Intelligent Instruments Help Plastic Resins Supplier Maintain Product Quality, Reduce Costs

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The clear plastic that is fast becoming the packaging material of choice for bottled water, household cleaners and numerous other food and non-food items depends on high quality resin for its strength and clarity. Wellman Inc, one of the world’s leading suppliers of this polyethylene terephthalate (PET) resin, has found that intelligent valve positioners are a critical component in providing the consistent product quality that its packaging customers need, while reducing maintenance and downtime to keep costs in check.

The clear plastic that is fast becoming the packaging material of choice for bottled water, household cleaners and numerous other food and non-food items depends on high quality resin for its strength and clarity. Wellman Inc, one of the world’s leading suppliers of this polyethylene terephthalate (PET) resin, has found that intelligent valve positioners are a critical component in providing the consistent product quality that its packaging customers need, while reducing maintenance and downtime to keep costs in check.

Wellman supplies PET in pellets, which it creates through controlled interaction of two main chemicals: purified terephthalate acid (PTA), and monoethylene glycol (MEG). These chemicals are blended in reactors fed by a tightly controlled system of valves and tubing to assure consistent product quality.

“Controlling the injection of PTA and MEG, from a small trickle to an almost gushing chemical flow, is very difficult, and very, very critical,” said Robert Goetzman, senior controls engineer at Wellman’s Pearl River, Miss., facility. “The process must be precise and repeatable to maintain the quality of our plastics, whether for clarity or strength.”

Vital to orchestrating the opening and closing of valves that control the flow of the PET ingredients are valve positioners. To be certain it was using the most reliable valve positioners available, Wellman evaluated products of several suppliers and selected Foxboro Intelligent Positioners from Invensys. They would configure the positioners from their Foxboro I/A series distributed control system, which was already in place and the positioner would communicate with the I/A Series system through the Invensys FoxCom field device protocol.

“Given the importance of the positioner, we had specific selection criteria. These included robustness, self-calibration, and ease of installation, startup, and replacement. Our process has to be precise, and positioner performance is paramount,” said Goetzman. If a positioner fails, it sets off an alarm, which is read in the I/A Series control room. The PET resin production line is either temporarily shutdown at the failed control valve or the flow is made to bypass the failed valve. The next step is replacement. The Foxboro SRD991 is designed for ready installation. The positioner is unbolted and removed, a new positioner is pulled from supply and, using the same bolts, the new positioner is installed.

To assure optimum positioner performance, automatic self-calibration takes over at this point. ”The automatic self-calibration enhances quality control by eliminating or reducing mistakes that might result from incorrect calibration. This is critical, when you consider that a mis-calibrated positioner will fail to open or close the valve properly, allowing the wrong amounts of PAT or MEG to be injected into the process. This could result in the entire batch being ruined, one of our worst nightmares,” said Goetzman.

The positioner, utilizing its FoxCom information and communication instrumentation, automatically performs all the necessary checks and diagnostics in two to three minutes, sending the results directly to the Pearl River control room. “From my office, I can check the status of all valve positioners and transmitters. I don’t have to go out and actually look at the diagnostics, which allows me to perform more value-added activities. The Foxboro I/A Series system enables us to monitor and maintain precise process control by conducting self-calibration from our desk,” said Goetzman.

"The benefits of Foxboro standardization at Pearl River are numerous," said Goetzman, citing the positioners’ ease of installation, ease of replacement, and the equipment’s robustness and accuracy. “You are only as good as your instrumentation and the information you receive from the field,” said Goetzman. “We now use a 991 Foxboro Positioner for every process where we are continuously controlling the opening and closing of a valve. We use Foxboro in utilities. We use the positioners in our melt polymerization process, our sold-state polymerization unit, and in chip handling. We put the 991s through the test, and they came through with flying colors. Based on proven performance, we have standardized on Foxboro smart instrumentation,” said Goetzman.

In 2006, Wellman will expand capacity of the third Pearl River PET resin line by 50 percent and has already selected Foxboro controls and instrumentation. “Foxboro is the perfect partner for our control and instrumentation needs,” said Pete Woody, plant manager of the Pearl River facility. “Based on product performance, technical support, and ease of doing business, Foxboro is our single source solution. For existing operations and future expansions, when we need a pressure transmitter, valve positioner, or vortex meter we will be buying a Foxboro product,” said Woody.

For more information on the Foxboro Intelligent Positioner line 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 Foxboro intelligent positioner line 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.

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, 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.

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