Re: [Biofuel] Dewatering with vacuum.

[William Adams]

Your water-to-steam volume change calculation is not correct.  The correct volume increase is 1,244x, obtained as follows:  One mole (molecular wt. in gm) of liquid water = 18 gm = 18 cc. One mole of steam = 18 gm h2o vapor = 22,400 cc. At standard temperature and pressure, and for equal molar quantities, the volume change is simply: steam volume / liquid volume = 22,400/18 = 1,244.44... Cheers, Bob (West Linn) ----- Original Message ----- From: Joe Street To: Biofuel@sustainablelists.org Sent: Monday, January 09, 2006 7:09 AM Subject: Re: [Biofuel] Dewatering with vacuum. Hey Logan and David; These numbers are reasonable. (don't forget to factor in an amount for a steady state leake rate on your system as this adds to the load your pump will see as it approaches base vacuum)  Actually I can get on the order of 100 to 200 ml water out of 25 liters of oil at times collecting in my liquid trap.  This is estimated I have not measured it.  Perhaps I should.  But this is after heating to 55 degrees celsius and draining any liquid water that precipitates.  So 200 mls in 25 liters is 0.8% water by volume. I'm not sure what your batch size is but as a conservative figure use 1% to figure the amount of water you will have to remove by vacuum.  Also remember that a 5 CFM pump will not necessarily give you 5 CFM as was pointed out before.  And even after correcting it using gas law equation it still is hampered by conductance of piping between the pump and chamber.  Rule of thumb here is use large diameter pipe (as large as the pump inlet if possible) and as few elbows as possible will help a lot. To give you a feel for these factors consider my system takes about an hour to remove said amount of water.  My system is relatively leak tight I can get to 29 inches ultimate on a dry system, so I am getting an EFFECTIVE throughput of about 4 to 5 liters per minute at vacuum BUT I am using a dual stage rotary pump which is designed to do 18 CFM.  Throughput is reduced dramatically by the fact that I am pumping through a 1/4" tube!!  Bear in mind that from the standpoint of throughput bigger is always better, but as a girl I once knew taught me; quality counts for more.  When I was pumping through 1/2" copper pipe I only succeeded in causing the contents of the reactor to froth up and " boil over" contaminating the liquid trap in the process.  So it is possible to have too much of a good thing.  You can reduce the conductance of the piping or install a valve for throttling the pump to avoid this problem and toward the end of the drying cycle open up the valve to speed up the end game.  If your reactor starts rumbling and dancing around on it's stand it is a good bet that you will suck liquid up into the condenser, especially if the reactor is filled to a high level. I hope I have helped and not made it seem a lot more complicated.  If so take a hint from the fact that my pump is more than adequate for my 30 liter size reactor.  I get a sense that it could easily handle a 150 liter tank.  There is a tradeoff between heat and vacuum. Either one can speed the drying process but you don't want froth!  When I started learning about vacuum my mentor said " you can't rush a vacuum son - we got time for a coffee"  so true. Cheers Joe logan vilas wrote: David Sorry if that number's wrong it's what I've been told from the only person I know who does AC work. But that number makes it sound a lot better. You will not have 1 cubic foot of water in your oil after you settle and drain it. If you do then you need to get a better method. There is likely less then 1 cubic inch after setteling and draining. That would only take 6 miniutes to remove. Logan Vilas ----- Original Message ----- From: "David Miller" <[EMAIL PROTECTED]> To: <Biofuel@sustainablelists.org> Sent: Friday, January 06, 2006 1:13 PM Subject: Re: [Biofuel] Dewatering with vacuum. logan vilas wrote: Water boils off at 43F at 20-50mmhg of vacuum at sea level. At 140F it takes about 150-200mmhg. When fluids are mixed togther the Pressure of Vaporization changes especially when thouroughly mixed. You do not need a condensor if you are useing a AC type vacuum pump(that's what they are designed for). I know iowa's BECON program flash heats their oil to 230F then runs it through a vacuum chamber to achieve dewatering. Unless you have a very large vacuum pump or very little water in your oil it will take a long time. Water multiplies in volume by 10-18 thousand times when boiled. Say WHAT? I'm not sure what number you mean by "10-18 thousand". The number I remember is about 1700 times. 1 Cubic foot = 1728 cubic inches 1 Cubic Inch of water when boiled off = 5.79 cubic feet minimum 1 gallon = 231 cubic inches Vacuum Distilation alone would take a huge amount of time. I would still heat then let it settle and remove the water off the bottom. Then use vacuum distilation. Remember if you buy a 5CFM vacuum pump that is displacement of the piston at no load and full rpm. When you start pulling a vacuum that number falls off quickely and at 30" that is probably less then 1CFM. You have to multiply the CFM by the pressure. 1/30 atmosphere * 5 CFM = 1/6 CFM. It you're trying to pump off a cubic foot of water it would take something like 1700 * 6 minutes. That's a long time to wait:) --- David _______________________________________________ Biofuel mailing list Biofuel@sustainablelists.org http://sustainablelists.org/mailman/listinfo/biofuel_sustainablelists.org Biofuel at Journey to Forever: http://journeytoforever.org/biofuel.html Search the combined Biofuel and Biofuels-biz list archives (50,000 messages): http://www.mail-archive.com/biofuel@sustainablelists.org/ _______________________________________________ Biofuel mailing list Biofuel@sustainablelists.org http://sustainablelists.org/mailman/listinfo/biofuel_sustainablelists.org Biofuel at Journey to Forever: http://journeytoforever.org/biofuel.html Search the combined Biofuel and Biofuels-biz list archives (50,000 messages): http://www.mail-archive.com/biofuel@sustainablelists.org/

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