WVO Dissolved water and % saturation versus temperature

Collecting, filtering and dewatering of WVO SVO vegetable oil. For Biodiesel producers too.

Moderators: SunWizard, coachgeo

WVO Dissolved water and % saturation versus temperature

Postby SunWizard » Mon Aug 30, 2010 1:24 pm

I am using the term dissolved water to mean water so small its below detection by the HPT or by most microscopes. Characterized by individual water molecules dispersed throughout the oil. Dissolved water in oil is similar to humidity in the air - the water is there, but it is too small to see because it is dispersed molecule-by-molecule. Its handy to dicuss it just like humidity, as a % saturation. WVO or Biodiesel can hold a significant concentration of dissolved water and still appear clear. Most vegetable oils can easily hold 200 to 600 PPM of water (0.02 to 0.06 percent) in the dissolved state depending on the temperature and age of the oil, while used oils can hold three to five times more water in the dissolved state than new oil.

For example, say a batch of old WVO can contain 700 PPM water at 100% saturated dissolved and above that I get suspended water and it fails the HPT. Here is an article about % saturation with charts that may help (even though its about hydraulic oil the concepts apply.)
http://www.machinerylubricatio...50/pall-water-sensor
which states:
"Because changes in fluid temperature will vary the percent saturation, a system with constant water content measured in PPM that experiences significant temperature changes creates the possibility of turning dissolved water into damaging free water. "

It would be interesting to develop a % saturation versus temp chart like that for WVO. Because WVO behaves like the hydraulic oil shown, but old WVO holds even more water dissolved, this means you could have WVO that is well below saturation at 160F, yet goes past saturation to form suspended water at 20F. Another area where more testing is needed. Maybe our tests should be performed with WVO at the coldest temp you want to run at.

Dewatering with with a Centrifuge or evaporative methods can get you well below 100% saturation, and well below what settling the same WVO would. Older higher FFA WVO will be more hygroscopic (water attracting and holding) due to the FFA. The further you go below 100% saturated, the more hygroscopic it becomes. This isn't bad however since then you have a larger margin of safety than if you simply dewatered with settling to say 90% saturation. Say you dewater to 50% saturated, and it slowly absorbs water again while in your fuel tank up 90% saturated, that is still better than dewatering to 90% to start with. You could visualize it as 2 rooms with a small door between, 1 room is at higher relative humidity, and would slowly equalize between the 2 rooms (your fuel tank and the outside air.)

The hygroscopic issue is just the nature of old used WVO and Biodiesel made from it. But you need to watch out for it especially in humid climates. Some are starting to add dessicant breathers to their fuel tank vents, to lessen this issue.
Last edited by SunWizard on Wed Sep 29, 2010 10:45 am, edited 2 times in total.
YVORMV - Your veg. oil results may vary.
95 Dodge Cummins 4x4 SVO WVO conversion.
81 Mercedes 300D- stock and happy on V80/D20 blend.
Low fossil net zero house- 100% solar power and heat.
SunWizard
Site Admin
 
Posts: 1720
Joined: Mon Dec 11, 2006 2:53 pm
Location: N. Colorado

Postby SunWizard » Sun Sep 26, 2010 11:36 am

I ran 6 tests on the same calibrated samples of VO used in my Homebrew capacitive water in oil meter testing then I temperature compensated the readings using my Capacitive water in oil meter Percent saturated calculator The samples were first tested at room temp 64F, then chilled in a sealed jar to 30F and tested, then heated while sealed to 140F and tested again. I kept the jars sealed since putting them in the freezer would otherwise have gained water, and likewise while heating if they weren't sealed they would have lost some water.

Here are the results showing how I could have WVO that is well below saturation at 140F, yet goes past 100% saturation to form suspended water at 30F. This matches the description I gave in post#1 with real samples with both a low FFA and a high FFA where both respond very similarly to temp:

Image

This testing tells me that I always want to get well below 70% saturation when running my centrifuge at 160F, since at that level it would be close to 100% saturated at 30F. Sample AD gained 21.7% and C gained 23.7% from the cool down. The slope of the line is ~ 4 F / % saturated.

Note that testing samples with my sandy brae would not be of any use since they would measure the same PPM no matter the temp. And the HPT doesn't tell me anything about this either since all the samples would pass the HPT with no bubbles at all temps. This was one of the main reasons I did all this work to find a better test than the HPT, since I always got to 0 bubbles on every batch.
YVORMV - Your veg. oil results may vary.
95 Dodge Cummins 4x4 SVO WVO conversion.
81 Mercedes 300D- stock and happy on V80/D20 blend.
Low fossil net zero house- 100% solar power and heat.
SunWizard
Site Admin
 
Posts: 1720
Joined: Mon Dec 11, 2006 2:53 pm
Location: N. Colorado


Return to Vegetable oil Collecting, Filtering and Dewatering

Who is online

Users browsing this forum: No registered users and 0 guests

cron