The South Kitsap Water Reclamation Facility in Port Orchard, Wash., doubles as an energy test site for a company pioneering a new kind of hydropower technology.
Facility manager John Poppe wondered whether it would ever be feasible to generate a little hydropower from the water that falls over a weir before discharge to Puget Sound.
When Burt Hamner of Hydrovolts told him about his new barrel-rotor low-head hydroturbine generator, Poppe obtained permission from his supervisors to evaluate it. A Hydrovolts crew installed the prototype in the plant chlorine contact basin’s 10-foot-deep outfall well.
The unit ran for four months, powering a 300-watt floor space heater inside the plant, along with Christmas tree lights. The treatment facility uses hot water from a boiler fired with mesophilic digester gas to heat the buildings. “Recovering the energy from the outfall warms the building and reduces the demand on the boiler,” says Poppe.
“The pilot study determined the best pitch on the paddles for maximum efficiency during variable flows, how much power could be captured, how often the unit would break down, and its maintenance requirements.”
The plant’s 4.2 mgd (design) activated sludge process running parallel with a membrane bioreactor averages 1.7 mgd. Before discharge, effluent goes over a chlorine contact basin weir at 300 gpm during low flow and 1,400 gpm at high flow, dropping 10 feet.
The plant completed field testing of Version 1 in January and in April began testing Version 2, designed by Hydrovolts engineers after analyzing data from the prototype. They enlarged the unit to 4 feet long by 24 inches in diameter and built a stainless steel chute to funnel water directly onto it. Engineers also designed a new weir for mounting the chute and field-fabricated removable stainless steel brackets with a 6-inch-high backsplash.
Hydrovolts staff used a portable crane to install the components, then adjusted the chute so that the water hit the turbine blades with maximum force. The backsplash directed water that would have gone over the weir into the chute. “The upgrades enabled us to capture 10 percent of the overflow’s energy potential,” says Poppe.
Initially scheduled to operate for one month, Version 2 ran for three months, providing data and power for the space heater.
A programmable logic controller (PLC) mounted inside the plant adjusts the hydroturbine’s energy output to variable flows. During the day, the electronics increase resistance on the blades, enabling the generation of more energy. At night, the opposite occurs, allowing low flows to turn the blades. Hydrovolts staff updated the software and some hardware several times during the trial.
The chain on the sprocket driving the shaft connected to the turbine blades was rated for 30 rpm but ran continually at 700 rpm. When it failed in four months, Hydrovolts staff replaced it in two hours after hoisting the unit from the outfall. Plant operators have done no maintenance.
Third-party monitoring of the turbine is done by Prof. David Stensil, P.E., from the University of Washington, and his senior and graduate students who analyze the treatment plant’s energy usage and production.
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The Version 3 waterfall turbine will be twice the size of its predecessors and will use a significantly more efficient rotor. The new design also allows for adaptability to more facilities. An outdoor control panel houses the upgraded PLC, and Web access allows operators to view live data. If the unit works well, Hydrovolts will install a second one next to the first to capture all the flow.
Hydrovolts says its turbines have a good value proposition in facilities where the average flow is over 5 mgd and the waterfall drop is at least 6 feet. Poppe is realistic about the hydroturbine and its energy-saving potential in his plant, where flow averages 1.7 mgd: “Helping to demonstrate new clean energy technology from a local company is a matter of principle and doing the right thing, making choices that best serve the customer.”