Reflux Condenser Sizing - Packed Columns

[haggy]

Hugel,

I think you should run a reflux column with a high amount of reflux and measure the cw flow and temp rise in both the RC and the PC and get the heat duty ( watts ) from each then add the two. Compare that total heat remover in watts to the pot watts. That is the only way to get the true answer you insist on.

I disagree with your statement - it makes no sense to calculate with the pot abv.

Too bad you will not take the time to understand my calcs and method to find the vapor rate.

In my condenser calcs,
I use real established chemical engineering equations developed and published by experts for the hi and hc to get an overall U. Then I fit the calcs to real HD scale data. The U does vary with process conditions.

Yes, there are many process variables that need to be involved, but I think I have found the key ones and have a good model.

Thanks for agreeing that a reflux condenser calc is possible. The product condenser does have sensible cooling of the condensed liquid - not as easy to get the true LMTD. The PC exit temp can be estimated, but maybe not as accurate.

Why don't you follow the current and future posts in my new thread "New Condenser Calculations" - observe the data and results - and do not make any judgement until you see a lot of the examples and results using real run data.

I think good ballpark results can be obtained with the new condenser calculator. It is not impossible. I have successfully tested the calcs with many data sets and welcome many more data sets to test its accuracy.

haggy

[Hügelwilli]

I think you should run a reflux column with a high amount of reflux and measure the cw flow and temp rise in both the RC and the PC and get the heat duty ( watts ) from each then add the two. Compare that total heat remover in watts to the pot watts. That is the only way to get the true answer you insist on.

No, I simply can trust physics. I mean, I have done measurements of condensers, but not exactly what you describe in the quote. It makes no sense for me to invest in good water flow meters only to prove what I can read in papers.

You could read about the term "constant molar overflow". It describes that the molar flow upwards the column is constant. So if you have 1mol/min vapor flow from plate 1 to plate 2, you also have 1mol/min from plate 2 to plate 3. Regardless if the alcohol strength rises. This is simplified, in practice with ethanol and water distillations the molar flow rises a little bit from plate to plate. But this is negligible, except you need mathematically precise calculations.
Of course, if mol/min is constant, this doesn't mean that also g/min or ml/min are constant. You would have to convert your calculations to mol, if you are interested in checking your calculation results.

Too bad you will not take the time to understand my calcs and method to find the vapor rate.

Now it gets unfair. You are twisting my words. I understand your calcs to find the vapor rate. I posted the formula you use and pointed at the mistake.

Thanks for agreeing that a reflux condenser calc is possible

Also this I didn't write. I don't agree that it is possible. I think it is useless because of the lack of precision compared to recommendations of experienced distillers.

I use real established chemical engineering equations developed and published by experts for the hi and hc to get an overall U.

I think you tend to be satisfied way too early. There are so many formulas to calculate the Nusselt number and the other numbers you need, and all give out strong varying results. But I don't want to be the moaner here further. Perhaps it was not a good idea to jump into this discussion. Because it would need a few other members here with enough understanding of distillation physics to get a discussion that is fruitful for all the participants. Also for me and also for you. At the moment I think you make the calculator more or less alone and you defend it alone, and there is me moaning... And the few members that read the posts don't know what to think about.

[shadylane]

I don't understand the math and during a run the ABV is changing.
It's like trying to figure out how to hit a moving target with a calculator.

I'm ordering a watt meter, better thermometer and doing more runs.
This time with only water and a short-unpacked column to remove as many variables as possible.
No controller will be used so the power measurements will be accurate within a couple percent.
I figure steam runs will more accurately measure the knock down power of a dephleg.
If someone needs to figure out how it acts with alcohol, they can drag out their calculator.

[Yummyrum]

All this is hurting me .

I feel the need to go to Shed , pour some wines in the boiler , stick an RC on it .
Put exactly X amount of power up it while wrapping the whole thing up in blankets and do the RC in/out temp while maintaining constant coolant flow .
( going for full reflux here….. no take off )

Then repeat the whole thing but with the RC on top of a packed column . …. All wrapped up again …. Same wines , same power , same coolant flow .

One of you guys maybe right ….. I have no Idea which .

But I am now curious .

But then again , maybe the truth is somewhere in the middle . …. or maybe my blankets need replacing .

[haggy]

I will keep posting a lot of the reflux condenser run data that I have collected and show everyone how the the calculations fit with the data. That is all I can do, judge for yourself the viability.

Sorry, but I think there is a place for something like this in HD as an addition / update / improvement to the current Condenser Size calculator, so I am putting the information forward for evaluation. I can take the heat.

More and detailed information about this condenser calculator is posted in the thread "New Condenser Calculator". You can check out that thread also.

So,
Here is a post from OtisT that is very similar to shady's run. A packed reflux column at total reflux. His Dimroth condenser is discussed in a different post. This is a VM column.

Re: Otis’ 4” VM/CM Column Build
Post by OtisT » Sun May 08, 2022 12:38 am

I finally washed my new packing and was able to get in a cleaning/test run today. I can’t tell you all how excited I am to finally have this new head and to be able to run my column like a VM again. And I’m very happy with the results.

