Crossflow build for my Bok

[Expat]

After much reading and thinking I got around to building the crossflow condenser. Definitely the most complex build i've undertaken to date, so I thought I would share the results and some of the details.

Previously I was using a double wound coil, which was functional but essentially used up every inch of head room available in my work space. My intent is to maximize the amount of height available for packing; also its hard to resist a fun build project

So here is the completed build:

The shell of the condenser is 2", and the total width is 18"; internal setup is 21 flow tubes of 1/4" that are 16" long. To be clear, its designed to be overkill I'd rather have more than I need.

Reading through the forums, one of the biggest build issues noted was the blind weld of the end caps over the tube plate; with this in mind I thought it would make sense to go with a removable cap joined by an EasyFlange. As a side benefit this means that the water path is open an inspection/repair if required.

To be continued...

[Expat]

Some pics of the build components:

Plate and tube assembly in progress

Not shown in any of the pics is the vent, since it was added afterwards I deliberately added a slight slant to the arms of the condenser to ensure that there would be no pooling.

I did a pressure test on the vapour side and there was no leaking whatsoever; Next step will be a cleaning run, and with that its ready to use!

Its not the most artistic build but i've had a lot of fun doing it.

[Tap]

Love it, very well thought out.

Did you use soft and hard solder? I couldn't imagine soldering 21x1/4" within a 2 incher.

[Expat]

Thanks Tap

Truthfully, I'm not 100% what the difference between those would be; everything was done with a silver solder if that helps.

[Soggy Bottom Boy]

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On my first read-through of your post, I missed the part where you said that you added vents later, skimmed right over it. I even made a post that asked where in the H-E-double-hockey-sticks are the vents to atmosphere. (deleted it after I re-read the post again)

You should post up a pic of the vents, too. Just so some n0Ob doesn't build himself an explode-o-still by just looking at the pics.

[MBF]

Man, I love the evolutionary inventiveness of the folks here. I'm planning to use a cross-flow reflux condenser for my LM/VM setup, so I am reading through all the JCF designs I can find.

1) I love the idea of capping the ends with tri-clamp plates.... for repair/inspection access AND for cleaning.

2) I also am intrigued with the idea of pre-building the "v-slant" into the arms to encourage condensate flow.

Let me offer another evolutionary idea:

Core End Plates:

1) Increase the plate thickness to 1/4".
2) Mill a groove in the outer diameter of the plate (flat end-cutter will work, but you could also go the extra step and use a ball-end cutter)
2-1) Optional? round over the inner/outer edges of the plate perimeters. This will minimize potential plate dragging on insertion.
3) Select a PTFE o-ring of sufficient size to fit this groove

Now, with the proper depth of groove and proper o-ring sizing, you have a removable cooling core.

Additionally, making this a removable core will also negate the need to hard solder the cooling tubes into the end plate.

[MBF]

Came up with another REALLY good reason to use the tri-clamp end plates:

Theory dictates that your inlet should come in from the bottom and that your outlet should exit at the top (or use a standpipe or other solution to insure the warm water exits at the top to work with the thermodynamic properties and prevent voids). IF you can remove the end-plates, you can vary the orientation of the inlet/outlet angles.

THUS, your cross-flow condenser can have multiple orientations (horizontal Tee with a 0 degree, 45 degree or 90 degree offset, et al.) You simply clamp the end plates at the desired angle.

Now, this would also necessitate the re-orienting the angle/height of your vent tube. This can be accomplished by simply by putting a sweat-on to threaded fitting on the end of the tube. Then, if you aren't set at the typical 0-degree offset, you can add a 45 or 90 degree threaded fitting with a short piece of tubing in the other end and bent as required to get the vent above the top of the main tube (with a j-bend at the top of course).

Finally, we arrive at a true, modular, multi-orientation, cross-flow condenser that can be used in almost any column design.

[sungazer]

Very nice and a great solution to maximize the still efficiency with the space you have available. I wanted to make a comment on the vent not sure which post to put it in?

