Toward a Novel Standard Vessel for Testing Dust Explosion

In chemical processes, a high number of accidents are imputable to explosions of flammable dust or dust-gas/vapor in air causing failure to equipment, injuries and damages to people and surrounding environment. Protection from accidental explosion coming from dust-air or dust-gas-air mixtures necessarily requires prevention and mitigation measures. Such measures are based on the knowledge of the main parameters that characterize the flammability and explosion features of both dust-air and dustgas-air mixtures. Measurement of the most important explosion and flammability parameters is performed according to standard procedures, in a standard explosion apparatus that consists of a closed steel combustion chamber with an internal volume of 20 l, spherical or cylindrical in shape. One of the major requirements of the apparatus is that it must be capable of dispersing a fairly uniform dust cloud in the vessel and of realizing a controlled turbulence level. Recent studies have shown that the standard procedure suffers from many issues. The main issue is the inability to control the turbulence level inside the sphere which varies in time, space and with the properties of the dust (Dahoe et al., 2001; Di Benedetto et al., 2013a; Hauert et al., 1994; Pu et al., 1990). Furthermore, it has been shown through CFD simulations that with the standard procedure/equipment it is not possible to generate a uniform dust-air cloud dispersion (Di Benedetto et al., 2013a; 2013b; Di Sarli et al., 2014). The third issue is that the method of dust injection in the sphere may cause severe particle fragmentation, thus changing the particle size distribution of the dust and altering its flammability and explosion features (Kalejaiye et al., 2010; Sanchirico et al., 2015). In this work, we show the effect of the method and equipment of testing on the values of the minimum explosive concentration (MEC). In particular, we show, through coupled CFD simulations and experiments, that the measurements according to the standard procedure in the standard equipment give MEC values significantly higher than the real values. All these results drive a novel equipment design for testing dust explosion.