Seawater desalination is a process of producing fresh water from seawater for production and living. It is one of the most practical and effective means to solve the problem of large-scale water shortage in coastal areas. It is estimated that more than 18 billion tons of fresh water will be produced by desalination in 2019, which can be used by nearly 500 million people.
The dream of desalination has lasted for thousands of years. Driven by this dream, seawater desalination technology has been developed continuously. In the past 70 years, seawater desalination technology has made continuous breakthroughs, and large-scale seawater desalination has become a reality from a dream.
Part 1
The origin of the dream of desalination
The salt content of seawater is about 3.5%, which is about 4 times that of normal saline. Entering the human body will cause serious dehydration of cells, so it is not suitable for drinking. I believe that the ancients who lived by the sea realized the fact that the sea water could not be drunk very early. Although they may not be able to understand the reason, they naturally gave birth to the dream of sea water and fresh water.
Some scholars believe that the earliest written description of seawater desalination comes from the Western Bible. It is said that in 1512 BC, Moses wrote Exodus. Chapter 15 records that Moses led the Israelites from the Red Sea. After three days, they couldn't find water and came to a place called Marah, where the water couldn't be drunk because of bitterness (it must be sea water or brackish water with high salt content). According to the instructions of the Lord, Moses threw a tree into the water and the water became sweet.
This somewhat magical biblical story reveals man's original dream of desalination. Over the next three thousand years, similar dreams constantly appeared in various written records in the West and China, including the light of science and wisdom.
Around 340 BC, Aristotle described the evaporation and condensation process of brine in his book Meteorologica. He believes that salt water becomes sweet when it turns into steam, and steam will not turn into salt water when it condenses. This is the first description of the principle of evaporative condensation desalination.
In the same book, the gifted Aristotle also imagined a kind of seawater desalination artifact which was quoted and recited by countless posterity& mdash;“ Jar of wax. He said that if you make a jar out of wax (some scholars think that his original meaning is clay), cover it well and throw it into the sea, you will find that the water that seeps into the jar through the wall of the jar becomes thin.
Even at today's technical level, it is not easy to make and use such a "wax can". Not only the tank itself should be able to withstand high pressure, but also the tank wall should be made of semi permeable ceramic materials. When it is used, it should be sent to sea water below 500 meters.
In 77 A.D., Pliny, an important Roman naturalist, compiled natural history based on a large number of ancient works. In addition to repeating the idea of "wax can", he also provided the crew with a specific method to solve the problem of water shortage at sea, that is, the wool will be scattered along the ship, the wool will absorb the evaporated sea water and become moist, and the water squeezed out of the wool will get fresh water.
After 1000 years, similar desalination methods, including sand or clay filtration, appeared repeatedly in some western literatures. There are many similar records and legends about desalination in ancient Chinese books.
Around 140 BC, Liu An, the king of Huainan in the Western Han Dynasty, compiled the book "wanbishu of Huainan", recording all kinds of man-made and natural changes. Among them, there is a record of "I Ji Zhi Xian": "take the sauce in Ji, salty Ji Yi.". The main idea is that the saltiness can be removed by putting bamboo utensils into brine.
Around 200 A.D., Kong Rong, who was four years old, wrote an essay on the same age for his brother rang Li. It follows the description of "I Ji Zhi Xian" that "I can't save the salt in the salt pond by the diameter of the vessel", which is extended to the meaning of a drop in the bucket.
In addition, there are two legendary sea water desalination artifacts in ancient China: the sea well and the water fixing belt.
Around 1265, the famous ci writer of Song Dynasty carefully wrote the book zhiyatang Za Chao, which describes Haijing. This sea well is very magical, "like a bucket without bottom, not wood, not bamboo, not iron, not stone & hellip& hellip; Fill it with large vessels to store sea water. Put this well in the middle of the well, and all the water will be sweet. "
Around 1697, Dong Han, a Jinshi in the early Qing Dynasty, wrote a collection of short stories about Sangang, which recorded the dingshui belt. This fixed water belt is also described very interestingly, "the ancient iron bar is about three feet down and two inches wide, which is strange. It is empty in the middle but rusty in the outside. It's hard to distinguish between the two sides of the drum and nail... Every bitter water is salty, a water belt is thrown to set up a sweet spring.".
