Diameter of column after the reflux condenser?

[tiramisu]

Seeking knowledge from my betterers....

This is something I have been wondering about for quite a while.
Not being any kind of enginerd or HVAC magician I mostly just copy what I see and am happy with what works...

I have noticed that most of the reflux stills columns that I have seen reduce the column diameter after the reflux condenser.

Does this result in result in improved(?)/increased velocity flow to the product condenser and is this for some reason a gooder thing?

OR

Is this simply a cost savings where a 2" product condenser has no problem keeping up with a 3 or 4" reflux condenser
so don't bother wasting your money on bigger pipes?

Thanks in advance,
t

[Salt Must Flow]

I read this a few times and I'm not sure exactly what you are asking. When you say "after the reflux condenser", do you mean at the vapor takeoff?

[juana_b]

I'm having trouble pinpointing the question as well.
But when refluxing, you're only sending a percentage of the vapor from the boiler to lyne arm. The rest is knocked down by the relux condenser. Not like a pot still where 100% is going there.

[ThomasBrewer]

He's referring to this situation on most CM stills. They typically go from a 3-4" column to a 2" vapor path.

The answer is intrinsic efficiency of your dollar. There's no need for anything larger since your reflux ratio is ideally more than 12:1.

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[Yummyrum]

He's referring to this situation on most CM stills. They typically go from a 3-4" column to a 2" vapor path.

The answer is intrinsic efficiency of your dollar. There's no need for anything larger since your reflux ratio is ideally more than 12:1.


45288.png

Agree with everything there ThomasBrewer.

Also another case of using the wrong terminology creating confusion . On a CM , we need to refer to the RC as a Deflagmator , then everyone knows what you are talking about .

Not having a go at you personally tiramisu , its a common problem here.

And yes , a 4” Product condenser and lyne are would be totally wasted on a 4” CM .Some with big pockets have done , but not needed……even if one wanted to crank up and run in Pot mode :

[tiramisu]

Thanks for the corrections and the answer. Yes that was the question. Naming of names is often a challenge. I have been educated.

[RC Al]

There can be a downside to using small diameter in the wrong place.

IF it causes a restriction, it increases pressure in the boiler, thereby increasing the boiling point of the contents, this means that there is less seperation of the fractions going on, ie more smearing.

In the real world if your boiler is doing its thing 0.1 of a degree higher than it would have because of one thing, your never going to know. Stack up a number of them and you might pick a difference in operation - power use and reflux required vs other setups to achieve the same flavour purity and abv

[Ben]

IF it causes a restriction, it increases pressure in the boiler, thereby increasing the boiling point of the contents, this means that there is less seperation of the fractions going on, ie more smearing.

Thats a big if, and a big assumption on smearing.

The if: If you study the ideal gas law and Bernoulli's principle you will quickly realize you need a would need a huge decrease in orifice size to create an increase in pressure. Gasses are readily compressible, but the flow speed can come up past supersonic.

There is always pressure in a column still. This has been discussed.

The smearing: The effect of pressurization will increase separation of the distillation constituents. It also increases throughput. It will require more power, and increase the heat in the boiler but none of the chemicals we are concerned with taking off will decompose at the heats we are talking about.

There is a great peer reviewed paper on this here: https://www.researchgate.net/publicatio ... throughput

[Tōtōchtin]

@Yummyrum
" On a CM , we need to refer to the RC as a Deflagmator "
I thought a deflagmator was a water jacket surrounding a single vapor tube. If I put a shotgun condenser there would that then be called a deflagmator?
JK

[Yummyrum]

@Yummyrum
" On a CM , we need to refer to the RC as a Deflagmator "
I thought a deflagmator was a water jacket surrounding a single vapor tube. If I put a shotgun condenser there would that then be called a deflagmator?
JK

Yes is would . A deflagmator is a partial condenser .How it is built , whether it be a water jacket around a single tube , several tubes running through a water jacket ( a shotgun style) or a single tube with a coil of coolant flowing through it , it is still a deflagmator .

It is a partial condenser because it partially lets some vapour through while condensing rest .Sure it can be run so it is 100% or fully condensing during equalising and it could be argued that at that moment it is a Reflux condenser.

Partial condensers or Deflagmators as they are known , a specific to Coolant management stills .

Reflux condensers refer to condensers who’s sole purpose is to fully condense all vapour as reflux like would be the case in a Liquid or Vapour management still .

[RC Al]

Ben, the searches I did on pressure came back with results similar to "When pressure increases, relative volatility between the components will decrease". You did qualify with chemicals we are concerned with, but clearer cuts is clearer cuts?

I know the pressure in a home sized booze still is considered negligible generally, but some of us use steam so its not always next to nothing.

I feel that pressure and restriction is pretty much the same thing in this discussions context? If restrictions didn't matter, why isnt every riser on a bubble cap plate fed by a 1/2" or smaller pipe regardless of cap size? Its only the slots that matter? I think not. Any time the vapour changes speed its loosing energy, if you have to push through a restriction it takes energy to compress the vavour.

