condensate temperature issue

stoker · Post by **stoker** » Mon Apr 17, 2006 4:02 am

http://s25.photobucket.com/albums/c69/s ... system.jpg" onclick="window.open(this.href);return false;" rel="nofollow

how cold can the spirit in the reservoir become? new heat continuously passes the reservoir, so I think not very cold.

any experiences? (with the ministill)

I've done a test run, and the water is still +-60°C, and I wonder if it has something to do with my condenser or something else.

would a mini liebig be an solution (after the take off valve)

ty
stoker

stoker · Post by **stoker** » Mon Apr 17, 2006 4:57 am

and I think I'll make a 'jacket' with 6mm coil around my condenser
(not fixed yet)

furball · Post by **furball** » Mon Apr 17, 2006 5:32 am

Some of the things that I have been contemplating is at what temp does the ethanol condense out, but the methanol still stays as a vapor. I would like to be able to set up a still where I could get enough of a gradient to where I can get refluxing of the ethanol but have the methanol vapor pulled off though a different condenser. Sorry for the minor hijacking of the thread, but it seemed to be going into the same direction that I have been thinking.

Furball

knuklehead · Post by **knuklehead** » Mon Apr 17, 2006 2:22 pm

Methanol has a lower boiling point then ethanol so it will condense out before the ethanol will.

Thorin · Post by **Thorin** » Tue Apr 18, 2006 1:20 am

yeah, what KH said, but hte difference is very small (10 degrees or something?) so it will be quite hard to do...

besides, when there is not more methanol left, the ethanol may also go out in that condensor.

Maybe some way to do it technologically now though.... maybe use some kind of CPU to digitally controll cooling water flow in the condensors and so on... would be very cool, but it would be a little expencive...

prbbly some easier way too...

furball · Post by **furball** » Tue Apr 18, 2006 3:22 am

Knucklehead, I think I am going to have to disagree with you on part of your reply. Yes the methanol has a lower boiling point then the ethanol. The temperature gradient across the still is from hot at the bottom to cooler at the top, The higher volitility of the lower alcohols allows them to travel further up the column until they reach a temperature zone that puts them into a saturated condition in that system, this is one of the reasons that you want to allow the column to stabilize for an hour, and maintain a steady heat rate. This is so that you can get stratification of the differnt components and make tighter cuts, because your going to have the lower boiling point stuff come off first, then progressively higher boiling products to follow.
So, if I were to set up a tall enough column I should be able to maintain the stratification that allows me to tap off the methanol at the same time as the ethanol( after allowing the reflux to get to equilibrium).
One of the ways I was thinking was to use cooling water a couple of degrees cooler then the ethanol boiling point, but still warmer then the methanol boiling point to get it higher up the column.

Furball

Swag · Post by **Swag** » Tue Apr 18, 2006 6:20 am

I see what you are saying Furball and agree with your basic analysis. However, I still think the simplest thing is what we do now. That is to equalize the column and then draw off 99.9 percent of the methanol as forshots. The rest of the methanol, if any, is collected in the heads.
If you were building a continuous feed still this would be a concern. You could build a column with thermometers stuck in it every inch or two to see exactly where the temperature gradients are. Then you could adjust the heat to put the purest ethanol gradient right on your takeoff.

TEC · Post by **TEC** » Tue Apr 18, 2006 6:31 am

Swag,

I agree with you completely, I was just too lazy too try to explain that various takeoff points would only be needed in a continuous setup.

Tom

furball · Post by **furball** » Tue Apr 18, 2006 7:59 am

There you guy's go, you had to throw in the practicality flag on me......LOL
I have to agree, but it would be nice to have a set up that once it reached equilibrium then you could just open the taps and have two product streams. One for drinking and another for what ever you wanted to use the methanol for( directly as a fuel, or as part of the production of biodiesel).
Well, I am still going to ponder the process, never know maybe this could be my claim to fame some day!

Furball

stoker · Post by **stoker** » Tue Apr 18, 2006 8:41 am

can some one answer the original question, please?

furball · Post by **furball** » Tue Apr 18, 2006 9:55 am

Hey Stoker, sorry for the hijack on your thread.
You want to know how cold can the distillate be in the internal resevior?
I think that would be a function of the water temp in your coils and the contact time the fluid and vapor has. Your then going to have heat input as the vapor travels up the column and through the nozzle in the middle of the pool. This sounds like your going to have to calculate the heat transfer going into the fluid pool from your vapor as well as the heat rejected through the exterior shell. Can you install a tap into your resevior and take a direct measurement over the coarse of a run? Is there a reason for the importance of the temperature of your resevior?

Furball

stoker · Post by **stoker** » Tue Apr 18, 2006 10:03 am

no, but the output is right now +- 60°C, and I'm wondering if it can be lowered.
but I think I'll install the mini liebig condenser after the valve

Swag · Post by **Swag** » Tue Apr 18, 2006 10:31 am

stoker wrote:no, but the output is right now +- 60°C, and I'm wondering if it can be lowered.
but I think I'll install the mini liebig condenser after the valve

I think that is the only way you are going to get cool distillate from that type of still.
However, having warm distillate can be a good thing too. If you let it drip a ways into your collection vessel, it will have a tendency to evaporate the fusels on the way down.

stoker · Post by **stoker** » Tue Apr 18, 2006 10:37 am

then, the fusels are already supposed to be gone
I think I'll loose more ethanol then fusels.

an aditional question: if the temperature of the reservoir is pritty high, are there then problems to seperate the vapour, make a good equilibrium,... ??
or is it the same as it would be at 20°C

ty

Swag · Post by **Swag** » Tue Apr 18, 2006 11:00 am

stoker wrote:then, the fusels are already supposed to be gone
I think I'll loose more ethanol then fusels.

an aditional question: if the temperature of the reservoir is pritty high, are there then problems to seperate the vapour, make a good equilibrium,... ??
or is it the same as it woult be at 20°C

ty

Your column will eventually equilibrate. As long as there is cool distillate flowing into the reservoir faster than the hot vapor can evaporate it, you will have equilibrium. The temperature in the reservoir will be dependant on how much coolant is flowing through your condenser and the vapor temperature and flow rate coming up the column.

