Explosion characteristics of pulverised torrefied and raw Norway spruce (Picea abies) and Southern pine (Pinus palustris) in comparison to bituminous coal

Pre-treatments, such as torrefaction, can improve biomass fuels properties. Dedicated and coal co-firing plants, in which pulverised biomass and torrefied biomass can be used, are exposed to explosion hazards during handling, storage and transport from the mills to the boiler. Data on the explosion characteristics of biomass and torrefied biomass are scarce. This study presents explosion characteristics (maximum explosion pressure, deflagration index and minimum explosible concentration) of two torrefied wood samples and compares their reactivity to that of their corresponding untreated biomass materials and to a sample of Kellingley coal. Torrefied biomass samples showed higher reactivity, overpressures were around 9bar (0.9MPa, 1bar=10⁵Pa) for all biomass samples irrespective of size or sample composition. Derived laminar burning velocities ranged between 0.1-0.12ms^-1, and were therefore similar to that of coal (0.12ms^-1). The differences in explosion reactivity influence the design of explosion protection measures and can be used to introduce suitable modifications for safe operations with torrefied biomass.