Promoted Ignition-Combustion Tests of Brazed Aluminum Heat Exchanger Samples in Cold Supercritical Oxygen

Abstract

A common practice in the industrial gas industry is to produce product oxygen by boiling pressurized liquid oxygen in a heat exchanger. Multistream brazed aluminum heat exchangers (BAHX) typically are used as oxygen product vaporizers. This method inherently exposes liquid and gaseous oxygen to aluminum material. Customer demands continue to increase the product oxygen pressure requirements, and it is recognized that higher pressures could increase the severity of an aluminum/oxygen combustion event. A series of experimental programs were conducted from 1993 to 1995 to evaluate the safe use of BAHX for boiling oxygen at elevated pressures to 6,996 kPa. The present experimental study is a companion test program that was conducted from 2010 to 2012 to evaluate BAHX promoted combustion response in cold supercritical oxygen to 15,602 kPa. Promoted combustion experiments were conducted with miniature headered BAHX samples. Two types of samples were tested. The first were approximately 3.3 kg, having a thinner parting sheet thickness, and the second approximately 3.9 kg, having thicker parting sheets. The oxygen passages contained commercial purity cold supercritical oxygen having a pressure ranging from 10,197 to 15,603 kPa and the adjacent passages contained cold supercritical air (“inert” fluid) at pressures ranging from 10,440 to 15,170 kPa. Tests were conducted with the air passage pressure both higher and lower than the oxygen passage pressure. Nichrome wire was used to ignite a hydrocarbon promoter located within an oxygen passage, simulating a promoted ignition-combustion event. The experiments provided insights into the combustion mitigation behavior of BAHX used for producing high-pressure product oxygen via pumped liquid oxygen (LOX) gasification. Data are applicable in supporting the safe use of BAHX for high-pressure oxygen service.