The main methods of seawater desalination treatment are as follows:
Distillation: Using the difference in evaporation temperature between seawater and freshwater, by heating seawater and condensing the vapor into freshwater. This is an ancient desalination method that completely removes salt from seawater, but consumes more energy and has a larger footprint.
Reverse osmosis (reverse osmosis): The semi-permeable membrane is used to push the seawater through a high-pressure pump, so that the water molecules and microparticles pass through the semi-permeable membrane, and the solutes such as salt are trapped on the side of the seawater, so as to remove the salt in the seawater. The reverse osmosis method is widely used in the desalination of small and medium water volumes, and has the advantages of compact device, small land occupation and simple operation.
Evaporation crystallization method: Desalination of seawater is achieved by evaporating seawater to saturation to crystallize and precipitate the salts dissolved in seawater. This method can recover a variety of inorganic salts from seawater, such as sodium chloride, and is a method that can comprehensively recover salt resources.
Ice crystal method (freezing method): The salt and other impurities in seawater are frozen into ice crystals, and the ice crystals and salts are separated by physical separation to obtain fresh water. This method has low energy consumption and is suitable for cold areas in low temperature environments.
Water evaporation desalination: Seawater is placed in a large area of shallow tanks, solar radiation is used to evaporate the water surface, and then the evaporated fresh water is collected.
In addition to this, there are also desalination technologies such as electrodialysis and ion exchange. Electrodialysis uses a specially manufactured membrane to achieve desalination, which has low energy consumption and stable effluent quality, but the desalination rate is not very high, and it is rarely used in the field of seawater desalination. The law of ion exchange is the use of specific resins to remove salts and impurities from seawater.
What is the difference between distillation and reverse osmosis
Distillation method and reverse osmosis method (reverse osmosis) have their own characteristics in seawater desalination treatment, and the main differences are reflected in the following aspects:
Principle and process: Distillation mainly uses physical principles to evaporate seawater into steam by heating it, and then condensing steam to obtain fresh water. This process mainly removes salts and impurities from seawater. The reverse osmosis method uses a special semi-permeable membrane to pass seawater through the membrane under high pressure, thereby filtering out the salts and impurities in the seawater.
Energy consumption: Distillation mainly consumes heat energy, which requires heating seawater to boiling, so the energy consumption is relatively high. The reverse osmosis method, on the other hand, mainly consumes electrical energy and is used to drive high-pressure pumps to pass seawater through a semi-permeable membrane.
Equipment and investment: Distillation desalination units can be built to be larger, suitable for extra-large seawater desalination treatment, but they require thermal energy supply facilities such as thermal power plants, so the construction cost is relatively high. The reverse osmosis method has compact equipment, small footprint, and relatively low construction cost.
Product Water Purity and Feedstock Water Utilization: Reverse osmosis filters out smaller ions than distillation, so product water is generally of higher purity. At the same time, the utilization rate of raw water in the reverse osmosis method is also relatively high.
Operation & Maintenance: Reverse osmosis is generally easier to operate and maintain, while distillation may require more heat supply and maintenance.
In general, distillation and reverse osmosis are both effective desalination technologies, but the application needs to be selected according to specific conditions (such as available energy, water demand, investment budget, etc.). As technology advances, both methods are being optimized and improved to meet the growing demand for freshwater resources.
Which is better, distillation or reverse osmosis
Distillation and reverse osmosis (reverse osmosis) have their own advantages and disadvantages in desalination treatment, and the choice of which method is better depends on the specific application scenario and needs.
The advantages of the distillation method are its high heat utilization efficiency and relatively simple equipment structure, which is especially suitable for large-scale production. However, the distillation method also has some disadvantages, such as serious damage to pot scale, large amount of brine circulation, and high operating costs.
The reverse osmosis method is an energy-efficient method of desalination. It uses a semi-permeable membrane with selective permeability to separate fresh water from seawater, with a high desalination rate and the ability to remove a large number of inorganic salt ions, organic matter, colloids, viruses and bacteria from the water. However, there are also some challenges associated with reverse osmosis, such as the susceptibility to contamination of semi-permeable membranes, their short service life, and the presence of energy recovery and brine discharge, which increase the energy consumption and cost of reverse osmosis technology.
In terms of the capacity of the desalination plant, it is generally believed that when the capacity of the plant exceeds 6000 tons of fresh water per day, the dual-purpose distillation method may be more economical than the reverse osmosis method. However, reverse osmosis can be at a disadvantage when treating large-scale seawater due to the lifetime of the membrane and the limitations of the membrane device.
In addition, for some areas, such as coastal islands and remote inland areas, where the demand for fresh water is small, it may not be economical to use either distillation or reverse osmosis. In these cases, it may be more appropriate to develop small-scale and efficient desalination technologies and devices.
In summary, distillation and reverse osmosis have their own advantages and limitations, and the choice of which method is better needs to be comprehensively considered according to the specific application scenarios and needs. In practice, the most suitable desalination method can be selected according to local conditions, energy supply, investment budget, and fresh water demand.
