The Longannet coal-fired power station in Central Scotland is one of the largest plants operated by Scottish Power. Each of its boilers generates approximately 600MW of power. The “dirty” flue gases exiting the boilers pass along ducting encased by insulated cladding. These ducts convey particle-laden gases into electrostatic precipitator (ESP) units. The ESPs remove fine, silica-based fly-ash from the warm gas before it exits the plant through a central chimney.

The analyses focused on redesigning the ESP manifold bend and turning vanes to minimize fly-ash buildup and erosion from particle-laden flue gases

Just prior to Longannet’s summer shutdown of its Number 1 Boiler, the plant engineers asked Fluent Europe’s consultants to propose a redesign of the existing ducting with the aim of improving performance. The aim of the study was fourfold:

1. To minimize pressure drops in the flue gas ducting, which would, in turn, allow more power to be generated from the boiler.
2. To maintain the existing external infrastructure of the ducting, although internal modifications could be made.
3. To modify the turning vanes in the ductwork that were being selectively eroded by the particle-laden flue gases. Any changes must include recommendations for reinforcing certain vanes and provide designs that would reduce maintenance during future outages.
4. To reduce the number of vanes (and, therefore, reduce the costs) based on the CFD study, as long as the walls of the duct were protected and performance was not compromised.

Multiple CFD simulations were carried out, depicting the original ductwork, the original ductwork without vanes, and the redesigned ductwork based on CFD simulations. Fluent Europe consultants worked closely with plant personnel and recommendations were made in advance of the plant outage.

The CFD study ultimately pointed to fewer, longer vanes strategically placed in bends as being the best option. The number of turning vanes incorporated into the ducts was reduced by two thirds. Together with the insertion of curved “false” corners in selected bends, these changes improved both pressure drop and flow distribution.

Recommendations as to where to reinforce the new longer vanes were also made, following extensive dispersed phase particle tracking simulations in FLUENT. This part of the study highlighted points of high particulate impact and thus, likely areas of high erosion.

Once the boiler was re-commissioned after the outage, gas flow rates through the flue gas ducting increased significantly and a 10 percent power generation improvement within the boiler, partly due to the CFD analysis, was noted. Planned maintenance shutdowns have already shown excellent vane performance. The plant has experienced considerable savings – not only through reduced maintenance time compared with the original ductwork, but also through the upgrading of the other boilers’ ducting during successive annual outages.

FluentNEWS