stripping with packing

[eternalfrost]

i was just thinking about this today, and i dont have a good answer so wondering if anyone else does

it is conventional wisdom round here to take all the packing out of your column when you do a stripping run. the idea being to just run it through as fast as you can the first time around. now i am not questioning the strip/spirit method as that works wonderfully and make perfect sense (hosing the muddy dogg off inside before you bring him into the tub to scrub behind his ears)

but taking the packing out dosent make any sense to me once i sit down and think about it. given a constant wash, there are only two things that govern the output of your system. the heat input and heat-loss/reflux (heatloss causes reflux. i.e. condensation that ends up back in the boiler and takes up more heat to re vaporize)

so assuming a perfectally insulated column (mine is pretty damn close to this) reflux is a null point. 100% of what is vaporized reaches the output tube on the first trip.

so whatever path the vapor takes, wether there is packing or not, is a moot point. if you want to get super-technical it will slow you down a tiny bit since it will suck up some energy to get the extra copper mass up to temperature.
but once we are in equilibrium it shouldnt matter one bit.

the copper packing isnt what causes reflux in a column. it is the liquid being returned back into the top of the column from the head. the mesh simply catches this and gives it a place to mingle with the hotter vapors and re-vaporize.

anyways, i guess its not a big deal. i guess ill just have to try it out my next time around. i guess im more interested in discussing theory rather then the 30 seconds it will save me to leave the mesh in.

[eternalfrost]

i guess the only thing i can think of is to avoid accidental puking into your mesh creating a mess?

[Master-Peter]

From my (still newbie) point of understanding, the extra surface of the packing makes most of the reflux. So as long as you have packing you have at least some reflux or refractionating or whatever, because of the extra surface. On a stripping run you dont want this for what comes out is high abv. enough for a second run and you want it fast ...

Just my understanding from reading and figuring out. Might be bullshit ...

Cheers Peter

[eternalfrost]

yes that is the notion most people seem to have but im trying to explain that is just not possibly true...

reflux=vapor condensing then eventually being re-vaporized before returning to the main boiler.

in order for a vapor to condense (or any state change for that matter) heat must be exchanged. vapor contains more energy then liquid. even at the same temperature. period. basic thermodynamics and chemistry. to condense you must give this extra energy away to fall into the liquid state.

after equilibrium all the copper (even the sides assuming insulation) will be the same temp as the vapor. therefore no energy transfer, therefore no phase changes,no condensation on the mesh. therefore no added reflux.

i realize this isnt a big issue in practice. but i think it underlines many of the big misconceptions people have about the fundamentals of how distilling actually works.
thermodynamics - phase changes. chemistry - partial pressures

[eternalfrost]

as an example:

putting a sponge(lots of surface area) in a humid room wont result in anything...
but a cold glass of water (or a cold anything. what matters is that there is a temperature difference between the air) and liquid from the air condenses to it.

an extreme example is your freezer. every time you open the door some moist air mixes in. this moisture condenses to the sides and the temperature difference is great enough that it even goes through another phase changes and freezes making those pesky ice crystals the build up over time.

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bottom line, surface area dosent do jack with out temperature differences. in normal reflux mode, the dribbling back down the column is COLDER then the vapor.
the mesh simply soaks up this liquid and gives it a place to hang out and wait for the hot rising vapors to re-boil it. rather then simply falling stright back into the boiler and being diluted.

[pintoshine]

It seems you and I are in the minority about the insulated column concept. Like you I believe the temperature differential and heat radiation from the column itself is an important part of the refluxing.
I started a huge argument about this once upon a time.
http://homedistiller.org/forum/viewtopi ... n#p6733450 has it somewhere.
But anyway, I resorted to just doing stripping in a pot still with a good condenser.

Are you using your VM or LM?
LM strips pretty good if you have a reasonably good sized takeoff.

[Dnderhead]

I do not run a column often but when I do, I do not insulate ,tried it once. did not work as well.

