Combustion and Explosion Characteristics of Pulverised Wood, Valorized with Mild Pyrolysis in Pilot Scale Installation, Using the Modified ISO 1 m3 Dust Explosion Vessel

Biomass is a renewable energy source with great potential worldwide and in the European Union. However, valorization is necessary to turn many types of waste biomass into a tradable commodity that has the potential to replace coal in power plants without significant modifications to firing systems. Mild pyrolysis, also known as torrefaction, is a thermal valorization process of low-quality biomass that could be suitable for such a purpose. In this work, typical Spruce-Pine-Fir residues from a sawmill were tested in terms of the explosion and flame propagation properties. The ISO 1 m3 dust explosion vessel was used, with a modified and calibrated dust dispersion system that could cope with very coarse particles. The deflagration index, Kst, was higher for the torrefied sample, with a peak at 36 bar m/s compared with 27 for the raw biomass. The peak flame speeds were similar for both samples, reaching 1 m/s. The peak Pmax/Pi was between 7.3 and 7.4 bar for both untreated and torrefied biomass. The mechanism for coarse particle combustion is considered to be influenced by the explosion-induced wind blowing the finer fractions ahead of the flame, which burns first, subsequently devolatilizing the coarser fractions.