Comparison of Explosion Characteristics of Torrefied and Raw Biomass

Biomass is one of the most attractive and versatile sources of renewable energy. However, biomass properties such as high moisture and volatile matter, low energy density and poor grindability affect the overall efficiency of traditional combustion processes, fuel supply chains, storage, handling, by­product management, etc. Pre­treatments, such as torrefaction, can upgrade some of such properties. Dedicated and coal co­firing plants, in which pulverised biomass and torrefied biomass can be used, are exposed to explosion hazards during handling, storage and transport from the millers 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 9 bar (0.9 MPa, 1bar=105 Pa) for all biomass samples irrespective of size or sample composition. Derived laminar burning velocities ranged between 0.1­0.12 ms­1, and were much higher than for coal (0.04 ms­1). These differences influence the design of explosion protection measures and can be used to introduce suitable modifications for safe operations with torrefied biomass.