Biomass in Scotland: Taking the high road

E.ON inaugurated its new 44 MW Steven’s Croft biomass plant near Lockerbie, Scotland on 18 March. Project manager Andy Carling explores how the UK’s biggest wood fired power station will play its part in Scotland’s long-term plans to become self-sufficient in renewable energy.

Andy Carling, E.ON, UK

On a clear afternoon in January 2006, E.ON UK Chief Executive Paul Golby officially broke ground on Steven’s Croft power station near Lockerbie, Scotland. Just over two years later, on a similarly clear afternoon on 18 March, the à‚£90 million ($178 million), 44 MW project was opened by First Minister of Scotland Alex Salmond. Built on time and on budget, Steven’s Croft is the biggest biomass plant in the UK and will generate enough electricity to power the equivalent of 70 000 homes every year.

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In recent months biomass has started to gain a higher profile, but it is still much less well known than its renewable cousins, wind, wave, and solar energy. Being carbon neutral, it is classed by the government as a renewable fuel and is part of the UK government’s Renewable Obligation Scheme, which encourages a more sustainable approach to energy use. The government has said that 15 per cent of electricity supplied in the UK must come from renewable energy sources by 2015. With this target in mind, E.ON is investing more than à‚£1 billion in renewable energy projects in the UK over the next five years.

At the Steven’s Croft opening ceremony, E.ON Climate & Renewables Chief Executive Frank Mastiaux described the scheme as a major step forward for the company and for Scotland. He said that it “is a pioneering project, which offers huge benefits to the local community as well as to the battle against climate change”. When built, the power station could displace the emission of up to 140 000 tonnes of greenhouse gases every year.

As one of the leading power and gas companies in the UK, E.ON, which generates, distributes and supplies electricity to millions of homes across the country, takes its leadership position and responsibility to the environment very seriously.

David Rogers, E.ON’s head of renewables in the UK, said: “As one of the leading renewables businesses in the UK, we’ve a major part to play in helping the government meet its tough targets on renewable generation. Building this biomass plant at Steven’s Croft will produce 44 MW of carbon-neutral, green electricity à‚— which is a fantastic step in the right direction.”

Initially the power station will use a mixture of biomass fuels derived from forestry co-products such as sawdust from local saw mills.

Rogers said: “The station will require 480 000 tonnes of biomass each year. Our initial contracts are likely to be for sawmill co-products and small round wood. Within four years of operation, it’s expected that around 90 000 tonnes a year will come from willow harvested by local farmers.”

Ensuring that the fuel contracts and supply were just right has been a careful balancing act for E.ON UK. They have sourced local suppliers that can provide wood by-products, and AW Jenkinson Limited, a wood fuel processor and logistics company, will manage the fuel supply chain, providing around 80 per cent of the station’s fuel.

Renewable Fuels Limited, a specialist in energy crop development, will supply E.ON with short rotation coppice (SRC) willow wood chip, which they plan to contract from local farmers and landowners close to the station and will eventually account for around 20 per cent of the station’s fuel requirement.

To ensure smooth running of the fuel supply and generation sides of the station, it will be made up of two adjacent sites, with one dedicated to fuel processing and the other being the actual generation plant.

The fuel processing plant allows for the preparation and storage of the wood chip fuel. As it arrives, it is stored according to fuel type and fed into a processing system, which is designed to mix the fuel streams to provide the right fuel mix to the generating plant. The wood chip is then screened to remove larger pieces of wood and is put through a magnetic separator to remove metals that might have become mixed in with the wood. It is then be conveyed to a two-day buffer store, before entering the generation plant, which allows control of the fuel feed rate and further mixing of the fuel.

Flexible and Efficient Combustion

The power station will burn this sustainable fuel using a very efficient and flexible combustion process known as a fluidized bed combustion process. In this process, the fuel is fed onto a bubbling sand bed, where it is burned to maintain a combustion chamber temperature of approximately 850 à‚ºC. The heat from the combustion process is used to raise steam, which is then used to generate the plant’s 44 MW power output.

This bubbling fluidized bed combustion offers excellent fuel flexibility and efficient combustion, as well as very low emissions. Staged combustion, limestone and activated carbon injection, together with filters, is used to clean the combustion gases before being released into the atmosphere.

E.ON UK is not new to biomass generation. Since 2003 it has been co-firing biomass alongside coal at its Kingsnorth power station in Kent and Ironbridge power plant in Shropshire. At the latter site, a range of biomass fuels such as wood, cereal co-product and milled palm nuts have been used to produce enough green electricity to power around 250 000 homes.

Rogers said: “We’ve learned a lot from the co-firing process and the new dedicated station at Steven’s Croft will give us the opportunity to develop the technical skills we’ve already acquired. We’ve recently submitted a planning application for a 25 MW biomass plant in Sheffield and the lessons learned at Steven’s Croft put us in a good position.”

The biggest of the National Lottery distributors, the Big Lottery Fund, supported the development of the Steven’s Croft biomass plant with a sizeable grant from the Bio-Energy Capital Grants Scheme. However the power station will also see a further significant investment in local and regional economy by E.ON.

It is estimated that Steven’s Croft will create 50 direct jobs and help to maintain up to 300 indirect jobs in the local forestry industry. Local farming will also benefit form the long term, low risk energy crop initiative being developed by E.ON.

Successfully building the Steven’s Croft biomass station will be another landmark for E.ON UK’s renewables business. It already has 21 operational wind farms across the UK and owns the largest hydro power station in England and Wales. To continue this pattern of growth, the company has enough renewable energy projects currently in development to power more than a million homes and displace the emission of two million tonnes of carbon dioxide every year. E.ON is currently building the 180 MW Robin Rigg offshore wind farm in the Solway Firth and is part of a consortium looking to build the London Array, which at 1000 MW would be the world’s biggest offshore wind farm in the world.

Looking to the future, Rodgers said: “Getting Steven’s Croft up and running has been one of the cornerstones in our renewables strategy. Now we’re looking to build on those successes and will continue to work towards helping the government meet its tough renewable energy targets.”

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