Throughout the steam generation system of a coal-fired power plant, there are numerous opportunities to measure and improve process conditions. Using accurate, reliable level control instrumentation is a key way to improve the safety and efficiency of the entire steam generation process. However, to achieve precise level measurement, it is important to understand the application challenges that exist within this process flow, which is illustrated below.
In this post, we’ll discuss how level control technology can help you achieve accurate level measurement for critical applications within steam generation systems, including the condenser hotwell, condensate storage tank and deaerator.
Steam enters the condenser, where it cools and condenses into water before being sent to a low-pressure feedwater heater. The condenser hotwell serves as a water reservoir for the turbine cycle. When the hotwell level reaches the low point, a valve opens to supply make-up water to the cycle. When the hotwell level reaches the high end of the level range, a dump valve opens to move the condensate from the hotwell to a condensate storage tank.
Water loss in the turbine cycle due to leakage, steam venting or other usage depletes make-up water. Level control in the hotwell ensures adequate make-up water is supplied to the cycle or diverted to storage.
An Eclipse® Model 706 guided wave radar (GWR) or displacer transmitter, such as the E3 Modulevel®, is the most suitable continuous level control technology for a condenser hotwell, while a float-actuated switch, such as the Magnetrol® Model B40, can provide the point level control that this application requires.
Condensate Storage Tank
When the condenser hotwell level reaches the high point, a dump valve opens to drain excess condensate from the hotwell to a condensate storage tank. When loss of condensate from the turbine cycle is reflected in a low level in the hotwell, a make-up valve opens in the storage tank to supply make-up water to the condenser hotwell.
Proper functioning of the liquid level control in the condensate storage tank ensures the proper supply of make-up water. A Model 706 GWR transmitter, pulse burst radar transmitter (such as the Pulsar® Model R95) or non-contact ultrasonic transmitter (such as the Echotel® Model 355) can provide a reliable continuous level control solution for a condensate storage tank. For point level control, displacer-actuated switches, such as the MAGNETROL B10 or B15, are recommended.
The deaerator is an open-faced water heater that removes non-condensable gases from feedwater. In addition to the condenser hotwell, the deaerator’s storage tank is the remaining reservoir in the turbine cycle. Positioned below the deaerator and before the boiler feed pumps, the deaerator storage tank serves as a surge tank for the boiler feedwater. Tank level is often controlled by a control valve on the condensate supply line to the deaerator.
Pressure fluctuations are extensive in the deaerator storage tank and result in flashing. Level controls must contend with the tank’s fluctuating temperatures and pressures.
The most frequently used continuous level control for this application is GWR (such as the Model 706), while an external cage float-actuated level switch, such as the MAGNETROL Model B35 with ASME B31.1 construction, can provide point level control for this application.
Follow Our Level Control Discussion
Next week, we’ll examine how level controls can provide an effective solution for combined-cycle power plants. For more information on this topic, you can also download our guide to level instrumentation for power generating plants.