[eternalfrost]

pinto - i have a LM and only a LM at the moment. it works great for stripping but i would for sure use a pot if i had one (when i get one )

just to be clear i DO remove my packing on my stripping runs. and not saying there is an advantage to leaving it in. but just trying to point out and discuss what i see to be flaws in the status-quo logic

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as for insulating a reflux column i am 100% certain it provides a more stable and efficient run. at least according to the theory. I cant say that i have done extensive testing with/out so there might be some quirky real-world things that makes it better to tun with it naked.

but i have had multiple in depth discussions with my physics and chemistry professors and they agree. and have given me some very lengthy explanations
the heart of a column is separation based on differences in latent heat(and boiling points) of different compounds. the temp gradient is created by the heat source at the boiler and the heat sink at the top condenser. NOT by loosing heat out the side as you travel up. that just creates imbalance between the sides and center giving poorer results. and also leaves you vulnerable to wind gusts etc.

[Thirsty Bob]

Eternal:

Great thread, and in my limited, but expanding understanding, I agree, as long as you can capture 100% of the condensate above the column, otherwise you are sucking out energy using the condensor and then adding energy back in as the reflux flows back into the column and is re-heated. The packing itself doesn't and can't consume energy after equilibrium. Most slant plate designs can't capture 100% reflux.

Eternal and Pint.

I agree about insulation. It seems to me that what a column is all about is a temperature gradient where the top of the boiler is ~100 C and the takeoff/condensation/thermometer point is around 75, give or take. Insulation is all about keeping the energy in to effect the phase change.

Unless the boiler is pressurized, god forbid, the vapour going into the neck will never exceed 100 C, so getting a temperature of 75 at the top is determined by how much energy the boiler is putting in, and how well the boiler and column are insulated. The boiler is a heat source, everything else is a heat sink.

Considering it is about -30 C (-22 F) here, we have a fundamental understanding of entropy and insulation. If I do it right, I should be able to do a long, low run with no increase in my horrendous heating bill.

I'm definitely not lecturing here, this is just my view. from what I've learned from this great site. I look forward to any corrections.

Bob

[eternalfrost]

otherwise you are sucking out energy using the condensor and then adding energy back in as the reflux flows back into the column and is re-heated.

this is correct and exactly what we want. it IS inefficient but necessary to produce azeotrope purities. idealy you will have a tall enough column that azeotrope is reached WITHOUT reflux

The packing itself doesn't and can't consume energy after equilibrium.

correct, the packing merely gives the reflux liquid a place to hang out before being re-vaporized. it transfers heat energy from the rising vapors into the vaporizing liquids

Most slant plate designs can't capture 100% reflux.
this is INcorrect... ALL slant plates can capture 100% reflux. simply completely shut the takeoff valve. everything refluxed, nothing collected

I agree about insulation. It seems to me that what a column is all about is a temperature gradient where the top of the boiler is ~100 C and the takeoff/condensation/thermometer point is around 75, give or take.
this is a VERY important concept!! it is absolutely true and also applies to the entire column. at equilibrium, each height in the column will have its own special temperature. this temperature will always remain constant. for imagine if some aberrant 'gust' of extra vapor were to come up the column, it would enter a region of cooler temps and condense, transferring its energy to the liquid in waiting in this region which would vaporize and carry away the extra energy.

the system is self-damping. it WANTS to remain stable. we should do all we can to eliminate any driving forces

the vapor going into the neck will never exceed 100 C,
exactly correct, the same as above

The boiler is a heat source, everything else is a heat sink.
exactly. ideally the only heat sink should be the condenser, above the take off plates. any other heat sink only robs you off power reducing the efficiency of the system and costing you money

with no increase in my horrendous heating bill.
bingo. insulation is HUGE. even in pot stills, especially in the boiler

I look forward to any corrections.
I would say you are pretty much on the ball here...know whats going on more then alot of people

Bob

[Thirsty Bob]

Eternal:

Thanks for taking the time to reply so completely. I appreciate the feedback and confirmation.

I do take exception on one point (the only one you disagreed with LOL!)

"Most slant plate designs can't capture 100% reflux."
"this is INcorrect... ALL slant plates can capture 100% reflux. simply completely shut the takeoff valve. everything refluxed, nothing collected"

Perhaps I erred in saying "most" but the slant plate designs I have seen operate on a "catch as catch can basis". Obviously, a slant plate that captures all condensate falling, blocks the column, which also blocks vapour rising. The Boka design in the home page section is an example of this.

