Waste wood: branching out into biomass

Some £10M tonnes of waste wood are produced in the UK each year - that's a lot of material that could be tapped into and utilised as a biomass fuel source

Wood is one of the oldest fuel sources known to man. While recycling and energy markets for clean, virgin wood have been growing in recent years, waste wood has been a largely overlooked resource.

This is partly due to it often arising as part of a mixed waste stream, with limited availability of facilities for its segregation, but also sometimes due to contamination making recycling impractical. With around 10M tonnes of waste wood produced in the UK each year, most of which goes to landfill, this is clearly a missed opportunity.

To address this, Defra has released a market information report Waste wood as a biomass fuel, as part of its waste infrastructure delivery programme. It outlines the carbon and energy benefits of recovering energy from waste wood, and says that, while the aggregation points and supply chains for waste wood are in their infancy, these are expected to grow.

Waste wood was identified as a priority material for action in the Waste Strategy for England 2007, which outlined the Government’s intention to facilitate greater recovery of energy from waste wood. Waste wood arises from many sources, in varying quantities and levels of purity. But, in the MSW waste stream, the two main areas in which it arises are household collections and civic amenity sites.

While it can be tricky to segregate waste wood from household collections, waste wood arising at CA sites is easier to segregate and aggregate. CA sites in close proximity to end markets for waste wood are in some cases already collecting it for energy recovery at existing biomass plants.

The key routes for recovery or disposal of waste wood are recycling, energy recovery/incineration, and landfill. Recycling outlets for wood are within the panel board industry, animal bedding, equine surfacing and garden mulches. All these outlets require high grades of waste wood that can be achieved through front-end sorting, or back-end cleaning processes. Unlike energy recovery, the main recycling outlets are unable to use material that has a high level of contamination, such as plastic coatings and resins.

The rise of recovery

While there may be scope for further capacity in recycling waste wood, it is unlikely to increase significantly in the near future. But demand for energy recovery from non-fossil fuels is likely to rise, and biomass fuels are expected to play an important role in this.

In May 2007, the Government announced plans to band the Renewables Obligation that will significantly increase support for electricity generated from biomass such as waste wood. Further measures to boost renewable energy generation will be needed to meet the UK share of the EU renewables target – these will flow from the Heat call for evidence, published last January, and the work leading up to a Renewable Energy Strategy intended for 2009. Waste wood, along with clean wood, can be used as a biomass fuel as follows:

  • in existing infrastructure which is run on fossil fuels
  • as a replacement for, or co-fired with, other types of biomass
  • in specifically constructed wood-fuelled biomass plants

However, if lower-grade waste wood is to be used as a biomass fuel, the plant must be WID-compliant. There are 105 WID-compliant incineration plants in England, which range in size from 1ktpa to 550ktpa. But it is unlikely that these plants could be used to divert existing waste wood from landfill due to limits in capacity.

Incineration plants are also designed to accommodate fuel of a certain calorific value – a change to the fuel would require a change to the firing diagram of the plant. Of England’s operational WID-compliant plants, one is known to accept waste wood – Slough Heat & Power. A further three plants are currently under construction or commissioning in the UK – Shotton, Stephen’s Croft and Wilton 10.

Currently, wood-fuelled biomass plants in the UK are either large facilities, typically 20-40MW producing only electricity, heat or CHP; or smaller installations typically up to 3MW, which generally produce heat only. There are a few large wood-fired plants being planned, with one under construction in Port Talbot.

But security of supply is a fundamental concern to investors in biomass projects. And in this respect forestry and biomass crops may be preferable to waste wood as they are available under long-term contracts. But it’s worth noting that the demand for forestry biomass crops is increasing, which will affect the availability and price of these materials in the future.

Biomass energy content is critical in obtaining ROCs, which in turn, is fundamental to the economics of a biomass project. Forestry and biomass crops have a biomass content close to 100%, whereas low grades of waste wood may have a biomass energy contents as low as 80%.

Some projects use a blend of forestry, fuel crops and waste wood (ratio 60:40) to achieve the overall 90% biomass energy content required to obtain ROCs.

Barriers to overcome

Besides a lack of facilities to segregate or burn waste wood, there is also a lack of financial or regulatory incentives for producers to segregate the material. There are no statutory obligations for local authorities or the private sector to separate waste wood for recovery, although the activity is encouraged through measures such as landfill tax, LATS and recycling targets.

Aggregators are likely to respond to the demand for secondary-use products, but currently there is low demand for low grades of waste wood so very few are focused on its collection and supply.

CA sites are regarded as good aggregation points, both from individuals and small businesses. And collecting commercial additional waste wood and diverting it from landfill aids a WDA’s LATS position.

Demand for low-grade waste wood could increase by introducing more WID-compliant incineration capacity in England. But there still remain several barriers to biomass capacity – economics, sites and planning, fuel supply, and knowledge. As a result, the current waste wood biomass market is immature and there is a lack of appropriate sponsors.

Renewable energy companies are mainly leading projects under development. It is unclear which of these developers, if any, will lead on the delivery of future projects.

Many potential users – intensive energy users – do not see electricity or heat generation as part of their core operations whereas electricity companies may not be focused on electricity generation from waste as it falls outside their core expertise. And waste management contractors are principally focused on the MSW market.

Lack of expertise

At present, there is a lack of knowledge and expertise within the market for the opportunities for waste wood to be used as a biomass fuel source. Looking ahead, local authorities may be able to support the development of future fuel supply chains by working towards regional procurement of waste wood biomass plants.

This is being pursued by Project Integra (Hampshire County Council) as it seeks to develop a regional waste wood catchment area for a waste wood fired, WID-compliant combustion plant in Hampshire.

CA sites in England collect around 500ktpa of waste wood. These tonnages could potentially be used to support funding for five regional facilities with a capacity of 100ktpa. This approach could be developed in regional spatial strategies, with plant potentially capable of being procured using PFI credits. A private sector partner could be procured to assist with electricity and heat and power offtake arrangements.

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