Wood Chips or Wood Shavings

Wood shavings or chips are made up of small pieces of wood from chipping or shredding, with a length ranging from 5 to 50mm, obtained by chipping in the fiber direction in disc chippers or in straight cutting in drum chippers containing still longer particles and a reasonable percentage of fines. The quality of the wood shavings or chips depends on the raw material and the technology used in their production. It is common to find three different types of wood chips:

Forest Residue Chips

Such as branches, tree tops, or whole trees, with reduced commercial value. They contain a moisture content of around 50%, their size varies from powder particles to chips, containing bark and leaves. This fuel is suitable for boilers in large heat or electricity production plants, such as Forest Residue Thermal Power Plants.

Shavings or chips produced in sawmills

With a moisture percentage of around 40-50%, which is used, for example, in the pulp and paper industry or in the manufacture of particleboards and other panels. Sawmill residues can be used for the production of pellets and briquettes, but for this, they need to go through a drying and grinding process before processing. These shavings have better combustion properties, but are still too wet for small boilers, unless dried before shredding.

Chips from tree cuts

Without branches and leaves, left to dry for approximately 4-6 months before shredding or chipping. These chips contain about 30% moisture and must be uniform in quality and size. This fuel is suitable for boilers installed in residential or service buildings. In this case, larger pieces of wood can cause operational problems and should be removed during production.

Comparison: Chips vs Pellets and Briquettes

Advantages

 

• Can be locally available;
• Its production stimulates local employment;
• Cheaper than pellets and briquettes;


• Disadvantages


• Requires more storage space;
• Fuel quality is harder to ensure;
• Higher need for operation and maintenance work on the plant;

 

Classification of chip sizes

Proper specification of size is crucial for chip consumers, as certain boilers, for example, will operate more efficiently with the correct material granulometry. Thus, the fuel buyer can include classifications as conditions in the contract with suppliers.

The size of the chips is influenced by:

• Chipper type;
• Feed speed x Rotation;
• Cutting angle of the knives;
• Tree species (Whole with or without branches);
• Presence of contaminants;
• Wood hardness (higher knife wear)
• Moisture content;


• The correct granulometric classification of the chips allows predicting the energy released in combustion as well as ensuring the flow of chips through the feeding system. Very large chips obstruct the material flow through the system, causing blockages. Very fine particles burn quickly in the combustion chamber, leading to heat variation and ash formation.