Another continuous stripper

[Jacksonbrown]

So here’s what I’ve been mucking around with tonight. It’s mostly StillDragon bits and pieces.

It didn’t really work as planned but here are the results anyway (not often you hear about the fails ).

Sorry, no photos but it was pretty much as the diagram suggests.


The heat recovery feature was a waste of time as I didn’t expect the condenser outlet temp to be so high.
Also, some additional vapour cooling was needed. The condenser couldn’t cope so another one was added at the end (not shown on the diagram).
There was a lot off strange burping and surging going on. I think I had stuff boiling in the condenser which didn’t help.
The ‘boiler’ (two RIMS tubes) was also surging and playing with pressures a lot which meant it didn’t really flow as gravity would normally suggest.
It did run continuously at the numbers on the diagram but they’re not really good enough for what I was after.

I think I’ll combine this set up with Lesters where the feed pours down a column through some packing. I wanted to avoid that as it might make a mess of the packing but it will bring other benefits like higher purity and less coolant requirements.
I think I’ll also have the heating tubes in parallel and mount them vertically next time as I think it will control surging a bit better. I might need a few more bits to try that out.

It would be great if I could get the vapour purity up and raise the feed rate a bit i.e. lower temp vapour with high coolant flow.
I would like to do away with that second condenser if possible and have the feed do all the cooling. Is there an ABV of the vapour that I should aim for, to match the cooling capacity of the feed? (a normal wash would be less than 10% not 15%)
In the end I learnt a bit and it didn’t cost anything as the bits were there already.

Thoughts?

[Maritimer]

How about taking us on a tour of the schematic.

M

[YHB]

I can't get the numbers to work.

Take the first condenser, if I am reading this correctly, you have 22 litres an hour being heated from 23 deg C to 94.5 deg C by the vapour given off by the heater, when most of the heat given off by the heater is going down the drain.

I maybe missing something or maybe there is something missing off the diagram.

[Edwin Croissant]

I think your heat recovery is doing fine. You heated your wash up to the boiling point with the condenser. And you are probably boiling away some feed in the heat exchanger in the bottoms too. You are using nearly 3 times the amount of power needed for your feed rate resulting in low ABV. I think that's the reason you need extra cooling for condensing the vapor. And is maybe an explanation for the burping and surging. I thing that a large amount of steam is not used to boil away the feed but simply going around the feed. I am beginning to suspect that you need a liquid distributor above your packing or a plate to fully mix the feed with the steam from the boiler.

Just my 2 cents.

[Jacksonbrown]

How about taking us on a tour of the schematic.

M

The idea was-

Wash is pumped from the fermenter through the condenser as the cooling medium where it condenses the distillate and gets a bit of preheating (ended up being too much preheating).

Warmed wash then flows to a second heat exchanger, the regen. (The idea was to recover as much heat as possible but the delta t on all sides was too small to bother IMO. Wash was boiling off in the wrong place)

Then, from the regen, the wash passed over two heating elements in a 2” tube where it was meant to boil.

The vapour and liquid then flow concurrently up and over to a tee where the spent wash flows down, past a temp transmitter and then through the other side of the regen heat exchanger to drain. The vapour moves up, over then down the through the condenser where is condensed (with some extra help from a second water cooled condenser, not shown)

There was no column or packing in this set up at all.

I can't get the numbers to work.

Take the first condenser, if I am reading this correctly, you have 22 litres an hour being heated from 23 deg C to 94.5 deg C by the vapour given off by the heater, when most of the heat given off by the heater is going down the drain.

I maybe missing something or maybe there is something missing off the diagram.

Are you suggesting there is missing heat or extra heat?

As I mentioned there was a second condenser added as the main one was overwhelmed which isn’t on the diagram. Are you including the heat in the vapour and regen?

I had a quick look at mass flow of ethanol and it didn’t seem right but my maths is generally a bit pathetic.
46.8 ml/min feed, 39 ml/min distillate, 4.2 ml/min waste, 3.6ml/min missing. I’m going to put this down as measuring errors but there could have been vapour coming out the waste line too.

I think your heat recovery is doing fine. You heated your wash up to the boiling point with the condenser. And you are probably boiling away some feed in the heat exchanger in the bottoms too. You are using nearly 3 times the amount of power needed for your feed rate resulting in low ABV. I think that's the reason you need extra cooling for condensing the vapour. And is maybe an explanation for the burping and surging. I thing that a large amount of steam is not used to boil away the feed but simply going around the feed. I am beginning to suspect that you need a liquid distributor above your packing or a plate to fully mix the feed with the steam from the boiler.

