Torrefaction
Torrefaction also torrefication (from latin " torrere " = roasting, dörren ) refers to the thermal treatment of biomass without access of air, resulting in pyrolytic decomposition and drying results. The process is carried out at 250 ° C to 300 ° C, a relatively low temperature for pyrolysis. The aim, similar to coking , is to increase the mass and volume-related energy density and thus the calorific value of the raw material, to increase the transportability or to reduce the effort involved in subsequent grinding of biomass.
Implementation and product
In the process, which takes around 15 to 120 minutes, biomass , mostly wood , is first pre-dried and heated, then a partial pyrolytic decomposition takes place with the release of water, carbon dioxide , carbon monoxide and organic acids .
Through torrefaction, a stable water content of only 3% is achieved, the mass is reduced by around 30%, while the energy content only decreases by around 10% and smoke- producing substances (i.e. substances that would rather incompletely burn to soot ) are removed. The calorific value of the black, crumbly product is 19.9 to 22.7 MJ / kg (green, water-containing wood has 10.5-17.7 MJ / kg). The energy that is "gained" by increasing the calorific value is required to evaporate the water contained in the process. The product obtained can easily be pressed into pellets or further crushed.
commitment
The process is used for biogenic solid fuels , but also as a method for the production of weather-resistant, thermally modified wood for construction purposes. The pellets obtained through torrefication are also an ideal additional fuel for power plants with pulverized coal combustion or for boilers that do not use the condensation heat (= latent heat ) of the vaporous substances contained in the exhaust gas, which are therefore not condensing boilers .
literature
- Martin Kaltschmitt , Hans Hartmann, Hermann Hofbauer (Hrsg.): Energy from biomass. Basics, techniques and procedures. 2nd Edition. Springer, Berlin 2009, ISBN 978-3-540-85094-6 .
- James R. Arcate: Torrefied Wood, on Enhanced Wood Fuel. Lecture at Bioenergy 2002 in Boise , Idaho / USA, 22. – 26. September 2002.
- PCA Bergman et al .: Torrefaction for biomass co-firing in existing coal-fired power stations. (PDF; 1.8 MB), ECN, Utrecht 2005.
- Andreas Ohliger: Experimental and theoretical investigation of the torrefaction of beech wood (PDF; 35.4 MB), dissertation, RWTH Aachen, 2015.
Individual evidence
- ↑ M. Kaltschmitt, H. Hartmann, H. Hofbauer (Eds.): Energy from biomass. Basics, techniques and procedures. 2nd Edition. Springer, Berlin 2009, ISBN 978-3-540-85094-6 , p. 708.