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Lesson 7.1 INTRODUCTION TO

CRYSTALLIZATION

In this chapter, our discussion on crystallization is

restricted to the crystallization from liquid solution.

Crystallization is a unit operation that involves

the separation of a solute from its solution in the form of

crystals.

Crystallization involves simultaneous heat and

mass transfer.In crystallization, mass transfer takes place from

solution to solid crystalline phase.

Here phases in contact are (1) liquid and (2) solid.


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Lesson 7.2.1 METHOD OF SUPER

SATURATION

Supersaturation:

Supersaturation is the quantity of the solutepresent in

the solution in which crystals are growing compared with

the quantity of the solute that is in equilibrium withthe solution. The supersaturation may be expressed as a

coefficient s which is given as

Agitated tank crystallizer:

Scrapped surface crystallizer:

(1) Swenson-walker crystallizer and

(2) Double pipe crystallizer.


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Lesson 7.2.1 METHOD OF SUPER

SATURATION

Swenson-walker crystallizer:

The Swenson-walker crystallizer is a cooling type,

continuous, jacketed trough crystallizer.

It is an example of the scrapped surface crystallizer

andis probably most widely used crystallizer.


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Lesson 7.3 INTRODUCTION TO DRYING

Drying is frequently the last operation in the

manufacturing process and is usually carried after

evaporation, filtration, or crystallisation.Moisture content on wet basis : It is expressed as the

ratio of weight of moisture to the weight of wet feed

material. If X is the kg moisture associated with one

kg of dry solids then.

Moisture content on wet basis = X

1+X


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Lesson 7.3 INTRODUCTION TO DRYING

Equilibrium moisture content (X*) : The moisture

content of substance that is in thermodynamic equilibrium

with its vapour in gas phase under specified humidity andtemperature of gas is termed equilibrium moisture content.

Constant rate period : It is that part of the drying

process during which the rate of drying expressed as

the moisture evaporated per unit time, per unit area of

drying surface, remains constant.Falling rate period :It is that part of the drying process

during which the rate of drying varies with time and

instantaneous drying rate expressed as amount ofmoisture evaporated per unit time.


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Lesson 7.3.1 FACTOR EFFECTING ON

DRYING RATE


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Lesson 7.4 CLASSIFICATION OF DRYER

1. Tray dryer.

2. Rotary dryer.3. Direct-indirect type dryer.

4. Drum dryer.

5. Spray dryer.6. Fluidised bed dryer.

7. Tunnel dryer.

8. Flash (pneumatic) dryer


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Lesson 7.4 SINGLE DRUM & DOUBLE DRUM

DRYER


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Lesson 7.4.1 THIN FILM DRYER DRYER


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Drying is removal of small

amount of moisture from theSubstance below its boiling

point.

Generally hot gas or steam is

used for this operation.

Types of dryer are:Rotary drum dryer , spray Dryer

Vacuum dryer , peddle dryer,

Tray dryer , fluid bed dryer.

Lesson 7.4.2 VACUUM DRYER


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Lesson 7.5 PRECAUTIONS FOR DRYING

*TO BE EXAMINED THE PRILLS FROM SPRAY DRYER

*TO BE CHECK VACUUM

*TO BE CHECK TEMPERATURE

* TO BE CHECK PRESSURE

* TO BE CHECK NOISE

* TO BE CHECK CYCLONE BUILDUP

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