Pretreatment of Biomass

Most common sources of biomass for energy purposes are wood and waste products. Such biomass is a porous and bulky material of low density and high moisture content and this makes it difficult and expensive to handle, transport and store. One way to upgrade the value of biomass and to use it more effectively is to treat it in an energy densification process involving pelletization and/or torrefaction.

Biomass pellets have several advantages compared to unprocessed biomass. The energy density is significantly increased on weight and/or volume basis, pellets are more homogeneous in shape and composition and standardization facilitates international trading of biomass. Low moisture content and the standardized sizes make bio-pellets an ideal fuel for heating systems varying from small scale stoves and boilers to full-scale power plant CHP.

Torrefaction is a heat treatment in the temperature range from excessive drying (200 °C) to mild pyrolysis (300 °C). Torrefaction of biomass increases the heating value on weight basis, renders the material less hydrophilic and more homogeneous and increases the grindability and reactivity.

Pelletization and torrefaction can be applied individually or in combination. All pre-treatment processes have benefits and drawbacks and a pre-treatment process should be designed to fit the specific biomass or bio-waste product and process chain.

Research goal and purpose

The research within pre-treatment of biomass covers fundamental understanding and characterization of various types of biomasses and processes as well as situation specific combinations and uses.

The research is often conducted in collaboration with industry e.g. DONG energy, Dansk Teknologisk Institut or Vattenfall and the overall aim of the research is an improved understanding, increased efficiency and better economy in the use of biomass for energy purposes. Present research involves:

  • Mechanical characterization of various biomasses and biomass residues – raw and pre-treated, involving grindability, durability, particle fluidization, humidification etc.
  • Chemical characterization of various biomasses and biomass residues – raw and pre-treated, involving composition, reactivity, evolved gas analysis etc.
  • Development of a biomass catalogue including an overview of characteristics of various raw and pre-treated materials
  • Test and evaluation of pre-treatment methods and processes in lab and pilot scale
  • Development of new or improved pre-treatment processes or process combinations in lab and pilot scale
  • Field trials with storability of pelletized and torrefied materials
  • Energy balance and process chain models involving bio-energy potential estimations