Study On Performance Prediction And Coupling Characteristics Of Sea Water Reverse Osmosis Desalination High Pressure Pump And Turbine Energy Recovery Integrated Machine

With the rapid development of island development,ocean-going vessels and drilling platforms,the demand for small and medium-sized seawater desalination devices is rapidly increasing.The high-pressure pump impeller and turbine impeller adopt the coaxial integral design form,which has the advantages of small land occupation,low energy consumption and low noise.It is an urgently needed device in the domestic reverse osmosis seawater desalination field.However,the permeability characteristics of membrane modules in reverse osmosis systems vary with temperature,membrane fouling and other parameters,the operating conditions of turbine energy recovery integrated machine are complex and variable,which in turn affects the energy recovery efficiency and operational stability of integrated machine.Therefore,the study of the coupled operation characteristics of integrated machine is essential to solve the matching of the coupled operation parameters of the integrated machine and provide the coupled operation control strategy.In this paper,the performance prediction and coupling characteristics of the seawater desalination high-pressure pump and turbine energy recovery machine are investigated under the funding of the National Key R&D program.This paper uses a theoretical derivation to investigate the method of selecting the design speed of the physical model of the coaxial coupling of pump and turbine.Theoretical derivation is used to study the selection method of the design speed of the physical model of the coaxial coupling of pump and turbine.The performance of pump and turbine under multiple operating conditions are predicted by the artificial neural network method.The prediction method of the coupled conditions of the integrated machine under different constraints is constructed,and the internal flow field and energy loss distribution characteristics of the integrated machine under the coupled operating conditions in different seasons are analyzed.The main research of this paper is as follows:(1)Based on the working principle of the physical model of the coaxial coupling of pump and turbine,the change process of the turbine from acceleration or deceleration to stable operation is analyzed.Based on the relevant conversion formula of centrifugal pump and pump as turbine,the prediction method of the design speed of the physical model of the coaxial coupling of pump and turbine is established by the method of theoretical derivation,and the prediction software of the design speed of the physical model of the coaxial coupling of pump and turbine is written.(2)Based on the optimal Latin hypercube sampling method,the training sample working points and testing sample working points of the high-pressure pump and the training sample working points and testing sample working points of the turbine are selected respectively.The performance data of the corresponding operating conditions are calculated by numerical simulation,and the training sample data set and testing sample data set of the multi-conditions performance prediction models for high-pressure pump and turbine are established respectively.Based on the training sample datasets and BP neural networks of high-pressure pump and turbine multi-conditions performance,the 3-layer BP neural network models for predicting multi-conditions performance of high-pressure pump and turbine are established respectively,and the respective neural network prediction models are tested using the testing sample datasets of high-pressure pump and turbine respectively.The results show that the established BP neural network model can accurately predict the performance of high-pressure pump and turbine under multiple operating conditions,and can provide a more accurate performance database for the coupling of the integrated machine.(3)A method is established to match the coupled operating conditions of the turbine energy recovery integrated machine.Under the constraints of shaft power and speed of the integrated machine,the coupled operating conditions of the integrated machine in spring and autumn,summer and winter are matched by taking into account the flow and head of the highpressure pump and the flow and head of the turbine.It provides a coupling matching scheme for solving the corresponding parameter matching and parameter calculation of the integrated machine,and provides corresponding control strategies for accurately regulating the operating conditions of the integrated machine.(4)One coupled operation condition each in spring and autumn,summer and winter is selected as the representative condition,and energy loss distribution characteristics of the high-pressure pump and turbine during the coupled condition of the integrated machine are analyzed with the entropy production theory.The results show that the energy loss of the volute and cavity of the high-pressure pump is larger,and the energy loss of the turbine impeller and the outlet extension section is larger.The wall entropy production at the inlet and outlet of pump impeller is larger,and that at the outlet of turbine impeller is larger.In addition,the analysis of the internal flow field,radial force and axial force of the integrated machine in different seasons shows that the radial force of the turbine is greater than that of the pump,and the axial force of the pump is greater than that of the turbine.The above analysis results of flow characteristics can provide suggestions and references for the later hydraulic model optimization design of high-pressure pump and turbine.