Khushaboo Dahikar#1, Sonal Shende#2, Poonam Ghodke#3 , Dr. (Mrs) Swarda. R. Mote #4
1,2,3Student, Chemical Engineering, RTMNU, India
4Associate Professor, Chemical Engineering, RTMNU, India
Cryogenics deals with the generation of extremely low temperatures which does not naturally occur on earth and the phenomenon associated with these temperatures. Idea of Cryogenic was first investigated by Michael Faraday, who demonstrated that gases could be liquefied leading to the production of low temperatures of around 173 K. Cryogenic technology obtainedwidespread recognition during the 1960s, with emphasis on cryogenic techniques and its applications in various fields.Cryogenic technology has become so advanced that its application is found in field of chemical engineering to medical field. In this paper an attempt has been made to review cryogenic and its application in chemical engineering process industry.
Keywords—Cryogenic, Cryogens, Adiabatic Demagnetisation, Grinding, Cleaning, Cryogenic Fluids, Dry-Ice Blasting
Cryogenics is the science of producing and studying low-temperature conditions and their effect on matter, a formulation which addresses both aspect of attaining low temperature which does not naturally occur on earth. The word cryogenics comes from the Greek word Cryos meaning “cold,” and Genic meaning “to generate.” It has come to mean the generation of temperatures well below those of normal human experience. More specifically, a low-temperature environment is termed a cryogenic environment when the temperature range is below the point at which permanent gases begin to liquefy. Cryogenics involves refrigeration at temperatures below 120 K. These low temperatures, which are not natural on earth, make it possible to liquefy gases such as methane, oxygen, nitrogen and hydrogen. The most commonly used industrial gases that are transported, handled, and stored in the liquid state at cryogenic temperatures are argon, helium, hydrogen, nitrogen, and oxygen. One aspect of cryogenics involves the development of methods for producing and maintaining very low temperatures and another aspect includes the study of the properties of materials at cryogenic temperatures and applications of cryogenic technology.
How to Produce to Produce Cryogenic Condition
There are basically four physical processes that are used to produce cryogenic temperatures and cryogenic environments: heat conduction, evaporative cooling, cooling by rapid expansion (the Joule-Thompson effect), and adiabatic demagnetization.
Heat conduction is one of the methods for producing cryogenic temperature and condition in which samples may be cooled to cryogenic temperatures by immersing them directly in a cryogenic liquid or by placing them in an atmosphere cooled by cryogenic refrigeration. In either case, the sample cools by conduction (or transfer) of heat to its colder surroundings. Evaporative Cooling is the second physical process with cryogenic applications wherein, a liquid is allowed to evaporate. Heat from within the liquid is used to convert particles at the surface of the liquid to gas which is then pumped away. More heat from the liquid converts another surface layer of particles to the gaseous state, which is also pumped away. The longer this process continues, the more heat is removed from the liquid and the lower its temperature drops. Once some given temperature is reached, pumping continues at a reduced level in order to maintain the lower temperature. The Joule-Thompson effect in conjunction with the process of heat conduction is used as another method for producing cryogenic temperature. The two effects together comprise the common refrigeration process. First, a gas is pressurized and cooled to an intermediate temperature by contact with a colder gas or liquid. Then, the gas is expanded, and its temperature drops still further. Cryogenic refrigerators work on the same principle but cryogenic gases such as helium is employed and repeat the process in stages, each stage having a successively colder gas until the desired temperature is reached. Another process for producing cryogenic temperatures uses a phenomenon known as Adiabatic Demagnetization. In this process paramagnetic salts are used, which consists of a very large collection of particles that act like tiny (atom-sized) magnets. Initially this salt is not magnetic but when it is placed between the poles of a magnet, the magnetic field of the magnet causes all the tiny magnetic particles in the salt to line up in the same direction and turning the Salt magnetic. In this case, randomness in the alignment of magnetic moments has been reduced, resulting in a decrease in entropy (measure of randomness in a collection).When the electromagnet is switched off, and the paramagnetic salt is placed within a liquid. Almost immediately, the tiny magnetic particles within the salt return to their random alignment. To make this change, however the particles require an input of energy and in this case, it is taken from the liquid into which the salt was placed. As the liquid gives up energy to the salt, its temperature drops and the magnetic moments of the salt will tend to return to more random orientations. Adiabatic demagnetization has been used to produce some of the coldest temperatures ever observed within a few thousandths of a degree kelvin of absolute zero.
