Chemical oxygen generator
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A chemical oxygen generator is a device that releases oxygen created by a chemical reaction. The oxygen source is usually an inorganic superoxide, chlorate, or perchlorate. A promising group of oxygen sources are ozonides. The generators are usually ignited mechanically, by a firing pin, and the chemical reaction is usually exothermic, making the generator a potential fire hazard. Potassium superoxide was used as an oxygen source on early manned USSR space missions, for firefighters, and for mine rescue.
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[edit] Chemical oxygen generator in commercial airliners
Commercial aircraft provide emergency oxygen to passengers to protect them from drops in cabin pressure. Chemical oxygen generators are not used for the cockpit crew. In narrow body airliners, for each row of seats there are overhead masks and oxygen generators. In wide body airliners, such as the DC-10 and IL-96, the canisters and oxygen masks are mounted in the top portion of the seat backs, since the ceiling is too high above the passengers. If a decompression occurs, the panels are opened either by an automatic pressure switch or by a manual switch, and the masks are released. When the passengers pull down on the mask they remove the retaining pins and trigger the production of oxygen.
The oxidizer core is sodium chlorate (NaClO3), which is mixed with less than 5 percent barium peroxide (BaO2) and less than 1 percent potassium perchlorate (KClO4). The explosives in the percussion cap are a lead styphnate and tetracene mixture. The chemical reaction is exothermic and the exterior temperature of the canister will reach 260 °C (500 °F). It will produce oxygen for 15 to 20 minutes.[1][2] The two-mask generator is approximately 63 mm (2.5 in) in diameter and 223 mm (8.8 in) long. The three-mask generator is approximately 70 mm (2.8 in) in diameter and 250 mm (9.8 in) long.
Accidental activation of improperly shipped expired generators caused the ValuJet Flight 592 crash. An ATA DC-10, Flight 131, was also destroyed while parked at O'Hare Airport, on August 10, 1986. The cause was the accidental activation of an oxygen canister, contained in the back of a broken DC-10 seat, being shipped in the cargo compartment to a repair station. There were no fatalities or injuries because the plane contained no passengers when the fire broke out.
[edit] Oxygen candle
A chlorate candle, or an oxygen candle, is a cylindrical chemical oxygen generator containing a mix of sodium chlorate and iron powder. When ignited, the mixture smolders at about 600 °C (1,112 °F), producing sodium chloride, iron oxide, and about 6.5 man-hours of oxygen per kilogram of the mixture. It releases oxygen at a fixed rate. The mixture has an indefinite shelf life if stored properly; candles stored for 20 years have shown no decrease in oxygen output. The oxygen is released by thermal decomposition. The heat is supplied by the burning iron. The candle has to be wrapped in thermal insulation to maintain the reaction temperature and to protect surrounding equipment.
Potassium and lithium chlorate, and sodium, potassium and lithium perchlorates can also be used in oxygen candles.
An explosion caused by one of these candles led to the deaths of two Royal Navy sailors on HMS Tireless, a nuclear-powered submarine, under the Arctic on March 21, 2007. The candle had become contaminated with hydraulic oil which caused the mixture to explode rather than just burn. [3]
[edit] Solid oxygen generator from Mir
The TGK generator contains a replaceable cartridge, a thin walled steel tube with a three-part block of oxygen-releasing mixture based on lithium perchlorate. Two parts are tablets of the chemical mixture and the third one is the igniter tablet with a flash igniter. The igniter is struck by a firing pin when the device is activated. One cartridge releases 600 litres (160 US gal) of oxygen and burns for 5–20 minutes at 450–500 °C (842–932 °F)[4] The oxygen is cooled and filtered from dust and odors, and released into the space station atmosphere.
On 23 February 1997, during the exchange of an air filter, a failed chemical oxygen generator spewed a torch-like jet of a molten metal and sparks across one of the Mir space station modules, burning for 14 minutes and blocking the escape route to one of the Soyuz spacecraft. The accident was caused by a leak of the lithium perchlorate from one of the canisters.
[edit] PSA Oxygen Generators
Recent advances in technology have seen a new type of industrial Oxygen Generator system. PSA or Pressure Swing Absorption incorporates a material called molecular sieve for gas separation. In the case of oxygen generation a zeolite based sieve forces preferential adsorption for nitrogen. Clean dry air is passed through the sieve beds on the oxygen generator, producing an oxygen enriched gas. PSA is a popular method of extracting oxygen from the air and being used more and more for industrial and medical purposes. The technology is such that appliances of any size can be developed and uses include; Hospitals, Vets, Glass Blowing, Aquaculture and Ozone Generation.
Manufactures include OGSIUK and Shenzhen Sibo Industria
[edit] Uses
Chemical oxygen generators are used in aircraft, breathing apparatus for firefighters and mine rescue crews, submarines, and everywhere a compact emergency oxygen generator with long shelf life is needed. They usually contain a device for absorption of carbon dioxide, often a filter filled with lithium hydroxide; a kilogram of LiOH absorbs about half a kilogram of CO2.
Self-Contained Oxygen Generators (SCOGs) are used in submarines.
Self-contained self-rescue devices (SCSRs) are used to facilitate escape from mines.
On the International Space Station, chemical oxygen generators are used. Each canister can produce enough oxygen for one crewmember for one day.
[edit] References
- ^ Yunchang Zhang, Girish Kshirsagar, and James C. Cannon (1993). "Functions of Barium Peroxide in Sodium Chlorate Chemical Oxygen". Ind. Eng. Chem. Res. 32 (5): 966–969. doi:.
- ^ William H. Schechter, R. R. Miller, Robert M. Bovard, C. B. Jackson, and John R. Pappenheimer (1950). "Chlorate Candles as a Source of Oxygen". Industrial & Engineering Chemistry 42 (11): 2348–2353;. doi:.
- ^ 'Oxygen candle' caused explosion
- ^ Oxygen Generators
