New England power plant reduces maintenance and improves accuracy
A 400 megawatt power plant in New Hampshire, which burns both natural gas and low-sulphur fuel oil, has recently installed a Rotork CVA electric control valve actuator to help to reduce maintenance costs and improve accuracy in a demanding outdoor fuel oil flow control application.
The Rotork quarter-turn actuator (model CVQ 1200) in a NEMA 6 enclosure was installed in June. It replaced a traditional I/P positioner and spring diaphragm pneumatic actuator operating a 6-inch class 150 ball valve. The valve and actuator are located outdoors and control the flow from a fuel oil day tank to fuel oil pumps. The valve modulates frequently to maintain the correct flow as the load on the unit changes.
Both the New England weather and the accurate control of oil flow pose rigorous challenges. According to plant personnel, the traditional pneumatic spring-diaphragm actuator required frequent maintenance and was prone to accuracy problems. Since its installation, plant personnel report they are impressed with the CVA’s performance. Specifically, they report that the maintenance and accuracy problems have been resolved. Furthermore, the plant’s instrument and control technicians and supervisor liked how easy the CVA was to set-up and calibrate.
After initial set-up, they conducted several tests of the CVQ’s performance from the control room using their DCS. The position was monitored in the field using a PDA. They found that their CVQ model responded very accurately, with no deviation, to a wide range of different DCS set points, matching them all.
CVA actuators provide extremely precise control valve operation with repeatability and resolution performance at <0.1% of full scale. In addition, they include, as a standard feature, wireless Bluetooth communication technology that can be used for quick and easy actuator set-up and adjustment.
Plant personnel also did extensive tests on the fail-closed feature and verified proper performance in both loss-of-power and loss-of-input-signal situations. CVA actuators utilise a built-in super-capacitor that provides an advanced, programmable method for fail-to-position protection.
Another feature that plant personnel like is that all Rotork CVA actuators incorporate a data logger, which provides an extensive record of such operational and maintenance-related data as valve torque profiles, dwell times, and statistical information.