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Old 05-07-2009, 00:01   #16
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Yes, the big ship types use vacuum distillation.

Reasonable overview of types here:
How the marine evaporators work?
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Old 05-07-2009, 02:34   #17
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Could you use the intake on the engine to produce the proper vacuum?
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Old 05-07-2009, 04:55   #18
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They are commercially available.

I nearly bid on one listed on Ebay in Australia a couple of months ago. Not too big and standard commercial item for a motor yacht. Cannot recall the name though.
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Old 05-07-2009, 05:37   #19
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Waste heat recovery from diesel engines is common in the electric power industry. The dry exhaust gasses are passed through a shell and tube boiler, which extracts heat and produces steam to drive a turbine-generator set. That energy could be used to boil seawater, but you'd need a pretty large yacht to accommodate the setup.
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Old 05-07-2009, 19:47   #20
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Hi: There are a whole bunch on the market. Your engine has to run 24 seven. Go to Maxim Evaporators, LLC to learn more. dino
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Old 05-07-2009, 21:17   #21
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How much water could you make

Decided to take the day off from working on my boat. Ended up doing some calculations about how much heat is available in the exhaust of an engine that could be used to distill water either by direct boiling or vacuum distillation.
The temperature of the exhaust of 900 F was supplied by Captain58sailin in an earlier post. I checked the literature and found that it could be as high as 1300 in turbo charged performance engines, 900 F is a comfortable load on a marine engine. At this load the fuel air mixture is around 30 to 1 (half of the oxygen is consumed). At 22.5 to 1 (75% of oxygen) you begin to get black smoke.

Burning 0.5 gallons per hour and cooling the exhaust from 900 F to 300 F will give you 14,000 BTU/hr of heat (4200 watts). That is enough to evaporate 7 lbs of water (3.2 Kg) an hour or 7/8 gallon/hr (3.2 litre/hr). This was calculated by using the specific heats of the exhaust gasses etc.

You would need to run your engine (0.5 gallons of diesel/hr) for 6 hours to produce 5 gallons of water.
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Old 05-07-2009, 22:17   #22
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Originally Posted by mesquaukee View Post
I am a ChemEng by training also.
It would be a fun project to play with. A prototype boiler could be cheaply made of welded steel plate and pipe.

There are a whole pile of things to play with on a boat. One of which is right up a ChemEngs alley, phase changes or refrigeration. I spent some time and $ to design and build the most efficient system possible. It is so very simple.
Commercially available refrigeration systems are designed to be inexpensive to build and easy to install for the do it your self boat owner. It is easy to knock off 10-20% of the energy use without any trouble at all. Relocating or enlarging certain other parts you can gain another 20% to 30%.

Then there is the whole electric power issue which is continually talked about. Battery capacities, charge rates etc. all once again in a ChemEngs field.
Get a damn boat and drive everyone crazy. And your self too. Best of luck.
How did I miss this post!

In anycase on problem at a time. I need a boat!
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Old 06-07-2009, 02:35   #23
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It sounds like it might be easier to put in a Stirling heat engine to use the difference in energy between exhaust and outside world, then use that mechanical energy to drive a (small) conventional RO system. (I have visions of Ockham turning over in his grave at this complex Rube-Goldberg type construct).
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Old 06-07-2009, 04:30   #24
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There is another company that does produce a distillation from the waste heat, they are Alfa Laval, I don't have time to look them up right now, later today I'll give them a visit. I used the 900*F as an average exhaust temp. for sustained running, the temps can get a good bit higher under a load, I try not to run my equipment any harder than I have to.
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