Another continuous stripper

[Edwin Croissant]

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.

You need a normaly open on button that energize a power relay with a take over contact, stop button and pressure switch etc. are normally closed contacts. My experience with this type of protection is when they protect to often they often got bridged. I agree that the best thing is not to choke the column.

5° or 6° more in the feed would account for 40° difference in the distillate temp, yes?

A feed of about 22 °C would give the measured temperature. A feed concentration of 8,5 % ABV would produce the same distillate temperature and lower the distillate concentration to 51% ABV and the distillate flow of 42 ml/min which is more in line with my calculations.
I can't explain the overall lower distillate concentration by inefficient packing. Inefficient packing would mean that steam is diluting your distillate but would also mean that you should get more distillate then measured. This would also mean that you need more power which would also raise the distillate temperature. And I don't see this in the 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.

I think that you are getting so close to what is possible that the you need to take a lot more accurate measurements. The stopwatch and by the looks of it the temperature probes are ok, instead of a measuring jug I would recommend a digital kitchen scale and weight the output as this will cancel out any temperature influences. Compensate the boiler temperature for the barometric pressure and get something to accurately measure your feed concentration

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.

Based on your numbers and my calculations I would say that for a continuous stripper cooled by the feed:
Higher feed temperature will produce higher distillate temperature. A small variation in feed temperature will have a much larger influence on the distillate temperature. best stay below 24 °C
Higher feed concentration will produce higher distillate temperature. Best stay below 10% ABV or compensate with colder feed.
More feed means more heating power. I think the limit will be the packing.

I still think you have to much packing, try 30 cm and see what the numbers are. You could also try lava rock.

[Jacksonbrown]

So I got a new element in today.

I put in 300mm of copper (I don’t have any rock) 3x rolls totaling under 100grams.

The wash was 23° and it ended up at 7% after the last tests mishaps.

The bottoms temp was at 98° and slowly dropping with 90% power (1.98kW) so I gave it full noise (2.2Kw)

I think I ended up with feed coming out the distillate outlet.
It could be the mass of steam being produced was holding the feed at the top of the column where it back filled over the 180° bend and poured out the condenser.
It didn’t blow backwards out the over flow this time which I’m still pondering.

I can’t actually be sure it was feed coming out but it seemed like an excessive amount of liquid and it didn’t taste very strong so I’m assuming.
I'm not realy sure what happened but I quickly killed the system as I was paranoid of burning out another element.
It is possible I may have had the flow rate a touch to high but I don’t think it was excessive.

I will try again once it all cools down tomorrow but I think I’ll try a sparsely packed column.

Sorry, I wasn’t able to get any feed rate info.

[Jacksonbrown]

Once again...

STRIPPER TEST10.pdf

(25.3 KiB) Downloaded 132 times

A few notes.

There was 1m between the overflow and the feed point with 300mm of packing just under the feed point (3x2” rolls of copper mesh)
I changed the throttling valve on the pump to a globe type but I only had a ¾” not a ½”. I seemed to work a bit better anyway.
I also piped up a method to switch between water and product without mucking around with the lines or pump settings, this also made things a bit easier on start up and shut down.
The feed was only 5%ABV this time which wasn’t ideal and the feed rate and power were also dropped.
Distillate was very hot and ABV was way down.
I think feed was boiling in the condenser again. If preheat and the distillate temps seem too high could it be vapour temp putting it out maybe???
Every time a do a re-run I lose a bit more so I’m slowly running out of waste for testing.
Interestingly on shut down when I switched to water to purge the system out the power went down to 35% but the bottoms temp was climbing passed 99.5°. The distillate also cooled down to ambient but I shut it down when it started tasting more like water.

So I got 300mm of packing to work but I don’t think it was ideal.
Would higher feed ABV plus higher feed rate/power help? I think it might be have been worse but the boiling in the condenser would be doing strange things to the system.

Any ideas? I can probably do another one or two 10L runs at 10%.

[Edwin Croissant]

So I got 300mm of packing to work but I don’t think it was ideal.

The 300 mm /100 gram is clearly not enough to boil away all the ethanol you are evaporating about twice the amount of water with twice the amount of power then theoretically needed, resulting in to much, to hot and to much diluted distillate.
Test 4 was done with 800 mm / 500 gram of packing which is 62.5 gram for each 100 mm. Test 5 was done with 480 mm and the same packing density.
I would suggest 400 mm / 250 gram of packing for the next run

Can you give me some details of the pump you are using and how that beautiful control box is working. How exactly is the temperature controlled, is it on/off, proportional or a phase angle triac control with a PID controller ?

