environment magazine

The Role of Wood Waste as a Source of Biomass Fuel in the UK

By Miles Brown BSc, MSc, CBiol, MSB, AIEMA & Victor Kearley BSc, PhD, FIWSc

Biomass is a generic term for a wide range of organic materials including wood, which are used to generate electricity and/or heat. Waste wood is just one form of biomass for which there is rapidly growing interest in the UK. This paper review outlines some of the issues involved.

A key difference between using biomass and fossil fuels is that with biomass, if sustainably managed, the carbon dioxide (CO2) released from combustion is in theory re-absorbed by replacement growth via photosynthesis. The process therefore remains essentially carbon neutral, so unlike the combustion of fossil fuels, the only contribution to greenhouse gas (GHG) emission comes from processing and transport. Generation of low carbon energy is of increasing interest to the government, as implementation of the 2008 Climate Change Act means that the UK has a series of legally binding targets en route to a long-term goal of reducing GHG emissions to 20% of 1990 levels by 2050.

As a signatory to the European Energy Directive, the UK is now required to generate 15% of its energy overall from renewable sources by 2020. This is seven times greater than that achieved in 2008, and the government envisages that, nationally, renewables will provide 30% of electricity, 12% of heat and 10% of transport energy requirements. To help achieve this demanding target the government launched its Renewable Energy Strategy in 2009, which considers that about 30% of the 2020 renewables target will be met by biomass heat and electricity (DECC, 2011a).

The significance of biomass, however, extends beyond achievable levels of output. Biomass energy production is flexible and controllable so it can easily be adjusted to match required levels. This is in contrast to technologies like solar and wind energy, where output is intrinsically dependant on the capricious forces of nature, whose delivery may be quite independent of human demand. Biomass will help to regulate and balance the grid as increasing levels of intermittent renewables make a contribution. It can also exploit a diverse range of feedstocks which includes both plant and animal matter in the form of virgin materials and waste. The government considers that such diversity will provide greater confidence in security of supply. The government also sees numerous potential commercial opportunities from exploiting biomass energy, including:

• Growing energy crops (typically as short rotation coppice of willow or poplar, or miscanthus).
• Increasing the proportion of UK forest under sustainable management
• Identifying new markets for wastes and residues
• Developing a fuel processing sector
• Developing a sector for the design, manufacture and installation of equipment and plant at all scales of operation from domestic heating to power stations supplying the national grid.
• Developing new technologies such as gasification and pyrolysis.

Drivers for the development of Biomass
To stimulate the production of renewable energy from biomass and other technologies, the government introduced the Renewable Obligation (RO) through the Utilities Act (2000), which was implemented in 2002 (2005 in Northern Ireland). Initially anticipated to run until 2027, the scheme has now been extended until 2037 (2033 in Northern Ireland). The RO operates by the government setting targets for the proportion of renewable electricity that has to be supplied to the market. The Office of the Gas and Electricity Markets (Ofgem) who act as the industry’s regulator, initially issued a Renewable Obligation Certificate (ROC) to producers of renewable electricity for each megawatt hour (MWh) generated. The principle is that producers sell the ROCs to the suppliers who offer them as proof of meeting their obligation. As an alternative to presenting certificates, the suppliers have the option of paying a ‘buyout’ price for any shortfall in their quota, which for the 2010 – 2011 compliance period, has been set at £36.99 per MWh. Finally, the proceeds from all of the buyout payments are distributed to the suppliers in proportion to the number of ROCs that they presented.

In 2009 the RO was amended to introduce banded ROCs, thus rather than issuing one ROC per MWh, the ROC allocation became dependent upon the technology generating the energy (Table 1). Advanced thermal technologies such as gasification and pyrolysis saw an increase in their allocation, as did the use of biomass sourced from energy crops, and biomass use for the generation of combined heat and power (CHP). The reason here was to focus support on emerging technologies, so the established technologies saw no increase in support, and in cases such as co-firing non-crop biomass with fossil fuels, support actually fell to 0.5 ROC/MWh.

Table 1 Examples of banded ROC allocation for established and emerging biomass- related technologies.