Just my 2 cents.

I think the big issue was there just wasn’t enough hot vapour/liquid interaction. The next iteration should remedy this.
I will have the vapour flow up through the descending wash in a packed column. Hopefully this counter current interaction within the packing should keep stripping in one place rather than stuff boiling off all over the place.

I was thinking a lot about heat recover but it didn’t click that the temp of the hot spent wash could be a lot more than the boiling point of the feed. If I get control of the boiling and also get the distillate ABV up with the wash ABV down it should flow much better I think.

You mentioned I’m using three times the power needed for that feed rate. Does that mean if I get this right I should be able to push passed 15ml/s with the available power?

[Edwin Croissant]

I completely missed the point that you are not using packing and your column is horizontal. I thought is was an error in your schematic I think there is not enough interaction between the feed and the steam. I got the feeling that liquid distribution ( google for the term to see some examples) is a key factor for the efficiency of a stripper.

You mentioned I’m using three times the power needed for that feed rate. Does that mean if I get this right I should be able to push passed 15ml/s with the available power?

According to my calculations you need 1721W for the 6 ml/sec to get 60% ABV. Because of the poor interaction you need more steam resulting in low ABV output. When you increase the efficiency of your stripper your feed should be sufficient to condense the vapor. With the available power you should be able to push much more at a much higher ABV.

[Jacksonbrown]

I had another crack yesterday with a set up that look a bit more like this (attached).


The sightglasses above and below the column worked well to control flooding but I couldn't get the thing to stabilise and the pipework wasn't ideal so I stopped. I haven't got the bits to try it properly and the top element was getting exposed which was very not good.
I don't think the issue was the process more the set up and scale.


Would liquid distribution be over kill in a 2" column, unless I've misunderstood?

The column was packed way too tightly as it flooded quite easily and balancing the waste take off with the feed was also a problem. To be honest 2" is probably way to small. The amount of liquid moving down the column is massive when compared to a normal 100% reflux set up. There's 10 times more water than ethanol moving down.

In the reflux set up that column will start flooding at 60% power so I think I was pushing it way to hard for 2".

I might try again later at much lower power but that 'boiler' set up is flawed so it would just be for proof of concept, not a permanent arrangement. Really I need an extra 2" tee to do it properly.

[Jacksonbrown]

OK, so this one worked a lot better as you can see by the numbers.
Everything flowed very well and the element was flooded at all times without any input from me.
The set up was extremely stable and would have continued all day if I could feed it.

Not exactly sure on the power input as it was PID controlled this time (I was running manual with the other tests).
I had the waste outlet temp set to 98°C and it comfortably sat there give or take 0.5°C with the power floating around 80% so around 2kW seems about right (one 10A element @ 240V).


There was no packing above the feed inlet but it had a 1m column and less than 100 grams of copper mesh in it for packing. I should be able to increases the efficiency there pretty easily.
Didn’t bother with a regen section and forgot to measure the feed temp (after condenser preheat).

No further cooling was required which was great. The feed condensed all the vapour and cooled the distillate to less than 26°C all on its own.

I really like not having a boiler and start-up was quick and easy. Just prime the system, shut the feed tank valve and turn off the feed pump.
Once it’s boiling and the distillate has flowed for a while just wait for the liquid in the preheater/condenser to heat up a bit more and it’s ready to roll.
Turn the pump back on and open the tank valve. Once the pump run for a few minutes, anything that has flowed out of the system at this point can be thrown back in the feed tank as it won’t have been stripped.

On shut down I probably lost over a litre in the preheater and column but the concept worked.
I should have thrown a bucket of water in the tank once it emptied to flush through the system and cut back on wastage.
A few drain valves for pack down would have been nice too.


So 20 litres in under an hour, using 2kW and no water.
What’s normal running a batch system (including heat up)?

[Edwin Croissant]

Would liquid distribution be over kill in a 2" column, unless I've misunderstood?

The reason I came up with liquid distribution was the problems lester mentions in his thread to get a proper vapor concentration (IIRC badbird seems to have the same problems). But now you show us a really nice result
I have entered your data in my spreadsheet Necessary feed heating power is 1630 W, condensing your vapor and cooling the distillate needs 1388 W When you add the difference of 242 W to the minimum boiling power of 1302 W you need 1544 W. Good job

[Edwin Croissant]

So 20 litres in under an hour, using 2kW and no water.
What’s normal running a batch system (including heat up)?

