Experimental Study On Combined Desalination Process Based On Freezing Method

With the rapid economic development and the increase in population,the shortage of fresh water resources has become one of the bottlenecks for the further development of China's coastal areas.In recent years,China has vigorously developed the seawater desalination business.In 2016,it proposed the goal of a total national seawater desalination scale of over 2.2 million tons per day at the end of the 13th Five-Year Plan.The main methods of seawater desalination are distillation and reverse osmosis.The freezing method is restricted by cold source conditions and low salt removal efficiency,and it has not been widely used in industry.China is the second largest importer of LNG(Liquefied natural gas),and the LNG terminal at the seaside will still be in the development stage in the coming period.The cold energy released in the LNG gasification process provides the possibility to solve the problem of high cost of cold source in the seawater desalination process based on the freezing method.It is of theoretical value and practical significance to carry out the research on the high salt removeal efficiency desalination process based on the freezing process.In this paper,three parts of experimental research work are carried out on the compound desalination process based on the freezing process.The first part of the work is to use the?LNG cold energy-based seawater freezing experimental device‘to produce ice and study the desalination effect of FMCD(Freezing,microwaving and centrifugal desalination)and FMGCD(Freezing,microwaving,gravity-induced and centrifugal desalination)processes.The water quality of the product water was compared with the water quality standards of major industrial and civilian water.The second part of the work is to use the refrigerator to make ice,cooling seawater as the soaking liquid,and break the ice to carry out the FSCD(Freezing,soaking and centrifugal desalination)process experiment.and study the centrifuge speed,centrifuge time and soaking time on the desalination effect of FSCD process.Combined with gravity-induced,the process experiment of FSGCD(Freezing,soaking,gravity-induced and centrifugal desalination)was carried out using the cooled seawater as the soaking liquid in summer ambient temperature,and the effect of gravity-induced desalination time on the desalination effect of FSGCD process was studied.The third part of the work explores the application of ultrasonic technology in gravity-induces desalination and soaking desalination,the FUGD(Freezing,ultrasonic aided and gravity-induced desalination)experiment,FUSD(Freezing,ultrasonic aided and soaking desalination)experiment and FUSCD(Freezing,ultrasonic aided-soaking and centrifugal desalination)process experiment.Compared with FGD(Freezing,gravity-induced desalination)experiment,FSD(Freezing,soaking desalination)experiment and FSCD process experiment without ultrasonic wave,the effect of desalination was studied.The main conclusions of the experiment are as follows:1)Due to the application of microwave treatment,the time required for the desalination process of FMCD and FMGCD is greatly reduced compared to the FGCD process.And when the brine reject proportion is greater than 29%or 37%,taking TDS(Total dissolved solid)and Cl~-concentration as the reference indicators,the water quality of the FMGCD process product ice can meet the carbon steel equipment or stainless steel equipment requirements in?Water quality standard of water supply and drainage in petrochemical industry‘.When the brine reject proportion is greater than 54%,the water quality of the product ice can meet the requirements of surface water and drinking water.2)For the FSCD process,the desalination effect can be improved by increasing the speed of the centrifuge within a certain speed range.Without changing the speed,the effect of prolonging the centrifugation time on the desalination effect is limited.Prolonging the soaking time can improve the desalination effect,but the desalination effect does not increase significantly after soaking for 5 minutes.In the FSGCD process,prolonging the time of gravity-induced can effectively improve the salt removal efficiency.After 1 minute of soaking,the higher salt removal efficiency can be quickly obtained.The final salt removal efficiency is slightly lower than the FGCD process but can reduce the time spent on the experiment.3)The mechanical vibration caused by ultrasonic waves can speed up the desalination process,and the application of ultrasonic waves during the soaking process can achieve a higher desalination effect in a short time.Under the same ice yield rate,the desalination effect of FUSCD process is better than that of FSCD process.