Energy Saving Optimization Of Seawater Desalination System Based On Coal Fired Power Plant

Thermal power generation occupies a dominant position in China.Water safety is also the basic guarantee for stable economic and social development.Many seawater desalination equipment had been established in coastal areas of China.Among them,low-temperature multi-effect seawater desalination systems require heat as power,but the demand for heat taste is low.Then it is a good idea to combine thermal power generating units with low-temperature multi-effect seawater desalination equipment,and to extract the steam from the connecting pipes of the low-pressure cylinder and medium-pressure cylinder in the thermal power units with insufficient power generation potential as the working steam source of the seawater desalination equipment.After the thermal power unit is combined with low temperature multi-effect desalination,the thermal economy index of the thermal power unit has been significantly improved,and the power problem of the desalination system has also been solved.However,the parameters of extraction steam are still significantly higher than the import parameters of the first-effect of the desalination equipment.At present,TVC(Thermal Vapor Compressor)valves are mostly used to recover the residual pressure of extraction steam in the project,but the utilization effect of the residual pressure is not ideal,and there is a large exergy loss.In view of this situation,this article proposes two optimization schemes.Direct residual pressure utilization scheme:replace the TVC valve with a back pressure turbine to recover the residual pressure of the extraction steam,and the exhaust steam directly enters the first effect of desalination equipment;Comprehensive optimization scheme for desalination system:use the back pressure turbine to recover the residual pressure of the extraction steam,the exhaust steam enters the low-parameter TVC valve to extract the final effect steam,and the mixed steam enters the first effect of desalination equipment.In order to evaluate the pros and cons of the two schemes,this article firstly uses EBSILON software to model the case unit,evaluates the accuracy of the model,and then selects the typical operating conditions of the unit,and relies on the model to perform detailed calculations on the two optimization schemes,and obtain the thermal performance and economic benefits of the two schemes.The exergy loss of the two schemes is analyzed by the exergy analysis method,and finally the operational flexibility of the two schemes is analyzed.It was found that the two schemes can solve the problem well that of insufficient utilization of extraction steam residual pressure by TVC value.The economic benefits are higher,the thermal performance of the thermal power unit is significantly improved,and the operation range of the desalination system can be expanded,which is beneficial to the peak shaving of the unit.The two energy-saving optimization schemes proposed in this paper can better reduce the exergy loss of the system,and provide a reference for the energy-saving optimization of low-temperature multi effect desalination system widely existing in coastal areas.