Prinz, Robert

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FINNISH FOREST RESEARCH INSTITUTEForest Biomass for Pellet ProductionInfocardContact:METLAMr. Robert PrinzP.O. Box 68FI-80101 Joensuu, Finland050 391 3086robert.prinz@metla.fi1© Robert Prinz, Metla © Robert Prinz, MetlaIntroduction/BackgroundTo be reliable part of fuel supply, pellet plants have to have balancing raw material available. An important issue with raw materials from forests is the moisture content of the diffe-rent materials. Fresh timber can be assumed to have a moisture content of approximate-ly 50%, pellets have a moisture content of approximately 10 to 12%. When using tim-ber for pellets the difference of these moi-ture contents has to be lowered. This can be Storage and drying of raw materials for pelletsdone as natural drying of the raw material or artificially during the processing of the ma-terial to pellets. Natural drying before the processing of the raw material can lower the moisture content to approximately 20–25%, the remaining 10–15% have to be lowered during the further processing of the material. The lower the moisture value before the pro-cessing the lower the costs of drying during the pelletizing process. Also the sensitivity to-wards mould infestation will decrease. Fresh whole trees from thinning operations as raw material source for pellets have a high moisture content. At the begin-ning of the trial (July 09) whole trees of pine had an average MC of 58.9%, birch whole trees had 43.4%.© Robert Prinz, MetlaQuality factors of pine whole tree pellets:Moisture content of raw material 13.4% →Moisture content of pellets 8.9% →Bulk density of raw material 208.1 kg/m → 3Bulk density of pellets 571.7 kg/m → 3Temperature 81.0˚C →Pellet weight 1.93 g →Pellet length 27.51 mm →Pellet diameter 8.72 mm →Hardness (Kahl-hardness) 9.62 kg →2Infocard: Forest Biomass for Pellet ProductionFINNISH FOREST RESEARCH INSTITUTEQuality for pelletsQuality requirements for the raw material in order to produce high quality pellets are high. Critical factors are purity, low bark content and low shares of unwanted elements.Fine particle emissions from the pine pellets were on a similar level with the commercial pellets. Generally, pellets that contain bark have higher amount of ash forming elements. CO and OGC emissions from the modern small-scale pellet boilers are relatively low, when the boiler operates optimally, which was also seen in the current tests. However, diffe-rences between the tested fuels were observed. Both CO and OGC emissions were higher with the studied pellets than with commercial wood pellets. Furthermore, the NOX emissions were also higher from the studied fuels when com-pared to the commercial pellets which can be explained by different fuel nitrogen contents.The pellets produces of these alternative raw materials are suitable for larger-scale, but aut-hors do consider that the whole-tree pine has potential to become raw material for higher quality pellets.Broad-leaved trees are very poorly used as raw material for wood pellets in Finland and using birch could greatly wide the useful raw mate-rial base. According our studies good quality pellets can be produced and cost level is near to be appropriate when using undebarked pine and birch-pine mixture as raw material.Moisture content development of pine and alder during drying trials in Finland. Obernberger, I., Thek, G. 2010. The Pellet Handbook. The production and thermal utilisation of biomass pel-lets. Earthscan. 549 pp.Okkonen, L., Paukkunen, S., Lamberg, H., Sippula, H., Tissari, J, Jokiniemi, J. 2009. PELLETime investigates alternative raw materials of pellet production. Bioener-gy 2009 – Book of Proceeding: 755–759. 2009.Paukkunen, S., Sikanen, L., Okkonen, L., Vilppo, T., Lamberg, H. 2009. Energy pellets in the future – mar-kets and raw materials.  -10.00-5.000.005.0010.0015.0020.0025.00AprJunAugOctDec FebAprJunAugTmaxTmax 30 yrs2007 2008T max ('C)Finland (Kajaani)  -25.00-20.00-15.00-10.00-5.000.005.0010.0015.00AprJunAugOctDec FebAprJunAugTminTmin 30 yrs2007 2008T min ('C)Finland (Kajaani)  0.0020.0040.0060.0080.00100.00120.00140.00160.00180.00AprJunAugOctDec FebAprJunAugP mmP mm 30yrs2007 2008P (mm)Finland (Kajaani)© Robert Prinz, MetlaMeteorological characteristics of the trial area.Storage of raw materialThe aim of a storage is to lower the moistu-re content in a certain time period. An ideal storage facility is highly, aligned towards the sun and has a dry ground which is accessible throughout the year. 0.0010.0020.0030.0040.0050.0060.0070.00Pine ControlPine DebarkedAlder ControlAlder DebarkedFinland (Covered)MC0.0010.0020.0030.0040.0050.0060.0070.00Pine ControlPine DebarkedAlder ControlAlder DebarkedFinland (Uncovered)MCJanMarMayJulSepNovJan FebAprJunAugOctDecFeb

Storage and drying of raw materials for pellets

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