REXA: Steam Turbine Control

Background

Steam turbines, whether small scale or heavy-duty, are a crucial part of any processing plant or power generation facility. In processing plants, steam turbines are used as the driver for other rotating equipment, converting thermal energy to rotational energy, which ultimately controls the input speed of a driven device. Precise control and availability of steam turbines is critical for process optimization and overall plant profitability.

In power generation facilities, steam turbines assist boiler feed pump turbines, as well as turbine generator sets to generate electricity. Any detrimental impact on the performance of a steam turbine can affect boiler control, ramp rate, and/or synchronization to the grid.

Key to Success

Many of the thousands of steam turbines in use across a variety of industrial applications are decades old, therefore require upgrades to help improve operations. To do this, many plants have quantified immediate return through modernizing the controls and upgrading the actuation of these turbines.

To achieve optimal steam turbines, one needs to select a technology which offers high frequency response and precise resolution in a highly reliable package. Typical steam turbine requirements are:

• 1% repeatability
• 100% duty cycle
• <100mSec dead time
• Fail safe capability
• Ability to withstand high ambient temperatures
• Fast Stroking Speed (<1-2 seconds for full stroke)

Problem

Most existing steam turbine designs use a hydraulic system comprised of a hydraulic power unit (HPU) and servo or proportional valves for control. Although hydraulic systems are the preferred technology, these systems can be difficult to maintain and are generally unreliable.

Since traditional hydraulic systems are open-loop, utilizing an HPU, a gravity-fed reservoir, and a series of servo and/or proportional valves for controls, they utilize a high quantity of oil. Because of this, the owner faces a need for extensive oil maintenance for proper operation.

REXA’s Solution in Action

Steam turbine operators at a local power plant recently upgraded their process using REXA’s Electraulic™ actuators. Switching to these actuators for their application has already proven to be extremely beneficial. Thanks to REXA’s patented “flow match valve” (FMV) technology, our customer was able to use the FMVs in conjunction with a bi-directional gear pump within a positive pressure sealed hydraulic system, eliminating the need for a hydraulic reservoir and problematic servo and proportional valves.

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