Column flooding. How is it caused?

[Harley]

Hi guys,

The ultimate question here is: What causes column flooding and how can it be fixed?

1. How and why does the ABV of the boiler charge affect this?
2. How and why does the column design affect this? Consider height:diameter ratio, packing material, packing density and forced reflux.
3. How and why does the boiler energy input affect this?

If there's any other questions that I should be asking then please add them. Thanks in advance for the insights!

[Stonecutter]

If a there's any other questions that I should be asking then please add them. Thanks in advance for the insights!

I think the one question you should be asking yourself is…. “Now where the hell is that search function?”

[shadylane]

Hi guys,

The ultimate question here is: What causes column flooding and how can it be fixed?

1. How and why does the ABV of the boiler charge affect this?
2. How and why does the column design affect this? Consider height:diameter ratio, packing material, packing density and forced reflux.
3. How and why does the boiler energy input affect this?

If there's any other questions that I should be asking then please add them. Thanks in advance for the insights!

That's a bunch of questions considering the variables.

A packed column floods when vapors push upwards enough to impede or stop the falling reflux.
To avoid flooding when pushing the limits, there's a balance between power and reflux vs take off rate.
That's were all the variables come into play.

Also, if the pot charge is other than lowines, flooding can start with a puke.




"

[Yummyrum]

The only thing that causes reflux to fall back to the boiler is gravity whereas the vapour leaving the boiler is forced up due to the pressure of expansion it has received in the boiler .

When the upward pressure is so high that it impedes the natural flow of liquid downwards , we have a flooded state . Things that impede the flow are insufficient spaces in the packing or choke points like packing support structures or reflux centring Rings .


Once flooding has commenced , the column is no longer in the correct operating point , more vapour is entering the bottom than its condensed form can exit back to the boiler .
So two things can be done .Reduce the power to the boiler to reduce the vapour entering the column ….or…. Increase the takeoff rate so that less of the vapour is condensed as reflux .

Now the ABV of the boiler will also effect things because the surface tension of water is higher than that of alcohol so flow back to boiler is easier when it is high in alcohol but harder when it contains more water .

So you might think that flooding is more likely to happen towards the end of the run when there is less alcohol but in reality , flooding is more likely to happen at the start of the run when the boiler is producing more vapour .

[Saltbush Bill]

To much stuff going up hill and not enough going down hill.

[Salt Must Flow]

It could be something as simple as the packing is too tight. It could be caused by a screen that people often install to support the packing (screens cause restriction and can cause flooding).

1. What packing you are using?
2. Are you using any screens to support your packing?
3. What diameter is your column?
4. How many watts are you running at?

[ecir54]

power vs velocity speed is the equation per the design, salute.

[Harley]

power vs velocity speed is the equation per the design, salute.

Can you please explain what you mean by velocity speed - is this the speed at which the vapour travels up the column? If so, how is this controlled?

[Harley]

It could be something as simple as the packing is too tight. It could be caused by a screen that people often install to support the packing (screens cause restriction and can cause flooding).

1. What packing you are using?
2. Are you using any screens to support your packing?
3. What diameter is your column?
4. How many watts are you running at?

1. SS scrubs. These have been squashed in.
2. No.
3. 50(D) x 900mm (H) column.
4. The watts are variable depending on what the column doesn't flood at. I try to run this as high as possible so that I'm getting the maximum amount of reflux, then control the off-take (reflux ratio) with a valve.
(5.)The low wines in the boiler are 50%ABV. I understand that this should be 40% but the liquid isn't flammable at room temperature and if it's a higher ABV then I require less watts to evaporate it. I think this is contributing due to the picture:

[shadylane]

Many times, flooding is due to the restriction caused by what's used to hold the packing up.
Ya have to look at the big picture.

[Sporacle]

(5.)The low wines in the boiler are 50%ABV. I understand that this should be 40% but the liquid isn't flammable at room temperature and if it's a higher ABV then I require less watts to evaporate it. I think this is contributing due to the picture:

But you are heating it

[Yummyrum]

So what power are you running it at ?

I have similar setup . 2” column just under a metre long :
Stanless scrubbers . Nothing holding them in at the bottom .
I have a 2400w element and most of the time I can run it flat out . Occasionally it will start to flood and I have to turn the power down a smidgein to stop it .

And I run 30% abv in the boiler . Incidentally , you are better off running lower abv … circa 25-30% than 40% as it helps with the tails separation .

Don’t run 50% …. It’s pointless and potentially dangerous .

[Saltbush Bill]

The low wines in the boiler are 50%ABV.

As above, there is no good reason to run low wines of that ABV in the boiler, and regardless of what you might think it is dangerous.
No one on this forum is going to condone running that sort of high abv.
I'll leave it to you to search the forum to find out why and what can go wrong.
When running a packed column you are infact better off to run a lower ABV of between 25-30% as the water used to dilute the low wines will act as a filter and trap more of the tails in the boiler.
Part of your flooding problem will probably also be due to the High ABV in the boiler.

[Salt Must Flow]

It's possible, if not likely that the scrubbers are packed too tight. I've used scrubbers a lot in my 3" VM and I just don't like them at all. If I loosely stuffed them in, % ABV would be low. If I packed them a little too tight, it would flood. I've teased the scrubbers out and the same would happen. I'm not saying scrubbers don't work, but they are finicky in my experience. I imagine they would be even more finicky in a smaller 2" column especially if you're operating at a high range of power.

[The Baker]

To much stuff going up hill and not enough going down hill.

Succinct.

Geoff

[Wildcats]

Too much power.

[kimbodious]

To much stuff going up hill and not enough going down hill.

Agreed! I would also suggest “ and or when the way down the hill is restricted”

[Harley]

Many times, flooding is due to the restriction caused by what's used to hold the packing up.

And I run 30% abv in the boiler . Incidentally , you are better off running lower abv … circa 25-30% than 40% as it helps with the tails separation .

Thanks Shady - that was the issue. Thanks for this info Yummy.

I've fixed the issue and also pushed the system to it's limits to find the problems. I swapped the column out for a glass one so I could observe the affect of making changes. Changes were made one at a time. Hopefully this new info will help others.

1. Try changing the ABV - I changed the low wines from 50%ABV to 30%ABV without much difference in performance. The only difference was the requirement to input more energy to achieve boil temperature.
2. Try removing the filter gasket - The 2" tri-clamp filter gasket at the bottom of the column (which was there to hold the packing in place) was causing the flooding issue. I noticed flooding was always originating from the bottom of the column. This was even occurring when running at 750W. I think this is because it could create a solid layer of condensed liquid, which would then lead to burping.
3. Try creating flooding due to high energy - I replaced the filter gasket with a stainless scrub to hold the packing in place and slowly ramped up the still from 1kW to 3.5kW. Flooding was now caused at the top of the still where the condenser is. This was because condensate was collecting at the top, perforated, collection cone; however, there was so much vapour moving upward that it was preventing the perforations from draining the condensate.
4. Try creating flooding due to dense packing - I replaced all the stainless scrubs with dense, spiral prismatic packing (SPP) and extended the column by 25% (1100m, 2" column). The column now has three copper scrubs at the top, SPP, then one stainless scrub at the bottom to hold in the packing. The column would now start to flood toward the top of the column where the packing transitioned from copper to SPP. The flooding was occurring at 2.3kW, but it found a happy ground at 2kW - I think this change in medium (from copper scrub to SPP) lends credit to the problem of the filter gasket.

The column is now happily running and creating 96%ABV neutral spirit. Thanks for the help everyone. Let me know if you have any questions about my findings.

[kimbodious]

Great observations, should be a huge help for people with column flooding problems!