I ran 5 gallons of 28% feints. That would be 5.4 liters at 93%.
Running the column within an inch if the ceiling, I was able to get 52” of packed rock.
I love this space saving head.
It took a shoe horn to get 52” of packing

I let the still settle in at 5000w under full reflex. 3.5 lpm cooling for just warm output.

I took samples at various takeoff rates:
Turns open / 100ml time / 150 ml time / temp / abv
3 / 5:35 / 8:50 / 170.5F / 95%

Next is the Condenser Calculator inputs and results for this run using a 3.5 L/min cw flow rate. Notice the watts for the Heat Transfer Required ( 3465 watts ) and the calculated Condenser Heat Transfer ( 3388 Watts ) for the 3.5 L/min cw flow rate. Not a perfect match, but pretty close. And again, this is not the 5000 watts pot power. And the cw exit temperature is warm.

This is good data, one of the few stillers who post the condenser cw flow rate and the measured product flow rate for a strip run, but this is a total reflux run and the product flow rate is not included here. I will find some stripping runs where the product from the condenser is measured and also reported so my vapor rate correlation can be checked.

And,
Thanks for your interest, Yummy. More good data will be appreciated. You did help a while ago and sent me some good stripping run data with a shotgun PC condenser. I will report on that next.

haggy

[shadylane]

Sorry, but I think there is a place for something like this in HD as an addition / update / improvement to the current Condenser Size calculator, so I am putting the information forward for evaluation. I can take the heat.

haggy

I think a Condenser Size calculator is a great idea.
All that's needed is real life data.

RC's for VM and LM rigs are easy, make it big and it will be efficient.
Dephlegmators are a different story, they need to be just barely big enough to get the job done.

[haggy]

I just posted this in the New Condenser Calculator thread. I think it should be in this thread also.



A critical part of this condenser calculator is the vapor rate out the pot or out the top of the reflux column and into the condenser. How does the calculator predict this?

Well, go take a look at the Pot Still Purity Calculator in HD developed by Tony Aukland ( not sure of the person, correct me if it was not Tony ). For a pot still strip run, it gives the the ml of distillate collected for different times during the run for different inputs of pot watts and pot abv%, the two main variables.

I used the initial ( first 30 minutes ) distillate rate information from that calculator at no heat losses and with no internal passive reflux to develop the curves in the chart below. The values would be a little lower if you have heat losses and internal reflux.

Then I developed a CORRELATION to predict the stripped vapor rate values you see in the curves. The correlation is based on the pot watts and pot abv%. That correlation is in the New Condenser Calculator and used for pot stripping runs. A separate calculation is made for the stripped vapor abv% going into the condenser, it follows the standard alcohol - water equilibrium data and depends only on the pot abv%.

I tested the vapor rate values of the curves with many posts of stripping run data and they were good fits. The vapor rates also agreed with the pot vapor rates calculated in the Pot - Thumper Calculator on HD.

So, the vapor rates out of the pot for stripping runs were established.

Then a curious and unexpected thing happened.

When I examined the good and complete run and shotgun deflegmater condenser data of 13 real 2" packed reflux column runs that PoolGuy sent me, the vapor rates up the column found from that condenser data were nearly the same as the values in the curves for the pot still. Wow!

So, I use the vapor flow rate correlation for both pot still stripping and for packed reflux column condensers in my New Condenser Calculator.

That is how the vapor rates estimated in the New Condenser Calculator were obtained - and the vapor rate curves below are for both a pot still and a packed reflux column. That is what agreed with many sets of condenser data. I will show examples of different stripping and reflux column runs which fit the condenser calculations which are based on the vapor rates in the chart below.

If there are significant heat losses in the pot or column and /or some internal passive reflux, the vapor rates would be a little lower than the curve values.

haggy

[haggy]

About a year ago, Yummyrun ran a stripping run for me and took a lot of condenser data, and then sent me the data. I found in my files several data points of the run. I put the data into this new condenser calculator and report the results here.

He used a shotgun condenser for the 4" unit. The good thing here was the measurement of the product rate in L/hr so we can compare it to the pot strip rate estimated by the condenser calculator.

Data was taken at the start and during the strip, so we can see the effect as the pot abv decreased. The run was made at a high 6000 watts power, cw flow rate of 2.73 L/min, cw inlet temperature of 21.3 C . I cannot find the cw exit temperature data. These were the same throughout the run.

The copper shotgun condenser was 7 x 0.5" tubes , 13.4" long in a 2.5" shell.

Here are data for three points during the run:

Here are results of the condenser calculator for these data points:

You can compare the calculated product rates L/hr above and see a good enough agreement with the data. Also, the calculated Shotgun Condenser Heat Transfer using the 2.73 L/min cw flow rate is close enough to the Required Heat Transfer. For points 2 and 3, the lower pot abv% was input in the calc to give the product abv% of the data.

And for this strip run where there was little or no reflux, the calc heats are close to the 6000 pot watts used. There probably also was some subcooling, but that would be a small addition to the heat required vs the larger effect of the condensation heat.

The Condenser Calculator results for the three data points are shown next.

