Realtime sediment monitoring in power plants

Sediment monitoring

RESEARCH ON SEDIMENT TRANSPORT

3D modeling of sediment transport using CFDFigure 3 illustrates the results of the numerical

simulation of a self-forming and meandering channel. The simulation started from an initially straight channel. The numerical model results were compared to the data of a large scale physical model test with a length and width of 40m and 12m, respectively.

CFD (Computational Fluid Dynamics) computer programs offer a wide range of applicability in the field of hydraulic engineering. One is the modeling of the 3D flow field in hydro systems, coupled with the calculation of the river bed changes in the vertical and transversal direction.

With this ability and today’s increasing calculation speed of a PC, CFD in hydraulic engineering will be a powerful tool in e.g. flood protection measures as well as life time prediction of reservoir storage volume.

Figure 1 illustrates the simulation of the distribution of the suspended sediment concentration at a water intake in an irrigation reservoir.

Figure 2 shows the results of the numerical simulation of sediment transport in a 180° channel bend. The flow was highly unsteady and the sediment size distribution fairly non-uniform.

Fig.2: Transient bed changes

Fig.1: Suspended sediment concentration

Fig.3: Free-forming meander evolution

Reservoir sedimentation studies

Fig.1: Reservoir sedimentation

Fig.2: Bathymetric map of Kulekhani Reservoir

Fig.3: Differential Global Position Systems

Globally, the average loss of storage capacity is higher than the increase of storage due to sedimentation. (see Fig.1). Consequently, a loss of energy production or water use is observed. The present study is investigating the most reliable method for bathymetry survey, in order to document (see Fig. 2) and understand the sedimentation process ongoing in Kulekhani Reservoir as an example for reservoirs in the Himalayan range. Within this study, Differential Global Position System (see Fig. 3) is considered to give the most reliable results when surveying the reservoir. Further studies will then investigate in how far it is possible to counter act this sedimentation process and to prevent the loss of storage volume.

Kulekhani Reservoir

Base stationWith GPS sets

Reservoir sediment handlingConsequences of reservoir sedimentation are proving to be more sever than expected. This requires handling strategies that can achieve the sediment balance to stabilize and promote optimum use of reservoirs storage capacity

Fig. 1:Sediment problem during dry season but hidden when reservoir is full of water

Intakestructure

Fig. 3: Hydrosluicing through the dam intake

Fig.4: Water jetting to break consolidated clay deposit

Water jetting

Pressurehose

Suction hosesupport

Suctionhead

Consolidatedclay sediment

Fig.5: Sediment removal from a small irrigation reservoir in Ethiopia

Sediment handling technologies, have been developed and tested which enables efficient suction and transport of sediment from reservoirs. Removal of sediment from a reservoir by hydrosluicing is using the potential energy at the dam. Hydrosluicing is one of several sediment removal techniques. This system is simple and possible to operate in reservoir for continuous and long time. When applied in irrigation reservoirs the removed sediment can be released directly to the field to improve land fertility.

Fig.2: Sediment removal at a test rig at NTNU hydraulic laboratory

Effects of turbine wear Reduction in turbine efficiency Increase in O&M costs Increase in production losses Reduction in supply regularity

Do we have answers? No, not yet.

Where to monitor? At the upstream of turbine for

collecting database needed for optimisation

At the headworks to use as early warning system

Motivation What is the optimum size

of settling basin? What is the guaranteed life

time of a turbine? What is the optimum

operation regime of a power plant w.r.t. sediment handling?

Why monitoring? Quantify the sediment load Guide the HPP operation Collect sediment data for

economic optimisation

SMOOTH sampler

1500 MW Nathpa Jhakri HPP, India

Pressure breaker

Sensor and transmitter box

Flow

Fig.2: Installed real-time sediment monitoring system at power plants

Pressure breaker

12 MW Khimti Power Plant, Nepal

Sensor and transmitter box

SMOOTH sampler

Wear in the guide vanes

Wear in the runner

Fig.1: Sediment induced turbine wear

For further information you may contact Durga Sangroula, durga.sangroula@ntnu.no For further information you may contact Kiflom.Belete, kiflom.belete@ntnu.no

For further information you may contact Nils Rüther, nils.ruther@ntnu.noFor further information you may contact Meg Bishwakarma, meg.bishwakarma@ntnu.no