Drying and dehumidification

PRESENTED BY - SUBMITTED TO-
SURAJ KUMAR
M.Tech.(pre.) Er. A. kalne
Agril. Processing and food engineering Assis. Prof. APFE
SVCAET,IGKV Raipur
Farm structure and environmental control
PFE-512
PRESENTATION
ON
DRYING AND DEHUMIDIFICATION

Point to be cover
• Definition of drying
• Importance of drying
• Difference between drying and evaporation
• Equipment
• Dehumidification and dehumidifier.
3

Drying
• Drying is commonly the last stage in a manufacture
process.
• Drying is the final removal of water from material
(usually by heat)
• Non-thermal drying
1 As Squeezing wetted sponge
2 Adsorption by desiccant (desiccation)
3 Extraction.
4

Drying means……
Drying is commonly the last stage in a
manufacture process.
Drying is the final removal of water from
material.
The removal of all or most of the liquid by
supplying latent heat
to cause thermal vaporization.

Purposes Of Drying
1. Avoid or eliminate moisture which may lead to
corrosion and decrease the product stability.
2.To improve or keep the good properties of a material,
e.g. flow ability, compressibility.
3.To reduce the cost of transportation of large volume
materials ( liquids)
4. To make the material easy or more suitable for handling.
5.Preservative .
6.The final step in evaporation ,filtration ,crystalization.

TYPES OF DRYING
 Direct :Convective Dying
Drying is established through direct contact between the
product and the gas heating medium .Material reaches steady
state temperature near gas wet temperature.
  Indirect Drying:
Established from heated surface in contact with the product.
The heating medium and product are separated by wall.
Material reaches steady state temperature near liquid
boiling point for contact rate drying .
  Radiation :
Heat transfer establishes by radiation from energy source. This
is no contact from heated surface or medium and product

MECHANISM OF DRYING
  Liquid diffusion: if the wet solid is at atemperature
below the boiling point of the liquid


 Vapor diffusion: if the liquid vaporizes within
material
 Condensation diffusion : if drying takes place at
very low temperatures and pressures, e.g., in freeze
drying
  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
 Combinations of the above mechanisms

Importance of drying
1.To avoid or eliminate moisture which may lead to
corrosion and decrease the product.
2.To improve or keep the good properties of a material,
e.g. Flowability, compressibility.
3. To reduce the cost of transportation
of large volume materials ( liquids).
4.To make the material easy or more suitable for handling.
5.Preservative.
6.The final step in Evaporation, Filtration, Crystallization.
9

The moisture contents of solid when it is in
equilibrium with given partial pressure of
vapour in gas phase is called as equilibrium
moisture content.
Three major stages of drying can be observed
in the drying curve.
•Transient early stage, during which the
product is heating up (transient period)
•Constant rate period, in which moisture is
comparatively easy to remove
•Falling rate period, in which moisture is
bound or held within the solid matrix.
“the moisture content at which the constant rate drying period ends and
the falling rate drying period starts is called critical moisture content.”
DRYING CURVES

Equipments
1. Drum dryer (Film drying)
2. Spray dryer
3. Freeze Dryer
4. Tray drier
5. Fluidized Bed Dryer
6. Vacuum Dryer
7. Foam mate drying
1
1

Drum Dryer (Film Drying)
• It consists of a drum of about 0.75-1.5 m in diameter
and 2-4 m in length, heated internally, usually by steam
and rotated on its longitudinal axis.
• Operation: The liquid is applied to the surface and
spread to a film, this may be done in various ways, but
the simplest method is that shown in the diagram,
where the drum dips into a feed pan. Drying rate is
controlled by using a suitable speed of rotation and the
drum temperature. The product is scraped from the
surface of the drum by means of a doctor knife.
1
2

ADVANTAGES OF THE DRUM DRYER
1. The method gives rapid drying, the thin film spread
over a large area resulting in rapid heat and mass
transfer.
2. The equipment is compact, occupying much less
space than other dryers.
3. Heating time is short, being only a few seconds.
4. The drum can be enclosed in a vacuum jacket,
enabling the temperature of drying to be reduced.
5. The product is obtained in flake form, which is
convenient for many purposes.

