Foxboro pH sensors cut costs and optimize operations in corrosive petrochemical application

The Foxboro Measurements & Instruments Division of Invensys (www.foxboro.com/instrumentation) is providing robust, high-temperature pH sensing technology to aid Eastman Chemical Company in reducing costs and optimizing operations in its gas scrubbing process. Headquartered in Kingsport, Tennessee, U.S.A., Eastman Chemical Company is a global manufacturer and marketer of more than 1,200 chemicals, fibers, and plastics and is the world’s largest supplier of polyester plastics for packaging.
In harsh applications such as chemical and petrochemical processing, one plant-floor device that can represent significant costs is the sensor. Often exposed to or immersed in highly corrosive solutions and subject to extremely high operating temperatures, sensors are the critical front-line probes that gather and deliver key data; support safe, reliable operation; provide regulatory monitoring and validation; and ensure quality control, process efficiency and optimization.
Eastman Chemical Company turned to Invensys — specifically to its Foxboro® line of DolpHin™ series pH sensors — to provide these solutions for a gas scrubber at the company’s Longview, Texas, manufacturing complex. Eastman’s Texas operations manufacture and ship 8.8 million pounds per day of chemicals and plastics to customers worldwide. At Longview, its gas scrubber uses water and caustic in a 20% sodium hydroxide solution to remove hydrochloric acid from flue gas before venting.
To meet company standards and federal environmental requirements, acid gas content in vented emissions must remain within acceptable levels. Reliable measurement of pH level in the caustic solution is critical for effective scrubbing, regulatory compliance — and reduced caustic chemical consumption costs. To monitor pH levels, the scrubber uses a two-probe, redundant system. Scrubber conditions present significant challenges, including exposure to liquid caustic at a nominal operating temperature of 185° F and pH of up to 10.5. Existing pH sensors thus had to be replaced frequently — often within 2 weeks of installation, and even as frequently as 3 times per week.
Because the sensors could not withstand the environment, readings were not accurate, so operators had to add caustic. This drove up use of this costly material and gave higher pH values. In turn, higher pH etched the sensor glass, leading to inaccurate performance and faster failure. Results: unacceptably high manufacturing and maintenance costs.
Determining that other options were inadequate, Eastman Chemical engineers tested new Foxboro brand DolpHin high-temperature pH sensors from Invensys. They proved to be the ideal solution. These sensors are designed specifically for challenging process applications that span the entire pH scale, exhibit strong chemical concentrations and high solids, run at high temperatures, and cycle from high to low temperatures. Their unique, patented pH glass formulation provides superior measurement stability and accuracy, plus longer service life in high-temperature applications up to 250° F (121° C). The pH glass also increases response speed up to five times and provides longer duty cycles than conventional sensors. A DolpHin sensor’s innovative reference electrode construction includes an ion barrier to protect and stabilize the reference potential in harsh conditions. Its electrodes are packaged in a rugged mechanical housing that facilitates installation, removal, cleaning and calibration, reducing maintenance time and costs.
Eastman reports most impressive results. The DolpHin sensors’ pH glass formulation increased sensor life to 6 months — a dramatic improvement over previous products that operated properly for 3-4 weeks at best. This longevity reduced equipment and related maintenance/replacement costs eightfold! “With the Foxboro DolpHin pH sensors, Eastman’s equipment and maintenance costs were eight times lower than with the previous sensors, and the efficiency of our scrubber operation was optimized,“ noted Wyatt Partney, senior control systems technician at Longview. “In fact, the DolpHin sensors were so successful in solving the problems of high costs, reliable pH measurement, and process optimization for our scrubbers that we implemented them in a number of other demanding applications as well,” he added.
Besides significantly reducing equipment and related maintenance costs, the DolpHin sensors provide more accurate pH readings, ensuring that operators can use online pH measurements to optimize efficiency of scrubber operations. And since inaccurate pH level measurement no longer causes operators to continuously add sodium hydroxide scrubbing solution, DolpHin sensors have slashed caustic use levels by a remarkable 50%.
For more information on the DolpHin series pH sensors or other advanced Foxboro measurement and instrument devices, readers can contact their local Invensys/Foxboro representative, visit the Foxboro Measurements and Instruments Web Site at www.foxboro.com/instrumentation or call 866-746-6477 (508-549-2424 outside the U.S. and Canada). The DolpHin series pH sensors can also be purchased on-line at www.buyautomation.com.

About Invensys
Invensys is the world leader in industrial asset performance management. In addition to its rapidly expanding Global Solutions and Performance Management services groups, Invensys’ automation businesses includes industry-leading brands such as Foxboro, Triconex, SimSci-Esscor, Wonderware, and Avantis, whose products are installed in more than 100,000 plants across the world. These range from small hybrid and batch plants to the world’s largest upstream projects, refineries, gas plants, petrochemicals plants, power plants, and pulp and paper mills.
The Invensys Group (www.invensys.com) is headquartered in London and is listed on the London Stock Exchange, with approximately 30,000 employees working in 60 countries.
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Invensys, SimSci-Esscor, Foxboro, DolpHin, Triconex, Wonderware, and Avantis are trademarks of Invensys plc, its subsidiaries, or affiliates. All other brands and product names may be trademarks of their respective owners.