Requirements for a Hybrid Dust-Gas-Standard: Influence of the Mixing Procedure on Safety Characteristics of Hybrid Mixtures

Abstract

While developing a standard for the determination of safety characteristics for hybrid mixtures the authors discovered, that, beside the ignition source, the mixing procedure is the main difference between the single-phase standards for dusts and gases. The preparation of hybrid mixtures containing a flammable gas and a flammable dust in the 20 L-sphere can be realized in different ways. Either the flammable gas is filled only in the sphere or only in the dust container or in both. In previous works, almost always the first method is applied, without giving any information on the accuracy of the gas mixtures. In this work the accuracy of the gas mixtures and the results of the tests applying two methods of mixing were studied. No significant influence of the mixing method itself on the safety characteristics explosion pressure pex and the normalized rate of pressure rise (K-value) was found. Obviously, homogenization of the gas mixtures can be obtained sufficiently by the turbulence that is caused during the injection from the dust container into the explosion chamber within a short time. However, the mixing procedure has a great influence on the accuracy of the gas amount of the mixtures obtained. Without modifying the 20 L-sphere by installing precise pressure sensors, assuring its tightness and performing gas analysis, it must be expected, that the accuracy of the gas mixtures is very low. This has a significant influence on the measured safety characteristics and may lead to unsafe facilities or unnecessary expensive safety measures.

Parameters Affecting the Explosion Characteristics of Hybrid Mixtures Arising from the Use of Alternative Energy Sources

“…Some facts from the now obsolete ISO 6184-3:1985 [31] were also used. For the measurement of explosion parameters for the problem of this paper, the methodology [32] published at the German BAM Institute To measure the explosion parameters of hybrid mixtures in the explosion chamber with a volume of 1.00 m 3 , the author of the paper compiled a methodology in [28]. This methodology characterizes the procedure for measuring the explosion parameters p max and (dp/dt) max of hybrid mixtures of flammable gas and combustible dust in an explosion chamber with a volume of 1.00 m 3 .…”