TORREFACTION – REINVENTING WOOD FUEL

Torrefied fuel compared to traditional wood fuel

Torrefaction is a very efficient process of slow-roasting biomass, in an atmosphere with zero oxygen concentrations, to remove all moisture and low energy volatiles to create a combustible product with an increased energy density.

Torrefied wood is completely desiccated biomass, with devolatilised hemicellulose, which has not yet reached the point of ‘char’. That is to say – that pyrolysis, in any form, has not yet commenced. When the critical surface moisture content of the particle is reached, the evaporation is assumed to take place inside the particle in the moving front between dry and moist regions. In the next stage the surface temperature of the particle never exceeds the pyrolysis temperature. In this case, it means that the drying isotherm reaches the centre of the particle and vanishes before the pyrolysis isotherm appears at the particle surface. In the above context - the drying isotherm is meant to be the torrefaction temperature (from surface to core) that initiates and completes the devolatilisation of hemicellulose.” (2)