The more energy you point at the boiler the faster the vapour and it isn't as seperated as if you used less energy, thats part of stilling 101?

I would love a better understanding of Bernoulli's work, I'll try to check it out more thoroughly one day soon, but in the meantime i really dont have enough meaningful info to plug through the equations in that link. perhaps you could work through an example or two for us?

[Ben]

Ben, the searches I did on pressure came back with results similar to "When pressure increases, relative volatility between the components will decrease". You did qualify with chemicals we are concerned with, but clearer cuts is clearer cuts?

I know the pressure in a home sized booze still is considered negligible generally, but some of us use steam so its not always next to nothing.

I feel that pressure and restriction is pretty much the same thing in this discussions context? If restrictions didn't matter, why isnt every riser on a bubble cap plate fed by a 1/2" or smaller pipe regardless of cap size? Its only the slots that matter? I think not. Any time the vapour changes speed its loosing energy, if you have to push through a restriction it takes energy to compress the vavour.

The more energy you point at the boiler the faster the vapour and it isn't as seperated as if you used less energy, thats part of stilling 101?

I would love a better understanding of Bernoulli's work, I'll try to check it out more thoroughly one day soon, but in the meantime i really dont have enough meaningful info to plug through the equations in that link. perhaps you could work through an example or two for us?

Your right on it, you just need to tie it all together neatly. For now lets set the energy losses due to vapor speed to the side, they are (relatively) small and the math and physics are kind of advanced.

Where you seem to be a bit off is where you are talking about one instance where you are increasing vapor speed due to an orifice (or restriction) and another line where you are talking about increasing vapor pressure due to a restriction. The same thing is actually occurring in both cases, and neither is mutually exclusive. I also phrased my last response poorly, I should have said you can have a big increase in vapor speed through the column without a big increase in pressure. Lets look at ideal gas law to start.

PV=nRT

P= pressure
V= Volume
n= number of moles (of the substances)
R= Gas constant
T= Temp (if you are going to work the problem for a solution it needs to be in °Kelvin)

Look at the equation as a relationship rather than some formula with a bunch of irritating and confusing numbers. R is just a constant, you can ignore it for this purpose, and to simplify it a little further you can think of n as a constant since we are going to act like the quantity of vapor molecules is the same.

That leaves you with PV=T (often called a PVT calculation)

So the relationship is:
if pressure increases, volume has to decrease and/or temp has to increase
If volume increases pressure decreases and/or temp increases
if temp increases pressure increases and/or volume increases.

It is really important to recognize none of these are mutually exclusive, usually if you change one both of the others change.

Bernoulli is a lot more complex, and I don't know what your foundation is. A quick summary: "Bernoulli's principle: Within a horizontal flow of fluid, points of higher fluid speed will have less pressure than points of slower fluid speed."

Think of it like this: the area that is before the restriction is going to be high pressure, the area at the restriction is going to be low pressure (venturi effect is a little more relatable).

How high those pressures are, and how fast we are going to accelerate the gasses is the question on the table. Remember how hydraulic force works, a small amount of pressure over a large area can exert a great pressure on a small area. It seems like the rule of thumb on plates is something like 5% open area (that number seems low, it was the thing that came up on a site search), which represents a 20x hydraulic advantage.

So the answer is "it depends", it depends on the size of the feed area, and the restriction. We are creating a seemingly significant restriction when we go from the liquid surface in the keg to a 2" diameter column. 5500w on a stripping run seems common on this site, and we don't seem to notice pressure from it, But we do see a big increase in vapor speed.

On the separation, and my claim that increased pressure improves separation of the constituents. You are correct in saying "When pressure increases, relative volatility between the components will decrease" but think of all the craziness I just spit all over the screen... As pressure increases velocity increases (PVT), the relative pressure difference between the low pressure side of the orifice and the area inside the orifice increase (Bernoulli), my assumption is the mingling of the vapor and the next fluid bed, and most of the energy transfer of the plate are occurring at a low pressure area (Venturi) the fluid bed is suspended and trying to fall back through the holes in a perf plate system, in a bubble plate system the bubble cap slots are smaller than the feed area, making them an orifice.

My intuition (could be wrong) is this has a much greater effect (especially on home scale where pressures are low and speeds are high) than the pressure inside the boiler.

So why does the bigger column allow us to process faster? It has nothing to do with pressure, its vapor speed (exposure time to condensers, fluid beds, etc). Same deal with bubble caps, you want to be able to control the speed the vapor is going through them, it helps keep the fluid bed (relatively) calm. Stilling 101 is absolutely correct.


Also, remember with steam injection that as the water is transferring heat into the still the steam is contracting in size dramatically (PV=nRT, and phase change), the pressures might not be as high in the still as you would expect.

[cob]

Water is 1700 times smaller than uncompressed steam.