Studies in coal dust explosions: Influence of additives on extingtion of high intensity coal dust flames

Abstract

The effects of 9 additives on the extinction limits of coal dust flames have been studied in a 200 c.c. jet-mix stirred reactor, and the behavior of 6 of the 9 have been shown to be described by a common equation based on thermal loading, incorporating chemical decomposition of the additives where this is approprioate. The remaining 3 are presumed to be acting as chemical reaction inhibitors, in agreement with other studies. The additives were: N 2 , He, CO 2 , fly ash, limestone (rock dust), MgSO 4 .7H 2 O (Epsom salts), KHOCO 3 (Purple-K), NaCl (TVBCD-1)., and NH 4 H 2 PO 2 (ABC). The last three are commercial fire retardants: they are all presumed to be acting as chemical inhibitors (chain terminators), but our results support the presumption only for the last two, and also for the Epsom salts. Curves of: additie percent to suppress the flame; and temperature at extinction; were obtained as a function of stoichiometry and plotted as closed extinction loops. Extinction temperatures were found to be substantially independent of the type of additive, a result not previously reported, with essentially constant values of about 900C for >1, and declining withfor 4 Conditions in the reactor are known to be comparable to those at the head of a coal dust explosion flame 1 so that extension of these results and the extinction analysis to such flames should be valid.