4” bokabob

Reflux still design and discussion

4” bokabob

Postby Lockyc » Tue Jun 04, 2019 3:44 pm

I am currently in the process of building a two piece 4” slant plate boka bob.

Lower section will be on a 50L boiler with gas to heat and a 2400w controllable element to run.
Lower section will have 1 kg of copper mesh and be roughly 800mm
Upper section will be of slant plate design.

Will have a 4” x 6” dephlag and have a spare 2” product condenser I was going to bolt on top of that
As I fear the dephlag won’t knock down all the vapour. Install some copper mesh in between the condensers

My question is :
Do the measurements etc sound correct or should I modify them?

Cheers
Lockyc
 
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equipment: 2” boka
4” glasser

Re: 4” bokabob

Postby The Stig » Tue Jun 04, 2019 3:50 pm

Your going to need more packing than just 1kg copper mesh.
1kg is only 100mm tall and will slide in as a perfect fit.
What else will you use to fill the 800mm packed section? others use stainless scrubbers, scoria etc.
cheers
Last edited by The Stig on Tue Jun 04, 2019 3:55 pm, edited 1 time in total.
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Re: 4” bokabob

Postby Lockyc » Tue Jun 04, 2019 4:06 pm

Thanks stig
:handgestures-thumbupleft:
I have ceramic rings but am unsure of their exact material so am dubious about using them.
Guess I’ll have to buy some more copper mesh

Can you recommend any material stig?
Do you think I could get away with a 8” dephlag only?

I am building it as I have some 4” tube and the still should do me over until I get a glasser.
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equipment: 2” boka
4” glasser

Re: 4” bokabob

Postby The Stig » Tue Jun 04, 2019 4:13 pm

Lockyc wrote:I’ll have to buy some more copper mesh
Can you recommend any material stig?

More copper would be best but if cost is an issue use 1kg roll and fill the rest with stainless scrubbers.
Im not a builder so cant really comment on the workings but deflags arent normally seen on boka's.
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Re: 4” bokabob

Postby Lockyc » Tue Jun 04, 2019 5:02 pm

Yes I think the holes are too big and allow the vapour to pass if not sufficent.
I’ll await any other suggestions before building.
Thanks stig
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4” glasser

Re: 4” bokabob

Postby RC Al » Tue Jun 04, 2019 7:56 pm

A condenser is a condenser
Each will handle X amount of power based on design efficiency
Boka's usually get a internal coil due to ease of construction
A defleg below the take-off would you to add a gin basket afterwards
A defleg below the take-off would let you run at lower than 1:1 reflux ratio
If you have a good look through the plated column builds, you will frequently see the wish for a shorter, faster to react defleg. Lots of small diameter tubes @100-150mm long is heaps - 8" would be a pig to adjust

The 800mm packed section will only net you around 9-10 theoretical plates, you get 1 for the boiler, meaning that to hit 95%, you will need to add 4-5 plates worth of reflux (15 is the magic number, higher = speed). This will make the still a little on the slow side and you may not have enough electric power to make that much reflux, you may need another element, but luckily you can try the gas first If that scenario happens

Another 4-500+ of packed section will reduce the amount of reflux required - you most likely would be able to poke up to twice the 2400w at it then and have a really decent take off rate
Last edited by RC Al on Tue Jun 04, 2019 8:03 pm, edited 4 times in total.
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Re: 4” bokabob

Postby RC Al » Tue Jun 04, 2019 8:10 pm

Ok ignore the first paragraph, I was off in vm land...
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Re: 4” bokabob

Postby Lockyc » Tue Jun 04, 2019 8:17 pm

Thanks RC AL

So to achieve 95% I should add another 500mm of packing
Would you recommend Coles/Woolys scrubbers as the cheapest option

I had a 2” boka so anything should be an improvement speed wise.
I have a crab cooker burner so should have plenty of heat.

When you say run the dephlag below the take off, is this to achieve full reflux of Vapour until take off is required
If so I would need another rc above the takeoff.

I have 1/2 stainless as the dephlag core, though the tube wall is thick (2.5mm) possibly, I suspect thin copper would be the best for responsiveness though I may not have it.
Any other thoughts RC AL?
Lockyc
 
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equipment: 2” boka
4” glasser

Re: 4” bokabob

Postby Lockyc » Tue Jun 04, 2019 8:34 pm

Ok I see

It’s all a bit of a balancing act isn’t it ?
Matching heat to rc to output

If I turn the heat up too much it may puke/raise vapour speed/overcome the rc but I should get a better take off speed at a higher purity, is this correct.

