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FUEL PROPERTIES OF PAULOWNIA BIOMASS

Future of bioenergy industry strongly depends on the biomass availability. For sustainably managed forests supply is governed by increment/annual cut, but the availability of biomass feedstock for energy is strongly influenced by competition with other sectors (wood industry and pulp and paper industry). One of the promising ways to increase the amount of biomass on the marked is establishing dedicated energy plantations of fast growing wood species. The goal of this research is to determine the properties important for biomass to bioenergy conversion (density, moisture content, bark content, ash content, elemental content -CHNS and heating value) of three Paulownia hybrids (9501, Shang Tong, OXI). Samples were taken during the field research conducted in December 2017 to determine the productivity of selected clones on sample plots established in Spring 2015 with plants produced in various ways of vegetative propagation. Sample discs were taken from the root collar upwards every 1.30 m. Basic density and moisture content of individual sample disc was determined. Bark was peeled and bark to wood ratio was established after drying the samples. Laboratory sample was prepared by comminuting wood and bark samples of the same hybrids. Ash and elemental contents as well as heating value of wood and bark were determined. Moisture content in fresh state (just after the felling) amounted to high 62.4±1.7% when compared to our commercial species in winter felling. Basic density averaged 335±27 kg/m3 ; or 60% of the basic density of hardwood species, 75% of the basic density of softwood broadleaves and 85% of the basic density of coniferous species. Bark to wood ratio ranged from 15.8% to 9.3% strongly following DBH increase. Ash content of wood averaged 0.75±0.0.8% and that of bark 4.29±0.92%. Despite the 5.7 times larger ash content of bark compared to wood, higher heating value of wood samples (19.32±0.35 MJ/kg) was slightly lower than that of bark samples (19.70±0.26 MJ/kg). Fuel properties determined by this research indicate that comparing biomass yield of Paulownia with other tree species, due to the lower basic density (i.e. quantity of fuel per volume units) demands comparison to be made primarily on (oven-dry) biomass level (t/ha). Stock and increment levels should also be reported on (oven-dry) biomass level (if the feedstock is to be used for energy), especially having in mind that hollow pith of stemwood lowers the »actual« basic density of roundwood for average 5% (in DBH span 3 – 11 cm). Based on the results of this research it can be concluded that supply chains of Paulownia biomass for energy have to be adopted to deal with the increased values of moisture content and enable the efficient use of natural drying. In this respect, future research should be focused on selecting the optimal felling, storage and chipping time.

density, moisture content, bark content, ash content, heating value

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