This document provides information about spray drying processes used to dry milk and dairy products. It discusses the purposes of drying milk, which include reducing weight and transportation costs, extending shelf life, and creating ingredients. It then describes the key components of spray drying systems, including air heaters, atomizers, drying chambers, cyclones, and powder handling equipment. The document gives details on drum/roller dryers and spray dryers, and provides specifications of the spray drying plant at NDRI Karnal, including its evaporator, technical data, labeled diagram, and operational instructions.

1. DAIRY PROCESS
ENGINEERING (DE – 221)
PRACTICAL
ASSIGNMENT NO. 7
ON
INTRODUCTION:
Milk and by-products of milk production are often dried to reduce weight, to aid in
shipping, to extend shelf life, and to provide a more useful form as an ingredient for
other foods. In addition to skim and whole milk, a variety of useful dairy products are
dried, including buttermilk, malted milk, instant breakfast, sweet cream, sour cream,
butter powder, ice cream mix, cheese whey, coffee creamer, dehydrated cheese
products, lactose, and caseinates. Most products are dried to less than 4 percent
moisture to prevent bacterial growth and spoilage. However, products containing fat
lose their freshness rather quickly owing to the oxidation of fatty acids, leading to
rancidity.
PURPOSE OF DRYING:
1. To reduce cost of transportation
2. To improve storage of product
3. To increase keeping quality.
4. To increase its availability throughout the years at far off place.
5. To bring moisture around 4-5%, etc.
Two types of dryers are used in the production of dried milk products- drum dryers or
can also be called as roller dryers and spray dryers. Each dryer has certain
advantages.

2. Drum or Roller Dryers-
The simplest and least expensive is the drum, or roller, dryer. It consists of two large
steel cylinders that turn toward each other and are heated from the inside by steam.
The concentrated product is applied to the hot drum in a thin sheet that dries during
less than one revolution and is scraped from the drum by a steel blade. The flake like
powder dissolves poorly in water but is often preferred in certain bakery products.
Drum dryers are also used to manufacture animal feed where texture, flavour, and
solubility are not a major consideration.
Spray dryers-
Spray dryers are more commonly used since they do less heat damage and produce
more soluble products. Concentrated liquid dairy product is sprayed in a finely
atomized form into a stream of hot air. The air may be heated by steam-heated
“radiators” or directly by sulphur-free natural gas. The drying chamber may be
rectangular, conical, or silo-shaped (up to five storeys high). The powder passes
from the drying chamber through a series of cyclone collectors and is usually placed
in plastic-lined, heavy-duty paper bags.
The basic principle of spray drier involves atomization of concentrated milk in the
form of spray of very fine minute droplets where they get mixed with the current of
hot air and moisture is removed instantaneously due to larger surface area and dried
to a fine powder which is removed continuously. The spray drier can be used for
drying of many products viz. high protein, high carbohydrate and high fat products.
The general principle of spray drier is that milk is divided into droplets size of 100
micron, increased surface area of 800-1000 times which causes instant drying of
milk particle in presence of hot air. The milk has to be concentrated into evaporator
(Double stage Falling Film Evaporator) before feeding to spray drier.
Componentsof spray drier:
1. Air-heater (to heat incoming air to drier)
2. Atomizer
3. Mixing drying chamber
4. Powder discharge equipment
5. Cyclone separator
6. Powder cooling and conveying system.
PARTS OF THE SPRAY DRYING PLANT

3. 1. Air heater: - It is a shell and tube type heat exchanger in which air is blown and
heated to a temperature of 190-195°C. The heated air is supplied to spray drier from
the top for a concurrent drying.
2. Balance tank: -There is a feed tank for receiving the concentrate from the
evaporation plant. It is double jacketed tank provided with the coils in between the
jackets to maintain the temperature of feed. This tank is equipped with necessary
CIP system, level & temperature indicator etc. accessories. The inlet for the
concentrated milk is provided at the top which guides the milk towards the wall to
avoid foam formation. The out let is at the bottom of the tank which is further
connected to a positive displacement pump to pump a constant feed to atomizer.
3. Feed pump
A feed pump is used for pumping concentrate from concentrate tank through
shell & tube heat exchanger heat exchanger to atomizer.
4. Shell & Tube heat Exchanger: - It is provided to heat the incoming milk from 45
⁰C to 75 ⁰C. Here milk in tube side is heated by using steam/hot water in the shell
side.
5. Atomizers: -It is a Centrifugal disc type of atomizer. It is consisting of a stainless
steel disc having radial-vane (vanes placed between two discs) & a bowl shaped
liquid chamber through which the product moves (milk in swirling motion). The
atomizer is revolving with the help of a shaft which is rotated through belt drive by a
motor at high speed. The milk enters through a milk tube into the milk cup in the disc.
The concentrated milk while coming out of channel get subjected to a large
centrifugal force resulting it split into very fine particles in numbers ranging from 50-
150 micron, with average size of 100 micron. The speed of atomizer varies from
20000-30000 rpm. The size of particles is proportional to the speed of disc.
6. Drying chamber: - It is a cylindrical at the top and then conical chamber at
bottom made up of stainless steel provided with thermal insulation. This is the place
where in atomized particles come in contact with hot air and are dried due to
convection current within 3-4 seconds. Particles come down due to gravity and also
conveyed by a moving chain towards the bottom of the chamber followed by moved
out through a star valve. In drying chamber there is slight vacuum due to which
particle dried at lower temperature. The inlet & outlet temperature of moist air is
around 180-195⁰C &90-95⁰Crespectively.
7. Cyclone separator: -The outlet air at the bottom of drier with fine powder
particles entrapped in it enters the cyclone separator. When the outlet air with
powder fines enters tangentially (45⁰) into the cyclone hits the wall & takes a circular
path resulting the centrifugal force act on it, also the force of weight of particle act on