So, while I was off-base saying "most can't", I suggest you were equally off-base saying "ALL can".

Cheers,

Bob

[punkin]

Eternal:

Thanks for taking the time to reply so completely. I appreciate the feedback and confirmation.

I do take exception on one point (the only one you disagreed with LOL!)

"Most slant plate designs can't capture 100% reflux."
"this is INcorrect... ALL slant plates can capture 100% reflux. simply completely shut the takeoff valve. everything refluxed, nothing collected"

Perhaps I erred in saying "most" but the slant plate designs I have seen operate on a "catch as catch can basis". Obviously, a slant plate that captures all condensate falling, blocks the column, which also blocks vapour rising. The Boka design in the home page section is an example of this.

So, while I was off-base saying "most can't", I suggest you were equally off-base saying "ALL can".

Cheers,

Bob

Seems to me you two are just talking at cross purposes on this point.

I believe what Bob's trying to say is 'Most slant plates cant capture 100% OF THE reflux' for running in stripping mode.

And i believewhat ef is trying to say is 'All slant plates can RUN AT 100% reflux' in reflux mode.

[Thirsty Bob]

Punkin:

You are 100% bang on. The key word is "capture". Eternal misunderstood my point, as you noticed, and I misread his reply.

Good catch!

[Lowerarchy]

Eternal:


Perhaps I erred in saying "most" but the slant plate designs I have seen operate on a "catch as catch can basis". Obviously, a slant plate that captures all condensate falling, blocks the column, which also blocks vapour rising. The Boka design in the home page section is an example of this.

So, while I was off-base saying "most can't", I suggest you were equally off-base saying "ALL can".

Cheers,

Bob

As I understand it returning condensate won't block the column because an amount of liquid is smaller in volume than its vapour equivalent. Vapour velocity increases where it meets the return stream, but it'll still get through.

Of course, there's the whole other thing that strong ETOH sticks to surfaces. Not sure what the technical name for that is but I've noticed that it'll run on surfaces that water would drop right off, which seems to be a problem for many slanted-plate designs, especially the classic tab on the bottom plate of the Bok mini.

[Thirsty Bob]

Lowerarchy:

I wasn't talking about the condensate blocking the column, I was talking about the slant plate.

I was just pointing out a limitation of the slant plate design, that it couldn't capture 100% unless it covered 100% of the column, which would be silly 'cos nothing could get past it in either direction.

As for condensate blocking rising vapour, I suspect the only place that might happen would be in the packing.

Bob

[Freedave]

thirstybob, I've read this thread a few times now and still don't understand what you mean by

"I wasn't talking about the condensate blocking the column, I was talking about the slant plate.
I was just pointing out a limitation of the slant plate design, that it couldn't capture 100% unless it covered 100% of the column, which would be silly 'cos nothing could get past it in either direction."

As i understand my bokakob slant plate, if i had the take off valve full open , i could take off 100% of the condensate. only prob would be if the inside dia of my take off tube was not capable of passing the higher flow rate. which i think it could.

what am i missing? am i alone?

[eternalfrost]

I was just pointing out a limitation of the slant plate design, that it couldn't capture 100% unless it covered 100% of the column, which would be silly 'cos nothing could get past it in either direction.

i hope we re not simply misunderstanding words here again... but a slant plate DOES cover 100% of the column. the whole point of the plates is to let vapors raise through and catch the liquid falling down.

now a vapor dosent realy care what path it takes, so it dosent even notice the plates really. but liquid does care about the path. it falls straight back down off the condenser. the plates overlap so from the distillate 'rain' the column is completely covered. that is, if you were to open your valve wide enough, zero condensate would return to the column. in other words 0% reflux. it can also go all the way to 100% reflux by completely closing the valve, then none is taken off thus all returned to the column.

im with freedave, a bok can do anything from 0-100% reflux. only trouble with it is it takes very very tiny adjustments in the needle valve to change this, making it hard to control. which is the main reason people like VM

[Thirsty Bob]

Dave:

I think you may be reading more into what I said. Several posts ago, there was a misunderstanding about capturing condensate when doing a stripping run. If 100% of the condensate is not captured before it returns to the column, then you are wasting energy, that's all. The original question was whether there is any point in removing packing during a stripping run.

