Erosion wear on a double-suction centrifugal pump of the Zuncun Pumping Station based on two-fluid model

Abstract

The Zuncun Pumping Station is located at Yuncheng of Shanxi Province, North China. This station consists of series of second-stage pump stations and is an important input part of the Yellow River Diversion Project (YRDP). Normal operations of double-suction centrifugal pumps in the Zuncun’s second-stage pump stations are always troubled seriously in sediment wear resulting from the Yellow River’s hyper concentrated sediment concentration and pump impeller’s high speed rotation. In general, the sediment wear occurs at seal rings, blades and volutes and results in an increment of seal clearance, deformation of volute tongue and decrement of impeller size. Therefore, the component life, efficiency and reliability of pump stations reduce largely. Especially in flood seasons, the sediment wear becomes much severe due to increments of sediment size and concentration and results in a large waste of energy and capital. Two-phase numerical models have been widely applied for sediment-laden flow in pumps to predict the distribution of sediment wear indirectly in recent years. Due to the theoretical insufficiency in modeling two phases’ turbulence behaviors, the previous two-phase numerical models are weak on the effects of sediment size and concentration which are the major factors for sediment wear. This paper mainly studies the effects of sediment size and concentration on sediment wear in the double-suction centrifugal pumps used in the Zuncun’s second-stage pump stations. A new developed Eulerian two-phase numerical model, which considers the turbulence effect into drag force and performs the change of water turbulence structure in sediment diffusion coefficient resulting from the turbulence scale effect (TSE), is applied for sediment-laden flow in the double-suction centrifugal pumps. The TSE consists of the turbulence intensity and the sediment dynamic scale to perform the combined turbulence behavior of flow strength and sediment. The k-e turbulence model is used for the closure of water phase, and Hinze-Tchen’s algebraic particle turbulence model is used for the sediment phase. Based on the two-phase numerical results, the sediment wear is calculated by the Oka model which takes into account the role of sediment size. Sixteen cases grouped by four typical sediment sizes are studied with four representative inlet sediment concentrations. Results demonstrate that the sediment wear mainly and severely occurs on the pump’s blade and volute in all cases. The sediment wear on the blade gradually increases along the radial direction and is severer on the pressure side than on the suction side. The severest regions are on the middle of pressure side and the trailing edge of suction side. The sediment wear on the volute inner surface increases as the decrement of the cross section area, and the severest wear region in the volute is at the volute tongue. As the increment of inlet sediment concentration, the sediment wear rate almost increases linearly. As the increment of inlet sediment size, the sediment wear rate increases slightly, and the increment speed gradually slows down. On this basis, it is suggested to prevent the Zuncun’s double-suction centrifugal pumps from sediment wear by reducing the sediment size and concentration of water through the pumps.