COMPARATIVE ANALYSIS OF HYDROCYCLONE WITH VORTEX SETTLING BASIN AND SETTLING BASIN

Abstract

Settling basin and vortex settling basin are the most commonly used sediment removal structures to minimize the sediment load passing through the turbine. The application of hydrocyclone in sediment removal of hydropower is very limited and yet to be investigated. This dissertation work focuses on investigating the application of hydrocyclone for sediment removal in hydropower projects. Hydrocyclone has been compared with vortex settling basin and settling basin in terms of space requirement, overall sediment removal efficiency, construction cost, impact on turbine runner and percentage loss in efficiency due to abrasive erosion. Revenue loss due to energy loss has been compared with the construction cost of sediment removal structure for economic analysis. Hydraulics lab of Institute of Engineering Nepal, having a physical model of hydrocyclone, was visited to investigate the working and performance of hydrocyclone. Similarly, Vanala Small Hydro Power in Chamoli district of Uttaranchal, Marsyangdi Hydropower Station, and Middle Marsyangdi Hydropower Station in Nepal were visited to observe working and performance of settling basin and Upper Marsyangdi “A” Hydropower Station in Nepal for vortex settling basin. Sediment data collected during the visit was used to compare the performance of settling basin of Marsyangdi Hydropower Station and vortex settling basin of Upper Marsyangdi ‘A” Hydropower Station. Based on this study, particle size larger than 0.3 mm has 100 % removal efficiency for settling basin of Marsyangdi Hydropower Station. Erosion depth estimated is 1.83 mm/year in runner outlet and 4.56 mm/year in runner inlet for 0.63 kg/m3 of annual average sediment concentration passing through the turbine, with a hardness factor of 0.77. Particle size larger than 0.26 mm has 100 % removal efficiency for vortex settling basin of Upper Marsyangdi ‘A” Hydropower Station. Erosion depth estimated is 1.25 mm/year in runner outlet and 2.93 mm/year in runner inlet for 0.43 kg/m3 of annual average sediment concentration passing through the turbine with a hardness factor of 0.70. Due to the limitation of hydrocyclone in handling high discharge and head loss associated with the operation of hydrocyclone, comparative analysis of hydrocyclone with settling iv basin and vortex settling basin is done for Upper Chhandi Khola Small Hydropower Project located at Lamjung, Nepal with a net head of 710 m and design discharge of 0.67 m3/s. Based on this study, vortex settling basin is more economic, efficient, lesser space required option for Upper Chhandi Khola Small Hydropower Project with lesser turbine erosion and revenue loss. Vortex settling basin with basin diameter of 9.2 m is found to be more economical. All relevant data required for dissertation work has been taken from feasibility report, initial environmental examination report and project financial analysis report provided by Department of Electricity Development, Nepal.