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Wood Energy Overview

Forestry and wood-based industries provide a wide range of different fuels including logs, bark, chips, sawdust and pellets.

Wood fuel heating systems have been developed as an alternative to oil, LPG, coal or gas fired heating systems. They can be operated as independent boilers, or can be installed in series (partnership) with fossil fuelled boilers. Most wood fuel boilers are fully controllable and automatic and can be incorporated into building energy management systems. Wood heating systems are more expensive to install than fossil heating systems, however they are cheaper to operate. This usually means the existing energy bill to be replaced must be large enough to justify the capital investment. Wood heating systems can be installed in a new build project or retro-fitted into an existing building that already has gas or oil boilers. In either case the wood fired system will be providing hot water so the building should have a wet system of radiators. There is usually an advantage in retro-fitting because it means the existing boilers can be retained to provide a back-up system and to provide ‘peak load’ heat.

If you are looking for more detailed information on Wood Energy, or are looking to see how much you could save by converting to wood energy, please visit the RASLRES Bioenergy Tool.

Benefits of wood energy for fuel users

Wood energy brings many benefits to both private and commercial users. It can be used in both new buildings and also fitted to existing systems. Large-heat users, such as hospitals, care homes, leisure centres, schools, and so on can benefit particularly from wood chip heating systems. However, private homes can also take advantage of wood energy by installing a single wood chip boiler through a heat network.

The benefits to converting to wood energy to the fuel user include much lower fuel costs; stable priced fuel over the long term; massively reduced C02 emissions; and fuel supplied locally from sustainable supplies.

Benefits of wood energy for fuel providers

For fuel providers, wood energy can provide a range of benefits. For example, the economic returns are typically spread across the supply chain and bring additional income to:

  • forest owners – who will gain a new market for forest thinnings
  • forest contracts, since use of wood energy means an increase in thinnings contracts from the private sector
  • haulage companies – who will transport the fuel supply from source to end user
  • plumbers/engineering/electrician companies – who will install boilers and provide fuel storage (e.g. fuel silos, bunkers, handling systems).

Wood Energy Supply Chain

The fuel supply chain involves a process of:

  • Harvesting round wood from woodlands
  • Storage and drying of round wood
  • Chipping
  • Delivery

Quality standards underpin each stage in this process.

Harvesting, chipping and ancillary equipment

The timber (sawlog, palletwood and stakewood) can be sold standing by private forest owners. The fuel supply company must then organise sub-contracts to undertake the main elements of the supply chain; harvesting, chipping and the delivery of chips. Should the business expand and the economies of scale allow, then chipping and delivery equipment could be purchased at a later date. At the outset therefore the fuel supply business needs little by way of additional equipment (other than a drying shed).

A high output chipper, capable of screening to the appropriate particle size will have to be available as part for the production process. Hiring a contractor to chip at periodic intervals is the most likely option. Purchasing such a chipper, of sufficient output, in-feed diameter, consistent chipping quality and screening ability, will cost in the region of 75,000.00 when complete with engine and crane feed. However a chipper could be hired in and produce 150 tonnes of chips per day. This means a typical business producing 1500 tonnes of wood fuel per year could hire a chipper for 10 days a year.

When the wood chip storage facility is operating at a certain capacity (approximately 5,000t per annum), we recommend that a tele-handler with front end loader, or equivalent machinery, will be required to be permanently sited at the wood chip storage depot for the handling of the fuel in the shed, and the loading of delivery vehicles etc.

Drying methods

The required moisture content of the wood chip fuel can be achieved by air drying timber in anticipation of chipping. Through a planned programme of sourcing and stacking wood fuel in advance, a continual supply of seasoned wood chip fuel will be ensured, whilst minimising any labour or energy input required for this process. Any dead standing timber or seasoned windblown material sourced during forestry operations may also be targeted for use in the wood chip supply chain as a source of either fully or partially pre-seasoned fuel.

To achieve this process a round logs would need to be hauled to and stacked outside a wood fuel depot. The log piles will then be covered with a reinforced paper cover to prevent rain wetting the logs. The logs will be stored in the round until the required moisture content is achieved.

The accepted moisture content of the smaller to medium scale systems is generally between 25% and 35%. Again, depending on the model of the boiler, moisture tolerance may be as high as 50%; however a maximum of 35% and an average of 30% should be the production target. This will ensure all possible boilers can be supplied.

Grading Equipment

In order to build confidence in the supply chain the suppliers of wood chips must be able to demonstrate that the woodchips supplied meet the standards set by the boiler manufacturers. To build this confidence and to monitor the drying of timber following equipment is required;

  • Round Wood Moisture meter to determine and monitor the moisture content of round logs during the drying process, prior to chipping
  • Wood chip moisture meter, the device measures and records the moisture content of woodchips at the time of delivery, It can be linked to a printer and/or downloaded to an excel spread sheet which can then be used for invoicing. It provides a hardcopy record of the moisture content for both supplier and end user.
  • Wood Chip Grader to monitor the particle size of the chips to ensure that the chips comply with the boiler requirements.
  • Furthermore, sampling is used to ensure that the chipping contractor is chipping to the correct standard at the time of chipping.

Wood Fuel Quality & Standards

A wood chip fuel supply process must produce high standard of wood chip fuel required for small to medium scale wood chip heating systems.

Material used should be ‘virgin’ forest products free of contaminants. Such timber can be purchased from local forest owners. A fuel supply  business should be well placed to establish long term relationships with local private forest owners.

Fuel Storage/Yard

Typically wood fuel sheds should be about 15m x 30m and have partial block side walls to a height of 2m. The shed should be enclosed by a weather proof screen which can be opened to enable the chips to be blown directly from the timber pile into the shed thus reducing the handling costs and to allow for ventilation. The gables should be fitted with doors of sufficient size to allow access for loaders and trailers. The shed should have a storage capacity of around 1500m³ loose volume (about 400t of woodchips at 35%MC). At this moisture content the chips must be stored to a depth not exceeding 3.5m to prevent heating.

To enable indoor loading during wet weather an area of 150m² should be kept clear of chips to enable a loader and trailer access to the shed. This would reduce the storage capacity of the shed to approximately 275t and also allow the chips to be turned should heating be detected.

Delivery of Fuel

The method of delivery of the wood chip fuel to the customers’ on-site wood chip storage will be determined by the nature of wood chip storage and reception system available. The most simple and efficient means of delivery is to bulk tip the fuel into a below ground wood chip storage bunker, as this may be carried out by a standard bulk tipper.

However, the difficulty with this system is often at the client end, and in many cases the cost of installing an underground bunker can be off-putting for clients and developers.

For above ground storage silos, where gravity filling is not possible, alternative means of delivery include bulk bagged delivery using a vehicle with a crane, loading using a ‘clamshell’ grab bucket, and using a proprietary wood chip blower vehicle.

Delivering the wood chip fuel in bulk bags involves using a standard flat bed lorry with crane which may be co-opted for other uses, however the significant increased handling and equipment required for bagging the fuel and loading and unloading the delivery vehicle will have to be reflected in the delivered cost of fuel to the client.

The decision on how to plan and achieve delivery of wood chips to boilers must be taken in the light of an actual contract. Generally it makes most sense to contract hire haulage vehicles at the start of a business.

It can be seen that a wood fuel production and supply business requires investment to build a drying shed. It also requires a detailed business plan involving a series of sub-contractors to harvest, dry, chip and deliver wood fuel. This could create a viable new business if the demand for wood fuel was established.