Most air separation plants 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 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. One of these programs, involving flammability experiments with 3 kg to 13 kg miniature BAHX samples, was presented in an earlier ASTM publication, STP 1319. This is a companion to that study and the experimental work actually preceded the work reported in STP 1319.
In this experimental program, over 60 separate tests were conducted on 200 g – 400 g BAHX block samples in gaseous and liquid oxygen. Oxygen purities ranged from 86.90% to 99.96%. Test pressures ranged from atmospheric to 7858 kPa. Nichrome-hydrocarbon and several different reactive metal promoters were utilized. The purity of the liquid oxygen was found to affect the pressure threshold above which a violent energy release (VER) occurred. Data cited from the program form a part of the technical basis for a Compressed Gas Association pamphlet entitled: “Safe Use of BAHXs for Producing Pressurized Oxygen”.