 Operating conditions are critical and it is necessary to
introduce careful control on feed rate, film thickness, speed
of drum rotation and drum temperature.
 The uneven scrapping of the doctor’s blade at the
rubbery and glassy parts of the sheet forms wrinkles in the
sheet which eventually become ‘‘sticks’’ in the final product.
The ‘‘sticks’’ reduce the quality of the product by making it
very hard to disperse and physically unsatisfactory in
appearance.
DISADVANTAGES OF DRUM DRYER

APPLICATIONS:-
 low-sugar foods, such as tomato puree, milk, skim milk,
whey, beef broth, yeast, coffee, and malt extract, have also
been successfully dried on a drum dryer.
  Heat-sensitive products such as pharmaceuticals30 and
vitamin-containing products can be dried in a vacum
 The drum dryer has been used extensively to dry chemicals
and food products. Examples of Chemicals are
polyacrylamides, and various salts such as silicate,
benzoate, propionate, and acetate salts.
  Drum dryers have been successfully used in drying sludge
  The drum dryer is also extensively used to dry and
gelatinize or ‘‘cook’’ starch slurries, such as potato,
rice,wheat,maize,corn, soybean,banana,and cowpea slurries
to produce pre gelatinized starch for instant foods.
  Non-starchum drum dryer.

Spray Dryer
• The spray dryer provides a large surface area for heat
and mass transfer by atomizing the liquid to small
droplets.
• These are sprayed into a stream of hot air, so that
each droplet dries to a solid particle.
• The drying chamber resembles the cyclone ensuring
good circulation of air, to facilitate heat and mass
transfer, and that dried particles are separated by the
centrifugal action.
• Spray dryer can be operated efficiently at various
feed rates.
18

Working Mechanism of
spray dryer

COMPONENT OF SPRAY DRYER
•Centrifugal atomizer. Liquid is fed to the center of a rotating
disc or bowl having a peripheral velocity of 90– 200ms1.
Droplets, 50–60 m in diameter, are flung from the edge to form a
uniform spray.
•Pressure nozzle atomizer. Liquid is forced at a high pressure
(700–2000103 Pa) through a small aperture to form droplet
sizes of 180–250 m. Grooves on the inside of the nozzle cause
the spray to form into a cone shape and therefore to use the full
volume of the drying chamber.
•Two-fluid nozzle atomizer. Compressed air creates turbulence
which atomizes the liquid. The operating pressure is lower than
the pressure nozzle, but a wider range of droplet sizes is
produced.
•Ultrasonic nozzle atomizer. A two-stage atomizer in which
liquid is first atomized by a nozzle atomizer and then using
ultrasonic energy to induce further cavitation

CHARACTERIZATION OF SPRAY
DRIED PRODUCTS
 The products are uniform in appearance and have
characteristic shape, in the form of hollow spheres with a
small hole. This arises from the drying process, since the
droplet enters the hot air stream, and dries on the
outside to form an outer crust with liquid still in the
center. This liquid then vaporizes, the vapour escaping
by blowing a hole in the sphere.
 This method of drying allows a dry product to retain
some properties of feed , e.g., a drop from an emulsion
dries with continuous phase on the outside. When
reconstituted, the emulsion is easily re-formed.

ADVANTAGES OF THE SPRAY DRYING PROCESS
1. Product properties and quality are more effectively
controlled.
2. Heat-sensitive foods, biological products, pharmaceuticals
can be dried at atmospheric pressure and low temperatures.
Sometimes inert atmosphere is employed.
3. Spray drying permits high-tonnage production in continuous
operation and relatively simple equipment .
4. Spray drying produces relatively uniform, spherical particles
with nearly the same proportion of nonvolatile compounds as
in the liquid feed.
5. As the operating gas temperature may range from 150 to
600C, the efficiency is comparable to that of other types of
direct dryers .

DISADVANTAGES OF SPRAY DRYING
1. Spray drying fails if a high bulk density product is
required.
2. In general it is not flexible. A unit designed for fine
atomization may not be able to produce a coarse
pro duct, and vice versa.
3. For a given capacity larger evaporation rates are
generally required than with other types of dryers.
The feed must be pump able.
4. There is a high initial investment compared to
other types of continuous dryers.
5. Product recovery and dust collection increase the
cost of drying

APPLICATIONS OF SPRAY DRYER
1. Drying of any substance in solution or in suspension form.
2. It is most useful for drying of thermo labile materials e.g.
antibiotics.
3. Suitable for large quantities solution.
4. Suitable for both soluble and insoluble substances e.g.
citric acid, gelatin, starch.
5.It can produce spherical particles in the respiratory range
e.g. dry powder inhalers.
6. Drying of milk, soap and detergents which is
pharmaceutically related compounds.

