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.
Nadine, I agree about graywater usage. I live in a hotbed of it here in Santa Cruz county. If it wasn't for the expense, we would have installed one a long time ago on our own property. I still plan to, but it's still behind other homeowner fixup priorities. That's a big part of the problem in leaving it up to the private sector, i.e., homeowners. I wish there were incentives like tax deductions, such as there have been for solar.
Thanks, Jack. The surface material must be both sticky and slippery, so the chemical- and salt-laden seawater stays on only long enough to evaporate completely and efficiently, but no longer. Ideally, it also must shed deposits relatively easily. There's no continual cleaning here: regular maintenance is required, as with metal, but lower process temperatures allowed by the material will help residues build up more slowly.
There are very strict restrictions on grey water usage here in California. Regulations loosened up a little a few years ago. Many people in the Bay Area promote grey water usage, and sell how-to kits and books. Technically, some of the movement is breaking the law but it's moving the debate in a positve direction.
My POV is based in research and observation. Desalinization seems like a good idea but only offers short term relief.
Mydesign, that's a distillation process you describe, so it sounds like the majority form of desalination, the one I cover here. I'd be interested to know more about what exact processes are being used and what challenges, obstacles, problems, etc. the Arab countries have encountered. I'm also very curious about reverse osmosis, the much less often used method, and wonder why it isn't used more often.
William, I think that's an excellent point: some areas are simply not inhabitable by a certain number of people after a specific threshold has been passed, without either importing huge amounts of water, such as in Los Angeles, or without needing a huge, expensive, artificial infrastructure of some kind. We have come to think such an infrastructure is the norm, but it's quite recent in human history. And thanks for quoting Bob Dylan :)
Thanks, Nadine. Your POV is held by many here, regarding using other options such as graywater conversion and conservation. The problem with conservation in Santa Cruz County is that we've done just about as much as we can, short of graywater conversion both public and private: our water usage rates here are very low already compared to other areas of the US. And why we haven't done graywater conversion more on a public scale, I don't know--it seems so obvious.
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.
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.
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.
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