[Lester]

Excellent work JB!

I have been busy with other things and have not moved forward on my build. Besides, I still need to catch up on my reading.

Thanks for all the info!

[badbird]

Not sure where to post this but i don't think we need too many more continuous stripper threads?

OK so I got around to seeing what 4 by 4" bubble cap plates could do in place of my usual 2” volcanic scoria packed column for steam stripping, got to say I was surprised just how well it went.

A regular 50l keg boiler with a single 2200w element producing roughly 4kg of steam per hour served as the steam generator, spent wash was diverted at the base of the column to a J trap before it could enter the keg.

Weetbix/Allbran wash at ~10% was fed by a small 12v gear pump with speed controlled by a variable voltage power supply, the wash passed through a regular liebig preheater then my spiral wrapped preheater before entering the column just above the top plate (submerged). There was no significant surging this time, not sure if this is the new wash heater or the fact that the wash has sat around for a few weeks so most of the co2 should have dissipated

As usual it takes a while to get the wash flow balanced with the heat input but the column was quite stable once running properly. When everything was perfectly balanced the cold wash was just able to knock down all the vapour but to keep it safe I ran an additional small water cooled liebig as it didn't take much of a change for uncondensed vapour exit the wash heater.

The 2200w element produced steam at something like 4kg per hour.
The wash (~10%ABV) injection speed averaged around 300ml per minute producing a >60% ABV distillate at around 50ml per minute, presumably the spent wash ran about 1% ABV but I don’t have a decent thermometer to monitor this. At maximum efficiency the head vapour temperature was around 92 degrees C (I really need to get a decent thermometer)
The distillate came out with plenty of heads as you would expect but not so bad for tails, maybe not so much tails are generated by the short wash heating or maybe a lot stayed in the spent wash stream as part of the ~1% ABV?? who knows?


I'm certain the 4" column will handle a lot more power but with the current ½” pre-heater that has quite deep crimps to induce turbulence, upping the wash flow much above 300ml producing instability and to much back pressure causing a steam blow out from the J trap. Then you have back off the wash feed so then there is insufficient vapour cooling then venting (without the additional water cooling). So maybe its time to get the copper out and rethink the condenser/wash heater.

[Jacksonbrown]

Hi Badbird, thanks for joining us.
Again, it seems that getting the pressures right is the biggest gremlin with these set ups.

I would defiantly be aiming to get an accurate temperature for the bottoms. The tiny jump from 98° to 99° is a real test for the system.
Looking at the mass flow of the ethanol in the feed and the distillate it looks like you removed all of it

I would suggest 400 mm / 250 gram of packing for the next run

I have a feeling that packing density that high is asking for trouble. It's set up for 850mm of light packing now (will weigh it when dry)
I may give 400mm/250 gram a tentative go after just to see.
Some of the earlier test packing weights were guesstimate so don't take them too literally. I had no idea it would require so much balancing so so I didn't worry about it to much. Will be taking better measurements from now on. If using rolls it turns out to be about 30 grams per 100mm.

Can you give me some details of the pump you are using and how that beautiful control box is working. How exactly is the temperature controlled, is it on/off, proportional or a phase angle triac control with a PID controller ?

Pump is just a chugger. It now has a ¾” globe valve on it (all the other tests it was a smaller ball) and an IFM flow switch.

Element power is controlled by PWM although the shortest pulse length to choose from was 0.5s which I thought was a bit odd but it seems to work OK.

Here's the elec drawing I did for the box, not sure what else you're after

[Jacksonbrown]

Inside

.


If I was doing it again I would have got the 24V option with the controller instead of the 240V one and used more correct wiring colors and gauges. What's in there is fine but it could be better.

[Jacksonbrown]

Well I just had another back fire.

8% feed @23°, 850mm packing. Did the blow test and there was very slight resistance (too much, I guess).
I had the flow rate right down again and the feed was boiling in the condenser again. There was vapour coming out with the distillate so I thought I’d add a bit more flow to cool it down.
It worked but then the power went back up towards 100%. It spewed out the breather and I quickly shut it down.


With my design I think a big issue is the lag between inputs and bottoms temp change. With very little or no flow the boiling liquid doesn’t move to the temp transmitter quick enough.

I’ve run out of juice now but I have a few more ideas to try in the future. Moving the temp transmitter closer to the element whilst keeping out of the vapour is one.
I do have some molasses in the fermenter but I think I’ll drop the temp before it goes in, just to be safe. Is 5° likely to cause unforseen issues?