Freeze Dryer
• Freeze drying is a process used to dry extremely heat-
sensitive materials. It allows the drying , without
excessive damage, of proteins, blood products and
even microorganisms, which retain a small but
significant viability.
• In this process the initial liquid solution or
suspension is frozen, the pressure above the frozen
state is reduced and the water removed by
sublimation.
• Thus a liquid-to-vapour transition takes place, but
here three states of matter involved: liquid to solid,
then solid to vapour.
27

FREEZE DRYING
 Freeze drying is a process used to dry extremely heat –
sensitive materials. It allows the drying , without
excessive damage, of proteins, blood products and even
microorganisms, which retain a small but significant
viability.
 In this process the initial liquid solution or suspension is
frozen, the pressure above the frozen state is reduced
and the water removed by sublimation.
 Thus a liquid –to-vapour transition takes place, but here
three states of matter involved: liquid to solid, then solid
to vapour

ADVANTAGES
 Reduction in thermal exposure to heat sensitive
foods, dried foams retain a porous structure,
allowing rapid rehydration characteristics.
 More retention of nutrition .
APPLICATIONS
 Several applications of foam drying have been
developed, including vacuum puff drying, foam
spray drying, and foam-mat drying

THE PHASE DIAGRAM FOR WATER
 The diagram consists of three
separate areas representing the
phases of water, solid, liquid, and
vapour . The point O is the only
point where all the three
phases can coexist, and is known
as the triple point .
 On heating at constant atmospheric pressure ice will melt when
the temperature rises to 0 C . At this constant temperature and
pressure it will then change to water. Continued heating will
raise the temperature of the water to 100 C where, if heat
addition is continued, the liquid water will be converted into
water vapour at 100 C.

 If , however, solid ice is maintained at a pressure
below the triple point then on heating the ice will
sublime and pass directly to water vapour without
passing through the liquid phase.
 This sublimation, and therefore drying, can occur
at a temperature below 0 C.
 This will only happen if the pressure is prevented
from rising above the triple point pressure .
 It may be thought that as the process takes place
at a low temperature the heat required to sublime
the ice will be small.

Stages Of The Freeze
Drying Process
1. Freezing stage
 Shell freezing
Centrifugal evaporative freezing
2. Vacuum application stage
3. Sublimation stage
 Primary drying
 Heat transfer
Vapour removal
 Rate of drying
4. Secondary drying and
5. Packaging

Advantages Of Freeze drying
1. Drying takes place at very low temperatures, so the
chemical decomposition, particularly hydrolysis is
minimized.
2. The solution is frozen occupying the same volume as
the original solution, thus , the product is light and
porous.
3. The porous form of the product gives ready solubility.
4. There is no concentration of solution prior to drying.
Hence, salts do not concentrate and denature
proteins, as occurs with other drying methods.
5. As the process takes place under high vacuum there
is little contact with air, and oxidation is minimized.

Disadvantages & uses of freeze drying
Disadvantages:
There are two main disadvantages:
1.The porosity, ready solubility and complete dryness yield a
very hygroscopic product. Unless products are dried in their
final container and sealed in situ, packing require special
conditions.
2.The process is very slow and uses complicated plant, which
is very expensive .It is not a general method of drying but
limited to certain types of valuable products.
Uses of freeze drying :
 The method is used for products that can not be dried by any
other heat method. These include biological products,
e.g.antibiotics, blood products, vaccines, enzyme preparations
and microbiological cultures.

1. The freeze drying of products such as blood plasma, although simple in
theory, presents a number of practical problems.
2. The depression of the freezing point caused by the presence of
dissolved solutes means that the solution must be cooled below the
normal freezing temperature for pure water (-10-30).
3. At low pressure large volumes of water vapour are produced which must
be removed to prevent the pressure rising above the triple point
pressure.
4. The dry material often needs to be sterile, and it must also be prevented
from regaining moisture prior to the final packaging.
Application of freeze drying

Tray drier
• Air flows in direction of the arrows over each
shelf in turn.
• The wet material is spread on shallow trays
resting on the shelves.
• Electrical elements or steam-heated pipes are
positioned as shown, so that the air is
periodically reheated after it has cooled by
passage over the wet material on one shelf
before it passes on the next.
38

TRAY DRYING
 These types of dryers use trays or similar product
holders to expose the product to heated air in an
enclosed space.
 The trays holding the product inside a cabinet or similar
enclosure are exposed to heated air so that dehydration
will proceed.
 Air movement over the product surface is at relatively
high velocities to ensure that heat and mass transfer will
proceed in an efficient manner.
 In most cases, cabinet dryers are operated as batch
systems and have the disadvantage of non-uniform
drying of a product at different locations within the
system. Normally, the product trays must be rotated to
improve uniformity of drying.

