Newbie here, so excuse the stupid question... I'm in the process of designing a processor and have the following question regarding a sight tube. How "accurate" is the sight tube in determining the level of glycerin after settling? What im trying to get at is: you pour in the oil, and add Methoxide. after 8-12 hours you come back and in your sight tube, you should see a layer of glycerin. Would this level be exactly the same height in your tank as well? Basic laws of fluids would say that the level at the top of the sight tube would be the same as the level on the tank, but im thinking that with 60 or 80 gallons of biodiesel in the tank that presses down on the glycerin layer, that weight might push the level of the glycerin in the tube upwards. im convinced that the TOTAL level would be the same in the sight tube and tank, but has anyone experienced what im trying to say here?
i wouldn't think it would be very accurate. in fact i'm quite sure of it. biodiesel and glycerin don't like eachother, so that makes it hard to "equilibrate" their levels in two connected "tanks". they would have to flow thru each other to equilibrate.
my site tube is set up (by complete accident really) so that i can open the valve at the base and drain it before and during reaction. in other words, it's empty during reaction. once i'm done mixing, i open the valve and fill the site tube and then immediately close the valve. then i can monitor how the settling is going, and once it is done you can simply measure the relative heights to calculate % crude glyc.
alternatively, (and slightly more accurate) is to draw off 500 mL into a graduated cylinder right after mixing is done.
I have my sight tubes set higher than the upper level of the where the settled glycerin will be. I have found that on our glycerin storage tanks, the glycerin gets cold in the sight tubes, which causes them to get solid. the tank can be emptied, and it will still read in the sight glass. on my processors, I have my sight tubes set up with valves top and bottom, and an air line plumbed into the sight glass so I can purge the oil in the tube, and shut the bottom valve off. This leaves the tube empty during processing, and reduces the chance of having unreacted oil in the tube.
For what it is worth, I have switched out all of my sight tubes to clear schedule 40 pvc. I got it on mcmaster carr, and it will work with regular pvc fittings. after a few catastrophes with the braided pvc hose, and hose clamps blowing off, the extra cost is worth it.
2 bobcats, an excavator, and a ventrac mower. looking for a diesel weedeater!
This "sight tube accuracy" thing is something that i have wondered about for a while. im in the process of building a processor, and have been wondering if one can improve on the sight tube. One of my sources where i get my oil from, creates a batch where the glyserin and biodiesel is very simular in colour after mixing and settling. The glyserin is also a little less viscous than with other oil, which makes it difficult to drain correctly (when the draining changes from glyserin to diesel, it is very difficult to spot, although-once the glyserin is drained and the diesel is washed, the colour of the diesel is significantly lighter). But... if I shine a torch through my sight tube, the difference in colour is much more vissible. THats what made me wonder about the accuracy of the tube, if the level in the sight tube can be considdered accurate, I can measure the height, and with some simple calculations, work out exactly how many liters/gallons of glyserin is in the tank, and then drain out only that amount...
I find the site tube on my reactor to fairly accurately represent the glycerin level after I let it settle, it is at about 170F though and therefore quite viscous.
There is a much simpler way though, Biodiesel is non conductive and glycerin is very conductive. Check out the glycerin sensor article in my sig line. I mention in that article that a $5.00 water sensor from HD will probably work the same way, if you dont have any soldering skills its worth a shot. You just have to drive a couple nails through your drain hose to sense the liquid. An ohm meter will also work.
FWIW, I put a calculator in my biocalc that will accurately measure the volume of your glycerin, even in a cone bottom tank, you need to know the diameter and height of the glycerin for it to calculate it.
Simple schematic for a pump and heater control with a high limit
Sensor for the biodiesel/glycerin layer
Had i lived in America, i wouldve just bought the $5 version, and the report back, but out here in the sticks, we have to build everything ourselves... (lol-just a joke, South Africa is amazingly 1st world(ish)... Anyway, i like to tinker, and building my own would give me more satisfaction. ive even made my own version of the Dry-Pro dewatering nozzle... Will put pics up when all is done.
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