Experimental and thermodynamic study of aerosol explosions in a 36L apparatus
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2019 Elsevier Ltd Explosions involving vapor-liquid mixtures have a tragic history in the chemical industry. Numerous incidents such as the Buncefield explosion and the Flixborough disaster have demonstrated the importance of investigating the mechanism and consequence of aerosol explosions. ASTM D3065-01 presents two standard test methods, the flame projection and closed drum tests, for the flammability of aerosol products. The flame projection method involves the spraying of aerosol directly into an open flame to measure whether the aerosol can be ignited. The closed drum test requires the spraying of aerosol directly into a closed drum containing an open flame. The flame projection and closed drum tests in this ASTM standard, are not adopted widely due to the lack of quantification. Motivated by this consideration, this study proposes a test method to quantitatively investigate the flammable hazard and consequence assessment of aerosol explosions. The proposed method has the potential to surpass the existing go/no-go standard test method through an approach quantifying the aerosol hazard. The first stage of the procedure was to characterize the aerosol cloud properties, such as droplet size distribution and concentration. The second stage was to ignite the aerosol cloud in a closed vessel to measure the maximum explosion pressure (Pmax) and the explosibility characteristics (Ka). These parameters can be considered a thermodynamic and kinetic assessment of the explosion, respectively and are critical when designing a venting system. In this experimental study, Pmax and Ka were determined for a range of equivalence ratios for n-octane and n-dodecane. The experimental results were compared to a thermodynamic model, which estimates Pmax, revealing evaporation was the controlling step during the aerosol combustion process. A thin flame and three-zone model were investigated to model the rate of pressure rise during the aerosol explosion. In addition, this study of n-octane and n-dodecane has demonstrated that liquids can be ignited below their flashpoint when they are in aerosol form. It also shows that the aerosol lower flammable limits (LFL) are lower than the corresponding gas vapors.
