Torrefaction- A Warmer Solution to a Colder Climate
By R.H.N Columnist Robin Johnson
Torrefactionof biomass, e.g. wood can be described as a mild form of pyrolysis at temperatures typically ranging between 200 to 320°C. During torrefaction the biomass properties are changed to obtain a much better fuel quality for combustion and gasification applications. Torrefaction leads to a dry product with no biological activity like rotting.
Biomass can sometimes be an important energy source to create a more sustainable society. However, nature provides a large diversity of biomass with varying characteristics. In order to create highly efficient biomass-to-energy chains, torrefaction of biomass in combination with densification, is a promising step to overcome logistic economics in large scale sustainable energy solutions, i.e. make it easier to transport and store it. Pellets or briquets are lighter, drier and stable in storage as opposed to the biomass they are made of.
The Scientific Process
Torrefaction is a thermochemical treatment of biomass at 200 to 320°C. It is carried out under atmospheric pressure and in the absence oxygen, i.e. with no air. During the torrefaction process, the water contained in the biomass as well as superfluous volatiles are removed, and the biopolymers (Like cellulose) partly decompose giving off various types of volatiles. The final product is the remaining solid, dry, blackened material which is referred to as “torrefied biomass” or “bio-coal”.
During the process, the biomass loses typically 20% of its mass (dry bone basis), while only 10% of the energy content in the biomass is lost. This energy (the volatiles) can be used as a heating fuel for the torrefaction process. After the biomass is torrefied it can be densified, usually into briquettes or pellets using conventional densification equipment, to further increase the density of the material and to improve its hydrophobic properties. This means that the final product repels water and thus can be stored in moist air or rain as opposed to the original biomass it is made of.
With relation to brewing and food products, torrefaction occurs when a cereal (barley, maize, oats, wheat, etc.) is cooked at high temperature to gelatinize the starchendosperm creating the expansion of the grain and creating a puffed appearance. The cereal can then be used whole or flaked. In brewing, the use of small quantities of torrefied wheat or barley in the mashing process aids in head retention and cling to the glass. Additionally, torrefied cereals are generally less expensive than equal amounts of malted products. An example of this can be found in all superstores in the form of say Sugar Puffs.
The history of torrefaction goes back to the beginning of the 19th century, and it was also used on a large scale during the Second World War.
Torrefaction is indeed a complex process, but it appears to have a simple outcome that can solve a lot of the Worlds Energy Problems. Providing an income for impoverished farmers in developing countries of the world and producing an efficient substance to create biomass, which as everyone knows will provide a sustainable, easily combustible and more environmentally friendly (not producing a large proportion of greenhouse gases). However Farmers who cannot afford to pay their bills signing up to this issue of torrefaction, rendering their farm products up for the process, will in fact surrender their crops and whilst the money may still be there, will the crops be there as food? A new and complex process whereby the useless farm products are used instead of the useful nutritional parts, which can lead the way to a brighter more sustainable future in energy production.