Customer Challenge
Managing pH in high-temperature chemical applications is critical for consistent product quality, efficient process reaction and compliance in environmental regulations. But because accurate measurement requires immersing pH sensors in hot, strongly acidic substances for extended time periods, companies have to replace them every few days.
To reduce maintenance costs, some chemical plants are now using DolpHin™ pH sensing technology in their harsh, high-temperature applications. |
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% alcohol. The beer is then heated to 235 F to evaporate alcohol content, which is collected, 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 F 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 to 140 F and measure that," says Feickert.
Lloyd Feickert, instrumentation supervisor at the ADM Cedar Rapids facility, is using Foxboro pH & ORP sensors to achieve accurate and reliable pH sensing for ADM's ethanol production. |
"At the lower temperatures, pH sensors could last for weeks, but process conditions caused temperature fluctuations within the slipstreams that reduced sensor life significantly. We had standardized on the Foxboro 871 rebuildable pH sensors, so we turned to them for the solution," says Feickert. The Solution
To accommodate ADM's application, the Foxboro Measurements and Instruments division of Invensys worked with Feickert to develop a field replaceable measuring electrode that could withstand severe temperature cycling up to 250 F. The replaceable electrode incorporates patented technology from the proprietary DolpHin™ pH sensor line.
"I heard about the DolpHin line and asked Foxboro if they could develop a similar product for rebuildable sensors," says Feickert.
The newly developed measuring electrode features a pH glass formulation that provides superior measurement stability, accuracy and longer service in high-temperature applications. Also, this pH glass 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 F and extreme chemical concentrations. All electrodes are interchangeable and their plug-in design facilitates easy replacement to address changes in measurement conditions or application.
The newly developed measuring electrode in the Foxboro pH & ORP sensors features a unique pH glass formulation that provides superior measurement, stability, accuracy, and longer service in high-temperature applications. |
Results
"The domed 871PH electrode has increased pH sensor service life from 10 days to 4 months," says Feickert. "That's a 1000% 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, 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 to 3 hours per electrode," says Feickert.
John Connelly, sensor product manager, may be contacted at John.connelly@ips.invensys.com or by phone at 508-549-4681. For more information visit www.foxboro.com or www.admworld.com.