The Colombian area of Antioquia creates much of its clean power from hydropower plants along the Guadalupe River. The Guadalupe IV hydroelectric plant generates power with three vertical axis turbines that discharge water below the river level.
To prevent flooding, however, the plant needed a solution that ensured the ejector pumps would work regardless of power or pressure differentials.
The Problem: Constant Flooding
The lower part of the plant is susceptible to water leakage because the river runs beside a roundhouse that discharges water from the three turbine units, so the plant is designed to continue operating with a certain amount of flooding.
Filtered water leakage from the turbines, hydraulic valves, regulators, water snails, penstocks and draft tubes cones is collected in a well. Three vertical pumps have been installed inside the draw-well, two pumps have a suction capacity of 100 l/s (1,585 USGPM) and there is a flooding pump with a capacity of 200 l/s (3,170 USGPM). The pumped water travels through two 30-inch pipes that discharge into the river.
Level sensors are installed on the drainpipe so when the level in the sump reaches 330 cm above the bottom slab, a signal is generated to indicate potential flood risk. This in turn signals a butterfly valve installed on the valve chamber to partially shut down the plant, and the plant is unable to generate the power it should until the problem is rectified.
The Solution: Ejectors and Automatic Control Valves
With several flooding events in the past, the Guadalupe IV hydroelectric plant designed a group of ejectors that do not depend on the electrical systems and serve as a reliable backup in case of flooding. With this system in place, the power plant can continue to produce uninterrupted power to its customers.
The ejectors receive water through a 6-inch pipe with three legs installed upstream of the generator's inlet valves. The inlet pressure generated is 40 bar (580 Psi) (static pressure) with a total flow of approximately 235 l/s (3,724.75 USGPM). The problem is the ejectors are designed for a specific flow and pressure conditions, so any changes on those variable values will affect the performance significantly. The optimum operating conditions for those ejectors is 80 l/s (1,268 USGPM) at 27 bar (392 Psi).
The original project was designed with a plunger valve. However, a pressure drop across the valve would have caused cavitation. Not only is cavitation loud and capable of causing vibrations and choking the flow, it also creates erosion that results in equipment failure and surging that can lead to pipe bursts.
To ensure these variable conditions remain constant, the engineering team chose selected automatic control valves (ACVs), picking Singer Valve’s 8-inch pressure reducing control valve with anti-cavitation trim.
Using a Specialized Automatic Control Valve
The ACV chosen for this project comes with a single rolling diaphragm — an innovative 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 version.
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 anti-cavitation cages have been designed for a flow of 80 l/s (1,268 USGPM) and can reduce the pressure up to 27 bar (392 Psi), thus allowing the ejectors to operate at optimum conditions. This anti-cavitation technology contains two heavy stainless steel sliding cages that maximize the full flow capacity. The first cage directs and contains the cavitation recovery, allowing it to dissipate harmlessly. The second cage allows further control to a level as low as atmospheric pressure downstream.
“By installing this pressure reducing control valve with anti-cavitation, instead of the original plunger valve we reduced the cost of the operation from 130 million of Colombian pesos (70K US$) to 18 million of Colombian pesos (9.8K US$),” said engineer Santiago Ramirez, spokesman for the hydroelectric plant.