SYMPOSIA PAPER Published: 01 January 1997

Flammability Tests of Miniature Brazed Aluminum Heat Exchangers in Liquid Oxygen


Most air separation plants currently in use employ compressors to increase oxygen pressure for customer usage. An alternative approach is to extract liquid oxygen from the separation column which is pumped to higher pressure and then boiled in a heat exchanger to directly provide an elevated pressure gaseous oxygen product. Brazed aluminum heat exchangers (BAHX) are normally utilized as the product oxygen vaporizers. The process results in substantial contact between high pressure liquid oxygen and aluminum material. The increased use of BAHXs to produce pressurized oxygen as an alternative to the use of oxygen compressors led to a series of experimental programs pertinent to the safe use of BAHXs for boiling oxygen at elevated pressures.

In the 1993 to 1995 period, 29 individual flammability experiments were conducted with 3 kg or 13 kg miniature headered BAHX samples. In the oxygen passages, commercial purity liquid oxygen was used at pressures ranging from 170 kPa to 6,996 kPa. Alternate passages contained air, nitrogen or oxygen at pressures ranging from 108 kPa to 10,443 kPa. Nichrome wire was used to ignite hydrocarbons placed within an oxygen passage to simulate a promoted ignition event.

The experiments provided insights into the combustion inhibition mechanisms in BAHXs used for producing pressurized oxygen. Data cited form a part of the technical basis for a Compressed Gas Association pamphlet entitled: “Safe Use of Brazed Aluminum Heat Exchangers for Producing Pressurized Oxygen”.

Author Information

Zawierucha, R
Materials Engineering Laboratory, Praxair Inc., Tonawanda, NY
Million, JF
Materials Engineering Laboratory, Praxair Inc., Tonawanda, NY
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Developed by Committee: G04
Pages: 297–316
DOI: 10.1520/STP12061S
ISBN-EB: 978-0-8031-5372-1
ISBN-13: 978-0-8031-2401-1