Torrefied biomass is regarded as one of the most efficient biofuel manufacturing processes to produce the coal substitute known as torrified pellets. In the torrefaction process, biomass is processed at the temperature of 250-350°C in the absence of oxygen atmosphere, decomposing the Biomass components, preserving energy content so that the energy density of the torrefied biomass becomes in pellet or briquette form which is much higher than other solid biomasses in trade.

The properties of the final product depend on the torrefication process and on the kind of feedstock are used. Depending on factors such as time, temperature and residence time, the biomass can be torrefied to different torrefaction degrees/temperatures. Directly connected to the degree of torrefaction is the net calorific value (NCV) of the resulting product. Theoretically, NCVs of 28 + MJ/kg could be reached, even though the overall process efficiency seems to be best at 20-22 MJ/kg NCV (depending on feedstock).

Properties of transportable biomass and competing fuel

  Fresh Wood Wood Pellets Torrefied Pellets Coal
 
Moisture (%) 35-50 7-10 1-5 10-15
Calorific Value (GJ/T) 9-12 16-18 19-23 23-28
Bulk Density (T/m3) .2-.25 .6-.68 .65-.75 .8-.85
Energy Density (GJ/m3) 2-3 9.6-12.2 12.4-17.3 18.4-23.8
Ash (% by wt) 0.4-2 0.4-2.5 9.7-20.2
Grindability Poor Poor Good Good

Benefits:

  • Improved combustion properties (Energy content and heating content)
  • No biodegradation of the product when stored.
  • Increased energy density, significantly low transport cost.
  • Increased grindability, hence requires less energy during processing.
  • Reduced Co2 emissions.