Efforts to Reduce Environmental Impact through Products

Significantly improved power generation capacity due to improved hydraulic turbines
Contributing to solving environmental issues by technical evolution
Voith Fuji Hydro K.K.

Hydropower is a representative form of renewable energy but it may not be as familiar to the general public as photovoltaic power. However, hydraulic power generation technology has advanced greatly over the last dozen or so years and is now making a major contribution to solving environmental issues, such as reducing CO2 emissions. Here we present an approach for reducing the environmental impact with a case example of equipment repair at Nishi-Kadohara Hydroelectric Power Station No. 3 carried out in 2017.

Evolution of hydraulic turbine realized by computational fluid dynamics

Nishi-Kadohara Hydroelectric Power Station No. 3 is a hydroelectric power plant owned by Hokuriku Electric Power Company located in Ono City, Fukui Prefecture. It was built in 1968 using Hotokebara Dam as the water source and with Fuji Electric’s technology employed for the central parts such as the hydraulic turbine and generator.

Nishi-Kadohara Hydroelectric Power Station No. 3

Hydraulic power generation system

While components such as the runner have been maintained regularly, a plan for fundamental renovation was brought up due to aging of the equipment. The idea was to increase efficiency and reduce the environmental impact by improving the runner and ancillary equipment. Many may wonder if there is any room for more improvement in such old technology as hydraulic power generation. We threw this question at Shogo Nakamura, Vice President and CEO Representative Director, Voith Fuji Hydro K.K.

“Certainly, development of an even higher-efficiency hydraulic turbine was at one time considered to have come to a dead end. What brought about a breakthrough in this situation was the establishment of a technology called computational fluid dynamics (CFD) for precise simulation of water flows.”

Simulation of flows, which was originally carried out at limited points, has come to allow accurate grasping of flows through technical development. This has made it possible to design a higher-efficiency runner.

Dr. Shogo Nakamura Vice President and CEO Representative Director, Voith Fuji Hydro K.K.

CFD of bulb turbine runner

Why simply turning a screw propeller faster does not increase boat speed

Many may question again here: “Does an efficiency increase not simply mean bringing more water to hit the runner?” However, the principle of turbines is not that simple. Nakamura explains.

“From the end of the 19th century to the beginning of the 20th century, there was competition to increase the speed of boats. In those days, engineers believed that simply turning the screw propeller faster would provide a larger driving force. For some reason, however, once the rotation speed of the screw reached a certain level, the speed of the boat stopped increasing no matter how fast the screw rotated. Then the screw rapidly eroded. The cause was found to be a phenomenon called cavitation.”

Cavitation is the formation of voids in liquid. Between the two sides of a blade of a rotating screw, a pressure difference is generated that is similar to dynamic lift generated under the wings of an aircraft. As a result, fine bubbles are generated in a large amount in the lower-pressure area, which not only hinders realization of the estimated power but also causes the screw surface to disintegrate and wear out. Accurate simulation of flows for design to prevent this cavitation led to significantly increased efficiency in hydraulic power generation, resulting in successfully reducing environmental impact.

Large-scale model experiment conducted

For replacing the runner of Nishi-Kadohara Hydroelectric Power Station No. 3, in addition to simulation using CFD, a large scale experiment using a model was also carried out. The experiment using the model, which is not always carried out, was carried out because the runner for Nishi-Kadohara was of a type called a diagonal flow turbine.

Types of turbines include the Pelton turbine, which draws energy by directing a high-pressure water jet against the runner and the Francis turbine and Kaplan turbine, which draw energy by guiding the flow to the blades. The application is determined based on the water head and flow rate. The diagonal flow turbine is used at a point in between the Francis and Kaplan turbines. There are not many examples of application of the diagonal flow turbine and the flow inside the runner differs from the Francis turbine and Kaplan turbine, which poses the risk that CFD may not be capable of analysis with the expected accuracy. Accordingly, we decided to conduct a model experiment to verify the analysis accuracy.

