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Engine & Turbine Technology 


Fogging system provides maximum power boost without compressor damage


Kelly Oeffinger reports how to correctly design nozzles and control systems to minimise blade erosion.


G


as turbine inlet fogging has long demonstrated its ability to increase output, while lowering fuel costs and emissions. But as one Latin American power plant learned, not all fogging


systems are the same. System and nozzle design and operation are not only critical to obtaining the greatest power boost, but also for continued safe operation of the turbine. A poorly designed system leads to excessive erosion and eventually catastrophic failure. Te early 1980s vintage power plant contains four


Siemens Westinghouse W501 D24/D5 Gas Turbines in a 2 x1 combined cycle configuration – one block producing 290MW and the other 309MW. To boost output, in 2005 they installed fogging systems from a


34 www.engineerlive.com European manufacturer.


Te fogging system could inject about 16,000 litres of water into the inlet air stream, with a guaranteed power increase of 10 per cent. To achieve this result, the fogging system used overspray, injecting more water into the airstream than could evaporate before entering the compressor. Te fogging units did produce the desired power boost, but also produced severe turbine damage. Within four years of installing the fogging system, an unusual noise was detected in Unit 2. Te unit was brought off line and a subsequent inspection found that one of the fog spray nozzles had broken loose and damaged the blades and diaphragms on compressor Stages 1 through 19. Shortly thereafter, that same unit


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