According to Pot Calc (v2):
Heat-up time 46 minutes.
Runtime 60 minutes.
Distillate ABV 34,7%

If you can reduce the Bottoms ABV (by setting the boiler temperature higher and maybe better packing) the time difference will be much larger as the runtime of the pot still will be much longer..

[ga flatwoods]

I tried a continuous stripper once but ran out of dollars and decided to marry the bitch. Still don't have any money! Now an ex but still a bitch!
Ga Flatwoods

What can I say? I was young and she could move that thing in ways I never imagined!

[badbird]

Good result! and more to think about.
Maybe a lot of column packing is not the way to go for stripping. I think next time i do a run ill try with just 4 bubble cap plates in place of the scoria and see what happens.
I am surprised that you are condensing all of the vapor with your wash feed, My wash heater never managed that but it probably isn't nearly as efficient as yours. Do you think additional cooling will be required if the spent wash ABV is reduced to <1%?

[Jacksonbrown]

Do you think additional cooling will be required if the spent wash ABV is reduced to <1%?

About to find out

Getting the product ABV up is the key I think and this comes down to the efficiency of the column ie my cooling capacity is fixed with the feed rate so i don't want to waste it on condensing excess water.

I'm still wasting a lot of heat energy in the bottoms but there are issues (and solutions ) to recovering it which will complicate things.
I'm still walking, I'll work up to running.

[Jacksonbrown]

Thanks for looking at the numbers for me Edwin.

OK, I tried again with a few things slightly tweaked.
Same feed rate.
Same power but set to manual this time so it was fixed at 2kW.

There was no flooding at all last time so this run I packed the column very tightly with copper (maybe a pound?? over 800mm)
I also insulated more of the column too which may have actually been a mistake.


Once I got it stable it sucked a lot more out of the wash but the distillate ended up with extra water in it too. The condenser coped but was just about at capacity. The numbers are all on the pdf.

Because the amount of preheat is dependant on the amount of vapour being produced it is too easy to have the system ‘fall down’ without good control.
With a touch to much flow you’ll lose a bit of preheat which can stop the boil. Then you’ve lost all the steam and all the preheating thus the temperature plummets.
Then the system has to be restarted i.e. cut pump and preheat everything again.
At the start of this run I tried to give it 100% power and control the bottoms temp by adjusting the feed rate. Big mistake.
This was my attempt at maxing the system and I’m sure it’s possible but definitely not with the level of flow control I had (a ball valve on the outlet of the pump).
I lost a bit of time on this run at the start because I had trouble getting it to stabilise with to higher flow rate but settled on a similar flow rate to last time.

Things learned.
My flow control is rs. Set it and forget it then let the PID controller adjust the heat input to keep the system stabilised.

The overall set up worked well but I think some more work needs to be done on column design. It should be quite reasonable to expect 2kW to strip 400+ml/min to <1%ABV if the distillate is at least 60 %ABV.

Tomorrow I might try to introduce the feed half way down the column. My gut feeling is that it will worse but you never now.

Is anyone doing anything similar?
I might put it up on the SD site.

[Edwin Croissant]

This is scary, your results match my calculations I don't expect you can get anything better then this.
You condenser is doing a excellent job. Can you give us some details about the condenser? Distillate condensing power and distillate cooling power is a little bit more then the feed heating power resulting in a distillate temperature of 60 C. When I look at all the old pictures from more then 100 years ago none of the distilling columns are isolated. I think they needed the extra air cooling.

[Jacksonbrown]

Can you give us some details about the condenser?

It’s an off the shelf shell and tube heat exchanger from Still Dragon but I couldn’t really get a spec sheet with it.
I was told that two in series was capable of knocking down 10.8kW but that’s the only performance data I had. Enough for my purposes.
51mm insulated shell, 7 tube, 9.5mm ID, 490mm length, 304 stainless.

When I look at all the old pictures from more than 100 years ago none of the distilling columns are insulated. I think they needed the extra air cooling.

This is what I thinking too.

Last night I tried introducing the feed half way down the column but it still had the insulation on it so performance was predicably worse. I should have removed to top half to get some passive reflux going.

