Torrefied Wood - Green Coal
Woody biomass consists of hemicellulose , cellulose, lignins and extractants
(chemicals absorbed during the growing cycle through air and dirt, generally <3%). During torrefaction the molecular structure of the wood is altered, enhancing some of the wood’s physical properties.
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Torrefaction liberates water and releases volatile organic compounds (VOC) through the devolitization of primarily the hemicelluloses and extractants. The lignins are loosened and have limited devolitization while the cellulose is nearly unimpacted at these temperatures. As the hemicellulose, which binds the cellulose, is burned away, the wood is unbound making it more brittle. This increases the grindability of torrefied wood and makes its handling properties more like coal. This unbinding also releases the last of the water not stored at the cell level, leaving the wood hydrophobic. This new nature allows the product to be stored outdoors without concern for exposure to water.
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During the torrefaction process most of the energy value of the wood is preserved with the product losing 20-30% of its mass while retaining 90% of its energy. The calorific value of the wood increases to 9,500-11,500 Btu per pound.
