Anthracite dust explosion specificities in 20 L chamber

Introduction. The “overdrive” effect is well known, when dust/air mixture, explosive during testing in a 20 L chamber, turns out to be safe according to the results of more reliable testing in a 1-m3 chamber. The overestimation of the dust explosion hazard in the 20 L chamber is explained by the preheating of the fresh dust/air mixture with the flame of an energy-intensive (Eig) ignition source. The possibility of “overdrive” is judged by the following basis: at Eig = 10 kJ, the explosion index Kst < 4.5 MPa∙m/s (Proust et al., 2007). This paper is devoted to the identification of additional signs of “overdrive” in the 20 L chamber using the example of non-explosive anthracite to reduce the probability of the above-mentioned qualitative error.

Analysis of publications. The random nature of anthracite explosiveness over a wide range of dust concentrations at Eig = 5 kJ was observed (Cashdollar, Chatrathi, 1993). Two inflection points on the ascending branch of the dependence of the anthracite explosion pressure P on time t are observed, corresponding first to the minimum and then to the maximum dP/dt, respectively. All these features may be signs of “overdrive” after experimental testing.

Anthracite and its research method. Anthracite with the volatile content of 2.7 % wt. was studied in a 20 L. Siwek chamber, Eig = 10 kJ, with video recording of radiation through an observation window.

Results. Time dependences of the medium radiation intensity and the pressure in the chamber on time in the range of dust concentrations from 125 to 750 g/m3 are obtained.

Discussion and conclusions. Three additional signs of the “overdrive” effect for anthracite were confirmed experi­mentally and proposed: probabilistic nature of the explosion hazard; two inflection points on the ascending branch of the graph P(t); noticeable weakening of the medium radiation after the ignition source burnout and before reaching the lower inflection point. The explosion pressure exceeded 400 kPa and was mainly caused by the burning of fixed carbon.

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