Environment - Powered up for the green challenge06 June 2005
Ratcliffe-on-Soar Power Station was constructed during the late 1960s, with the final unit being commissioned during 1970. All units have achieved over 230,000 running hours; at present they are required to operate to a mixed running regime, where plant can be required to generate continuously (base load in winter time), two shift operation (during summer) or peak lopping (at holiday periods). Since that time, the station has had to meet the challenges arising from developments in environmental legislation.
The Large Combustion Plant Directive (LCPD), which initially came into force in 1988 and was subsequently revised in 2001, limits the emissions of certain pollutants (SO2, NOx and particulates) into the air from power stations and other installations. In order to reduce NOx, modified coal burners were installed in each boiler front at the Ratcliffe station - a programme that was well under way by 1987. Between 1989 and 1993, necessary improvements were made to all the unit electrostatic precipitators, which remove particulates from boiler flue gas. This was followed by a £250m retrofit of flue gas desulphurisation (FGD) plant to each unit, which was commissioned between 1993 and 1995.
In the FGD process, flue gas enters an absorber and comes into contact with a limestone slurry mixture; a chemical reaction occurs, converting the limestone into calcium sulphite (the limestone slurry also removes up to 95% of the hydrogen chloride present). Injection of compressed air oxidises the calcium sulphide to gypsum (calcium sulphate). The gypsum produced is de-watered in centrifuges to give a high-grade product suitable for commercial use, principally the manufacture of plasterboard for the building industry.
The FGD plant dramatically reduces SO2 emissions by at least 90%. The plant also reduces other flue gas pollutants including fine dust and heavy metals - including mercury - by a significant amount. However, the operation of the FGD process results in a small increase in CO2 emissions. The government's long-term policy is to encourage the efficient use of energy and to lower carbon emissions by around 5 Mt/year by 2010, so reducing the impact of climate change. Electricity generated from qualifying renewable sources - including the biomass fuels burnt at Ratcliffe - qualifies under the Renewable Obligation for Renewable Obligation Certificates (ROCs). At Ratcliffe, biomass fuels (co-cereal product and wood pellet) are introduced to the total boiler fuel supply without adverse effect on thermal performance.
To achieve the reductions in CO2 emissions agreed by EU member states under the Kyoto Agreement, the EU has established an Emissions Trading Scheme (ETS). The first stage of the EU ETS began in January 2005. Under EU ETS, all eligible plants are required to monitor emissions of CO2 and surrender allowances equal to their reportable emissions for the year by the end of the following April. The allowances are tradeable: operators can buy credits from participants across Europe who have cut their emissions by more than they needed to hit their targets. E.ON UK has fully integrated CO2 emissions trading into the day-to-day trading activities, which are managed from its headquarters in Coventry.
Looking further ahead, the revised LCPD (2001) seeks to further reduce NOx, SO2 and particulate emissions from 1 January 2008. From this date, existing plants must comply with either prescribed emission limit values (ELVs), and/or will be subject to a National Emission Reduction Plan (NERP). To comply with the reduced levels of NOx emissions required, Boosted Over Fire Air (BOFA), where some of the air from the Forced Draught duct is, with additional fan assistance, admitted higher up the furnace than the windbox, has been installed on No 1 Boiler, in conjunction with further modified burners. It is intended to install similar equipment on the remaining boilers prior to 2008.
Some generators have chosen to opt out their plants from the LCPD, as the age and condition of their plant does not merit the expensive refurbishment required. These plants are permitted to operate for a maximum of 20,000 hours during 2008-15, and must close by the end of 2015. However, as the government has not yet decided how the Directive is to be implemented in the UK, it has allowed plant that had opted out by 30 June 2004 the option to opt back in before 31 December 2005.
This article was written following a visit by SOE East Midlands Regional Group members and guests to Ratcliffe-on-Soar Power Station, owned and operated by E.ON UK plc. Our thanks to our hosts John Pacey (plant manager) and Howard Simmons (shift team leader).
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