Investigation Into The Key Problems Of Axial Piston Pump For Seawater Desalination

High pressure pump is one of the most important components in Sea Water Reverse Osmosis (SWRO) desalination engineering. Compared with multi-stage centrifugal pump and reciprocating pump which are widely used in SWRO projects, high-pressure axial piston pump based on water hydraulic technology has many advantages, such as high efficiency, small size, low noise and full water lubricated, and it is suitable to be used in small and medium scale SWRO systems. In order to develop the axial piston pump, this dissertation focuses on its main characteristics and key technology.In this dissertation, as the cavitation caused by high vapour pressure and slightly compressibility of seawater, the variable fluid properties such as elastic modulus, mass density and viscosity were considered in pressure and flow model of the high pressure axial piston pump for SWRO. Compared with the model without considering variable fluid properties, the new model avoids the negative pressure value in simulation process and can predict cavitation and sucked empty of the pump to a certain extent. Base on the main operating parameters of the pump, the gap flow pattern of the hydrostatic bearing slipper pair lubricated by seawater was analyzed. It was concluded that the flow regime of the variable damping is laminar but the fixed damping is turbulent. The corresponding design and calculation formulas were derived. Because the micro deformation of slipper body can influent the pressure field of the flow regime, the correction and compensation methods based on fluid-solid coupling numerical analysis were presented. The prototype of high pressure axial piston pump for SWRO was successfully developed in the domestic. This pump is directly lubricated by seawater and uses valveplate as it distributor. The rated operating pressure of the pump is8MPa, and the rated rotation speed is1500rpm. From the results of performance test at rated operating condition, the actual flow rate of the pump is over110L·min-1and the total efficiency is over80%. The practical application of the pump in SWRO projects shows that the pump has stable performance, high reliability, and can replace similar imported products in the small and medium scale SWRO systems.In Chapter1, current status of high pressure pumps in SWRO projects were described. The advantages of high pressure axial piston pump were analyzed. The main research objects and academic significances of this dissertation were pointed out. The main contents of this dissertation were introduced.In Chapter2, the main fluid properties of seawater varying with pressure were modeled, and the pressure and flow model of the axial piston pump for SWRO was built by the combination of fluid properties models and pressure-flow equations of axial piston pump. The dynamic pressure, flow, leakage, cavitation and efficiency of the pump were analyzed by the numerical calculation of this model.In Chapter3, the dynamic CFD model of the pump at working was established, and the cavitation flow in the pump was numerically simulated. At different inlet pressures, the dynamical cavitation position and duration, the mass flow rate of single cylinder chamber, the oulet mass flow and pressure ripple rate were analyzed.In Chapter4, the design method of slipper pair lubricated by seawater was discussed, the calculation formulas of hydrostatic bearing slipper pair were derived. The structure field and flow field of hydrostatic bearing slipper pair lubricated by seawater were analyzed by fluid-solid coupling numerical method. The influence of micro deformation of slipper body to hydrostatic supporting ablity was analyzed.In Chapter5, the dynamic mechanical characteristics of main parts of the pump were analyzed. The dynamic pv values of key tribo-pairs of the pump were acquired. The virtual prototype of the pump was built, and comprehensive analysis of the dynamic mechanical characteristics, stress and deformation displacement of the main parts, pressure and flow of the pump were analyzed.In Chapter6, tribology tests under water lubrication of variety corrosion resistant metals against composite PEEK materials were completed. Corresponding friction and wear data, morphology of friction surfaces were presented. This test is a basis for materials selection of the key tribo-pairs for the pump.In Chapter7, the main machining processes of the pump’s prototype were introduced. The performance test of the pump was carried out. The pump, which was completed performance test, was used as high pressure pump at a SWRO experimental system. The pump was also used at a SWRO sytem in a desalination plant at a certain island as demonstration application.In Chapter8, the research work of this dissertation was summarized, and some advices on further research work were presented.