[badbird]

I don't have a PID controller to try it yet but am reasonably certain that setting the heat input at a fixed level then controlling the wash input volume with solenoid valves or variable pump will work more reliably, then maybe just an alarm on the bottom temps to avoiding loosing alcohol if things go wrong. As you say there is a lot of thermal lag even with your small volume boiler.

[Jacksonbrown]

If I had better control of the flow rate I would defiantly be doing it your way, but I don't
Ideally I would use both methods. Manual heat control and slowly increase the flow on start up then switch to PID to hold stability.
There will still be a lot of lag with the flow method I think. It takes a few minute for feed to get form one end of the system to the other. If heated up to the point where vapour is coming out with the distillate it will take a while for all that heat in the condenser to get washed out.

[badbird]

It certainly takes a while to get the column balanced and fine tuned in the first place but one thing i noticed using the 4 bubble cap plates in place of the volcanic rock (with all its thermal mass) and feeding at the top plate with no packing above that point is just how much quicker the thermometer at the top of the column responds now. After a change in the voltage to the gear pump the column top temperature starts to change in a couple of seconds now.
I think I'm seeing why the commercial operators mostly use something along the lines of sieve plates for this but bubble cap plates is what I have for now and I hate drilling holes

[Lester]

I think I'm seeing why the commercial operators mostly use something along the lines of sieve plates for this but bubble cap plates is what I have for now and I hate drilling holes

Just thinking out loud: Would it be possible to use very fine SS screen material, stacked one on top of the other (multiple layers), in place of a single drilled plate? I also hate drilling lots of holes.

[Jacksonbrown]

I think that's what badbird meant by the sieve plates.
Is the an easy 2" drop in that I can get? I seem to recall seeing on here somewhere a long 'chain' on 2" screens tied together with opposing downcomers.

I could clip on more or less plates/screens as required then drop the whole insert in the column and away we go.

Where did I see that?

[Edwin Croissant]

Where did I see that?

Here?

[badbird]

I think I'm seeing why the commercial operators mostly use something along the lines of sieve plates for this but bubble cap plates is what I have for now and I hate drilling holes

Just thinking out loud: Would it be possible to use very fine SS screen material, stacked one on top of the other (multiple layers), in place of a single drilled plate? I also hate drilling lots of holes.

Its just speculation without actually trying but unless you have a realy open sieve/ mesh I think down-comers or weirs or whatever are important in controlling the amount of liquid in the column and so keeping the back pressure under control. The hd.ru people seem to be using a lot of small plates (like 20 or so) with large holes, something like this

from somewhere on hd.ru

tarelki20.jpg (3.76 KiB) Viewed 4498 times

[Edwin Croissant]

Just some random thoughts:

badbird's numbers are quite surprising. 13% feed should produce 60% vapor. When you look at the problems to reach a decent vapor concentration I think plates or at least one top plate are the way to go. When I feed badbird's numbers into my model, a feed of 13% ABV with a temperature of 20 ºC , the cooling power to condense the vapor is equal to the power to heat the feed. So the feed is just able to condensate the vapor. This is in line with his observation. Distillate temperature might be a good indication to see if the system is in an efficient balance. A table with a distillate temperature for each concentration and feed temperature combination will do that trick.

I think some kind of feed forward control is needed. Maybe a table with the power setting for each feed rate – feed concentration combination.

When you adjust the feed rate the result on the end of the line is virtually instantaneous. I have experienced delays of 1 to 2 seconds but this was in 1/4” o.d. hydraulic lines more then 200 m long. Reaction time of the boiler temperature on the bottom concentration on the other hand is something different. When the bottom flow is 250 ml/min and the boiler content is 1 liter it will take several minutes before the boiler temperature is a good indication of the bottom flow concentration. A PID controller can compensate for slow variations in the feed rate but for following a fast changing feed rate I think the response time of the boiler temperature is just to slow. At least you will need a slow attack – fast decay control.

[badbird]

The sugar wash involved had a starting SG of around 1.075 and fermented out to .998 (slow ferment probably caused by using old frozen yeast) so in theory the ABV should be 9.93%
Maybe there is some passive reflux involved to reach 60%, unlike using SS those copper columns leak heat rapidly in cool weather and as there was a weeping seal halfway up the column I didn't try to insulate at all. I think the air temp was around 18C that day and the wash temp was around 16C.

The wash feed control will need more testing, with a much better condenser / wash preheater in my case. At least that will remove one more of the variables

[Jacksonbrown]

I have a few of these... http://www.stilldragon.com.au/filter-disc-2/

They sit on the seal and are too big to fit in the column as they are.

