Chemical Processing - April 2008 - (Page 44)

>> making it work perature controls have been notoriously difficult. Previous manual attempts at improving controller performance left us with controls that worked but were less than optimal. Using the integrated tuning and loop optimization tools within PlantTriage allowed us to push controller performance closer to optimal. The results were immediately apparent (Figure 3). The robust controller tuning approach eliminated loop cycling and interactions, adding a great deal of stability to the process. This, in turn, allowed APC to be used to the fullest, actively pushing the entire process toward optimum performance. We also focused on the control valve, because it’s the most likely point of failure in a control loop. Using valve travel diagnostics, we’ve been able to identify control valves with the highest level of wear. The root cause usually is related to tuning or inadequate instrument signal filters — and so can be addressed quite easily. Appropriate filtering and tuning can dramatically reduce valve travel. >> Improved performance Figure 3. Effective tuning provided close-to-optimal control of process variable. We’re now using the performance supervision tools to identify and eliminate bottlenecks, further increasing production. Standard measurements and thresholds — e.g., for valve stiction, valve hysteresis and instrument noise band — will guide future maintenance action for valves and instrumentation. Setting an accurate metric and a definite threshold helps in two ways, by: 1. drawing attention to valves and instruments as they start to deteriorate; and 2. reducing unnecessary maintenance. Hardware that performs within the thresholds receives low priority from the maintenance team. impressive results The startup was the quickest in our plant’s history. Borealis achieved production at the new nameplate capacity within 20 days after startup, with all product on-spec. The plant now is exceeding design output. It’s impossible to separately measure the return on investment from the operator training, advanced controls and performance supervision. However, the net effect was to reduce the start-up curve by several days. These investments also have paid for themselves in the ability to run the plant closer to bottlenecks. With 44 • April 2008 the increased capacity, Porvoo is pushing the process further and simultaneously hitting several new bottlenecks. These tools enable Borealis to drive closer to new production limits while at the same time adding stability and safety. “This was a fantastic start-up. The tools and techniques used at Porvoo are state-of-the-art, and helped us to deliver a high rate of return to our business,” says Hannu Luoto, Plant Manager at Porvoo. Maintaining good control performance and equipment reliability are key goals for the future. But Borealis also is continuing to find opportunities to improve. We’re now using the performance supervision tools to identify and eliminate bottlenecks, further increasing production. With most of the obvious constraints eliminated, we’re applying some of the more advanced tools to find and remove oscillations, improving efficiency even more and pushing production rates higher. As we integrate performance supervision into our daily routine, we expect to continue to uncover more opportunities not just to sustain but to continually improve plant performance. Borealis also is looking at the possibilities of applying these tools and techniques at plants around the world. CP Mikko Rönkä is an automation engineer with Borealis Polymers Oy, Porvoo, Finland. E-mail him at mikko.ronka@borealisgroup.com. George Buckbee, P.E., is director of product development at ExperTune, Inc., Hartland, Wis. E-mail him at george.buckbee@expertune.com. www.chemicalprocessing.com http://www.chemicalprocessing.com

Table of Contents Feed for the Digital Edition of Chemical Processing - April 2008

Chemical Processing - April 2008 Contents From the Editor ChemicalProcessing.com Field Notes In Process Energy Saver Compliance Advisor Is It a Tragedy or Comedy for Engineers? Better Understanding Boosts Mixer Scale-up Don't Err With Air Compressors Control Performance Supervision Enhances Revamp Process Puzzler Plant InSites Equipment & Services Product Spotlight/Classifieds Ad Index End Point

Chemical Processing - April 2008

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