Today I’ll use the same set up but will pull out the sight glasses to make room for a small reflux condenser at the top of the column.
I’ll run the feed through it as a second preheat and try to clean up the vapour a bit. I’ll keep the feed pump where it is and let the PID control the heat.
I’m thinking the performance will be greatly improved but it will take a while to stabilise. I’ll try to get times for this run too.

Here’s last night’s numbers.
Keep in mind that a stop watch, measuring jug and 0 to 100 alcometer are hardly high precision instruments and I’m getting my feed rate by adding the two outputs.
This last run I may have lost a bit of vapour as product was coming off way too hot. I didn’t finish the run for that reason. I'm still convinced that getting the distillate ABV up is the key.

[Jacksonbrown]

Ok, so this one was no better.
It was putting out +70% ABV on start-up but once the bottoms temp rose to +98°, the feed heated up too much and it stabilised in a worst state that the last run.

I think the reflux condenser was a dumb idea as introducing the feed at the top of the column should do the samething.
It's just acting directly rather than indirectly through a heat exchanger.
Getting the bottoms from 98° to 99° seems to be pushing the system a lot harder too.

The last thing I'll try is the test 3 set up but with a longer column and more packing.
I’m not sure what’s going on with column length vs packing density..

[Jacksonbrown]

Last one for a while as it doesn’t seem like anyone else is overly interested.

Feed rate and power both reduced this time but overall was very efficient.
1.3 m column packed to a standard level with copper mesh.
Feed introduced at the top of the column.
Distillate coming off at around 50% and with no additional cooling required, bottoms temp well over 99.
Everything was insulated with 1” foam tube.

Have come to the conclusion that if I want to push it harder I need a taller column but I’ve run out of room. I also need better control over the flow rate as this is critical, maybe some sort of PD pump is in order.

Feel free to give any input/feedback.

[Edwin Croissant]

Regarding “Stripper test6” I expect that the feed temperature at the exit point of the product condenser is already so high that the reflux condenser is not doing anything. If you want higher ABV then your supply can produce, you will have to connect the feed to the reflux condenser first (probably with a bypass to get CM control) and then the outlet from the reflux condenser to the product condenser. Then you have the combination of a stripper and a rectifier. This will give you a higher distillate ABV. Please note that you can't strip more ethanol out of the feed then there is present. You are already there. You have done it. Congratulations .

I think you made an excellent contribution You showed that controlling the beast is done by controlling the heating power by maintaining a constant boiler temperature, which is the complete opposite of how you control a pot still or a reflux still. The boiler must following the feed. I think that this is a much faster control the when the feed follows the heating power. When you control the stripper by controlling the feed while maintaining the heating power constant there is probably a large time delay that make you always overshoot and undershoot so you never get the system in balance. I thing that this is the problem Lester ran into (and not the liquid distribution what I first thought ).

When the boiler is following the feed you can probably do with a DC low power voltage controlled pump. If you want to, you can make a control loop that adjust the feed to the desired heating power.

What is of interest to know is how much packing you actually need. You only need one theoretical plate to go from 1% to 10% ABV. When I look at the Bunker Still I got the feeling that they are using maybe 30 cm of packing or raschid rings in the stripper. Now that would reduce your hight considerable.

Thank you for your posts and I must say you got some fancy equipment to work with

keep up the good work

Edwin

[Jacksonbrown]

I think you are right with test 6. I was hoping to induce a small amount of reflux and suck the last bit of cooling potential out of the feed but it was all too much for it.
I think with a longer column and a touch less heat it may have worked but I have a height restriction here

I do have a condenser with a bypass already hard piped into it but it was only one valve on the bypass line. I tried to do away with the second valve by creating a high pressure drop over the condenser using an orifice plate on its outlet.
It works fine as my CM reflux condenser but that is what it was tuned to.
I could try that but it will mean losing 0.4m of column and I have a feeling that the flow rate through it might be a bit too high even with the bypass valve fully open. This adjustment would also change the back pressure on my little mag drive pump which would change the feed rate. I've already discovered how much this can wreak havoc on the overall system so making adjustments on the fly would have to be kept to a minimum.

Another thought I had is if I could direct flow along the walls I might be able to do away with the packing altogether. It would become a bit like a single tube, falling film evaporator which is more like what I was going for when I started thinking about this. I'm just not sure what this would do to the distillate ABV.

