Cryogenic grinding

Cryogenic grinding in food is a very new technique. It has a vast advantages over the conventional grinding process. This presentation contents a brief introduction about conventional grinding, different types of grinders and problems of conventional grinders. Its also describe a brief introduction about cryogenic grinding, its components, uses and various advantages.

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WELCOME

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CRYOGENIC GRINDING
Presented by:
NINGTHOUJAM MANDA DEVI
M.Tech ( 2
nd
Year )
Reg. no: J4-01245-2013
Processing and Food Engineering
Department
CAET, Junagadh

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What is Grinding
Grinding is a process of reducing the size of solid materials by
mechanical action, dividing them into smaller particles.
Perhaps the most extensive application of grinding in the food
industry is in the milling of grains to make flour, but it is
used in many other processes.
The grinding of corn for manufacture of corn starch, the
grinding of sugar and the milling of dried foods, such as
vegetables

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Grinding process
Grinding size reduction is achieved by fracturing the materials
 The material is stressed by the action of mechanical moving
parts
Time also plays a part in the fracturing process and it appears that
material will fracture at lower stress concentrations if these
can be maintained for longer periods of time.
The energy required depends upon the hardness of the
material and also upon the tendency of the material to crack -
its friability

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Size reduction equipment can be divided into two classes –
• Crushers : The major action is compressive, breaking large pieces of
solid material into small lumps.
• Grinders: Grinders combine shear and impact with compressive forces,
reduce crushed feed to powder form.
Force for reduce the size of food
a)Compression forces
b)Impact forces
c)Shearing(or attrition) forces
-Both the magnitude of the force and the time of application affect the extent
of grinding achieved.
- For efficient grinding, the energy applied to the material should exceed,
by as small a margin as possible, the minimum energy needed to rupture the
material.
GRINDING EQUIPMENT

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Fig. 1: Jaw crusher Fig. 2: Gyratory crusher
Crushing head
Funnel shaped casing
Stationary jaw
reciprocating jaw

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Fig.3 : Hammer mill Fig. 4 : Plate mill
Circular plates
Axis of rotation

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Fig. 5: Roller mill
Both Rollers rotates at same speed- compression is the primary force
If at different speeds- shearing and compression are the primary forces
If the rolls are grooved, a tearing or grinding component is introduced
Coarse grooves provide less size reduction than fine grooves do

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Fig.6: Ball mill

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PROBLEMS FACED IN CONVENTIONAL
GRINDING PROCESS
High heat generation.
Introduction of tensile residual stress.
Less tool life.
Oxidation
Clogging and gumming of the mill
Loss of enteric oil in spice grinding.

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CRYOGENIC GRINDING

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INTRODUCTION
The word “ CRYOGENICS’ originates from the Greek word
“cryo”, which means creation (or) production by means of cold.
It deals with low temperatures as low as below −150 °C or 123 K
to absolute zero.
Cryogenics is the study of low temperatures and behavior of
materials under these low temperatures.
A person who studies elements that have been subjected to
extremely cold temperatures is called a CRYOGENICIST.

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Cryogens
The extremely low temperature are produced by using substances
called “ cryogens” such as liquid nitrogen and liquid helium.
All cryogenic liquids are gases at normal temperatures and
pressures. So, these gases must be cooled below room
temperature to liquefy them.
They have boiling points below -150°C. (Carbon dioxide and
nitrous oxide, which have slightly higher boiling points are
sometimes included in this category).

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There are several cryogenic liquids such as Nitrogen, helium,
neon, argon, krypton, hydrogen, methane and liquefied natural
gas etc..
Liquid Nitrogen are the most commonly used.
Cryogens are stored in vessels called as Dewar flask which
provides good insulation
Different cryogens become liquids under different conditions of
temperature and pressure, but all have two properties in common:
they are extremely cold, and small amounts of liquid can expand
into very large volumes of gas
Cryogens

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Liquid Nitrogen
Nitrogen gas makes up the major portion of the atmosphere
(78.03% by volume).
Inert, colourless, odourless, non-corrosive, non-flammable liquid
Extremely cold (boiling point -195.8°C, 77°K).
Similar appearance to water.
Volume of expansion liquid to gas (at 15°C, 1 atm.) is 682 , i.e. 1
litre of liquid nitrogen evaporated to form 682 litres of nitrogen gas.