And this was real, accurate stripping run data.

haggy

Edit: Well, I just looked harder and found the data sheet Yummy sent.
CW Exit Temp....... Product Exit Temp
Point 1 54.4 C...... 32.4 C
Point 2 55.6 C...... 35.3 C
Point 3 57.3 C...... 33.6 C

The cw exit temp data is higher than the cw exit temp in the results sheet and the product exit temp is lower. That indicates there was some subcooling. I did not include the subcooling in the results. Maybe that should be done for a PC, but not there (yet). Anyway, the condensing part in the results seems ok with the data.

[haggy]

In the New Condenser Calculator thread, Yummyrum correctly pointed out that in the same chart that is two posts above, the lines represent the liquid Distillate L/hr, not the vapor rate. Thanks
__________________________________

You old-timers might remember in 1966 there was a movie called " A Funny Thing Happened on the Way to the Forum - A comedy musical film based on a stage play, starring Zero Mostel, Phil Silvers, Buster Keaton - A wily Roman slave schemes to earn his freedom by romantically uniting his master with a courtesan. But matters get complicated and he ends up dragging in his neighbors around him, leading to chaos.

___________________________________

Well - A funny thing happened to me on my way to post something in the HD Forum.

I stopped by the hobbybrennan.ch web site and looked over the Calculator section. And I saw two calculators that drew my attention.

The first calculator ( Theoretical Floors ) can find the equilibrium vapor abv% from the pot abv% if the result is one theoretical floor ( plate / distillation step ). So, the vapor abv% is just a function of the pot abv%. They are connected at the equilibrium conditions. The hobbybrennen calculator says that for a 10% pot abv%, the equilibrium vapor abv is 55%. Ok - That agrees with the value that I calculate also.

The second calculator ( Watts -----> Amount of Distillate ) Ok, that is what we are looking for for a pot strip operation. But you need to put into the calculator both the Watts and the vapor abv% also. So I ran that calculator with 5000 watts and the above vapor abv of 55%.

So that says 12.3 L/hr distillate rate for 5000 watts at vapor abv 55% ( or pot liquid abv 10%). Let's check this out with the multiline chart two posts above. Well, at 10% pot abv and 5000 watts, we get a vapor/distillate of 12 L/hr, pretty close. That lends some credibility to the chart above.

___________________________________
Let's do it again. No pictures this time. Check it out yourself.
For 20% pot abv, the equilibrium vapor is 68.6%, from the first hobby calculator.
For 3000 Watts and 68.6% vapor abv, the distillate rate is 8.7 L/hr, second hobby calculator.
The chart above at 20% pot abv and 3000 watts gives 9 L/hr. Not exactly the same but not bad.
________________________________________
You can do this many times and get similar results, not an exact match, but close.


The moral of this story is that the chart above which is based on an HD calculator does have credibility ( via hobbybrennan calcs) and can be used for the condenser pot strip operations. Yummyrum acknowledged this also. He said ( That graph looks pretty much in line with what I have found ) in the post I referenced above.

And the chart above is based on the pot abv% and the pot watts.

I developed a correlation equation to predict very well the lines in the chart above. This equation uses the pot abv% and the pots watts. The chart and correlation equation agree fairly well with hobbybrennan calcs, so It must not be a mistake.

haggy

[Hügelwilli]

I am looking at the green line of your chart (water steam):

And I see that with 0.5kW you get 1lt/hr. And when you use ten times the power (5kW), why don't you get ten times the vapor? Why 8.3lt/hr instead of 10lt/hr?
At those wattages (0.5kW and 5kW) the hobbybrennen calculator calculates 0.8lt/hr and 8lt/h.

The hobbybrennen values are what physics say. It's theoretical by means that no heat losses are taken into account, at least in this simple watts -> amount of distillate tool. But also your calculator doesn't try to consider heat losses, right?
There is a physical constant, how many Joule you need to evaporate one mol of water. And there is another constant for one mol of ethanol. I think you know those constants. I would start to calculate with those and then check if practice differs. And then perhaps you have to think about why it differs and if it matters for your calculator.

(By the way, there are English versions of the hobbybrennen calculators too. You don't have to auto-translate them. Then it doesn't say "theoretical floors" but the right term "theoretical plates". And some of the English calculators have also °F, gal and lbs implemented)

[haggy]

I have been reading more and more and have just found some stuff that might explain some things about the reflux column that I had not realized before.

The stuff I have been calculating for a pot stripping operation using the distillate rates in the above chart should be valid - there is little or no reflux. The input heat by the pot watts is about equal to the calculated heat condensed. Good

But that chart probably does not apply to a reflux column - it gives too low a vapor rate at the top and does not give an energy balance.


Hugelwilli's input below about the reflux column saying the heat in ( pot watts ) and heat out ( condenser heat dissipation ) have to be about the same and that the the top vapor abv% matters most got me doing more investigating. Thanks for the push, Hugelwilli.

Post by Hügelwilli
Energy doesn't get lost. It has to go somewhere. Some will go into the air, because no still is perfectly insulated. But one half of it?
Vaporizing costs energy, but you get it 100% back when you condense. So rectification theoretically doesn't consume energy.

