Foxboro pH Sensors Cut Costs, Improve Performance in High Temperature Chemical Application

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The Foxboro Measurements & Instruments Division of Invensys Process Systems (http://www.foxboro.com/instrumentation) has worked with Archer Daniels Midland to develop a solution for robust pH sensing in high temperature chemical applications. Archer Daniels Midland Company (ADM) (http://www.admworld.com) is one of the largest agricultural processors in the world producing food ingredients, animal feed ingredients, renewable fuels, and naturally derived alternatives to industrial chemicals.

The Foxboro Measurements & Instruments Division of Invensys Process Systems (http://www.foxboro.com/instrumentation) has worked with Archer Daniels Midland to develop a solution for robust pH sensing in high temperature chemical applications. Archer Daniels Midland Company (ADM) (http://www.admworld.com) is one of the largest agricultural processors in the world producing food ingredients, animal feed ingredients, renewable fuels, and naturally derived alternatives to industrial chemicals.

The application is high-temperature ethanol production at ADM’s Cedar Rapids, Iowa facility, where managing pH is critical for consistent product quality, efficient process reaction, and compliance with environmental regulations. The ADM/Foxboro collaborative effort resulted in a pH sensor that extends service life from days to months without replacing, thus significantly reducing equipment and labor costs, while maintaining high process quality Ethanol is a high-alcohol, renewable fuel additive that helps gasoline producers meet environmental regulations. Maintaining accurate pH levels during ethanol production is critical to control the sulfur dioxide levels. Excessive sulfur dioxide in the ethanol corrodes the carburetor and other engine components involved in gas distribution.

Ethanol production involves fermenting and distilling starch and sugar crops. In the early stages, liquefied starch is converted to sugar (dextrose), which is then fermented. Yeast is added to the mash to convert the sugars to ethanol and carbon dioxide. The fermented mash, called “beer,” contains about 11 percent alcohol, as well as all the non-fermentable solids from the corn and the yeast cells. The beer is then heated to 235 degrees F, to evaporate alcohol content, which is collected and condensed, and run through a rectifier to eliminate the remaining water. The final product is 199-proof, almost pure alcohol, ethanol.

“We tried taking pH readings directly from the process, but the 235 degree temperature ate sensors up,” says Lloyd Feickert, instrumentation supervisor at the ADM Cedar Rapids facility. “To reduce excessive sensor costs we set up a slipstream arrangement, whereby we run a sample of the ethanol offline to cool it down to 140 degrees F, and measure that,” says Feickert.

While the slipstream arrangement significantly extended pH sensor service life, inherent process conditions still caused frequent replacement of components in the rebuildable pH sensors. “At the lower temperatures, pH sensors could last for weeks, but process conditions caused temperature fluctuations within the slipstreams. These reduced sensor life significantly. We had standardized on the Foxboro 871 rebuildable pH sensors, so we turned to them for the solution,” says Feickert.

To accommodate ADM’s application, the Foxboro Measurements & Instruments division of Invensys worked with Feickert to develop a field replaceable measuring electrode that could withstand severe temperature cycling up to 250 degrees F. The replaceable electrode incorporates patented technology from the award-winning Foxboro DolpHinTM pH sensor line.

“I heard about the DolpHin line of high temperature pH sensors and asked Foxboro if they could develop a similar product for rebuildable sensors. They studied my application and came back with a replaceable electrode that, after a cooperative testing period, increased our sensor service life from days to months,” says Feickert.

The newly developed measuring electrode features a unique pH glass formulation that provides superior measurement stability, accuracy, and longer service in high-temperature applications. This pH glass also increases response speed up to five times. The electrodes are available in domed, spherical, or ruggedized flat glass. The domed glass electrode is for the harshest applications: temperatures up to 250 degrees F and extremes of chemical concentrations.

The spherical glass electrodes are for standard process applications up to 212 degree F, and the flat ruggedized glass electrodes are for applications where the process water contains solid materials with pH between 2 and 12 and temperatures up to 185 degrees F. All electrodes are interchangeable and their plug-in design facilitates quick and easy replacement to address changes in measurement conditions or application.

“Rebuildable sensors are definitely the most cost effective way to measure pH for our applications,” says Feickert. We have standardized on the Foxboro 871 line and now, with the addition of the high temperature domed electrode, we have all the tools to cost effectively handle pH sensing throughout our plant.”

“The domed 871PH electrode has increased pH sensor service life from 10 days to four months,” says Feickert. “That’s a 1000 percent increase. When you consider that we use the domed sensor in four beer stills, as well as other processes within the plant, that’s an enormous savings.”

In addition to the product cost savings, ADM has significantly reduced labor and maintenance costs. “Every time you send a person out to work on a sensor, it’s at least an hour’s worth of labor. I estimate that we have reduced time spent on changing electrodes over the course of a year from 36 hours per electrode to three hours per electrode,” says Feickert.

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 http://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 http://www.buyautomation.com.

About Foxboro M&I Division

The Foxboro Measurements and Instruments (M&I) Division has a long-standing reputation for providing world-class measurement solutions. With a legacy of accurate, reliable, and innovative products, the group prides itself on working with customers to achieve industry-best total solutions for optimum measurement or analysis of temperature, pressure, flow, and electrochemical variables.

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. For more information on Invensys’ process automation businesses, please visit http://www.invensys.com/ps.

The Invensys Group (http://www.invensys.com) is headquartered in London and is listed on the London Stock Exchange, with approximately 30,000 employees working in 60 countries.

Invensys, SimSci-Esscor, DYNSIM, SIM4ME, Foxboro, 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.

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Joni Littleton