Air separation

Getting the products of air separation. Making an inert atmosphere

To get the main products of air separating – nitrogen and oxygen – air-separating equipment is used.

This equipment is divided into three main groups according to its principle of operation:

  • cryogenic – with air separating using low-temperature rectification;
  • adsorptive – working at ambient temperature and providing air separating due to adsorbents;
  • membrane – working at ambient temperature and providing air separating due to polymeric membranes (molecular sieve) made like capillary tubes.

The criterion of choosing the type of equipment is a required product, its condition (liquefied or gaseous), purity, the pressure of product gas, productivity and economy.

Cryogenic air-separating plants (ASP)

The principal of operation of air-separating plants is based on low-temperature rectification of liquefied air. They consist of compressor, technological and auxiliary equipment. Air after pressure is exposed to purification, where it is exempt from moisture, carbon dioxide and hydrocarbons; then it goes through expander, the system of heat exchangers; then it is liquefied and goes to the rectifying column for dividing.

Cryogenic ASP are technically complicated, demand quite long time to reach needed regime and to change the regime. They include power-intensive purification system, heat- and mass changing equipment, expander, complex automatic system. Beside they demand high-qualified maintenance and they are quite power-intensive. These disadvantages are compensated by the possibility of getting liquid and gaseous products of air-separating – nitrogen and oxygen, pure medical oxygen, and pure technical nitrogen.

NPO “Geliymash” produces cryogenic ASP in two basic types: stationary ASP on the cycle of high pressure (СКДС-100В) and transportable variant – the plant ТКДС-100В, placed in two standard 20-foot containers. The station ТКДС-100В is designed for getting liquid and gaseous oxygen or nitrogen of high purity, as well as dry air of high pressure free of impurities.

According to customer orders it is possible to produce the plants – modifications of basic models.

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Adsorptive air-separating plants

For the consumers of gaseous nitrogen and oxygen that need in easy-to-use plants with rapid starting and short-term using, there are adsorptive air-separating plants. Their work is based on selective absorption of air components by molecular adsorbents using the technology of Pressure Swing Adsorption (PSA).

When air is going through one of the absorbers working in turn, nitrogen or oxygen are adsorbed from air (along with water vapors, carbon dioxide and hydrocarbons), and the rest gas goes to the consumer. Adsorbent regeneration occurs at pressure drop in the absorber after its work. The process of work at each stage occurs at room temperature automatically.

Factors providing the competitiveness of PSA plants are their low prices, easiness of assembly, of using and engineering service. Beside the plants of this type are characterized by their compact size, high level of safety, reliability, workflow automation (including starting and stopping), short period of starting, and unlimited time of working campaign.

Adsorptive method of air separating in a wide variety of productivity and concentration is characterized by higher economy in comparison with cryogenic method, which is connected with decreasing pressure in the plant in comparison with traditional low-temperature cycle. However this method does not allow getting technical oxygen and liquefied gases.

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The plants КБА for oxygen production

The air-separating plants work according to the КБА principal and are designed for producing gaseous oxygen. They give quite low product concentration (less than 95%). It limits usage of these plants. Despite the limitations of oxygen concentration they are used extensively.

These plants are used:

  • to get oxygen for autogenous works (excluding automatic metal cutting);
  • in silicate industry and in pulp and paper industry;
  • in fishing;
  • to process waste waters and to provide ozone plants with oxygen;
  • in processing organic waste (pyrolysis);
  • in microbiology;
  • in food and pharmaceutical industries;
  • in agriculture.

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The plants КБА for nitrogen production

The air-separating plants work according to the КБА principal and are designed for producing gaseous nitrogen. They ensure the product purity of 99,9995 %. Applying additional modules allows getting purer nitrogen.

These plants are used:

  • to provide fire and explosion safety during erecting, service and repairing work in plants, blocks and elements of oil-and-gas complex;
  • to make “nitrogen cushion” during overflowing and transporting of oil products;
  • to make an inert atmosphere in chemical industry during separating complex solutions and mixtures, as well as varnish-and-paint industry;
  • to make inert atmosphere in electronic industry;
  • as a means of firefighting and stopping the processes of smouldering in technological processes;
  • to make neutral atmosphere during packaging of food products.

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Membrane air-separating plants

Membrane air-separating plants are characterized by giving only one product – nitrogen.

Constructively these plants are similar to adsorptive ones, but instead of adsorptive separating block there is a block with standard membrane cartridge. The volume and purity of product nitrogen is determined by productivity of compressor, throughput capacity of membrane cartridges and ratio between processed and product flows.

Membranes are very sensitive to condensed moisture and oil pollution. That is why the plants should be used at the temperature more than 0?С, and it is necessary to pay more attention to the process of air preparation.


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