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Larry,
Keith, I noticed these small RO systems put in boats use quite a bit more pressure than the commercial units, say for a muni water system. Wouldn't that make them break down the dead bacterium much faster, releasing their toxins into the water supply? I doubt it. The water bugs that create the biofilm are pretty tolerant of pressure, they just balance internal and exterior pressure. Hardy little beasts. I would certainly expect a higher level of membrane compaction, shortening the life, and a much greater propensity for o-ring and membrane failure. The additional pressure will, of course, help move any cellular debris through any holes, including the membrane 'pores'. Most of the commercial systems I've dealt with operate closer to 600-650 psig, and they still have leakage problems. Keith |
Keith Hughes wrote in
: to 600-650 psig, and they still have leakage problems. I love my distillers.... I love my distillers.... I love my distillers.... I love my distillers.... I love my distillers.... -- Larry This jerk called my cellphone and was nasty. Continental Warranty -- MCG Enterprises -- Mepco- 24955 Pacific Coast HWY Suite C303 Malibu California 90265 888-244-0925 Fax: 310-456-8844 Email: Read about them he http://www.ripoffreport.com/view.asp...3&view=printer |
On Sun, 10 Jul 2005 20:47:35 -0400,
Larry wrote: Keith Hughes wrote in : to 600-650 psig, and they still have leakage problems. I love my distillers.... I love my distillers.... I love my distillers.... I love my distillers.... I love my distillers.... How much power does it take to make a gallon of fresh water from seawater with your distillers? -- Jim Richardson http://www.eskimo.com/~warlock Silence is one of the most effective forms of communication. |
I am not sure either of you guys has any idea what goes on inside a R/O
pressure vessel. First of all the normal pressure range for a seawater system is between 750 and 850PSI. Seawater R/O membranes are made from completely different materials and construction from municipal and most other industrial purification membranes. They can withstand pressures almost twice that high. Unless they are damaged by chlorine they don't leak. The only O-ring that might potentially leak brine into the product is at the output end of the product tube. Any leakage there would immediately raise the salt level above the drinkable level. The other two O-rings seal the pressure vessel itself and when they start to leak with 800PSI behind them the result is more than a little bit noticeable. Now as to squashed bacteria. The process of reverse osmosis is not simply squeezing water through super small holes. The salt is rejected by the electrical charge of the salt ions. The charged ions are pushed away from the membrane surface. In the process bacterial is pushed away with the ions. The seawater flow across the membrane surface is 7 times that of the product flowing through it. Bacteria being several million times larger than the salt ions are swept away so they never get a chance to collect on the membrane in normal operation. If you leave the membrane idle for several days however the bacteria can settle on the membrane and start reproducing and THAT can cause clogging. What causes scaling is the accumulation of molecules of minerals with very low charge. A flush with a mild acid every couple of hundred operating hours will take care of that. Normally R/O desalinated water is 100% free of bacteria but if you are drawing from a harbor or other polluted water with a high virus count statistically some viruses can get through the membrane and that is what UV post treatment is for. -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
On Sun, 10 Jul 2005 18:32:24 -0700, Jim Richardson
wrote: On Sun, 10 Jul 2005 20:47:35 -0400, Larry wrote: Keith Hughes wrote in : to 600-650 psig, and they still have leakage problems. I love my distillers.... I love my distillers.... I love my distillers.... I love my distillers.... I love my distillers.... How much power does it take to make a gallon of fresh water from seawater with your distillers? Hmmm...let's pencil in the numbers on back of an envelope. A (US) gallon of water is 8 lb that's 8/2.2 kg = 3.636kg = 3636 gm From 20 degC, it takes 80 cal to get to BP then 540 cal/gm to get to steam. Totals....3636 X (80 + 540) = 2.254 Mcal = 9.5 MJ So if you could be happy with one gal/hr, it would take 9.5 MJ.hr or 9.5MJ / 60X 60 = 2.63 kilowatts. But some or all those heating watts could maybe get returned to the feedwater from the distilled water, and that's the trick to cutting the power consumption of a still. Or how about a low vacuum process, so the water feed boils at low temp? Brian Whatcott Altus, OK |
On Mon, 11 Jul 2005 03:08:26 GMT,
Brian Whatcott wrote: On Sun, 10 Jul 2005 18:32:24 -0700, Jim Richardson wrote: On Sun, 10 Jul 2005 20:47:35 -0400, Larry wrote: Keith Hughes wrote in : to 600-650 psig, and they still have leakage problems. I love my distillers.... I love my distillers.... I love my distillers.... I love my distillers.... I love my distillers.... How much power does it take to make a gallon of fresh water from seawater with your distillers? Hmmm...let's pencil in the numbers on back of an envelope. A (US) gallon of water is 8 lb that's 8/2.2 kg = 3.636kg = 3636 gm From 20 degC, it takes 80 cal to get to BP then 540 cal/gm to get to steam. Totals....3636 X (80 + 540) = 2.254 Mcal = 9.5 MJ So if you could be happy with one gal/hr, it would take 9.5 MJ.hr or 9.5MJ / 60X 60 = 2.63 kilowatts. But some or all those heating watts could maybe get returned to the feedwater from the distilled water, and that's the trick to cutting the power consumption