A Quick Way to Find Reflux Ratio

[haggy]

In doing calculations for a reflux column, I have found a quick way to find the Reflux Ratio ( RR ).

All you need to know are these three parameter values:

1. Pot ABV ( % )
2. Pot Wattage ( KW )
3. Distillate Flow Rate, D ( L/hr )

Step 1
You know the pot starting ABV and the KW you are running at, and you measure the distillate flow rate D early in the run. Then go to this chart to get the Vapor Flow up the column ( V ) in L/hr.

Step 2
From the V value - subtract the Distillate flow D to get the Liquid flow down the column L in L/hr.
L = V - D

Step 3
Divide L by D to get the Reflux Ratio RR;
RR = L/D


Example:
The pot charge is 30% ABV and pot heating is set at 3000 watts ( 3 KW) after heads are taken. You measure the distillate flow D at 2 L/hr at the start of hearts. You are still probably close to 30% ABV in the pot.

So, from the chart, we get V = 8 L/hr.
So, L = V - D = 8 - 2 = 6 L/hr
And, RR = L/D = 6/2 = 3


During the run:
Now, the pot ABV % will change during the run, so it is best to do this just after the heads are taken. During a run, from an accurate pot temperature measurement you can get an estimate of the ABV %, so use that ABV % in the chart to lookup the new V value and the possible change in RR depending on the D value. Here is a Pot ABV % vs Pot Temperature chart for getting RR later in the run.

You can get a hard copy of the above charts by clicking on them, then do a Control-P to print them out. Keep the copies by your still and a quick RR can be done whenever you measure the distillate rate and estimate the pot ABV %.

So, I hope many reflux column distillers try this method and report back on its accuracy and use. Of course, the product ABV% is the most important parameter, but this may help you get the result you want.


For Advanced Study
A side benefit of the two charts could be to determine the pot power ( watts ) to set during a run to keep V constant. So, you find the V rate at 8 L/hr early in the run ( at 3KW ). Then, later in the run, the pot does down from 30% ABV to 15% ABV as seen from the pot temperature of 90.6 C. So you go to the first chart and see that at 15% ABV and V at 8 L/hr the power would need to be 4.5 KW. Doing this at several intervals, say every 5% change in ABV could let you vary the power to keep RR constant keeping the D at the initial value, 2 L/hr.

Anybody understand this advanced study? Do you see it in your runs? Is it valid?

Also
Not making changes in the pot watts ( KW ) or RC settings ( to get a set D flow rate ) is done in many ( most? ) run operations. Both V and D can decrease with run time. Maybe RR stays constant or increases. You can estimate the RR with the two charts using the current values of the three parameters, Pot ABV%, KW and D.

You know the Pot wattage and KW when using an electrical heating element. But with a gas burner, you have to make your best estimate of the effective watts ( KW ) used.

[Kareltje]

Interesting!
I suppose you assume the kW are in total delivered to the fluid. I.e. there is no loss from flame to contents of the boiler. And no loss from boiler to surroundings.

[haggy]

Exactly, Kareltje
Nice to hear from you.

It is for an insulated column with no heat losses in the pot or column, using the effective pot KW. Should have mentioned that. With heat losses of say 10% in the column, the V would be 10% about less.

I calculated the vapor flow out the pot and into the column. The V flow rate in the chart is for vapor flow out the top of the column. The vapor rate is likely reduced as it travels up the column. At the top of the column the V in the chart is about 86% of the flow out the pot into the column for a 40% ABV wash. The V in the chart for a 10% wash is about 58% of the flow out the pot. These ratios may be ok, but need to be further evaluated.

Edited 3/26/203
haggy

[drmiller100]

A couple of things. Vapor Velocity will increase as you go up the column as you will have more etoh the higher you go and water has about 3 times the latent heat of vaporization as etoh.
I think vapor velocity is meaningless.

I'm also a firm believer some columns are more efficient than others and your equation does not account for that. For instance a 32 plate column could easily make 95 percent. A one plate columnn will never make 95 percent.
Because of this the abv of the product will probably need to be included.

I guess I also wonder why reflux ratio matters. Column efficiency could certainly matter. Flavor could certainly Matter.

The theoretical minimum reflux ratio for a given wash abv vs product abv can be calculated.

[haggy]

drmiller100,

That is a good point on vapor flow up the column. It should increase because of more ethanol and the big difference in latent heat of alcohol and water.

