Production and maintenance of deep low temperature, so that the raw gas liquefaction or separation and purification of its components of the equipment, also known as deep freezing treatment equipment. Deep low temperature refers to the temperature far lower than that reached and applied by ordinary refrigeration engineering, and its range is generally 120K to close to zero degrees. The use of cryogenic equipment is very wide. For example, oxygen liquefaction equipment and hydrogen liquefaction equipment can produce liquid oxygen and liquid hydrogen as rocket propellants; helium liquefaction equipment can produce liquid helium for the study of superconducting materials, superconducting technology, space technology, etc. Another example is the use of natural gas separation equipment to separate raw materials, which can produce ethane, ethylene and other light hydrocarbon chemical raw materials; air separation equipment can produce oxygen and nitrogen for smelting steel and manufacturing synthetic ammonia. In the 1970 s and 1980 s, air separation equipment was applied and promoted in new fields such as coal gasification, sewage treatment, pulp bleaching, petroleum protein fermentation and integrated circuit board production.
There is no natural deep low temperature environment and deep low temperature material on the earth, and it is necessary to use deep low temperature equipment to obtain such low temperature. In 1877, France's L.P. Ketai and Switzerland's R. Pickett respectively used laboratory refrigeration equipment to reach a deep low temperature below 90.2K to obtain mist-like liquid oxygen. In 1893, the British J. Dewar in the deep cryogenic liquefied gas container first made of vacuum bottle, known as the Dewar bottle. In 1895, Germany's C.von Linde applied the Joule-Thomson isenthalpy throttling effect to form the original cryogenic equipment with a compressor, a tubular heat exchanger and a throttle valve, and used it to liquefy air to a temperature of 80.9K. In 1898, on the basis of Linde's work, Dewar used liquid air to pre-cool hydrogen, and then expanded through a throttle valve to reduce the temperature to below 20.4K to obtain liquid hydrogen. In 1902, G. Claude of France added a piston expander on the basis of Linde liquefaction equipment, and the isentropic expansion refrigeration method was mainly used to make liquefied air equipment. In 1903, there was a commercial oxygen generator. In 1908, H. Camerin-Ones of the Netherlands used the same principle to pre-cool helium with liquid hydrogen and expand it under adiabatic conditions, reducing the temperature to below 4.2K to obtain liquid helium. In 1965, the Soviet Union's beta. С. Neganov and others invented the dilution refrigerator, so that the temperature reached 0.025K. Since the 1970 s, people have applied demagnetization refrigeration technology to further reduce the refrigeration temperature of the equipment.
Deep cryogenic distillation is the first raw material gas liquefaction, and then according to the different components of condensation (evaporation) temperature, the application of distillation principle to separate the components, the separation process is realized in the deep cryogenic distillation tower. This method is suitable for the separation of the components of the condensation temperature of the feed gas, such as the separation of oxygen and nitrogen from the air.
Deep low temperature separation is the use of raw gas components in the condensation temperature difference, in the heat exchanger to reduce the temperature of the raw gas, from high to low component by component liquefaction, and in the separator will separate the liquid. This method is suitable for the separation of feed gas, such as coke oven gas, where the condensation temperatures of the separated components are far apart.
Deep cryogenic adsorption is the use of porous solid adsorbent with selective adsorption characteristics, in the deep low temperature adsorption of some impurity components, in order to obtain a pure product method. Such as the use of molecular sieve adsorber in liquid air from crude argon adsorption of oxygen and nitrogen, in order to obtain refined argon. According to the needs of the process, sometimes a principle is used alone, and sometimes several principles are used at the same time.

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