Wood Chip has many advantages as a source of fuel for a biomass boiler
- Wood chip is a very low cost wood fuel. Typically 2.5 – 3 p/kWh
- Those with access to woodlands can bring down fuel costs significantly (1 – 1.5 p/kWh)
- Fully automated chip boilers require very little intervention
- Quality boilers operate very efficiently with wood chip (95%)
- Wood chip is readily available; there are a large number suppliers and contract chipping companies.
Wood chip specification
Things to consider:
- The moisture content of wood chip should be below 30%.
Too much water in the wood chip reduces boiler efficiency – the boiler will be heating water in the burning chamber of the boiler not in the heating system!
Very damp wood chip can start to compost during storage
Excessive smoking and can occur with high chip moisture content and the flue will need more frequent cleaning.
Chip may be bought by weight; excessive water content will affect the cost competitiveness of the chip supply.
- Size of chip is important. The international standard for wood chip uses size grades based on its ability to pass through a screen, for example G30 chip will pass through a screen 30mm x 30mm, G50 through a 50mmx50mm screen.
Many biomass boilers are warranted for G30 chip, the ETA boilers supplied by Asgard Biomass are warranted for G50 chip.
Larger chip has advantages, the greater surface area means there is more air circulating so that it remains drier in the store.
Over sized pieces of wood in the chip supply have the potential to block the chip feed mechanism. ETA chip boilers have a patented cutting knife to cut through pieces of wood up to 2” x 5” however it is best to ensure that wood chip is the correct specification.
Too much dust or ‘fines’ in the chip can lead to an inefficient burn.
- Bark has a very low calorific value and should be avoided.
- The boiler can be damaged by contaminants in the chip supply; stones, metal, nails and plastic must be avoided. Asgard Biomass supply top quality boilers that are not warranted to burn non-wood waste.