That is what the above chart says. At a constant KW, the vapor flow is higher as % ABV increases. But the lines get closer together, and above 40% ABV, there is less a difference in the vapor flow rate. And in most all columns, the %ABV is above 50% on the first plate and above 70% ( and so on ) from there and up the column. So, there is less a difference in the vapor flow rate after the first plate. My last paragraph referred to flow out the pot and must have used a different basis for the calculation.

The reflux ratio is important. It helps determines the final product %ABV. A higher value will get higher product % ABV. But, it may be less important than other factors.

The liquid reflux flow rate and distillate flow rate are used to get the reflux ratio. The liquid flow rate is determined from the vapor flow minus the distillate flow. So, knowing the vapor flow rate, or being able to estimate it does matter, it is not meaningless.

Column efficiency is also important, but that is another factor in determining the product % ABV. With weeping or flooding, column efficiency goes down. Plate spacing and entrainment also matters. Probably other things also affect efficiency. The column efficiency will also determine the final product % ABV. I did not include column efficiency in the reflux ratio calculation.

Of course one plate will never make 95% ABV. Never said it did.

The % ABV of the product is a result of the starting pot % ABV, the number of plates, the reflux ratio, and the column efficiency. We should rank these factors. Any more factors? A first look at these factors says reflux ratio less important than the others. But it is important for a low charge pot % ABV, for less than four plates, and also at the end of the hearts run.

My point was:
The % ABV of the wash in the pot is a number you know at the start. I found a way to estimate the likely reflux ratio from that value, the pot wattage you set and the distillate flow rate you set. The reflux ratio is a factor that will partly determine the product % ABV you will make. Other factors may be more important and must be considered. Thanks drmiller100 for the comment.

haggy

[drmiller100]

Again your formula can't work.

Compare one plate to 50 plates. Assume some arbitrary distillate rate, wash abv, and wattage.

One has about 100 proof and the other could have 190 proof.

the 190 is about twice the reflux ratio as the 100 proof again due latent heat of vaporization.

Vapor velocity is meaningless. Theoretical minimum reflux rate is easily calculated. If you want to have excessive reflux rate as you have nothing else to do in life feel free.

[shadylane]

I don't know the proper way of figuring reflux ratio, but here is how I guestimate it.

Start with what the boiler can produce as a potstill. Lets say 4ltrs/hr.
At the same power setting, if your reflux column has an output of 1ltr per hour.
Then the reflux ratio is 4:3 ? or is that 3:4 ?

I prefer to think of it, as 25% take off rate.
The other 75% is reflux raining down inside the column.

[kennstminet]

shadylane
Your example of 25% take off rate equals an Reflux Ration of( 1/0.25) - 1 = 3
I agree that this is a very simple way of getting a idea about RR. I use it often and I think it is close enough to reality.

[Hügelwilli]

The vapor speed is almost independent from the abv. Only the distillate speed depends a lot on the abv. The reason for this is, that the difference in volume between vapor and liquid is very high for water and much lower for ethanol.
For example vapor made with 1000 watt in a pipe with 20mm inner diameter varies only between 233 and 239 cm/sec. 239 is water steam and 233 is steam with around 88%abv.
Vapor speed depends much on the air pressure. It rises by 1% when the pressure drops by 10 hPa. 10hPa means something like 87 meters in height. An under pressure distillation at 500hPa means around twice the vapor speed compared to normal pressure.

drmiller,
what formula you use for the minimal reflux ratio? I only know very complicated ways to calculate it. That's why I am asking.

I don't know the proper way of figuring reflux ratio, but here is how I guestimate it.

Start with what the boiler can produce as a potstill. Lets say 4ltrs/hr.
At the same power setting, if your reflux column has an output of 1ltr per hour.
Then the reflux ratio is 4:3 ? or is that 3:4 ?

I prefer to think of it, as 25% take off rate.
The other 75% is reflux raining down inside the column.

The problem is that what the boiler can produce as a potstill is very different to what it can produce at a reflux still. The reflux still set at a 25% take off rate has probably much more than that 4ltrs/hr at the top of the still.

[Yummyrum]

I don't know the proper way of figuring reflux ratio, but here is how I guestimate it.

Start with what the boiler can produce as a potstill. Lets say 4ltrs/hr.
At the same power setting, if your reflux column has an output of 1ltr per hour.
Then the reflux ratio is 4:3 ? or is that 3:4 ?

I prefer to think of it, as 25% take off rate.
The other 75% is reflux raining down inside the column.

I tend to agree that this method is about as quick and easy as you can get . No need for temp, pressure or ABV readings and conversions .