TRAY DRYING
Cabinet Type Tray Drier

ADVANTAGES OF TRAY DRYING
  Simple in handling
  Lesser capital cost
DISADVANTAGES
  Non-uniform drying of a product at different
locations within the system.
  Time required for drying is more
  The major disadvantages of this type of dryers
are the high labor cost involved during the loading
and unloading of the drying materials and the low
capacities of the units.

Fluidized Bed Dryer
• ‘Fluidized’ means something that behaves like liquid.
In the fluidized bed dryer, the mixture of solids and
gas behave like a liquid and solid are called fluidized.
• It provides good contact between hot air and particles
to obtain efficient drying.
• The hot air is passed through a mesh, which supports
the conical vessel with a porous base.
• This vessel is filled with powder to be dried.
• It has wheels and can be clipped to the central plate
by means of a rapid acting ring closure.
43

FLUIDIZED BED DRYING
 The product pieces are suspended in the heated air
throughout the time required for drying. The movement of
product through the system is enhanced by the change
in mass of individual particles as moisture is evaporated.
 The movement of the product created by fluidized
particles results in equal drying from all product surfaces.

WORKING PRINCIPLE
Good contact between the warm drying air and wet
particles is found in the fluidized – bed drier.
Principles of fluidization: The particulate matter is
contained in a vessel, of which is perforated,
enabling a fluid to pass through the bed of solids
from below.
 If the air velocity through the bed is increased
gradually and the pressure drop through the bed is
measured, a graph of the operation shows several
distinct regions,
 As indicated in the fig. Effect of air velocity on
pressure drop through a fluidized bed........

EFFECT OF AIR VELOCITY ON PRESSURE
DROP THROUGH A FLUIDIZED BED

ADVANTAGES OF FLUIDIZED-BED DRYING
1.The fluidized state of the bed ensures that drying occurs
from the surface of all the individual particles and not just
from the surface of the bed. Hence, most of the drying will
be at constant rate and the falling –rate period is very
short.
2.The temperature of a fluidized bed is uniform and can be
controlled precisely.
3.The turbulence in a fluidized bed causes some attrition to
the surface of the granule. This produces a more spherical
free-flowing product.

1. Fine particles may become entrained in the fluidizing
air and must be collected by bag filters, leading to
segregation and loss of fines.
2. The vigorous movement of particles in hot dry air can
lead to the generation of static electricity charges. The
danger is increased if the fluidized material contains a
volatile solvent such as isopropanol. Adequate
electrical earthling is essential.
Disadvanteges:-

Vacuum Dryer
Steam or
Water Jacket
50
Condenser
Connection to
Vaccum Pump
Condensate
Receiver

Advantages Of Vacuum Oven:
 Drying takes place at a low temperature.
 Maximum retention of nutrition
 There is little air present, so there is minimum risk of
oxidation.
Limitations:
 Sometimes burning onto trays in vacuum shelf driers,
 Shrinkage in food which reduces the contact between
the food and heated surfaces of both types of equipment.
They have relatively high capital and operating costs and
low production rates and
 Used mainly to produce puff-dried foods.

Vacuum Dryer
• This equipment is a good example of conduction
drier. The vacuum oven consists of a jacketed vessel
to withstand vacuum within the oven.
• There are supports for the shelves giving a larger area
for conduction heat transfer. The oven can be closed
by a door.
• The oven is connected through a condenser and liquid
receiver to a vacuum pump.
• Operating pressure can be as low as 0.03-0.03 bar, at
which pressures water boils at 25-35 0C.
52

VACUUM DRYING
• This equipment is a good example of conduction drier.
The vacuum oven consists of a jacketed vessel to
withstand vacuum within the oven.
• There are supports for the shelves giving a larger area for
conduction heat transfer.
• The oven can be closed by a door. The oven is connected
through a condenser and liquid receiver to a vacuum
pump.
• Operating pressure can be as low as 0.03-0.03 bar, at
which pressures water boils at 25-35 C.

