Wood torrefaction: Pilot tests and utilisation prospects

The research project "Torrefaction of woody biomasses as energy carriers for the European markets" was carried out within the Tekes BioRefine programme in 2010-2012 and was coordinated by VTT. The main objective of the project was to create a discussion platform and collate basic information for the Finnish industrial stakeholders involved in developing torrefaction technology or planning to include torrefied biomass in their fuel supply for energy production. Given the availability of torrefaction pilot facilities in Europe, it was decided at an early phase of the national torrefaction research project not to build and operate separate pilot equipment and thus save time and money. Experimental research was conducted in cooperation with ECN, the Netherlands. Finnish wood chips and crushed forest residue were tested at different torrefaction temperatures in the PATRIG torrefaction test rig with great success, and large quantities of torrefied wood chips and pellets were produced. CFD simulation work was carried out at VTT to investigate the feasibility of tor-refied fuels to replace some of the coal. From the combustion point of view, it seems feasible to replace coal with torrefied wood biomass with shares of up to 50% by weight. Basic small-scale experiments were carried out to compare torrefied wood pellets with conventional wood and straw pellets with regard to their handling and storage properties. The experiments showed that the torrefied pellets are clearly more hydrophobic than wood and straw pellets and do not disintegrate completely on exposure to water. A study on dust explosion and self-ignition characteristics indicated that the torrefied dust does not differ significantly from normal biomass dust, but is clearly more reactive than coal dust. Commercial development of torrefaction is currently in its early phase. The current general view is that most of the demonstration plants have technical problems which have delayed their commercial operation. The market is expected to move forward but the available public information is very limited, especially with regard to the technologies used and volumes produced. Woody feedstocks will be the main raw material source. The utilisation rate of forest industry residues and by-products is relatively high in the EU and the wood supply in Central Europe remains more or less stable, hence the price of the raw material is at a fairly high level. The utilities' capability to pay for the product depends mainly on the national feed-in tariffs of green electricity. The energy price for the user is at least twice as high as that of coal.