Proseso ng kemikal ng desalinasyon

Ang paglilinis, na tinatawag ding desalting, pag-alis ng mga natunaw na asing-gamot mula sa tubig-dagat at sa ilang mga kaso mula sa mga brackish (bahagyang maalat) tubig ng mga dagat sa lupain, lubos na mineralized groundwaters (hal. Geothermal brines), at mga munisipal na wastewater. Ang prosesong ito ay nagbibigay ng tulad ng kung hindi man hindi magagamit na tubig na angkop para sa pagkonsumo ng tao, patubig, aplikasyon sa pang-industriya, at iba pang mga layunin. Ang umiiral na teknolohiya ng desalination ay nangangailangan ng isang malaking halaga ng enerhiya, karaniwang sa anyo ng mga fossil fuels, at sa gayon mahal ang proseso. Para sa kadahilanang ito ay karaniwang ginagamit lamang kung saan hindi magagamit ang mga mapagkukunan ng sariwang tubig. Bilang karagdagan, ang halaga ng mga emisyon ng gas ng greenhouse at wastewater ng brine na nabuo ng mga halaman ng desalination ay nagdudulot ng mga makabuluhang hamon sa kapaligiran.

Mga agham sa daigdig: Desalinisasyon, lakas ng tubig, at mineral mula sa dagat

Para sa mga edad isang mapagkukunan ng pagkain at karaniwang asin, ang dagat ay lalong nagiging mapagkukunan ng tubig, kemikal, at enerhiya. Noong 1967 Key West,

Ang pag-desalting ng seawater ay isang sinaunang paniwala. Inilarawan ni Aristotle ang isang paraan ng pagsingaw na ginamit ng mga mandaragat ng Greek ng ika-4 na siglo bce. Isang Arabong manunulat ng ika-8 siglo ay gumawa ng isang treatise sa pag-distillation. Noong ika-19 na siglo, ang pagbuo ng pag-navigate ng singaw ay lumikha ng isang kahilingan para sa mga hindi pang-tubig na tubig para sa mga boiler, at ang unang patent para sa proseso ng paglilinis ay ipinagkaloob sa Inglatera noong 1869. Sa parehong taon, ang unang planta ng paglubog ng tubig ay itinayo ng gobyerno ng British sa Aden, upang magbigay ng mga barko na huminto sa port ng Red Sea. Ang unang malaki pa rin na magbigay ng tubig para sa mga komersyal na layunin ay itinayo noong 1930 sa Aruba, malapit sa Venezuela.By 2019 tungkol sa 18,000 mga halaman ng desalination na gumagawa ng isang higit sa 95 milyong kubiko metro (sa labis na 3.4 bilyong kubiko paa) ng maaaring maiinit na tubig bawat araw ay nagpapatakbo sa buong mundo.

Desalination processes

Desalination methods can utilize either thermal processes (involving heat transfer and a phase change) or membrane processes (using thin sheets of synthetic semipermeable materials to separate water from dissolved salt). Multistage flash distillation is a thermal process for desalting relatively large quantities of seawater. Based on the fact that the boiling temperature of water is lowered as air pressure drops, this process is carried out in a series of closed tanks (stages) set at progressively lower pressures. When preheated seawater enters the first stage, some of it rapidly boils (flashes), forming vapour that is condensed into fresh water on heat-exchange tubes. Fresh water is collected in trays as the remaining seawater flows into the next stage, where it also flashes, and the process is continued. One of the largest of these systems, located in Al-Jubayl, Saudi Arabia, can produce more than 750 million litres (200 million gallons) of desalted water per day.

In small communities where salt water and intense sunlight are both abundant, a simple thermal process called solar humidification can be used. The heat of the Sun partially vaporizes salt water under a transparent cover. On the underside of the cover, the vapour condenses and flows into a collecting trough. The principal difficulty in this process is that large land areas are required, and energy is needed for pumping the water. Another thermal process makes use of the fact that, when salt water is frozen, the ice crystals contain no salt. In practice, however, objectionable amounts of salt water remain trapped between the crystals, and the amount of fresh water needed to wash the salt water away is comparable to the amount of fresh water produced by melting the crystals.

Membrane processes for desalting include reverse osmosis and electrodialysis. Of the two, reverse osmosis is the more widely used, particularly for desalting brackish waters from inland seas. The salt content of brackish inland water, though undesirable, is considerably below that of seawater. Electrodialysis uses electrical potential to drive the positive and negative ions of dissolved salts through separate semipermeable synthetic membrane filters. This process leaves fresh water between the filters. In reverse osmosis salt water is forced against the membranes under high pressure; fresh water passes through while the concentrated mineral salts remain behind. To conserve space, the membranes are packaged in multiple layers in a collection of long tubes. One of the largest reverse-osmosis desalination plants now in operation is located in Sorek, Israel, and can produce some 627,000 cubic metres (22 million cubic feet) of desalted water per day.

Global production

In many areas of the world, particularly in densely populated arid regions, desalted water is the main source of municipal water supplies. Desalination is used in more than 120 countries, and about half of all desalted water is produced in the Middle East and North Africa. By 2019 the largest producers of desalinated water were Saudi Arabia, the United Arab Emirates, and Kuwait. The United States is another major producer, accounting for roughly 13 percent of the total output (mostly in Florida, Texas, and California). The majority of all desalination plants are reverse-osmosis systems, with multistage flash distillation being the second-ranking process.

In general, a population usually can afford to pay about 7–10 times as much for water for domestic purposes as it does for agricultural water. Large-scale desalination facilities promise to lower the cost of desalted water at the desalination sites to a level that most industries and some agricultural enterprises can afford. In the future it can be expected that the ocean will become an increasingly important source of fresh water. If production and transportation costs can be lowered sufficiently, it may be possible to produce fresh water to irrigate large areas that border the oceans in many parts of the world.