Effect of dust dispersion on particle breakage and size distribution in the minimum ignition energy apparatus
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2017 Elsevier Ltd For dust explosion studies, some of the standard parameters are the maximum overpressure (Pmax) and deflagration index (Kst). These parameters are typically measured with a 20-L dust explosion apparatus in accordance with ASTM standard (ASTM E 1226). Another important parameter is the minimum ignition energy (MIE), which is found using the MIKE3 MIE apparatus, according to the ASTM E2019-03 (2013) standard. Recent studies have shown that the dispersion system for the required dust cloud formation in the standard 20-L apparatus induces significant mechanical shear, resulting in breakage of dust particles. Therefore, the explosion parameters obtained (Pmax and Kst) are not representative of the original dust size distribution prior to testing. In this work, the influence of dust dispersion on particle size distribution and particle breakage in a standard minimum ignition energy apparatus (Khner MIKE3) is presented and compared to a 36-L dust explosion apparatus. The 36-L dust explosion apparatus was developed at the Mary Kay O'Connor Process Safety Center, Texas A&M University to give similar Pmax, Kst results to that of a standard 20-L apparatus. Previous work has shown that similar particle breakage occurs in 36-L and 20-L apparatus. Anthraquinone, Ascorbic Acid, and Acetaminophen (Paracetamol) were used to achieve the goals of the current study. The results show particle breakage due to dispersion does not occur in the MIKE3 MIE apparatus. However, a minor portion of smaller particles can escape the Hartmann tube through the top lid, stick to the Hartmann tube and become trapped in the crevasses around and under the electrode. Additionally, it was found that for electrostatic materials such as Acetaminophen, the particle size distribution shifts significantly as the particles stick to the Hartmann tube. Thus, these particles are not part of the dust cloud, which can lead to erroneous minimum ignition energy results.
