High-surface-area metallic structured packings are finding increasing use in the cryogenic distillation of air. An experimental program was performed to determine the oxygen compatibility of selected metals under the high-surface-area-to-volume ratios and adiabatic conditions encountered in commercial use.
Under some conditions brass packing unexpectedly had a higher relative flammability than aluminum, which is contrary to reported test results using metal rods and strips. This is due, we believe, to the specific geometric and adiabatic configuration of the packing material which appears to enhance the propagation of combustion in brass. Aluminum flammability in gaseous oxygen has been shown to be very dependent upon argon dilution and, in the presence of liquid oxygen, strong energy releases have been observed, similar to those experienced with aluminum powder and liquid oxygen. Copper was found to be nonpropagating in all tested oxygen purities.
These findings suggest that results from oxygen compatibility tests on rods and strips cannot be used reliably for ranking the suitability of materials in high-surface-area-to-volume ratio and adiabatic configurations.