High-surface-area aluminum structured packings are finding a wide use in the cryogenic distillation of air. An experimental program was performed to determine the oxygen compatibility of commercial packings. In particular, the influence of pressure increase up to 0.6 MPa (6 bar absolute) and the effect of the replacement of nitrogen by argon as O2-diluting gas were investigated. Additionally, the impact of reducing the sheet thickness from 0.2 mm to 0.1 mm was tested.
The packing samples weighing 120–250 g were ignited on top by a 3 g thermite pill, resulting in a combustion channel which was either contained within the sample or passed through it. Incidents causing a noticeable downward widening of the channels were evaluated as “promoted combustion.” Typically, a promoted combustion occurred when the weight loss of corrugated sheet exceeded 10%.
The increase of pressure reduces the O2-threshold concentration for propagated combustion, as expected. Reducing the thickness of the sheets from 0.2 mm to 0.1 mm affects the O2-threshold concentration only slightly. A replacement of N2 by Ar as O2-diluting gas at 0.6 MPa shifts the O2-threshold somewhat beyond accuracy, but the extent of combustion in O2/N2-mixtures is much more substantial than in O2/Ar-mixtures. Thus a complete destruction of the Al-samples is reached in O2/N2-mixtures at much lower O2-concentrations.