Desalination attempts for converting seawater to fresh, drinkable water are on the rise. The decision to pursue or not pursue desalination projects is a ballot item right now in Santa Cruz, Calif., the city nearest to the town I live in. It's a pressing issue in many parts of the world, including here where the aquifer has been shrinking for a couple of decades.
A new composite material invented by researchers at the Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM) may help bring down the cost of some desalination plants. These processing plants require highly specialized, expensive infrastructure, including pipelines made of titanium and various forms of high-alloy steel that resist the corrosive action of salt water. Although pipeline cost isn't the only expense, expense in general is one of the objections to desalination.
A new composite material for saltwater desalination plant pipelines may help bring down the cost of the process. (Source: Fraunhofer IFAM)
The most common desalination method is multi-stage flash distillation, a form of thermal distillation. In thermal distillation desalination methods, the pipes must also be heat-resistant, since this process requires them to be heated until water sprayed on them boils and evaporates, leaving behind salt and chemical residues. Pipes in desalination plants must therefore be highly durable, corrosion-resistant, heat-resistant, and long-lasting. They must also have a surface that can be easily coated with seawater, so the fresh water evaporates correctly.
The Fraunhofer IFAM's polymer composite conducts heat and can be produced in continuous lengths, which the researchers say will make it less expensive than the specialty metals it can replace. Although a plastic, the composite conducts heat because it contains copper microfibers, about 50 percent by volume. "This does not change the processing properties of the composite, and it can still be processed as any other polymer would," said Arne Haberkorn, an IFAM scientist, in a press release.
The material has been developed, and the researchers exhibited it at the Composites Europe 2012 trade show in Dusseldorf, Germany, October 9 to 11. Their next step is to optimize its thermal conductivity by testing it in a pilot seawater desalination plant.
During testing, they expect to measure the composite's thermal conductivity, observe how much microorganism-based coating forms on the pipes, and see to what extent the pipes corrode in a salty environment. In the pilot plant's evaporation process, hot gas heated to 70C will run through the pipelines. This temperature is lower than some of the highest temperatures in multi-stage flash distillation, which can run up to 120C. The benefit of lower temperatures is that the material doesn't corrode as quickly, there's less deposit buildup on the pipes, and the inside and outside pressure differential is much less. This results in pipes that last longer and a process that requires less maintenance.
Very interesting development, Ann. Providing a more economical way to attack the desalination process could really make a big difference in pushing more of these projects to the fore and help them gain a foothold in developing areas that are really desparate for fresh water sources.
When reading of flash-tube boilers I envisioned tubes heated to several hundred or more degrees, not 70-130. The concept of having water spray and evaporated steam in close proximity without excessive mixing is interesting. I wonder if flash-tube could be economically superior to Reverse Osmosis? Certainly the next 30 or so years will see the need for many more water purification methods.
Reverse osmosis and other membrane technologies are the methods I'm more familiar with and have heard mentioned more often, so I was surprised to discover that thermal distillation is the technology used in the majority of installations. Although RO presumably uses somewhat less energy, both processes are quite intensive energy users. Re temperatures, thermal distillation is a form of vacuum distillation, which allows water to boil at a lower than normal temperature due to lower pressure. The Wikipedia article on desal is helpful.
Desalinization isn't a good long term solution. It's been used in Israel for years for crop irrigation. The strawberries in Israel today aren't nearly as delicious or nutritious as they were decades ago. I think the berries are telling us something. Legalizing and building infrastructure to utilize grey water would offer a longer solution for potable water shortages.
This may be easily used for manufacturing and energy creation. Many newer processes seem to involve massive amounts of fresh water.
It would seem that removing the salt and other minerals froom seawater would be the preferred method, not only because of the magnesium recovered, but because sea water is an easy to get resource that we won't be in any danger of running out of. If the berries are different after a few years it is probably because of cost being taken out of the growing process, not because of the water. What quality reduction has been implemented to increase profits?
Of course desalination does need a lot of energy, I don't know any way around that, one other option is for people to not live in that area that has no water. Did anybody ever stop and consider that some places that seem uninhabitable ARE UNINHABITABLE? Even if some developer puts houses there?
REmember the Bob Dylan quote: "One should never be where one does not belong"? It is also appropriate for areas without water.
The problem is that while we can make potable water out of seawater, we can't make the energy to do the process.
Ann, I know in most of the Arab countries, they are distilling the sea water for residential purpose other than drinking. Am not sure about the technology they are using for this purification, but I heard that it's a multi stage purification, where water is evaporating to remove the salt content. In such cases I think the new technology seems to be superior and affordable.
Beth, we know that eventhough 2/3rd of earth is covered by water, most part of the world still have scarcity of drinking/fresh water. So the best option to bridge the gap is purification or desalination of sea water. Most of such projects required huge investment and complex technology/machinery for purifying the salt water. A new more economical and simple technology has yet to be discovered and I think these new technology may comes under that category.
Very interesting article, Ann. Living in the Midwest on the shores of one of the largest bodies of fresh water in the world, I didn't have a lot of background in how desalination is accomplished. Using the method you described, I would assume that they materials being used would have to be rather "slippery" too. If you are spraying salt water on them specifically to cause steam and leave the salt and contaiminate behind, I would think that the pipes would be covered in a relatively short period of time...either that or there is a good method for continual cleaning.
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