Actuators help fans cut power station emissions

Paul Boughton

ABB has supplied six rotary electric actuators worth over £40k as part of a major project to improve the environmental performance of a 2000MW coal-fired power station in the UK.

The actuators were supplied to Halifax Fan of Brighouse in West Yorkshire, which is providing six fans to help reduce emissions of nitrogen oxides (NOx) from three power station boilers.

The emissions reduction project – known as BOFA, or Boosted Over Air Fire - is being introduced because the Large Plant Combustion Directive (LPCD) requires the power station to cut its emissions of NOx to less than 500 milligrams per cubic metre by 2008.  NOx is produced as a result of high-temperature combustion processes and the BOFA system cuts the level of NOx released into the atmosphere by enabling the power station to burn coal at a lower temperature.

BOFA works by forcing air into a higher section of the boiler. This 'over fire' air is injected into the boiler above the main burner, where it mixes with the tails of the flames to cool the hot gases. The boosted air is transported from the secondary air duct to the air duct at the top of the boiler by two fans mounted at the base of each boiler. The units supplied by Halifax Fan are almost 2.5 metres in diameter. They handle up to 370,000m3/hr at a pressure of 4400 Pa.

The six ABB RHD8000 Contrac electric part-turn actuators control the pitch of the vanes on the BOFA fans. The BOFA actuators apply a force of up to 8Nm to move the fan vanes by up to nine degrees per second. RHD-range actuators are ideal for operating this type of control element, which has a 90° rotary movement.

The six actuators currently being supplied follow an earlier order for two actuators, which have been operating trouble-free at the same power station for around 18 months. “The power station specified ABB actuators because they already use them and know they’re reliable. We’ve had no problems at all with the ABB side of things,” says Ian Crum, project manager for Halifax Fan. “The latest order required a delivery schedule of just four weeks for the actuators, but ABB met the challenge.”

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