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Blending Agrobiomass with Peat or Wood in Finland
Finland is aiming to utilize reed canary grass (RCG) and straw for energy production together with peat and wood fuels, both to filtrate run-off waters from peat production and as a raw material of chemical pulp.
The production potential of reed canary grass (Phalaris arundinacea) and straw on mineral soil is estimated to be 7.9 TWh (28 PJ), which means cultivation of RCG on 170 000 hectares and harvesting of straw on 230 000 hectares. Currently 4 000 hectares of reed canary grass is cultivated for energy purposes by Vapo Oy and Pohjolan Voima Oy. A typical amount of harvested crop is 5 500 kg dry matter per hectare, which is equivalent to 25 MWh/hectare.
In Finland some 50 000 hectares of peatlands are used for commercial peat production. Of this amount 1 000–2 000 hectares are annually withdrawn from peat production because of gradual exhaustion of the fields. Most of these fields are suitable for cultivation of RCG. RCG plantations are one method of purifying the run-off waters of production areas and landscape production sites.
VTT together with Vapo Oy and Pohjolan Voima Oy have developed harvesting chains of RCG and straw. The research tested both loose harvesting methods and baling methods. In both cases one harvesting chain was based on farm-scale equipment and the other chain was based on efficient heavy-duty equipment. In addition the combustion of RCG and straw was studied. The existing transportation chains of peat and wood chips were utilized to determine production logistics.
Due to low energy content RCG and straw are only supplementary fuels: the typical energy share is 10% on a fuel blend, when chopped into pieces less than 5 cm. Harvesting chains are based on existing farming equipment. The combustion of RCG can be managed when spring-harvested RCG is used. The relatively high production costs compared to peat or coal can limit the use of RCG and straw. The competitiveness is better if compared to wood chips. Total production costs were from 2.7 to 4.2 €/GJ without subsidies (EA).
Mrs Tuulikki Lindh, VTT Processes