And this about the vapor rate at the top of the column:

Post by Hügelwilli » Tue Jul 02, 2024 8:35 am

When you want to know what vapor rate, you need to know the vapor abv. This number and the wattage will decide how much vapor you have. If you want to know, what the vapor rate directly above the liquid is, you need to use the abv of the vapor directly above the liquid. If you want to know the vapor rate at the top of the column below the condenser, you need to use the abv there. The vapor amount at the bottom of the column is therefore smaller than at the top of the column. How can this be true? Simply because of the reflux stream also is different at the lowest and the highest plate. You have not only more vapor flow at the top but also more reflux flow.

That info did not sink in until I found this article that explains something about a reflux column and the vapor rate out the column and heat dissipated in a reflux column:

https://www.brewiki.org/fractional-dist ... 5%20water.


It is hard to understand everything in that article, but it gives a way to calculate the reflux rate at the top of the column.

I am current updating my reflux column calcs for several sets of real reflux column data - more sets will be done later. I have modified my calculations based on some information from the article and I do calculate that the pot watts vs the heat dissipated by the RC and PC condensers are about equal to each other. Yeah

The vapor rate we want for the reflux condenser is the vapor rate at the vapor abv at the top of the column and the pot watts. The vapor rate along the column can also be calculated if we know the vapor abv at that plate or packed length.

The article helped me to better understand what you were saying Hugelwilli. Sorry that I did not get it right away. I was thrilled with the fit to most of the reflux condenser data using the pot still vapor rate, but it did not meet the criteria that you mentioned.

I will post some discussion of what I think the article is saying and post some of the data set results and update my Condenser Calculator and update the Packed Reflux Column HD file.

haggy

[haggy]

Hugelwilli said while I was writing my mea culpa:

And I see that with 0.5kW you get 1lt/hr. And when you use ten times the power (5kW), why don't you get ten times the vapor? Why 8.3lt/hr instead of 10lt/hr?
At those wattages (0.5kW and 5kW) the hobbybrennen calculator calculates 0.8lt/hr and 8lt/h.

The curve values below 1 kw are not as accurate. The curves should probably go from the value at 1 kw down to zero at zero watts, they don't.

I think most pot strip stillers and reflux column stillers are more concerned with > 1 kw watts than the 0.5 kw. Hmm Maybe I am wrong there also.

I like the 8 vs 8.3 L/hr comparison at 5 kw.

Any comments on my post before this one?

haggy

[Hügelwilli]

Any comments on my post before this one?

I think you are on the right track for a reflux column calculator. And probably also for a cooling water calculator. But a condenser calculator including dimensions of condensers is a different beast, especially for product condensers. We were trying very long to build such a calculator. The problem is, that the htc is not a constant. If you change one thing, the htc changes too. For example it changes massively when the distillate amount changes. And it changes massively if you change the angle of the condenser. And the htc is not the same for the whole condenser. Every cm has a different htc. At the end our calculation was iterative: The calculator at first guessed the product temp, then calculated based on this guess something like 1000 htcs for every 1/1000 of length of the condenser (and all the Prandtl, Reynolds, Nusselt numbers you have to calculate first) and calculated from that the product temp. Then the calculator corrected its guess and again and again calculated the 1000 htcs and the product temp until the guess of the product temp and the calculated product temp were matching.
But still: In practice the condensers behave different. At least if you run them with as little water as possible. Of course, if you have a large pc running with much water, you will have a product temp only a little over the water inlet temperature. This also predicts our calculator. But for this you don't need a calculator. A calculator that finds out if your distillate has 20 or 22°C with inlet 18°C cooling water doesn't help. A condenser that identifies cases, where your distillate has 50°C although your outlet water still is pretty cold would help.
So we didn't release this calculator. Perhaps we would have if there were at least a good amount of theoretical knowledge to learn from. We have calculators with not much practical use which we released because they are interesting anyway.
So what is the use of the htc if it changes all the time? It describes how good the condenser is running after you have measured how good it is running. And then you have a value you can use when you use the same condenser for the same task next time.

[haggy]

Thanks for a good, informative response, Hugel.

Yes, it is a difficult calculator task, these reflux column condensers, but I have a lot of run data and I will use this latest vapor rate calc method to see if I can get results close to the data.

I do have a model where the htc does vary a lot depending on the run conditions. I will do condensing only since a liquid cooldown is a different calc and the LMTD is easier. This would apply to a CM deflegmater partial condenser and the minimum case for a VM total condenser.

My calcs now give a heat balance between the pot watts and the condensers when there are no heat losses ( very good insulation ). But I am seeing that some heat losses should be taken into account, maybe up to 20% heat losses in the pot, lid, along the column, etc. The article I referenced did speak of significant heat losses. It said they got about a 45 ml/min measured vapor rate vs 58 ml/min calculated with no heat losses.

And that makes it a little harder, also having to take into account the heat losses.

haggy - aka Don Quixote

[haggy]

The Condenser Calculated has been updated ( Version 15 ). A description of the improvements has been posted in the last post in the following thread. An example of the calculator for a real CM reflux column run is also included.
Check it out!

viewtopic.php?t=93059

This last update was for the reflux column flow rate to the condensers. It depends on the pot watts, vapor abv at the top plate or packing and the pot/column still heat losses.

