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Survey says …
The EPRI report includes a long list of industry lessons learned and opportunities for future R&D. Hussey said the most important takeaways included:
Sequential automation – 1) Although the sequential automation capability is available to many power plants, most use the bare minimum, relying mostly on the operators for executing written procedures; 2) Although the sequential logic itself does not require routine maintenance, operating procedures do change and these changes then need to be made to the sequences too; and 3) Automating routine operator actions encapsulates the behavior of the best operator and brings consistency between operators.
Loop performance assessment and tuning – 1) Power plant controls make extensive use of cascade and feedforward controls, and most tuning tools do not lend themselves very well to tuning these control strategies; 2) Unskilled users who don’t understand the basics of process control and controller tuning very likely will fail when trying to use tuning software; and 3) Control loop performance assessment software can save significant time by identifying all the problem loops on a unit so that the control engineer can focus his attention on the correct loops.
Advanced process controls – 1) Two corporate-level engineers at different companies pointed out that their company would find implementation of APC very difficult because the skill level at sites are more geared toward maintaining the DCS, instrumentation and control valves; 2) APC systems require very little maintenance in addition to the normal system patches, software upgrades and hardware replacements; and 3) APC software suppliers have a wealth of experience with their software and have access to in-house or third-party consultants for implementing their technology on power plants.
Changing industry needs bring new roles for ACAs
Early in the decade, advanced process control systems were a common low-cost method for reducing nitrous oxide (NOX) emissions through combustion optimization. These systems also often reduced heat rate. Unfortunately, the NOX reduction benefit has been diminished by the installation of selective catalytic reduction systems. While heat rate improvement still is possible in many cases, it is not as attractive as environmental compliance benefits used to be, especially in regulated markets. Today, cost justifications for advanced process control must be based on a combination of benefits, including heat rate reduction, improved ramp rate, improved reliability and a possible reduction in NOX and/or ammonia use.
Sequential automation systems are favored by combined cycle plant operators because of the high rate of startups and shutdowns at many of these plants. Sequential automation can help minimize startup times and reduce the chances of operator error. Project implementations are relatively straightforward, since all programming is done in the existing control system. Some investment usually is required for implementation; in some cases, field instrumentation upgrades and automation of hand-operated valves are needed. In the long term, scheduled maintenance on valves and instrumentation is essential for sustaining the system. And any changes to written operating procedures also need to be implemented in the control system.
Challenges to ACA implementation remain
The value of loop assessment and tuning software remains difficult to express in monetary terms.
Justification hinges on the ability to identify potentially costly control problems, time savings and possibly superior loop performance, compared to trial-and-error tuning methods. Loop assessment and tuning software potentially make control engineers more effective by pointing out loop problems and providing tools to help resolve those problems. Training in process control and the software tools are required for success. Long-term maintenance is minimal and consists of software upgrades and maintaining the servers.
The power industry remains short on experience with advanced process control systems, and power producers must rely on the expertise of technology vendors or outside consultants to ensure proper technology selection, appropriate designs and smooth implementation of these systems. Long-term maintenance includes planned maintenance of all field instrumentation and final control elements used by the system, updating of process models after changing mechanical or thermodynamic properties of equipment, software upgrades and server maintenance.
While cost-justification and implementation specifics vary based on the type of advanced control application, some benefits are common, including improved consistency of operations, extending plant life by reducing stresses on equipment and leveraging control system expertise in an aging workforce environment.
Aaron Hussey is a project manager for the Instrumentation, Controls and Automation program in EPRI’s Generation Sector, where he is responsible for developing monitoring techniques and processes to assess equipment condition. He joined EPRI as an engineer for fossil and nuclear I&C projects in 2002. Earlier he was a manufacturing engineer at Corning and also worked at Turbocam Automated Production Systems. Hussey received a bachelor’s degree in mechanical engineering from the University of North Carolina at Charlotte.
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