I think what I will try next is some sort of knockout pot between the boiler and the column to help separate liquid and vapour. You say the column is a lot longer than it theoretically needs to be. Perhaps the boiler water is making its way up the column along with the steam as it is boiling quite violently. You can see how high the sight glass is above the overflow from the photo and there is still a lot going on in there.

How do you work out column length in this scenario as the stripping adds a whole new dimension too it.
The feed needs enough hang time flowing through the steam so that what drops into the boiler has already lost most of its volatiles.

I think it’s the boiler design that set this one apart. It holds less than a litre and flows very well. No cooling water is another perk.

I’m not sure what happens when the feed ABV changes.
If the feed drops to 8% will that work in my favour?
I’m thinking it will as if the ABV is very high then maintaining 99° bottoms will require a lot more energy and I will be condensing a lot more distillate too but cooling power won’t have gone up in accordance.

[badbird]

That is a nice piece of kit you have there JB, I'm afraid it's a bit out of my budget at the moment though.
With the tests I made a while ago I found the column only became unstable when i was trying to wring the maximum efficiency out of the gear, it got along quite happily if the wash feed is kept down, only problem then is that aditional cooling is require
There appears to be a catch22 withbth small boiler volumes, you get super responsive heat control but as you say the boil is quite violent, maybe a good sized bubble ball on top is the go?
My next plan is to setup a seperate steam generator under some bubble cap plates and see what happens, your setup has inspired me to build a more efficent wash heater / PC but I'm away trout fishing at the moment so stilling has to wait
I think quite a few have messed with this stuff but its not discussed much on the public forums, in english anyway (there are hundreds of pages of it on homedistiller.org.ru if u can get google translate working for you). Or maybe buy Riku's book then you can see whats going on on that forum, I have been meaning to order it for ages.

[Jacksonbrown]

That is a nice piece of kit you have there JB, I'm afraid it's a bit out of my budget at the moment though.

Thanks, I put a lot of thought in to the controller so it has a few good safety features. It's able to program mashing cycles too.
Most of it is an electric HERMS set up that I haven’t got around to building a frame for.


Here’s some more data, this time with the full run details.

STRIPPER TEST8.pdf

(83.16 KiB) Downloaded 144 times

This set up looks a bit ridiculous but I was trying to stop the boiler surging up the column (top part is the same.

It seemed to work OK but I’m sure there is a much more elegant solution. I wanted to keep this thing a simple as possible but it’s starting to get a bit elaborate.
It also cost me some column length. I only had 880mm of packing this time and I guess the distillate ABV reflects this but with it coming off at 27° and the bottoms temp above 99° with no additional cooling I suppose the system is working.
I’m not familiar with bubble balls. They are a 4” plate in a 2” line? Will they cope with liquid surging back and forth through it? I’ve never used plates but I think just a lower velocity cavity to knock out the foam is what is needed. The ball without the plate in it?
Someone mentioned a cyclone separator in another thread but that might be going overboard.
I’m still convinced that if I want to push it harder I need to get more water out of the distillate. I haven’t got the equipment to try it but an LM head with a bit of packing between the take-off and feed injection point might be an easier way to get a bit of reflux going and control it. I understand that others have approached it that way.

I'm away trout fishing at the moment so stilling has to wait

Hmm, I’m jealous.
I’m stuck in QLD now so no more hunting and fishing for a while. Kinda why I’m keeping busy with these tests.

[Edwin Croissant]

If the feed drops to 8% will that work in my favour?

Good question! Lower feed concentration does indeed give you more cooling power as your "Stripper Test8" confirms. The feed heating power is about the same as the distillate condensing power plus distillate cooling power at 9,2% ABV.

[badbird]

The ball without the plate in it?

Thats about what I had in mind though it would be cool to try making a cyclone plate somtime
The LM head would be interesting but unless you are going the full continuous still thing with a seperate heads removal column etc I cant see the point of pushing the ABV too high. I water it back to ~30% for the neutral run anyway.

Your not missing much on the fishing front, at the moment theres a lot more wind than trout

[Edwin Croissant]

I only had 880mm of packing this time and I guess the distillate ABV reflects this but with it coming off at 27° and the bottoms temp above 99° with no additional cooling I suppose the system is working.

Your system is working fine

From the “Stripper Test8” I get the impression that you start directly with the feed.
Maybe this will go better (just a suggestion, this is your still) :

Fill the boiler with water.
Apply 100% power and wait until steam is coming out of the condenser.
Reduce power to about the right level for the forthcoming feed, distillate temperature might be a indicator after feed is started.
Start the feed, feed will be heated by the steam.
When the feed enters the column (drop in vapor temperature?) switch to automatic.

