The document discusses cryogenic grinding, a method that reduces material size by cooling it to extremely low temperatures, typically using liquid nitrogen. This technique solves issues faced in conventional grinding, such as high heat generation and loss of volatile compounds, while improving productivity and preserving material quality. It outlines the process, equipment required, benefits, demerits, and health hazards associated with cryogenic liquids.

1. CRYOGENIC GRINDING
PRESENTED BY-
16BCH016 VISHAL NAIDU
16BCH035 ARPIT MODH

2. CONTENTS
• Introduction
• Problems faced in Conventional Grinding
• Cryogenic Grinding Technology
• Working Principle of CryoGrinder Performance Data & Technical Data
• Merits & Demerits
• Field of applications
• Conclusion

3. 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.

4. 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).

5. • 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

6. SIR JAMES DEWAR
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.

7. THE DEWAR FLASK

8. 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

9. GRINDING PROCESS
• Grinding size reduction is achieved by fracturing the materials
• 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

10. GRINDING EQUIPMENT
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.

11. 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

14. 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

16. 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

17. HOW TO ELIMINATE THESE PROBLEMS??

18. 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

19. • 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

20. CRYOGENIC GRINDING
• For pulverizing many materials, Cryogenic Grinding Technology increases productivity &
lower power cost.
• Many elastic/soft materials are very difficult to pulverize(crush to fine particle), requiring
long cycle times & high power/energy consumption.
• Cryogenic grinding involves cooling a material below its embrittlement temperature with
a cryogenic fluid, typically liquid nitrogen.
• After cooling, the material is fed into an impact mill where it is reduced in size primarily
by brittle fracture.

22. GENERALAPPLICATIONS 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.

23. 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)
GENERALAPPLICATIONS OF CRYOGENIC
GRINDING

24. PROBLEMS WITH CONVENTIONAL GRINDING
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 90oC resulting in loss of etheric oils whose boiling
point ranges down to 50 deg C. This results in the inferior quality of the ground product.
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.

25. 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

26. CRYOGENIC GRINDING PROCESS
The cryogenic grinding system consists of two main units:
• Precooling unit
• Grinding unit.

27. 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.

28. 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.

30. SCHEMATIC DIAGRAM OF CRYO-GRINDING
SYSTEM

31. WORKING
• Material is to be ground is cleaned manually & fed into the hopper.
• From the exit of the hopper the material enters into the vibratory feeder, which is
positioned with a small inclination towards the entry of the helical screw conveyor, It has
ability to control the fed rate.
• Liquid nitrogen from the storage container is sprayer into the screw conveyer, The time of
stay of material in the conveyer can be maintained by varying the speed of the drive i.e.,
conveyer drive.

32. • The sensors monitors material’s temperature in the conveyer.
• When the mill is running, the material gets crushed between the studs & comes out
through an optional sieve as a ground product.
• To the bottom of the mill a collecting bin is housed where the ground product gets
collected.
• The vaporized nitrogen from the mill is sucked by a centrifugal blower & through the
filter assembly is fed back to the mill, And the cyclic process is continued.
WORKING

33. SCHEMATIC DIAGRAM OF CRYOGRINDER

36. DIFFERENCE

37. MERITS
• Increased throughput & power saving.
• Finer particle size.
More uniform particle distribution.
• Lower grinding cost.
• No heat generation.
• Prevent oxidation

38. • High power consumption.
• High operation cost.
• Maintenance cost is above the range.
• Filtering of Screw Conveyer is Difficult.
DEMERITS

39. HEALTH HAZARDS OF CRYOGENIC LIQUIDS
• 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.
• 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.
• 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.

40. PRECAUTIONS
• Be familiar with hazards associated with cryogen use.
• Work in an open, well-ventilated location.
• Always wear safety goggles and/or face shield and appropriate cryogen gloves.
• Examine containers and pressure relief valves for signs of defect.
• 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.

41. CONCLUSION

42. CRYOGENIC SYSTEMS ARE ENABLING FOOD
PROCESSORS TO IMPROVE BOTH THEIR PRODUCT
QUALITY AND OPERATIONAL

43. THANK YOU