Why do you need performance supervision?

DO YOU ever get the feeling that your control system is hiding the secrets of the universe? After all, it’s supposedly gathering information from the process 24 hours a day. Unfortunately, you only get to see a small part of this information, and only when you go looking for it and have time to analyze it. What plant has the manpower or time to go hunting in the data haystack for information that might or might not pan out into performance improvement? At the same time, can you afford not trying to do whatever possible to improve your plant’s performance?

Michael Kennedy, global process control engineering manager for Columbian Chemicals Co. in Marietta, Ga., says, “In today’s global marketplace, there are enormous pressures to obtain the best overall performance from our manufacturing facilities.”

Performance Supervision Systems
Because it’s easier, given short staffing and a lack of time, many plants still operate on a “run-to-fail” model. That is, the plant runs until either a planned shutdown or an expensive, unplanned breakdown occurs. How expensive? Here’s an easy way to figure it out for your own plant. Find the value of the plant’s output per hour. Take a look at your last unplanned breakdown, and determine how many hours the plant was producing zero output. Multiply the number of zero-output hours by the value per hour of plant output. This gives you a value to put on the cost of the unplanned shutdown. In most cases, the value is very high, and can be a real eye-opener to management when presented as a real cost.

Thankfully, there are solutions to this extremely costly problem, but Kennedy advises, “Considering the limited number of skilled personnel, there are limits to what we can accomplish. In order to remain competitive, we need the right tools to streamline our process improvement, while adding a greater leverage to our existing knowledge and skills.”

One of these solutions is a software-driven Performance Supervision System (PSS). Because it’s software-based and uses your existing control system to operate, a PSS is often the least expensive way to reduce the costs of unplanned breakdowns.

PSS uses the DCS or historian as a window into the process, sorts through mountains of data, and delivers targeted, actionable knowledge about the process. Because it looks at the entire plant, PSS can find all manner of process, equipment, and control problems. Performance supervision has been used to uncover failing pump seals, problematic valves, fouling heat exchangers, improper repairs, process-upset sources, controller tuning problems, and process-behavior changes.

This information is used by process engineers, operations management, and maintenance, as well as the process control community. Every user can customize the information they want to see. Maintenance can focus on valve and instrument issues, while process engineers can look for bottlenecks and other improvement opportunities. At the same time, everyone is working with a standard set of metrics for overall performance, so the overall focus is clear.

Figure 1 below shows a typical display of the highest priority issues in a plant. In this case, the loop shown at the top of the list was identified as having the highest economic impact on the plant, based on a combination of its economic value and its measured performance. By looking at one chart, engineering efforts could be focused. As you’ll see below, drill-down tools enabled engineers to quickly find the problem, which was a series of interacting control loops. However, probably the most important thing PSS can find is time…your time.

FIGURE 1: ORDER OF IMPORTANCE

A Performance Supervision System (PSS) displays the highest-priority issues in a plant. In this case, the loop at the top of the list was found to have the most economic impact on the plant, based on its economic value and its measured performance, which helped focus engineering efforts. (Click image to enlarge).

Need More Time?
Everyone needs more time these days. Plant budgets are stretched, headcount is down, and everybody is balancing multiple responsibilities and multiple projects. When do you have the time to sit at the control console, and look for ways to optimize your process? Ian Nimmo, president of User Centered Design Services, says, “In a properly run plant, the operator should not have to intervene in its operation, except in the case of an upset, and any time the operator has to do anything it is an upset.”

If you’re spending all your time running around putting out fires, what will you do in a real emergency? In many plants, when multiple alarms go off together, the operators no longer know which are the most critical and which to respond to first. And in alarm cascades, plant operators that don’t know these things are usually going to do something wrong. We’ve seen this many times in many accidents, such as last year’s BP Texas City disaster. In that case, bad decisions were compounded by poor maintenance, which caused the deaths of more than a dozen people.