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Valves Introduction

Issue 7 and Volume 99.

Valves Introduction

Part 1 of this report discusses advantages gained when a new boiler feed pump (BFP) recirculation control valve design was used at an Illinois Power Co. installation. One author, Mark Liefer, Baldwin Power Station engineering coordinator, (page 24) provided the following separate comments on the experience.

Installation of the new design BFP recirculation valves has been quite successful. When the 1A and 1B turbine-driven BFPs on Unit 1 were put into service on March 28 and March 30, 1995, the pumps and valves had “no vibration or cavitation at any point in the speed ramp.” During tests, the pumps were held for a short time at 4,400 RPM, which is just below the pumping speed needed to move water into the BFP header. Both pumps never ran quieter or smoother at this speed and the flow was 800,000 pounds per hour (lb/hr). Under these conditions, the flow with the original valves and capillary tubes in place would have been much less at 375,000 lb/hr.

Reduced noise and cavitation also is attributed to the higher flows made possible by the new valves. “The modulating control for the recirculation flow is smooth and consistent, which allows operators to keep the BFP controls in the automatic control mode when starting or stopping the turbine-driven BFPs.”

A new generation of technology also is the theme in the article on motor operated valves that begins on page 27. The author discusses how New England Power achieved significant cost savings and improvements in efficiency using new valve actuator technology on a flue gas desulfurization (FGD) system at its Brayton Point power plant. According to plant engineers, the new technology was less expensive to install than traditional methods and has helped to increase reliability.

Actuators and standardization

Details on advances in valve controls, such as actuators, is premium information wherever and whenever it is available. Sometimes discussions on the subject can go far beyond just the controls. As an example, the Valve Manufacturers Association of America (VMA) presented an interesting variety of papers during its 1994 Technical Seminar. Among these was one by Leon J. Niessen of Mekanotjanst International UK titled “Development of the Quarter Turn Pneumatic Actuators for Global Markets.”

Niessen listed burdens faced by the power generation and other industries that are all too familiar to industry engineers. Demands to reduce costs, yet boost productivity and efficiency are shared by all industries. Power plants also suffer the highest costs for maintaining operation while the pressures of possible deregulation and seemingly growing numbers of independent power producers (IPPs) is increasing. We say `seemingly` because signs of attrition among the weaker IPPs has appeared.

According to Niessen, the average maintenance costs, expressed as a percentage of total operating costs, are 20 percent for a cogeneration plant, 25 percent for a fossil plant and 40 percent for a nuclear plant.

The author relates the high cost of maintenance to his discussion of the value of standardization in valve actuator technology. He explained, as an example, that standards for quarter-turn pneumatic actuators were introduced in Europe as a result of efforts by various end-user industries. However, “to date, this standardization program has been ignored by U. S. industries.” He said that legislated safety standard continues to grow and, hence, the demand for automated valves increases. More automation translates into higher maintenance costs.

Niessen reviewed five stages of actuator development. He began with the mid-1930s when the linkage arm and clevis pin arrangement that converted linear motion to rotary motion was introduced. In 1950, the first quarter-turn pneumatic actuator had a vane with off-centered drive shaft. The “last of all current `parent` design quarter-turn pneumatic actuators,” introduced in 1970, combines the rack and pinion (vintage 1960) and scotch yoke (1961) features.

“None of these actuator designs are directly interchangeable on a valve.” They also have no common way to mount accessories.

The author`s conclusions on the need for and advantages of global harmonization of valve standards include a common base for valve automation worldwide, including valve/actuator mounting details, common mounting configuration for solenoid valves, and mounting standard for positioners and feedback devices. His suggestions would lead to component interchangeability worldwide, shorter ordering lead times and down times, and would allow a common in-house parts stock; all of which leads to lower costs.

Unless or until standardization is realized, either through manufacturer-induced technology transfer or under the urgence of valve user groups, there is another development that will cut costs for in situ testing and non-intrusive condition monitoring of power plant valves.

Modern test equipment cuts costs

Advanced versions of vibration, acoustic, ultrasonic and other techniques avoid unnecessary valve disassembly when used to monitor/test selected valves, according to M. K. Au-Yang of B&W Nuclear Technologies. The variety of valves used in power plants present a challenge to monitor and maintain. Predominant among these are check valves, air-operated valves, and motor- and solenoid-operated valves.

More specifically, observed Au-Yang, many of the 1,000 or more valves commonly found in a nuclear power plant are crucial to reliable performance of safety functions. Hence, most recently developed techniques in valve condition monitoring, non-intrusive and in situ testing, and preventive maintenance were developed by the nuclear industry.

“Now that development costs are absorbed, other power plants can take advantage of this modern test equipment. Its use to monitor valve performance can reduce their operating and maintenance costs as it did for nuclear power plants,” concluded Au-Yang.

