Coil Condenser Problem – Vapour Huffing / Not Knocking Down

[Nays_Shine]

Hi folks,

I am having ongoing condenser problems where I am experiencing vapour huffing and cannot seem to find a solution. I am hoping someone may be able to help me out with some advice. I spent last year building my boka and this year have been refining it and learning how to operate it.

Since finishing my build I have performed 18 stripping runs (charge: 35l x 8% abv birdwatchers) and 5 spirit / reflux runs (charge: 45l x 40% abv). I have experienced mixed performance from my condenser and am finding that more often than not, it fails to knock back all of the vapour, even when I set the power to a very low setting (800-1000w). Basically, when I put the mirror and tourch up to my vent hole at the top of the column, I can see see medium to light vapour huffing.

These are the things I have played around with so far:
- reducing boiler power
- reducing coolant input temperature and increasing flow
- using mains supplied water from the tap
- reducing the vapour speed (by experimenting with various packing and wrapping of the coil with un-rolled copper scrubbers)

My most successful results have come from packing three quarters of the inside coil with copper, then wrapping copper scrubbers between and around the outside coils. Using this approach I have been able to compete stripping runs of low wines, using both elements (4400w total); while using my recirculated coolant (reservoir temp holds at about 50oC / 122oF).

Unfortunately I have not been able to replicate my results and every time I fire up the still, I have to play around for an hour with various wrapping / packing approaches before I can get the condenser to work at the desired power. Sometimes no matter what I try, nothing seems to work.

Ideally I want to minimise the amount of copper scrubbers used on the condenser and to be able to run the still at full power for stripping of low wines.

Can I fix this issue using my current condenser or do I have to build / buy a new one?


Still Facts

CONDENSER HEAD

20cm long - 3/8” double coil condenser; inside a 3" head
I have experimented with various packing and wrapping of the coil with un-rolled copper scrubbers
There are general gaps of around 1/4" - 1/8" between the coils
The coil does have some imperfections and minor crimping where flattened out parts have been squeezed back to shape during the building process

COOLING
150l reservoir
550w submersible pump with variable return valve (maximum operating flow of 5-6 litres p/minute when connected)
Evaporative cooling tower – this is not very effective and only takes between 5 - 10oC / off condenser outflow temp, dependent on flow rate.

BOILER
2x 2200w electric elements. One of which has variable power.
(No insulation as of yet)

CHARGE
Birdwatchers sugar wash
35l x 8% abv - stripping runs
45l x 40% abv – spirit runs

COLUMN
1.5m x 2" packed column
(No insulation as of yet)


Thanks people!

(Photos to come soon)

[Nays_Shine]

Here are some pics of my approach to slowing vapour speed in the condenser head...

[Nays_Shine]

...continued

[Nays_Shine]

...final pics. Let me know if you need more info! Thanks so much for any advice!

[TheMechwarrior]

Just some comments:

Firstly, I never used any packing around my condenser.
My condenser was 3m of 1/4" and it made around 250mm of double helix condenser.
I only ran 2400W and found you only needed 150mm of the condenser to knock down all that vapour.
My rig was a Vapour Management 2" still.
You are throwing way too much power at a 2" rig, 4400W is what you throw at a 4" rig during a stripping run.
I was running a 550W pump from a 1000L IBC.

What are your condenser inlet and outlet water temps?

Cheers,

Mech.

[Nays_Shine]

Hi Mech,

Thanks for helping. I have a few little issues with my set up but this is the one that is really holding me back right now; so I really appreciate any advice you or the other members can offer.

I will be doing another run soon and will record my input temp, output temp and flow rate then.

In the meantime, I did boil off some water through the still tonight and have recorded a few figures from that. Hopefully this gives you what you need. The reservoir temps were much lower than usual as I didnt run it for very long. I think normally my reservoir sits at 50oC once I am into a run.

Heat Exchange and Pump Flow Rates (Boiling water using 2200w):

Max flow (fully open, return line closed): 5l p/minute
Heat exchange: 5.0oC (in temp 16.8oC, out temp 21.8oC)

Min flow (open a crack, return line fully open): 1.075l p/minute
Heat exchange: 21.4oC (in temp 16.8oC, out temp 38.2oC)

A lot of steam was escaping (I am aware that it is harder for the condenser to knock back steam). I did not use packing in the column or around condenser either.

Thanks again Mech (and my other AD compadres)!

Nay.

[Pete8686]

Im no expert but it seems to me the 150l cooling tank would heat up rather quickly. If your cooling water is too warm it will drastically reduce the cooling effiency. Try mains water for a run and see how you go

[TheMechwarrior]

Im no expert but it seems to me the 150l cooling tank would heat up rather quickly. If your cooling water is too warm it will drastically reduce the cooling effiency. Try mains water for a run and see how you go

It will heat up pretty quick and hopefully he'll see that just as soon as he starts recording/checking cooling water temps.
He'll find he needs a minimum of 2 x 200L drums but ideally a 1,000L IBC. If that is not an option then as you pointed out direct mains water is the only option.

