Classification of particle breakage due to dust dispersion
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2018 Elsevier B.V. Dust explosions are a major challenge in the area of process safety. Incidents occur on a frequent basis causing loss of life and property. Several standards such as ASTM, ISO etc. provide methods and procedures for explosion risk assessment by testing explosion parameters (Pmax and KSt) in the standard 20-L or 1-m3 apparatus. However, it is assumed that particle size distribution of the dispersed dust remains unaltered throughout the testing procedure. Recent studies have found that dust particle size distribution can significantly reduce upon dispersion in the standard 20-L and 36-L apparatus, which can affect the explosion parameters. The reduction in particle size distribution due to the dispersion process depends on the dust and explosion apparatus. Therefore, it is necessary to quantify the particle size reduction of different dusts due to dispersion in various explosion apparatuses (20-L, 36-L and 1-m3) and correlate it to the dust properties (brittleness index (hardness, fracture toughness) that influence particle breakage. This study aims to investigate post-dispersion particle size reduction in the 20-L, 36-L and 1-m3 dust explosion apparatus and classify dusts into particle breakage categories, with a range of brittleness index associated with each category. It will help the process industries identify dusts that are susceptible to breakage based on their brittleness index and prone to give misleading explosion results during dust explosion testing, permitting a proper dust explosion risk assessment. Ascorbic Acid, Acetaminophen (Paracetamol), Anthraquinone, Active Charcoal, Pittsburgh Pulverized Coal (PPC), Cornstarch, Lycopodium clavatum, and Polyethylene were used in this study. These materials were dispersed in the 20-L, 36-L and 1-m3 apparatus at a concentration of 500 g/m3 and post-dispersion samples were analyzed for particle size distribution changes. The mechanical properties (hardness and fracture toughness) of these materials were measured using Nanoindentation. The dispersion-induced change in size distribution was correlated to the measured mechanical properties of the dusts. Dispersion results show the 20-L and 36-L dust explosion apparatus cause significantly more particle breakage than the 1-m3 apparatus. Particle breakage is highest in Ascorbic Acid followed by Acetaminophen, Anthraquinone, Active Charcoal, and Pittsburgh Pulverized Coal, respectively. Cornstarch, Lycopodium clavatum and Polyethylene did not undergo particle size reduction due to dispersion. In addition, the 1-m3 apparatus caused particle breakage only in Ascorbic Acid, Acetaminophen and Anthraquinone. Nanoindentation results show Ascorbic Acid has the highest brittleness index value followed by Acetaminophen, Anthraquinone, Active Charcoal, and Pittsburgh Pulverized Coal, respectively. The brittleness index correlates directly to the particle breakage trend. Based on the results, Ascorbic Acid, Acetaminophen and Anthraquinone were classified into class I breakage category (high breakage). These materials are most susceptible to giving misleading explosion results because of altered particle size distributions. Active Charcoal and Pittsburgh Pulverized Coal were classified into class II breakage category (medium breakage), while Cornstarch, Lycopodium clavatum and Polyethylene were placed into class III breakage category (little or no breakage).
