Chemical Processing - April 2008 - (Page 42)

>> making it work • normal operation; and • abnormal and emergency situations. Advanced controls — With the changing process, Borealis needed to revise the APC. They were extended to include the new process equipment; models also were updated to reflect the performance of the new system. To ensure that APC could deliver the most value, Borealis focused particularly on stabilizing and improving the underlying regulatory controls. Even small levels of cycling or instability may cause the APC to back away from optimal operation. Regulatory control improvements — Borealis recognized that issues such as control valve mechanical problems, poor controller tuning and instrument failures were undermining regulatory control and directly affecting the performance of the plant. To address these issues, we installed PlantTriage performance supervision software from ExperTune. This software connects to the control system via OPC and then identifies and prioritizes opportunities to improve regulatory control. The software allowed us to see, for the first time, the performance of all the important control loops in our plant. Within a few days of software installation, we had uncovered a host of control system opportunities. Dashboard insights The Borealis team used plant performance dash- boards (Figure 1) to determine the most important issues. Through these dashboards plant personnel could quickly identify the issues, drill down to root causes and then take appropriate actions. One of the most useful tools was the “Biggest Payback Loops” list, which singles out the 10 most important opportunities in the plant ranked by technical and economic criteria. Using this list, control engineers could allocate their time to deliver the greatest value. Drilling down on each loop in the Biggest Payback list shows specific de- “When plants first start with performance monitoring, it is quite common to find some ‘low hanging fruit.’” tails and the likely root cause of poor performance. For instance loop FC-16026 was diagnosed as having extremely high valve travel — which causes high process variability, increased valve wear-and-tear and valve mechanical problems. Simply adding a small filter to the instrument signal can address the issue. Process stability improves almost immediately. “In most plants, valve travel may be reduced by a factor of 50% or more through the application of a filter and some appropriate tuning,” notes John Gerry, president and founder of ExperTune. “When plants first start with performance monitoring, it is quite common to find some ‘low hanging fruit.’ These are problems that have been overlooked because most plants do not monitor some of the most important key performance indicators,” Gerry adds. Borealis found “low hanging fruit” in the form of underperforming control valves, lack of instrument filters and some controller tuning opportunities. Uncovering valve issues The performance supervision system automatically identifies a variety of mechanical control valve issues. These include: • oversized valves; • undersized valves; and • valves with stiction and hysteresis. The standard reports prioritize valve repair issues according to both technical and economic factors. This information helps the team to plan and schedule the appropriate maintenance and to focus on issues to investigate in more detail. In some cases overcoming valve problems requires only minor adjustments, such as recalibration of positioners or adjustments to valve air pressure. www.chemicalprocessing.com >> Plant performance dashboard Figure 1. The dashboard provides an overall view and, with drilling down, highlights major opportunities for improvement. 42 • April 2008 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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