Anyone who has been faced with measuring pH in the high-purity water required for high-pressure boilers knows that the traditional methods of measurement are costly. The traditional solution – a “sidestream” sensor with an electrolyte reservoir that can be used to continuously replace the electrolyte – has a high purchase price, as well as expensive ongoing consumables that must be purchased, stored and maintained. And the hidden cost of these units is water.
To better understand how to avoid these issues, here’s a brief explanation of the problem. A pH control system measures the pH of the solution and controls the addition of a neutralizing agent (on demand) to maintain the solution at the pH of neutrality, or within certain acceptable limits. It is, in effect, a continuous titration. pH measurement is taken by comparing the electrical potential at two points – the reference electrode, which is surrounded by a constant pH electrolyte solution, and the pH glass electrode, which is in direct contact with the solution being tested. A “reference junction” is used to maintain the electrical connection between the reference electrode and the solution being tested.
The major challenge in measuring the pH of low-conductivity water is minimizing the difference between the liquid junction potentials in the calibration buffers and sample. The junction potential is the charge separation that arises when the reference electrolyte diffuses into the sample and the sample diffuses into the reference electrode. Electrolyte is critical to the proper functioning of the reference system for electrical connection, and ultimately, for the pH measurement, so when it runs out, the electrical connection between the pH electrode is broken and the measurement is impossible. Ultrapure water accelerates diffusion of the electrolyte into the low-conductivity process water. The loss of electrolyte substantially shortens pH sensor life and increases the amount of maintenance required for each measuring point. Surprisingly, full diffusion can take place in the course of just a few months, requiring replacement of the pH sensor or a recharge of electrolyte fill solution.
A recent white paper describes a unique and elegant alternative to the traditional method of overcoming this problem. With a range of advances in technology, the issue 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 unique low-flow controller. Controlling the flow rate of water across the sensor directly, at a flow rate that’s held constant at less than 3 gph, reduces the rate of electrolyte depletion, increasing sensor life and reducing water usage by more than two-thirds versus other sidestream solutions.
To learn more about this money-saving approach to high-purity water measurement in high-pressure boilers, download a copy of this white paper today.
Do you currently use a sidestream sensor to measure high-purity water?