On the left side good chips of uniform quality. On the right side low-grade chips of variable quality and particle size.
The quality of wood chips is determined based on three criteria: moisture content, uniform quality and particle size of the chips. These three factors determine the quality of wood chips.
Uniform Quality and Particle Size
The moisture content of the chips is linked to the amount of energy they release. Woodchips of uniform quality and the right particle size guarantee reliable and undisturbed functioning of the heating system.
The right particle size for a wood chip is 5-50 mm. The more there are chips made of trunks, the more uniform is the quality and size of the wood chips.
Depending on the wood species and the time of felling, the moisture content of a freshly felled tree is about 50–60%. In practice, it is useless to burn wood that has the moisture content of 55% or more, because the energy value is as low as 2kWh/kg, which equals the energy loss of a heating boiler.
Low moisture content means that the wood has an excellent energy value. Dry wood may have even 4–5kWh/kg energy value. For wood chips to be classified as of high-quality, they should have the moisture content of 30% or under.
The chips cannot go mouldy if the moisture content is under 30%, and this is not the only advantage of low moisture content. Below are listed the challenges that low-grade and moist chips might bring along.
Low-quality and moist wood chips
Low-quality fuel causes various problems if used in heating systems. Heating with wood chips using modern technology is easy and carefree for all of us, but using low-quality fuel will undo this ideal situation.
Below is a list of the undesirable situations that using low-quality chips usually leads to. It should also be remembered that using mouldy chips is a risk for health: breathing the mouldy dust is extremely dangerous.
- a great portion of energy goes to drying the wood, and a smaller portion to heating,
- sooting boiler,
- over-accumulation of ash,
- higher discharge level,
- higher risk of backburn,
- in extreme cases, self-ignition,
- vaulting of fuel, unnecessary waste of heat,
- problems in preserving fuel – moulding and freezing in storage,
- greater consumption,
- higher transportation costs,
- higher energy consumption of the heating system,
- very low heating-efficiency.
Excellent raw material for wood chips: felled and lopped trees.
Felled and lopped trees are loaded onto truck to be transported for chipping.