4. it. Particles being heavier than the air it begins thrown towards the wall. Air being
lighter it occupies the central zone & exits from the top. The particles which are
thrown towards the wall, hit’s the wall resulting loses its velocity (velocity of air at the
wall is zero). The particle drag/slide along wall & fall down due to the gravity & gets
collected at the bottom. The air is taken out by exhaust fan located at the top of
cyclone.
8. Star/rotary valve: - It is a pump like assembly located at the bottom of cone of the
spray drier or the cyclone. It helps in maintaining vacuum inside drier and conveys
the dried powder downward with each rotation. It does not allow the air to go inside.

5. DESCRIPTIONOF THE SPRAY DRYING PLANT INSTALLED IN
DAIRY ENGINEERING DIVISION, NDRI KARNAL.
In the spray drier plant with Double stage Falling Film Evaporator all the process
variables are to be controlled by providing electrically operated control. Drying
chamber is designed such that it is suitable for nozzle atomizer as well as rotary disc
atomizer.
Double stage Falling Film evaporator
Function: The Double stage falling film evaporator is used to concentrate
skimmed/whole milk from 9% -14% solids to 45% total solids before being dried in a
spray drying plant. Plant design is suitable to process whole milk as well as baby
food.
TECHNICAL DATA FOR SPRAY DRYING PLANT
Make: - NIRO
Reinstalled & commissioned by: - ALFA process vessel (P) Ltd.
Feed rate:- According to required moisture
Total solids in feed:- 45%
Powder production:-Depends upon feed(kgs/hr)
Moisture in powder:-4% (max.)
Air - inlet temperature: - 180°C
Air Outlet temperature: - 90-95⁰C
Ambient air temperature: 20-35⁰C (assumed)
Feed temperature: - 70-75°C
Number of cyclone separator: - 01
Number of air heater: - 01
Editable diagram:
SPRAY DRYER.docx
Labelling:-

6. 1. Feed balance tank
2. Valve
3. Feed pump
4. Shell & tube type heat exchanger
5. Feed inlet line
6. Atomizer motor
7. Insulation of Drying Chamber
8. Exhaust fan to remove air from cyclone separator
9. Powder drawing chain
10.Cyclone separator
11.Rotary / star valve
12.Powder outlet
13.Balance tank coils
14.Balance tank insulation
15.Fuel inlet
16. Pre heater tubes
17. Pre heater insulation
18.Air heater
19.Air blower 1
20.Air filter 1
21. Mixture of air and powder and powder fine particles
22. Powder drawing chain motor and gear assembly
23.Drying Chamber
OPERATIONAL INSTRUCTIONS
1. First of all clean the drying chamber thoroughly. There should be no left material
inside.
2. Start the supply and exhaust air fans.
3. Check oil level in the atomizer.
4. Thoroughly rinse the feed line with water.
5. Check the level of diesel in the fuel tank and then ignite the burner.
6. Wait until the temperature of the air going to the chamber reaches to 170-180⁰C.
7. Start the atomizer and set the speed at 28000 rpm. Have a look at the values of
current.
8. When the feed reaches to desired consistency i.e. 40%, start the feed pump and
maintain its rpm at 250-270.