of a still. Or how about a low vacuum process, so the water feed boils at low temp? Brian Whatcott Altus, OK It was somewhat of a rhetorical question, but thanks for the numbers :) As an aside, while pulling a vacuum will enable lower temp distillation, I don't think you reduce your energy load any, just using a different method, which may be easier to get, (mechanical, rather than electrical) Distilation may make sense in large power boats, (read, 100' and up) with plenty of waste heat, but it's not going to work well for small sailboats. At some point, a distilation system would make more sense than an RO system, but it's going to need a fairly large vessel for that. And this ignores the issues of scaling in the boiler with salt water as feed stock. -- Jim Richardson http://www.eskimo.com/~warlock Words fail me. Thank goodness I can make gestures. -- Mark Hughes (in asr - 2001 |
Glenn Ashmore wrote: I am not sure either of you guys has any idea what goes on inside a R/O pressure vessel. Well, you'd be wrong there Glen...at least by half. First of all the normal pressure range for a seawater system is between 750 and 850PSI. If you'd followed the thread, you'd know that my response had *nothing* to do with seawater systems *in seawater*. The post I was responding to was about purifying lake water using RO followed by UV sanitization. Seawater R/O membranes are made from completely different materials and construction from municipal and most other industrial purification membranes. They can withstand pressures almost twice that high. Withstanding higher pressures is no guarantee they won't suffer from compaction and membrane/o-ring failure over time. Unless they are damaged by chlorine they don't leak. Right. I've seen a number of TFC membranes leak at lower pressures. It all depends on usage, care and feeding. The only O-ring that might potentially leak brine into the product is at the output end of the product tube. Any leakage there would immediately raise the salt level above the drinkable level. No salt in *this* discussion. The other two O-rings seal the pressure vessel itself and when they start to leak with 800PSI behind them the result is more than a little bit noticeable. Now as to squashed bacteria. The process of reverse osmosis is not simply squeezing water through super small holes. The salt is rejected by the electrical charge of the salt ions. The charged ions are pushed away from the membrane surface. In the process bacterial is pushed away with the ions. Sorry, but this does not follow. Bacteria are not pushed away from the membrane concomitant with ions. In the case of bacteria, its a mechanical exclusion, or sieving effect. The seawater flow across the membrane surface is 7 times that of the product flowing through it. Bacteria being several million times larger than the salt ions are swept away so they never get a chance to collect on the membrane in normal operation. For the most part yes, you have tangential flow. You still have impaction, and bacteria will embed and adhere to membrane surfaces. How quickly they proliferate depends on feedwater flowrate, temperature, and nutrient content. If you leave the membrane idle for several days however the bacteria can settle on the membrane and start reproducing and THAT can cause clogging. That was my point. I've seen many industrial systems running 24/7 that develop a significant biofilm. And how many boat systems run 24/7? What causes scaling is the accumulation of molecules of minerals with very low charge. A flush with a mild acid every couple of hundred operating hours will take care of that. Normally R/O desalinated water is 100% free of bacteria but if you are drawing from a harbor or other polluted water with a high virus count statistically some viruses can get through the membrane and that is what UV post treatment is for. Normally yes. With any membrane penetration, that's a problem. And UV is only effective short term, as bacteria can repair themselves within 36-48 hours following UV exposure, and exposure to visible light. Do you cycle through all your stored water in that time? And UV is ineffective against larger pathogens such as giardia and cryptosporidia - likelier to be found in lake waters. In unpolluted seawater, I wouldn't worry too much about it, but in inland lakes? RO followed by sterile filtration doubtful (organics and heavy metals dontcha know), RO alone, no thanks! Keith Hughes |
Brian Whatcott wrote in
: But some or all those heating watts could maybe get returned to the feedwater from the distilled water, and that's the trick to cutting the power consumption of a still. Or how about a low vacuum process, so the water feed boils at low temp? Brian Whatcott Altus, OK What "power"? How much "power" (heat) is available in the exhaust of a Detroit Diesel burning 20-30 gallons an hour at 30% efficiency? God, heat is EASY in a power boat....going to waste up the stacks. -- Larry This jerk called my cellphone and was nasty. Continental Warranty -- MCG Enterprises -- Mepco- 24955 Pacific Coast HWY Suite C303 Malibu California 90265 888-244-0925 Fax: 310-456-8844 Email: Read about them he http://www.ripoffreport.com/view.asp...3&view=printer |
Jim Richardson wrote in news:63b9q2-
: And this ignores the issues of scaling in the boiler with salt water as feed stock. Same as evaps in a steamship....backflush. Salt dissolves in seawater...(c; -- Larry This jerk called my cellphone and was nasty. Continental Warranty -- MCG Enterprises -- Mepco- 24955 Pacific Coast HWY Suite C303 Malibu California 90265 888-244-0925 Fax: 310-456-8844 Email: Read about them he http://www.ripoffreport.com/view.asp...3&view=printer |
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