[Jacksonbrown]

Maybe this will go better (just a suggestion, this is your still)...

Suggestions welcome I feel like I'm on my own here.


Well test 9 was a bit of a disaster.

It cost me two elements. I went back to test 7 and 3 only I thought I’d see what 2m of packing would do. I was hoping that I may be able to push it a bit harder with a higher feed rate.
Well, the back pressure over the column was too much and it literally shat itself.
It started with condensate and steam coming out the condenser which seemed fine then I switched on the feed and dropped the power a bit.
After another minute or two it started boiling backwards out the exhaust and overflow which exposed the element.
I quickly dropped the power when it started burping out the vent but the feed didn’t re-flood the boiler quick enough then all of a sudden, no more heat.
One burnt out element.
It was steaming through the system OK on start up so I thought that possibly it was the fact that I primed on water this time and was way too slow dropping the power. I still had another element and a tank of cool feed so I thought I’d have another go.
Two burnt out elements. Idiot!

If I find a spare element I might have another go with a 2m column but I will pull out a lot of the packing like the test 3.
This boiler design needs minimal pressure drop over the column. I found another system limit.

Priming on water is a better way to go in terms of wastage but it was a bit of a PITA to prime with the way it was piped up.
It has to be pumped up through the condenser then the boiler will fill. Once over flowing the valve at the pump is shut off and the normal feed can be hooked back up to the pump.
I have some more valving that can make this much easier.

So another fail more but some more knowledge gained so a success in that regard.

[Edwin Croissant]

I feel sorry for you loss of 2 heating elements Lester had the same experience that the pressure in the boiler dumped the content and it cost him nearly an element. This is a limitation of this kind of overflow. Either use a level-switch as safeguard, use a float as dump-valve or connect the outlet above the heating element. The last option will not protect you against boiling the element dry, (which takes a little bit longer) , but will prevent exposing the element during a pressure surge.

I think that you are pursuing the impossible. When I look at the numbers from test 8, I conclude that you are at the theoretical limits of your system. More packing will not make your system better. Halve the packing and see if you get the same numbers, if you do, halve the packing again. Less packing is less pressure is less change of dumping.

I have been doing some work on my spreadsheet to incorporate the distillate temperature. What I see is that your feed has to be below 11,5 % ABV to condensate all of the produced vapor. When your feed is below 9 % ABV your distillate will come out cold.

[Jacksonbrown]

I feel sorry for you loss of 2 heating elements

No big deal. They’re not that expensive, are very easily replaced and we gained some knowledge for it.
FYI, in looking for replacements I realise that what I had were actually 2200W elements, not 2400W.
10A was the number I had in my head when I was designing the control box so I guess those tests were actually a bit more efficient than first thought.

This is a limitation of this kind of overflow. Either use a level-switch as safeguard, use a float as dump-valve...

I don’t believe your first two options are really viable in my situation. On the element side of the boiler there is no defined surface as the 2” tube is boiling very violently and putting them on the vent side it won’t make any difference.

I was thinking about incorporating a float switch into my main batch boiler.
My control box is already wired up with the flow switch and relay that kills the pump and SSR signal whist turning on an alarm so it wouldn’t be hard to add a NO level switch in series.
I just don’t see it working very well in the continuous set up. It doesn’t fix the problem either, it just protects against it.
2m of dense packing was just pushing the envelope to bit too far me thinks.

… or connect the outlet above the heating element. The last option will not protect you against boiling the element dry, (which takes a little bit longer) , but will prevent exposing the element during a pressure surge.

My outlet is about 200mm above the top of the element but the U shape of the boiler means that a pressure build one side up can (and did) blow the contents to the other side.
I did this so that all the liquid must pass the full length of the element and the temp is read after that point. It worked brilliantly under normal operating conditions (minimal pressure differential) until the column was blocked up.
I’m not sure how to link the top of the U without losing vapour out the vent (don’t know if I described that right, turn the U into an O??)
Is there a best of both worlds design that holds a minimal amount and will separate the liquid coming in from that coming out?

I conclude that you are at the theoretical limits of your system. More packing will not make your system better. Halve the packing and see if you get the same numbers, if you do, halve the packing againI have been doing some work on my spreadsheet to incorporate the distillate temperature. What I see is that your feed has to be below 11,5 % ABV to condensate all of the produced vapor. When your feed is below 9 % ABV your distillate will come out cold.