Limited by the level of knowledge and technical conditions at that time, most of these ancient records about seawater desalination still stay in the stage of legend and imagination, but they provide an important cognitive preparation for seawater desalination from dream to reality.
Part 2
The emergence of early seawater desalination technology
Desalination in the real world began about 1800 years ago. From the late 2nd century to the early 3rd century, a critic of Alexander of Aphrodisias, who was known as aphrodinia, first described the use of distilled sea water to obtain fresh water when commenting on the general weather code.
After that, some sailors began to learn how to boil the sea water and collect its steam condensate to obtain life-saving fresh water. This is the earliest application of seawater desalination.
In the next 1300 years, this simple distillation desalination technology was hardly developed, and its application was limited to sporadic ocean going ships. It was not until after the Renaissance that experimental science was developed that people began to study and improve the desalination process through experiments.
In 1675, William walcot obtained the first patent on desalination in England. Seawater desalination has gradually gained more attention.
In 1682, Wilhelm Leibnitz, a famous German philosopher and mathematician, wrote an article on seawater desalination, discussing its importance, especially for seafarers.
In 1683, Robert Fitzgerald also obtained a patent similar to Walcott's for desalination, and designed and produced a desalination distiller with a diameter of about 84 cm and a daily fresh water yield of 240 liters.
It is said that Fitzgerald's distiller business is very good, and even caused a patent dispute with Walcott. This should be the earliest patent dispute in the history of water treatment.
At the same time, the famous British chemist Robert Boyle and others have noticed that the sea water can be desalinated after freezing. Some people have also conducted experimental investigation on the salinity of the natural sea ice melting water.
In the 18th century, with the development of the world's navy, the desalination technology for ships has received great attention. In 1717, French doctor Jean Gautier invented a marine rotary seawater evaporator, which aroused great interest of the military.
From 1786 to 1790, Anton Maria lorgna, a professor at a military academy in Venice, carried out experimental research on seawater desalination by freezing method.
In one of the experiments, rogona desalinated seawater from 36200ppm to 15000ppm, 3250ppm and 800ppm through three freezing operations. He also personally tasted the desalinated water and thought it tasted good.
In 1874, the world's first large-scale solar desalination plant was built in the Las Salinas region of northern Chile. On sunny days, the unit produces 23 tons of fresh water a day for local workers at niter and silver mines. It has been running for nearly 40 years.
Since the 19th century, the rapid development of European sugar industry has promoted the development and application of multi effect evaporation technology. In 1898, Russia put into operation the first land-based desalination plant based on the principle of multi effect evaporation, with a daily fresh water output of 1230 tons. In 1912, Egypt built a six effect desalination and evaporation device, with fresh water output of 75 tons / day.
From 1929 to 1937, with the rise of oil and gas industry, the demand for seawater desalination was increasing. From 1935 to 1960, although the total capacity was still at a low level, the annual compound growth rate of desalination capacity, which was dominated by high temperature multi effect evaporation, reached 17%.
Part 3
Development of mainstream seawater desalination technology
Now we know that there are three mainstream desalination technologies for large-scale industrial application, namely multi-stage flash (MSF) technology, reverse osmosis (RO) technology and low temperature multi effect distillation (LT-MED) technology.
In 2020, more than 95% of the total installed capacity of global seawater desalination will adopt these three technologies, and their development and evolution mainly occurred in the past 70 years.
After the Second World War, international capital entered the Middle East to develop oil resources, and the local economy and population grew rapidly. Due to the serious lack of fresh water resources in this area, but the coastal and low energy prices, seawater desalination has rapidly become a realistic choice.
At the same time, some arid areas in the United States are also facing a serious shortage of water resources, and there is a national problem of excessive use of groundwater. The Kennedy administration also began to place hopes on desalination.
In 1952, the U.S. Congress passed the saline water conversion act, and began funding desalination technology research the following year.