[hillzabilly]

Firstly your top condencer section join is very dangerouse considering the height of it,and the boiler ?dog?,the hood that you made could be like viewtopic.php?f=29&t=8194&p=142163&hilit=glass+boka#p142163 would in my opinion work better and reduce huffing ,plus 2-3 more vent holes in the top cap , :text-+1: to easeing up on the power.cheers hillzabilly ;-)

[Nays_Shine]

I have just done another spirit run and my condenser held up well (using 2200w), even right down to the end of tails. Other than use copper mesh around the coil in a slightly different configuration, I am not sure what else I did differently to previous runs where the condenser failed while using the same power input and cooling system.

My evaporative cooling tower seems to hold the reservoir at around 40-42oC with the output from the condenser sitting at 50-52oC. Even over long runs of 15+ hours. I believe the reason the reservoir holds at this temperature and not lower is due to the inadequacy of my cooling tower induction fan. When water enters the cooling tower at lower temperatures, the fan can only create enough updraft to drop the temperature 3-5 degrees. After the water increases to 40 or so degrees, the extra heat creates a strong natural updraft which creates a sufficient evaporation rate required to cool the water to a stable and consistent temperature (by taking 10oC off the outputted coolant water). I am losing about 1l p/hour to evaporation. Regrettably, I do not have the space (or floor structural integrity!) to keep a 1000l reservoir; which would be the simplest, cheapest, most effective option for recirculated cooling.

Even though the condenser worked well this time, I am going to keep this thread active as I am having inconsistent results and ideally, I do not want to have to use any copper packing around my condenser, which I have found to be necessary even when I am condensing using water directly from the town mains water tap. So, moving forward and given that I have already experimented with a few ideas as per in my initial post, here is the direction I think I need move in order to find a solution. I would really like to hear what you have to say:


To start with, although I cannot explain it; and while not a solution on its own; I would assume that lowering the coolant temperature will usually help with any condenser performance issue. Now that we have the obvious solution out of the way (I will talk about flow rates and reduced power shortly), let’s move on!

I think it really comes down to this key question:

“Am I achieving maximum heat transfer potential / extracting the expected heat energy out through the coil given my coolant flow rates and power input?”

If the answer to this key question is NO, then I probably need to address these issues to achieve the coils maximum heat transfer potential:
- Vapour passing over the coil too quickly (I have already tried to address this through packing and wrapping the coil with copper - not an ideal solution).
- Spacing between coils and the condenser head wall might be too widely spaced (or perhaps even to tight?), resulting in vapour not making contact with the coil
- Issues with reduced thermal conductivity due to dirty or badly oxidized inner wall of condenser coil
- Issues with reduced thermal conductivity due to turbulence / air pockets as a result of kinks in the coil

If the answer to this key question is YES, then I probably need to reduce the amount of heat going into the condenser head by:
- Lowering vapour temperature (I am already more or less achieving azeotropic point so not sure how this is going to help my spirit runs)
- Reducing power (not a preferred option!)
- Reduce the amount of heat energy passing up through the column walls into the walls of the condenser head (is this correct physics?) (possibly isolating the column, condenser head and the coil from one another)
- Enable excess heat (but not vapour) to escape through the top of the column by adding extra vent holes (as suggested)?

Or, increase my capacity to remove more heat by:
- Is this where using colder coolant water would sit? Again, I am not sure how this would be the case as I would assume cooler input water just means cooler output water. Does water become less efficient at cooling as it warms up? If so, is there a threshold that you should sit below? Please explain if I am incorrect.
- Bigger coil
- Add a cold finger
- Replace 3/8 coil with a jacket condenser and 1/4 coil (I‘ll upload a sketch of this if required)
- Increased water flow ( I can already achieve 5l p/minute which hasn’t always proved to solve my problem)

This is all I have got on the matter! I would live if someone can tell me if they think my condenser is achieving its maximum heat exchange potential based on my input temp, output temp, flow rate and power input figures (my still is not insulated and I have a 1m x 25mm x 9.5mm leiburg condenser using the same coolant line which takes flow before the main coil); and if you can elaborate on the physics surrounding ideal coolant water temperature.

Thanks again people!



Nay.

[hillzabilly]

The vapour will take the path of least resistance ,wich may in your case be straight up the middle of the coil to the vent hole,have a look at this one,?dog?boiler?.cheers hillzabilly :D

[Muppet]

I've read about this a few times and experience it on my pot leiberg. On my pot I just slow the water down and feel the leiberg, around 2/3 warm the huffing stops, I've also read that some put a little ball of mesh up there. I havnt tried the mesh and would think you would need to be careful... Last thing you want is it sealing the output.

[Nays_Shine]

Thanks guys,

Muppet, my hunch is that you would have to really pack the mesh in super tight to make the still pressurize. Vapour seems to find its way out pretty easily!

So Hillzabilly, you think my problem might be that I am not achieving my heat transfer potential through the coil and by reducing the internal volume of the condenser head, there is more chance of vapour coming into contact with the coil?

