Air on the structure is non-uniform. It is the mix consisting on average of 78% of nitrogen, 21% of oxygen, 1% of argon and insignificant amount of carbon dioxide, vapors of water, noble gases, dust. Nitrogen, oxygen and argon are used in the industry and medicine. And air is raw materials for their receiving. There are three main methods of division of air into gases.
Instruction
1. The method of low-temperature distillation is based on a difference of temperatures of boiling of the gases making air. So boiling temperature nitrogen with an atmospheric pressure is near (-196) wasps, argon – (-186) wasps, oxygen – (-183) wasps. This way allows to receive the cleanest components, but is feasible only in the conditions of large enterprise. Process proceeds in special airdividing installations.
2. At the first stage air is compressed the compressor and cleaned from dust, vapors of water, carbon dioxide. Carbon dioxide freezes at rather high temperature. Its office occurs in air coolers where it together with residues of water vapor accumulates on the surfaces of the device. Also carbon dioxide is separated sometimes chemical reaction with hydroxide of potassium or sodium.
3. Then air is liquefied, reducing temperature at elevated pressure. The liquefied air comes to rectifying columns where it is divided into nitrogen, with small impurity of neon and helium, and oxygen mix with argon. For high extent of cleaning for each component at the enterprises a number of such columns is provided.
4. The method of adsorption applies substances – the adsorbents which are selectively absorbing a certain component. Then in the course of regeneration the absorbed substance is released and removed in the atmosphere. Process is carried out in the installations consisting of two columns adsorbers. This way allows to receive products – oxygen or nitrogen – rather high purity at average capital expenditure.
5. The membrane method is a division of air by means of membranes – the semipermeable partitions which are selectively passing molecules of separate components. In modern gas-dividing installations membranes from porous polymeric fiber are used. This method is good for division of small volumes of air, but is uneconomical for large production. Also a shortcoming is rather low degree of purity of a product.