By Patricio Egan, Singer / Mueller
Hydropower, next to thermal generation, plays an important role in Argentina’s energy mix. Responsible for around 36 percent of the country’s electricity with a capacity of 10.1 GW (Gigawatt), hydropower is used for both industrial facilities and private households. Futaleufú, one of Argentina’s hydropower plants in the south of the country, was faced with a repowering of generators that gave rise to changes in water pressure that affected the valves used in cooling of the generators—a vital function.
Built between 1971 and 1976, the Futaleufú hydropower plant produces 472 MW (Megawatt), from its three vertical-axis 157 MW Francis turbines. They are subsequently used to power four 118 MW (Mega Watt) generators. The electricity—on average around 2,900 GWh (Gigawatt per hours) per year—primarily powers the Aluar aluminum plant in the nearby city of Puerto Madryn and any excess power is fed into the grid for public use.
DIAGNOSING THE PROBLEM
The initial problem started with the old pressure regulating valves that fed the turbines, those were making a lot of noise caused by cavitation and those valves became so bad the plant decided to uninstall them and look for an alternative. In 1980 they were replaced by “multi-stage valves” which is nothing more than a pipe with four plates of two holes installed in series, in such a way that they produce the necessary pressure drop (with trial and error) from 15kg/cm2 (213 psi) to around 3kg/cm2 (43 psi) (Cavitation Factor σ = 0.33 – very severe cavitation). This valve feeds all the cooling systems (generator radiators, four-bearing exchangers, carbon gasket, or packing gland that works with a minimum pressure necessary).
Head of maintenance for Hidroeléctrica Futaleufú, Engineer Santiago Llansa, adds, “Approximately two years ago we started repowering of the generators, which made more cooling necessary in the radiators. At the downstream of the radiator cooling circuit, we have a valve with which we regulate the flow through the radiators. As this flow increased, the pressure of the entire circuit dropped, which made it necessary to move the two-hole plates in such a way, so that the pressure drop is lower.
To give you an idea, the stroke of the valve has twenty turns for its total opening and if we turn only a quarter of a turn of the stroke, the group of the cooling system will shut off due to mechanical failure caused by low pressure in the carbon board.”
UNDER PRESSURE
In order to remain operational, the water-bearing, critical components of a hydropower plant have to be shielded against a hydrodynamic effect known as cavitation. Cavitation is a phenomenon that occurs due to rapid and significant pressure drops and fluid velocity increases. If not controlled, the generated shock bubbles can damage or destroy components by erosion, such as, internal valves that produce noise and vibration and can significantly restrict flow.
Hidroeléctrica Futaleufú sought counsel from a multi-company collaboration spearheaded by Klinger Argentina and Mueller Water Products to ensure that renewable energy would keep flowing in the region of Chubut. Over the years, many Singer valves have proved to be the most flexible for solving pressure and flow challenges in many South American Hydroelectric power plants.
The challenge for this project was to determine what valve would prove to be both durable and reliable with regard to the specific flow and pressure conditions found at the power plant. Not wasting any time, Cristian Gonzalez, sales manager of Klinger Argentina, says, “As a leader in the field of sealing technology, we are fully committed to plant safety and reliability by providing our customers with solutions that best fit their individual needs. In this specific case we opted for Singer pressure reducing control valves, a Mueller brand.”
SRD TECHNOLOGY: A CLOSER LOOK
What makes this valve unique is the Single Rolling Diaphragm (SRD) technology that provides smooth, steady and precise pressure control from maximum to virtually zero flow. The effective area of a single rolling diaphragm remains constant so the bonnet is much smaller and lighter than a flat diaphragm. A measured quantity into the bonnet control chamber always gives the same smooth movement of the inner valve through the entire stroke. A smaller bonnet also makes the valve lighter and safer for maintenance, while the smaller control chamber enables it to respond faster to changing pressures. By eliminating the seat chatter at low flows, the SRD avoids injecting small pressure pulses into the piping, which, over time, may increase leakage, losses or pipe bursts.
The actual installation of the required four valves, one is additionally being kept in reserve, took place over April and May of this year without any complication. “With the suggestion of the Singer valves to regulate pressure and have the anti-cavitation system, we were going with the optimal solution for having the necessary flow without dropping the pressure. Upon completion of installation, we opened the radiator outlet valve and the pressure dropped only 100 g/cm2, which totally exceeded our expectations, and it did not make any noise,” says Llansa.
“These new valves were flowing at 12,000 lts/min, and we had the radiators outlet open only 6 laps, and we imagined that by opening two more laps we would to exceed 12,000 lts/min and the pressure was going to fall but this never happened and we were able to fully open the valve—total satisfaction,” adds Llansa
BACK TO WORK
Following the completion of the task, the plant operators can now again focus on their core business—the provision of electricity—without having to worry about potential damage to the critical components of the plant or blackouts resulting thereof. This has become a crucial factor as they are currently planning to replace the current 118 MW generators with 140 MW variants.
Looking back on the project, Cristian Gonzalez adds, “Being willing and able to collaborate across both intracompany and intercompany borders is what ultimately led to the success of this project. Working together, we managed to ensure that a vital part of Chubut’s industry can remain operational and that households in the region can continue to be supplied with excess electricity. This is what we set out to do, and what we travelled more than 1,900 kilometers to achieve. Speaking for both my colleagues and myself, I’d say the result, together with the feedback we have received from our customer, was well worth the effort.”
ABOUT THE AUTHOR
Patricio Egan is Singer area sales manager for Mueller Water Products. Singer, a Mueller brand, designs and manufactures automatic control valves for the global water industry. Since 1957, Singer pilot operated diaphragm control valves have been installed on virtually every continent around the world. Whether it is water loss management in Southeast Asia, water conservation concerns in Saudi Arabia, or urban distribution demands in the United States, Mueller provides water management solutions to governments, cities, companies, and contractors around the world. For more information, visit www.singervalve.com or www.muellerwaterproducts.com.
MODERN PUMPING TODAY, February 2020
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