drying and applications

7/30/2019 drying and applications

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09051055 Elif MACUNLAR

09051703 Aydn AYRIK


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What is drying?

Drying is a mass transfer process consisting of theremoval of water or another solvent

by evaporation from a solid or semi-solid.


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Drying is perhaps the oldest, most common and mostdiverse of chemical engineering unit operations. Overfour hundred types of dryers have been reported in theliterature while over one hundred distinct types arecommonly available. Also drying is very old dailyapplication.


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Drying is involving transient transfer of heat and massalong operation and this may cause changes in productquality.

Shrinkage

Puffing

Crystallization

Color changing

Texture changing Odor changing


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Mechanism of drying In the process of drying heat is necessary to evaporate

moisture from the grain and a flow of air is needed tocarry away the evaporated moisture.


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There are two basic mechanisms involved in thedrying process.

1) The migration of moisture from the interior of anindividual grain to the surface

2) The evaporation of moisture from the surface to thesurrounding air. The rate of drying is determined bythe moisture content and the temperature of thegrain and the temperature, the (relative) humidityand the velocity of the air in contact with the grain.


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Drying rate-time graph


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The rate of drying is determined by ;

Moisture content

Temperature of the grain

Temperature of drying air

Velocity of the air in contact with the grain

Relative humidity


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In general, the drying rate decreases with moisturecontent, increases with increase in air temperature ordecreases with increase in air humidity.

At very low air flows increasing the velocity causesfaster drying but at greater velocities the effect isminimal, indicating that moisture diffusion within thegrain is the controlling mechanism

Grains are hydroscopic and will lose or gain moistureuntil equilibrium is reached with the surrounding air.


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the equilibrium moisture content is dependent on therelative humidity and the temperature of the dryingair.

The properties of the air flowing around the dryinggrain are a major factor in determining the rate ofremoval of moisture.


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Effects of Drying on Grain Quality Incorrect selection of drying conditions and equipment

can easily affect the quality of grain.

The desirable properties of high-quality grains include

1. Low and uniform moisture content2. Low susceptibility to subsequent breakage3. Minimal proportion of broken and damaged grains4. High viability5. Low mould counts6. High nutritive value7. Consumer acceptability of appearance and organoleptic

properties.


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Dryers and Applications


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Methods of drying Convection Drying Spray drying

Spray granulation

Fluidized dryers

Drying belts

Flash dryers Contact Drying Paddle dryer

Tray dryer

Mixer kneader dryer

Drum (rotary) dryer Disc dryer

Microwave Drying

Freeze Drying

Supercritical Drying


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Convective Drying Air heating increases the driving force for heat

transfer and accelerates drying. It also reduces airrelative humidity further increasing the driving forcefor drying. In the falling rate period, as moisturecontent falls, the solids heat up and the highertemperatures speed up diffusion of water from theinterior of the solid to the surface.


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Spray Drying Most widely used industrial drying process.

Highly suited for the continuous production of drysolid.

deal method if product have precise qualitystandards.


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Industrial applications of spray drying

Ceramic industry Ferrites

Carbides

Oxides

Food industry Tea

Soup mixes

Polymer industry e-PVC

Resins

Pharmaceutical industryVitamins

Enzymes

Antibiotics


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Fluid Bed Drying

Suitable for both heat sensitive and non-heat sensitiveproducts

Easily controlled

Uniform operarion conditions


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Industrial applications of fluid bed drying

Chemicals Detergent Fertilizers

Inorganic salts

Food and diary products

Baby food Carbonhydrates

Coffee

Polymers Polypropylenes

Poliethylenes Pharmeceuticals and biochemicals Drugs

Proteins

Yeast


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Drying Belts


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Flash Dryers Most economical dryers for low moisture solids Simplest gas suspension dryers

Residence time is very short (less than 3 seconds)


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Indusrtial application of flash dryers

Alumina

Animal feed

PVC Gluten

Proteins

Silica

Starches

Zeolites


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Contact Drying

Higher wall temperatures will speed up drying but this is

limited by product degradation or case-hardening.


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Paddle Dryers


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Tray Dryers


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Mixer Kneader Dryers


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Drum (rotary) Dryers

Heated to high temprature drying gas

Non-heat sensitive products

Drums rotating speed is important


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Disc Dryers


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Microwave Drying Radiofrequency or microwaves being absorbed inside

the material.


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Freeze Drying is a drying method where the solvent is frozen prior to

drying and is then sublimed passed to the gas phasedirectly from the solid phase, below the melting point

of the solvent.


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Supercritical Drying superheated steam drying involves steam drying of

products containing water. The process has potential for use in foods if carried out

at reduced pressure, to lower the boiling point.


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drying and applications

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