Control and Monitoring of the Feed Water Circuit in Coal-Fired Power Stations

The steam generated in a power station to drive the turbines is converted into liquid water after the last turbine stage. This process takes place in a capacitor, and cooling water is pumped into the capacitor via a pipework system. The steam condenses as a result of the temperature difference and is collected as feed water. A pump then feeds this back into the pipes in the boiler.

The fill level of the feed water reservoir and the delivery rate of the feed water pump are monitored to prevent fluctuations or any interruptions in steam generation. The temperature of the preheated feed water is also measured, as it can be used as an input value for the burner control system, for example. It is also important to measure the conductivity of the demineralized feed water, which must be supplemented regularly due to evaporation losses in the cooling tower. Ensuring the upper limits of the salt content not only prevents corrosion, but also deposits in the heat exchangers that prevent heat transfer and result in occasional overheating.

K-System interface modules, featuring galvanic isolation and functional safety up to SIL3, transmit signals between individual system components and the control room without any interference. Signal conditioners without explosion protection certification are generally used in feed water processes. With the K-System, any requirements that arise can be handled using modules from one portfolio. The SC-System, which features modules just 6 mm wide mounted on a DIN mounting rail, is compact and efficiently produces galvanic isolation between the field and control side, making it suitable to transmit analog values.

To prevent fluctuations in steam generation, frequency converters and transmitter power supplies are used to monitor the rotational speed and pressure of the feed water pump. In addition to measuring the rotational speed, frequency converters also offer slip and rotation direction detection. Also conductive switch amplifiers are used to determine the fill level in the feed water reservoir. This ensures a continuous supply of feed water. Temperature converters measure the temperature of the feed water. Suitable field devices in conjunction with transmitter power supplies continuously monitor the conductivity of the feed water.

• Transmitter power supplies and frequency converters monitor the pressure and rotational speed of the feed water pump respectively, preventing fluctuations in the water circuit.
• A conductive switch amplifier constantly monitors the fill level in the feed water reservoir.
• Temperature converters for thermocouples, potentiometers, and resistance thermometers ensure the temperature of the preheated feed water is monitored.
• Transmitter power supplies assist in the continuous monitoring of the feed water quality.