As for the capture, depending on the design, I'm just suggesting that there is a greater chance of losing condensate due to the much higher flow rates of a stripping run; to overflow, splashing, etc.

Second, depending on how aggressive you are with the cooling water, the cool condensate will lower the temperature of the slant plates and provide a surface for the vapour to condense on the underside of the plates as the vapour wends it's way up the column and around the plates. Copper is a very good conductor of heat,. At least 50% of the vapour will come into contact with both plates, depending on their size, i.e. how far across the column they extend. The slope could also be a factor, but how much would be guessing on my part.

Some slanted plate designs probably work quite well, but the only way to know for sure would be to make the column out of glass, like snuffy http://homedistiller.org/forum/viewtopi ... =17&t=8924.

All in all, probably not a big deal unless you are technically and energy anal like me.

Bob

[eternalfrost]

the cool condensate will lower the temperature of the slant plates and provide a surface for the vapour to condense on the underside of the plates as the vapour wends it's way up the column and around the plates.

that is a very good point i never thought of before. it wouldnt matter if there was insulation or not

but i would wager the effect is pretty small. at least on mine, the condensate come out HOT if you do not use the liebig. the takeoff tube above the liebig is hot enough to burn you if you touch it. so the liquid cant carry away much heat from the vapor and condensing it on the plates

excellent insight tho bob

Some slanted plate designs probably work quite well

i can say for sure that mine works great for stripping. the only thing i am a tad worried is that the small 1/4" takeoff may be getting flooded and forcing condensate to be lost by overflow reflux.

will be making a pot head for my boiler soon but need some more spare cash. i need a pretty monster liebig to handle my 5500W element stripping

[Freedave]

thanks for the clarification. i am in agreement and have renewed confidence in my understanding.

also, in relation to this "i can say for sure that mine works great for stripping. the only thing i am a tad worried is that the small 1/4" takeoff may be getting flooded and forcing condensate to be lost by overflow reflux."

flooding was not my worry, but rather, minor flow irregularities.
this is why i changed out my 1/4" take off line too 3/8". after the valve that is. i know it would be better if i changed all of it but "post valve" seemed to help even out the flow.

[Thirsty Bob]

but i would wager the effect is pretty small. at least on mine, the condensate come out HOT if you do not use the liebig. the takeoff tube above the liebig is hot enough to burn you if you touch it. so the liquid cant carry away much heat from the vapor and condensing it on the plates

I'm not so sure about that, but it's more of a question than a statement and I'm way to lazy to do any thermo calcs.

My thinking is this:

Because it is a condensate, it is by definition cooler than the vapour, so what appears hot to you can still carry away heat, particularly with the higher flow rates in a stripping run.
If I remember right, the higher the vapour density, the less temperature differential you need to form condensation. A glass of ice water will show condensation at 99% RH but maybe not at 20% RH, depending on ambient temperature. At the top of the column, the vapour density is very high.

Also, because the collection point has the greatest concentration of condensate, my guess is that the entire column has a noticeable temperature gradient shift at that point, providing another surface for condensation.

Now, all I have to do is track down a thermal imaging camera. Hmmm.......

[eternalfrost]

Because it is a condensate, it is by definition cooler than the vapour

that isnt true, two different states can have the same temperature. for example, in a glass of ice water both the ice and the water are 0C. or look up "triple point" in chemistry

but i agree that in this case the condensate will be cooler then the vapor. not by virtue of it being a liquid, but because it has spent some time on the cool condenser.

just as a side note,an IDEAL condenser however would NOT produce condensate that was cooler then the vapor. it would simply remove just enough energy to allow the phase change. any cooling past that is just further heating your coolant. also idealy, the liquid would jump off the condenser as soon as it condensed as to not transfer any heat further )
ideally, your coolant will exit your condenser at 171F (or whatever the vapor temp is at that time). this means that the coolant is 'saturated' and cant absorb anymore energy (because its the same temp as the vapor) anything cooler and you are wasting water.