Generation type ROCs/MWh
Co-firing fossil fuels with non-energy crop biomass 0.5
Co-firing fossil fuels with energy crop biomass 1
Co-firing fossil fuels with non-energy crop biomass for CHP 1
Co-firing fossil fuels with energy crop biomass for CHP 1.5
Dedicated non-energy-crop biomass 1.5
Dedicated non-energy crop biomass for CHP 2
Dedicated energy crop biomass 2
Dedicated energy crop biomass for CHP 2
Gasification & pyrolysis 2
Anaerobic digestion 2

In July 2011 the Government published an Electricity Reform white paper and a Renewable Energy roadmap to set out plans on how it will meet its 2020 targets under the Renewable Energy Directive. This includes the introduction of Feed-in-Tariffs (FiTs) with Contracts for Difference (CfD) as a form of subsidy that will eventually replace the ROC system. In practice the system aims to reduce investor uncertainty by establishing a set price, known as the strike price at the beginning of a contract. If the generator finds that market price has fallen below the strike price the FiT will make up the difference. However, if the market price rises above the strike price, the generator will be obliged to return the difference to the FiT operator, so whilst the generator is protected from falling market prices, conversely, there is no scope to receive a windfall profit. The government anticipates that CfD FiT contacts will be available in 2014, but the option will remain for accreditation under the Renewables Obligation will be available until 2017.

Further government support for biomass is to be achieved through the Renewable Heat Incentive, which is an initiative to help achieve a target set under the Renewable Energy Directive for the UK to generate 12% of its heat from renewables by 2020. Considering that the level of heat generation directly from renewable technologies in the UK was 1.6% in 2009 (Committee on Climate Change, 2011), this is an ambitious target. It is anticipated that at least 40% of this figure will be achieved by modern wood heating, with contributions from other technologies such as biogas, deep geothermal, ground and water heat source pumps and solar thermal (≤ 200 kWh). The scheme, like the RO, is to be administered by Ofgem and is scheduled to run for 20 years. Currently, £860 million has been earmarked to provide support for new installations.

The result of these incentives will be drastically to increase demand for a wide range of biomass fuels in the coming years, both for heat and for electricity generation. Throughout the EU, demand for wood pellets is anticipated to grow 10 fold by 2020 (Crowe, 2011). Within the UK in 2010, biomass electricity output from units equal to or greater than two megawatts was estimated as just over 305 megawatts of electricity (MWe), consuming various sources of biomass at a consumption rate of just under 1.7 million tonnes per year. However, if all installations both in planning and proposed come on line, output will increase by a further 4,000 MWe with a demand for fuel exceeding 35 million tonnes per year (Hogan, 2011). With increases in demand of this order, the UK and indeed the EU as a whole will find that they are importing increasing volumes of material. In response to this recognition, the UK government has introduced a requirement for sustainability reporting, where the generator is greater than 50 kW. In addition, from April 2013, the carbon intensity of biomass should not exceed 285.12 kg CO2/MWh (DECC, 2011b). Another outcome of this potentially rapid increase in demand is that much wood previously destined for the waste stream will have an application.

Waste Wood
The main sources of non-virgin wood are from the following waste streams:

• commercial & industrial
• municipal
• construction & demolition

The characteristics of the materials to emerge can be variable, and this may influence potential applications as a recycled product. 

Waste wood that is clean and contamination free is actively sought after for high value products such as high grade animal bedding and horticultural mulch. These are, not, however, rapidly growing markets and currently account for only a quarter of the wood recycled in the UK 

The panelboard sector will accept small levels of contamination, as it bases its acceptance criteria on the stringent requirements set for the European standard for the safety of toys (BS EN 71: 1995). Such a cautious approach is justified by the fact that panelboard products may be used in toys, and if permitted limits are acceptable for an application that will inevitably involve close contact with children; they should be safe for almost any other application. An initiative to produce an industry standard to control the quality of wood waste entering the panelboard sector came with the introduction of Publicly Available Specification (PAS) 104 in 2004. However, in practice it was not embraced, as typically wood recyclers were contractually obliged to exceed the specification limits required by the PAS to suit individual panel manufacturer’s requirements.

Wood recycling on a commercial scale has only emerged in the UK in recent years; the sector is therefore young and still developing. A decade ago, about 90% of the recycled wood produced was used by the panelboard sector, mainly for the production of chipboard. In 2010 the UK panelboard sector consumed just over 1.1 million tonnes of recycled wood (WRA, 2011), and although still the largest consumer, market share has declined, and in 2010 it accounted for just under 50% of the available material.