In 1955, the office of saline water (OSW) was set up by the U.S. Department of the interior to co-ordinate the research on desalination technology by domestic research institutions.
The first breakthrough is multistage flash technology
When the liquid heated to a certain temperature and pressure is suddenly depressurized, part of the liquid will instantly evaporate into steam, and the temperature of the remaining liquid will decrease and reach equilibrium with the new pressure, which is called flash evaporation.
Flash evaporation is also a kind of distillation technology. Compared with boiling evaporation, due to the separation of evaporation surface and heating surface, the local supersaturation caused by evaporation process is far away from the heat transfer surface, and the risk of scaling is greatly alleviated.
In 1957, Westinghouse built a four stage flash desalination plant in Kuwait, with a daily fresh water output of 2273 tons. The system still uses the design idea of traditional high temperature multi effect evaporation process, large temperature difference heat transfer and so on, so the water production rate is low.
In the same year, Robert silver, a mechanical engineer of weir company, invented MSF process in modern sense. Silver adopts the system design idea of small temperature difference, large stage and integral type, which greatly increases the water production ratio and effectively reduces the system investment.
Silver's invention of MSF process is an important milestone in the history of distillation desalination. It provides the earliest technical preparation for large-scale application of seawater desalination. Silver later went to Glasgow University as a professor.
In 1960, weir built two of the world's first modern MSF desalination plants for Kuwait and Guernsey, respectively.
The MSF plant located in SHUWAIKH port, Kuwait, has a daily fresh water output of 4546 tons, adopts 19 grade design, and the water production ratio reaches 5.7. MSF, located in Guernsey Island, has a daily fresh water output of 2773 tons, with a 40 grade design and a water production ratio of 10.5.
The prelude of large-scale application of modern seawater desalination technology was officially opened. Kuwait has also become the first country in the world to use desalinated water as a large-scale municipal water supply.
At the beginning of MSF application, polyphosphate was used as scale inhibitor, and the top temperature was limited at about 90 ℃. Later, sulfuric acid and polyelectrolyte were gradually used as scale inhibitors, and the top temperature was increased to 110-120 ℃.
In 1962, under the coordination of OSW, the US Navy also built a MSF desalination plant with a capacity of 3785 tons/day in Point Loma, California.
In 1964, the MSF installation at Cape Loma was sent to the US naval base at Guantanamo, Cuba. Because after the 1962 Cuban missile crisis, Cuba decided to stop supplying fresh water to the base. It is said that this MSF device has been operating at Guantanamo base for nearly 20 years.
The continuous application of MSF technology also promotes its large-scale. In 1969, the MSF plant at terneuzen port in the Netherlands reached 14500 tons per day. In 1973, the scale of MSF plant built in Porto Torres, Italy, has reached 36000 tons/day.
In 1980, the total installed capacity of global MSF reached 5 million tons / day. As the absolute main force of global desalination installation, MSF technology has entered the heyday of large-scale application.
In 1987, the global installed capacity of MSF increased to 7.5 million tons/day. Since then, with the development of reverse osmosis technology, the growth rate of MSF has slowed down.
However, Saudi Arabia and other major oil producing countries in the Middle East agree with the reliability of MSF technology very much, and they still have a special preference for MSF in the construction of large-scale seawater desalination plants.
In 2014, Saudi Arabia built a 1025000 T/D modern desalination plant in Ras Al Khair Industrial Zone, in which the scale of MSF plant is as high as 770000 T/d. The plant is also the largest desalination plant in the world.
In 2016, Saudi Arabia also built a 550000 T / D MSF unit at Yanbu phase 3 desalination plant. These projects show that MSF is still very competitive in specific projects.
At the beginning of 2020, the global total scale of MSF desalination plant is about 15 million tons/day, and its proportion in the global total installed capacity of desalination has dropped to less than 30%.
The second breakthrough is reverse osmosis technology
In 1949, Gerald Hassler of UCLA and others first started the research of membrane desalination.
In 1956, Hasler coined the term reverse osmosis. In the same year, Professor Samuel yuster of UCLA also carried out membrane desalination research with the support of OSW.
