Design And Mass Transfer Characteristics Of Rotary Energy Recovery Device For Seawater Desalination

The rotary energy recovery device is widely used in reverse osmosis seawater desalination projects due to its compact structure,simple operation,and high energy recovery efficiency.It has an important role in the energy saving of the seawater desalination process.In this paper,a new type of rotary energy recovery device was designed for the reverse osmosis seawater desalination system combined with hydraulic related theories.The theoretical analysis of the flow field mass transfer problem was carried out,which lays the foundation for the development and engineering application of the rotary energy recovery device prototype.This paper first determined the structure,design requirements and performance evaluation parameters of the rotary energy recovery device.After analyzing the principle of pressure energy exchange,combined with the design theory of the disc-distributive hydraulic pump,a set of rotary energy recovery device with a nominal processing flow of 60L/min and a nominal pressure of 6 MPa was designed.On the basis of the above structural design,the flow velocity and displacement curve of the liquid in the channel were obtained by building a mathematical model of the flow distribution process,and the change of the distribution pair compression coefficient was obtained from the change of the pressure field.Using the Crank-Nicolson central difference scheme to solve the diffusion partial differential equations,the change of the concentration field inside the rotary energy recovery device was obtained in one-dimensional state.The orthogonal simulation test method was used to examine the influence of various factors on the concentration field distribution.Rotary speed has the greatest effect on the increase in the concentration of the booster outlet,followed by the rotor length,then the number of channels and the diameter of the channels.Introducing the volumetric efficiency index of the channel,it was found that there is a best match between the rotary speed and the structure size parameters under a certain processing flow rate.Under this group of parameters,it can ensure that the mixing rate and channel volume efficiency of the device have optimal values.A three-dimensional model of the internal flow field of the rotary energy recovery device was established,and the NaCl concentration field distribution inside the tunnel under different operating parameters was obtained by Fluent numerical calculation.After the operation is stable,a stable and reciprocating ‘liquid piston’ will be formed inside the channel,effectively separating high and low concentration liquids.Taking the mixing rate and channel utilization as evaluation indexes,the influence of the treatment flow rate and rotor speed on the supercharged outlet concentration was studied.It was found that when the Strouhal St number of the device was valued between 1 and 2.5,the device’s outlet mixing rate was the lowest.The study also found that when the low-pressure seawater inlet flow rate is 1.05 to 1.1 times the high-pressure inlet flow rate,the mixing ratio of the energy recovery device is low,indicating that there is an optimal matching relationship between the low-pressure seawater inlet flow rate and the high-pressure concentrated brine inlet flow rate.By extracting the pressure contour of the flow field,the energy recovery efficiency of the device under the rated parameters is 95.77%.