I was thinking that the vent to the outside is not just needed for any Vapor to escape to prevent an explosion if the pressure went up. But also when thinking about it if you are taking liquid out of a confined space you have to replace that space with something or a vacuum would occur. We don't want a vacuum occurring we want the space once occupied by liquid to be replaced by air this has to get in somehow? Had the amount of air is going to be equal in volume to the volume of liquid we distill out.

so if you think about it If you are taking off spirits at 2L an hour 2L of Air per hour has to enter the barrel and that air is going to have to enter down the column and from a vent somewhere so don't shut them up too much.

Happy to be corrected if I am wrong about this.

[Expat]

Sungazer - Thanks for the feedback on the build.

Re the atmospheric vent, its an important safety feature. When you heat any material, particularly fluids and gases, they expand. Unlike a pot still LM stills like a BOK have a valve on the take off which would, without a vent, create a sealed vessel. Vapour expanding within a sealed vessel creates pressure which can build up to destructive levels. This could occur if an output valve is in shut or condenser cooling is insufficient. There really hasn't got any bearing on the need for air to equalize the reduction in volume from distillate removed, plenty of air will be able to move through the out take to replace it.

An atmospheric vent ensures that any pressure is released before it becomes a problem. Its a critical build component and must be included.

[sungazer]

I understand exactly what you are saying. But I have read a lot of posts about venting here and design considerations and no one seems to address the issue that the boiler needs to equalize for the reduction in volume from the distillate removed. From what I can see the only path that the air can take is through the vent that most people install or insure they have for the exact opposite function which is the over pressurization from the gasses expanding. I do not have a completely open top on the condenser column but I do have large enough gaps around the coil ends to allow venting either in or out. I think I could nearly measure the flow to some degree I can certainly feel a flow.

Sorry for putting this topic on your truly very nice Build post.

[joeymac]

I understand exactly what you are saying. But I have read a lot of posts about venting here and design considerations and no one seems to address the issue that the boiler needs to equalize for the reduction in volume from the distillate removed. From what I can see the only path that the air can take is through the vent that most people install or insure they have for the exact opposite function which is the over pressurization from the gasses expanding. I do not have a completely open top on the condenser column but I do have large enough gaps around the coil ends to allow venting either in or out. I think I could nearly measure the flow to some degree I can certainly feel a flow.

Sorry for putting this topic on your truly very nice Build post.

You don't need air to come into the boiler to make up for volume lost to distillate removal because newly boiled ethanol vapor will easily take up that volume. But yes, the vent does "breathe" in and out, but it's usually very minor depending on the steadiness of the equilibrium reached.

I actually don't run an open vent on my boka... I use a liquid airlock similar to what you see on a fermenter. I have a vent hole and a clear tube that extends from the vent away from the column and the end of the clear tube is submerged about 1-2 inches below the surface of a small container of water. This means that for my still to vent, it has to overcome a couple of inches of water pressure. Likewise, to suck in air, it has to pull water up the tube enough to expose the opening to air. So what I end up with a very visual and audible (bubbling/sucking) indicator of any over/under pressure condition. The whole foggy mirror/glass method works OK, but I like my method even more as it more easily gets your attention if something is out of equilibrium.

Anyways, the water level in my tube and airlock container is usually equal but it does flutter above and below level a few mm as the still tries to "breathe", especially while adjusting my cooling water or product takeoff rates.

I guess technically you do not need a vent tube at all... but this would extremely dangerous. In the event of a cooling coil failure or during column heatup and vapor rise within the column, the still could explode if the takeoff valve were closed. Likewise, if you lost heat input while your cooling coils were still running then a vacuum would be produced and your still could be "crushed" by the ambient pressure. See example of a boiling vessel sealed off and then cooled, haha: https://www.youtube.com/watch?v=uZ7WFhJvQOA" onclick="window.open(this.href);return false;" rel="nofollow

[sungazer]

I think you are underestimating the size or the amount of air that needs to get into the boiler to replace the distillate. In my case I normally aim for at least 10% ABV in the wash sometimes up to 18% ABV in a 40L wash that equates to 4-7L of of air that needs to come into the boiler to replace the distillate taken off. If this was not replaced there would be a huge vacuum in the boiler and the process just wouldn't work.

[skow69]

As the wash boils the volume of vapor produced is roughly 1600 times the volume of liquid consumed. That should handle the 4 - 7 l.

