It is the end of January and the media are still talking about severe frosts plaguing the Czech Republic. In the interest of their comfort, households must turn the cap on the radiators and thus increase the consumption of thermal energy. This energy comes from several sources, including a group of renewable sources, which also includes dendromas. Under this term, we can imagine all the wood and woody parts of plants used for energy production, i.e. the logs that we put into the fireplace, as well as the logging residues processed into wood chips.
The study of a team of scientists from the Faculty of Forestry and Wood Sciences at the CULS deals with wood chips as a renewable energy source. In their work, they focus on the properties and potential use of wood chips made from black locust (Robinia pseudoacacia) wood originating from the reclaimed area around Varvažov.
Surface mining began in this area at the end of the 19th century and the landscape was restored in 1930. Reclaimed landfills are important mainly in landscape, ecological, hygienic, soil protection, water management and aesthetic function. Considerable attention is paid to biological significance by professional circles. However, we must not forget the production function, as one of the most suitable methods of reclamation is afforestation. The result is then a forest stand, which has the potential to be used as a renewable energy source.
Places such as dumps after the former mining of minerals are characterized by poor soils with a lack of water, and because locust is undemanding, it is one of the most sought-after trees for reclamation. In addition, its wood is characterized by a higher density, thanks to which it has a good calorific value. The study examined the specific properties of Robinia wood from the middle former lignite mining in order to determine whether the biomass from this tree is suitable for energy purposes. The following characteristics were determined: chip dimensions (parameters determine the combustion technology), ash content, bulk density, bark content and content of organic and inorganic elements. The basic elements determining the quality of dendromas include carbon, hydrogen, nitrogen, sulfur and oxygen, which together with the moisture of the chips affect the calorific value. The determined values ??of these properties were compared mainly with the standard ČSN EN 14961-1-2010, which defines and determines the quality of solid biofuels.
The results of the particle size analysis of locust chips originating from recultivated dumps show that this wood mass can be included in the category of coarse-grained energy wood chips according to the said standard. Humidity parameters (up to 50%), ash content (up to 3%) and a minimum calorific value of 8-10 MJ / kg are also in accordance with the standard. The values ??of the content of organic elements were in all cases close to the standard values; on the other hand, inorganic elements were found to a greater extent. According to the authors, the differences resulting from the comparison of the results with the data of other studies depend on specific forest stands and their soil conditions. The determined ash content in wood samples and bark content is very favourable in terms of biomass quality. In addition, the resulting ash has a positive value due to the fact that it can be used as a fertilizer in reclaimed areas and thus close the cycle of substances in nature.
Thanks to these properties, which are in accordance with the standard, black locust wood chips can be included among the biomass suitable for energy purposes.
Cafourek, J., Gaff, M., Gasparik, M., Slavik, M., Macku, J. (2016). Properties and use of biomass from reclaimed land in the North Bohemian basin. Wood Research. 61, 777–790.
Josef Cafourek
Ing. Josef Cafourek is a doctoral student at the Department of Basic Wood Processing, Faculty of Forestry and Wood Sciences, CULS, Prague. The elaborated study comes from the field of research dealing with the determination of physical-mechanical properties of wood from atypical habitats and at the same time wood of introduced tree species.
Prepared by: Lucie Hambálková