Fuel Products

The three major factors to consider in conjunction with biomass fuels are moisture content, chip size and contaminants. 

Moisture content – the lower the moisture content of wood fuel the higher the energy value. To reduce moisture content the fuel needs to be left to season or actively dried. This increases the cost to produce fuel but also increases the energy content.  Fuel with a higher moisture content is normally only suitable for more expensive, step grate boilers. Moisture content is specified using the terminology “W30” where the “30” represents the maximum moisture content (in this case 30% moisture).

Chip size – screens on chippers are used to vary chip size.  Using too large a chip can result in bridging in the fuel feed system and the blocking/jamming of the auger.  Having too many fine particles can also cause problems for the fuel feed system and flue.  Chip size is specified using the terminology “G50” where the “50” represents the maximum sectional area of the chip size allowable (5.0cm2).

Contaminants – fuel must be substantially free from contaminants.  
For recycled wood fuel, only untreated wood is acceptable.

Fuel producers can produce a wide variety of products and these need to be well matched to the boiler systems in which they will be used.  There are the following broad categories of fuel available:
Wet Chip Sourced from hardwood and softwood products from the forestry, timber processing and arboriculture industries low cost, but high moisture content (~W50); requires a more expensive boiler.
Dry Chip Sourced from hardwood and softwood products from the forestry, timber processing and arboriculture industries dry (~W35) and suitable for a wide range of boilers; additional costs of storage and seasoning / drying.
Pellets Usually manufactured from sawdust higher cost fuel for lower cost boilers; suitable for smaller systems or systems with low usage.