“Conducting an experiment naturally incurs costs. Nevertheless, we were given approval for the experiment and had to achieve results. It was a lot of pressure.”

Typical model of diagonal flow turbine
Hydraulic Power Station No. 3
(Diameter: 0.4m Weight: 70kg)

Model of new runner for Nishi-Kadohara

Manufacturing floor faced with challenges of complicated geometry and delivery time

The staff on the manufacturing floor must have been the ones who felt most under pressure. Yuji Hamaoka, Manager of the Turbine Production Engineering Group, Production Department, who was actually engaged in the manufacture, thinks back.

“Replacement and maintenance of runners is always a battle against the delivery time. Without the runner, the hydroelectric power plant in question and any other power plant downstream as well are inoperable. It affects the business activities of customers.”

While the CFD technology has brought epoch-making progress to runners, it sometimes seems to puzzle the shop floor.

“We encounter design with a totally different geometry such as a large thickness difference between blades, unlike conventional designs. With Nishi-Kadohara Power Station No. 3, the outer spherical surface of the blades of the runner has a peculiar geometry that combines two spherical surfaces, which can only be realized with a computer. Blades with such a peculiar outer spherical surface shape make installation and adjustment on site, as well as machining, difficult.”

Yuji Hamaoka, Manager, Turbine Production Engineering Gr., Production Dept.

CFD in periphery of runner blades of Nishi-Kadohara Hydroelectric Power Station No. 3 

Effect produced exceeded the expectations of the people involved

In this way, the new runner designed and developed in cooperation with the customer and manufactured by the committed on-site staff that gave up their days off, was installed at Nishi-Kadohara Hydroelectric Power Station No. 3 in April 2017.

Diagonal flow turbine runner delivered to Nishi-Kadohara Hydroelectric Power Station

The result exceeded expectations. The maximum output increased by approximately 1,500 kW to 49,500 kW, or an increase as large as approximately 6.6 million kWh in terms of annual output. The output increase is equivalent to the annual power consumption of 2,100 households and the effect on reducing CO2 emissions is approximately 3,900 tons annually*

Vice President Nakamura gives an explanation about the effect.

“Nishi-Kadohara Power Station No. 3 was an efficient power plant from the beginning. Still, we were able to improve its efficiency this much by only replacing the runner. The customer was very satisfied with these figures. Besides, it was not the only improvement made. The hydroelectric power plant changed into one that is quieter and vibrates less.”

Environmental impact to be significantly reduced by improving many turbines ready for replacement

As explained above, the effect brought about by improving the runner and ancillary equipment is not limited to increased output.

“The water pressure varies greatly inside a turbine, which causes fish that pass through an area with extremely low water pressure to burst. For that reason, the survival rate of fish that pass through a turbine is used as an indicator of the environmental impact in Europe and the US. We develop runners that are friendly to fish, which is appreciated by customers in the US. To prevent contamination of river water, we also switched the operating mechanism (servomotor), which was hydraulic, to an electric one and employed water lubrication for bearings and runner hubs, instead of oil which was conventionally used.”

Hydraulic power generation was supposedly completely matured but its evolution produces a tremendous effect.

Nakamura concludes:

“In Japan, many hydroelectric power generation plants with a large capacity were built in the 1960s. They are now all ready for renovation. Power generation capacity can be reliably increased by replacing hydraulic turbines in use for over 60 years, which exist in large amounts in Japan, with new efficient ones, leading to a significant reduction in environmental impact. Hydraulic power generation will continue to evolve from now on.”

Runner construction and overhaul (Kaplan turbine)

* Source: Hokuriku Electric Power Company, Inc. Press Release

http://www.rikuden.co.jp/press/attach/17040302.pdf

Links:

Stop Global Warning (CSR)

https://www.fujielectric.com/company/csr/global_environment/preventing_warming.html

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