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Liquid oxygen
Oxygen is the second largest component of the atmosphere, comprising
20.8% by volume. Liquid oxygen is pale blue and extremely cold.
Although nonflammable, oxygen is a strong oxidizer. Oxygen is
necessary to support life. Oxygen will react with nearly all organic
materials and metals usually forming an oxide. Materials that burn in
air will burn more vigorously in oxygen. Equipment used in oxygen
service must meet stringent cleaning requirements and systems must be
constructed of materials that have high ignition temperatures and that
are non-reactive with oxygen under the service conditions. Vessels
should be manufactured to American Society of Mechanical Engineers (ASME)
codes and designed to withstand the process temperatures and pressures.
Liquid oxygen is a cryogenic liquid. Cryogenic liquids are liquefied
gases that have a normal boiling point below -238°F (-150°C). Liquid
oxygen has a boiling point of -297.3°F (-183.0°C). Because the
temperature difference between the product and the surrounding
environment is substantial—even in the winter—keeping liquid oxygen
insulated from the surrounding heat is essential. The product also
requires special equipment for handling and storage. Oxygen is often
stored as a liquid, although it is used primarily as a gas. Liquid
storage is less bulky and less costly than the equivalent capacity of
high-pressure gaseous storage. A typical storage system consists of a
cryogenic storage tank, one or more vaporizers, a pressure control
system, and all piping necessary for the fill, vaporization, and
supply functions. The cryogenic tank is constructed, in principle,
like a thermos bottle. There is an inner vessel surrounded by an outer
vessel. Between the vessels is an annular space that contains an
insulating medium, from which all the air has been removed. This space
keeps heat away from the liquid oxygen held in the inner vessel.
Vaporizers convert the liquid oxygen into a gaseous state. A pressure
control manifold then controls the gas pressure that is fed to the
process or application. Vessels used in liquid oxygen service should
be designed according to ASME codes for the pressure and temperatures
involved. Piping design should follow similar codes, as issued by the
American National Standards Institute (ANSI).
Physical Properties
• Molecular Formula: O2
• Molecular Weight: 31.999
• Boiling Point @ 1 atm: -297.4°F (-183.0°C, 90oK)
• Freezing Point @ 1 atm: -361.9°F (-218.8°C, 54oK)
• Critical Temperature: -181.8°F (-118.4°C)
• Critical Pressure: 729.1 psia (49.6 atm)
• Density, Liquid @ BP, 1 atm: 71.23 lb/scf
• Density, Gas @ 68°F (20°C), 1 atm: 0.0831 lb/scf
• Specific Gravity, Gas (air=1) @ 68°F (20°C), 1 atm: 1.11
• Specific Gravity, Liquid (water=1) @ 68°F (20°C), 1 atm: 1.14
• Specific Volume @ 68°F (20°C), 1 atm: 12.08 scf/lb
• Latent Heat of Vaporization: 2934 BTU/lb mole
• Expansion Ratio, Liquid to Gas, BP to 68°F (20°C): 1 to 860
• Solubility in Water @ 77°F (25°C), 1 atm: 3.16% by volume
Additional tables
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