The concentration limits for coal dust-air mixtures for upward propagation of flame in a vertical tube

Abstract

The upper and lower limits of concentration for upward propagation of flame in a vertical tube are given on a probability basis for coal dust-air mixtures. The 0·5 probability value of the lower limit varied from 0·23 to 0·31 g/l. and the upper limit varied from 2·07 to 1·02 g/l.; the actual value depending on the definition of propagation used. The standard errors are given and are all less than ten per cent of the limit values. The merits of this particular method of defining limits are discussed and compared with those of other methods. The apparatus consists of a vertical Perspex tube of 14·2 cm internal diameter and 4·68 m in length, with a vibrating hopper at the upper end which feeds dust into the tube at predetermined uniform rates. The dust, a silkstone coal dust ground to give a nominal 85 per cent through B.S.S.240, is ignited at the open lower end of the tube by means of a small methane flame and the coal dust-air flame propagates upwards towards the closed end.