is something wrong

[brewhead]

Hi guru's,
I am seeking some feedback or at least assurance that I am not doing anything wrong. I have built a Bokakob mini and it produces 95-96% which is great at arounf 500ml/hr. I seem to however be experiencing 3 problems or at least to my novice experience.

1. I have significant pressure build up leading up to the boiling temp of the mash. I have the Bokakob sitting on a CUB keg with a cork gasket which cannot keep the pressure in. The outlet also pours out huge amounts of steam and get hot to the point I cannot touch the copper. Once I get to the right temp everything stabilises, no more steam nor excessive pressure on the cork gasket (which tends to leak due to the pressure). Is this normal or is something wrong?

2. I seem to get around 2.7L out of a wash with 8kg of dexstrose (alcotec yeast) at 95-96% Is this a good amount or is it a bit low? My perception is that I loose some during the initial pressure build up which creates a leak in the cork gasket.

3. Once everything stabilises the temp hardly moves until nearing the end of the run(normal). I do however get to a point that nothing comes out (i.e. no tails) unless I turn the temp up. It literally stops. From what I have read I should be experiencing tails without a temp increase. It is also interesting to note that once I stabilse things I can turn the heat (gas) up or down slightly without any change to the column temp. Have I missed something or is this a good thing

Any feedback is much appreacited.

happy brewing and thanks

[rad14701]

brewhead, it sounds like you need to do some fine tuning of your still... You should NEVER have vapor escaping from your boiler... And there should NEVER be vapor coming out your take off point... The boiler should not be generating pressure... It sounds like you either don't have whatever cover you are using fastened down properly or you need to use some flour paste along with the cork, which should be music grade cork rather than composition cork... You just don't know what type of binder the manufacturer used to hold the cork granules together... Another possibility is that your column is packed too tightly... You should be able to breathe freely through the packed column when properly packed... "Packed" is actually a relative term... The column just needs to be uniformilly filled with structured material...

As far as the run is concerned, if you are using enough heat input you should be getting tails... A Bokakob reflux column should not be hitting an auto-shutdown wall... This could also be caused by the column being too densely packed...

Your take off rate sounds about right for a Bokakob mini... The amount you are collecting is dependent on the amount of wash you have in the boiler... You didn't mention what size wash you had, just the amount of sugar used... As an example, 8kg of sugar in a 25 liter wash will have a potential yield of ~18.8% ABV, which is high even for the best turbo yeast... That wash would have ~4.7 liters of ~95% ethanol in it before making proper cuts... And with a high gravity turbo wash you should only expect about 1/3 of that to be drinkable hearts... If you could get 1/2 I'd be very surprised... So, you're either missing making proper cuts or you are losing precious ethanol... Even considering how you didn't get any tails you numbers are still off...

Do some more research now that you are where you need to be, here in the HD forums, fix the leak problem, and consider getting away from the turbo washes... You can do much better for a lot less expense and overall aggravation... I'll state it again, the two worst traits to avoid in this hobby are greed and impatience...

I hope I covered everything...
Good luck, and welcome to the HD forums...

[kiwistiller]

I can't figure out why steam would gush out the output... you do have a valve there, right? You still isn't capped, is it? There is a vent in the top? Why don't you take some detailed pics, and post them. That will help us help you.
pics that will help - pic of the whole head; pic of takeoff, pic looking up bottom of column, whole rig set up like you run it. Don't run it til we sort this out though, not with vapour spewing everywhere and running on gas.

It is also interesting to note that once I stabilse things I can turn the heat (gas) up or down slightly without any change to the column temp. Have I missed something or is this a good thing

No, that is normal. You'd have to push fairly hard to decrease the efficency of the rig to raise the temp enough to show. what does your thermo measure to? 0.1 degrees?

[brewhead]

guys thank so much for your ideas and insight. A few of things stand out.
I should not get pressure build up. Interestingly this only happens for around 15-20 mins just before everything stabilises. At that point it stops for the duration of the run. I had put it down to the methonol at the start but obviously not the case. Basically just before I get anything out it starts steaming. I take out around 200ml (metho) at which point it stops. I have a slight leak (which need my friend to fix). This also leaks until things stabilise and then stops. I will redo my packing but since I got pressure in the column as well I had not put it down to that. Just got some mile hi copper which I will use to replace the pot scrubbers.
I am obviously not putting enough heat which might be why I do not get tails. Again after this auto-cutoff I can turn it up then tails come through.
I have 21 ltrs of wash when I get the 2.7 ltr out. I measure every 500ml I take out which is 95-96% at room temp.