So,
At the bottom in this post is a graph of what to expect for the flow rate to the condenser for reflux columns at 95% and 80% top column vapor abv run conditions and for three heat losses. It has been seen that a 30% heat loss fits data from many reflux columns.

I did a lot of studies early this year to find a good model calculation to predict / estimate the heat transfer in a reflux condenser. Much of the data for those studies came from many runs that PoolGuy made on a 2" CM packed reflux column. He took complete run data including cw flow rate and cw temperature in and out the condenser. We worked together to find good run conditions to give 95%-96% abv product and he sent me all the run data.

From the PoolGuy runs, I determined the vapor flow out the top of the column from the reflux condenser data and the product rate. All of those runs were made with low wines and in the watts range of 1500 watts to 2100 watts. Also some other run data from higgins was studied and that was from low wines plus wash in the pot and a watts range of 2000 to 2700 watts.

So what!

Well, the reflux column vapor flow rates in the runs I studied were very similar to the what was expected from a pot strip run, the values given in the above curves.

If you take the reflux column curves in the first graph below for 30% to 35% heat loss and 95% vapor abv and superimpose them on the pot strip graph above - you get the second bottom graph.

In the range I studied, the two lines ( pot strip and reflux column ) give about the same vapor flow rate. So that is why I thought the pot strip and packed column had about the same vapor flow rate.

I will post some more run examples and show that the New Condenser calcs are valid for both the pot strip condenser and the reflux column condenser.

haggy

[drmiller100]

H20! Has three times the latest hear of vaporization as etoh so flow rates will be different.

But that is meaningless.

The condenser and inefficiency knock down the energy the heater makes.

What I get from all of this is you have proven most reflux columns lose 30 percent of the heat.

If you insulate up your column it might run faster. I know on my continuous still I have to insulate it.

[haggy]

With the new reflux condenser vapor flow calculation, we can get a better result using shady's run data.

The run data post was:

Re: Reflux Condenser Sizing - Packed Columns
Post by shadylane » Sun Jun 30, 2024 5:38 pm

10% wash, 4" packed column. 5kw
The dephleg flow and temp for just barely 100% reflux is 4.1ltr/min and 44'c.
The run was 92% at 5.3ltrs/hour during this time the cooling flow was 1.4ltr/minute at 58.8'c.

The updated Condenser Calculator for the steady run at a 38% heat loss is:

Results next show a good agreement in the Heat Required and Condenser Heat Transfer at the 5.3 L/hr product rate and the 1.4 L/min cw flow rate. The vapor rate condensed here is 8.7 L/hr vs 6.9 L/hr before. And that increased the Heat Transfer Required to match the Condenser Heat Transfer close enough. The total vapor rate at the top of the CM reflux column into the condenser is 14 L/hr.

So, the calculations are on the right track now and we can understand shady's data. The low reflux ratio of 1.7 could lead to the 92% product abv. But the cw exit temperature measurement can be better, it seems too high.

haggy

[haggy]

One more example of the Condenser Calculator for reflux column runs, then I will give a summary of almost all the data sets I have studied.

This example is from a run by Reefer1. He has a nice 2" CM reflux column with a Dimroth RC deflagmater. I suggested some set points for him to run and he made the run and sent me the complete run data in good detail. Here is his CM reflux column condenser:

The run was at 1800 watts with 26% low wines in the pot and had a steady product takeoff of 1.5 L/hr at 95% abv. the cw flow rate was at 300 ml/min most of the time.

Next is the Condenser Calculator info for that run. It was found that 30.5% Heat Losses give a vapor flow rate off the top plate of 6 L/hr and 1.5 L/hr takeoff subtracted from that gives condensed reflux flow of 4.5 L/hr. When 4.5 L/hr of 95% alcohol condenses it gives off 940 watts heat. And this dimroth condenser operating with 300 ml/min cw flow rate can condense 938 watts heat. The heats are balanced.


Input Data

Results

So the Condenser Calculator agrees with the data using a heat loss of 30.5%. If other heat losses were tried, like 25%, the cw flow rate at 300 ml/min would not give the same condenser heat duty as required, the heats would not be balanced.

The vapor flow rate at the top of the column of 6 L/hr (using my updated calc) is about the same as I found for PoolGuy's 2" reflux column runs at about the same watts and top vapor 95 abv%. And that is also about the same vapor / distillate rate you would get if it were a pot still at 1800 watts and 26% pot abv. Like one of the above graphs shows.

I have updated and examined many reflux column run data sets and get good enough condenser calc results for all of them. I will post a summary of the runs examined and their results in a future post.

haggy

[haggy]

The updated Condenser Calculator has now been tested with several/many real run data sets that I have collected. I will report here CM reflux column data where the "Deflagmater" Condenser Heat Transfer about equals the Required Heat Transfer from the condensing reflux vapor. Good data to test the calculator includes the cw flow rate, and that is not reported very often. But several stillers have sent me good data and I have summarized the test runs here.

The run data was input to the calculator and a still heat loss % was found which gave the cw flow rate reported in the data. There is only one value of the heat loss % that will give the reported cw flow rate and balance the required heat transfer with the condenser heat transfer. Here are the results for both shotgun and dimroth condensers:

The Heat Loss% results varied from about 20% to 38%. OtisT data had low values and shadylane and ckdistills values were high. The average of all the runs was about 31% heat loss and a many runs were around 30% heat loss.

