Study On Solar Desalination And Co-generation Of Water And Electricity

With the rapid development of society economy,the increasing urgency of fresh water and energy has become a global concern.Compared with the mature membrane and thermal desalination technologies on the market,which mainly rely on the consumption of fossil energy,Using the abundant clean and renewable solar energy on the earth for desalination and power generation can not only effectively alleviate the shortage of fresh water and energy,but also speed up the goal of carbon neutralization in China as soon as possible,which is a work of great strategic significance.In order to make more efficient use of solar energy for desalination and power generation,this paper focuses on new methods and new ideas of solar desalination and power generation.The specific research contents and key results are as follows:(1)A multi-stage desalination system using the waste heat of solar panel is proposed.The multi-stage membrane distillation technology is used to recover the solar panel surface waste heat for desalination to produce a large amount of fresh water.At the same time,the solar panel temperature is reduced by evaporative cooling technology to improve its photo-electric conversion efficiency.The water production rate and cooling effect of the coupling system are studied from both experimental and theoretical aspects.The experimental results show that under one sun illumination and four-stage membrane distillation system,the coupling system can achieve a water production rate of 1.42 kg m^-2 h^-1 and a 1%increase in photoelectric conversion efficiency,which are in good agreement with the theoretical calculation results.In order to evaluate the performance of the coupling system in the practical application of electricity and water co-generation,the coupling system with a four-stage membrane distillation module is used to output electric energy to an external load of 10?and to produce fresh water at the same time under one-sun illumination.The coupling system can achieve a stable electric energy output of 66.6 W m^-2 and maintain a stable water production rate of 1.11kg m^-2 h^-1.(2)A solar thermal concentration multi-stage desalination system is proposed to solve the problems of low steam temperature(steam grade)and waste of condensation latent heat.High temperature heat source is obtained by using solar thermal concentration technology,which can generate higher temperature initial steam to improve work ability and reduce system heat loss.Latent heat recovery technology is used to reuse steam condensation latent heat for many times.The experimental results show that the water production rate of the six-stage distiller is as high as 1.84 kg m^-2 h^-1 under one-sun illumination,which is 2.5 times of that of the single-stage distiller.When the multi-stage latent heat recovery system is combined with the thermal concentration technology,the water production rate can be further increased to 2.2 kg m^-2 h^-1 under three times of thermal concentration.Finally,a mathematical model corresponding to the solar thermal concentration multi-stage seawater desalination system is established,and the change rules of the water production rate and thermal efficiency of the system under different working conditions are studied,and the mechanism of the solar thermal concentration multi-stage latent heat recovery technology to achieve efficient solar desalination is obtained.(3)A system for recovering the flow mechanical energy(hydraulic pressure energy)of solar desalinated water is proposed.Firstly,we established the corresponding physical and mathematical models of the solar membrane distillation and pressure energy recovery of desalinated water system.Theoretical calculations show that under the temperature difference of 40?,the electricity-water co-generation system can achieve a water production rate of 31 kg m^-2 h^-1,and the maximum volumetric work power density that can be generated is 534.6 W m^-2,and the corresponding relative Carnot cycle efficiency is as high as 9.55%.In order to convert volume work into real high-grade electric energy,a set of experimental system for co-generation of electricity and water is built by using the PTFE hydrophobic membrane and the self-made Al₂O₃electrokinetic power generation membrane in series.Under the temperature difference of 40?,the water production rate of the system can reach 13.5 kg m^-2 h^-1,and the additional power output is 147?W m^-2,indicates that this new type of electricity and water co-generation system provides a feasible research direction for the recovery of pressure energy from solar desalinated water.