In 1959, Sidney Loeb and Srinivasa sourirajan of Professor Uster's research group first prepared synthetic reverse osmosis membrane with asymmetric structure. This achievement provides the most important technical basis for the reverse osmosis desalination technology to be applied on a large scale.
In 1965, the world's first commercial reverse osmosis plant was built in the small town of Coalinga, California, with a water production of 18.9 tons per day under the participation and guidance of Lobo. The device adopts tubular reverse osmosis membrane.
In the same year, Donald T. Bray, a World War II veteran of general atomics, applied for the patent of the world's first multi diaphragm roll reverse osmosis membrane module (us3417870). This invention laid the foundation for the basic structure of modern reverse osmosis membrane elements.
In 1965, Chen Yen Cheng et al. Applied for the first patent related to reverse osmosis energy recovery (us3489159). In 1975, the energy recovery unit was first tested on a 50 t/D reverse osmosis desalination unit in Bermuda.
In 1979, John E. Cadotte of filmtec company applied for the first patent (us4277344) to prepare reverse osmosis membrane by interfacial polymerization in the world. Thin layer composite membrane (TFC) was born, which further improved the performance of reverse osmosis membrane.
The invention of roll structure of reverse osmosis membrane elements and interfacial polymerization technology greatly promoted the application and development of reverse osmosis desalination technology.
As the Middle East was in favor of multi-stage flash evaporation at that time, reverse osmosis desalination was first applied in Europe, and then entered the Middle East.
In 1982, Maltese built a 20000 t/D reverse osmosis desalination plant, becoming one of the largest reverse osmosis desalination plants in the world at that time.
At the same time, reverse osmosis desalination membrane components, pretreatment, energy recovery, system integration and other technologies are also maturing. They promote the reverse osmosis desalination technology to large-scale.
In 2000, the scale of the world's largest reverse osmosis desalination plant has exceeded 100000 t/D, 200000 t/D in 2003 and 500000 T/D in 2009.
In 2013, Israel built a 624000 T/D reverse osmosis desalination plant in Sorek, south of Tel Aviv. It is also the largest reverse osmosis desalination plant in the world.
In 2019, the reverse osmosis desalination project of taweelah in UAE signed a contract, with a scale of 909200 tons/day. It is expected to be completed and put into operation in 2022, and will become the new largest reverse osmosis desalination plant in the world.
According to the latest report, Saudi Arabia is planning to build a 1000000 T/D reverse osmosis desalination plant to replace the aging Jubail thermal desalination plant. After completion, the world record of reverse osmosis desalination plant scale will be rewritten once again.
At the beginning of 2020, the cumulative scale of RO seawater desalination in the world is about 30.6 million tons/day, accounting for nearly 60% of the total installed capacity of global seawater desalination.
The third breakthrough is low temperature multi effect distillation technology
In the late 1970s, low temperature multi effect distillation technology originated in Israel. It is developed from the traditional multi effect evaporation, the most important feature is that the operating temperature is controlled below 70 ℃, and the horizontal tube falling film evaporation mode is adopted.
The low temperature operation mode of LT-MED greatly reduces the risk of corrosion and scaling, while the horizontal tube heat transfer mode achieves higher heat transfer coefficient, reduces the space height, increases the effective heat transfer temperature difference, and makes it more convenient to use low-grade heat sources.
In the 1980s, the LT-MED desalination plant with a daily output of several thousand tons was gradually applied in the Middle East. In the 1990s, LT-MED devices were continuously enlarged.
In 1995, the LT-MED plant with a fresh water output of 18000 T/D was built in Trapani, Italy, with a unit capacity of 9000 T / d.
In 2008, a LT-MED plant with a fresh water output of 272760 tons/day was built in Bahrain, with a unit capacity of 27000 tons / day.
In 2009, Saudi Arabia built the world's largest LT-MED desalination plant in Jubail industrial city, with an amazing fresh water output of 800000 tons / day. The plant consists of 27 LT-MED units with a unit capacity of 30000 T / D, each unit is composed of eight efficiency units, and the water production ratio reaches 9.8 after steam compression (TVC).