[joeymac]

I think you are underestimating the size or the amount of air that needs to get into the boiler to replace the distillate. In my case I normally aim for at least 10% ABV in the wash sometimes up to 18% ABV in a 40L wash that equates to 4-7L of of air that needs to come into the boiler to replace the distillate taken off. If this was not replaced there would be a huge vacuum in the boiler and the process just wouldn't work.

If you're removing ethanol from the system, it's because the column is full of ethanol due to boiling. If ethanol vapor is heavier than air, how do you propose the air displaces the ethanol and gets down to the boiler... and then what keeps the heavier ethanol vapor from just pushing the lighter back up and out the column?

There is some air in a reflux still but it sits within or above the coil. Everything below the coil is distillate vapor or reflux. Everything.
If air were to get in your still, it would be about the most dangerous thing ever. Vaporized ethanol + Air (oxygen) + Heat = Explosoin.

[sungazer]

I am happy to be proved wrong so I am not taking a back against the wall stance here. I am happy to accept that Vapous could be expanding and taking some of the room of the removed distillate however if what you are saying is true then there would be an almighty rush of air trying to get into the boiler when the gas is turned off. I have had to turn off the gass once before and throw a bucket of water onto the keg to remove as much heat from the system before tackling a small fire. There was no sudden implosion which I think is what would happen if there was not a return of air continuing to happen throughout the process.

As for the vapor being heavier than air this may be a fact but I am sure it doesn't exclude all air from being able to mix with it and return back down the column with the re-fluxing liquid.

[joeymac]

As I mentioned a day or so ago, I run an airlock on my still instead of an open vent because I prefer the visible & audile indicator versus a plain mirror fogging. Otherwise, my still is airtight.

I primarily use an induction hotplate. If I pop a circuit breaker or the burner times out (60min "safety" shutoff feature if I forget to hit a button ) the still sucks the water out of the airlock in about 5 seconds until the vent hose is exposed. It then proceeds to gurgle on the tube for another 10 seconds or so like a fat kid trying to suck the last bit of milkshake from his his straw. The first time that happened I almost did away with the whole airlock thing... but then I decided to just use 95% neutral spirit so that when it happens I only end up dumping good spirit onto the column.

So yeah, at least my still sucks in a ton of air when I turn it off.

[skow69]

Sounds like time for sungazer to put an airlock on his still because, obviously, logical arguements are not going to sway him

[sungazer]

Sounds like time for sungazer to put an airlock on his still because, obviously, logical arguements are not going to sway him

Skow I don't know why you say that. I said in my post I was happy to be proved wrong and I am debating here and listening to people especially those that have some math or practical examples that show evidence one way or another. Not just reaping stuff that they have heard from someone else that has never been tested. In fact joeymacs last post shows that his boiler did in fact need to take a large breath of air when it was turned off. I think that clearly proves that I am not totally misguided. If joeymac's still didn't have the airlock on it it would have been harder to see but this defiantly shows it. What if the airlock wasn't there, it would be creating a pressure drop to some degree for reverse flow would the air have been able to get in more slowly?

[skow69]

OK, I was getting the impression that you were rejecting all arguments that disagreed with you, but maybe not.

if what you are saying is true then there would be an almighty rush of air trying to get into the boiler when the gas is turned off.

Consider this. You turn off the gas. A few seconds later you hear the boiling stop. You are monitoring column temperature. It takes what? maybe 60 seconds for the column to cool below boiling temp. In that 60 seconds all o the vapor in the column condensed, diminishing in volume by a factor of 1600. [Actually that is water, ethanol is less, but let's go with that.] It effectively vanished. and was replaced by air from outside, just like you say. A 2" X 48" column has a volume of 150 cu. in. or roughly 2500 ml. But some of that is occupied by liquid reflux and packing, say 50%? Then 1250 ml of air had to rush in over 60 seconds, or 20 ml/sec. Think half a shotglass per second. we breathe more than that. A 1/16 inch hole won't have any problem with it. And that was the big rush. Any more volume loss has to come from the charge contracting as it cools, which takes what? an hour or more?

So there is nothing going on there that is even detectable unless you have some clever method like joeymac. Certainly nothing that would collapse your still because the air couldn't get in fast enough because of restriction at the vent. If you don't believe my specs, please look them up. Check the timing on your own still. I could be off, but at 20 ml/sec I've got a wide margin of error.

