stills

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stills

Postby Bushman » Sun Mar 02, 2014 7:21 am

COMPOUND STILLS
This is an attempt at explaining the various types of compound stills and the components that make up a compound still. First we need to clear up some basic terms as they can be confusing as distillers/would be distillers use similar terms to mean the same thing.

Fractional Stills, Compound Stills, and Reflux Stills all used interchangeably throughout the Web to describe some type of still that separates and stacks vapor. Here we will define Fractional Stills as the part of the still between the boiler and the reflux condenser which has some design or material that allows for separation of the different ethanol vapors (more on this later). Compound Stills will be interchangeable with Reflux Stills in that it has the fractionating portion of the still but also has some type of reflux condenser on top that allows the vapor to be condensed and then fall back down the column for better separation.

Fractionating Column
The fractionating portion of the column can be built in many different ways but basically it’s any physical device that provides good contact between the vapor rising and the liquid present on the material.

First we will discuss different types of packing as a means of separation. Probably the most used at our level are copper or stainless mesh, SPP (Spiral Prismatic Packing), lava rock, and other material such as marbles that don’t seem to be as efficient.

Copper mesh
copper2.jpg
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Link to making your own copper mesh


spp.jpg
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SPP

Making your own SPP

The other method of creating separation is through trays sometimes called plates. There are different designs in this area as well. I will mention two of the more common ones used at the hobby level but by no means is this list complete.

Bubble cap trays: A bubble cap has a riser fitted over each hole and a cap that covers the riser. The cap is mounted so that there is a space between the riser and cap to allow the vapor to pass. The way it works is vapor rises through and then goes downward due to the cap on top and then bubbling through the liquid on the tray.
bubblecap3.jpg
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Sieve trays: Sieve trays are simply metal plates with holes in them sometimes called perforated plates. The size of hole is important, as vapor passes straight upward through the liquid on the plate. The advantage to this design over bubble cap is perforated plates are inexpensive to make and they drain themselves after distillation.
perferated tray copy.jpg


Before getting into more detail on how these work we need to discuss a couple of terms that affect these designs:

HETP: This refers to plate height or height equivalent to a theoretical plate (HTEP). Liquid wets the surface of the packing or tray and as the vapor rises it contacts the wetted surface this is where transfer occurs.

Weir: Defined as a barrier across something to alter its flow. In the design of the tray it ensures that there is always some liquid that is held-up on the tray.

Downcomer: This is a designed part of a tray and in our application usually a pipe that allows the liquid to fall through the pipe by gravity from one tray to the next one below. For this to work efficiently each downcomer is staggered from one side to the other.

Some people design their trays/plates to also include some packing material to improve separation. Packing would be considered a passive device that increases the contact area between vapor and liquid.

So the question comes up Packing vs Trays. Packed columns are called continuous contact columns and tray columns are referred to as staged-contact columns. In our application it’s mainly cost but with larger commercial stills trays are used in applications with liquid rates of 30m3 /m2–h and above or if solids are present. Packing is used where there is a lower liquid rate.

Reflux Condensers
There many different types of reflux condensers and depending on the diameter of your column and type of Reflux still you are running will determine the type and location of the condenser. Usually the condenser is located at the top of the column directly above the fractionating portion of the still or at the top of the column but offset. A lot depends on if you are running an LM (liquid management), VM (Vapor Management), or a CM (Cooling Management) system.

The reflux condensers purpose on a Compound Still is to condense the vapors so that the heavier liquid drops back into the packing. As the liquid drops down and the vapors rise up the column the heat evaporates the liquid, this process is what separates the ethanol and layers it in the column with the lighter vapors at the top. We call the process equilibrium. Thus the lighter heads are formed at the top and depending on the rate of takeoff will determine how well you separate the heads, hearts, and tails during collection.

Types of Reflux Condensers:
Dephlagmater copy.jpg

double wound coil2 copy.jpg
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coldfinger copy.jpg

crossflow2.jpg


Links to building Reflux condensers:
Double wound coil
Coldfinger
Bushman's CM Build
Crossflow Condenser

After the reflux condensers we should talk about valves. Several different types of valves are used depending on the type of still. We have needle valves used in an LM still and we have ball valves or gate valves used primarily for VM and CM stills. The valves are used for managing vapor take-off, liquid take-off, or controlling the amount of coolant to the various condensers. This is as far as I am going to take this discussion as you should find an appropriate link on the one you choose and its location by linking to the build design of your choice.

