ESB International - O&M Case Study: Design Out Process
Design out of Exhaust Duct Problems on Frame 9E plant
Background
A 2-2-1 CCGT plant which has 2-shifted for many years, accumulating multiple starts each year. The Gas Turbine is a hot end drive machine which requires the exhaust gas to turn through 90 degrees prior to entry into the HRSG. This results in considerable turbulence which has a negative impact on exhaust ductwork life and integrity.
The first cracks in the exhaust duct were reported as early as 2000. Despite on-going repairs, which only proved to be temporary, there was a high risk to personnel safety due to hot surfaces and hot air (> 500°C), as well as to plant availability and reliability.
Process
ESBI undertook a comprehensive design review which recommended complete redesign and replacement in the 2008 overhaul.
Key design parameters included:
- Cold casing (insulation on the outside only)
- Floating liners
- Flue gas temperature 650°C
- Noise not greater than 80dB
- Casing temperature = ambient temperature plus 20°C
- Project under CDM Regulations
A business case was prepared and the board approved the investment in April 2007.
The termination points were:
- gas turbine exhaust plenum expansion joint flange
- diverter damper box expansion joint flange
- foundation steel work
Three duct suppliers were invited to tender and the contract was awarded in mid 2007.
Outcome
The project was completed on time and on budget during a planned outage in 2008. One year later, the new exhaust ducts are operating in a most satisfactory manner.
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