The recent economic downturn saw consumption by the panelboard sector fall by nearly 12%; although by 2010 demand had bounced back by 5% over the previous year. On the other hand, an emerging biomass sector was reported as having consumed 551,000 tonnes of recycled wood in 2010 (WRA, 2011), a figure which has more than doubled since 2007. Looking into the future, predictions suggest that demand from the biomass sector for recycled wood could exceed four million tonnes by 2015. This figure is about twice the current level of the UK wood recycling industry’s annual output, and whilst recycling levels may continue to grow, operators seeking sources of biomass waste will increasingly be looking further afield. In addition to wood recycled for the UK market, it is estimated that in 2010 an additional 377,000 tonnes was exported to European countries for biomass (WRA, 2011), quite a jump from the 71,000 tonnes exported in 2009 (WRA, 2010).

Although Environment Agency (EA) estimates for recycled wood exports are lower than those of the Wood Recyclers’ Association (WRA), recent trends suggest that an export market may be developing. The WRA considers much of this to be a short-term trend as suppliers wait for the commissioning of biomass power plants. There is however, also an opinion that developing export markets will be a long-term phenomenon. High demand in Europe has in particular led to feedstock shortfalls in Germany and Sweden, which is in now having an influence on gate fees in the UK wood recycling market (Holland, 2011). The future may therefore see significant additional competition from continental and northern Europe for recycled wood as biomass, especially for wood that is processed with ready access to a port.

The quantity of wood waste generated in the UK annually has proved difficult to determine with any great certainty, because the timber industry contains a high proportion of small operators. A thorough study would require a large number of surveys to be completed by a group who may lack the information or capacity to respond to detailed questionnaires. Gathering accurate and representative survey data is therefore challenging and, as a result, estimates of national arisings have shown considerable variation over the years. A study published in 2005 suggested that the UK could be generating as much as 10.5 million tonnes of wood waste per year (MEL, 2005), was considered by many in the wood recycling sector to be too high. However, in 2009, this figure was drastically revised down to nearer 4.5 million tonnes for 2007 in a survey undertaken for the Waste & Resources Action Programme (WRAP) (Pöyry and Oxford Economics, 2009).

At this time, biomass buyers were pursuing 10 million tonnes per year of waste and virgin wood, to meet demand for existing and proposed biomass power stations (Beadle, 2009). In addition to having considerably less waste wood available than was thought, it also became apparent that most of the then virgin supplies available were already committed. Therefore, as a biomass energy sector develops, not only will waste and virgin biomass be sought from abroad, but much new plant will have the capacity and flexibility to include non-wood based biomass.

It is estimated that 2.25 million tonnes of wood was recycled in the UK for home consumption during 2010, and that WRA members, believed to account for nearly 80% of UK recycled wood output, exported a further 540,000 tonnes (WRA, 2011), suggesting a total figure in the order of 2.8 million tonnes. However, in addition to wood waste products that are exported from the UK, a WRAP study to be published later this year identified in 2010 that a similar volume is being imported, largely from North America, as many biomass operators establish long-term contracts to ensure a secure supply. The capacity of the UK wood waste stream seems to have diminished further from the 4.5 million tonnes generated in 2007 to 4.1 million tonnes generated in 2010 (WRAP, 2011). These figures therefore suggest that well over half the wood waste being produced in the UK is being diverted from the waste stream, which further re-enforces the limited capacity of the domestic waste stream to accommodate the increasing demand for biomass fuel.

As the cleanest wood in the waste stream has already found markets via the wood recycling sector, the remaining wood will inevitably consist of lower grade material. This will include various degrees of physical contamination such as metal fixings and nails, as well as materials like paper, cardboard, plastics and stones that have found their way into the waste stream. Much of the wood may also be chemically contaminated through treatment with paints, varnishes, coatings and preservatives. Other materials will include panelboard products such as chipboard, plywood and MDF. Although chipboard often contains a high proportion of recycled wood, panelboard products are not in turn readily recyclable into new products. A major barrier to recycling is that during manufacturing, resin is absorbed into the wood fibres, which undermines their capacity to absorb further resin as part of a future manufacturing cycle.

