The pounds 640m flue gas desulphurisation (FGD) equipment removes about 90 per cent of the sulphur dioxide from the 4,000 megawatt coal-fired station's exhaust fumes. The gas is a leading air pollutant and a major contributor to acid rain, which damages forests and buildings.
The shut-down is due to cracks in the 12 gigantic fans, each 15 feet across, which blow the hot gases through the station's six FGD units. They were discovered during emergency checks made after a similar fan at an Italian power station shattered at speed.
Inspectors found that all of Drax's fans were failing, but while some had only tiny cracks others had spread more than halfway through inch- thick steel. The steel structures carry vast stresses, since they each weigh 11 tons and spin at 10 revolutions per second.
All the fans, built by Howdens in Belfast, will now have to be replaced.It could take two years to complete the job and will cost millions of pounds.
Under its authorisation - or licence to pollute - from the Government's Environment Agency, Drax can produce 100,000 tons of sulphur dioxide a year. But with the FGD out of action, the power station will break this limit by mid-summer if it carries on burning coal.
National Power has applied for a temporary increase in annual emission levels up to 270,000 tons. The agency has not yet decided whether to grant this, but has asked the company to explain how it will get the FGD equipment repaired as fast as possible.
The company said it was vital that Drax was allowed to carry on working, even though its pollution output was now much higher. "The fact is, that even with the FGD out of action, it is still one of the two cleanest coal- fired power stations in Britain," a spokesman said. It is a modern, high- efficiency plant using low-sulphur coal from the nearby Selby pit. The only other British power station with FGD is PowerGen's Ratcliffe on Soar plant in Nottinghamshire.
Don Ridley, the Environment Agency manager handling the Drax shutdown, accepted this argument for keeping Drax running. "But we also want to ensure pollution is minimised," he said. He hopes that some of the FGD units whose fans have the smallest cracks can be put back into action while the others are being replaced.