Stolen from the Rime of the Ancient Mariner, the title to this post asks the question every sailor and seafarer has pondered when running short of fresh water on board: how ironic it is to be surrounded by water, but unable to drink any of it.
Of course that was in the days of wooden-hulled sailing ships, where the practice was to stock fresh water in barrels.
Modern ships use desalination plants which utilize excess power from their power generation systems to evaporate sea water before condensing it into water, minus the salt. Further treatment is still required to make the water drinkable, but the power required to perform that first step is where the prohibitive cost of commercial desalination plants sits.
Although not viable in South Africa in 2015, what with load shedding still looming large, drought solution debates always return to harnessing the massive reservoir of water contained in the globes seas and oceans. Some strides are being made to make the process of extracting potable water from the seas more affordable and efficient – this article by Hannah Furlong published in www.SustainableBrands.com on 30-Nov-2015:
GE Global Research and US Department of Energy (DOE) scientists are developing a small, extremely efficient desalination machine. The technology freezes saline water at a cost up to 20 percent lower than conventional thermal evaporation approaches, and with a much smaller product.
Douglas Hofer, a GE senior principal engineer and steam turbine specialist, and Vitali Lissianski, a GE chemical engineer, used the same miniaturized, 3D-printed turbo-machinery used in the steam turbines developed with the DOE for the new product.Hofer explained, “In traditional steam turbines, steam condenses and turns to water. We thought maybe the same principle could be applied to water desalination.”
The water desalination technology compresses and streams a mixture of air, salt and water through a hyper-cooling loop. The mixture freezes, naturally separating the salt in a solid crystal form and the water as ice.
“97.5 percent of the earth’s water supply is virtually inaccessible because water desalination is still too expensive and difficult to deploy at a large scale. By putting desalination ‘on ice,’ we hope to change that dynamic,” said Lissianski.