Drying Biodiesel.

[dgs]

I'm sure we all dry our biodiesel in one way or another. From testing lots of peoples samples, I'm sorry to say that most ways don't seem to work. Bubbling with ambient air, sprayring devices, etc.

Now don't get me wrong here guys, I'm not trying to preach to you but I think getting the water down to reasonable levels is important. I personally like mine down to below the german spec of 300ppm. I know lots of others would disagree.

One of the difficulties we face is that testing bio for water is not one of the easiest tests we can do.

For years I dried my bio by bubbling with ambient air. When I got my Sandy Brae I was horrified that the level was 8 to 900ppm. I never had any trouble with my bio, but at the time it was going into two older indirect injection vehicles. I gave a sample to a commercial producer who had a KF and he confirmed the 800ppm.

So I thought I would do a simple experiment and put the compressor inlet into a cardboard box. At the opposits side of the box I cut a flap and directed a small fan heater to inside. I left it for 4 hours. Result was 400ppm water.

It was after this that I got interested in making one of IMB's turbo dryers. He had experimented with all sorts of things, dehumidifiers, fan heaters, spray devices etc and in the end came up with this idea.

I will post a drawing when the wife comes in (still learning)
Basically the dryer is a plywood disc that sits on top of the processor/wash tank. On top of the disc is a 10-15 litre plastic drum with a sealed lid. on top of the drum is something like a tuppaware sandwich box with about 2" of self-indicating silica gel inside. Small holes are drilled in the lid of the sandwich box and the base (through the top of the 15 litre tub)

inside the tub is an aquarium bubbler, with the pipe going down to the tank bottom. At the back of the plywood disc is a 4" computer fan pulling air out of the headspace, driven from a small led transformer also inside the tub. All joints, lead exits are sealed with silicone.

The air pump can only pull air that has come through the silica gel, as the air goes down the line it gets warmed by the biodiesel (50 to 65 degs)

The results my dryer gives are;

before dryer after water washing, @ 1200ppm
after 4 hours 500ppm
after 7 hours 150ppm 
after 13 hours 50ppm

I usually leave mine 7 to 8 hours, the 13 was just to see.

I heat the bio to 60 degs, when it gets to 40 I start the dryer, when at 60 I leave it for 3 hours, then swith off the heat, when it gets down to 40 I turn off the dryer. Total time 7 to 8 hours.

[knighty]

aren't you limited by the amount of water the silica gel can absorb ?

I assumed you'd need shed loads of it for something like this


does dewatering at a higher temperature not have the same effect ?

[dgs]

aren't you limited by the amount of water the silica gel can absorb ?

I assumed you'd need shed loads of it for something like this


does dewatering at a higher temperature not have the same effect ?

No, not at all. My silica container is a see through plastic coffee container (simply so I can easily see if the silica needs changing) about 2/3 full this holds about 600gms and will work for up to 10 hours. I do 50% of the drying cycle with the silica from the previous drying, then change it for new(dried)

I have 2kgs in total and simply leave it on top of the c/heating bioler to re-dry.

Higher temperature helps, but there are electric costs to consider and remember you are at the mercy of the R/H when you bubble with ambient air. So you could potentially be drying to a very low level because of the temp, but wetting it all the time with the moist air. There are also oxidation issues to consider if heating to high temperatures.

[Julian]

That's very close to what I've been doing for about a year, but without the ullage space fan.  I don't think my set up works because I've probably ruined the silica gel trying to dry methanol ... it hasn't changed colour since I made the set up.

My desiccant is in a jam jar.  The inlet is a dip pipe through the desiccant to the bottom of the jar and the outlet is from the empty space at the top.  I had tried a long acrylic tube filled with silica gel in conjunction with a small compressor, but I don't think it held nearly enough.

I think I may need to invest in more desiccant!

If you recon it's an effective means of drying, we could do a wiki page ... would we need to get permission to use the design?

[dgs]

I asked IMB a while ago if I could use the details on the UK forums, he didn't have a problem, great guy.


Originally the design had an additional fan in the tub that blew down on the headspace, although it worked, it pulled too much air through the silica and thus meant it needed changing every 3 hours or so.With this version only the one fan pulling out is required.

Using one of the 'sander' wooden air diffusers has made my set up a lot more efficient (more very tiny bubbles)

The drawing doesn't show the silica gel container on top of the 15 litre tub. I have built quite a few of these for people, usually after they have visited and seen mine.

I think a wiki page on this would be excellent. I know the 13 hour test I did is totally impractical, but it gives some idea of how efficient the dryer is and it is very difficult to get bio down to 50ppm water.

