CVA is a 'fit and forget’ solution for power station’s sticky valve problem

The Rotork CVA electric control valve actuator has proved to be a ‘fit and forget’ solution for a challenging application in the harsh environment of a UK coal-fired power station.

The CVA actuator has replaced a pneumatic actuator and I/P convertor on one of the fuel oil purge lines for the burners at the RWE Tilbury power station.  The power station is coal fired, but oil is used to light and start the burners on the station’s three boilers.  Installed over eighteen months ago, the CVA has proved to be a ‘fit and forget’ solution, requiring no maintenance.

In particular, it has been noted that there is never a problem with sticking and overshooting, which happens with the pneumatically actuated valves on the same duty when the valve has been closed for a while and the oil congeals on the seat and plug.  In addition, the pneumatic actuators require regular maintenance, sometimes including the replacement of damaged diaphragms, all of which is eliminated through the use of the CVA.

RWE’s Kevin Wade, who is in charge of the fuel oil purge line installation at Tilbury, confirmed that “the CVA has worked above all expectations and I would be pleased to use it on other areas of the plant.”

It is estimated that there are over 500 pneumatically operated control valves in a typical fossil-fuelled power station, so the use of the CVA as an all-electric alternative presents the potential for huge savings in maintenance and repair times. The other significant benefit of the CVA is the lower use of energy. Because pneumatically operated control valves rely on an instrument air supply, compressed air has to be constantly available to operate the actuators even when they are resting at a fixed set point. The losses due to leakage, compression and transmission in an air supply system means that approximately half the input energy is lost. The CVA, being a high efficiency electric actuator, uses little energy when it moves, and the losses associated with a pneumatic supply are eliminated.