I think the reason I had the best result with this run was due to the way I packed the mesh so as to influence the path of the vapour. I wanted it to run through the middle of the coil, then be forced outwards as it got to the top. This seemed to work, but yeah, I want to get rid of the mesh ideally as it requires is a lot of mucking around (and I have heard it adds to smearing).

I hadnt seen that Bokabob diagram, must have missed it all those months ago. I have been toying with the idea of adding a cold finger which would reduce condenser head internal volume (in the same way as bokabobs 2" tube would) whilst increasing my capacity to transfer heat. It is something I am contemplating.

Does any maths wiz know if my coil is achieving its maximum potential for heat transfer?

Thanks again, my friends really appreciate it (as they are the main benefactors of my efforts!) :music-deathmetal:

[Pete8686]

I have a 2 inch , a dodgy coil double wound helix with no end cap above and it handles 3 rings on my burner with adequate water flow. I can reduce the flow to a trickle if I have a tiny bit of loose ss scrubber inside the top half of the coil and a loose ring of scrubber around the lower section of the coil. Not sure if that'll help mate just my experience. It can run with all 3 rings of my burner on high

[Nays_Shine]

Thanks Pete,

Sounds like you have an effective condenser.I wanted to go overkill wit mine,, hence constructing it out of 3/8 tube. Now if I can only get it to work!

Can you tell me what the temperatures are of your cooling water going in and coming out; and at what flow rate, when boiling at full power? That way I could get an indication of how much heat energy you are transferring through your coil and compare that with my one.

I am guessing that you have a 1/4 coil? Is it kinked or crimped at all?

Thanks again!

[Pete8686]

Heres a couple pics, as you can see it is not a very well crafted coil. Though it seems to work well, apparently the gaps and unevenness help the vapours swirl. With no ss scrubber around it or in the middle it takes a fast flow to knock down all the vapour. I experimented with scrubber on different locations of the condenser and on my boka this was the most efficient, with about a 3 inch piece of loose scrubber in the top as well, the top half of the condenser is cold as a rock with only a trickle of water even in pot mode with all 3 rings. I use mains but on my next run ill check the outflow temp for ya

[Nays_Shine]

What are your condenser inlet and outlet water temps?

Cheers,

Mech.

Hi Mech (and others),

I believe you are right in asking this question as a troubleshooting first port of call. By knowing this I would say that we could understand if the coil is achieving the expected heat exchange / working to expected potential.

Is there a calculation that you know of that can answer this question? Or rather, is it simply a matter of comparing your input output differentials to others?

This is what I am currently achieving (without packing):

Max flow (fully open, return line closed): 5l p/minute
Heat exchange: 5.0oC (in temp 16.8oC, out temp 21.8oC)

Min flow (open a crack, return line fully open): 1.075l p/minute
Heat exchange: 21.4oC (in temp 16.8oC, out temp 38.2oC)

Is someone able to tell me if this amount of heat being exchanged is about what you would expect?

Thanks!

[Nays_Shine]

So that I could add to the figures from my previous post, I have done some more wash stripping experiments and unlike previous attempts, this time I was not able to get my condenser working well at all.

In order for me to knock back all vapours using 2200w of power, I had to run very cold (11oC) mains water at 2l p/minute. Flow less than this was not sufficient. (The condenser would extract 10oC)
With 2200w of power and cooling the condenser using 5l p/minutes (my maximum flow capability) of (19.8oC) recirculated water, I experienced continuous huffing – even when I dropped the power right back. (The condenser was extracting 5oC)

RESULTS:
Power input - 2200w
Vapour temp 93oC
Coolant source – reservoir
Coolant flow – 5 lpm
Coolant input temp: 19oC
Coolant output temp: 24oC
Huffing? – Yes, lots

Power input - 2200w
Vapour temp 93oC
Coolant source – mains water
Coolant flow – 2 lpm
Coolant input temp: 11oC
Coolant output temp: 21oC
Huffing? – No, but used a lot of water

(I should have pumped the reservoir water through at the same flow rate as the mains water (2lpm) to see if the outputted water increased by the same value using both sources – next time I will)

To me this does not seem as if I am extracting anywhere near the expected heat, which brings me back to my question from my previous post:

Is there a calculation that you know of that can answer this question? Or rather, is it simply a matter of comparing your input output differentials to others?

Hopefully someone can help out with this – I really appreciate it ;-)

Nay

[hillzabilly]

G-day mate,I can't help with calcs,but have a suggestion,lightly pack the area between the condencer coil and collection cup with copper mesh (how big is the gap from coil to the cup?) have you run it without the hood ?and either add a few more breather holes or de-solder the cap and wrap copper packing around the top of the coil and test run without the cap.cheers hillzabilly

[hillzabilly]

And the more I look at the pics of the hood and cup area the more I think that may be the cause of the problem,your 2inch gets reduced a fair bit causeing the vapour to speed up hitting the hood and then slowing down as it enters the 3inch section,the last pics I posted shows a desighn where this is not the case ,if your 2inch came through the 2-3 reducer and had no hood or a 2inch disc mounted 25mm above it may work better,it may be a presumption that the coil is the problem and after building a few myself have found out the hard way ,keep an open mind .cheers hillzabilly ;-)