In practice, the following types of seawater desalination technologies are considered effective: the first category is distillation, including multi-stage flash distillation (MSF), compressed gas distillation, and multi-effect distillation (MED); The type is membrane method, including reverse osmosis method, electrodialysis method, etc .; the third type is other methods, such as freezing freezing method, solvent extraction method, dew point evaporation desalination technology, etc.
Low-temperature multi-effect distillation process
In the late 1970s, Israel IDE developed the LT-MED process to desalinate seawater, which was widely used in the newly-built thermal process. A typical low-temperature multiple-effect distillation process (LT-MED) is generally performed in more than seven evaporation chambers, and fresh water is generated by the continuous evaporation and condensation of the evaporation tube bundle. The LT-MED system has a long operating life and low maintenance, and the system is very little affected by seawater quality. It is thought that the decrease or increase of the steam volume has little effect on the operation of the LT-MED, so the system operation flexibility is an important advantage. However, the operating temperature of the LT-MED system has limitations, which limits the further improvement of the thermal efficiency of this process technology.
Multi-stage flash evaporation process
The multi-stage flash process (MSF) has rapidly occupied the Middle East market since the 1960s, which is also the beginning of large-scale application of seawater desalination technology. The principle of MSF is to heat the seawater to the highest temperature, then vaporize it in a series of gradually reduced pressure flash chambers, then remove the salt substances through the demister, and finally condense to produce fresh water. The oversized MSF desalination plant can have 50 flash chambers. MSF is more traditional, with mature and reliable technology, safe and stable operation, and the flash device has the characteristics of large scale and super large scale. http://euhowblog.com
Osmosis and reverse osmosis processes
Permeation is to pass seawater through a semi-permeable membrane through atmospheric pressure in a pressure vessel. The semi-permeable membrane intercepts the salt in the seawater to pass fresh water. After passing through multiple osmotic membranes, the final fresh water resource is collected by a collection device. Reverse osmosis is the reverse process of osmosis. A pressure pump is used to pass seawater through the membrane element, and after filtering and permeating through multiple membrane elements, freshwater resources are collected. The higher the pressure, the faster the seawater passes through the membrane. The synthetic reverse osmosis semi-permeable membrane is the core component of the reverse osmosis process, and almost only water molecules can pass through. Generally, a pressure vessel can contain 6 to 8 membrane elements, and a medium-sized SWRO system consists of thousands of pressure vessels. Membrane module service life, energy consumption and product water quality will be affected by process pretreatment accuracy. Reverse osmosis began to compete with traditional thermal processes in the 1980s. http://euhowblog.com