Among the methods of water desalination is shock distillation: seawater is brought to a boil, resulting in the formation of water vapor, which is then condensed into water. Since shock distillation does not sufficiently purify water and requires a lot of energy, large industrial facilities use the reverse osmosis method, which is based on the use of membranes that pass clean water, retaining salts and other impurities. However, membrane systems have a drawback: they need to operate under high pressure, which also entails high energy consumption.
An alternative method is desalination via gas hydrates. “For that purpose, we introduce a hydrate-forming gas into frozen saltwater, separate gas hydrate crystals from the brine, clean them and melt them to obtain freshwater,” senior researcher Anton Meleshkin is quoted as saying by the Institute of Thermophysics SB RAS.
In order to obtain gas hydrates from seawater, the scientists used the process of gas boiling: in the course of the experiment, gas was liquefied on the walls of the reactor system and boiled on the heated bottom. This allowed them to solve several problems. “Firstly, the bubble surface is constantly being renewed due to the boiling and subsequent condensation of the gas. Secondly, the amount of gas introduced into the system is large, as the gas is in a liquefied state. Finally, when the gas is released, the temperature in the bubble is at its lowest and almost equal to the saturation temperature. The overlapping of these factors leads to the formation of hydrates on the emerging bubbles,” Mr. Meleshkin is quoted as saying.
Under carefully selected conditions, a gas hydrate cap begins to actively grow on the water surface, as a result of which clean water is obtained after extraction and squeezing. The resulting gas hydrates can also be used to store natural gas: one volume of methane gas hydrate can accommodate up to 170 volumes of gaseous methane. Moreover, the storage temperature of gas hydrates (minus 20 degrees Celsius) is significantly higher than the liquefaction temperature of natural gas (minus 162 degrees Celsius). This is why gas hydrates could be used to transport gas to remote northern regions.
