Measuring pH is one of the great challenges for manufacturers and producers. In an Emerson Exchange Americas Virtual Series presentation, Emerson’s Andrew Smith and Zach Blum shared their thoughts on proven solutions for tough pH applications. Here is their presentation abstract:
Aqueous applications across industries depend on a reliable measurement of pH. Typical applications include reaction control, corrosion prevention, and ensuring environmental compliance. Despite this importance, the technology is often misunderstood and misapplied. Choosing the right sensor for your process is critical to maximizing the quality of your measurement while minimizing maintenance frequency. Come learn how Emerson’s differentiated solutions are solving customer challenges in difficult, but crucial applications to ensure operational excellence.
Zach opened describing why pH measurements are typically taken. pH measurements are taken for several reasons.
The focus of this presentation is on online, continuous pH measurement. The pH sensors are composed of a measuring electrode, reference electrode and temperature compensator. pH sensors do not last forever.
They are like batteries where the reference electrode becomes depleted as the electrolyte solution flows out through the reference junction. Dirty process fluids, harsh chemicals, high temperature, and high-pressure applications can all shorten the life of these sensors.
For general purpose applications the 3900, 385+ and 389 families of sensors are recommended.
For dirty process fluids, the 396 and 398 families are recommended.
For harsh operating conditions, the 3300, 3400 and 3500 families are recommended. For other applications, there are a range of specialty pH sensors.
Zach described an ethanol corn mash application with high temperatures and thick corn mash coating the sensor. These sensors had to be replaced frequently, had slow response time and the measurements were not trusted. The solution was a 3300/3400 PERpH-X family sensor with high temperature gel electrolyte to minimize evaporation and can be refilled. The high temperature glass bulb was designed for longer life and a large reference junction resists plugging and is replaceable. Advanced diagnostics help proactively address plugging and coating issues.
Andrew described a pork processing wastewater treatment application on a dissolved air flotation (DAF) system. pH was measured at the inlet and outlet. The challenges were light levels of fats, grease and solids causing coating. Unreliable measurements could lead to fines for discharge non-compliance.
The solution was 396P TUpH sensors which resist plugging and coating. Their large surface area junction decreases noise and drift from coating and processing.
Andrew next described a pulp and paper mill pH measurement application. The measurements are in kraft pulping process where pH directly affects product quality. This process has sulfide poisoning challenges as liquor leaches out of the fibers. Strong oxidants are used in the bleaching process and high solids plug the reference junction.
The Rosemount RBI pH sensor has a unique junction design for high poisoning ion resistance and multiple ionic paths which resist coating. The sensors provided greater reliability for this application.
The final example Andrew described was a high purity boiler feedwater application. This application uses high purity water with corrosion rates of metals sensitive to variations in pH. The measurements are sensitive to flow rates where low pH leads to corrosion and high pH to caustic gouging. Oxygen scavenging reactions are pH dependent.
The Rosemount 3900 pH sensor with low flow panel helps eliminate flow sensitivity and helps minimize water usage.
Visit the Liquids Analysis section on Emerson.com for more on these pH sensors and other liquid analytical products for your measurement applications. Read this article to learn more tips on pH measurement and control.
