Who's Minding the Plant?

During normal operations, plant processes may largely be handled automatically. But what happens during abnormal operations? A plant's operating team is critical in detecting and preventing incidents. However, if the operator has become a passive monitor instead of an active participant, or if the control equipment is poorly designed, the operator may not be able to respond quickly or efficiently. The answer then, to the question above, according to Kenneth Emigholz of petrochemical supplier Exxon Research and Engineering (Florham Park, N.J.), should by now be a familiar one to our readers: intelligent manufacturing technologies.

The drive to make refining and chemical processes more efficient, and to produce products at a lower cost, has led the industry to design tightly integrated processes, which may carry an upset through the entire process, or loop it back to the original unit several times. Since many plants are now run with a smaller operating staff, the console operator may also be responsible for more process units. This creates a significant challenge to industry to design a plant's base systems correctly the first time, and ensure operators are properly trained.

According to Emigholz, two critical factors must be addressed when designing control house information and systems: changes in the operator's role, and the possibility of abnormal operations. "By carefully designing the operator's environment and information systems, this challenging work environment can be run more safely than in the past, giving the operator the best capabilities for doing his or her job," he said.

While process operators were once physically active in operating processes and gathering information, that is no longer the case. Thanks to computers, telecommunications and advances in process control technology, most of today's normal process variation is handled automatically, eliminating the need for a person to continually make small adjustments. With these changes, the console operator's major responsibilities are to monitor the process for developing problems and respond to alarms signaling abnormal conditions.

Emigholz explained that the operator's displays should be designed to include all important diagnostic measurements in just a few displays. Designing this system requires understanding just which data are important during abnormal operations, possible sources of problems, and how each source can be diagnosed. "The analysis of abnormal sources and diagnostic procedures for building the operator displays ties in very closely with the thought needed for building the operator training program," he said.

Even with well-designed systems, console operators may still be responsible for performing difficult tasks during periods of high stress, such as searching high volumes of data quickly, and accurately making complex trade-offs among interacting processes. Emigholz explained that advanced technology can help take over those tasks more suited to computer-based applications. Expert systems are particularly appropriate for such purposes. "The operator's job could be restructured to use the strengths that people can bring to a task. With the proper tools, the operator could be made a more active manager of the process, seeking opportunities to improve the profitability of the operation," he said.

Each operator must have a good mental image of the process. An operator training program, according to Emigholz, should instill this process understanding, as well as the mental tools for conducting a diagnosis. Also, the operator must maintain learned response skills, particularly through simulator-based training, so that in the event of abnormal conditions, which should be few and unique, the operator's response to the situation will be second nature. [See the June 1995 issue of IM for a story on virtual reality-based simulator training.]

Click here to return to Table of Contents for the Intelligent Manufacturing August issue.