The development of an experimental method for the determination of the minimum explosible concentration of biomass powders

Biomass powders, in both raw and thermally treated (torrefied) form, are used in 100% biomass fired or in coal co-fired plants for power generation. They pose significant fire and explosion risks during storage, handling, processing and combustion, and therefore their explosibility characteristics need to be assessed for the design of safe systems and operations. Wood biomass powders are difficult to characterise for explosibility through standard methods because of their bulky and fibrous nature. This has resulted in the lack of reliable data on the explosibility of these materials. In this study we present a new methodology - with example measurements - for the determination of the minimum explosible concentrations (MECs) of raw and torrefied wood biomass powders, using a modified Hartmann tube. This equipment can also be used as a fast screening tool for the determination of other reactivity parameters, such as flame speeds and rates of pressure rise, through which the most reactive mixture can be identified for more detailed measurements in the larger ISO 1 m3 vessel. MEC measurements reported in this paper showed that both raw and torrefied pulverised wood biomass, were explosible at equivalence ratios as low as 0.2. This was one-third (1/3) the corresponding concentration for Kellingley coal (measured with the same method). Flame speeds 5-10 times higher than those of coal were measured for biomass. Flame speed differences will also have a direct effect on burner performance and flame stability for systems originally designed to burn coal and now firing biomass without modifications.