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The Dewar flask
Fig. 7: Dewar flask

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Sir James Dewar (20
September 1842 – 27 March
1923) was a Scottish chemist
and physicist.
Invention of the Dewar flask
The man who first liquefied
hydrogen.
Sir James Dewar

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CRYOGENIC GRINDING
Also known as freezer milling/ freezer grinding / cryomilling.
is the act of cooling/chilling a material and then reducing it to
smaller particle size
Also a method of powdering herbs at sub-zero temperatures
ranging from 0 to -70°F
All materials embrittle when exposed to low temperature
Utilizes the cooling effect of liquid nitrogen to embrittle materials
prior to and or during the grinding process

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Normal grinding processes which do not use a cooling system can
reach up to 200°F.
These high temperatures can reduce volatile components and
heat-sensitive constituents in herbs.
But cryogenic grinding process does not damage or alter the
chemical composition of the plant in any way.
Materials which are elastic in nature, having low melting points,
low combustion temperatures , sensitive to oxygen can be
ideally machined by cryogenic grinding process
CRYOGENIC GRINDING

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GENERAL APPLICATIONS OF
CRYOGENIC GRINDING
Cryogrinding of steel:
The large amount of heat is generated during
machining/grinding at high speed and feed rate raises the
temperature at the cutting zones excessively.
to overcome this problem liquid nitrogen is fed to the grinding
spot.
Thermoplastics and thermo sets:
To which nylon, PVC, polyethylene, synthetic rubber are
commonly used in powder form, but not limited to, a variety of
applications such as adhesives, powdered coatings, fillers and
plastic sintering and moulding.

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Adhesives and waxes;
To avoid the pliable and sticky of certain materials which is
unable in conventional grinding
Explosives;
To grind the explosives materials below their ignition temperature
Spices;
To overcome the volatility of etheric oils ( gives the taste and
smell of spices)

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Spices are the most important constituents of Indian food, not only in
household purposes but also in hotels, restaurants, food processing industries
etc.
Spices like Pepper, cinnamon, chilly, Ginger, Cumin seed, Nutmeg, clove
etc., have a characteristic taste and aroma and medicinal values.
These characteristic qualities are essential in them to have their value as
‘spice’.
These qualities exist in them due to the presence of etheric oils within it.
(boiling points ranging down to 50
o
C)
SPICES

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PROBLEMS WITH CONVENTIONAL GRINDING OF SPICES
1. Loss of etheric oil
The applied energy gets dissipated in the form of heat (>99%)
and hence the temperature in the grinding zone rises to more than
90
o
C resulting in loss of etheric oils whose boiling point ranges
down to 50
o
C. This results in the inferior quality of the ground
product.
2. Clogging and gumming of the mill
Spices like nutmeg, clove, cinnamon, etc.., contain
high level of fat while capsicum, chilli, etc, contain high moisture
content. These cause clogging and gumming of mill thus affecting
the throughput and quality of the ground product. High moisture
content materials often stick to the parts of the mill.

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3. Oxidation and related degradation:
Due to intimate cyclone effect of the air in the vicinity of
grinding zone, aromatic substances in materials oxidize and become
rancid.
In addition the formation of fresh and exposed surfaces due to
grinding, accelerates the process of oxidation.
PROBLEMS WITH CONVENTIONAL GRINDING OF SPICES

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CRYOGENIC GRINDING PROCESS
The cryogenic grinding system consists of two main units, namely…
1)Precooling unit and
2)Grinding unit.
1). Precooling unit
The cryogenic precooler is a cooling device made up of a screw
conveyor enclosed in a properly insulated barrel and a system to
introduce liquid nitrogen into the barrel, thereby providing
refrigeration (liquid and cold gas) within the system.
The function of the cryogenic precooler is to remove the heat from the
material before it enters the grinder.

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1). Precooling unit
It consists of a screw conveyor assembly, an air compressor, a liquid
nitrogen (LN2) dewar , a power transmission arrangement and
control panels.
reduce the temperature of the seed below its brittle point as well as the
freezing point of its oil, before it enters the grinder.
The temperature of the precooler and the feed rate to the grinder are
control to minimise the loss of quality of the final powdered material.
Consumption of liquid nitrogen and the operating cost are important
considerations and matters of concern for a cryogenic precooling system.
The liquid nitrogen losses can be minimized to a great extent by proper
consideration of the design and insulation of the precooler.

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The main engineering considerations which can be adopted in the
design and development of a cryogenic precooler are:
1. Retention time of the seed in the liquid nitrogen and gaseous zone
should be accurately proportioned so that the available refrigeration
could be utilised at its optimum level.
2. Appropriate insulation should be used such that losses to the ambient
could be minimised.
3. Various components of the precooler should be arranged in such a manner
that dismantling and cleaning could be easier.
4. Cooldown losses should be reduced by keeping the machine size and
structural components to a minimum
1). Precooling unit

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2). Grinding unit
The operation of grinding was performed by impact and attrition.
The grinder was operated by an electric motor.
The ground powder was collected in the collector pan from an
outlet and the nitrogen vapour let out.

