-phase systems
 Purification of peptides and small proteins
Extractions have been used for different purpose.
 To separate active agent from solvent
 To eliminate the undesired product from required one
 To control quality product
The main advantages of extractions are
 It is less threating to the environment
 It require minimum electrical energy
 The solvent are completely recycled within the system.

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REFERENCES
1)Keey, R.B., 1992, Drying of Loose and Particulate Materials, Hemisphere, Washington
2)Miura K, Miura T, Ohtani S. Heat and Mass Transfer to and From Droplets. American
Journal of Chemical Engineers, Symposium series 1977; 73 (163).
3) R.E Treybal mass transfer operation 3rd
edition