Liquid Nitrogen

Multi-Industry Uses of Nitrogen

The inert properties of nitrogen make it a good blanketing gas in many applications. Nitrogen blanketing is used to protect flammable or explosive solids and liquids from contact with air. Certain chemicals, surfaces of solids, and stored food products have properties that must be protected from degradation by the effects of atmospheric oxygen and moisture. Protection is achieved by keeping these items in a nitrogen atmosphere. “Inerting” or “padding” are other terms used to describe the displacement of air and nitrogen blanketing.

“Sparging” with nitrogen is the bubbling of nitrogen gas through a liquid to remove unwanted volatile components, including volatile organic compounds (VOC) which may be necessary to meet pollution reduction regulations.

Certain substances are difficult to pulverize or shred because they are tough or the materials will be degraded by the heat generated by mechanical processes such as grinding. Liquid nitrogen can be used to freeze soft or tough substances prior to their entering a size reduction process. Cold vaporized nitrogen can be used to keep materials cool (and in an inert atmosphere) during grinding. Cryogenic grinding is used in diverse applications, including production of finely ground pharmaceuticals, plastics and pigments; and for shredding tires in recycling plants.

Metals Manufacturing Uses of Nitrogen

Nitrogen is used to treat the melt in the manufacture of steel and other metals and as a shield gas in the heat treatment of iron, steel and other metals. It is also used as a process gas, together with other gases for reduction of carbonization and nitriding.

“Flash” or “fins” on cast metal can be removed by cooling with liquid nitrogen, making them brittle, allowing then to be broken off by mechanical action.

Manufacturing and Construction Uses

Shrink fitting is an interesting alternative to traditional expansion fitting. Instead of heating the outer metal part, the inner part is cooled by liquid nitrogen so that the metal shrinks and can be inserted. When the metal returns to its normal temperature, it expands to its original size, giving a very tight fit.

Liquid nitrogen is used to cool concrete, which leads to better-cured properties.

When construction operations must be done in soft, water-soaked ground such as tunnel construction underneath waterways, the ground can be frozen effectively with liquid nitrogen. Pipes are driven into the ground, liquid nitrogen is pumped through the pipes under the earth's surface. When the nitrogen exits from the soil, it vaporizes, removing heat from the soil and freezing it.

Chemicals, Pharmaceuticals and Petroleum Uses

Refineries, petrochemical plants and marine tankers use nitrogen to purge equipment, tanks and pipelines of dangerous vapors and gases (for example, after completing a pipeline transfer operation or ending a production run) and to maintain an inert and protective atmosphere in tanks storing flammable liquids.

Cold nitrogen gas is used to cool reactors filled with catalyst during maintenance work. The cooling time can be reduced substantially.

Cooling reactors (and the materials inside) to low temperature allows better control of side-reactions in complex reactions in the pharmaceutical industry. Liquid nitrogen is often used to provide the necessary refrigeration as it can produce rapid temperature reduction and easily maintain the required cold reaction temperatures. Reactor cooling and temperature control systems usually employ a circulating low-temperature heat transfer fluid to transfer refrigeration produced by vaporizing liquid nitrogen to the shell of the reactor vessel. The liquid nitrogen is vaporized in specially-designed heat exchangers that transfer refrigeration to the circulating heat transfer fluid.

Liquid nitrogen is used during well completion to “frac” natural gas bearing rock formations, in particular, tight gas formations, including shale gas and natural gas from coal (coal bed methane) where water based methods should be avoided. Nitrogen is also used to maintain pressure in oil and natural gas producing formations. Unlike carbon dioxide, which is also used for pressurization, nitrogen has little affinity for liquid hydrocarbons, thus it builds up in and remains in the gas cap.

Nitrogen is used as an inert gas to push liquids through lines, to clear lines and to propel “pigs” through pipelines to sweep out one material before using the line to transport another material.

Rubber and Plastics Industry Uses

Materials become hard and brittle when cooled by to very low temperatures. This property permits the removal of “flash” or “fins” on cast plastics and rubber. The castings are cooled by liquid nitrogen and the flash broken off by mechanical action.

Food and Beverages

The intense cold in liquid nitrogen allows very rapid freezing of food items, resulting in minimal cell damage from ice crystals and improved appearance, taste and texture. Well-designed cryogenic tunnel and spiral freezers efficiently capture refrigeration from liquid vaporization and from the cold nitrogen gas as it flows through the freezer.

When substances such as vegetable oil and wines are stored, the inert properties of nitrogen can be used to protect against loss of quality by oxidation by expelling any air entrained in the liquid (“sparging”) and protecting liquids in storage tanks by filling the vapor space (“blanketing”).

Nitrogen (and nitrogen mixed with CO2 and oxygen) is used in transport trucks and in Modified Atmosphere Packaging (MAP) to extend the shelf life of packaged foods by preventing oxidation, mold, insect infestation and moisture migration.

Health Care Uses

Nitrogen is used as a shield gas in the packing of some medicines to prevent degradation by oxidation or moisture adsorption.

Nitrogen is used to freeze blood, as well as viruses for vaccination. It is also used to freeze livestock semen, which can then be stored for years. The quick freezing resulting from the intense cold minimizes cell wall damage. Liquid nitrogen is also used in some MRI (Magnetic Resonance Imaging) devices to pre-cool the low temperature magnets prior to using much more expensive liquid helium for final cooling.

Liquid nitrogen is used in cryo-surgery to destroy diseased tissue.

Miscellaneous Uses of Nitrogen

Nitrogen is used directly as a coolant for severe environmental testing of many items, or as a refrigeration source for chilling circulating dry air.

Properties

Nitrogen (N2) Applications and Uses