Is there any advantage to adding a venturi for vapor recirculation during recovery? Has anyone tried this? The venturi would only need to move vapor so I am guessing a larger throat would be OK and wouldn't impede the flow as the glycerol thickened. I am building a still with a 17 gallon tank, Taco 19gpm pump and reflux column. Would the venturi be a benefit or a needless complexity?

Thanks,
Tony

(bump)

Anyone???

Hi Tony,

That is a good question. I have been wondering the same thing.

Ryan P. built a still with a pump and inline heater and did not use one ?

I was thinking of making one like his but with a venturi. It is on a little trailer so he can do it in the yard.

Ryan P. ? Anyone ?

Thanks, Steve

Hi Tony

Yes, it is an integral part of the EcoSystem processor.

It means you can start to recover methanol from as low as 40C, because it includes evaporation, not just boiling. Ant it doesn't introduce any fresh air into the system, so you don't blow a stack of methanol fumes out.

And you can get more complete methanol removal , for a given max temperature, again thanks to the evaporative effect.

See here.

If you are de-mething glycerol, you need a seriously beefy pump, because the glycerol is so thick it doesn't flow very fast with a HF or Clearwater pump, so the venturi doesn't get to draw much suction.


hope that helps,

Graham

Graham-

When you say a seriously beefy pump for glycerine, are you referring to flow rate or power rating or what?

You gave some examples of what you thought might be inferior choices. Do you have some examples of pumps you think would be successful?

Thanks!

Marsh

Graham,

I currently do distill out of the BD, my concern was that the glycerol would get too thick for the venturi to work properly. I am trying to decide weather to use my processor to de-meth the glycerol or build a dedicated still using your design. I was thinking that as the venturi was only going to be used to pull vapors that it could be a little more open throated and that would allow for the thickness of the glycerol.

Tony

Tony,

Do you use NaOH or KOH?

Hi marshalld

No, I'm on the lookout for one myself.

Certainly as you get near the end of the de-mething process, the glycerol becomes so thick my small pump really struggles.


Hi tgomes

The more I think of it, the more I believe a venturi may not work well with glycerol, regardless of pump type. It is just too syrupy and sticky.

I've just had another idea which may work well enough with thick glycerol to move vapours around the condenser ... let me put a drawing together to explain ... later ...

Rick,

NAOH


Graham,

Thanks, look forward to it.

Tony

Hi,

I use KOH and the glycerin does not get so thick. I have several reasons for using KOH. KOH soap also drops out of the biodiesel with the methanol out. It takes longer but the results are the same and all I do is let it sit.

No filtering at all. Just a window screen when I put the oil in the processor.

Rick, do you think your venturi and B-100 pump would work with hot KOH glycerin ?

I don't think it is as thick as biodiesel during the thick mixing stage.

Thanks, Steve

Hi,

I agree with SteveD. KOH glycerine is very liquid at operating temps, although I'd expect it to become progressively thicker as the distillation process proceeds to completion.

Marsh

OK, so here's the plan ....

The main concern I have had with distilling methanol out of the WHOLE unseparated batch, with catalyst neutralized to minimize back-reaction, is the glycerol becomes mighty thick once much of the methanol has gone.

This is even more of an issue if you are distilling from glycerol alone... but you can do it from the WHOLE batch without separating glycerol.

DO NOT DO 5% PREWASH with this method. NOT necessary.

Here's my way around this....

I was using a traditional appleseed setup, you know, bottom of tank feeds the pump inlet, pump outlet sends flow to top of tank.

The thing is, my pump just cannot handle the viscosity of glycerol collecting at the bottom of the tank, when methanol levels become very low later on in the process, so I did
it the other way round - sort of ...

I tried taking biodiesel from half-way up the tank, heated it with an in-line heater, and pumped 1/2 of it to the bottom of the tank, UNDER the glycerol.

