Page 14 - Dust Explosions in the Process Industries

Contents xi

5 Ignition of Dust Clouds and Dust Deposits: Further Consideration
of Some SelectedAspects 385
5.1 What is ignition? 385
5.2 Self-heating and self-ignition in powder deposits 388
5.2.1 Overviews 388
5.2.2 Some experimental investigations 389
5.2.3 Further theoretical work 397
5.2.4 Applications to different powder/dust types: a brief
literature survey 401
5.3 Ignition of dust clouds by electric spark dischargesbetween
two metal electrodes 404
5.3.1 Historical background 404
5.3.2 The ohmic resistance of a spark channel between
two metal electrodes 404
5.3.3 Influence of spark discharge duration on the minimum
electric spark ignition energy for dust clouds 407
5.3.4 Influence of some further parameters on the minimum
ignition energy of dust clouds 415
5.3.5 Theories of electric spark ignition of dust clouds 414
5.4 Ignition of dust clouds by heat from mechanical rubbing,
grinding, or impact between solid bodies 419
5.4.1 Background 419
5.4.2 Sparks and hot-spots from rubbing, grinding,
and multiple impacts 420
5.4.3 Sparks, hot spots, and flashes from single accidental impacts 421
5.5 Ignition of dust clouds by hot surfaces 423
5.5.1 Experimental study of the influence of size of the hot surface 423
5.5.2 Theories for predicting the minimum ignition temperatures
of dust clouds 424

6 Sizing of Dust Explosion Vents in the Process Industries:
Further Consideration of Some Important Aspects 431
6.1 Some vent sizing methods used in Europe and the United States 431
6.1.1 Vent ratio method 431
6.1.2 “Nomograph’method 431
6.1.3 The Swedish method 433
6.1.4 The Norwegian method (modified Donat method) 434
6.1.5 The Radandt scaling law for vented silo explosions 434
6.1.6 Other vent sizing methods 434
6.2 Comparison of data from recent realistic full-scale vented
dust explosion experiments with predictions by various
vent sizing methods 435
6.2.1 Experiments in large silos of LID I4 435
6.2.2 Experiments in slender silos of LID = 6 438
6.2.3 Pneumatic pipeline injection experiments in vessels
of small LID 443