I do however have a cap on the top with no vent . Wont a hole in the top basically make me loose huge amount of the good stuff???

I will take some pics as it might point out something I have failed to explain or highlight.

once again thank you
brewhead

[Ayay]

Wont a hole in the top basically make me loose huge amount of the good stuff???

There must be a hole on top to prevent pressure. The vapors do not rush up the column like smoke up a chimney. They prefer to stay in the boiler but are pushed up when more vapors fill up the space in the boiler. When the vapors being pushed up reach the condenser they are very eager to condense and none will go past the condenser unless something is wrong. If any vapors are coming out the hole above the condenser then something is wrong and needs immediate fixing...either the condenser is not working or there is too much heat for the condenser to handle.

When I say the vapors are pushed up I mean they do not exert much pressure in the boiler, just the weight of floaty vapors, only a gram or two. If there is a leak lower down then the vapors will prefer to go out the leak.

Basic rule: no leaks, and no pressure (must have a vent hole).

If there is no hole on top and the needle valve is closed, and more and more vapors are trying to go somewhere, and they are trying to push out the air in the boiler, then the vapors will not push the air out of the boiler and column. The air will stay on top, and more and more vapors will be fill up the bottom space, and you are looking at a bomb. Nothing will happen except maybe a BIG BOOM! You may have escaped the BIG BOOM because of the leaks.

[kiwistiller]

Also, as you've found out, if the condenser isn't vented, then the air filling the column at the start can't escape, and you get a pressure situation like you've had. You've had a very lucky miss - glad you're ok and haven't blowen yourself up, but I think you need to slow right down and understand what you're doing.

Learn safe stilling, then practice safe stilling.

[brewhead]

Kaboom. I think the cork gasket would have blown first but none the less need to make some serious changes. I will implement all the suggestions and let you know how my next run goes.
Great to have a place where people are willing to contribute and help out.
thanks again peeps

cheers
brewhead

[olddog]

I do however have a cap on the top with no vent

This is the reason your cork gasket leaks, your building up pressure, and it's blowing the gasket.



OD

[ScottishBoy]

My friend, you dodged a rather large, steam propelled bullet...You may want to do a bit more reading on the basics of a still. It may save you some trouble down the road.

[WalkingWolf]

Can't help but feel a cold shudder down my spine for what could have happened. We thank the almighty you're alright and we've all been given another reminder that this aint solitaire where playing here.

[brewhead]

did a run with a vent hole at the top and changes to the packing (reduced it) and introduced the copper packing (mile hi stuff). There was no pressure build up at all and none came out the top. . I did however have to slow down the take off rate to around 400ml/hour. Not a problem however long time to finish run. Without the slow down it was at around 92-93%. I have put this down to insufficient packing as previously I had more and using a more dense stainless scrubber. in both cases I could easily breathre through the take off.
I also kept the temp up and did get the tails comes through. thanks for the input and assistance. I just need to find the balance for the packing which I hope will help with the flow and get to .5l/hr.

cheers

[kiwistiller]

what forced you to slow down?

[brewhead]

was trying to improve quality by having more reflux. once I slowed it I got an improvement however didnt crack 95.

[C. Morrison]

I am a novice distiller, but I do have a lot of experience with steam/hot water heating systems.The original poster was very fortunate to have not damaged himself or his property.
Not only the danger of flammable vapors building unwanted pressures,the lack a vent in the top of the column is like an old cast iron steam heating radiator with an inoperative automatic vent. The radiator never gets hot, as the "dry" air convects almost no heat. In the column, the "dry" air trapped at the top prevented the moist steam vapor from reaching the condenser coil. The only cooling was the cold temps going down the outside wall of the column.
Be sure to monitor the water temps coming out of the cooling coil, I run mine very warm, almost hot to the touch. This lets the temps go high at the plates and helps with ABV levels.
Read much, much more before proceeding, every question I had was answered in the library of knowledge compiled here.
Be safe.

Morrison

[Braz]

Just as a data point, I consider 400ml/hr the target takeoff rate for my 2" Bok still. At that rate I am pulling product off at 96% throughout the run and the cuts are sharp. Downside of course is that a spirit run is pretty much an all-day endeavor.