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PROCESS FLOW CHART OF CRYOGENIC GRINDING OF SPICES
Cleaning of spices
Cleaning of spicesLoading in Hopper through Vacuum ConveyorFeeding in cryogenic
screwChilling of spices with liquid nitrogenFeeding of spices in Pin MillGrinding of Spices in
Mill at low temperature andinert atmoshereExtracting low temperature from grounded
spicesPacking of Spices in Liquid Nitrogen (inert)atmoshere
PDF created with pdfFactory trial versionwww.pdffactory.com

Loading in Hopper through Vacuum Conveyor
Feeding in cryogenic screw conveyor
Chilling of spices with liquid nitrogen
Feeding of spices in Grinders
Grinding of Spices at low temperature and inert atmosphere
Extracting low temperature from grounded spices
Packing of Spices

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Fig. 8: Schematic diagram of cryogenic grinding system
Feeding of Manually cleaned
materials to be ground
LN
2
from the storage tank is spray
into the cooling conveyor
Ground powdered product are
collected in collecting bin
Vaporized LN
2
is sucked
by a centrifugal blower
and fed back to the mill,
and cyclic process is
continued

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ADVANTAGES OF CRYOGRINDING WITH LIQUID
NITROGEN IN SPICES
1.Higher retention of etheric oils- Due to lower operating
temperatures, the etheric oils will be retained in the product
almost to the original level.
2.Prevention of oxidation and rancidity - The heat developed
during grinding will be absorbed by liquid nitrogen and converted
to vapour and eliminates the possibility of oxidation.
3.Increased throughput and power saving- Due to usage of liquid
nitrogen, the raw material becomes brittle. This in turn keeps the
oil and moisture content in the crystallized condition during
grinding and avoids clogging. Required less power to crush.

33. © Food – a fact of life 2009
4. Finer particle size
5. Reduction in microbial load- By cooling with liquid nitrogen, some
bacteria’s may become dormant.

6. Possibility of fine grinding of difficult spices –
- By use of low temperatures, the raw materials become brittle
which causes fibers to shatter
- fibrous spices like ginger can be ground easily to finer particle
size.
- High oil content spices like nutmeg can be ground easily
- can grind green spices like chilies with no pre-drying and also
with the retention of its original colour.

ADVANTAGES OF CRYOGRINDING WITH LIQUID
NITROGEN IN SPICES

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Traditional Grinding System Cryogenic Grinding System
The heat is developed inside the grinding
mill
Temperature below 0
o
C inside the
grinding mill
The heat, which is developed during
grinding, leads on one hand to
evaporation of the essential oil and on
the other hand, heat sensitive fats are
melted.
Negligible loss of volatile component
This in turn can lead to the grinding
elements become greasy (oily) and even
harms the machine by blocking it.
Not in Cryogenic process
High energy consumption Low energy consumption
High capacity motors are required to
grind the material
Low capacity motors are required to
grind the material
No control on particle size Particle size are under controlled
TABLE 1: DIFFERENCE BETWEEN TRADITIONAL AND CRYOGENIC GRINDING SYSTEM

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Table 2: Superiority of the whole cryogenically
process over standard grinding process spices w.r. t
Essential Oil Content
Spices
Ungrounded
essential oil
content
(ml. Per gm.)
%
Cryogenic
Grinded
essential oil
content
(ml. Per am.)
%
Standard
Grounded
essential oil
content
(ml. Per qm.)
%
Turmeric 5.5 1005.5 1003.5 64
Coriander 0.6 1000.6 1000.4 67
Black Pepper 2.9 1002.9 1001.5 52
Cumin Garam 3.5 1003.5 1001.6 46
Garam Masala 4.6 1004.6 1002.0 43
http://www.cryofoods.com/what-is-cryogenic.asp, accessed on 28-11-14

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Table 3: Superiority of cryogenically processed wheat flour
over wheat Grain
Comparative Chart of Nutritional Values, App. Per 100 gm of Whole Wheat and
Wheat Flour
Parameters Whole Wheat
Cryogenically Ground
Flour
Report Result% Report Result %
Energy 364 K cal. 100% 364 K cal. 100%
Protein 11.77 Gm 100% 11.77Gm 100%
Carbohydrates75.17 Gm 100% 75.17 Gm 100%
Fat 1.83 Gm 100% 1.83 Gm 100%
Saturated fat0.36 Gm 100% 0.36 Gm 100%
Sodium 25.63 mg/kg100% 25.63 mg/kg 100%
Cholesterol 0 Gm 100% 0 Gm 100%
Dietary fiber12.48 Gm 100% 12.48 Gm 100%
http://www.cryofoods.com/what-is-cryogenic.asp, accessed on 28-11-14