7. 9. When the dried product comes out of the drier, its temperature should be around
70-75⁰C.
10. As soon as the feed runs out of the in the balance tank, start water taking in to
flush the product from the pipelines.
11. Stop the burner and feed pump.
12. When the temperature of the drying chamber reaches to atmospheric
temperature clean the atomizing wheel/disk.
TO START AND STOP SPRAY DRIER (OPERATING MECHANISM)-
PROCEDURE:
How to start a spray drying plant -
1. First of all observe the cleanliness of plant and all covers and valves are
closed.
2. Switch ON the main switch of the control panel i.e. the control supply is ON.
3. Then the red colour reset button was pressed to reset all previous parameters
and if there is anything is wrong then it will show the red signal.
4. After that the supply fan was turned on and manual inspection was done to
check whether the fan has started or not.
5. Then the burner and exhaust fan was started together [The exhaust fan must
be started after the supply otherwise due to high pressure there is more
chances of damage or bursting of dryer chamber etc.]
6. Then the rotary valve of cyclone was turned ‘on’ which is helpful to maintain
the partially vacuum in the dryer plant and also is most important and main job
i.e. remove if any hold brunt particle is there which not help full for
manufacturing of good quality powder.
7. Then the rotating chain switched ON so that the power stuck to the inner
sides of the dryer is removed.
8. Then the RPM of the atomizer was set to maximum and then the atomizer
was started.
9. After that the feed pump (positive displacement pump) was turned ON then
slowly set to its minimum RPM i.e. 300 and initially run by water as a feed.
10.Then wait till the inlet and outlet air temperature are reached up to require i.e.
190-2000C inlet air temperature and 85+50C outlet air temperature.
11.After that all the required conditions are maintained then turned on the feed
(milk) instead of water.
12.Continuously check the quality of powder and the amount of feed is adjusted
according to the moisture content of the final product.

8. Stopping (shutdown) of the plant -
1. As soon as the feed tank is empty first turn the feed from the milk to water.
2. Then turn off the atomizer [there is chance of burning of some particles
because feed was already off due to that hot air temperature (outlet
temperature) will also increases].
3. Then after half an hour switch off the exhaust fan.
4. Then switch off the burner and supply fan.
5. After the all product is completely removed then close the rotary valve.
6. Finally plant will undergo cleaning i.e. dry cleaning or CIP as per requirement.
ADVANTAGES-
 The dry particle size can be easily controlled.
 Many heat sensitive products can be spray dried easily at relatively high inlet
temperature.
 Short residence time is required.
 Minimum overall flavour loss in the food industry.
 Ensures high product quality.
DISADVANTAGES-
 The equipment is very costly and bulky.
 Cleaning is time consuming.
 A lot of heat is wasted as thermal efficiency is low.
PRECAUTIONS:
1. If there is any electrical tripping, start the feed pump, burner and atomizer again.
2. If there is clogging in atomizer, stop the plant and clean the disk and then restart
the plant.
3. If any abnormal sound is heard, stop the plant immediately and call the
maintenance people.
CONCLUSION:
From the above practical we could get proper exposure of the spray drier plant
installed at dairy engineering division of NDRI, KARNAL. The above assignment
helped us to study the spray drier much better along with double stage falling film
evaporator. From our work we could define the different parts, structure, objectives,

9. size and values of the spray drier in which the dairy plant is working or can be of
better help and use in other dairy or food industries.
QUESTIONAND ANSWERS:
1. Which type of insulation is used in balance tank placed after
evaporator and before spray drier?
A. The insulation used in the balance tank is glass wool.
2. What is the temperature of concurrent hot air mixed with milk from air
distributor in atomizer?
A. The temperature of hot air coming from air distributor is 200 degree Celsius
3. Where are the final product/ powdercollected from?
A. The final product of powder is collected from the cyclone separator with the
help of star valve which rotates at slow r.p.m.
4. What is the principle behind cyclone separator?
A. The cyclone separator separates the atmospheric air and cyclone separator
air. The air passes out through the dryer exhaust and separator brings down
the powder which is collected down since air is lighter and particles of powder
being heavy.
5. What is the bypass line meant from near air distributor?
A. The bypass line is meant for CIP purpose which carries out cleaning solutions
through it.
6. How is CIP done for Spray Drier?
A. The drier is cleaned using hot air and the atomizer is opened with the help of
chain pulling from above by a pulley system. And the bypass line helps in
cleaning of the spray drier.
7. What is the work of chain placed inside the drier?
A. Powder have chance to block the pipeline or stick to the drier wall. Therefore
a chain is placed inside which agitates with the help of motor and blends the
powder mixture properly. The chain setup is in between 120 – 150 degree.
8. Which is the place where atomized particles come in contact with hot
air and how does powderform?
A. The drying chamber is the part where atomized particles come in contact with
hot air and are dried due to convection current in 3-4 seconds. Hot air flows in

10. rotational movement in the whole chamber. When in contact with liquid mist
fast evaporation of solvent begins.
9. What are the other food commoditiesthat are spray dried?
A. The other food commodities that are spray dried except milk are egg, tea,
coffee, fruit and vegetable extracts, meat extracts and other heat sensible
foods.
10. Why stainless steel is chosenas the constructing material of spray
drier?
A. Stainless steel is chosen to construct the parts in contact with material to
avoid pollution and prolong service life equipment.
SUBMITTED BY-
NIBEDITA BARMAN (17-B-DT-09)
ADRIJA CHAKRABORTY (17-B-DT-19)
B TECH 2ND YEAR, FOURTH SEMESTER
NDRI, KARNAL, HARYANA 132001
YEAR – (2018-2019).