On-line pH measurement in low conductivity samples
In power plant operations, control of the pH value is crucial to minimize corrosion, prevent various kinds of deposits and to ensure an efficient power plant operation. pH levels are particularly important for controlling boiler feed chemistry, as well as for adjusting the ammonia and/or amine content of the water cycle.
This white paper, which was published by VGB PowerTech e.V., the international technical association for generation and storage of power and heat, explains how in power plant applications, the low conductivity of the sample makes on-line pH measurement more difficult than in most other industries and applications. pH is much more specific than the more commonly used conductivity measurement, since pH responds only to the hydrogen ion, whereas conductivity responds to all ions in a sample. pH is a key parameter in cycle chemistry control to minimize corrosion in makeup water treatment to optimize efficiency, and in generator stator cooling to minimize copper corrosion. All these applications involve low conductivity samples that make the measurement more difficult and involve more temperature influences than in more common applications such as cooling towers and wastewater. As a result, there are more demands on instrumentation used in these applications.
Download the white paper to read the full details, including the following topics:
- pH applications
- Calculated pH
- Measured pH
- pH sensor design
- Digital pH sensors
- Temperature compensation
A new probe to be used in power plant applications for on-line pH measurement in low conductivity samples, is described in this white paper. The design includes a built-in measuring circuit, analog-to-digital signal conversion, calibration memory and operating condition history. This approach is part of an instrument platform design that includes similar intelligent sensors for conductivity, dissolved oxygen and oxidation-reduction potential (ORP), as well as pH. The internal memory of digital sensors enables calibration remotely, in the laboratory if desired. All of the calibration data is retained within the sensor and is automatically uploaded to the connected transmitter wherever it is finally installed. The internal memory also maintains a real-time record of sensor exposure to process conditions to enable maintenance planning. The intelligence is used to forecast when the sensor will require calibration, maintenance or replacement, based on its operating history.