Upgrade in Steam Balancing Valve Actuators at Combined-cycle Power Plant Lead to Kinetrol

The customer for this application note is an electrical power station with a combined-cycle, natural gas-fired generating unit with two combustion turbines, two heat recovery steam generators and one steam turbine. The output of combustion turbines can vary at different times throughout the year. The nominal output for this facility is 577 megawatts. The station burns natural gas.

A combined-cycle power plant uses a gas and a steam turbine together to produce up to 50% more generated electricity, using the same fuel, when compared to a traditional simple-cycle plant. The gas turbine waste heat is routed to the nearby steam turbine which, in turn, generates the extra power.

One of the most common components for managing high-pressure steam in a combined-cycle plant is the HRH bypass valve (HRH stands for "hot reheat"). Since the valve actuator controls the valve’s ability to reliably and accurately respond to system demands, it can be argued it is one of the most important elements in the steam bypass system, and therefore the entire combined-cycle plant.

In this application, the customer had two 18" steam balancing valves using large, high torque, scotch-yoke actuators that had to cycle 20 times a day. These actuators presented significant performance issues (they were failing), plus they were very large which presented maintenance difficulties.

The customer approached the local Kinetrol USA Distributor and inquired if they could suggest a better alternative. The goal was to provide replacement actuators that provide very high torque, be highly reliable, and save space.

The Distributor recommended Kinetrol Model 30 pneumatic rotary actuators. The Model 30 provides 168000 lbf ins (19140 Nm) at 100 psi (7 bar) of torque and were significantly smaller and lighter than the legacy scotch-yoke actuators. Most importantly, they carried the world-renowned Kinetrol reputation for outstanding reliability, long life, and maintenance-free operation.

Kinetrol USA
https://kinetrolusa.com
972-447-9443

Challenging Steam Balancing Valve Application at Southwest Power Plant

Steam balance valve
with Kinetrol model 30.

In combined-cycle power generation plants, the most common design for managing high-pressure steam is with cascading bypass systems. Balancing valves are used on the hot reheat line to respond to control loop demands. The application is difficult because of high pressures, high temperatures, and large valve sizes (high torque). The valves must shut off tightly and also be capable of precise throttling.

Outfitting these valves with pneumatic actuators is also difficult. Because of the valve size and valve design, actuators must have high torque output, without taking up vast amounts of space. The actuators must also act quickly and eliminate hysteresis.

Most pneumatic actuator designs simply cannot meet the operating and size restrictions, and hydraulic actuators, with all of their associated maintenance problems, are used instead.

A Kinetrol Distributor in the Southwest USA was asked to recommend a better alternative to a line where very large scotch-yoke actuators controlling two (2) 18" valves were controlling poorly and were taking up too much space.

The Distributor's challenge was to:

• Deliver very high torque output.
• Provide as small a package as possible.
• Improve the actuators stability and reliability.

The solution was to apply Kinetrol model 30 vane actuators. The model 30's deliver 168,000 lbf (at 100 psi) of torque in a compact envelope (comparatively). Additionally, the Kinetrol Model 30's, combined with third-party digital valve positioners, provided the precision and response the application required to eliminate oscillations and instability.  The actuators cycle about 20 times per day and have been performing without problem for years. Huge annual fuel savings can be directly attributed to the actuators reliability and precision due to fewer turbine restarts.

Power plant steam balancing valves in service.

For more information, contact Kinetrol USA by visiting https://kinetrolusa.com or by calling 972-447-9443.