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How Desalination Works

Aug 23, 2022

How Desalination Works

As the world's population continues to grow and our limited freshwater resources become ever more scarce, we are fortunate that the earth's oceans can provide an alternative and ensure a sustainable supply of drinking water. Seawater can be economically and reliably converted into drinking water by a well-known process called seawater reverse osmosis, the process begins with the extraction of water from the ocean with the help of shore wells or by using an intake structure in the open ocean. Osmosis is a naturally occurring process in which a solvent such as water passes through a semi-permeable barrier. A semi-permeable barrier or membrane allows some things to pass but not others the opposite happens by pressurizing the concentrated solution of seawater that we are able to allow water molecules to pass through force to pass from the salty seawater solution to the freshwater through the membrane to protect the reverse osmosis membranes from clogging by solid particles that may float in the seawater.
how desalination works
The seawater is filtered before passing through the membranes using multimedia filters, which are tanks or vessels containing a series of layered granular materials, these materials may be anthracite garnet sand pebbles and/or gravel, arranged in layers. The filters remove sand sprigs, algae and other particles from the seawater, in some cases other types of membranes known as ultrafiltration and microfiltration membranes are used instead of multimedia filters to pretreat the seawater. The filtered seawater then goes to the cartridge filters, which serve as the second stage of filtration. Cartridge filters are typically used for seawater reverse osmosis, made from a yarn-like synthetic material that is wound into cartridges.
how desalination works
These remove even smaller solid particles from seawater, such as fine sand and clay, before the seawater reaches the reverse osmosis membranes. High pressure pumps increased the pressure of seawater up to 1,000 psi naturally occurring osmotic pressure and pressure of water from the saltwater side through the reverse osmosis membranes to the freshwater side. The salt particles in the seawater are prevented from passing through the membrane to the freshwater side and being able to remain on the concentrated saltwater side of the reverse osmosis membrane. This can be thought of as a number of sealed envelopes connected to a tube at their open ends.
how desalination works
Between each shell are spacers that allow water to flow across the membranes. The membrane wraps and spacers are then wrapped around the tube like a roll of paper towels. Osmotic membranes are then encased in a fiberglass wrap. The diaphragms are joined end to end, typically six tons o seven diaphragms together and housed in vessels rated for pressures up to 1200 psi. As the pressurized seawater enters the pressure vessel and flows across the membrane surface, the water molecules are forced into and through the membrane envelopes leaving the salt molecules behind. The desalinated water flows through the membrane and exits at low pressure where it is collected in a tube and to one end of the pressure vessel.
how desalination works
The concentrated salt stream that does not pass through the membrane continues to flow across the membrane surface, where it is collected separately. The concentrated salt stream retains approximately 55% of the total energy of the seawater stream that was originally fed to the membranes to provide the energy needed to operate the reverse osmosis system reduce, the pressurized concentrated streams are sent here up to an energy recovery device 98% of the energy of the concentrated salt stream is transferred to an equal volume of the Inco seawater in an isobaric energy recovery device The energy recovery device significantly reduces the operating costs of the plant by concentrating the energy of the Salt stream and uses it to pressurize 60% of the seawater fed to the membranes 60% higher salinity than the incoming seawater The concentrated salt stream is discharged through a brine disposal well or device known as the brine outlet is returned to the ocean The brine outlet is located in an area of ​​significant ocean currents, so the salinity will drop rapidly rebalanced with the sea the location for the outflow should not contain sensitive marine ecosystems in a proper manner designed brine outlet, no appreciable increase in salinity can be detected a few meters from the outlet The pressurized seawater exits the energy recovery device The pressure is increased by a small booster pump so that it has the same pressure as the seawater leaving the Hi gh pressure pump, the boost is required because some pressure has been lost as the current passes through the reverse osmosis system.
how desalination works
Approximately 40% of the seawater entering the system is converted into drinking water during the reverse osmosis process, which further purifies the drinking water by adding calcium carbonate to improve taste and raise the pH to neutral. Chlorine is also injected to provide disinfection properties achieve when the water flows from the reverse osmosis system through the distribution pipes to homes and businesses when proper conservation of natural water resources is practiced Water reuse has been applied and there is still a water deficit Seawater reverse osmosis can provide a sustainable alternative with good management provide life-sustaining water for coastal communities desalinated water supplies not prone to drought and other natural disasters can provide clean safe drinking water supply you
how desalination works
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