Accommodating low grade wood waste as biomass Whilst offering potential as a biomass fuel, one hurdle to the exploitation of waste wood-based panel material was that initially under the RO, fuels were required to contain a minimum of 98% biomass for the purposes of receiving ROCs. As panelboard materials typically contain 5 – 10% resin, they were effectively excluded under rules as they stood. This was rectified in 2006 when government lowered the limit to 90%, therefore making panelboard material eligible for ROCs, so the emergence of a biomass sector will play a key role in steering this material away from landfill. In addition to government support under the RO, a major advantage enjoyed by the biomass sector is that, depending upon boiler specification, it is in a position to compete for all of the wood that enters the waste stream. This is of concern to the panelboard sector, which views such competition as an economic threat.

Many small-scale domestic and commercial heating boilers rely on pellets made from virgin or clean recycled wood. There is much equipment, however, especially for larger scale energy generation, and a new breed of smaller, more specialist devices that will exploit wood chips with varying degrees of contamination, such as waste panelboards and treated wood. A major issue, however, is that wood which has been treated with heavy metals or halogenated organic compounds can only be accommodated in plant that complies with the requirements of European Directive 2000/76/EC, better known as the Waste Incineration Directive (WID), which provides legislation to control emissions to air and water and limit the risks that combustion imposes on the environment and human health. Therefore for the biomass sector, WID compliance will be a key factor in developing the capacity to exploit a large proportion of the wood waste stream.

Future developments
In recent years the EA and WRAP in partnership have worked on series of waste streams under their Waste Protocols Project to determine the point at which a potential waste material can be considered suitable for alternative applications. The significance of this is that, free from the requirement of waste legislation, such materials are open to be treated on the market as a resource. As well as reducing the burden of unnecessary waste, the process simultaneously increases the availability of valuable raw materials. Whilst this has been successful for some waste streams, an attempt to apply one to wood waste failed due largely to the lack of a clear industry standard that could determine the point at which a waste material met the criteria necessary to be exploited for its intended purpose. A second attempt is now in progress, but in its present guise it will not be considering biomass. A new industry standard in the form of PAS 111 is also nearing completion, and is expected to be published during 2011.

The exclusion of biomass from the pending Wood Waste Protocol is of concern to a wood recycling industry that saw this as an opportunity to boost for their main growth area. They argue that for low grade wood waste, WID-compliant combustion is the only viable solution for a material where no recycling options exist. The EA however, was not confident that it could derive acceptable environmental limits via a generic risk assessment, either for the wood waste as a fuel, or for the emissions generated through combustion.

References
Beadle, T. (2009) Wood Waste: a valuable fuel. Resource Waste Management & Recovery. 18th September p8

BSI (2004) Publicly Available Specification 104 Wood recycling in the panelboard manufacturing industry. British Standards Institute

Committee on Climate Change (2011) The Renewable energy Review May 2011. Committee on Climate Change. London. www.theccc.org.uk

Crowe, R. (2011) EU’s Renewable Goals Driving Wood Pellet Growth. http://www.renewableenergyworld.com 25th March

DECC (2011a) Biomass for heat and power [on-line]. http://www.decc.gov.uk/en/content/cms/what_we_do/uk_supply/energy_mix/renewable/explained/bioenergy/heat_power/heat_power.aspx [accessed 24th May 2011]

DECC (2011b) Government Response to the Statutory Consultation on the Renewables Obligation Order 2011. Chapter 2 Sustainability Criteria for Biomass & Biogas. http://www.decc.gov.uk/assets/decc/Consultations/Renewables%20Obligation/1059-gov-response-ro-order-2011-cons.pdf

H M Government (2009) The UK Renewable Energy Strategy. The Stationary Office

Hogan, G. (2011) UK biomass power stations, current and planned. Forestry Commission and Biomass Energy Centre

Holland, T (2011) Exporting wood waste ‘to become a long-term trend’. www.mrw.co.uk 30th June.

MEL (2005) Reference document on the status of wood waste arisings and management in the UK. Waste Resources & Action Programme

Pöyry and Oxford Economics (2009) Wood Waste Market in the UK. Waste Resources & Action Programme

WRA (2010) Waste Wood to Market Statistics 2009. Wood Recyclers’ Association

WRA (2011) Waste Wood to Market Statistics 2010. Wood Recyclers’ Association

WRAP (2011) Realising the value of recovered wood Wood Waste Market Situation Report. Waste Resources & Action Programme