Electricity consumption in the United States was about 4.05 trillion kilowatt-hours in 20221, and demand for energy continues to grow. In an effort to meet this demand, 987 natural gas power plants are running across the country, and these power plants rely on pumps, motors, boilers and other energy-guzzling equipment to generate electricity. The reality is that it takes energy to make energy. One natural gas power plant in the Great Lakes region proactively looked at the amount of energy used by various pieces of equipment, and they decided to work with one of their trusted service providers to investigate possible solutions to optimize energy usage at their power generating facility.
The operations and maintenance team at the power plant collaborated with service solutions specialists in Battle Creek, Michigan, in 2022 to think outside the box about their ring section boiler feed pumps. Their power generation plant uses four boiler feed water pumps to supply 1,505 gallons per minute (gpm) of water to the boiler, at a head of 2,780 feet. The pumps are fixed speed, operating at 3,582 revolutions per minute (rpm) with 1,500 horsepower (hp) motors to power them.
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With these particular ring section pumps, there was an opportunity to reduce energy consumption by tightening the clearances. The ring section boiler feed pumps had metal-on-metal between the rotating elements and the outer casing, and in these instances, there is a tendency to leave looser running clearances in an effort to prevent galling. However, when the clearances are opened, it seriously affects the pump’s operational efficiency, which in turn consumes more energy and does not prevent pump seizure.
The service center in Michigan has been refurbishing an array of different pumps since 2019—servicing centrifugal, reciprocating and steam pumps. A common problem in pumps with metal fittings is rapid thermal expansion. Rapid thermal expansion causes loss of clearance that results in pump seizure, so clearances get opened as a response, but this has the unwanted impact of increasing vibration and reducing pump efficiency. Graphite-metal alloys are dimensionally stable and have a low coefficient of thermal expansion across a wide temperature range, allowing very tight clearances without risking pump seizure. This is one reason why the service solutions team has been integrating the self-lubricating, graphite-impregnated material into their vertical condensate pumps since 2019.
When the decision-makers at the power plant wanted to proactively use their planned outage periods to make some engineered upgrades that would enable their facility to reduce the amount of energy they consumed, it was the service team who advised them on the engineered pump upgrades that were possible.
The engineers consulted with the team and helped them specify the stationary case wear rings made from graphite/metal alloy that could be incorporated into the boiler feed pumps.
The power plant personnel learned how tighter clearances would decrease vibration, shaft deflection and leakage across the wear rings. This can result in several percentage point increases in efficiency, leading to money saved in annual energy costs.
After a thorough review, the power plant went ahead with the engineered pump upgrades. The field service and engineering repair teams provided comprehensive support during the outage periods. They upgraded the first two pumps in the fall of 2022 and the third pump in June 2023.
The service team was able to reduce running clearances by half and improve pump efficiency by 4%, and the life cycle of these casing wear rings will last twice as long as the original material. The properties of graphite-metal materials have been shown to result in a longer equipment lifespan.
Graphite-metal alloys can be designed to run at 50% of American Petroleum Institute (API) 610’s recommended clearances for metallic wear part materials. Some service providers might use coatings to reduce the coefficient of friction, but making those clearances tighter is really the best way to gain pump efficiency. Clearances can be closed with graphite-metal alloy components, and there is no need to worry about galling if parts happen to rub together. With this nongalling material, the pump’s operational efficiencies and reliability can be improved.
Feedback from the power plant personnel has been positive. Since the first pump was reinstalled in the fall of 2022, there have been no issues—no seal failures or bearing failures. The three boiler feed pumps have been reported as operating “very reliably.” The fourth boiler feed pump is scheduled to undergo its engineered upgrade at the service center in 2025.
It is important to rely on a service provider with seasoned engineers—who ask a lot of questions, bring a wealth of knowledge and make sure they get the right material for the specific application.
References
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