Brain surgery breathes new life into aging plants

—By Jason Makansi, Pearl Street Inc.

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Age is wreaking havoc on the U.S. generation industry, especially the coal-fired sector. Industry conferences are replete with hand-wringing over the "brain drain," the lack of skilled personnel, the meager number of students pursuing engineering degrees, and the accelerated retirement of the older workers who make up the industry's experience base. On top of this, the industry's physical infrastructure is aging. Almost all new U.S. generating capacity added over the past decade has been gas-fired, which means that existing coal-fired capacity isn't being replaced.

Sure, there's a queue of over 100,000 MW of planned coal-fired capacity, but it's a long slog between putting a resource plan in front of a public utility commission and putting megawatts on the grid. Plus, the industry hasn't figured out a model for building and financing the attendant transmission system upgrades necessary to move that power to where it's needed. And, of course, global climate change is the elephant in the room when new coal plants are discussed, and that beast is getting less and less modest.

The fuel-diversity aspect of the plant aging issue is even more depressing to ponder. Because natural gas prices have been so high, all that new gas-fired capacity only runs about 20% of the time. So, these newer but still-aging stalwarts are being run longer and harder. Five years ago, the national average capacity factor for coal plants was around 70%; today, it's more like 80%, and some flagship plants are pushing 90%. In some cases, these coal plants also have to be more nimble, to function within new guidelines for transmission organizations or to capture spot- or day-ahead market revenues.

It would be worth a Letterman flashback segment to watch merchant genco CEOs from the 1990s predict the replacement of up to one-third of the "dirty, aging" coal-fired capacity by "clean, affordable" natural gas. Not even the Clinton-era New Source Review (NSR) could knock this capacity out of the market, although it certainly contributed to an attitude of underinvesting in these assets.

The bottom line is that these plants will probably run until they can't.

Enter control upgrades

One of the most prevalent ways to manage the aging process is through control system upgrades. The new "brain" not only helps the physical equipment respond within the limits of its age, but the advanced software and control techniques that accompany the brain also capture and automate at least some of the expert knowledge resident in human operators and performance engineers. After all, airline pilots are now taught to "keep their hands off" the controls and let the automation system do what it is designed for.

Today, the power plant control system is also converging with the data acquisition system to create a more complete plant information system. With the integration of key software packages, advanced sensors and control elements, and intelligent plant devices, the automation system will, in time, truly become like a brain, responding in real time to dynamic input changes and optimizing outputs across the many demands imposed on the plant (POWER, September 2005, p. 56).

Every controls upgrade project is driven by a combination of imperatives, including these:

Replace obsolete control equipment.
Integrate separate, "islanded" control systems for boiler, turbine, burner management, coal handling and preparation, and the like.
Incorporate new capital equipment—such as scrubbers, selective catalytic reduction (SCR) systems, low-NO_x firing systems—into the plant controls.
Reduce NO_x emissions incrementally through more-stable boiler control.
Improve unit flexibility and response to grid and market dispatch requirements.
Enhance plant and worker safety (see box).
Increase unit output incrementally.
Reduce heat rate (improve plant efficiency).
Avoid forced outages and improve commercial availability and plant reliability.
Reduce plant staff.
Implement a comprehensive corporate, enterprise, portfolio, or asset management strategy based on standardized information technology and knowledge management platforms.
Enhance plant security.

NFPA 85 Code revisions: Age requires new look at boiler safety

National Fire Prevention Association (NFPA) 85, a safety code that applies to burner management systems (BMS), is undergoing revisions expected to be finalized this year. According to Fred Ingram and Richard Kimball of HF Controls Corp. (Addison, Texas), most of the changes are "clarifications," although at least one is a change in "philosophy."

The new code expressly forbids the routine practice of "blinding" the scanners on out-of-service burners. Ingram notes that the BMS flame scanner must have some positive method of proving no flame, which is not the same as confirming that the BMS does not detect flame from a blinded scanner. BMS suppliers commonly use the external blind signal to blind the scanner and block flame detection. If the scanner detects a flame when blinded, the scanner is assumed to be faulty and the burner cannot be released for service. This provides one level of safety, but not enough.

NFPA 85 likely will not force modifications to existing BMS except as part of a substantial upgrade to the boiler. For this reason, the safety issue needs to be raised during control retrofit and upgrade programs. Possible solutions range from fairly minor logic changes to scanner replacements.

Steps that plants need to take include these:

Determine whether your current BMS employs a blind function in the hardware or software.
Test the equipment to determine if the scanners can be made to work without the blind signal. If they can, schedule BMS modifications through a qualified vendor.
If the existing scanners cannot provide the required discrimination, initiate testing with a scanner supplier and, if necessary, write a request for quote for purchase of new scanners. Here, discrimination is defined as the ability to detect the flame on one burner while ignoring the flames present on adjacent burners.
Schedule the installation and commissioning of the new hardware and software.

Most plants will be able to make the change with little impact on cost or schedule. However, some will have to re-sight the scanners to achieve reliable results. This often will necessitate the use of high-cost fiberoptic components. In the worst case, scanners may have to be relocated, which could involve cutting and welding of pressure parts. Ingram and Kimball stress adequate testing of the scanners in step 2, above. This requires expertise that most plants do not have on staff.

Other NFPA 85 mechanical and control clarifications include:

Revised definition of safety shutoff valves to avoid misinterpretations of which valves are safety shutoff and which ones are not.
Addition of a section to address flue gas piping/ductwork. Because the flue gas path is to be treated the same as a fuel line, the BMS must monitor the status of the valves and associated equipment and include them in the permissives and safety logic. This could affect virtually all low-NO_x burner upgrades employing flue gas recirculation, although such upgrades usually require significant BMS changes anyway.
The table for minimum piping sizes for vent lines is being upgraded to include metric equivalents.
The requirement for a "watchdog" timer will be edited to broaden the range of devices that can be used, allowing the use of more-sophisticated testing devices.

A seminal report on this subject, Upgrading Instrumentation and Control in Coal-fired Plants (issued in January 2004 by Hermione Nalbandian of the London-based IEA Clean Coal Centre), notes that the average life of modern instrumentation and control (I&C) systems ranges between 10 and 15 years for PC-based systems and between 15 and 20 years for proprietary distributed control systems (DCS). In particular, this report dissects 15 I&C upgrade case studies. The cost of these projects ranged from $1 million to $6 million. However, the report also notes that other plant modifications are invariably carried out in conjunction with the controls upgrade, making it impossible to accurately assess the monetary value of the I&C portion.

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