Ignition and combustion of isolated and binary array of coal particles

A digital image processing technique is employed to investigate the ignition and combustion characteristics of isolated coal particles as well as the interactive combustion of a binary coal array in low Re flow. When an isolated coal particle is suddenly subjected to hot vitiated gases, the following sequence of events is observed: (i) primary heterogeneous ignition (HI) at the leading edge of the particle, (ii) ejection of volatiles as jets in the direction of the convective flow, (iii) secondary gas phase ignition of volatiles (SGI), and (iv) formation of wake flame due to combustion of volatiles with a black inner zone along with heterogeneous combustion of char. Also, for high volatile nonswelling bituminous coal (PSOC 1447, hvCb) intermittent volatiles ignition and combustion are observed to occur during the combustion process, for a few of the experiments. The experiments are then repeated for a binary array. A group flame is formed for the binary array at closer interparticle spacing. Intermittent ignition does not occur for the binary array of hvCb coal particles. Such a behavior persists even at larger inter-particle spacing, which suggests that radiation interaction between the particles might be occurring even though mass transfer interactions are absent. Flame characteristics and flame merging times are obtained for the binary coal particle array.