SEDIMENT ABRASIVE EROSION ON HYDROPOWER PLANTS IN NEPAL

Abstract

Hydro energy is the most economically feasible renewable energy for Nepal due to favorable topographic and climatic conditions. Although there is high potential of hydropower in Nepal, presently only two percent of 43,000 MW as economically feasible hydropower has been developed. High sediment erosional transport cause problem in operation and maintenance of Hydropower Plant and at the same time the hydraulic efficiency of the system also reduces. Sediment abrasive erosion is one of the most challenging circumstances for hydro energy development in Nepal. In this research work, sediment data collected from the hydro plant out of 13 hydro plants visited. Sediment samples were taken from different Hydropower Plants (HPP) owned by Nepal Electricity Authority (NEA) in different locations and capacity. The five hydropower plant stations situated at different locations in Nepal having sediment problems comprising three river basins are a) Trishuli hydropower plant, b) Kaligandaki A hydropower plant, c) Marsyangdi hydropower plant, d) Middle Marsyangdi hydropower plant, and e) Upper Marsyangdi A hydropower plant. Sediment particle concentration, and mineral analysis were carried out to find the mineral content and particle shape of the sediment. Under the study not only analysis has been carried out for the sediment abrasive erosion potential of the turbine due to the shape and the hardness of particle, but also the sediment abrasion in various components of HPP and corresponding reduction in efficiency due to abrasive erosion have been predicted. Revenue loss due to the reduction in energy generation has been also taken in account for financial analysis in addition the cost involved for repair and maintenance and or replacement of components at those plants. All relevant data required for dissertation has been taken from feasibility report, initial environmental examination report and project financial analysis report provided by Department of Electricity Development (DoED), and Nepal Electricity Authority, Nepal. All sediment samples were measured in sediment monitoring and erosion R&D lab at IITR for calculating relevant factors associated with them. The mineral particles found to be contained with large extent of Quartz as a hard minerals ranges from 44.6% in Upper Marsyangdi HPP to 68.32% in Kaligandaki HPP. According to IEC-62364 (2013), the shape of sediment particles in HPP found to be sub angular as their aspect ratio (b/l ratio) lies in between 1 to 2 whereas, the factor KShape for Upper Marsyangdi HPP has been taken as unity. The subangular shaped iii sediment particles are prone to more abrasive erosion. The Erosion in runner inlet and runner outlet and other turbine components is not uniform in all five cases. Based on this study, out of 5 hydro plants investigated minimum erosion found at Upper Marsyangdi HPP where the least rate of turbine erosion is 0.61mm/yr with corresponding lower reduction in efficiency 0.069% per year resulting only 3.8 M INR total losses due to abrasive erosion. At Trishuli HPP, has the highest erosion rate of turbine 3.42 mm/yr with higher reduction in efficiency 1.265% per year causing about 16.5M INR losses due to abrasive erosion. In addition while the revenue loss is concerned the Middle Marsyangdi HPP has the highest value of loss in revenue with 11.97 M INR associated with energy generation among the five hydropower projects while the least value of total loss in revenue only 0.08M INR is found in Upper Marsyangdi HPP.