CUED Publications database

Igniter-induced hybrids in the 20-l sphere

Taveau, JR and Going, JE and Hochgreb, S and Lemkowitz, SM and Roekaerts, DJEM (2017) Igniter-induced hybrids in the 20-l sphere. Journal of Loss Prevention in the Process Industries, 49. pp. 348-356. ISSN 0950-4230

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Abstract

Dust explosibility is traditionally described by two parameters, namely the maximum explosion pressure, P$_{max}$, and the deflagration index, K$_{St}$, usually determined through testing in a closed, pressure-resistant spherical vessel, either 20 L or 1 m$^{3}$ in volume. These parameters constitute key variables in the design of explosion protection systems, such as venting, suppression or isolation systems. The potential for overdriving dust combustion with pyrotechnical igniters in the 20-l sphere has been recognized, discussed and analyzed for many years, notably in the determination of the minimum explosible and limiting oxygen concentrations, which has led to specific guidelines regarding the ignition source strength in ASTM standards. The current paper presents new experimental evidence that the energy provided by pyrotechnical igniters may, in some instances, physically alter the dust being tested in the 20-l sphere. K$_{St}$ values can be several times greater in the small vessel compared to those measured in the 1-m$^{3}$ chamber. Further visual evidence is provided to show that high energy ignition can produce a turbulent flame region, possibly consisting of a hybrid mixture of flammable gas (or vapor) and dust, which can propagate faster than the corresponding pure dust. The experiments suggest that K$_{St}$ values measured in the 20-l sphere may no longer be representative of a dust deflagration in a real process environment. We recommend additional tests in a 1-m$^{3}$ chamber when a dust exhibits a low flash point, or when it's K$_{St}$ is above 300 bar m/s in the 20-l sphere.

Item Type: Article
Uncontrolled Keywords: dust deflagration igniter 20-l sphere overdriving hybrid
Subjects: UNSPECIFIED
Divisions: Div A > Energy
Depositing User: Cron Job
Date Deposited: 17 Aug 2017 01:21
Last Modified: 19 Sep 2017 01:33
DOI: