How big is big enough for a pot stripping column

by **Bootross** » Mon Mar 17, 2014 9:50 pm

Hi stillers, this thread started as an offshoot to the thread on converting a plated column to a continuous stripper.
A bit of a debate started over the output rates of different pot still diameters and whether a larger pot still will strip faster and at what size the input power becomes the limiting factor instead of the column diameter.

What we are trying to learn with this thread is how big does your pot still need to be to take full advantage of your input power without causing a restriction.
I'm hoping that together we can figure out how to get the most out of what we've got and avoid unnecessary cost and work involved in upgrading still size, when the return is not justified

I'm hoping that members can give their experiences on upgrading their column/condenser diameters without upgrading their heat source and what effect it had on output rate/run time.
Ideally there will be comparisons using the same wash, same input energy, with the only difference being column diameter or condenser.

So please post your experiences so that we can see the big picture. :handgestures-thumbupleft:
It would be handy if you could post your input power, wash type including abv, column diameter, condenser design (size and quantity of vapour tubes) and output rate/run time. :-B

by **bang300** » Wed Mar 19, 2014 7:27 am

There is a design BALANCE between the desired output, the boiler, vapor speed and the condenser.

Start with output...12 liters an hour, a boiler with enough power to vaporize 12 liters an hour and a condenser capable of condensing 12 liters an hour.

Boiler holds 200 liters, needs 5,000watts to make 12 liters an hour, 2" or larger takeoff, requires 2" x 20" shotgun...and a water flow of two liter a minute. Feel free to balance water flow for more/less condenser.

If you are talking about the boiler output pipe dia...vapor speed becomes a question. The still design above will function well as long as the vapor speed off the boiler doesn't exceed what the condenser can manage. If the pipe to the condenser is undersized, some vapor will make it through the condenser without condensing and the condenser must be larger.

My experience is this...most often we are limited by the Product Condenser, not the boiler! Build the biggest, baddest PC you can and you will use it forever.

by **Andy** » Wed Mar 19, 2014 12:18 pm

Bootross wrote:I'm hoping that members can give their experiences on upgrading their column/condenser diameters without upgrading their heat source and what effect it had on output rate/run time.
Ideally there will be comparisons using the same wash, same input energy, with the only difference being column diameter or condenser.

im not too sure what you mean. if the heat source is the same there would be no change- apart from such a small decrease in the already small amount of internal reflux, making the run slights quicker, we are talking a few minutes.

its like saying if I make the spout on a kettle bigger will it boil faster or slower

by **P3T3rPan** » Wed Mar 19, 2014 5:56 pm

Nice analogy Andy

by **Bootross** » Thu Mar 20, 2014 7:59 am

There is some more information in this thread viewtopic.php?f=36&t=5642

Andy wrote: if the heat source is the same there would be no change- apart from such a small decrease in the already small amount of internal reflux, making the run slights quicker, we are talking a few minutes.

This is what I believe too, (until you get down to really small diameters). But the reason I ask is that I was informed by some experienced members that upgrading from a 2" pot still to a larger still would allow you to increase output speed.
There is no question that if you pumped enough power into a boiler, that eventually the column diameter (or more likely the condenser tube diameter/s) would become a restriction. This would reduce the output speed, and also put back-pressure on the boiler.

What I'm trying to figure out from the real-world experience of this community, is that at what amount of power input does a 2" column (or the condenser tubes) become the limiting factor so that an upgrade is warranted.

I think the most reliable way of gathering this information is to try to find members that have upsized their pot stills and gather information on what upsizing they did and what affect it had on output rates.

In the thread listed at the top of this post, Brendan mentioned that his 3" pot and 4" pot have exactly the same output rate with the same 4800W power input on a stripping run.
So for 4800w it seems that the point at which the column becomes the limiting factor is less than 3" (although information on the condensers he used would be valuable too.)

by **Sam.** » Thu Mar 20, 2014 8:29 am

When I talk about upping the diameter I am also talking that I am running on gas and can throw as much heat at it as I like ;-)

Unable to calculate it but my burner and reg combo would put 4800W to shame I would say :D

Having a larger diameter column lets me strip much faster, if limited to a single element there may not be a need, then again bigger is always better :handgestures-thumbupleft:

by **Bootross** » Thu Mar 20, 2014 9:00 am

It is difficult to compare gas to electric, perhaps we could compare boil up times for a given wash. Half the boil up time = double the power :think:

I'm not sure what burner you've got, but hose BD747 burners are certainly impressive. Talk about heat. I've only ever seen photos, in person it reckon they would be downright scary. :scared-eek:

There's no doubt that a big fat pot looks more impressive, but someone on a limited budget could certainly benefit from knowing that he could add another element, and take full advantage of it without upgrading his still head or boiler port. It would allow him to understand where he can get the best return from his dollar, and maybe invest the cash he would have spent on fatter pot on even more power or upgrade his circuits etc. :handgestures-thumbupleft:

by **Andy** » Thu Mar 20, 2014 12:36 pm

Bootross wrote:In the thread listed at the top of this post, Brendan mentioned that his 3" pot and 4" pot have exactly the same output rate with the same 4800W power input on a stripping run.
So for 4800w it seems that the point at which the column becomes the limiting factor is less than 3" (although information on the condensers he used would be valuable too.)

the condensers would have to be able to deal with the vapour. so i would say a 2 inch diameter with a 3 or 4 inch shotgun could handle as much heat as a 4 inch with the same condenser- up until pressure starts to be affected, which would be after a ridiculous amount of heat is supplied. the amount of vapour that would need to be flowing would be insanely high.

and lets not forget that the difference between 3 inch and 4 inch isnt 1 inch or 1/3rd larger, but about ~70% larger. which is a pretty big difference to not see a change.

by **Andy** » Thu Mar 20, 2014 12:57 pm

I was thinking, I know a pipeline engineer haha, so next time I see him I will see if he can do any calcs to see how much vapour can flow through a 2 inch pipe before chocked flow occurs.

by **bluc** » Sun Dec 20, 2015 6:43 pm

Anything ever come of this wondering how much a 2" can handle also and how it compares to 4" at 4800w...

by **scythe** » Mon Dec 21, 2015 5:03 am

I always thought that:
Increasing power input just decreases heat up times, most switch off their 2nd element once they have a nice rolling boil happening.
Although for stripping your not too worried about ABV most of the time.

Column diameter increases are most important for reflux type stills.
Because its not just shooting out the end of the still its going up the column while some of it is coming back down and their needs to be room for the two directions of flow to pass each other without restriction, or you end up with a flooded column.
Essentually larger diameters mean higher ABV is possible at higher flow rates.

I guess the more pertinant question that needs to be asked regarding pots is what can your PC handle.
A 2ft liebig will only handle so much, a 2ft 4 tube shotgun should handle atleast twice as much given the same vapour tube dimensions.
If all the other factors stay the same increasing pc capacity will get you faster output rates

by **bluc** » Mon Dec 21, 2015 1:08 pm

I agree watts and pc are limiting but what about still diameter if you have a pc that can knock down everything on a 2" pot attached to a keg with 4800w of electrical elements, is there going to be a jump going to 4" for the pipe between keg and condenser or does 2" handle everything 4800w has to offer?

by **rumdidlydum** » Mon Dec 21, 2015 1:29 pm

No idea untill you build both but
If you take a breth and blow through a straw air flows but there is restriction.
Then if you blow into a vacuum cleaner pipe there is alot less restriction.
:laughing-rolling:
At the end of the day its your money and your choice. :D

by **bluc** » Mon Dec 21, 2015 3:07 pm

Agree but is a 4800w keg boiler blowing more air than a 2" pipe can handle...

by **P3T3rPan** » Mon Dec 21, 2015 3:31 pm

I have 5Kw going through a 50mm keg opening into 100mm stripper no problems
All down to what your pc can handle

by **WTDist** » Mon Dec 21, 2015 5:04 pm

Diameter in reflux and plated column matter because the bigger you go the more volume it can hold. volume on a 4" column is 400% bigger than a 2" making the reboiling liquid volume bigger which can increase the take off rate

by **warramungas** » Mon Dec 21, 2015 5:49 pm

I think you're getting hung up abit on this problem. If you run 5000 watts through the 2" pipe the vapour will travel through said pipe at x speed. If you chuck 10000 watts on the same pipe the speed will roughly double. 20000, double again.
I seriously doubt you will find the point where the pressure starts to dangerously rise in our hobby stills in pot still mode so long as no restrictions are placed inline.
We use two inch pipe to deliver some serious volumes of air around at work. Much more than a hobby boiler could ever deliver.
However, I believe if you tried you could blow up a reflux or plate still if you tried hard enough but not a pot still unless it was restricted in some way or you had some really incredible amounts of horsepower behind it.
It all comes down to your PC and what it can handle.