Case Studies
Flue Gas Desulphurisation Environmental Impact
A £170 million investment in Flue Gas Desulphurisation (FGD) at Longannet Power Station will reduce emissions of sulphur dioxide SO2 by more than 90%.
The project, which will be implemented over the next three years, will bring the Fife station in line with tightening European Union emission requirements, as specified in the Large Combustion Plant Directive (LCPD). Three of the coal fired plant's four 600 MW units are being fitted with a Seawater Scrubbing Flue Gas Desulphurisation system that capitalises on the plant's coastal location. Flue Gas Desulphurisation is regarded as "Best Available Technique" for abatement of
sulphur dioxide under the terms of the Pollution Prevention and Control Regulations.
Seawater Scrubbing Flue Gas Desulphurisation works by using seawater's inherent alkaline properties to absorb and neutralise acidic SO2, which is associated with acid rain. Longannet uses vast quantities of water from the River Forth as cooling water for its condensers. This estuarine water will be brought into close contact with the station's flue gases to absorb the SO2, resulting in a harmless soluble sulphate (SO4) that can then be discharged back to the river. This process results in only a slight increase of sulphate - well within natural variations - in the seawater returned to the river and, within a very short distance of the point of discharge, the difference from background levels is undetectable. The process does not require the addition of any chemicals - only seawater and air are used - and the discharged seawater complies fully with environmental regulations.
Unlike other Flue Gas Desulphurisation systems that use limestone, Seawater Scrubbing does not have the problem of disposal of gypsum slurry. Although waste gypsum can sometimes be sold as a by-product for plasterboard manufacture, it is not always of saleable quality and can cause environmental problems to dispose. The adoption of Seawater Scrubbing Flue Gas Desulphurisation at Longannet represents the largest deployment of the technology anywhere within the UK and trials have suggested that more than 90% of all SO2 emissions will be captured.
ScottishPower Chief Executive Philip Bowman said: "We believe that installing Flue Gas Desulphurisation provides both a good investment opportunity and tangible environmental benefits. "It will help us to maintain a balanced portfolio and will also contribute significantly to the security of energy supply in Scotland with the potential for Longannet's life to be extended beyond 2020."
In addition to the main Flue Gas Desulphurisation project, Longannet's units will be fitted with
Boosted Over Fire Air (BOFA) - an emissions reduction technology that tackles oxides of nitrogen (NOx) - in a concurrent project. Under the Large Combustion Plant Directive (LCPD) and the Integrated Pollution Prevention Control (IPPC) regulations, NOx levels must also be reduced in order to comply with increasingly stringent controls.
Longannet has operated a similar system, Gas Reburn, on Unit 2 since 1996 however installing Boosted Over Fire Air (to all four Longannet units will ensure compliance at the plant until 2015 when NOx emissions are set to be further reduced.
