Global sourcing approach
Like all projects, controls retrofits must work within the envelope of business realities. One faced by AES Corp. (Arlington, Va.), went like this: About half of its plants around the world employ control systems now supplied (as a result of mergers and acquisitions) by one vendor. Many of these plants in the U.S. needed control system upgrades. On the one hand, it was impractical, for cost and schedule reasons, for some of the plants to bid and replace these systems with offerings from other vendors. Obviously, this situation can be exploited by the system's OEM.
The solution for AES proved to be a "preferred customer agreement" (PCA) with the supplier, Emerson Process Management's Power & Water Solutions division. As a result, nine AES plant businesses—Greenidge (New York), Deepwater (Texas), Harding Street (Indiana), Cayuga (New York), Westover (New York), Thames (Connecticut), Red Oak (New Jersey), Warrior Run (Maryland), and Alamitos (California)—will be upgrading their systems over the next five years. According to AES's Bill Rady, the company expects to save an additional 10% on costs for upgrades, new systems, maintenance agreements, and other ongoing support services. Each plant also reduces its cycle time by avoiding the bidding process. Plants are motivated to buy through the agreement by an annual volume discount available in succeeding years, based on the total purchases in the previous 12 months.
Rady's plant, Greenidge (Figure 3), has what could be the oldest control system of its type, one of the first all-CRT-based DCS known as the WDPF. Obsolescence is the main driver of the project. "The controls are 20 years old," observes Rady, "and we started noticing mysterious things happening that we couldn't explain." Maintainability and reliability of the system is paramount to the business. AES's performance group had instituted a program to reduce "high-impact events," and any forced outages caused by an obsolete, outdated, or vintage control system would certainly qualify. Although there had not been a history of derates or events, the plant is taking no chances. The upgraded components will be installed during the fall outage this year.
3. Volume discounts available. AES Greenidge will have its control system modernized this fall, under a preferred-supplier agreement governing nine AES plants. Obsolescence is the main driver of the updating. Courtesy: AES Greenidge
Another key benefit of the PCA, negotiated by AES's Global Sourcing Group, is flexibility. Some plants may need a complete replacement, including thousands of I/O devices; others may need better processors and graphics. With the PCA in place, individual plants can pick and choose what they need.
Future pieces of the puzzle
Not all modernizations are control system upgrades; sometimes they are upgrades to how control is accomplished. A case in point was the installation of a full-stream elemental online coal analyzer (OLA) at Unit 1 of Minnkota Power Cooperative Inc.'s Milton R. Young Station (Figure 4). The OLA, from Energy Technologies Inc. (Knoxville, Tenn.), combines prompt gamma neutron activation analysis (PGNAA) with multi-gamma transmission and microwave attenuation to provide a complete elemental analysis of the coal stream as delivered to the plant on the conveyor belt. The justification here was control of slagging.
4. Full stream ahead. This online coal analyzer is used as an adjunct for control of boiler slagging at Minnkota Power's Milton R. Young Station. Courtesy: Energy Technologies Inc.
Milton Young Station is a lignite-fired plant close to its mine source. Cyclone boilers there have suffered slagging, fouling, and ash-related problems for years. They also have infrequently, but annoyingly, exceeded plant opacity limits as a result of collection and transport problems. Slagging events are handled by burning oil, an expensive proposition. Plant personnel have conducted boiler optimization studies by correlating coal quality to cyclone performance. In particular, the studies have shown that slagging occurs when there in an increase in silicon-rich components such as illite and montmorrillonite clays in the ash.
Simplified relationships were developed between ash content and acid/base ratios of the coal, and resulting cyclone performance characteristics. This has helped the plant reduce oil consumption by 80% or more. Similarly, the new OLA has shown that when low base-to-acid-ratio coal constitutes even a small fraction of furnace feed, opacity will be affected. Thus, the analyzer is now being used to monitor and control the quality of each truckload of coal delivered to the plant.
In this application, the OLA could be considered an offline adjunct to the plant's control capability. However, it takes little imagination to see how OLA data could be incorporated into the control and automation system for such functions as intelligent boiler cleaning, coal blending, emissions control, and heat rate and efficiency monitoring.
Security concerns next?
What might drive additional control system activity? Several experts say security issues. Obeying the law of unintended consequences, the transition away from proprietary control systems to open architectures has also led to greater security threats, both internal (for example, disgruntled employees) and external (such as cyber-terrorism, hackers, and pranksters). Thus, notes Tim McCreary of HF Controls Corp. (Addison, Texas), staff once devoted to plant operations are increasingly being diverted to address system security. Unfortunately, all of this adds cost without adding value to the product. McCreary believes that some of the best solutions for fossil-fueled plants could be derived from nuclear plant control systems.
Security directives are coming from several different directions. The federal government obviously has an interest in preventing energy infrastructure attacks and recovering quickly in the event of an attack. The Departments of Energy and Homeland Security have been assessing our electric infrastructure for vulnerabilities. The North American Electric Reliability Council (NERC) has issued Critical Infrastructure Protection standards and guidelines, including the NERC Cyber Security Standard-Urgent Action Standard 1200. ISA and IEEE also are actively addressing the issue through industry committee work—as are suppliers, by reconfiguring their offerings. Because the ensuing changes will affect both new control systems and plant upgrades, the topic of control system security is best left to a future article in POWER.
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