i agree with your theory, but there are a few reasons i believe the plate-condensation isnt a big deal in real life.
-i run my coolant water as slow as it can go and not have any vapor escape the top, to conserve because i dont have a circulating system. my water comes out nearly steaming.
-the water runs through the final cooling liebig first then the top condenser. if you feel the water input on the top condenser, it is already quite hot from the liebeg. this is the coldest the condensate could possibly ever get. (it cant get colder then the coil itself)
-the instant it becomes liquid, it is still at the vapor temp. then cools down for the ammount of time it is in contact with the coil by newtons cooling law. now the time of contact, as well as the temp difference between the liquid and coil is pretty small, so the actual cooling effect will be pretty minimal


im for sure not doubting your idea bob, just its practicality in real life. but again this has turned out to be a pretty esoteric thread which is snubbing its nose at the real world and wallowing in theory so keep the good ideas coming bob

[Thirsty Bob]

that isnt true, two different states can have the same temperature. for example, in a glass of ice water both the ice and the water are 0C. or look up "triple point" in chemistry

Doh! You got me there. Yep, triple point, latent heat et al. In theory

just as a side note,an IDEAL condenser however would NOT produce condensate that was cooler then the vapor. it would simply remove just enough energy to allow the phase change. any cooling past that is just further heating your coolant.

True, but because almost all of the coil will be below that ideal (exit) temperature, there will be a lot of condensate way below the condensation temperature, with some re-heating as it falls through the vapour to the catch point. One way to avoid that is to have the coolant enter at temperature just slightly below the condensing temp and run it through at some rate waaay above the Reynolds number, with silly pressure. Condensate dwell time would have a minimal effect. Possible but not practical.

i agree with your theory, but there are a few reasons i believe the plate-condensation isnt a big deal in real life.

Probably not, but it forces me to understand what is going on in the process and strengthens my understanding. As Freedave pointed out, threads like this allow us to clarify and/or reinforce our knowledge. Fourth and fifth order terms likely don't matter much, but the trick is to determine if they are fifth order or second order. Before I started reading this site, I didn't properly understand how a fractionating column worked. I probably don't even now.

this has turned out to be a pretty esoteric thread

I like esoteric for it's own sake but it also has real value for me, and this thread has me rethinking my still design, particularly the condensor, and that's what it's all about right now. I appreciate the feedback.

Bob

[Thirsty Bob]

Because it is a condensate, it is by definition cooler than the vapour

that isnt true, two different states can have the same temperature. for example, in a glass of ice water both the ice and the water are 0C. or look up "triple point" in chemistry

I have re-read this post, for my own benefit and understanding the error of my ways. That said, just for shits and giggles:

As I said before, you are right, but to get even more technical, the condensate is not cooler per se, but it does contain less energy, so it does have the capacity to absorb energy without raising its temperature about the phase change.

So, in a perhaps weak attempt to strengthen my position, by saying "cooler" I meant having less energy.

Shit! This making me remember my thermodynamics classes, which I hated.

Final point, this is not a pissing contest, I just really enjoy the discussion.

Bob

[eternalfrost]

i enjoy it to bob no worries heh

as for the energy bit, i comletely agree with you. liquid will always contain less thermal energy then its vapor.

however, in this case i am not sure if it matters. because if i remember correctly, thermal energy flows from high TEMPERATURES to low, not from high energies to low.
so assuming the condensate is at the vapor temp, no thermal exchange will happen at all


for example imagine a perfectally insullated thermos/dewar. fill it with ice and water and the ice will melt (absorbing energy from the warmer water) and the water will cool. untill the water reaches thermal equlibrium with the ice, that is they are both 0C. at this point everything stops and will just sit there forever. even though 1g of ice has less thermal energy then 1g of the water.

-----

another good example on the difference between thermal energy and temperature is why we use water to cool our condensers. it takes much more energy to raise water by 1C then to raise the same amount of air the same degree. it WOULD be possible to run a coil by blowing compressed air through it but you would need much much more air to remove the same amount of energy. simply because it takes less energy to 'saturate' the air compared to water, once the coolant reaches the temp of the vapor, it can no longer absorb any enegry

[Thirsty Bob]

however, in this case i am not sure if it matters. because if i remember correctly, thermal energy flows from high TEMPERATURES to low, not from high energies to low.
so assuming the condensate is at the vapor temp, no thermal exchange will happen at all

Aarrghhh! Right again.!

I think I'll go ponder the wave/particle duality now. Something simpler