My experiment with a salt tower for dewatering

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

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My experiment with a salt tower for dewatering

Postby canolafunola » Thu Sep 25, 2008 9:05 am

I have always wanted to try using salt as a dewatering agent and built a salt tower out of 6" pvc a little under 4 ft tall. Here's a pic after it was partially disassembled. I'll describe the first test that I've done later and hopefully I'll get time to do more tests and post more pics.

Image
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Postby coachgeo » Thu Sep 25, 2008 9:15 am

If im seeing this right looks like your feeding oil from a storage drum into the tower via a tube that I assume actually runs inside thru the salt to the bottom of the tower.

Therfore, oil enters the bottom of tower and fills upward thru the salt?

As tower fills oil leaves the tower via another tube at the top and goes back to the storage drum?

close?
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Postby canolafunola » Thu Sep 25, 2008 9:26 am

Yes except for your last sentence. As I said pic was take after it was disassembled. The output hose was stuck in the barrel so it won't drip onto the ground. I hafta go now. Be back later.
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Postby coachgeo » Thu Sep 25, 2008 9:36 am

I like the still action shot of the dissasmbly.

The blue AA battery below the pump falling to the floor. Boy you must have really been in a hurry LOL
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I know... its actually a wired in resistor?? but at quick glance its either falling or floating.
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Postby canolafunola » Thu Sep 25, 2008 11:04 pm

Getting back to this. The 6" dia PVC pipe is about 36" tall and has a cap solvent welded to the bottom. The top cap has a nylon inlet tube which goes to the bottom of the PVC pipe and a nylon outlet tube 1/2" from the top. it was filled 3/4 full with water softener salt pellets from Lowes (sodium chloride). There's a gasket in the top cap held tight with 4 bungee cords. The nylon tubes are sealed to the top cap with grommets. A 12 V solenoid pump takes oil from a floating pickup in the 55 gal barrel and pumps it to the bottom of the upflow salt tower at a rate of 8 oz in 2 min 47 sec which works out to 1.35 gph. The oil in the barrel was about 95% full settling for the past 4 months. It sizzled and popped in the hot pan test indicating lots of water. I did a mini wash of the oil before running it through the salt tower and got a reading of 10 with the TDS meter. I did not measure the oil temp but my guess is it was at approx 60 F.

I pumped about 1/4 of a cubee through the salt tower and left it to settle overnight, figuring that whatever salt dust from the fresh pellets will settle to the bottom. Next morning I pumped out a little of the settled oil from the tower and did a mini wash and the TDS reading was 130!
Hot pan test of the oil that went through the tower still sizzled and popped.

I was suprised by the high TDS reading after running through the salt tower. Maybe the upflow salt tower is not a good way to use salt for dewatering? Maybe sodium chloride crystal is better? Maybe the oil needs to be at a higher temp?
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Postby SunWizard » Fri Sep 26, 2008 8:22 am

Interesting tests. I am surprised it didn't dewater. Was this PHO? The increase in the TDS is a very bad result, you are the first using salt I have seen to test for that. I wouldn't put any of that high of dissolved salt in my truck.
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Postby canolafunola » Fri Sep 26, 2008 10:28 am

It was not PHO and I would NOT put that oil in my car either. One thing I did notice was the output on the clear lines had what appeared to be many very small particles or bubbles. Were these maybe salt dust particles? Or maybe air bubbles from trapped air in the salt pellets? Maybe bubbles created by the solenoid pump? I didn't note whether the inlet lines had it also. I will repeat the test when I get a chance and make sure I look at the inlet lines.
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Postby coachgeo » Fri Sep 26, 2008 11:24 am

wow Im suprised too.

You called the Water Softener stuff salt "pellets" so not to assume anything..... it was in a pressed pellet or rock form?

If it's pressed pellets maybe they are falling apart and mixing in with the water in the oil.... buttttt. not enogh salt to get the water in the oil to combine with neighbor water soooo you ended up with salt wet oil.

when you poured pellets into the tube where their any salt crystals that could have made it's way in from the bag?

Might try washing thru the system with water a some to try to disolve and wash out smaller crystals. If the Salt is in pellets maybe this will get each pellot to bond together tighter; more like rocks, after you remove the water and let it dry.

Another experement would be to do your same setup but with water added to the salt in the tower. You would then have to make sure you GPH of oil is slow enough to allow the water to not get pushed upward via flow energy of the pump. If enough pump pushing is elminated the Water should not exit the top since oil is lighter and would over flow instead leaving the water behind you added AND the water out of the oil.
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Postby Burbarian » Fri Sep 26, 2008 1:58 pm

I've found that having the oil upflow through a large pool of dissolved brine to be much more effective than to upflow through straight salt. The moving oil will take up the fine salt particles, and there is insufficient stasis for the microscopic suspended water droplets to contact salt and settle out. A pumped salt upflow through a relatively narrow column (compared to a barrel 1/8th full of saturated brine) may not be ideal. Counter intuitively, dissolving most of the salt with water first, then doing a gradual upflow through the dense brine does a better job. At least according to my hot pan tests.

Also, some brands of water softener salt has other ingredients added to it, including surficants and anti-caking compounds unlike straight mineral salt.

A hot saturated brine-and-oil emulsion maximizes the density difference. Hot water soaks up a lot more salt, and hence rapidly becomes denser with added heat, whereas hot oil becomes less dense and less viscuous, allowing the much denser salt saturated water to fall out quickly. If the oil is at room temperature and there is no existing saturated brine, then separation takes more time.

These are just my observations.
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Postby canolafunola » Tue Sep 30, 2008 9:17 am

Burbarian, what you wrote makes a lot of sense. The salt pellets I was using is Diamond Crystal® Red-Out. It's what I had. It is sodium chloride with a very small amount of citric acid in it (as I remember reading the ingredient label).

http://www.cargillsalt.com/food/dc_salt ... outpel.htm

I have not done anymore testing with the upflow salt column. But I did dissolve and heated some salt pellets in water (to saturation) and mixed in 50% of the same wvo that was used in the salt tower testing. Seperation was immediate. Here's a pic taken approx 17 hrs later. It is still a bit cloudy. I'll let it settle more till clear then do a mini wash/ TDS test.

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Postby canolafunola » Wed Oct 01, 2008 8:19 pm

The oil and brine has settled for about 30 hours and I just did a mini wash and the TDS reading on the wash water= 5. The oil before mixing with the salt brine had a TDS= 10. Unlike the salt column, the salt brine did not increase the TDS reading. I will do a HPT on it tomorrow and report the results.
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Postby Burbarian » Fri Oct 03, 2008 12:13 am

I typically let the hot oil settle for a week in an insulated barrel, then take the top 2ft off of a 3ft tall barrel. The brine wash has a curious side effect of causing high melt point fats to aggregate and drop out, forming a kind of paste layer between the brine and the lighter oil. If you have PHO and the oil is allowed to cool, it will remain cloudy. I suspect it is due to suspended wax crystals, as heating the cloudy oil to about 120F (~50C) turns it immediately clear. The mild heating causes wax crystals to go back into solution and hence clarifying the oil. Once cleared, it stays clear even when it cools to room temperature.
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