Overcoming the Challenges of High-Purity Boiler Water pH Measurement

 Protecting costly boilers from corrosion requires the addition of chemicals, which in turn needs accurate pH measurement to assure the correct dosing. pH too high or too low can lead to corrosion, scaling, the need to replace equipment, and even system failures and downtime. In low-pressure boilers, pH measurement is fairly straightforward, but in high-pressure boilers requiring high-purity, low-conductivity water, pH measurement is, in short, a pain. A recent article by Michael Francis in POWER magazine explains why this is true and how you can overcome these challenges.

Michael says, “The cutoff point between low- and high-conductivity boiler water is 50µS/cm, which is the lowest conductivity at which conventional pH sensors have reliably been used. Below 50µS/cm the sensor of choice has traditionally been one purpose-built to measure pH in low-conductivity water, but the trend is moving away from that approach.”

Michael then explains why diffusion of the electrolyte in pH sensors occurs so rapidly in high-purity water, requiring frequent replacement or recharge of electrolyte as well as causing potential measurement errors. “Traditional methods of dealing with high-purity water pH measurement issues have involved using a sensor with an electrolyte reservoir that continuously replaces the electrolyte. This approach, however, requires additional consumables to be ordered regularly, as well as stored, and also adds substantial ongoing maintenance.”

“With a range of advances in technology, this problem of high-purity water pH measurement can now be solved with the combination of a high-performance, general-purpose pH sensor that provides a solution ground to minimize drift and an isolated stable measurement, along with a low-flow controller.” The general purpose sensor, however, must have certain characteristics. In addition, controlling the flow rate of water across the sensor directly, at a flow rate that’s held constant at less than three gallons per hour, reduces the rate of electrolyte depletion.

A general-purpose pH sensor enhanced with flow controller technology can provide users with:

  • Four times the sensor life. With a general-purpose sensor design that includes an advanced glass formulation that resists cracking, as well as a double junction reference, users can expect sensor longevity of up to two years versus the industry average of six months.
  • 60 percent less time in the field and less maintenance time. General-purpose sensors often have smart pH circuitry built in to store calibration information and enable auto sensor detection. This kind of circuitry can make a sensor “plug and play” and cuts time in the field by more than 60 percent.
  • Two-thirds less water usage.

General-purpose pH sensors have a lower initial cost than specialized high-purity designs. In addition, their extended sensor life and reduced costs of maintenance and upkeep means the ongoing cost of ownership is also reduced. Further cost reduction is realized when the general-purpose sensor is combined with the low-flow controller, because unlike traditional high-purity sensors, ongoing consumables are not required. Finally, a long-life, general-purpose sensor plus low-flow controller requires less than a third of the water usage of other systems.”

For more details on this solution to pH measurement in high purity water, check out the article in POWER magazine.

What kind of technology do you use to measure pH in high-purity water?