Hydroabrasion & sediment monitoring
Natural rivers may transport leaves and driftwood, gravel, sand and suspended mineral particles. Handling the so called “solid load” is a challenge for hydro power engineers and hydro power plant operators.
Hydropower plants in the Alps are generally equipped with trash rakes as well as gravel and sand traps. At hydropower plants in which water from highly glaciated catchment areas, so called “glacier milk”, is used and the water is not stored in lakes where also fine particles could settle, the turbine water may contain suspended mineral particles of considerable concentration. These may damage the turbines. At a head of 500 m for example, inside a Pelton turbine, the velocity of the jet towards the runner is about 360 km/h. Especially the hard particles, e.g. quartz, cause wear on turbine parts, what is also called hydro-abrasive erosion. Nowadays the problem of hydro-abrasive wear gets more important, as sediment yield tends to increase with higher variability of meteoroligical events, the energy efficiency shall be increased and the hydro power plants are expected to be operated in a sustainable way.
When investigating hydro-abrasive wear, a major challange is that suspended load varies strongly through the year. Thus, a continuous monitoring of suspended sediment concentration and particle size distribution is required. Up to now, particle size distribution could only be obtained by analyzing bottled samples in a laboratory. In this research project, an in-situ laser diffractometer is used at the Fieschertal hydropower plant in upper Valais, Switzerland. This device allows measuring continually suspended sediment concentration and particle size distribution.
The investigation of suspended particles in the water of a hydropower plant together with periodical inspection of the turbines and monitoring of their efficiency shall contribute to enhance the understanding and the ability to model hydro-abrasive wear. This serves as a basis for further improving the layout and design of hydropower plants and their components (e.g. desilting facilities, turbines), their instrumentation and operation.
Albayrak, Ismail, Dr.
Boes, Robert, Prof. Dr.
|Keywords:||hydro-abrasive wear, Pelton turbines, suspended sediment monitoring, in-situ laser diffractometer, turbidimeters, acoustic sediment monitoring, mineralogy, power plant operation and maintenance|
Swiss Federal Office of Energy,
Power plant operator (GKW)
|In cooperation with:||
Hochschule Luzern, Comptence Center Fluidmechanics and Hydro machinery (Prof. Dr. T. Staubli),
Worldwide there are numerous dams, which serve many functions. They store and regulate water for power plants, make flood retention volume available, ensure water supply for human consumption and make watercourse segment navigable. Due to the continuous sedimentation the silting ups are increasing and reduce the active storage volume. As a consequence severe sediment-related problems appear and endanger the versatile functions of the reservoirs. One of the possible approaches to counteract these problems is to build a sediment bypass tunnel. Bypass tunnels route most inflowing sediment around the reservoir into the tail water. As most sediment enters a reservoir during flood events, the sediment bypass tunnels are efficiently operated only during this time. This operation stops or in minimum reduces the sedimentation and prevents expensive loss of profit, while providing greatest possible retention volume. However, high velocities, sediment content of the discharge i.e. sand, gravel, medium-to-large sized rocks and other debris and the frequency of heavy loads in the flow may lead to a serious abrasion and thus costly maintenance in the bypass invert. Due to the high cost of construction and maintenance, sediment bypass tunnels are very unconventional and rarely deployed despite their advantages. Therefore there is a lack of experiences and necessary data with the lining, effects of amount, type and size of sediment carried by flow, flow discharge, sedimentbed material interaction and continuous monitoring. To find an economical and effective lining material on the tunnel inverts the operators have been testing different materials and their implementations (pictures) under operation, which have not led to a satisfying solution till this day. Overall, a great demand exits for economical and sustainable solution not only for sediment bypass invert abrasion problem but also for hydro abrasive wear on hydraulic systems.
The main objective of this research project is to quantify the correlation between the hydraulic operation conditions, sediment load, invert material and measured hydro-abrasion. In order to achieve this objective, six test fields with different abrasion resistant materials i.e. four concretes with different compressive strengths and mixtures, basalt and steel plates will be implemented in Solis sediment bypass tunnel in Grisons, Switzerland. Together with the high performance concrete invert of Solis sediment bypass tunnel, total of seven different invert materials will be tested. After every flood event the invert surface will be scanned with a laser scanner to quantify the abrasion. To establish a relation between the wear resistance of the materials and the influence of the flow conditions, the sediment load will be measured with geophones and the flow discharge will be monitored during the running time.
Consequently, the outputs of this research project will help operators of hydraulic systems facing to abrasion problem by providing economic measure to overcome the problems i.e. recommendations of optimization of hydraulic operation conditions, economical invert materials and their implementation.