Investigation of an air separation unit explosion

• Published in: Journal of loss prevention in the process industries 2001-05, Vol.14 (3), p.167-180
• Main Authors: van Hardeveld, R.M., Groeneveld, M.J., Lehman, J.-Y., Bull, D.C.
• Format: Article
• Language: English
• Subjects: Aerosols; Aluminium; Contamination; Explosion; Oxygen
• ISSN: 0950-4230
• DOI: 10.1016/S0950-4230(00)00045-0

This paper describes the investigation of the cause of a serious explosion in an air separation unit in Bintulu (Malaysia) on 25 December 1997. Since the cause of the explosion was not obvious, a large number of possible scenarios was generated, followed by a systematic process of elimination. Ultimately, conclusive evidence was obtained that combustible airborne particulates had passed the main purification section of the air separation unit. These combustible contaminants had accumulated on the aluminium main vaporisers of the distillation column. Once hydrocarbon combustion was triggered, it led to aluminium combustion which generated heat and vaporised the cryogenic liquids. This led to rapid pressure build up and explosive rupture of the distillation column. The exact ignition mechanism remains unclear, but a low activation energy chemical mechanism, involving radical reactions to provide the initiating trigger, has been proposed. However, by designing a purification system capable of efficiently removing aerosol material and other fouling contaminants, and by a proper design of the oxygen reboiler it is possible to design a plant that can be operated safely in an aerosol polluted environment. The analysis presented in this paper and the proposed solutions by the ASU vendors, Shell and independent experts were accepted by plant insurers and the shareholders of SMDS Malaysia, leading to a subsequent endorsement of the rebuild investment.