When you compare pot takeoff rate to reflux takeoff rate at the same power , It is exactly as it is .

Not saying your info is wrong Haggy . Just Shadys is easier fir the less mathematical or Graph phobic types .

Haggy , I like your graph or Power verses Takeoff rate . For me , on gas that is great , as I find it hard to guestimate my equivalent Power .

[Hügelwilli]

Yummyrum,
the question is, for what use you want to find out the reflux ratio. I think, shadylane has no real use for this number, so he doesn't have to care about. But haggy wants to calculate something with it. And at the end there could be a calculated result that looks precise, because it is a number with digits, but in reality is only a guess because the calculation bases only on guesses. So perhaps at the end he calculates a plate efficiency of 110% or 50%. Both will not be true. Or perhaps he calculates 85%. This can be true. But perhaps it is only a guess? Or perhaps he calculates a HETP for his packing material which is much better or worse than the manufacturer of the packing material states. What now? Or he calculates the same HETP what the manufacturer states. But what is this worth?
Perhaps shadylane could elaborate further for what he uses his rough calculation of the reflux ratio.


haggy,
why not calculating the distillate flowrate by the distillate abv instead of the pot abv? Most distillers have a thermometer on top of their reflux still, and a good thermometer together with the air pressure gives you a precise enough value for the distillate abv for calculating together with the wattage the total flowrate at the top of the column.

The reflux ratio controls everything between a pure potstill and a high rectified reflux still. So a calculation without the reflux ratio doesn't make sense. And to rate it like for example "a bit less important than the number of plates", what does this mean? There are cases where it doesn't matter if you pull off 10 or 20% product, and there are other cases where it doesn't matter if you have 5 or 10 plates. And there are cases where you have to pull off less than 10% product to reach your goal and there are cases where 5 plates will not be enough regardless of the reflux ratio.

[haggy]

Hugelwilli,

I am glad you see the importance of the reflux ratio. I too think that it is very important. How would you rank all the factors that I mentioned in a reflux still? Maybe they are all equally important.

I calculate the reflux ratio in my thread " Plate Reflux Column Characteristics" and am confident that it is close to reality. I think you have seen some of those posts. IT IS NOT ONLY A GUESS

Why make a statement like " a calculation without the reflux ratio doesn't make sense" , if you are implying that I do that - you are wrong.

All calculations are not only a guess, there is a lot of thought and effort and time invested behind them to insure they are the best possible result. That is what I do and I think that is what you do.

Plus, I search and find a lot of posts on real still runs and compare my calculations to those real results so that I can come up with something believable.

haggy

[drmiller100]

Note. As has been pointed out my theory is based on only neutral. If you want flavor you want a lot less reflux.
In fact it seems further to me reflux ratio is even more meaningless. Finding an "efficient" packing material is certainly worthwhile but once your reflux column is "long enough" run it for the flavor you want.

From me last year............
re limits. Onelimit is you are pulling NO alcohol. In this case the liquid dripping out is the same ratio as the vapor going up.

The other limit is you are pulling MAXIMUM alcohol.

The max limit is that the stuff dripping out the bottom of the column can NEVER Have less alcohol than what is in the boiler.
So for a 10 percent wash, the drips are 10 percent at max takeoff rate at 95 percent.

For a 10 percent wash the vapor off the boiler is 50 percent alcohol, 50 percent water.

So the MAX possible efficiency is 40 percent for a 10 percent wash.

The bad news is the water takes 3 times the energy per pound as does alcohol.

[shadylane]

I think, shadylane has no real use for this number, so he doesn't have to care about....
Perhaps shadylane could elaborate further for what he uses his rough calculation of the reflux ratio.

Theory is fine and dandy.
But mathematics and formulas give me a headache, without the benefit of getting drunk.
I'd rather measure what I've got than to spend time figuring out what I might get.

[drmiller100]

I think, shadylane has no real use for this number, so he doesn't have to care about....
Perhaps shadylane could elaborate further for what he uses his rough calculation of the reflux ratio.

Theory is fine and dandy.
But mathematics and formulas give me a headache, without the benefit of getting drunk.
I'd rather measure what I've got than to spend time figuring out what I might get.

Fair enough. I get bored watching it drip. So I spent a lot of time trying different packing and columns and it always seemed for a given wattage I hit a max of distillate at neutral.
So I did the math and I was pretty close to the theoretical max

Shrugs.

[Saltbush Bill]

I'd rather measure what I've got than to spend time figuring out what I might get.