Speaking of testing, cooperative activity already had accelerated in the world of valve testing in 1989 at a symposium sponsored by the Board on Nuclear Codes and Standards of the American Society of Mechanical Engineers (ASME) and the Nuclear Regulatory Commission (NRC). The power generation industry enjoyed cooperative dialog at the time, as best described by John J. Zudans of Florida Power & Light: “The ASME/NRC symposium brought together representatives of utilities, vendors and the NRC in an effort to clarify ASME code requirements and gain NRC guidance on how to prepare programs.” Suffice it to say that considerable progress has been made since then in the form of adjusted codes and advanced guidelines. (For background information on early generic letters and codes see “The dynamic world of valve testing,” Power Engineering, January 1990.)

AOV maintenance guide

Illinois Power Co. benefited when its staff used the Air Operated Valve Maintenance Guide to upgrade procedures. Produced by the Electric Power Research Institute`s (EPRI) Nuclear Maintenance Applications Center, the guide helped improve the quality of maintenance at Illinois Power`s Clinton Power Station.

Recommendations from the guide were used in a pilot test program to identify the type of valves that needed diagnosing and to implement an air-operated valve (AOV) testing program. The effort resulted in annual savings of $275,400 for maintenance and scaffolding ($10,400), as low as reasonably achievable ($15,000) and energy savings of 2.5 MW ($250,000), according to a report from Doug Koons at Illinois Power.

Steps taken in the Clinton power plant program included testing 12 known leakers. The ease of this diagnostic procedure allowed 16 more valves to be tested during one outage.

Slurry valve progress and application

A new generation of design figures strongly in the toughest of all duty for the world of valves–slurry valves. Three utilities gained advantages by seeking better design criteria in their slurry valves. However, another major element, improved maintenance techniques, contributed to greater reliability.

One utility eliminated all but 10 percent of its valve problems by using the combination of design and maintenance factors. This company also reduced maintenance labor costs by up to 15 percent. Another power plant boosted slurry valve life in its scrubber towers by 2.5 times before needing a replacement.

A third power plant chose its valve design carefully and introduced a quality predictive maintenance system. The combination extended the life expectancy of some valves in the roughest service from as little as 30 days to at least 10 years.

Not enough has been heard about recent improvements in slurry valves. In the upcoming August issue, we document some recent improvements to slurry valves in the article “Design, maintenance extend slurry valve life.” In the article, the authors examine experiences of power plant`s with slurry valves in Texas, Oklahoma and Florida. Most experiences relate to FGD systems.

Meanwhile in Nebraska

In Nebraska, however, another power plant`s experience with control and isolation of water in a sparging and screen wash application for an intake system shows the advantages of knifegate valves over the butterfly valves that they replaced.

The original butterfly valves failed three months after installation at this 800-MW unit, partly due to the sand content of the river water used. These valves were replaced with air-operated pinch valves that also failed. When the pinch valves closed, the water`s high velocity slashed the rubber and weakened the valve. Pipe erosion also accelerated because the high velocity of sandy water breached the leaking valves and deteriorated the piping.

The knifegate valves that were installed in 1984 have performed reliably ever since. Their gates and sleeves need replacement about once each year compared to every three months for the butterfly valves. Maintenance costs have dropped and system outages are greatly reduced because the knifegates are out of contact with the water flow when open and the valve bodies are not exposed to water.

Whether the subject is slurry valves or valve controls, the industry now has many guidelines available to help power plants improve their valve selection and maintenance needs. These are examined regularly at conferences, such as VMA Technical Seminar (November 1994) and EPRI`s recent Fifth Valve Symposium (June 1995). Considerable evidence of the benefits gained also can be found in the reports that follow. END

References

The Gypsum Industry and FGD Gypsum Utilization by L. M. Luckevich and R. E. Collins of Ortech and Dean Golden of EPRI. (EPRI TR-103652)

Processing and Potential Applications of Fly Ash-Aluminum (Ashalloy) Composite by P. K. Rohatgi et al of University of Wisconsin, D. M. Golden of EPRI and D. Odor of PSI Energy. Contact Dean Golden, EPRI, Palo Alto, Calif.

Ash Handling Conversion: Labadie Plant by J. C. Morgan of Union Electric, and G. L. Flandermeyer of Burns & McDonnell at POWER-GEN Americas `93.

Investigation of High-Volume Fly Ash Concrete Systems EPRI TR-103151, Final Report, Oct. 1993, 156 pages (Project RP3176-06). Contact D. M. Golden, project manager.

EPA, Miracle Concrete, Nonhazardous Wastes, “Environmentally Speaking,” October 1993, Power Engineering.

Supreme Court Decision has Implications for Power Plants, “Environmentally Speaking,” July 1994, Power Engineering.