Transcript CHAPTER 2 DRYING OPERATION

CHAPTER 2
DRYING OPERATION
By:
Dr. In. Nurul Hasyimah Mohd Amin
OBJECTIVES
At the end of this lessons, students should
be able to:
• Define the drying process
• Explain the classification of dryers
• Explain the principles of drying
• Perform calculation in this topics
INTRODUCTION
• Definition:
The removal of water from the solid material to
reduce the content of residual liquid to an
acceptable low value.
• Drying is the final step in a series of
manufacturing process.
• Drying is carried out before the products undergo
packaging or dispatched to the warehouse.
INTRODUCTION
• Water or other liquid may be removed from the solid:
a) mechanically by presses or centrifuges
b) thermally by vaporization – drying
• It is cheaper to remove liquid mechanically than
thermally.
• The product contain no liquid
Drying Process
Step-1
Solid + Liquid
To Vapor
by Heat
Step-2
Removal of Vapor from Solid’s Place
Drying Process
Moisture
Feed
Dryer
Heat
Dry Solid
INTRODUCTION
• The solid to be dried may be in many different forms:
flakes, granules, crystals, powder, slabs or continuous
sheets.
• The liquid to be vaporized may be:
a) on the surface of solid
b) entirely inside the solid
c) partly inside and partly outside of solid
INTRODUCTION
• Drying is carried out for one of the following reasons:
 To avoid or eliminate moisture which may lead to corrosion
 To improve or keep the good properties of a material, e.g. flow
ability, compressibility
 To reduce the cost of transportation of large volume materials
( liquids)
 To make the material easy or more suitable for handling
 Preservative
 The final step in: Evaporation-Filtration-Crystallization
INTRODUCTION
Drying can be categorized according to physical conditions
used to add heat and remove water vapor:
• Convective/Direct dryers/ADIABATIC > heated air at
atm pressure and water vapor removed by the air.
• Conductive /Indirect dryers/NON-ADIABATIC >
vacuum drying
• Dryers by radiant energy
INTRODUCTION
Types of dryer on the basis of feed:
• For solid

Tray dryer
 Fluidized bed dryer
 Vacuum dryer
 Freeze dryer
• For solutions
 Spray dryer
TRAY DRYER
TRAY DRYER
They are essentially hot air ovens
 The material is to be dried is spread in thin layers in
trays.
 The heating is done by forced circulation of large volume
of heated air by means of fans.
SPRAY DRYER
INTRODUCTION
Applications of drying process includes removal of
moisture from:
• Crystalline particles of inorganic salts and organic
compounds to cause them to be free flowing.
• Biological materials including foods to prevent spoilage
and decay from microorganisms that cannot live without
water.
INTRODUCTION
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Pharmaceuticals
Detergents
Dyestuff
Milk
Solid catalysts
Lumber, paper and fiber products
INTRODUCTION
INTRODUCTION
INTRODUCTION
IMPORTANT TERMS
• Equilibrium moisture, X*
The lowest moisture content obtainable at
equilibrium under the drying conditions used.
• Free moisture
The moisture that can be removed by drying
under the given % relative humidity: X – X*
IMPORTANT TERMS
• Bound moisture
The minimum moisture a material can carry.
• Unbound moisture
The excess moisture content in the material.
GENERAL PRINCIPLES
• The solids need to be dried at a specified moisture
content (specified in the quality of the end product)
• The moisture content of a material is expressed in
terms of its water content as percentage of the
mass of dry material
• The small amounts of liquid inside the solid –
moisture content
• Suitable dryer need to be chosen which allow the
specified moisture of the product to be obtained.