This hot biodiesel blooped thru the glycerol and helped release the methanol from it. The other 1/2 I spray into the vapour space above the
biodiesel, via the venturi to help it give off methanol too.

After you've got all the methanol out, drain the glycerol, then the biodiesel.

The neutralization certainly helps cut the back-reaction.

Using a venturi, you can employ evaporation instead of conventional 'boiling' distillation,
which means you can run the methanol collection process cooler, which probably further reduces
any tendency to back-reaction.



Note that the pump only has to deal with low viscosity biodiesel.

Heated biodiesel is passed thru the de-catalysed glycerol layer to encourage it to give off its methanol.

The pipework in the drawing is somewhat of a knot - it can be tidied up to have fewe crossovers and elbows.

In the reaction phase, the pump draws from the bottom of the tank, as in my standard EcoSystem

quote:

In the reaction phase, the pump draws from the bottom of the tank, as in my standard EcoSystem

I can't see how you do that. Is there a valve or two missing from the diagram Graham?.....

Just thinking about the viscosity issue... If you're distilling from the whole batch, with the Grundfos, HF/NT type pumps, the turnover rate is pretty low and we know that the by-product settles out. If a pump with a turnover sufficient to stop the glycerol settling out were to be used, woudn't that solve the problem, allowing you to retain conventional plumbing? I'm going to be using an eductor in my next procesor and I'm hoping that it will, when driven by a powerful pump, stir things up enough to prevent any separation.

Nick

quote:

Originally posted by steved:
Rick, do you think your venturi and B-100 pump would work with hot KOH glycerin ?

Steve, It's on my to do list of things to try. Just guessing, but I think it would work with KOH. I want to rebuild my setup with a 15 gallon drum before I try evaporating methanol from KOH glycerin with a venturi. Graham's method is not very efficient with excessive head space, hence the need for a smaller evaporation tank.

Hi Nick

quote:

I can't see how you do that. Is there a valve or two missing from the diagram Graham?.....

Yes, the drawing only shows the recovery phase. Just to make it less confusing, to understand how the recovery works.

There are 2 valves missing, one joining the bottom of the tank to the inlet of the pump, one at the 1/2 way takeoff.

This method seems effective with a typical small pump, so may be of interest to those using Clearwater or Harbor Freight or Grundfos pumps.

Near the end of the process, the glycerol is like thick treacle and just doesn't mix into the biodiesel as there is little methanol co-solvent. It settles instantly and if you switch off your pump for any reason, forget about starting again!

This is particularly so if you don't do the 5% prewash, and you specifically shouldn't do the 5% prewash with this process. It is probably worse still with NaOH, though my one KOH test batch was also too thick for my pump.



Hi Rick

quote:

Graham's method is not very efficient with excessive head space, hence the need for a smaller evaporation tank.

That is really true for any distillation process where you want to extract as much of the volatile material as possible.

If there is vapour space, the vapour will fill it. You want your vapour to be as concentrated as possible (least air) and to be in the condenser rather than in the tank.

Hi Rick,


Thanks. I make biodiesel that is not pumped until it sees the Mercedes fuel pump.

No pump on the oil either. We bucket it out of the drum.

The only filter it sees is a window screen on the drum.

I would have to use a separate setup to get the methanol out of the glycerin.


Anyway, it is on my to do list too. Do you have any of the B-100 pumps. Thanks, Steve

Hi Graham,

What size batch is that ? How long does it take to remove the methanol this way ?

Thanks, Steve

Hi Steve

I run 80 liters of oil + 17 liters methoxide.

It took me 4 hours to de-meth the whole lot with 3kW heating power, and I got 5 liters of methanol back.

Regards

Graham

Hi Graham,

Thank you for that info.

Thanks, Steve

Graham,

Without the 5% prewash...how do you nuetralize the catalyst? Did I miss something? Did you post that in another thread? I saw something about color indicators and using acid until there is a color change in the whole batch...is that the method you are currently using to nuetralize the catalyst for the entire batch?

Thanks,
Rich