Is there some advantage to this type of design?

stoker · Post by **stoker** » Tue Apr 18, 2006 11:11 am

Swag wrote: Is there some advantage to this type of design?

good question

well, I think because it looked easy, pritty cheap, and I partly designed it, and wanted to know if it works.
then (when I started with the assembling) I didn't tought about this problem.

The temperature in the reservoir will be dependant on how much coolant is flowing through your condenser and the vapor temperature

that's something I'm not sure yet. the warm condensate, is it caused by the flow of new heat, or a malfunctioning condenser.

btw, thanks for the quick replies

TEC · Post by **TEC** » Tue Apr 18, 2006 11:29 am

Stoker,

The condensed liquid will be almost the same temperature as the vapor. This is because as soon as the vapor condenses, it will drip off of the condenser and not be cooled any further. This is not a design flaw or an malfunctioning condenser.

Swag · Post by **Swag** » Tue Apr 18, 2006 12:16 pm

TEC is right. The condensate is sitting in contact with a copper wall that is being constantly heated by hot vapor coming up the column.
If you had icewater flowing through your condenser it might lower the temperature of the condensate somewhat.

stoker · Post by **stoker** » Wed Apr 19, 2006 12:10 am

bammer
the temperature in the reservoir is not that bad, if it will serperate propperly..

then i hope the extra cooling wil help
(the coat, 6 mm coil at the bottom (outside) of the condenser)
and the miniliebig
but that's something for later.
I have to work for school, I'm addicted!

Stangas · Post by **Stangas** » Fri Apr 21, 2006 8:56 pm

so what is the target temp for the head space in a super reflux..

this is easy to use, just checking temps.. i read in a book that 78 - 78.5 deg C

stoker · Post by **stoker** » Fri Apr 21, 2006 11:44 pm

I'm not talking about the head temperature. but the temperature of the liquid spirit, when it's already condensed.

possum · Post by **possum** » Sat Apr 22, 2006 11:48 am

When the still is on, the spirit will always be just a little cooler than the temp of vaporization for the mixture. If you would like to check the specific gravity if your spirit as it is coming out, then yes, a mini leibig built into the prouduct out line is a fine idea.

I don't have a collumn, but the laws of heat and evaporation and conduction, force the spirit to come out relatively warm in the picture you showed.

stoker · Post by **stoker** » Sat Apr 22, 2006 1:23 pm

that's what I think too,
but has everyone who has a ministill (Alex' design) warm spirit?

eventually, I added the jacket, and the spirit is almost at room temp (with a low heating for the boiler)
http://i25.photobucket.com/albums/c69/s ... jacket.jpg" onclick="window.open(this.href);return false;" rel="nofollow

TEC · Post by **TEC** » Sat Apr 22, 2006 4:05 pm

stoker wrote:

but has everyone who has a ministill (Alex' design) warm spirit?

It's not just the mini-still that has this issue, any design that the liquid does not flow through the condenser will be the same.

Think of it this way, the vapor is hot, it condenses and immediately falls off of the condenser thus not being cooled any further. What is the difference between 178f vapor and 178f liquid? change of state, that is all.

Maybe someone would want to do some testing on a design that cools the reflux liquid before it is reintroduced back to the center of the packing at the top of the column?

We could call it a LM with CM managed reflux temp...

stoker · Post by **stoker** » Sat Apr 22, 2006 11:41 pm

it's just curious nobody has complained about it yet.

TEC wrote:Maybe someone would want to do some testing on a design that cools the reflux liquid before it is reintroduced back to the center of the packing at the top of the column?

I am willing to try it. when I've time.

TEC · Post by **TEC** » Sun Apr 23, 2006 7:45 am

I never really saw it as an issue other than with %abv readings. Since it is a liquid already, it wouldn't take much to cool it.

stoker · Post by **stoker** » Sun Apr 23, 2006 8:37 am

an other reason: the higher the ethanol, the more will evaporate

furball · Post by **furball** » Mon May 01, 2006 4:03 am

You would be defeating the purpose of reflux if you cooled your condensate below the temperature threshold for vaporization before returning it to the column packing. By doing this you would end up sending to much liquid to far down the packing and wouldn't get effective separation, and you would end up choking the flow. Ideally, as long as the fluid is in side the still you always want the liquid and the vapors to be the same temperature( saturation temp) with stratafication up and down the column so you can get the separation of the different fractions. The only time you want to drop the temperature down below these conditions is during collection when your bringing your product out side the still.

Furball

stoker · Post by **stoker** » Mon May 01, 2006 4:33 am

so again my question, 'everyone collects hot spirit with his still?'

"you could also see the temp-issue like this: the cooler the returned spirit, the longer it will stay in the column = the more it is purified,.."
why isn't this thrue?

possum · Post by **possum** » Mon May 01, 2006 7:42 am

You want the reflux liquid to be close to it's evap temperature. You should get more action from the steam coming up through it if the liquid is close to its boiling point. That way the steam only has to add the energy to turn x-degree liquid into x-degree steam. The energy that the steam gives away to vaporize reflux liquid, causes the water in the vapor to be liquid.
This is all an aproximate description, but it is pretty acurate. The whole process is taking place up and down the collumn at different rates, but it is especially important where the reflux liquid enters the collumn.

I hope that helps more than it confuses you stoker.