Got to agree 100%
Build a reflux still to a proven design, of a length that is proven to produce azeotrope, use packing that is proven to work, then run that still correctly, using your god given senses and there is no need for a heap of graphs and 100's of figures.
For what its worth I've built a few stills now of all types and never needed numbers or graphs to help me do so........all stills have preformed exactly as they should.
I'll take the KISS method every time,and leave this geeky stuff to those who seem to thrive on such things.

[Hügelwilli]

haggy,
what I wrote about "guessing" was mainly towards shadylane not towards you. The only thing I didn't like was that you want to rate the reflux ratio against other factors like the number of plates. This sounds a bit like asking a mathematician what's more important, subtraction or addition.
If you want to find out more about the correlation between pot abv, distillate abv, number of plates and reflux ratio, the easiest method I think is the McCabe-Thiele-method. This method is not flawless. Especially at low % reflux the results are often not plausible, at least if you also want to calculate distillate amounts. But it is the easiest method available. Perhaps the only relative easy method.

drmiller,
reflux ratio is meaningful for neutral production regarding time and energy efficiency. If you can pull product faster (less % reflux) without much loss in %abv, you can save a lot. How fast you can do it, depends on the column height, the packing, the proper wattage for the diameter and the packing and the minimal reflux ratio. Unfortunately you didn't answer my question about calculating the minimal reflux ratio.

[haggy]

Hugelwilli,

OK, thanks, glad you cleared that up.

Also, you wrote,

If you want to find out more about the correlation between pot abv, distillate abv, number of plates and reflux ratio, the easiest method I think is the McCabe-Thiele-method.

Yes, that is very true and that is what I have done already. I have not written too much about this, but I have an Excel program that calculates running time operation of a 4 plate reflux column using the McCabe-Thiele-method. All the key variables you mentioned above are included.

You can see an example of that program in this post:

Re: LM temperature photo essay
Post by haggy » Thu Mar 30, 2023 8:04 am

My other program for "Plate Reflux Column Characteristics" is also included in that post. I cross check the two programs to make sure the results are consistent. A lot of my stuff I also check with your stuff in Hobbyburning.

So, we both keep on trying to advance this great hobby.

haggy

[RC Al]

Any chance we could get an expanded version of the kw table?
I can extend some lines, but there is a small curve to it. Adding a 5% line going up to 30lph would be very cool.
Edit, for completeness add plain water?
Thanks Al

[haggy]

OK, RC Al, I can do that.

Here is an expanded version of the first chart in my first post above. The chart gives V, the vapor flow up a reflux column as it varies with KW and %ABV. Now you can go up to a 6" column (or 8"?) and get the RR the same way as explained above. You need the pot KW and pot charge %ABV and a measure the distillate rate D very early in the run. Then get V from the chart, subtract D from V to get L, and L/D is the RR.

Also, for another 2 cents, here is that same V chart but as it varies with % ABV. So you can use either chart now, whichever is most convenient.

In the next post, I will add a steam generation curve.

These charts are for V, the vapor rate up a reflux column with reflux, not for a potstill only run. I will discuss the potstill only distillate rate vs KW and %ABV next and show the difference.

haggy

[haggy]

Two ideas are described here. First the vapor flow from a pot still. Next, how to calibrate your propane gas burner.

So, what about the vapor flow from a pot still with no reflux column ( or a reflux column with no reflux ). We will estimate the distillate rate vs KW and %ABV in a pot still and show the difference vs the vapor flow V to the RC at the top of a reflux column ( LM and CM operation ).

I have three sources from which to calculate the pot vapor flow. First, the Pot Still Purity calculator by rad14701 in the HD Calculator Section. Second, the Haggy Pot Still + Thumper calculator in the HD Calculator Section. And third, in my reflux column spreadsheet when I extrapolate the RR in several steps back to zero.

Well, all three sources gave the same result ( or very close to each other ). Zero internal reflux was used in the first two cases. So we will use the simplest way, the Pot Still Purity calculator by rad in the HD Calculator Section. Anyone can go there and do this and check this.

The results are:

If you go back and check these flows with the reflux column flows, you will see that these are all higher. Probably, because of the reflux action, the reflux column flow is lower. How much lower?

