Sand Erosion in Francis Runner: A Case Study of Middle Marsyangdi Hydropower Station (MMHPS)

Abstract

Middle Marsyangdi hydropower station (MMHPS) is situated in Siundibar, Lamjung and has an installed capacity of 70 MW. Sand erosion is one of the major problems faced by the station. Due to substantial presence of sand in the Marsyangdi river, the Francis Turbine components are hugely eroded, especially in the rainy season during the months of June, July and August. The runner is dismantled once every two years of continuous operation for overhauling and it was found that the eroded turbine components were the primary cause for MMHPS to bear huge financial losses due to maintenance activities as well as unit shutdown during overhauling. To prevent such losses, it is necessary to predict the erosion prone areas in the turbine components and necessary solutions like suitable coating are to be used for optimized performance and reduced financial and power losses. This study predicts the erosion prone areas of Francis runner at different wicket gate openings using the ANSYS CFX simulation software. The erosion analysis has been categorized into qualitative and quantitative analysis. The qualitative results from both simulation and actual data obtained during field visit were found to be of similar nature. The trailing edges of the runner blades were found to be mostly eroded. Leading edge erosion was found to be due to direct impact of sand-laden water emerging from guide vane opening and trailing edge side erosion was found to be due to high outlet velocity, pressure drop as well as curved runner profile. The quantitative measurement was performed at the site in which the reduction in blade thickness was measured. The erosion rate density from both simulation and site measurement have been compared. Elastomeric semi-soft coating applied in the runner blades were found to be effective for minimizing the sand erosion.