{"id":71201,"date":"2021-05-16T02:37:00","date_gmt":"2021-05-16T00:37:00","guid":{"rendered":"https:\/\/www.sonnenseite.com\/?p=71201"},"modified":"2021-05-14T16:37:36","modified_gmt":"2021-05-14T14:37:36","slug":"breakthrough-in-reverse-osmosis-may-lead-to-most-energy-efficient-seawater-desalination-ever","status":"publish","type":"post","link":"https:\/\/www.sonnenseite.com\/en\/science\/breakthrough-in-reverse-osmosis-may-lead-to-most-energy-efficient-seawater-desalination-ever\/","title":{"rendered":"Breakthrough in reverse osmosis may lead to most energy-efficient seawater desalination ever"},"content":{"rendered":"\n

Making fresh water out of seawater usually requires huge amounts of energy. The most widespread process for desalination is called reverse osmosis, which works by flowing seawater over a membrane at high pressure to remove the minerals.  <\/p>\n\n\n\n

Now, Purdue University engineers have developed a variant of the process called \u201cbatch reverse osmosis,\u201d which promises better energy efficiency, longer-lasting equipment and the ability to process water of much higher salinity. It could end up a difference-maker in water security around the world.<\/p>\n\n\n\n

Reverse osmosis is used in many countries; in arid places like the Middle East, more than half of the fresh drinking water supplies come from desalination facilities. But to maintain the high level of pressure required for the process \u2013 up to 70 times atmospheric pressure \u2013 a desalination plant must employ large numbers of pumps and other equipment. And that uses a lot of energy.<\/p>\n\n\n\n

\"Purdue
\u00a9 Purdue University photo\/Jared Pike | Graduate students Abhimanyu Das (left) and Akshay Rao adjust a piston tank, the key component to a new desalination process called \u201cdouble-acting batch reverse osmosis.\u201d <\/figcaption><\/figure><\/div>\n\n\n\n

\u201cAbout a third of the lifetime cost of a desalination plant is energy,\u201d said David Warsinger<\/a>, a Purdue assistant professor of mechanical engineering<\/a>. \u201cEven small improvements to the process \u2013 a few percentage points of difference \u2013 can save hundreds of millions of dollars and help to keep CO2<\/sub> out of the atmosphere.\u201d<\/p>\n\n\n\n

During his doctoral work at MIT, Warsinger first developed the idea of \u201cbatch reverse osmosis.\u201d Rather than keeping a constant flow of seawater at those high pressure levels, a batch process takes in a set quantity of water at one time; processes it; discharges it; and then repeats the process with the next batch.<\/p>\n\n\n\n

\u201cEach batch runs for about one to two minutes,\u201d Warsinger said. \u201cWe ramp up the pressure over time, reduce the volume over time, and we end up using much less energy to produce the same amount of fresh water.\u201d<\/p>\n\n\n\n

Though some desalination plants have attempted to use semibatch techniques, none has ever implemented a full batch system \u2013 partly because of the time breaks between batches.<\/p>\n\n\n\n

\u201cIt takes time and energy to pump each batch of water out, and then pump the next batch of water in for processing,\u201d Warsinger said. \u201cExpending that time and energy generally cancels out the efficiency gains you would get from using the batch process. That\u2019s why we developed a solution called \u2018double-acting batch reverse osmosis.\u2019\u201d<\/p>\n\n\n\n

Double-duty piston<\/strong><\/p>\n\n\n\n

This new process uses a piston tank \u2014 a high-pressure vessel with a piston in the middle. While one side of the piston sends seawater forward into the processing loop, the other side of the piston simultaneously fills up with the next batch of seawater in the queue. When one batch process ends, the piston seamlessly injects the next batch of seawater into the system while simultaneously filling its other side with the next batch of seawater in the queue, and the process repeats continuously.<\/p>\n\n\n\n

\u201cInstead of fully emptying the piston each time or using some other liquid or gas to pressurize the piston, we\u2019re filling it with the next batch of seawater,\u201d Warsinger said. \u201cSo rather than one side of the piston being essentially dead space, we are using the seawater itself to get double-duty out of this piston, so there\u2019s almost no downtime.<\/p>\n\n\n\n

\u201cAccording to our models, this proposed system offers the lowest energy consumption ever for seawater desalination. It\u2019s a best-in-class milestone.\u201d<\/p>\n\n\n\n

Their research has been published in Desalination<\/a>.<\/p>\n\n\n\n

\u201cDowntime is really something you want to avoid,\u201d said Sandra Cordoba, a Purdue master\u2019s student in mechanical engineering and first author of the paper. \u201cIf you have to service the system after every cycle, you lose all your energy efficiency. Reducing or eliminating that downtime is the key thing that makes batch reverse osmosis feasible.\u201d<\/p>\n\n\n\n

Cordoba also developed the theoretical hydraulic models used in the paper.<\/p>\n\n\n\n

\u201cReverse osmosis is a complex process,\u201d Cordoba said. \u201cTo gauge its success, you have to track many variables: water pressure, volume, salinity, recovery ratio, time and energy. With these models, we were able to determine the right amount of pressure over time to achieve the best results using the minimum amount of energy.\u201d<\/p>\n\n\n\n

How big is the piston tank? It depends on the size of the system.<\/p>\n\n\n\n

\u201cReverse osmosis operates on a wide range of scales,\u201d Warsinger said. \u201cHouseholds in India often have a micro reverse osmosis system for their own home, where you could hold it in your hands. For our experiments, we\u2019ve built a model system where the piston tank is about the size of a fire extinguisher. In a full-scale plant, it could be a hundred feet long. But the beauty of it is that it\u2019s not a complex piece of equipment; it\u2019s essentially a pipe, with a water-tight piston in the middle. But that piston tank changes everything.\u201d<\/p>\n\n\n\n

Read more<\/a><\/p>\n\n\n\n