Fuels - Energy Innovations

Wood Fuels

In our experience wood fuels generally offer superior performance over other fuels in biomass boilers. These fuels are usually clean burning and have a lower ash content than other biomass fuels. Importantly wood fuel will also not usually be produced on land competing for food production, which is likely to be an issue in the future.

Different types of wood fuel:

Logs

Logs are used in the most basic form of biomass boiler. These boilers are relatively cost effective to install, but the obvious disadvantage is that they will need to be filled up at least once a day. Logs for these boilers should ideally be well seasoned, as you would expect for a traditional log stove or fire. 

Woodchip

Through breaking timber down into small chips it is possible to use augers to automate the stoking of the boiler, and so fully automated wood fuel heating systems can be achieved.

How is wood chip produced?

There are no hard and fast rules about woodchip production, but the following process should usually be followed:

• Fell Timber.
• Cut to length (3 – 6 metres depending on chipper).
• Season Timber (upwards of 6 months depending on location. weather and timber).
• Chip Timber.
• Deliver to end user or bulk store for later use.

Timber felling can vary from simple on farm procedure using existing equipment or at the other end of the scale mechanised harvesting and forwarding in large commercial forestry.

The logs or timber heaps should be seasoned until they are around 30% moisture. The timber will not need to be stored under cover, but an exposed location where there is plenty of wind and sunshine is important. It is also important to store the logs on bearers, or dry hard standing, so that they do not absorb moisture from the ground.

There are now a number of contractors and co-operatives operating through out the country who are able to offer a chipping service by the day. Depending on the size of machine it is possible to chip any where between 20 and 200 tonnes of material at 30% moisture in a day.

In order to chip an economic volume of chip it is usually necessary to either chip into, or transport the chip to a local store. From this point the chip can be delivered out to boilers in the area using tractor and trailer or delivery lorry.

A woodchipper in operation

Bulk Density of Woodchip

Woodchip is a cost effective, low carbon fuel, but it does have a low bulk density. Woodchip is likely to have a bulk density of 200 – 250kg/m3 dependent on the species and quality of chip. This means that a tonne of woodchip at 30% moisture equates to 4 or 5m³ of storage volume.

This has an effect on storage and delivery costs of this material and is an important reason to source local fuel. If the large storage volume required for chip is likely to be a problem, wood pellets should be considered.

A large scale wood pellet production facility capable of producing upwards of 60,000 tonnes of pellets each year

Wood Pellets

Wood pellets are made from dried, compressed saw dust. The compression of this material into a pellet allows far more cost effective storage and delivery systems to be operated. This is usually carried out within large production facilities producing tens of thousands of tonnes of pellets a year. A number of these plants are now up and running in the UK. As well as these, a number of smaller processing facilities producing only a few hundred, to a few thousand tonnes a year are cropping up. There are even one or two mobile pelletting plants in operation.

In terms of stored energy, wood chip will require four times more storage volume than wood pellets. For this reason, wood pellets should be considered for projects where there are fuel storage limitations, or delivery limitations.

Due to their small compact nature pellets can also be blown, which allows additional delivery flexibility. Through this delivery mechanism it is possible to blow the pellets down a pipe into the fuel store.

Wood pellets can also be purchased in 15kg bags, which are suitable for smaller domestic boilers and stoves.

Wood pellets are now a very viable low carbon alternative to other fossil heating fuels and are fast becoming a major source of heat through out much of Europe