Understanding dust explosions. The role of powder science and technology

Abstract

Dust explosions in the process industries practically always start inside process equipment such as mills, dryers, mixers, classifiers, conveyors, and storage silos and hoppers. For any given dust type the ease with which dust clouds ignite and the rates with which they burn, vary considerably with factors well known in powder science and technology. The key factors include the primary particle size distribution of the dust, the degree of de-agglomeration of the dust particles in the cloud, the dust concentration distribution in the cloud, and the cloud turbulence. The last three factors are entirely dependent on the actual process situation in which the dust cloud is generated and sustained. The paper first discusses influences of these factors on the ignition sensitivity and explosion violence of dust clouds. Secondly, the concept of inherently safer process design to prevent accidental dust explosions is discussed, using design of hoppers and silos as an example. Then some consequences of the mentioned factors in design of mitigatory measures such as explosion isolation, explosion venting, and automatic explosion suppression, are discussed. The role of powder science and technology in understanding development and propagation of secondary dust explosions is also considered.