Completing a power plant's start-up and commissioning usually means pushing the prime contractor to wrap up the remaining punch list items and getting the new operators trained. Staffers are tired of the long hours they've put in and are looking forward to settling into a work routine.
Just when the job site is beginning to look like an operating plant, a group of engineers arrives with laptops in hand, commandeers the only spare desk in the control room, and begins to unpack boxes of precision instruments. In a fit of controlled confusion, the engineers install the instruments, find primary flow elements, and make the required connections. Wires are dragged back to the control room and terminated at a row of neatly arranged laptops. When the test begins, the test engineers stare at their monitors as if they were watching the Super Bowl and trade comments in some sort of techno-geek language. The plant performance test has begun (Figure 1).
1. Trading spaces. This is a typical setup of data acquisition computers used during a plant performance test. Courtesy: McHale & Associates
Anatomy of a test
The type and extent of plant performance testing activities are typically driven by the project specifications or the turnkey contract. They also usually are linked to a key progress payment milestone, although the value of the tests goes well beyond legalese. The typical test is designed to verify power and heat rate guarantees that are pegged to an agreed-upon set of operating conditions. Sounds simple, right? But the behind-the-scenes work to prepare for a test on which perhaps millions of dollars are at stake beyond the contract guarantees almost certainly exceeds your expectations (see box).
Long before arriving on site, the test team will have:
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Gathered site information.
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Reviewed the plant design for the adequacy and proper placement of test taps and for the type and location of primary flow elements.
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Developed plant mathematical models and test procedures.
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Met with the plant owner, contractor, and representatives of major original equipment manufacturers (OEMs) to iron out the myriad details not covered by contract specifications. Experienced owners will have made sure that the plant operations staff is included in these meetings.
Tests are normally conducted at full-load operation for a predetermined period of time. The test team collects the necessary data and runs them through the facility correction model to obtain preliminary results. Usually within a day, a preliminary test report or letter is generated to allow the owner to declare "substantial completion" and commence commercial operation. The results for fuel sample analysis (and/or ash samples) are usually available within a couple of weeks, allowing the final customer report to be finished and submitted.
The art and science of performance testing require very specialized expertise and experience that take years to develop. The science of crunching data is defined by industry standards, but the art rests in the ability to spot data inconsistencies, subtle instrument errors, skewed control systems, and operational miscues. The experienced tester can also quickly determine how the plant must be configured for the tests and can answer questions such as, Will the steam turbine be in pressure control or at valves wide open in sliding-pressure mode? What control loops will need to be in manual or automatic during testing? and At what level should the boiler or duct burners be fired?
For the novice, it's easy to miss a 0.3% error in one area and an offsetting 0.4% error in another area that together yield a poor result if they aren't resolved and accounted for. With millions of dollars on the line, the results have to be rock solid.
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