I would like to put a hole in the middle and have a center stem that incorporates the down comer and a slit in the plate so that it forms a very shallow cone when pushed into the column. it would also make a better seal with the side wall too. Not sure how the center stem works yet.

EC, I realise changes in flow rate will be virtually instantaneous. What I meant was the changes in temp take a while to work through the system. With very low flow velocities of a few cm/s in the 13mm feed lines, the 2"x2' condenser stays hot for a while.

[Jacksonbrown]

Where did I see that?

Here?

Like this too
http://homedistiller.org/forum/viewtopi ... 0#p7174326

Are people doing these using WAGs/trial and error or is there a sizing program somewhere on here to govern voids vs downcomer cross section ratio? Also weir heights etc If so what are the design parameters?

The spread sheet in this doesn’t look promising though.
http://homedistiller.org/forum/viewtopi ... e#p7059937

I don’t think it carries over to this application very well. I will have a lot more fluid moving down the column and the fluid properties will be very different but it seems the thinner the column the further the spacing required between plates.

20+ inches between each plate sounds ridiculous. Have I misinterpreted? No wonder everyone runs 4” columns and the 2” plate jobbies have got a bad rap.
Maybe sieves aren't the way forward in the 2" world.

[Edwin Croissant]

EC, I realise changes in flow rate will be virtually instantaneous. What I meant was the changes in temp take a while to work through the system. With very low flow velocities of a few cm/s in the 13mm feed lines, the 2"x2' condenser stays hot for a while.

Good remark, got me thinking about the dynamics of the system
I made a table showing the distillate temperature in respect to the feed concentration and the feed temperature.

Going through the numbers I think that there is a region of instable operation. In this region the amount of heat in the vapor is not enough to raise the temperature of the feed to its boiling point. A small increase in feed rate will lower the temperature of the feed that enters the column. Some of the energy that produce the vapor is now used to heat the feed so less vapor is produced. As the feed is heated by the vapor this drops the temperature of the feed that enters the column even further. Eventually the feed flows unheated through the condenser and packing into the boiler, is heated there and dumped with a temperature near the boiling point. Heat exchange between vapor and feed is shifted from the condenser to the packing until no vapor is produced. The system shifts from an instable distillation state to a stable, but undesired, feed heating state. To prevent this I think that it must be made sure that the feed enters the column at its boiling point by applying enough heating power the keep the distillate temperature above the feed temperature.

[Jacksonbrown]

I think you might be on to something there and it reflects a lot of what I’m experiencing.

I think the part where you talk about the three zones is dead on the money.
First is the feed boiling in the condenser (when hot vapour is also coming out with distillate), second is the steam stripping happening all in the column (where we want to be) and the third is where cool feed heads straight to the boiler and it performs like a continuous pot still (where my back fires happened).
Keeping it in that middle zone is the key.

I don’t think you want the feed to enter the column boiling but the closer the better.
The further from BP it is when it enters the more of your column height is wasted where it has to be brought up to temp as it flows down.
If the column isn’t long enough for the flow rate (or there’s insufficient steam i.e. power) then it hits the boiler cold and with all its ethanol still liquid and prevents any further steam being produced. The system falls down.
I also think that it’s not quite as simple as only those two parameters (initial feed temp and ABV).
The feed rate and power need to be tuned correctly too. A small drop in power or rise in feed can give the same cascade effect where you lose all steam.
You can’t increase one without the other.

The trick to keeping it in that middle section is to have a more efficient column IMO. It gives you more leeway.

You said that I should only need 300mm of packing to do the stripping.
Perhaps the very top section of my column is only serving a heating function making up the difference between the BP of the feed and what the preheat in the condenser could achieve for that duty.

If your table is correct then I may run into trouble when I chill my feed to 5°. What is a slight increase in power going to do in that scenario? (Assuming it doesn’t blow out backwards )

The general concept with this thing is sound. It works. The trick is just in getting everything balanced.

[Edwin Croissant]

I don’t think you want the feed to enter the column boiling but the closer the better.

I am not sure about that, the vapor from the feed goes directly back into the condenser so it will not disturb the operation of the column. The amount of vapor produced is is also small as evaporation takes a lot of energy. Got to do some more thinking about that

A small drop in power or rise in feed can give the same cascade effect where you lose all steam.

Exactly But now you now what to look out for, when your distillate temperature drops increase the power or reduce the feed. I expect that to crank the system up that you first have to increase the power and then increase the feed rate to get the distillate temperature to drop.