The percent lower of Reflux Col vapor flow to Pot Still vapor flow depends on the % ABV of the pot. It is fairly constant over the range of KW. The ratios are:

Pot % ABV..............40%.....30%.....20%.....10%.....5%
Ratio.Reflux/Pot....0.80....0.76.....0.69....0.58....0.37


So, this is just an exercise, nothing big. BUT THERE IS SOMETHING BIG ABOUT THE CHART

For those stillers who use propane gas burners, the chart can be used to find the approximate KW you are running at and can be used to calibrate your burner.

And here is the chart for bigger gas burners, up to 12 KW:

With each pot stripping run, you know the starting ABV in the pot and you measure the initial early distillate flow rate in L/hr. Then go to the chart and find the point where these two variables are and below that is the KW you are operating at.

For Example: 10% ABV in the pot and you measure 15 L/hr distillate rate during the first 20 minutes.
The point on the 10% ABV curve is at 6 KW.

And even better, there is a curve for steam ( water in the pot ). So you can do this with water before you run.

Remember, if you go to rad's calculator to use 0% Internal Reflux and find the rate the first 20 minutes while you still have about 10% ABV in the pot.

haggy

[haggy]

I now have a BETTER, EASIER way to estimate the reflux ratio (RR) of a reflux column still operation. You only need the pot power (kw) and distillate/product rate (D) in L/hr. Both are measured values. Here is the calc, I will describe how I got here.

RR = 3.4 * kw / D - 1

First, earlier in this thread, Hugelwilli said:

Re: A Quick Way to Find Reflux Ratio
Post by Hügelwilli » Sun Apr 02, 2023 6:20 pm

haggy,
why not calculating the distillate flowrate by the distillate abv instead of the pot abv? Most distillers have a thermometer on top of their reflux still, and a good thermometer together with the air pressure gives you a precise enough value for the distillate abv for calculating together with the wattage the total flowrate at the top of the column.

And I am doing that now. My original method was ok if the pot abv was above 22%, but not as good if the pot abv was below 22%. The vapor out the column only depends on the pot wattage and the top plate / distilllate abv. See this thread:

viewtopic.php?t=92819&start=30

In that thread, I developed the chart at the bottom that gives vapor rate ( V ) out the column if it were condensed into distillate in L/hr. Take a look at the red line. That is for a reflux column with 95% abv distillate and 30% heat losses in the total still. I have seen in many sets of real run data that 30% heat loss is typical of many reflux column stills and 95% +1% -2% is typical of neutral product operations.

Now, that red line has a slope of 3.4 in L/hr / kw. Great, lets use this. Call it V / kw. And we can now derive the above formula where L is the reflux rate in L/hr;

ok, think hard and follow this everyone

we know.........................V / kw = 3.4...... so, .....V = 3.4 * kw

we know........................ V = D + L .........and..... RR = L / D

divide by D.....................V/D = 1 + L/D

Sub for V........................3.4 * kw / D = 1 + RR

Therefore......................RR = 3.4 * kw / D - 1

That is for neutrals. If you were making a whiskey in the reflux column, you are likely to be on the blue 80% distillate abv line. The slope there is 2.6, so you would use 2.6 in the formula instead of 3.4. If your heat losses are more or less than 30%, the difference would only be about 3.2 at 35% or 3.6 at 25% for the factor.

Remember that RR is a measure of the reflux flow to distillate flow and the higher it is, the higher the product abv will be. Here is a chart giving the RR for some good operating values of different size reflux column stills.

So, I hope this helps and you can use it in planning your runs and in seeing and understanding what your still is doing.

haggy

[haggy]

For what its worth, maybe a few of you stillers would like a more complete and accurate way to get the reflux ratio and product rates to expect from your runs.

So, attached is a spreadsheet that you can download with all the complete calculations for strip runs and for reflux column runs. You can run many combinations of input variables and see what to expect.

One thing you need is an estimate of the heat losses. All the calcs for different heat losses and for different pot and distillate abv%'s are included. Heat losses are normally about 30% with average insulation. If you have a pot and column very well insulated, use 23%. If not well insulated, use about 36%+ for the heat loss. You will discover what best fits your still.

So the Excel file attached below calculates first the distillate product rate for a pot stripping run. Then, for a reflux column run, given the desired product rate, it calculates the reflux flow rate and the reflux ratio for the steady hearts run and for the total reflux period. The same calcs are in my New Condenser Calculator. The calcs are not pictured here, they are located to the right of the table. You can see below what Input data is required - it is inserted in the yellow cells.

I have tested the results with many real run data sets and these calcs give a good fit to all of them. Here is what the spreadsheet looks like:

Download the file if you want. It should be safe. No problem if you pass on it.

haggy