Chemical Processing - November 2007 - (Page 26)

PAT control software tend to have at least one or two inferential sensors running. It may be just for a purity measurement on a distillation column, estimating impurities online, or something like melt index in a polymer reactor or extruder — typically for a quality measure that you’re actually selling against.” The hybrid model also has opened up other markets for Pavilion, most notably in the pharmaceuticals sector. For instance, by providing online measurements from fermentation processes, notes Snyder, Pavilion’s model helps operators optimize their feed into the fermenter (Figure 4). “We’ve been able to reduce batch times by anywhere from 10% to 20%,” he says. While Pavilion’s solutions are still essentially neural-network-based, Matrikon’s ProcessMonitor product uses a partial least squares (PLS) algorithm to process its data. “The beauty of doing it this way,” contends Brown, “is that the PLS structure we use is very good at providing a tremendous amount of insight into how the model you’re developing ties back into the fundamental variables of the process that you understand.” Back at Dow, Kordon says two types of inferential sensors are in use around the company. Earlier ones are based on neural networks, such as those from Pavilion that have been used successfully on NOx emission control duties (see www.chemicalprocessing.com/articles/2007/064.html for more on predictive emissions monitoring systems). “It’s not closed-loop control,” he says, “but is generally accepted for the limits of the [emission] tests involved.” However, for other solutions for estimating properties and for closed loop control, Kordon says Dow “is gradually migrating to a genetic programming technology, especially its capability to derive a symbolic regression model — which looks not only at the accuracy of the data but its complexity as well, so we can find solutions that are relatively robust compared to neural nets.” This technology for the moment remains internal to Dow and the company filed patents for it earlier this year. However, Kordon believes more than technology might be needed to improve the acceptance of inferential sensors generally across industry. “The key challenge is the psychology, the credibility, the risk-taking culture that’s required,” he says. “It’s not really a technical issue — it’s relatively mature — but it won’t ‘turn your data into gold’ as was claimed at the beginning. But it is a viable solution, and we’re using it. CP www.chemicalprocessing.com Fully compliant with API 685 standards, vertical and horizontal in-line Canned Motor Pumps from Nikkiso Pumps America stand head-and-sholders above all the rest. API 685 1st Edition Canned Motor Pumps Nikkiso is proud to offer the world’s most advanced Bearing Monitor. Our patented E-Monitor digitally tracks Bearing Condition and Rotation directly at the pump or remotely. Highly reliable Canned Motor Pumps in amazingly compact designs. 600 Kenrick Drive, Suite C-1 • Houston, TX 77060 P: 281-310-6747 • F: 281-310-6771 www.nikkisopumpsamerica.com Canned Motor Pumps • Metering Pumps • Power Pumps erticalAd.indd 1 26 • November 2007 8/6/2007 8:23:02 AM http://www.chemicalprocessing.com/articles/2007/064.html http://www.chemicalprocessing.com/articles/2007/064.html http://www.nikkisopumpsamerica.com http://www.nikkisopumpsamerica.com http://www.chemicalprocessing.com

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Chemical Processing - November 2007

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