In 2012, the LT-MED desalination plant with a single unit capacity of 68000 T/D was built in Saudi Arabia.
However, the application of LT-MED is obviously limited by the rapid development of reverse osmosis technology. At the beginning of 2020, the total scale of global LT-MED desalination is about 3.3 million tons / day, accounting for only 6.4% of the total installed capacity of global desalination, about 1 / 5 of MSF and 1 / 10 of ro.
Part 4
Seawater desalination technology in China
The research of modern seawater desalination technology in China started from electrodialysis, and then developed to reverse osmosis, multi-stage flash evaporation, multi effect evaporation and other mainstream seawater desalination technologies.
In 1958, Mr. Zhu Xiuchang, Institute of chemistry, Chinese Academy of Sciences, published the first paper entitled "manufacture of ion exchange membrane and desalination and concentration of electrodialysis solution" in the journal polymer communication. Only nine years have passed since American scientists first prepared ion exchange membranes.
In 1965, Chinese scientists developed the first generation of electrodialysis desalination device with nylon mesh PVC separator and polyvinyl alcohol heterogeneous ion exchange membrane as the main components, and put it into field test.
In 1966, the Department of chemistry of Shandong Ocean University, the first Institute of State Oceanic Administration, Qingdao Institute of Oceanology, Chinese Academy of Sciences and other units began to study reverse osmosis technology and develop asymmetric cellulose acetate membrane. At this time, it is only seven years since American scientists first prepared asymmetric cellulose acetate membrane.
In 1967, the State Science and Technology Commission and the State Oceanic Administration organized a national sea water desalination battle. Shanghai is mainly responsible for the research and development of electrodialysis technology, while Qingdao and Beijing are mainly engaged in the research of reverse osmosis technology. In the same year, the domestic heterogeneous ion exchange membrane was officially put into operation in Shanghai chemical plant.
In 1970, part of the participants in the sea water desalination battle came to the second Institute of the ocean administration and set up the sea water desalination research laboratory.
In 1974, in order to solve the problem of serious water shortage in Tianjin and other places, the national science and technology leading group organized and held a national conference on desalination science and technology in Beijing, and formulated the "1975-1985 national desalination science and technology development plan", the first comprehensive layout of reverse osmosis, electrodialysis and thermal desalination technology research work.
In 1975, the Journal of seawater desalination was first published in Hangzhou, and later it was renamed water treatment technology. In the same year, the second Institute of the ocean administration and other units developed a disc plate type cellulose acetate reverse osmosis device with a daily fresh water output of 1.7 tons, and then carried out the research on hollow fiber and roll type reverse osmosis elements.
At the same time, Tianjin, Dalian and other places began the research of distillation desalination technology. Around 1980, Tianjin University and other units successfully developed China's first 100 ton per day multi-stage flash desalination pilot plant, with the main technical indicators comparable to the international level at that time.
In 1981, the 200 tons/day electrodialysis desalination plant designed and built by the second Institute of the ocean administration was officially located in Yongxing Island, Xisha, becoming the largest electrodialysis desalination station in the world.
In 1987, Tianjin Dagang Power Plant imported the US 2x3000 T/D multistage flash desalination unit. The designed top temperature of the unit is 110 ℃, including 36 flash stages of heat recovery section and 3 flash stages of heat release section.
At this time, the R&D of reverse osmosis technology in China entered the stage of composite membrane development, and the pilot scale-up was successful after tackling the key problems in the seventh and eighth five year plan. In China, reverse osmosis membrane technology began to move from laboratory research to industrial scale application.
In 1990, Daya Bay nuclear power station built the first reverse osmosis desalination plant in China, with a capacity of 200 tons/day.
In 1992, "domestic reverse osmosis device and engineering technology development" won the first prize of national science and technology progress award.
In 1997, China's first 500 t/D reverse osmosis desalination plant was put into operation in Zhoushan, Zhejiang Province.
In 1999, Dalian built the first 1000 t/D reverse osmosis desalination plant.
In 2000, Tianjin University took the lead in the research and development of valve controlled positive displacement energy recovery technology and device in China.
