Determining the relevance of power generation equipment’s field experience requires special expertise and dedicated research. The continuing evolution of technology, manufacturing processes, and quality control techniques demands updating the old approach to validating “proven technology.” Because equipment manufacturers’ product development never stops, it is difficult to determine what represents “pertinent” operational experience.
For example, although two gas turbines may have the same model number, they operate differently if one has been modified in the factory or in the field and the other has not. How to accurately evaluate the results of this experience when making a purchase recommendation is the challenge faced by all engineering/procurement/construction (EPC) contractors.
Original equipment manufacturers (OEMs) have significantly improved the ratings of prime movers, steam generators, and environmental control systems over the past few years. Thanks to technological breakthroughs, combined-cycle power plants are now pushing the 60% net efficiency (lower heating value) barrier. Similarly, coal-fired plants powered by boilers operating at supercritical and ultrasupercritical steam conditions have increased their thermal performance while decreasing their output of pollutants.
These technology improvements are a boon to power plant planners but represent a dilemma for EPC contractors, who must determine how to properly evaluate new and upgraded hardware. On the one hand, using the newest and most efficient turbine makes it easier to cope with rising fuel costs and growing pressures to reduce CO2 emissions. On the other, early adoption of advanced turbine technology could put the reliability and availability of a plant at risk—and expose the EPC contractor to penalties if the turbine doesn’t perform as advertised.
Power plant owners have always tried to avoid ordering “serial number one” of any device; for newer equipment, they have typically insisted on a track record of 8,000 to 16,000 operating hours before considering it “proven” technology. But, as all power engineers know, every plant is unique. In many cases, equipment modifications and supplier-recommended O&M practices continue to be implemented even after a plant has been commissioned. How can a contractor make a reasonable evaluation of equipment whose performance is a moving target and that may have been customized to meet site-specific needs?
Compared to what?
Technologies mature through incremental changes, yet technology breakthroughs occur only through revolutionary advances. For example, when a gas turbine supplier introduces a new model, it falls to the owner and EPC contractor of a proposed plant to determine whether the improvements incorporated in the new unit are significant enough to warrant a fresh assessment of the risks and rewards of using that particular turbine line.
These decisions must be informed by very specialized expertise. Ideally, they should also be based on a comparison of the operating experience of the new model to that of its predecessors. However, such comparisons cannot be made if the new model or a similar unit has yet to enter commercial service. To further complicate matters, the cumulative operating hours of a particular turbine model as a measure of its technology’s maturity may be irrelevant to evaluating the latest gas turbine uprate, because suppliers introduce hardware modifications on a continual basis.
The situation is even more complicated in the case of steam turbines. With the exception of the last three blades in its low-pressure section, the hardware of a modern large steam turbine is specifically designed to the flow and pressure conditions of a given application. Those steam conditions, in turn, are a function of fuel and site conditions, such as ambient temperature and humidity, and the kind of condenser used.
Bechtel Power Corp. has developed a process for evaluating gas turbines (GTs) and steam turbines (STs) that fairly identifies the risks and rewards of adopting new turbine technologies. This article presents several examples of such evaluations—and their bases and established best practices—made in the course of developing and/or executing more than 30 advanced combined-cycle power projects and five subcritical and four supercritical steam plant projects over the past seven years. The following discussions should be helpful to OEMs trying to understand how EPCs choose turbines and to plant developers seeking guidance on making similar decisions.
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