- Steam generators play a leading role in a variety of processes: They supply generators or turbines for power generation, drive steam engines, provide energy in thermal power stations and are used in heat-consuming processing the chemicals and metal industry.
- Since steam generator functions are critical to applications and their downtime or replacement is extremely cost intensive, it is important to avoid damage due to wear by properly monitoring the water quality. The system is exposed to risks from:
- Contamination of pipelines with biological or mineral substances that adversely affect the system’s efficiency
- Corrosion of system components, that can shorten their service life and become hazardous for personnel
- Inadequate condensate monitoring, which leads to a higher number of blowdown processes and inefficient water, chemical and energy consumption.
Monitoring water quality assures steam generator performance
Using digital pH, dissolved oxygen and conductivity sensors
The heating pipes of steam generators are a special concern. Normally, steam generators are supplied with alkaline water that helps a thin oxide layer to form on heating pipe surfaces to protect against corrosion. Sodium phosphate and sodium hydroxide, for example, are added to the water to make it more alkaline. However, since too much of these substances can lead to problems, the dosage should be based on the precise monitoring of pH measurement.
Knick developed the SE 558 sensor for high-precision pH measurement in liquids with extremely low ion activity. It is typically used in ultrapure water applications and for water treatment for power generation.
Oxygen is highly corrosive: even minimal concentrations in the ppm range can corrode metal surfaces. This property has a significant influence on the service life of steam generators. This is why chemicals such as hydrazine are used to bond oxygen radicals.
The SE 707 sensor measures dissolved oxygen up to the range of the detection limit in traces of 1 ppb, allowing adequate hydrazine dosage. Defective heating pipes or overdosing of chemicals lead to concentrations of harmful substances in water that can be detected by measuring the conductivity.
Rising conductivity indicates an increase in the contamination level of the water, which must be countered by blowdown or a system inspection if necessary. For the precise, reliable measurement of low and ultra low conductivity in ultrapure, cooling and boiler feedwater, as well as steam circuits, Knick developed the SE 604 Memosens sensor with robust stainless steel electrodes in coaxial arrangement. Like all Memosens sensors, the SE 604 has an integrated temperature detector for precise temperature compensation.
Since the connections of conventional analog sensors are not waterproof, analog product manufacturers encapsulate the cable in the sensor. As a result, users must remove the cable at the transmitter when replacing sensors. Memosens sensors feature contactless, 100% moisture-resistant measured value transmission, eliminating that effort. Thanks to inductive measured value transmission in the Memosens sensor coupling, neither moisture nor deposits can adversely affect transmission.
And digital Memosens technology permits sensor pre-calibration under ideal conditions in the laboratory: even untrained personnel can replace these sensors on site. The cell constants are automatically transmitted to the transmitter, remaining available for further calibration procedures.
Return on Investment
- With Memosens sensors and transmitters from Knick, you will reduce the calibration cycles you require and increase sensor service life. Since Memosens sensors do not need to be re-calibrated or replaced as frequently, they will significantly reduce your measuring loop maintenance and new sensor procurement costs.
- And for applications with high moisture volumes in particular, you will benefit from simplified sensor handling. Memosens sensors feature inductive transmission of data and supply voltage, and thanks to the high degree of protection of the transmitter, you no longer need to worry about wet or corroded contact points or effects that will harm the electronics. Knick provides a three-year warranty on the transmitters.