Comparison of the explosion characteristics and flame speeds of pulverised coals and biomass in the ISO standard 1 m3 dust explosion equipment

Abstract

Pulverised coal has been known to pose explosion risks since the 19th century, with the advent of biomass use in coal fired power generation boilers the explosion risk may need revision. The objective of the present work was to compare the explosibility of two samples of bituminous coal used in UK power stations with two biomass fuels and to review available explosion data in the literature for pulverised coal and biomass. The 1m3 ISO explosion vessel was used to determine the explosion characteristics: deflagration index (KSt), maximum explosion pressure (Pmax) and minimum explosible concentration (MEC). Flame speeds were also measured and these are relevant to understanding the mechanism of turbulent flame propagation in power station burners, which is related to the problem of flame flashback or blow-off. Despite the similarities in composition of both coals, the explosion reactivity of Colombian coal was much higher, with a KSt value of 129barm/s compared to 78barm/s for Kellingley coal. The main difference between the two fuels was the surface area of particles which was higher for Colombian coal. It was shown that the char burn out rate at 900°C in air was higher for Colombian coal, due to the greater oxygen diffusion in the higher porosity of the char. Results for two biomass fuels are also presented with similar values for KSt and the literature review shows that both coal and biomass have very variable flame reactivities. There is no general trend that coal is less reactive than biomass, although this could be the case for specific coals and biomass.