I also think that it’s not quite as simple as only those two parameters (initial feed temp and ABV).

When power and feed rate are matched these two parameters are all that counts. I find the outcome quite surprising and it give me the feeling that keeping the boiler temperature constant is not such a good idea. I wonder if keeping the distillate temperature constant is not a better idea. The control must be slow as I think that there might be a considerable time lag between adjusting the power level and the resulting change in distillate temperature.

You said that I should only need 300mm of packing to do the stripping.
Perhaps the very top section of my column is only serving a heating function making up the difference between the BP of the feed and what the preheat in the condenser could achieve for that duty.

Test 5 with 480 mm of packing was IMHO right on target. The last test were done with lower ABV IIRC. So it is possible that much of the packing was used to preheat the feed. Good thinking

If your table is correct then I may run into trouble when I chill my feed to 5°

A feed of 5°C will work for a feed concentration of 17% ABV

What is a slight increase in power going to do in that scenario?

A 10% feed of 5°C need about 20% more power. The extra steam will dilute the distillate, How much I don't know at the moment, I am going to extend my model to give me the resulting distillate concentration for a given power setting.

[manu de hanoi]

TL;DR
- wash is not enough to condense all the output, you need a water condenser on the product output
-1% on the spent wash is too much, lengthen the tower or get some SPP

[TheMechwarrior]

Well done Jacksonbrown, you've been busy!

I've punched in the data from your last run (Test10) and this is what it looks like (ignore the tower diameter):


Quick observations:
1. You need better control over your feed temperature, try and target 50oC even if that means installing a second heating control loop in the short term until you are able to better utilise your pot-ale temperature.
2. Add a second PC using cooling water to finish off your distillate, trying to do all your cooling from the beer AND achieve your desired beer feed inlet temperature are two different goals.
3. If your beer is entering the top as shown on the drawing in "Test10" consider adding a scrubber directly above it as a minimum. At point of entry you'll be seeing froth/foam and spray carryover, the scrubber will act as a "demister".
4. At 190mL/min of 5% wash and 96oC top temp you should be seeing something more like 64% abv distillate coming out at 176mL/min. The 22% you are reporting may be due to point 3 above.

What diameter is your column?

As you know, I'm working on a continuous stripper project as well so I'm keen to see progress and you have provided a wealth of real world data that's invaluable for anyone looking at this for the first time.
Well done.

Cheers,

Mech.

[Jacksonbrown]

Bit of an old one so kinda moved on since then . If I were to keep going I would start by ditching that packing and getting decent control over the supply flow rate (just like Badbird was doing from memory). I think that would fix most of the issues I had.
A combination of his and mine would be a winner I think. Plates would be a good albeit expensive option.
A perf plate tree/insert was the direction I was heading
Minimising pressure drop along the column was the big spanner, it caused a few blown elements when the steam pushed the boiler contents back out the overflow, exposing the element.
Supplying with a PD pump on a PID controller would be much more consistent and give much better control.

1. You need better control over your feed temperature, try and target 50oC even if that means installing a second heating control loop in the short term until you are able to better utilise your pot-ale temperature.

Why?? The temp of the feed from the pump going into the heat recovery HEX/condenser or after that when it’s feed into the column?

2. Add a second PC using cooling water to finish off your distillate, trying to do all your cooling from the beer AND achieve your desired beer feed inlet temperature are two different goals.

No water was my goal. Is feed temp a critical control element? I could put a RIMS tube just before on the feed just before the column to bump up the temp but then I'd loose my controller for the boiler. I could plug in another element for the boiler but it would be stuck on 2.2kW

3. If your beer is entering the top as shown on the drawing in "Test10" consider adding a scrubber directly above it as a minimum. At point of entry you'll be seeing froth/foam and spray carryover, the scrubber will act as a "demister

Could do but I'd be surprised if that was happening. A sight tower up there would be a good idea too, especially on the foamy ones.

4. At 190mL/min of 5% wash and 96oC top temp you should be seeing something more like 64% abv distillate coming out at 176mL/min. The 22% you are reporting may be due to point 3 above.

I think it was boiling in the THE from memory. If that 96° was boiling liquid it would be 5.2%, vapour would be 39.5%. I had a bit of both so 22% might be about right.
Edwin thought boiling in the THE was a good thing. I was going for just before. Why is 50° the right temp and where did you get 64% from?

What diameter is your column?

It’s all just 2” dairy tube so I guess 47.6mm ID

Edwins table a few posts up seemed like the start of something cool but probably isn't relevant if your preheating feed and adding extra cooling capacity.