Seawater treatment - seawater desalination
Sea water desalination is used to treat seawater for drinking, agricultural, industrial and recreational purposes. One of the methods of treatment and purifying seawater is the use of reverse osmosis (RO). By using reverse osmosis in a seawater desalination, water with a salinity of less than 500 mg / lit can be produced from seawater.
The use of seawater desalination by reverse osmosis, with regard to the initial cost of investment, and with regard to the ease of use of other sea water treatment methods, such as distillation and MED, are of prime importance. The cost of exploiting RO seawater desalination includes the cost of electricity and its chemicals.
TARHOKAR Engineering Company in designing, manufacturing and installing of seawater desalination plant in with reverse osmosis has a successful implementation experience and has been able to purify seawater for industrial use. In seawater, pre-treatment, chemical injection, flushing, reverse, and CIP are also used.
The process of sea water desalination
There are similar components in the water desalination, such as the reverse osmosis package. Sewage treatment equipment and facilities are divided into 2 sections of pre-treatment equipment and reverse osmosis equipment. The major difference between the seawater desalination unit and seawater water treatment with the reverse osmosis package RO is in the salinity and turbidity of the inlet water to them.
Due to the fact that seawater is 2 to 4 percent salinity and turbidity, suspended particles and marine organisms are abundant in it, it should choose pre-treatment equipment and reverse osmosis RO in proportion to the quality of seawater.
In general, seawater desalination pre-treatment equipment includes:
1- Intake pond for harvesting of sea water.
2- Strainer and Dirt stuck units to prevent the entry of coarse particles and fishes to seawater desalination installations.
3- Primary chemical clarifier units to reduce suspended particles in seawater.
4- Sand and Carbon Filtering to reduce water turbidity.
5- Chemical injection units such as antiscalant and acid to seawater desalination
6- Microfiltration unit to reduce sludge index.
The second part of the seawater desalination process is the reverse osmosis of RO, which reduces the soluble salts or the electrical conductivity of water (EC). This section includes special sea water membranes. Osmotic pressure supply for seawater treatment with TDS=40,000 is performed by a high pressure pump in the seawater desalination device. The use of turbocharger equipment to optimize energy consumption in seawater desalination is important in RO reverse osmosis and it can greatly reduce the cost of operation. The water entering the reverse osmosis RO is divided into 2 sections of the Permeate and the wastewater or the concentrate.
Physical and chemical specifications of seawater
The most striking feature of sea water is its high salinity. In general, salinity of sea water is about 2-4%. This amount varies in different parts of the world. For example, saline water of the Caspian Sea (Khazar Sea) is about 2 to 2.5 percent. While this number in the Persian Gulf water is 5.4 percent. In addition to salinity, the presence of microscopic organisms, the presence of sand particles on the beaches, as well as organic contaminants such as oil derivatives and human and industrial wastewater, are among the most important contamination factors in seawater. For this reason, treatment in seawater desalination requires careful consideration of design, construction and operation.
Currently, about one-fifth of the world's total oil is displaced from the Persian Gulf. The existence of numerous refineries and oil refineries on the Persian Gulf shores and frequent tanker transport has caused the pollution of these waters. In addition to the above, due to the very high sea level of water in the Persian Gulf compared with free waters, its salinity is also very high.
Persian Gulf Water Sample Analysis:
Chemical name (ion) Chemical symbol Concentration in mg / liter (ppm)
Potassium K 150
Sodium Na 14320
Magnesium Mg 1500
Calcium Ca 420
Bicarbonate HCO3 140
Sulfate SO4 2500
Chloride Cl 25500
Boron B 9
Total Dissolved Soluble TDS 44500
Acidity PH 8.3
In sea water desalination due to high salinity and high TDS, which is about 20,000 to 45,000, the pressure of RO in seawater desalination dramatically increases. In order to overcome this pressure, a reverse osmosis system using a high pressure pump is used in sea desalinating water. This pump is made of duplex or super duplex. Because the concentration of chloride in sea water is very high and causes corrosion in the pump.
Membranes in seawater desalination
Seawater desalination membranes are specially designed to withstand high osmotic pressure in the reverse osmosis process as well as to tolerate the high salinity of seawater. In these membranes, there are also all the limitations of brackish water reverse osmosis. The efficiency of seawater membranes is slightly less than 99.3% compared with saline water.
An important issue is the protection of sea membranes in seawater desalination. Because of the high salinity above the water, the possibility of formation of sediment on it is very high. The use of CIP periodic cleaning is one of the most urgent issues in exploiting seawater desalination. Another issue is the use of special sea water antiscalant. The next point is to make pre-treatments that can be used to increase the life of membranes in seawater desalination. Other issues are the use of automatic flushing systems as well as reverse pull.
Applications of seawater desalination
The uses of desalination in sea water treatment are similar to broader saltines. But a very important point is the economic estimate of the project when using a desalinating machine.
As said, sea water is a very large source that covers more than three-quarters of the Earth's surface. But its use is very costly.
The cost of investing in reverse osmosis facilities is high and there are also current costs such as power consumption and chemicals.
In short, the use of sea water treatment by reverse osmosis RO in seawater desalination devices is mostly cost-effective for offshore industries with high economic efficiency. The use of this method in the agricultural and beverage industries is by no means economical. Unless there is a need or availability of any other water resources.
Energy consumption in RO desalinating water
Water purification engineers have made this method cost-effective by reducing existing costs and investing in sewage and desalination treatment devices and, given the increasing demand for water, especially in hot and humid regions of the world, Expand.
One of the best practices is the use of a turbocharger system in a seawater desalination machine. In this method, the reverse osmosis system RO pressure is used to increase the pressure input to the membranes, and as a result the size of the pressure pump is reduced, followed by its power consumption and snow consumption.
In an engineering estimate, the use of a turbocharger in seawater desalination reduces 25 to 40 percent of energy consumption. (The following picture is refer to the turbocharger)
Results of the use of sea water desalination system
The Using of reverse osmosis water desalination in seawater treatment, especially for industrial and small and medium scale applications, is one of the most economically viable methods. Although this method is said to have a high initial cost and initial investment cost, it is more cost effective than the MED method used at the large sewage treatment installations. In addition, the quality of the sea sweetener is extremely high and can easily reduce total dissolved solubility to less than 500 mg / l.