So, using a 30% Heat Loss in the Condenser Calculator should be ok for many reflux column stills and give good ballpark or better results that should be close enough to the real still operation.


I have also done many calculator runs of a PC condenser for stripping runs. The calculator results agreed well with that data. I will report that information in the "New Condenser Calculator" thread.

viewtopic.php?t=93059

Using the Condenser Calculator to evaluate the suitability and sizing of new or current condensers or determining what to expect from different operating conditions should be valid.

haggy

[haggy]

So, with the updated Condenser Calculator ( new calc for top column vapor flow rate), do the initial Condenser Sizing charts in the first few posts still apply.

YES, .... why?

For the shotgun condenser in a 2" CM reflux column operating at 25% pot abv and 1000 to 2200 watts, the vapor rates were found from real data and are about the same for the initial calcs and the new updated calcs at the expected 30% still heat loss. So the 2" shotgun sizing chart is ok.

For the shotgun condenser in a 3" CM reflux column operating at 25% pot abv and 2500 to 4500 watts, there may be a difference at higher watts. Let's check it out.

Here is a 4000 watts, 25% pot abv and 2.5 L/hr product rate case run with the updated Condenser Calculator at a 30% heat loss. A 1 ft^2 surface area shotgun is used and is a good size for this set of conditions based on the condenser settings graph in the first post.

Input Data

Results

The 3" Shotgun Condenser Sizing chart above at 4000 watts with the 1 ft^2 shotgun had the cw exit temperature at about 120 F. Here we get 129 F due to a little higher vapor flow rate now, but that is acceptable. The above 3" shotgun sizing chart is ok.

This same validation procedure can be done with a Dimroth condenser. I have done this and compared the results with both the 2" and 3" Dimroth Condenser Sizing chart. The charts have the cw exit temperature about 120 F and the new calcs give 120 F and 123 F. So, we are ok with the Dimroth charts also.


I am now satisfied with the new Condenser Calculator and will check with Uncle Jesse and try to include it in the HD Wiki Calculator Section for all to test, evaluate and use. I hope it helps with your evaluation and sizing of new and current condensers and determining what to expect from your operating set points.

haggy

[Reefer1]

Question for Haggy.
I have another 5 gal rum wash to strip, i have stripped fermenter 1, i didn't take much data from this strip, i have a bit, i had to stop the run as i had a water drain leak to sort, then restarted.
As i say i have Fermenter 2 to strip if you require data for that, i can take accurate flow and PC production rate. i have a shorted 2" column i use for stripping i can measure that as well, no packing just straight pot.
I haven't decided how i will do the spirit run yet reflux or pot, it's a light tasting rum wash so i don't want a strong flavour, just enough t know it's rum.
So i could reflux run it at may be 85 - 90 ABV take off to allow some flavour through to the product, or i may just run it with a fully packed column with no reflux. not sure yet, any suggestions welcome folks.!!

So i am not sure any data taken off this run may not be any use to you.

[haggy]

Reefer1,

I will take all the good, complete data I can get, either strip or spirit runs. Something like the file you sent me with good, complete data, just add the cw exit temperature measurement.

I will continue to validate the condenser calculator. The data needed is the condenser design, cw flow rate and cw inlet and exit temperatures. That plus the run details: pot watts and abv%, strip and spirit run product rate, spirit run product abv% estimate.

About your light rum spirit run.
I have concerns on running a CM reflux column for this. To get a low product abv, you could use half the packing and run a higher product takeoff rate like 2 or 2.2 L/hr. I ran several cases on the condenser calculator and did not like them. The fairly large dimroth defleg condenser will require a very low cw flow rate ( 150-200 ml/min ) to condense the low flow rate of reflux ( lower reflux needed to get lower product abv of 85- 90% ). The control of this would be touchy and the cw exit temperature would be high ( 150 F ).

It might be best to do a slow pot still spirit run with (1)a riser or (2)the column with no packing or (3) the column with packing but no reflux. The passive reflux using the column may boost the product abv some and make cuts easier. The pot could have a charge of 20 Liters of 35% abv to boost the abv and the run could be at about 1000 watts.

Here is a calculation of what you might expect from a pot still spirit run with some passive reflux. The amount of passive reflux would be determined by the condensing heat losses on the pot and pipe/ column walls. The product rate is also reduced by passive reflux. The HD Pot Still calculator was used. About 4 hours to get to tails and you could make 20 x 500 ml cuts along the way. Initial product rate is about 3 L/hr. You maybe would make about 5-6 L of hearts at about 60-64% abv.

So, good luck on this next spirit run. I will like to get the run data. Thanks

haggy

[Reefer1]

Ok no probs Haggy,

[haggy]

This thread has been about reflux condensers that are used in packed reflux columns. But it also has included the Packed Reflux Column calculator which gives information on other process variables in addition to the reflux condenser operation.

There is a Packed Reflux Column calculator on the HD wiki now. But, based on the new information that was generated in this thread, I have modified that calculator and will add the UPDATE to the HD wiki soon.

