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Old 06-01-2017, 22:56   #1
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Join Date: Aug 2015
Location: Marina del Rey
Boat: Hunter 31
Posts: 618
DIY Water Maker - Closed Circuit Desalination

I came across an interesting desalination process called closed circuit desalination (CCD). It would be interesting to discuss the merits of the process and its applicability to small scale boat water makers. The process is patented by Desalitech, so this is strictly DIY unless someone wants to get a license from them.

The idea is to run salt water through the membrane in a closed loop (the brine is fed back into the membrane) for a few minutes then flush the brine for a minute then go back to closed loop (much better description on their website). During the closed loop cycle a HP pump feeds salt water equal to the product output! A circulation pump circulates the brine increasing the recovery rate above 90%. Then a valve opens briefly and replaces the highly concentrated brine with fresh saltwater. A major benefit of the system is that the brine replacement could be done in a positive displacement mode (using a second containter of equal volume) which is acting as an energy recovery device.

OK, so I see the following benefits for application on a boat:

1. Uses basic components, pressure vessels, membranes, two high pressure pumps (could possibly share a motor), salinity meter, solenoid valves and a control panel with timers. All easy to do.

2. The stop and go mode makes it really easy to use energy recovery without any special Clark pumps and so on.

3. It is claimed that scaling is not a problem as scaling apparently depends on salt concentration and time. So while the membrane is operating at high concentration there is not enough time to scale and then it is cleaned a few minutes later. How well it would work is unclear.

4. The company claims the equivalent of 0.5 AH/gallon for large scale water plants but I do not think this process is much affected by scale (and the company said so in a presentation).

So do you think it would make sense to play around with such a design? The potential is to get 2x Spectra efficiency at the cost of one extra HP pump, one extra pressure vessel for the recovery and some (Arduino controlled) valves.

S/V Pizzazz
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