(301f) Improved Combustible Dust Minimum Ignition Energy (MIE) Test Method and Prediction Using CFD Simulation

Dust explosions continue to be a persistent problem in the process industries due to recurring incidents. The combustible dust Minimum Ignition Energy (MIE) is an important dust hazard parameter that guides the elimination of possible ignition sources in solids handling facilities. Partial inerting is an important but underutilized mitigation technique in which the dust cloud MIE is increased through inerting, reducing the risk of an accidental explosion or more accurately, a dust deflagration. The MIKE3 is the predominant apparatus for combustible dust MIE measurement worldwide. The current version of the MIKE3 device is not specifically designed to measure partial inerting MIE accurately. Therefore, a primary objective of this work is to demonstrate that a properly designed add-on device and technique can accurately produce partial inerting MIE results with the MIKE3 or any other similar device. In the process industries, combustible dust MIE prediction could result in considerable time and cost savings during process development. The existing MIE prediction models for dusts are known to deviate significantly from experimental findings. Current MIE-O₂ prediction models in literature consider critical equation terms to be a constant.^1,2 This study demonstrates these critical terms are not a constant, but are linked to the type of combustible dust.

The add-on device developed in this work ensures complete purging of the MIE apparatus with the desired gas concentration before experimentation. The same gas is then used to make the dust cloud dispersions for ignition testing. This approach results in a very uniform gas concentration which is essential for producing proper measurements. Therefore, an important finding of this work is that purging before partial inerting MIE testing results in a proper characterization of the relationship between the MIE and oxygen for the dust. This work has also explored the influence of purge time on partial inerting MIE measurements. Oxygen sensor measurements were used to determine the purge time required to achieve the desired composition. It was observed that the apparatus should be purged for > 40 seconds. Additionally, an ANSYS Fluent CFD model was developed that supports the experimentally determined purge time. The CFD model also revealed ways to further improve the initial add-on device. These findings demonstrate the need to amend existing or develop new standards for this type of dust testing.

The performance of the add-on device and validity of the techniques are demonstrated through the experimental determination of partial inerting curves for Niacin (CaRo15), Anthraquinone, Lycopodium clavatum and Calcium Stearate using the MIKE3 apparatus. A mathematical model for the MIE-O₂ relationship was proposed and compared with the existing models in literature. The proposed model led to more accurate prediction of the MIE-O₂ experimental relationship. Therefore, through both experimentation and modeling, this study aimed at providing a scientific foundation for a partial inerting MIE test method to supplement existing testing standards such as ASTM E2019-03.