How do you run your boka? Any tips?

Thanks RC AL
Lockyc
 
Posts: 61
Joined: Sat Apr 14, 2012 2:30 pm
Location: North west Queensland
equipment: 2” boka
4” glasser

Re: 4” bokabob

Postby RC Al » Tue Jun 04, 2019 10:56 pm

Lockyc wrote:If I turn the heat up too much it may puke/raise vapour speed/overcome the rc but I should get a better take off speed at a higher purity, is this correct.

How do you run your boka? Any tips?

It's more the ballacing act, the still will have different sweet spots for different washes
The diameter is whats going to give you the speed, provided the correct amount of power and reflux is used. The fractions have to separate out and slowly be drawn from the column, generally the faster you go the less abv you get and the fractions don't separate as well and you get smearing, a taller column separates better, so can run a bit faster.

Speed isn't everything, it's possible to pull 95% and have flavours come through, this is what would happen with too much power and subsequently too much reflux, upsetting the equilibrium of the fractions with too much movement up and down

I haven't run a boka, I have a small cm and a pot, the column balance theory applies to any reflux still. One tip that I haven't seen mentioned much here is to track the rc's coolant exit temp, just on/above 70c implies that your not overcooling the refluxed product and it thereby requires less energy to revaporise
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Re: 4” bokabob

Postby Lockyc » Wed Jun 05, 2019 6:54 am

The general rule of vapour speed I believe is 12-20 inches

@ 2400w the vapour speed will be 8.74
@4800w the vapour speed will be 17.48 (element I don’t have)

Looks like I will need to convert the burner rings to watts to obtain 4800w until I get a second element.

My question is, should I still stick with a 6” long rc shotgun or upgrade to 8” long to handle the heat.
I will have a flow meter to control the water flow.
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equipment: 2” boka
4” glasser

Re: 4” bokabob

Postby woodduck » Wed Jun 05, 2019 8:43 am

If it's a boka the rc won't need to be adjusted as it will need to knock all.the vapor back into liquid. I think 6" should do it but if your worried go for 8" long. For a comparison, my rc on my 4" bubbler is 75mm long and has 5x 3/4" tubes and can hold 2800w in full reflux. I think you'll need to be careful with throwing too much power at it as it will just flood the colomn, I can't see you needing anymore than 3600w but not 100% sure.

Definitely go longer with the packed sections, it will give you much cleaner product. Don't use cheap stainless scrubbers as they will rust. Bunnings is where I got mine, make sure it reads 100% stainless.

Good luck with the build.
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Re: 4” bokabob

Postby Lockyc » Wed Jun 05, 2019 9:33 am

Thanks Wood duck

I was planning on using the rc as a dephlag in a bubbler build later, so will still need it to be adjustable (responsive) to let vapour pass

So does a 4” x 150mm long dephlag and 2” x 500mm rc bolted above sound good?

I will pack the lower section, run a centering ring between, then pack the upper section up until the lower slant plate
This will give me 1400mm of packed section.

How will I know if the column is flooding with no sightglass? Thermometer temps erratic?

Thanks for all the information guys.
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Posts: 61
Joined: Sat Apr 14, 2012 2:30 pm
Location: North west Queensland
equipment: 2” boka
4” glasser

Re: 4” bokabob

Postby woodduck » Wed Jun 05, 2019 10:02 am

Nah don't like that idea mate. It will be well over 3m tall, a bit top heavy with all that water up there. If your going for a bubbler eventually why not build both condensers and instead of putting one on top of the other why not get rid of the slant plate idea and build a blockhead or throw a 180deg bend in there and run it like a conventional bubbler without the plates? Use your rc for the take off rate and your pc to condence your product?
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Re: 4” bokabob

Postby Lockyc » Wed Jun 05, 2019 3:22 pm

You’re right, it’ll be pretty high.
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equipment: 2” boka
4” glasser

Re: 4” bokabob

Postby The Stig » Wed Jun 05, 2019 4:21 pm

woodduck wrote: why not get rid of the slant plate idea and build a blockhead or throw a 180deg bend in there and run it like a conventional bubbler without the plates? Use your rc for the take off rate and your pc to condence your product?

This is a great idea :handgestures-thumbupleft: :handgestures-thumbupleft: :handgestures-thumbupleft:
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Re: 4” bokabob

Postby Lockyc » Tue Jun 11, 2019 9:30 pm

Ok gents,
Looks like I should go the whole hog instead of half-jobbing it and making the boka.
My 2400w element arrived with controller.

I’ll continue to make the 4” glasser

Thanks for the advice.
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