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Finding answers with short-rotation forestry

A biofuel plant at Benburb in Northern Ireland
A biofuel plant at Benburb in Northern Ireland
A United Kingdom SME joined forces with a Swedish research institute and UK and Irish trade associations in this FAIR CRAFT project to improve biomass-fuelled combined heat and power (CHP) generation technology. Between them, the partners researched supply strategies, resources and markets for forest residues and short rotation forestry. Building on this, they developed technology to improve the efficiency and environmental acceptability of CHP generating units. Extensive market research has allowed them to better understand customer requirements. As a direct result of this work, a new, carbon neutral plant is being commissioned in London.

The principle of using biomass technology in power generation is well understood: instead of burning non-replaceable fossil fuels that increase the level of atmospheric greenhouse gases, wood or vegetable matter is used instead. Careful husbandry of the resources – in particular ensuring that for each tree felled another is planted – ensures that there is a continuing carbon 'sink' effect. The new tree absorbs the carbon dioxide produced when the one it replaced is burned. The result is that biomass power generation has no net effect on carbon dioxide levels.
That is the theory but, in practice, there are problems to be solved. Selecting the right fuel is one, whether it is felled trees from short rotation forestry, 'brash' – debris normally found on forest floors – or even the residues resulting from trimming roadside verges or the results of cosmetic tree surgery in parks. All are potential fuels, but they vary in water content and calorific value. The gasifier systems – in which the fuel is burned in a controlled atmosphere, to extract combustible gases to drive spark ignited gas engines that in turn drive electricity generators – must be optimised. The design of the internal combustion units is critical.

Working from the bottom up

"The challenge starts - literally - at ground level," says Peter Kernohan. "To implement a viable biomass energy project, the first thing you need is the biomass. We can, for instance, think of using brash as a fuel, but this has implications for the amount of soil nutrients present. Brash would normally rot down and provide soil nutrients for the trees it surrounds. If we remove it, the soil quality could potentially drop, hindering future tree growth. However, removing brash helps replanting."
Mr Kernohan is a member of the technical team at the Northern Irish SME, B9 Energy Biomass, which, as its name implies, concentrates on such issues. "There are other concerns to be addressed," he continues. "The foremost is the economic viability. Can a generating unit using biomass effectively compete with fossil fuels? Can farmers be persuaded to turn arable land currently under Common Agricultural Policy set-aside over to forestry use – something which is often viewed as a backward step? How is the transportation of the fuels going to be organised? After all, you can't pump wood down a pipeline."
B9 Energy Biomass decided that it was about time these questions – and others – were answered. Being an SME, however, they did not have the resources to go it alone: they needed to share the risk. The CRAFT scheme is specifically designed to help groups of SMEs to solve their problems through joint sub-contracted research. So they recruited a consortium of SMEs and trade associations in the United Kingdom and Ireland, along with a Swedish research institute, and formulated a CRAFT proposal under the FAIR (Fisheries, Agriculture and Agro-Industrial Research) programme.

Four-dimensional research

"The research was carried out concurrently, in four distinct areas," explains Mr Kernohan. “First, we needed to investigate and develop forest residue supply, resource and marketing plans. A similar exercise was carried out for short rotation forestry. The third task was to improve the generating efficiency of the gasification and engine technologies, and to make them more environmentally acceptable and suitable for these new fuels. Finally, the team carried out market surveys and formulated strategies to broaden the application of the conversion technology."
The partners now have a thorough understanding of the requirements for a successful biomass electricity and heat generation plant. Efficient and cost effective harvesting and transport strategies have been developed. Interestingly, wood fuel transport costs significantly affect viability, and the financial figures do not stack up if the fuel has to be carried long distances to the generating plant. The efficiency of the gasifiers and internal combustion engines has been improved, and emissions from the new designs are well inside EU limits.

Power to the people

"We are satisfied with what we and our partners have achieved," says Mr Kernohan. "We now have a much better appreciation of all the questions involved in biomass technology." B9 has reason to be pleased. It recently finished building, and is now commissioning, a fully automated 130 kW wood-fuelled Combined Heat and Power (CHP) unit at the Beddington Zero Energy Development (ZED) in Sutton, London, based on the technology developed in the project. The plant, which has created 1½ jobs, is entirely fuelled by the cuttings produced by tree surgery operations in London, which would normally be disposed of in landfill – at a cost. "The Beddington ZED energy supply is carbon neutral and environmentally sustainable," says Mr Kernohan, "and is showing much greater fuel efficiency than fossil fuel power stations. Typically, they are less than 30% efficient in energy production. This new biomass plant runs close to 75%."

Project Coordinator: Peter Kernohan/Debra Jenkins
Telephone: +44 28 7127 1520
Address: B9 Energy Biomass Ltd, Unit 22, Northland Road Industrial Estate, Londonderry BT48 0LD


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