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What is wood pellet?

Wood pellet is a solid fuel that is produced by crushing and densifying waste timber like sawdust, forestry residues, industrial byproducts like old paper and forestry wastes. The length is 1-2 cm and the diameter is generally 6, 8, 10, or 12mm. It is possible to produce 25mm wood pellet at maximum. In Sweden, 6mm wood pellet is encouraged to use in house as it can realize the best condition of combustion. Wood pellet production doesn't need to add binder as lignin, an element of wood, plays a role of binder and helps to pelletize when it is melted by heat.

Table. Characteristic of wood pellet fuel
Amount of heating generation (lower limit)4.7 kWh^kg  about4,000 kcal^kg
Kerosene conversion valuepelletFkerosene  about2.1tonsF1m3
Volume weight650 kg/m3
Hydrous rate8-13%
Ashwood except bark: under 0.5%, bark: over 2.5%

Characteristic of wood pellet is very easy to manage compared to other biomass fuel. As the shape and hydrous rate are stable, wood pellet is suitable to use in automatic combustion installation and it can remarkably save time and labor for both of electric power generation boiler and pellet stove for house. It is possible to transport long distance because wood pellet has high energy density and much energy can be transported at once. Also wood pellet which is heat-treated, can be stored in long term with less risk for molding.

Table. Advantages and disadvantages of wood pellet fuel
Advantages High quality (shape and hydrous rate are stable)
dry, easy to store
burning under environmental compliance is possible
suitable for automatic combustion operation
made of regional renewable resources
energy density is higher than wood chips, suitable for transportation and storage
transportable to areas with high energy demand density because of its high energy density
ideal for closed renewable energy system
possibility to be an alternative for energy system from smaller to larger scale
create employment
Disadvantages labor-intensive more than heating with gas, oil and electric power in house
credibility in fuel supply, transportation and combustion is inferior to gas, oil and electric power
need storage capacity three times as large as oil's
weak to moisture

Dried timber 1ton can generate energy equivalent to electric power 1,000 kWh or heat 4,500kWh. Energy ratio for pelletizing in comparison with wood pellet product's is as follows:

  • To pelletize dried materials needs energy equivalent to 8-13% of energy contained in wood pellet product
  • To pelletize materials (sawdust) after drying needs energy equivalent to 10-25% of energy contained in wood pellet product
  • Whole process of pelletization of wood chip (including drying and crush) needs energy equivalent to 18-35% of energy contained in wood pellet product
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