FOAM MAT DRYING
 Foam-mat drying is one of the simple methods of drying
in which a liquid food concentrate along with a suitable
foaming agent is whipped to form a stable foam and is
subjected to dehydration in the form of a mat of foam at
relatively low temperature .
 Rate of drying in this process is comparatively very high
because of an enormous increase in the liquid-gas
interface, in spite of the fact that the heat transfer is
impeded by a large volume of gas present in the foamed
mass.

FOAMING AGENT USE FOR MAKING
FOAM
1.Glycerol
2.Monostearate ,
3.Egg albumin,
4.Ground nut protein isolate,
5.Gur gum and
6.Carboxy methyl cellulose (CMC)
Fig. foam mat dryer

Humidity is
presence of
moisture or water
vapour in
air.Having high a
Humidity level
can be harmful.

Moisture increases
inside your home
through household
activities like cooking,
bathing, doing
laundry and washing
dishes.

The result of high humidity can cause skin diseases, respiratory issues
swelling in the ankles, etc.
Excessive amount of humidity in the air is not
only impure for health, but also makes it
appropriate for the growth of various insects.
Humid air can cause mold or fungus to
grow inside home. Metals begin to rust and
wood will wrap causing doors and draws to
stick.

CONSTRUCTION OF
DEHUMIDIFIER
1

Dehumidifiers remove excess amount of
moisture or water vapor fromair and helps to
maintain RH level. It keeps basements dry and
protects the surfaces from fungus and moths.
Also used in industrial climatic chambers for
keeping desired humidity level.

2
Dehumidifier
• A dehumidifier is generally household
application which reduces the level of
humidity in the air, usually for
health or comfort reasons, or to
eliminate musty odor.
• Large dehumidifiers are also used in
commercial buildings such as indoor ice
rinks to control the humidity level. By
their operation, dehumidifiers extract
water from the conditioned air.
• This collected water (usually called
condensate) is not normally used for
drinking, and is often discarded.

WORKING OF DEHUMIDIFIER
Working on the same principle as a refrigerator,
moisture-filled air is drawn into the dehumidifier
and passed over a cold, ‘refrigerated’ coil. The
damp air condenses on the cold coil into water
droplets which are collected in the water tank.
The air is then passed over a warm coil and sent
out from the dehumidifier, producing clean, dry
air.
In cold conditions the water that is passed over
the cold coil may freeze. Dehumidifiers utilize a
hot gas defrost system, enabling hot gas to be
transferred into the cold coil, reversing the
freezing process.
3

DEHUMIDIFYING BY REFRIGERATION
4
1. Warm, moist air is sucked in.
2. An electric fan draws the air inward.
3. The warm air passes over freezing cold pipes.
4. The air passes over a heating element.
5. Warm, dry air blows back into the room.
6. The moisture that was in the air originally drips
down into a collecting tray (or bucket) at the
bottom of the machine.
7. A plastic float in the machine rises upward as the
collecting
tray fills up.
8. The float trips an electric switch that turns off the
fan and switches on an indicator light telling you
the machine needs emptying.

DEHUMIDIFIER APPLICATIONS
 Use an extractor fan or open a window when
taking a bath or shower.
 Wipe down wet walls and floors in your bathroom
after use.
 Seal cracks in your walls with a caulk or sealant.
 Place wet clothes to dry next to an open window.
 If possible, dry your clothes outside.
 When cooking on a hob, use your extractor fan
hood.
5

 Used in basement area
 Controls odor
 Relatively more pint capacity
 Option for portability

 Compact
 Portable
 Designed for use in small, medium, and
large rooms or spaces
 Pint capacity ranges from 25 -75 units per day
 Also known as single room or mini dehumidifiers

 Usually used in damp climatic conditions
 Connected to house’s HVAC system
 Fully automated
 Low maintenance
www.edscomfortsolutions.com

 Exchange dry air for humid air
 Technology similar toAC
 Relatively efficient

 Moisture is reduced with an absorbent material
 Best in warm climates
 Mainly used in industries

If you want to keep the humidity in the desired level, it is
advised to install a good dehumidification system.
With the development in technology, dehumidification
machines have been able to effectively reduce problems
associated with high humidity.

Drying and dehumidification

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