Thanks heaps for looking into it for me. That’s the kind of info I’m after and the kind mathematical wizardry that doesn’t come easy to me.

You say I may have reached the theoretical limits of your system but I want to know what all the parameters are and what effect they have.

Note the difference between test4 and 5.
Test 4 had 800mm of packing under the feed point then for test 5 this was effectively reduced by 40%. The longer column seemed to give better results.
Test 7 with 1.3m of column was better again. Granted the column length wasn’t the only parameter that changed for each test but on those results I wanted to see what effect another increase in length would have.

I hear what you’re saying Edwin but I don’t know how well you’ve modeled the system (no offense intended) and the results I have hint at more gains to be had.

Aside from the pressure issue, what affect does the extra packing length have in your model?

Perhaps less power requirements, more efficient? Does it change the distillate ABV and will this help me to increase the feed.
Is there a max theoretical distillate ABV (using 8% feed & 1% bottoms) without resorting to a dedicated rectifying section and is a long, low pressure drop column the way to get there? 2m of marbles?
I haven’t got a definitive answer to those questions yet.

If I want to increase the flow rate what other parameters need to be increased in accordance? Tests seemed to show not just the power. What else is holding me back?

Distillate ABV seemed to range between 40% and 60%. Why?
Obviously feed ABV and bottoms ABV play a big part but anything else.
Lowering the feed rate and increasing the column length seemed to bring it back up again in test 7.

It seems the variables with the system are -

Feed (rate, temp and ABV)
Power input (controlling the bottoms temp/ABV, rate of separation)
How well the steam and feed are mixed.


I’m not sure it’s worth it but is there an easy way to make use of all that heat going to drain?


Sorry for all the waffle and questions but I’m not yet satisfied that I understand what’s going on.

[Edwin Croissant]

I don’t believe your first two options are really viable in my situation.

I was thinking of a new design. Maybe you can use a level pressure switch from a washing machine to kill the power in case of a pressure surge.

You say I may have reached the theoretical limits of your system but I want to know what all the parameters are and what effect they have.

Note the difference between test4 and 5.
Test 4 had 800mm of packing under the feed point then for test 5 this was effectively reduced by 40%. The longer column seemed to give better results.
Test 7 with 1.3m of column was better again. Granted the column length wasn’t the only parameter that changed for each test but on those results I wanted to see what effect another increase in length would have.

I have put most of your numbers in a spreadsheet.

There is something odd about test 7, measured distillate temperature is much lower as calculated. I don't see much difference between test 4 and 5 except that the feed temperature has a large impact on the distillate temperature. One degree Celsius of feed temperature raise the distillate temperature by eight degrees. So both the ethanol concentration and the temperature of the feed have a large impact on the distillate temperature.

I am running out of time today , this is very interesting, I will come back on this tomorrow.

[Jacksonbrown]

I was thinking of a new design. Maybe you can use a level pressure switch from a washing machine to kill the power in case of a pressure surge.

This could work but the switch would also have to be latching otherwise the cut in power would lower the pressure and it would just turn on again. It would also mean a restart every time it tripped which would be a right PITA if it was a bit finicky.
I will give it some more thought but I think the solution is just don’t choke the column.

There is something odd about test 7, measured distillate temperature is much lower as calculated. I don't see much difference between test 4 and 5 except that the feed temperature has a large impact on the distillate temperature. One degree Celsius of feed temperature raise the distillate temperature by eight degrees. So both the ethanol concentration and the temperature of the feed have a large impact on the distillate temperature.

I am running out of time today , this is very interesting, I will come back on this tomorrow.

Not sure about test7, the power should actually be more like 1.32kW and I may have dumped something warm back in the tank after I took the initial temp reading. 5° or 6° more in the feed would account for 40° difference in the distillate temp, yes?
I don’t know, I’m only thinking out loud. Test 7 also has the lowest flow rate and power setting but the longest (functioning) column.
I think I inadvertently changed too many variables at once to end up with definitive results but I have some more elements on order so if you’d like me to set up a specific test I can.
I will endeavour to take better measurements of the column and packing too as this seems to be playing a big part in the system performance.


PS the attachment had ‘unreadable content’ but all the measured powers in the table need to be dropped by 8% (I realised I had a 2.2kW element not 2.4kW)