The updates include a better estimation of the vapor flow from the top of the column to the reflux condenser, improved calcs for shotgun and dimroth coil reflux condensers, and the realization that heat losses in the pot/column/transfer lines do play a significant part in the distillation process.

Many ( 20+ ) reflux column run data sets have been examined. It was seen that an average of about 30% heat losses fit the data. That was even for many insulated columns. So, heat losses were made an input data to the calculator.

Uses of the Calculator
The Packed Reflux Column calculator can be used to help plan your runs, see the effect of changing input charges, see what amount of hearts to expect, find the reflux ratio you run at, see the approximate run time to expect, see how close to flooding the column you are, see if your reflux condenser is a good design, and determine the cw flow rate you should be running and the cw exit temperature to target during the run.

I am satisfied with this upgraded Packed Reflux Column calculator now, I have tested it with many complete data sets and it is a good enough representation of the distilling process. That is why I want to add it to the HD wiki.

_____________________________________________________________________

Real Run Examples
I have many packed reflux column run examples that I could show here to prove the calcs are good enough. I will show three of them and discuss details of the calculation results.

First, in the following post (above) I ran the Condenser Calculator - now I will show you the use of the Packed Reflux Column Calculator for a run by Reefer1.

Re: Reflux Condenser Sizing - Packed Columns
Post by haggy » Thu Jul 18, 2024 2:02 pm

One more example of the Condenser Calculator for reflux column runs, ......
This example is from a run by Reefer1. He has a nice 2" CM reflux column with a Dimroth RC deflagmater. I suggested some set points for him to run and he made the run and sent me the complete run data in good detail. Here is his CM reflux column condenser:

And, here is more details of that run with the Packed Reflux Column calculator:

Input Data

Results

Look through the results and see all the run information that is given. The reflux ratio is about 3.1 and 95+% product abv was estimated. About 2.9 Liters of hearts could be made and there are no column flooding issues and low entrainment. However, these conditions are fairly close to the flooding point, so the watts should not be increased too much.

The Dimroth reflux condenser calcs for this CM reflux column accurately showed the heat required and the condenser heat removed were about equal at the 300 ml/min data cw flow rate. So the dimroth coil calcs are ok. The cw exit temperature is a little hotter than desired. About 30% heat losses ( a typical value ) were used in the input data.

I will show more examples of this Packed Reflux Column calculator in another post.

haggy

[shadylane]

I greatly appreciate the formulas and math for figuring out "Reflux condenser sizing"

But something that hasn't be talked about is the 800 pound gorilla in the room.
A formula based on surface area exposed to the vapor works in theory, but in reality things are often different, due to the variations and design of reflux condensers.

A good example of a bad design looks like this, lots of surface area but the fins are too close together.
The reflux fills the gap between the fins and doesn't have enough room to drain and gets in the way of the rising vapor. Basically it causes localized flooding in the reflux condenser.

[shadylane]

Wished I'd taken pics, but another bad example was a shotgun with 3/8" tubing.
It also had the same problem, everything looked good until it was pushed hard and suddenly the knock down power crashed. Liquid reflux draining down the small tubing inhibited the rising vapor from cooling.

[haggy]

Post by shadylane » Thu Aug 15, 2024 1:09 am

I greatly appreciate the formulas and math for figuring out "Reflux condenser sizing"

Thanks shady.

It ain't easy searching through 100"s+ of posts trying to find good complete run data. I also have to thank at least eight stillers who have sent me their good run data. I can do my calcs and check them with the data and modify things until I get a good representation of the real thing.

In all my searching, I have seen less than 1% of the posts with non-standard condenser designs. That goes for both shotgun and dimroth coil condenser designs. There were some not well designed shotguns ( too short or not enough tubes ), but the calcs revealed the problem.

I did not see any 800 pound gorillas, except maybe when someone was doing a non-conventional condenser experiment.

And maybe 1 in 50 stillers might have run their reflux column way above the flooding point and saw some effect of vapor preventing the condensed liquid from draining down. A stripping run at 11000 watts might have some condenser problems, so that stiller should know he has to use 0.625" diameter or higher diameter tubes in a shotgun condenser.

But, it is wise to watch out for those kind of things, and we will.

haggy

[shadylane]

A stripping run at 11000 watts might have some condenser problems, so that stiller should know he has to use 0.625" diameter or higher diameter tubes in a shotgun condenser.

But, it is wise to watch out for those kind of things, and we will.

haggy

I'd recommend 0.500" or larger for all shotgun dephlegs, even those that only need to knock down 3 or 4kw. Dephlegs are a two-way street. Smaller than that and the rising vapor impedes the falling reflux.

[haggy]

I have to send out a thanks to OtisT.

Almost always, he includes the cooling water flow rate when he posts results of his reflux condenser runs. This helps me confirm or update my condenser calcs to agree with the run data.

He made a novel dual coil dimroth condenser with two independent coils and reported some run results. It has a 4" shell and was used on his 4" packed reflux column. It was used in both a VM and a CM column configuration. Here is a picture of that dual coil dimroth condenser.

image.png (141.74 KiB) Viewed 3978 times

The tubes are both 3/8" diam and the inner coil is about 45" long and the outer coil is about 60" long.