The last topic of discussion is product condensers. The product condenser in the reflux still is the final stage of condensing the vapor to liquid for collection. The following are a few images of different type product condensers:
liebig copy.jpg

Shotgun copy.jpg

Graham copy.jpg

worm copy.jpg


Links to Product condenser builds:
Liebig
Shotgun condenser

Links to different still builds:
Bokakob
Flute
Rad's Small scale Combo
Manu de Hanoi's VM
Dan's Flute build

Additional helpful build and design links:
Diagram & Plan Thread
Electric conversion
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Re: stills

Postby Bushman » Mon Mar 17, 2014 11:52 am

This post is both in the column and condenser area as it covers both subjects along with different packing and plate designs. As stated the definitions have been interpreted differently through out the internet and the fractional still definition that I give is different than our parent site however at least in my mind it makes more sense!
I hope by putting this together with build links it will clear things up for others and make things easier and if any of you have good links to builds that would help others please PM me with the link and I will try to add it in the appropriate place.
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Re: stills

Postby Shine NOLA » Sat Nov 22, 2014 8:49 pm

Great tutorial
beautiful work
Thanks Bushman
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Re: stills

Postby Rastus » Mon Dec 15, 2014 12:22 pm

Bushman, today is the first time i saw this thread!

awesome work i havent seen graphics since Samohon i am guessing it is an CAD program.
I have tried sketchup that google had for free but that is gone and done.

thanks for your efforts consolidating the info, that is what has really been needed...

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Re: stills

Postby Bing-Bot » Mon Dec 15, 2014 12:54 pm

Great post.
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Re: stills

Postby Da Yooper » Mon Dec 15, 2014 7:20 pm

Very nice write up, helpful to all that reads it. Thanks
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Re: stills

Postby jackfiasco » Fri Jan 16, 2015 12:21 pm

Wow, I just finished reading through all 68 pages of the Flute Talk thread (only took me... 6 hours?) - because that's what everyone on this forum tells you to do when you have a question about flutes, and they say "the answers are in there, just keep reading". Well guess what? The answers are NOT in there. I mean, I definitely learned some stuff, and saw a lot of pretty pictures, but mainly I had to figure out what stuff meant on my own based on context. And then of course there were plenty of pages of bickering to wade through. Then I find this post with all the info I was looking for in one spot, quick, concise, and free from pissing contests.. THANK YOU!!!
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Re: stills

Postby Bushman » Sat Jan 17, 2015 6:52 am

I haven't visited the thread for a while thanks for the compliments. The CAD program I am using is one given to me as I did the teacher training for our state while I was still working. It is called Rhinoceros but I did not add the material to make it look more realistic like Samohon's graphics. I really like the software as it works on NURBS (Non Uniform Rational B Spline) which means it is a modelling software that allows you to be exact in measurements or you can model by stretching points for ergonomic design. It also allows me to model in 3D and then do a roll-out to scale for cut patterns, calculates volumn, area, etc. Does just about everything but add the tabs. It is very useful in our design applications.
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Re: stills

Postby HookLine » Sat Jan 17, 2015 8:39 am

Nice work. :)
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Re: stills

Postby Grappa-Gringo » Wed Oct 07, 2015 4:49 pm

So, this is a question I should know the answer to, but I'm gonna ask... should the inside of the liebeg be close in size to the outer tube... example: I've got a piece of 2 inch outer tube and option of having a 1 inch inner tube or 1 1/2 inch inner tube.... what is the consensus ??
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Re: stills

Postby rad14701 » Wed Oct 07, 2015 4:57 pm

Grappa-Gringo wrote:So, this is a question I should know the answer to, but I'm gonna ask... should the inside of the liebeg be close in size to the outer tube... example: I've got a piece of 2 inch outer tube and option of having a 1 inch inner tube or 1 1/2 inch inner tube.... what is the consensus ??

The water gap should be a small as possible to reduce the water weight... You don't gain any real cooling efficiency by having more water in there because what water is in there will be closer to the heat... Coolant flows really aren't any different either...
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Re: stills

Postby DAD300 » Wed Oct 07, 2015 8:00 pm

But if the inner tube is too short or too large, vapor can fall right through it without contacting the inner surface.
A 1-1/2" tube in a 2" water jacket would be a disaster.
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Re: stills

Postby Grappa-Gringo » Thu Oct 08, 2015 3:58 am

so, what would be the optimal size ratio...I've got 3/4 inch I can use as an inner tube... or up grade to a larger diameter, but correct me if I'm wrong, you're saying
a smaller diameter inner tube is better.... What size jacket would you use with a 3/4 inch...? I could probably find some 1 inch as a jacket... let me know what you think...
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Re: stills

Postby Bushman » Thu Oct 08, 2015 6:07 am

Most liebigs on the forum have a 3/4" outer with 1/2" inner tubing. What Dad is referring to is the overall length of the liebig I think but not sure after re-reading.
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Re: stills

Postby skow69 » Thu Oct 08, 2015 8:25 am

G-G, DAD refers to two separate and unrelated problems.