In 2003, a 10000 ton reverse osmosis desalination unit was built in Rongcheng, Shandong Province, and a 20000 tons/day multi effect evaporation unit was introduced into Huanghua Power Plant, Hebei Province.
In 2004, China's first 3000 t/D low temperature multi effect distillation desalination unit with independent intellectual property rights was built in Huangdao, Shandong Province.
In 2009, Tianjin Dagang built the first 100000 t/D reverse osmosis desalination plant in China. The next year, Tianjin Beijiang power plant built the first set of 100000 t/D low temperature multi effect seawater desalination plant in China.
By the end of 2010, China has built more than 70 sets of seawater desalination plants, with a design capacity of 600000 tons/day. About 66% of them are reverse osmosis and 33% are low temperature multi effect distillation.
In 2011, the State Oceanic Administration issued the 12th Five Year Plan for the development of seawater desalination industry, proposing that the scale of national seawater desalination project will reach 2.2 million tons/day by 2015. However, during the 12th Five Year Plan period, the construction scale of domestic seawater desalination did not meet the expectation. By the end of 2015, the actual capacity of seawater desalination in China was about 1 million tons/day.
In 2016, the State Oceanic Administration issued the 13th five year plan for seawater utilization, which once again set the scale target of national seawater desalination project as 2.2 million tons / day in 2020.
According to the national seawater utilization report released in September 2020, by the end of 2019, there are 115 seawater desalination projects in China, with a scale of 1.57 million tons/day. 63.6% of the scale is reverse osmosis, and 35.9% is low temperature multi effect technology.
Part 5
Summary and Prospect
As an open source method, seawater desalination is one of the most effective ways to solve the problem of large-scale water shortage. In the past 60 years, seawater desalination has been widely used in many water shortage areas around the world, such as the Middle East, which meets the living needs of local people and supports the rapid development of local economy.
Seawater desalination technology is driven by the Millennium dream of "asking for water from the sea". In the past 70 years, seawater desalination technology has undergone numerous explorations and rapid development, and finally formed three modern mainstream technologies: multi-stage flash evaporation, low temperature multi effect and reverse osmosis.
In essence, the invention of multi-stage flash and low temperature multi effect embodies the inheritance of ancient wisdom. They are all thermal desalination technology, and the basic principle of evaporation and condensation has been clarified by ancient philosophers more than 2300 years ago.
Silver and others have used ingenious engineering design to greatly improve the energy recycling efficiency and operation reliability of the evaporation and condensation process. With the progress of modern metal materials and processing technology, the thermal desalination technology has rapidly realized large-scale and created its own glory under the traction of the urgent demand in the Middle East.
The invention of reverse osmosis technology is more based on the deepening of human understanding of natural science since modern times, which is a higher level of progress. It does not rely on phase change, is more efficient in nature, and its market application is catching up, which represents the highest achievement in the development of seawater desalination technology.
Looking forward to the future, reverse osmosis technology will continue to consolidate its advantages in the market share of seawater desalination, and its own efficiency will continue to improve with the progress of materials and other technologies.
Thermal desalination technology, especially low temperature multi effect technology, will still coexist with reverse osmosis technology for a long time. Through coupling with reverse osmosis technology, it will continue to play the advantage of effective utilization of low-grade heat energy.
With the widespread concern of climate change in the world, the voice of carbon neutrality is growing day by day, and the transformation of energy structure is imperative. In this context, the combination of desalination and renewable energy is emerging, and it will be the general trend.
As far as China is concerned, the existing desalination capacity is less than 4% of the total installed capacity in the world, and there is still huge room for development. Seawater desalination has the potential to become the main way to solve the problem of water shortage in northern coastal areas of China.
China also has great potential in developing seawater desalination technology. First, large scale demonstration projects of renewable energy power generation and seawater desalination can be planned timely; Second, it can further improve the technical level of domestic reverse osmosis membrane and other key desalination products, accumulate application experience, and enter the international large-scale desalination market as soon as possible; Third, we can strengthen the forward-looking technology research, and strive to lead the development direction of seawater desalination technology in the future.
Source: mym space