[joeymac]

I wouldn't describe the air suction as dramatic by any means.
Now, if you actually had no pressure relief it might get interesting and twist up your boiler some.
I wonder if a standard keg can support vacuum distillation

[sungazer]

I believe your math it sounds reasonable. I was never really thinking in terms of damaging a boiler or such, more just the thought that a vent was needed for air to pass both ways. The pressurization of the boiler is always talked about and for good reason the 1600 if that is the number is going to produce a significant result. Like you say the 4L of air to replace the distillate over 2-4 hours is not huge but just something I think should be considered in the complete system process.

A part of my job used to be working out the specifications or uncertainties for a particular measurement for this you have to look at each contributing factor so when I see a system I look for all the factors that are occurring this is one factor that doesn't seem to have be mentioned and quantified then the effect considered. So I just wanted to throw some light on it.

Personaly I like to think the air is being replaced in a steady flow. What effect does it have on the rising vapor if any? Perhaps as you say or as in joeymac's configuration this replacement all happens on the cooling down of the boiler.

[Hound Dog]

Way over thinking the process. When your old tea kettle sits on the stove and starts to boil, the steam is steadily whistling out of it, it's not sucking air in to replace the water. When you turn off the heat, you are done. Let it suck in all the air it needs then.

In the perfect world your condensing coil is returning it back to liquid so the cycle should be the same and it could be sealed BUT, anything goes wrong and it is a disaster.

Just vent the top.

[skow69]

I wouldn't describe the air suction as dramatic by any means.
Now, if you actually had no pressure relief it might get interesting and twist up your boiler some.
I wonder if a standard keg can support vacuum distillation

Given the shape of a sanke keg, it should work great under vacuum. A corney keg won't without reinforcement. They collapse around 29 inHg. A sanke has those ribs to stiffen it. For our purposes you really can't go past about 28 inHg (50 torr) anyway because that is where the distillate, at ~50% ABV starts to boil off at room temperature.

[BlueSasquatch]

Re the end plates I made easyflange and used triclamps, this really in my opinion is the best way as you wont end up with an inaccessible leak, which proved its value immediately. If I had to do them again I would just use SS ferrules.

Since the original build I've only made two small modifications; I shortened the length of pipe below the tee, and added a SS ferrule, thereby reducing the overall height and reliability of that connection. The other is that I added a second atmospheric port on the other arm of the crossflow, figured it would balance air escaping and not allow pockets to form. Note that the arms of my cross flow are tilted slightly upwards to allow distillate to return more easily, which isn't on any of the original designs I saw.

How is it working? The answer is... its bullet proof. My current setup is 5500w electric and it knocks down everything without breaking a sweat, only a tiny trickle of water is required. I'm using it on my 3" column with a 3-2 reducer and I couldn't be happier, as it maximizes the available height.

Almost messaged you asking for an update, good thing I just kept searching. Pulled this over from a different thread. The 2" Diameter was enough? I've been wanting to make one of these, but the price for 3" with fittings is a decent chunk of change.

Threw together an idea, using threaded end-caps rather than flanged+clamps, I just am not a huge fan of clamps, I know modular is king.

[StillerBoy]

Threw together an idea, using threaded end-caps rather than flanged+clamps, I just am not a huge fan of clamps, I know modular is king.

The water inlet and outlet are not located in the right place, as they should be at the ends, so that the water can flow through the 1/4" tubes..

Mars

[BlueSasquatch]

The water inlet and outlet are not located in the right place, as they should be at the ends, so that the water can flow through the 1/4" tubes..

Mars

Shoot, good catch! Will move those out, just finished a shotgun build so I got that on mind I guess.

[StillerBoy]

Shoot, good catch!

Good, that's why we are here.. plus I would add a second vent, one on each side/ends so as to not create a pressure spot..

Mars

[Yummyrum]

I like your idea Blue .
Here, we can't buy those 2" threaded copper adapters but we can buy 2" All thread which will fit over 2" . I could cut off a smell length of thread and solder it to the 2" .
Been thinking about a cross flow for a while now . Thanks for the spark .