Cryogenic grinding

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.

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 “ C ryo ”, 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

12. 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

13. 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

14. HOW TO ELIMINATE THESE PROBLEMS??

15. 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

16. 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

17. 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 .

18. 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 .

19. 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 ) GENERAL APPLICATIONS OF CRYOGENIC GRINDING

20. 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 .

21. 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

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

23. 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 .

24. 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 .

25. Schematic diagram of cryo -grinding system

26. 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 .

27. 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

28. SCHEMATIC Diagram of cryogrinder

29. DIFFERENce

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

31. High power consumption. High operation cost. Maintenance cost is above the range. Filtering of Screw Conveyer is Difficult . deMERITs

32. 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 .

33. 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 .

34. CONCLUSION

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

36. THANK YOU