Have you twigged yet?

Waste wood is fast becoming a real contender in the biomass fuel markets as interest in this material stream rises. Marcel Goemans explains more.

There has never been a more vibrant time in the UK or international bioenergy markets given the wide spectrum of new technologies for capturing the energy content of biomass. As most people now recognise, biomass is a renewable, low carbon fuel that is already widely, and often economically available throughout the UK.

One such source with significant potential is waste wood. Although some 10M tonnes of it is produced annually, most ends up in landfill. In 2007, only 1.2M tonnes were reused to manufacture panel board and 1.9M tonnes were recycled or burned - this was mainly clean material, relatively homogenous and free from contaminants.

The rapidly growing market for biomass heat is providing opportunities for space and process heating in industrial and even domestic sectors. People are looking at new ways of generating biomass power and in addition to traditional sources of biomass like agricultural waste, energy crops and virgin wood, waste wood and marginal virgin wood residues are generating much interest.

The main stimulus for biomass power is the Government's renewables obligation, which obliges licensed electricity suppliers in the UK to source an increasing proportion of electricity from renewable sources. The certificates produced from renewable energy have significant value which underpins the additional set up costs of biomass systems, compared with conventional power stations. Thermal treatment and generation of electricity from wood and waste wood is now looking increasingly attractive especially among merchant plant.

Similarly, many power generators and industrial sectors are including heat recovery in their processes because this allows them to run in combined heat and power (CHP) mode, resulting in higher plant efficiency and giving them enhanced eligibility for renewable obligation certificates (ROCs).

Tapping into waste
Potentially there is more wood for biomass available from waste streams than from forestry in the UK. The Forestry Commission's woodfuel strategy for England aims to put an additional 2M tonnes a year of woodfuel on the market by 2020. However, most fuel-grade material goes to other users such as paper mills. Therefore, biomass fuel for the UK market is being sourced from further afield like Canada and the Baltic States.

Rising landfill tax and local authority targets to divert biodegradable waste from landfill mean the drivers for developing a waste wood supply chain are becoming compelling. Key will be overcoming some of the associated issues like sorting waste wood, removing foreign objects such as bricks and metals and removing treated timber.

There is misunderstanding about the types of waste wood that can be burned in power plants without damaging equipment or exceeding waste incineration directive emissions limits. Contaminated waste wood can often only be used as fuel in dedicated waste wood fired power plants or CHP plants which are equipped with air pollution control equipment similar to that of energy-from-waste plants.

Technology developments and years of operating experience in Europe are steadily improving the efficiency of first generation mixed waste and biowaste fired power plants. Second generation techniques such as gasification and pyrolysis are maturing too. Additionally more merchant plants are being developed that utilise energy crops such as miscanthus, a tall perennial grass with a thick stem, and short rotation coppice - densely grown trees.

Here the complexities surrounding ROC eligibility are paramount. Similarly, third generation processing such as the gasification or digestion of algae, advanced digestion of wood waste or energy crops all offer tantalising glimpses of what the future might offer. Again, a careful understanding of the mass balance of systems, carbon lifecyles, technical reliability and suitability for purpose will be crucial to secure the long term success of biomass.

Marcel Goemans is business area manager for waste and renewable energy at MWH

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