Woodchip: a sustainable biomass fuel
Where locations are favourable, woodchip boiler systems are the preferred type of biomass installation. Woodchips are usually used to heat large commercial spaces, larger buildings or groups of houses. Woodchip typically requires more space both for fuel storage ad delivery access.
- Cheapest form of wood fuel, costing 1.5p - 3.5p to generate 1 kWh of heat, compared to 6p for oil or LPG.
- Automated handling and feeding of the fuel to the boiler, minimising manual labour.
- Woodchips are particularly efficient when they are sourced from woodlands near to the point of end use because it minimises handling and processing.
Readily available from increasingly large number of suppliers. Contractors can also chip your wood fuel if you have supplies.
Sweeper and auger fuel feed
Our designers evaluate individual situations before advising you on: woodchip specifications, sourcing woodchip and handling and receiving woodchip.
Woodchips need to meet the correct specifications, namely size, quality and moisture content, in order to avoid operational issues.
- The moisture content of woodchip in storage should be below 30% to stop the fuel from turning into compost and clogging fuel transfer machinery. Moist wood burns less efficiently, owing to the need to boil off its higher water content. If one is paying by weight, the amount of water will directly impact the purchase cost of woodchip.
- Regularity in the size of the woodchip is important because irregular woodchip pieces may cause feed blockages and burning inefficiencies. Whilst Dunster systems are able to self-clear most blockages and cut up excessively large pieces, it is best to begin with the correct size of woodchip.
- Excessive quantities of bark, leaf or non-woody material are best avoided as they have little or no calorific value and simply contribute larger quantities of ash.
- Contaminants such as stones, mud, and pieces of metal or plastic, may lead to feed blockages or unnecessary wear on the boiler and fuel transfer machinery.
At Dunster we will bring our expertise and experience to advice on the best fuel supply options, being totally independent from fuel suppliers, meaning we can offer objective and impartial advice.
Woodchip is generally produced from:
- Low-grade round wood – small round wood, thinnings and other poor quality timber arising from arboriculture activities.
- Slab wood – offcuts from sawmills (though these can contain higher proportions of bark).
- Timber waste / offcuts from wood processing – as this material is often kiln dried it can be mixed with wood chip that is higher in moisture.
- Private woodlands - many systems are fuelled by fuel bought in, either as timber or as wood chip.
Flexibility in the source of wood chip is recommended so that supply can be obtained from a variety of sources and also by different delivery mechanisms. It is a higher risk – in terms of supply and price – to tie oneself to a specific fuel supplier, since if that happens, only one supplier will have the material to fill your fuel store.
Handling and receiving woodchip
Woodchip is a bulky material and transfers to the fuel store can be difficult, especially as deliveries tend to come in large quantities, in order to minimise transport costs. Considerations include:
- Availability of, or potential access for, delivery vehicles. Delivery vehicles can range from lorries, tractors and silage trailers to articulated lorries.
- The mechanism by which woodchip is transferred into the fuel store. This can include tipping (at low or high level), front loader/tele-handler, conveyor/auger or blower.
- Delivery should be ‘deliver and go’, as a slow delivery will most likely incur higher labour costs.
Types of fuel deliveries
Tip and blown
The following dimensions are typical of vehicles carrying woodchip. Our site inspectors will be able to assess your property and ensure safe operation and delivery.
|6 wheeler||8 wheeler||Artic|
|Gross vehicle weight||26 tonnes||31 tonnes||44 tonnes|
Woodchip requires much larger storage areas than conventional fuels, such as oil, because it has a much lower energy density. Storage is a critical area, and correct design is vital. Woodchip storage considerations will include:
- The need for the store to be large enough to cope with the quantity being delivered – a rule of thumb would be 1.5 times the delivery size.
- Delivery frequency: unless we are looking at large commercial installations, it is advisable that deliveries occur no more than once month.
- The amount of useable space in the woodchip store – typically this may be around 70% of the actual space.
- The appropriate fuel transfer mechanism: normally this amounts to an agitator with sprung arms, which sweeps the wood chip into a transfer auger. Larger systems may use a combination of ‘walking floors’ and transfer augers.
- For those chipping their own timber or timber that has been purchased, there is need for a secondary woodchip store: modern chippers can often chip a year’s supply of woodchip in one day.
Combined fuel storage and heat centre
There are many storage solutions depending on individual circumstances and cost considerations. Solutions range from adapting existing buildings, to purpose designed and built heat/storage centres. Dunster has a wide range of standard and bespoke solutions which can be tailored to individual circumstances.