Here is the thread describing this condenser along with some data that I will use to check my packed reflux column calcs.

Re: Otis’ 4” Column Condenser - RC / Dephlegmator
Post Wed Dec 01, 2021 5:17 pm

MidnightThunder wrote: ↑That condenser is a beauty Otis! Can you supply any figures on how it performed? Perhaps max knockdown power and water usage.
Hi MidnightThunder. I think I will need to take measurements on a future run to give you detailed specifics. I’ve only got some early notes on this and have since been running by senses and not bothering with measurements. I only recorded data from my CM runs, and did not record any data from running this above my VM head. Here is what I do know from my early CM runs:

My max power output is 5500W and this condenser handles that with no problem.

I can knock down 5500w with a flow under 5 lpm. I think it was closer to 4 or 4.5 lpm for 100% reflux. Max flow potential is about 34 lpm.

Either coil independently was able to knock down all 5500w. The inner (smaller) coil required about .5 lpm more flow for the same knockdown. I tested this by seeing how low of a flow would keep any vapor from passing to the Product condenser (PC).

At 3000 watts I set the flow to roughly 1.75 lpm to achieve a reflux ratio around 8 to 1. I think output shut down to the PC at around 2 lpm flow.

Hope this helps ya.
Otis

I will show next the Packed Reflux Column Calculator results for the last run mentioned which was at 3000 watts. Both the total reflux case at 2 lpm cw flow and the steady run case at 1.75 lpm cw flow and about 8:1 reflux ratio will be studied.

The cw flow rate is split so that each coil would see about half the total cw flow. Input data to the calculator is two coils and the total cw flow rate. An average coil length of 52" for each coil was used to condense the reflux flow. From seeing other photos, the pot and column were both very well insulated, so a 24% still heat loss was used and a 95% product abv ( similar to other runs ) was likely made.


The Total Reflux Case

Input Data

Results

You see that 2 lpm cw total flow rate was fed, 1 lpm to each coil and the total heat knocked down by the dual coil condenser was 2266 watts. The 11.25 L/hr reflux rate needs about 2308 watts to condense it. So this was a good heat transfer match for the CM column calcs at total reflux, within 2% of each other.


The Steady Run Case

Input Data

Results

The distillate rate was input at 1.22 L/hr to give a reflux ratio of 8. The cw flow rate of 1750 lpm was equally split to feed each coil and the total knocked down was about 2168 watts. The 9.92 L/hr reflux flow needs about 2067 watts to condense it. The predicted condenser duty was a little higher, 4.9%, but right in the ball park. Other results not shown are the run time, hearts made, no flooding, etc.

So, the Packed Reflux Column Calculator is better now and good enough. I will update the one on the HD wiki. Also, there is a separate Condenser Calculator ( see above posts ) that is also good to go, and I will try to put that on the HD wiki.

haggy

[haggy]

Now that we have a better Condenser Calculator, I have updated the Reflux Condenser Sizing Charts that were given in the early posts. The sizing results have not changed too much, but we can now see the effect of heat losses in the still. You can use the chart to size a new reflux condenser or to see where your current reflux condenser fits.

The attached charts are for shotgun reflux condensers. There are three charts, for a 2", a 3" and a 4" reflux column. The run conditions the charts are based on are the following:

Item....................... ..2".............. ..3"..................4"

Condenser tubes.......5x 0.375".......10x 0.375"..........9x 0.50"
Condenser MOC............SS.................SS..................SS
Pot KW..................1.0 to 2.2.......2.5 to 4.5...........3 to 6
Pot ABV%................... 25................25..................25
Heat Loss................0%-30%...........0%-30%............0%-30%
Product L/hr.............. 1.0 .............. 2.5 ............... 5.0
Product ABV%..............95................95..................95
CW In Temp F..............57................57..................57
CW Exit Temp F..........120...............120..................120

The charts give the required shotgun reflux condenser ft^2 surface area, A.

A = 3.14/144 x tube diam x tube length x number of tubes

So, after you find the required surface area, you can get the tube length in inches from this equation and your tube design.

First you decide the pot watts you will run, then get the condenser surface area from the proper chart. But your run conditions may be a little different, so the following changes can be done while still adjusting the cw flow rate to give the 120F cw exit temperature.

If you want to run a higher takeoff rate, then decrease the chart surface area by 8% per 1 L/hr increase, but no change if it is a very low watts run. If you want to run at 130F exit cw temperature, increase the chart surface area by 15%. If you think you will get 90% abv from the still ( 5% abv less ) decrease the chart surface area by 4%. There is no change to the surface area if a different pot abv% is used.

The charts give the required condenser surface area for a CM reflux column at the above run conditions where the heat removed by the condenser equals the heat required to condense the reflux vapor. The best line in the chart to use is the 30% heat loss.

For a VM or CCVM reflux condenser, you need more surface area than the chart shows, so multiply the ft^2 by 1.5 or 2 times to insure complete vapor knockdown. A top section of the condenser tubes will not be used.

The updated Dimroth coil reflux condenser sizing charts will be given next.

haggy