1. The condenser is too short.

2. The vapor tube diameter is too large. The vapor needs to touch a cold surface to condense. A larger diameter tube has more unobstructed area in the cross section for the vapor to sneak through. So yes, a smaller diameter is preferred, down to 1/2 inch. Smaller than that can lead to problems of choking or clogging. A large cross section can be overcome by crimping the tube or inserting something like a twisted ribbon of copper. These measures are usually associated with creating turbulence, but the real advantage is to force vapor contact with a cold surface.

The size of the water jacket won't effect efficiency, so it is best to keep it as small as possible to save weight.
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Re: stills

Postby still_stirrin » Thu Oct 08, 2015 8:46 am

Grappa-Gringo wrote:So, this is a question I should know the answer to, but I'm gonna ask... should the inside of the liebeg be close in size to the outer tube... example: I've got a piece of 2 inch outer tube and option of having a 1 inch inner tube or 1 1/2 inch inner tube.... what is the consensus ??

The key to efficient heat transfer is surface area for conduction of the heat out of the vapor and dwell time (also known as vapor velocity), that is, the time the vapor lollygags inside the condenser.

A large diameter such as 1-1/2" ID sufficiently slows the vapor (or allows more vapor mass to flow with a higher heat input). But the efficiency suffers because you don't proportionally increase the conduction surface area. A solution for this would be to fill the center (vapor) tube with loosely packed scrubbies. Or add vanes inside the tube as with a piece of flattened and twisted copper. Either provide more surface for the vapor to condense on.

Another solution would be to use 3 separate 1/2" tubes as in a shotgun condenser. It has much more surface area for the vapor flow, yet provides a slower velocity than a single 1/2" tube. Shotguns ar more challenging to build, but much more efficient for a given condenser length.

If you've got the large diameter copper already and want to use it, I'd opt for stuffing the vapor tube with scrubbies.
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Re: stills

Postby Kegg_jam » Thu Oct 08, 2015 1:28 pm

Ok, I'm just gonna put this out there. The calc on the parent site says for a 1/2" jacketed condenser to knock down 2k watts it needs to be 48" long.

For a 1.5" it only needs to be 17" long.

I've got a 1.5" over 1.25" jacketed condenser that is 18" that is for a concentric pot still. It works fine for that or in a traditional Liebig configuration. I do stuff some loose scrubbers in the first 3 or 4 inches.

In hindsight I wish it was a little longer like 25" or so. It can't keep up with my 4500w heating element.
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Re: stills

Postby skow69 » Thu Oct 08, 2015 2:06 pm

Be aware that a liebig full of scrubbies will trap product and may contribute to smearing. If you go that way I would flush the hell out of it after a run, preferably with boiling water, just like the column packing.

I tend to discount the effect of vapor speed in a product condenser because the vapor is being condensed to liquid with an effective speed of zero.

I am a big fan of the crimped path liebig. Mine is 18 inches long and has 6 crimps, each turned 90 degrees to the previous to eliminate laminar flow. Crimped with a C-clamp, counting the turns for consistency. The cross section at a crimp is 1/8 X 9/16. The boiler is powered by 2625 watts of immersed elements. The condenser knocks it all down using just a trickle of city water run to waste. I like that it doesn't get in the way, doesn't need any accessories or special angles, and weighs almost nothing.
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Re: stills

Postby skow69 » Thu Oct 08, 2015 2:42 pm

Keg-Jam, some calculators are better than others. There are a lot of parameters that need to be accounted for in condenser design. That one probably puts a lot of stock in surface area.
The 1/2 X 48 unit has 75 sq.in. of SA. The 1.5 X 17 has 80. If you spec'ed 12 inch diameter it would probably calculate a length of 2 inches. It has to make some assumptions about things like coolant temperature and flow rate to arrive at a power rating. It prolly doesn't consider the possibility of vapor shooting straight down the center, either. And that's all fine as long as you stick to the norm. But the farther away from bog standard you get, the less useful the calculator will be.
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