Study On Axial Thrust Dynamic Balance Of Large Seawater Desalination High Pressure Pump

The high pressure pump is the key equipment in reverse osmosis desalination system.At present,most high pressure seawater desalination pumps adopt multi-stage centrifugal pumps in China,and the balance of rotor axial thrust uses automatic balance device.Therefore,the performance of the axial thrust balancing device is the main factor that directly affects the reliable operation of the pump.The seawater desalination high pressure pump operates with frequency conversion speed regulation and keeps constant flow rate.The outlet pressure of the pump depends on the requirements of reverse osmosis system,generally within the range of 5.5 MPa-6.2 MPa.The traditional calculation method often fails to obtain accurate axial thrust,and the axial thrust balancing device can not achieve the ideal effect,which exists a great threat to the stable operation of the pump.Therefore,accurate calculation of the axial thrust is an important guarantee for the efficient operation of the pump.The research content of axial thrust dynamic balance is Based on the research project of the 13 th Five-Year National Key Project "Development of key equipment and components for large-scale membrane seawater desalination"(2017YFC0403703).The distribution law of pump chamber pressure under different rotating speed and flow conditions is studied by combining theoretical simulation with experiment.On this basis,the program of axial thrust calculation and design is compiled,and the axial thrust dynamic balancing device is optimized.The main research contents are as follows:(1)The internal flow field of single-stage model pump of SWRO high-pressure pump and the pressure distribution in the pump chamber under different working conditions are studied by numerical method,and the pressure distribution and velocity distribution of the internal flow field are analyzed.The results show that the pressure change trend along the radial direction of the front and back pump chambers is the same,and the pressure in the front pump chamber is approximately the same as the pressure in the back pump chamber at the same radius;The gradient of pressure increase in the pump chamber increases with the increase of flow,and the gradient of pressure increase in the pump chamber decreases with the increase of speed;at the same time,the influence of the misalignment of impeller and guide vane on the pressure distribution in the pump chamber is studied,which will not only reduce the head and efficiency will also increase the axial thrust in varying degrees.(2)The pressure distribution test of model pump is carried out,and the pressure distribution law of pump chamber under different flow and speeds conditions is compared and analyzed.The results show that the change trend of pressure distribution in pump chamber is approximately the same as that of simulation,and the error between simulation and test is larger at the point of small flow rate;The simulation results,test results and theoretical formula calculation results of axial thrust are compared and analyzed under different working conditions.The error between test results and simulation results is smaller than the error between test results and theoretical formula calculation results.(3)On the basis of theoretical calculation,the axial thrust balancing device design program combined with the pressure distribution law of pump chamber obtained from experiment is compiled by using VB assembly language tool,and an efficient balancing device is optimized to meet the needs of engineering.The internal flow field of the optimized balancing device is analyzed by numerical simulation.The results show that the error between numerical simulation and theoretical calculation is small.(4)Through the operation test of high-pressure pump,the high-quality material of the balancing device is selected by comparing the temperature rise of return water of different clearance and different material balancing device.After 100 hours operation test,the reliability of the balance device is verified by the disassembly check of the high-pressure pump.