Product category:
Process and OEM Valves
News Release from: Emerson Process Management - Fisher Valves | Subject: Steam conditioning valves
Edited by the Engineeringtalk Editorial
Team on 01 March 2004
Replacement valves cut out power plant
trips
Emerson Process Management has supplied Fisher steam conditioning valves to Sutton Bridge Power station.
Emerson Process Management has supplied Fisher steam conditioning valves to Sutton Bridge Power station Operational since May 1999, Sutton Bridge is a 790MW combined cycle gas turbine plant, owned by EDF Energy
The new Emerson valves replace competitor valves that had become unreliable and were contributing to plant trips that were costing in the region of GBP 200,000 per annum; in addition the existing valves were prohibitively expensive to overhaul each year.
Steam conditioning by high pressure turbine bypass valves is critical to the efficient operation of power stations of this type.
The valves route steam around the turbine during startup, shutdown and load disturbances so that circulation is maintained within the water/steam process.
This prevents water carry over into the turbine, a potentially damaging occurrence, as well as allowing stable operation of the boiler at startup and shutdown.
Turbine bypass valves also cool the steam to a temperature slightly above the HP turbine exhaust temperature by injecting water droplets into the steam flow.
"We found that the high pressure turbine bypass valves were not operating as they should", said Andrew Green, the Engineering Manager for Sutton Bridge Power station..
"We knew we were losing heat rate which impacts on our efficiency.
This was due to the valves leaking across their seats.
In addition the valves did not always operate under trip conditions; this caused the relief valves to lift and the gas turbine to trip.
In that particular year, it happened two or three times.
Because of the unreliability of the bypass valves we had to overhaul them each year, something we wanted to get away from".
"The cost of a full plant trip will vary depending on the imbalance and electricity prices at that time", said Trevor Thorpe, General Manager for EDF Energy (Sutton Bridge).
"Imbalance costs can vary but generally are tens of thousands of pounds.
Additional losses of revenue can be incurred from having to buy electricity in the market, rather than supplying from Sutton Bridge.
This can also be tens of thousands of pounds per plant trip.
Following a full plant trip caused by these valves it could take three hours or more before we are fully operational again".
Despite numerous attempts, the original valve manufacturer had been unable to cure the problem that was causing the bypass valves to stick and fail to operate, so it was decided to place an order with Emerson.
The control valves supplied were steam conditioning valves from the Fisher range with 12in inlet and 42in outlet connections.
The assembly included Fieldvue digital valve controllers to position the valves with high accuracy as well as providing the ability to perform control valve diagnostic and monitoring checks.
"Just after we had restarted, following our shutdown, we had a turbine trip", said Martin Jones the Facility Manager.
"Previously the valves would not have worked, the whole plant would have shut down, and it could have taken us three to four hours to get back to full production.
In this instance, the valves operated and dumped steam back to the condenser, allowing us to keep the rest of the plant running.
In this event alone the new valves must have saved costs of around GBP 60,000.
We know that it is early days, but we are hopeful that the installation of these valves has resolved our problems".
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