Closed-loop control in the process industries typically entails using a proportional-integral-derivative (PID) controller to regulate a modulating process, maintain a desired setpoint and compensate for load changes. A plant can have hundreds or even thousands of control loops, and many of them are often running poorly, whether from bad tuning or poor operation. With so many loops, it’s almost impossible to analyze and maintain them all on a regular basis.
“We’re all being asked to do more with less, be more secure and do it quickly,” said Domenico Napoli, offer manager, Control Advisor, Schneider Electric, who explained the benefits of the loop-performance management software at this week’s Foxboro User Group conference in San Antonio. “Control systems are becoming increasingly complex with a high degree of interactions. Control systems are constantly being modified. Identifying changes are difficult. There are many controls to look after and not enough time.”
The process itself presents ever-changing control conditions, and the personnel with knowledge of the system are retiring in increasing numbers. And because there’s so much to monitor and maintain, plant personnel often let control systems function at an acceptable level or sometimes poorly, when optimizing that control would add to the bottom line.
“Control Advisor is a tool to speed up your existing work processes and make them more efficient,” explained Napoli. “It’s not supposed to be another task inserted into your busy day. What are your critical issues that you need to deal with? You don’t need a Ph.D.”
The cost of poor control
Loop performance is often under-monitored and under-maintained. Poorly functioning control loops can lead to off-spec product, increased equipment wear and tear, increased emissions and waste, plant-asset breakdown, increased waste, decreased profit and negative impacts on downstream processes.
Control Advisor is a browser-based analytics software that leverages real-time and historical data to monitor up to 2,000 plant loops. It provides performance reports, loop-tuning recommendations and plain-English actionable recommendations, allowing nonspecialists to improve loop performance.
“It can help you to increase efficiency and save time,” said Napoli. Through energy savings up to 2% and increased productivity up to 10%, Control Advisor typically offers a payback in three to six months, he noted. Better performing loops also can improve quality and reduce maintenance costs.
“Ultimately the goal of the control loop is to follow your setpoint,” explained Napoli. “A lot of control loops are in manual mode, which defeats the purpose of control. And a lot of the tuning being done is not optimal. These can affect the bottom line.”
With the quantity of control loops in a large plant, the time needed to monitor and maintain them can be overwhelming, and shortcuts are often taken. “With hundreds or even thousands of control loops, it’s hard to monitor them and keep them in control,” said Napoli. “A problem we see is bad tuning and bad operation, which can lead to a variety of problems. Control Advisor is here to help. It will help you to find the root causes to bad behaviors in your control loops.”
Loop performance analyzed
Once loop data is imported, Control Advisor shifts into analysis mode to see what problems it notices. “It also provides you with a level of confidence on the issues it shows you,” explained Napoli. “It will see if you have loops that are oscillating or valves that are sticking. It can also help to find undersized and oversized valves.”
Control Advisor is a server-based application and is designed to run on a Windows-based operating system, and it can run on VMware or a Hyper-V server. Licensing starts at 100 loops, and the first year of support is included. “We also have services that can go with the software package,” said Napoli. “We offer 24/7 remote monitoring.”
Schneider Electric also offers ongoing local and remote services to assess, monitor, prioritize, report and remediate suboptimal control-loop performance. In addition to the 24/7 monitoring, it includes full online diagnostic support for loops and valves, advanced loop analysis capability and on-site remedial action by Schneider Electric personnel.
Napoli shared two examples of companies that realized financial gains through their use of Control Advisor. The first found a poorly tuned loop that once corrected resulted in a 7% reduction in natural-gas demand—and an annual savings of $67,000. Another user was able to reduce thirteen tons per day of scrap wet pulp to only 2 tons/day. Product value and landfill expenses added more than $1 million to the bottom line.