In today’s world, plants are ramping up and down daily – consequently putting a strain on steam temperature control regulation. Therefore, plants should consider constant superheat temperature control over the entire range of boiler loads. Controlling superheat temperature enables plants to maximize efficiencies and improve heat rate. Superheat temperature control can be affected by many variables such as boiler load, steam pressure instability type of fuel being burned, and type of superheater.
Each plant, depending upon its type and design, uses multiple strategies across various systems to accurately control temperature. These plants use different mechanisms to control Flue Gas Temperature in the combustion process such as tilts, burners, bypass dampers, recirculation fans, etc. Almost every plant uses superheat spray valves as the “final” control of steam temperature entering the turbine. Although temperature control loops are generally slow loops, superheat spray valves offer the fastest response to the system.
Many plants have began using feed-forward, cascade, and adaptive-predictive control strategies resulting in tighter control of superheat steam temperatures. This is in response to plants being required to cycle to lower loads more frequently. REXA Linear and Rotary Actuators are key components in helping plants achieve their efficiency goals by maximizing performance through tighter resolution, stiff repeatable positioning, and high duty cycle operation.