The atmospheric dry air is a mixture containing by volume of oxygen and nitrogen 20.93% 78.03%, the rest - argon and other inert gases, carbon dioxide, etc. The content of water vapor in the air can vary widely depending on the temperature and degree of saturation. For technically pure oxygen, air, and subjected to deep cooling liquefies (the boiling point of liquid air at atmospheric pressure, -194,5 ° C.) resulting liquid air is subjected to fractional distillation or fractionation in distillation columns. The possibility of successful rectification is based on a rather large difference (about 13 °) boiling point of liquid nitrogen (-196 ° C) and oxygen (-183 ° C).
The air drawn multistage compressor, passes first through an air filter which is cleaned from dust, then passes sequentially compressor stage. For each stage of the compressor air pressure increases, and brought up to 50-220 atm, depending on the system installation and production stage. After each stage of the compressor air is drier, which is separated by water condensing in the air compression, and: water cooler, the cooling air, consuming the heat produced by the compression. In order to absorb carbon dioxide from the air turns the machine - calciner, filled with an aqueous solution of sodium hydroxide. Compressed air from the compressor runs out of battery drainage bottles, filled with lump caustic soda, which absorbs moisture and carbon dioxide balances. Complete removal of moisture and carbon dioxide from the air is of considerable importance, since freezing at low temperatures, carbon dioxide, water and clog the pipes of the oxygen machine and have to stop setting for defrosting and purging.
After a battery drainage, compressed air enters the so-called breathing apparatus, where the cooling and liquefaction of air and its fractionation with separation into oxygen and nitrogen. Nitrogen gas purity of 96-98% is usually not used and the heat exchanger is produced in the atmosphere. The oxygen is sent to the gas tank and fed to the filling of oxygen cylinders pressurized to 165 atm, 1 m3 of oxygen at 760 mm Hg. of Art. and 0 ° C weighs 1.43 kg and at 20 ° C, 1.31 kg, 1 liter of liquid oxygen weighs 1.13 kg and evaporates, forms a 0.79 m3 of gaseous oxygen at 0 ° C and 760 mm Hg ., 1 kg of liquid oxygen occupies a volume of 0.885 liters and evaporates, forming 0.70 l3 oxygen gas at 0 ° C and 760 mm Hg. Art.
According to GOST 5583-58 technical oxygen for flame treatment of metals is available in three varieties, the highest grade, with a purity of not less than 99.5%, 1st grade, not below 99.2% and 2nd grade, not below 98.5% oxygen by volume.
Significant economic interest in delivery of oxygen to the oxygen plant to customers in a liquid form, in which the tare weight is about 50% of the total weight of cargo, with the same weight of cargo transported liquid oxygen is 5 times greater than for the transport of its gaseous form. To be able to use liquid oxygen are necessary: 1) a transport tank for transportation of liquid oxygen, mounted on a vehicle, usually belonging to the oxygen plant, and 2) the gasifier, which serves to convert the liquid oxygen into gaseous, and is usually installed by the consumer of oxygen. The transport tank for transportation of liquid oxygen is essentially a ball of brass sheet, enclosed in a steel casing, the space between the ball and the housing is filled with insulating material - magnesium carbonate powder. Liquid oxygen is poured into the tank through the receiver-drain valve, fill the brass ball. The selection of oxygen should be performed through a flexible hose attached to the valve. Since the ambient air temperature is always above the critical temperature, oxygen, liquid oxygen will inevitably evaporate into the surrounding atmosphere. In good condition, tank insulation, this loss may amount to 0.5% per hour. In case of increase of pressure tank equipped with a safety valve.
Consumers should have a liquid oxygen gasifiers. Oxygen gasifiers are divided into stationary and portable, as well as: a) low pressure, or cold, feed oxygen into the distribution piping system at pressures up to 15 am, and b) high pressure, or warm, give oxygen cylinder filling pressure 150-165 am.
The most common plants in our standard stationary cold gasifier with a capacity of 1000 liters or 800 m3 of liquid oxygen gas. Gasifier is installed in a separate room. It consists of a thick-walled steel ball inside which is placed a thin-walled brass ball for liquid oxygen. The ball is in the gasifier housing, the space between the casing and a ball filled with chalk, as in the oxygen tanks. Gasifier is filled with liquid oxygen from a storage tank through a valve and flexible hose. From the gasifier liquid oxygen enters the evaporator coil, and thence gaseous oxygen is sent into the network of oxygen pipelines. To equalize the pressure fluctuations befall receiver (recipient) with a capacity of about 10m3.
See also:
Gas Welding Technology
Transportation and Storage of Oxygen
When To Use Oxgen Gas Welding
Production of Oxygen from Air
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