II. Cryogenic fluid and its properties
Cryogenic liquids are liquefied gases that are kept in their liquid state at very low temperatures. Cryogenic fluids are those whose boiling points at atmospheric pressure are about 120 K or lower, although liquid ethylene with its boiling point of 170K is often included. All cryogenic liquids are gases at normal temperatures and pressures. These gases must be cooled below room temperature before an increase in pressure can liquefy them. 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. The vapours and gases released from cryogenic liquids also remain very cold. They often condense the moisture in air, creating a highly visible fog. All gaseous cryogens are odourless and all liquid cryogens are colourless apart, and Fluorine, which is pale yellow from Oxygen, which is pale blue
. A list of the cryogenic fluids, together with some selected properties, is given in Table 1. Perhaps the most important and widely-used fluids are liquefied natural gas or LNG (boiling point about 120 K), liquid oxygen (bp 90.2 K) and liquid nitrogen (bp 77.3 K). All cryogenic fluids except
Helium and Hydrogen behave as ‘normal’ fluids, their common distinguishing features in general being a low specific heat and enthalpy of vaporization. They are all diamagnetic except oxygen, which is quite strongly paramagnetic. With the exception of oxygen, all the gases are asphyxiates, and even oxygen will not support human life in concentrations greater than about 60%.Fluorine and oxygen are powerful oxidizers even in liquid form. Some cryogens are flammable; hydrogen is especially delicate to handle. Hydrogen is an unusual fluid in that the molecule exists in two forms known as ortho and para, with somewhat different properties. Each cryogenic liquid has its own specific properties but most cryogenic liquids can be placed into one of three groups. First one is Inert Gases: these gases do not react chemically to any great extent and do not burn or support combustion. Nitrogen, helium, neon, argon and krypton are some example of inert gases. Second group is Flammable Gases: Some cryogenic liquids produce a gas that can burn in air. The most common examples are hydrogen, methane and liquefied natural gas and lastly the Oxygen: Many materials considered as non-combustible can burn in the presence of liquid oxygen. The hazards and handling precautions of liquid oxygen must therefore be considered separately from other cryogenic liquids . Cryogenic liquids are shipped and used in thermally insulated containers which are specifically designed to withstand rapid temperature changes and extreme differences in temperature. Thermally insulated containers such as Liquid Dewar Flasks, Laboratory Liquid Dewar Flasks, and Liquid cylinders are used to store and transport
Over the years, various researches have resulted in the identification of a number of useful properties of materials under the cryogenic condition. With development of methods to attain cryogenic temperature or producing cryogenic condition, its application has been expanded from the electronic field to medical and chemical engineering field. There are large numbers of application of cryogenic technology but in this paper, we have mainly focussed on the application related to chemical engineering. Some of the applications are discussed below:
Cryogenic Cleaning is also known as Dry ice-blasting which is a form of carbon dioxide cleaning, where dry ice, the solid form of carbon dioxide, is accelerated in a pressurized air stream and directed at a surface in order to clean it. An alternative media for non-abrasive blasting is water-ice, known as ice blasting. The method is similar to other forms of abrasive blasting such as sand blasting, plastic bead blasting, or soda blasting substituted for dry ice as the blasting medium. Dry-ice blasting leaves no chemical residue as dry ice sublimates at room temperature. It involves propelling pellets at extremely high speeds. The actual dry-ice pellets are quite soft, and much less dense than other media used in blast-cleaning (i.e. sand or plastic pellets). Upon impact, the pellet sublimates almost immediately, transferring minimal kinetic energy to the surface on impact and producing minimal abrasion. The sublimation process absorbs a large volume of heat from the surface, producing shear stresses due to thermal shock. This is assumed to improve cleaning as the top layer of dirt or contaminant is expected to transfer more heat than the underlying substrate and flake off more easily as shown in figure 1. The efficiency and effectiveness of this process depends on the thermal conductivity of the substrate and contaminant. Dry Ice Blasting is nonabrasive, nonconductive, non-flammable and environmentally-friendly cleaning because no additional chemicals or spray agents. Dry Ice Blasting generates no additional waste or secondary contamination unlike media and water blasting and does not require preparation prior to cleaning.
Cryogenic Preservation in Food Industry
Cryogenic gases are used in transportation of large masses of frozen food. When very large quantities of food must be transported to regions like war fields, earthquake hit regions, etc.; they must be stored for a long time, so cryogenic food freezing is used. Cryogenic food freezing is also helpful for large scale food processing industries. Cryogenic freezing is used to freeze food at an extremely fast rate. The food is moved through a spray of liquid nitrogen or directly immersed in liquid nitrogen. The liquid nitrogen boils around the food at a temperature of −196 °C (−321 °F) and extracts a large amount of heat.
Cryogenic grinding, also known as freezer milling, freezer grinding, and cryomilling, is the act of cooling or chilling a material and then reducing it into a small particle size. When chilled by dry ice, liquid carbon dioxide or liquid nitrogen, samples that are soft or flexible at room temperature and high temperature sensitive materials such as thermoplastics, samples can be finely ground to powders suitable for electrostatic spraying and other powder processes. The general set-up of cryogenic grinding is shown in figure 2.
Cryogenic grinding is viable technique for Spices condiments seasonings as high quality spices at controlled partial sizes with no evaporation of essential values and negligible loss of volatile components are obtained and also grinding materials that temperature sensitive such as thermoplastics and elastomers and Chemicals highly volatile or hygroscopic in natured. It can be also employed for fine particle size reduction of Oxidizable materials, e.g. fine metal powder, are best protected in an inert gas atmosphere Cryogenic grinding of plant and animal tissue is a technique used by microbiologists. For The major features of cryogenic grinding are that there is negligible loss of volatile oils and eventually aroma and taste are saved in case of spices or other products. In cryogenic grinding, temperature as low as -196 degrees Celsius is used. Due to very low temperature, materials became brittle and thus difficult to grind or even ungrindable products in conventional grinding become grindable and give better outputs. Imparts brittleness to the material thus making Initial cost and the running cost of a cryogenic plant is negotiated by the fact that the production per kilowatt is increased manifold, all grinding related issues like non grindability, choking, are eliminated. Quality of product is enhanced to a different level altogether.
Cryogenics is a multidisciplinary field using many aspects of physics and engineering. After the development of methods for producing cryogenic condition, Cryogenic Technology found its application in various field, from medical to manufacturing field and has been used universally and has several advantages over conventional technology. In cryogenic technology, different cryogens are used, are liquids under different conditions of temperature and pressure but they are extremely cold which make them hazardous and need to be handle with care.
- L. K. Sharma, D. Agarwal, Y. Sharma, S. S. Rathore and S. N. Saxena. Cryogenic grinding technology enhances volatile oil, oleoresin and antioxidant activity of cumin (Cuminum cyminumL) International J. Seed Spices 4(2), July 2014:68-72
- Ph. Lebrun, “AN INTRODUCTION TO CRYOGENICS”, Cryophysics and Cryoengineering of the IIR, Accelerator Technology Department, CERN, Geneva, Switzerland (2007).