37. © Food – a fact of life 2009
All grinding properties viz. average particle size, volume surface
mean diameter, mass mean diameter and volume mean diameter
were found lower in cryogenic grinding as compared to ambient
grinding of fenugreek, coriander, black pepper, turmeric and
cinnamon.
Specific energy consumption and energy constants were also
found lower in cryogenic grinding than ambient grinding.
Highest specific energy consumption was for ambient grinding
of black pepper (202.17 (kWh/tonne) and that of lowest for
cryogenic grinding of fenugreek (14.43 kWh/tonne).
Studies on cryogenic grinding for retention of flavour and
medicinal properties of some important Indian spices,
CIPHET, Ludhiana

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ADVANTAGES OF CRYOGENIC
GRINDING
Smaller particles size
More uniform particle size distribution
 Process cooling/temperature control
 Increased throughput
Reduced power consumption
Minimal loss of volatile components

Improves the aroma by minimizing the loss of essential oils when
compared with grinding at normal temperature

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DISADVANTAGES OF CRYOGENIC
GRINDING
Cryo-grinding do have distinctive advantages over the conventional
cooling processes, but…

The application of cryogen in moist atmosphere may cause
formation of ice around the delivery nozzle and the piping
system carrying the cryogen. This may cause a possible blockage
in the delivery system of liquid nitrogen.
Econonomic considerations should be solved.

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Health hazards of cryogenic liquids
1.Skin and eye hazard- Cryogens are extremely cold and can cause
instant, severe frostbite. The eye’s fluids will freeze in contact with
a cryogen, causing permanent eye damage.
2.Cold Embrittlement- At cryogenic temperatures many materials,
such as rubber, plastic and carbon steel can become so brittle that
very little stress can break the material.
3.Oxygen Enrichment- When transferring liquid nitrogen through
uninsulated metal pipes, the air surrounding a cryogen
containment system can condense. Nitrogen, which has a lower
boiling point than oxygen, will evaporate first. This can leave an
oxygen-enriched condensate on the surface that can increase the
flammability (combustibility) of materials near the system,
creating potentially explosive conditions.

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PRECAUTIONS
1)Be familiar with hazards associated with cryogen use.
2)Work in an open, well-ventilated location.
3)Always wear safety goggles and/or face shield and appropriate
cryogen gloves.
4)Examine containers and pressure relief valves for signs of defect.
5)Ensure that all equipment and containers are free of oil, grease,
dirt, or other materials which may lead to flammability hazard
upon contact with liquid oxygen.

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CONCLUSION
As prices for energy and raw materials rise and concern for the
environment makes safe waste disposal difficult and Costly,
resource recovery becomes a vital matter for today's business.
 Cryogenic grinding technology can efficiently grind most tough
materials and can also facilitate Cryogenic recycling of tough
composite materials.
It employs a cryogenic process to embrittle and grind materials to
achieve consistent particle size for a wide range of products.
The cryogenic process also has a unique capability for recycling
difficult to separate composite materials.

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Cryogenic systems are enabling food processors to Cryogenic systems are enabling food processors to
improve both their product quality and operational improve both their product quality and operational
efficiencyefficiency.

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1.http://en.wikipedia.org/wiki/Cryogenics, accessed on 28 November 2014.
2.http://www.cryofoods.com/what-is-cryogenic.asp, accessed on 28-11-14
3.http://www.nzifst.org.nz/unitoperations/sizereduction1.htm, accessed on 22-
12-14
4.http://www.angrau.ac.in/media/10829/fden223fpequii.pdf, accessed on 22-
12-14.
5.ICAR. 2014. Studies on Cryogenic Grinding for Retention of Flavour and
Medicinal Properties of Some Important Indian Spices. Final Report of NAIP
component-4 Sub-Project on Basic and Strategic Research in Frontier Areas of
Agricultural Sciences. 2009-2014. CIPHET, Ludhiana. 60p.
6.http://en.wikipedia.org/wiki/Cryogenic_grinding, accessed on 27-12-14.
REFERENCES

46. © Food – a fact of life 2009
7.M. Wilczek et al.( 2004) Optimised technologies for cryogenic, International
Journal of Mineral Processing. 74S (2004) S425 – S434.
8.Murthy K.L.N. et al. A review on cryogenic grinding of species ,
International Journal of Latest Trends in Engineering, Science and
Technology, 1(10).
9.A Technical Paper on Cryogenic grinding- by Dharmendra Kumar
Madhukar.
10.K.K. Singh and T.K. Goswami (1999) Design of a cryogenic grinding
system for spices, Journal of Food Engineering ,39 (359-368).