Design of Desanding Facilities for Hydropower Schemes Based on Trapping Efficiency

Abstract

Turbine wear caused by hydro-abrasion due to suspended sediment in the turbine water has a negative impact on the power production and revenue of hydropower schemes. Efficiency of desanding facilities that reduce suspended sediment load ahead of turbines is key to limiting hydro-abrasion. Existing facilities built according to common design approaches often show lack of performance, in particular under non-ideal site-specific inlet and outlet conditions. Consequently, a new design concept that allows for the optimized design of desanding facilities at hydropower schemes has been developed based on prototype field measurements and CFD modeling. The effects of facility layout and components, such as tranquilizing racks, transition zone and outflow weir and related design parameters on the flow field and involved particle settling have been investigated in a comprehensive numerical model study. Hence, length adjustment terms were deduced from resulting changes in trapping efficiency, which allow for the estimation of the required basin length and an optimized facility layout. Compared to design approaches considering linear settling trajectories of sediment particles, the proposed procedure leads to longer settling basins in general and thus to increased trapping efficiencies of desanding facilities. Furthermore, the findings about the effect of specific facility components may allow for the optimisation of existing desanding facilities in an economical way.

Keywords

• desanding facility
• suspended sediment
• turbine abrasion
• trapping efficiency
• CFD modeling