[knighty]

is it not better to circulate the air through the silica gel instead of pulling fresh air in all the time ?

[dgs]

That could be a very good idea. If the air coming out of the extraction fan was at lower RH than the ambient air then you are correct, it would work more efficiently.

[Bio-boy]

Never had an issue with my drying process. 2hrs circulated via 2 drying bars and then decanted via a Cimtek Hydrosorb filter. Crystal clear ever time!

PS Forgot to mention the Venturi air extraction unit than is powered by my air compressor to draw the water vapour away from the Bio.

[dgs]

Never had an issue with my drying process. 2hrs circulated via 2 drying bars and then decanted via a Cimtek Hydrosorb filter. Crystal clear ever time!

I'm not saying your bio is too wet Bio Boy, but how do you know it is dry enough? Being clear only tells you it is roughly under 1000ppm! From my experiance of testing peoples samples dried by using spraybars and the like, they don't work too well.

[dgs]

Over the last couple of days I have been doing a trial to see if I can get some correlation between the humidity of the air exiting the extraction fan in the turbo dryer and the actual amount of water contained in the biodiesel whist the drying cycle is underway.

This is the sort of R/H sensor I used.

                                        http://www.ebay.co.uk/itm/Mini-Digital-LCD-Thermometer-Hygrometer-Temperature-Humidity-Meter-Probe-Sensor-/361146290994?hash=item5415ff1332

It's just a cheap thing and probably not very accurate, however the object of the test was to see how the meter behaved in the 'wet' air from the surface of the biodiesel.

The biodiesel was first tested for water with the Sandy Brae, it was 600ppm. This was a batch that had been only settled for 10 days which is why the initial water level was lower than if it had been water washed.

The biodiesel was heated to 60degs in the wash/drying tank. When the temperature was at 40degs the dryer was started. Within a few minutes the R/H had dropped from an ambient reading of 57% to 52%.

The biodiesel was held at 60degs for 4 hours and after 2 hours the R/H had dropped to 30%. At this point the bio was tested for water which was 210ppm.

After the 4 hours the R/H had dropped to 26% and the dryer was left on until the bio temperature had dropped to 50degs. The biodiesel water content at this point was 120ppm. After the dryer was switched off the R/H sensor went back to reading ambient which was 40%

I have a biodiesel friend in the next village who has used this method for the last couple of years to indicate when his
bio is dry enough. He also leaves the dryer on until his sensor reads 26%. he has a manometer to check his water.

So as a cheap refrence it does seem to work. When I dry my next batch I will leave it drying until the sensor reads 26% then check the water content of the bio.

I do realise that there will be a lot of variables with this, also I don't think many use turbo dryers but I'm sure the sensor could be used with a lot of set ups.

As a matter of intrest I checked the soap level in this batch before and after centrifuging.
Before 42ppm After 16ppm.

[Bio-boy]

Any pictures of your set-up Dave?

[dgs]

I will post some pics tomorrow, also of the typical amount of residue I get in the centrifuge.

[Julian]

Interesting results.

Reduction in soap by centrifuging looks promising.  It would be interesting to see the results of a completed batch split, with half being centrifuged without washing and half water washed in your normal way.

When you consider the energy used to dry bio, centrifuging could represent quite a saving.

[dgs]

Interesting results.

Reduction in soap by centrifuging looks promising.  It would be interesting to see the results of a completed batch split, with half being centrifuged without washing and half water washed in your normal way.

When you consider the energy used to dry bio, centrifuging could represent quite a saving.

I'm sure the water washed batch would win hands down every time. the soap in my water washed batches is always <10ppm. Strangly enough though the glycerol residue in washed/settled batches seems to be the same. I'm sure my centrifuge is lacking some efficiency as with the peugeot 106 pas pump I can't get the pressure above around 56psi.

I've been speaking to Nathan who said when fuging bio the ideal pressure is 90-95psi so I think I will invest in a 'proper' pump.

There is the additional unknown question of the mono's when just settling. I have 2x 50/50 tests on the windowsill, one is washed and one settled. When we do a 50/50 the bio is of course is saturated with water, as the test settles depending on temperature the bio will totally clear, then if the temperature drops it will mist up. The bio in the settled batch will mist up at 3degs higher than the water washed batch and I'm sure this is due to the mono's being present. They were intentionally removed from the washed batch.

[Bill]

Monitoring the humidity in the space above the drying bio is how I dry mine. It is a splash dry arrangement. The software measures the voltage from the sensor to detect the minimum voltage or a value of 75% of the maximum value recorded during the drying process, which ever comes first. I don't bother to convert to RH.