Plate Reflux Column Operating Characteristics

Vapor, Liquid or Cooling Management. Flutes, plates, etc.

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bluefish_dist
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Re: Plate Reflux Column Operating Characteristics

Post by bluefish_dist »

I think the pro caps would flood around 5000-5500 and the regular caps around 4000 for a 4”. I used all still dragon parts, plates and caps. I think on the 4” there were 5 holes for the regular caps and 3 for pro caps. The regular were setup with 4 up, 1 down if I remember right. It’s been 4-5 years since I used them. After I tried sieve plates and found I could make them for a lot less money, I gave up on bubble caps. I liked the pro caps and if I could not have made my own plates would have used those instead.
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Re: Plate Reflux Column Operating Characteristics

Post by haggy »

More on Bubble Cap Reflux Columns.

I am trying to define and calculate the flooding point of bubble cap reflux columns. The 2", 3" and 4" builds have a single bubble cap under the plate that is used as a down comer. Sieve plates usually have a longer cylindrical tube as the down comer. This difference can give a different flooding point ( the pot wattage at flooding ) for bubble cap plates vs sieve plates. I have specified all the caps ( except Procaps )to have the same dimensions ( not true but close enough). All columns sizes have a bubble cap open slot area of about 9+%.

My research of HD posts has found 13 bubble cap posts with enough run information to put into my calculator. The posts covered all three column sizes. But only three of the post were run at the flood point and a few others were close to flooding. Here is a table of the runs with the key operating conditions. You see at the bubble cap flood point that the slot velocity is at or above 6 ft/sec, much lower than the 11 ft/sec flood point for sieve plates. Also the pot wattage at this flooding point is lower than sieve plates wattage.

image.png

To determine the bubble cap flood point, a calculation involving the bubble cap down comer slot/hole velocity was developed. The calculation did come up with predicting the pot watts and a 6 ft/sec slot velocity at the bubble cap flood point. So, an updated Excel spreadsheet is now being used in my calculations.

We can now estimate the flood point of bubble cap reflux columns. :clap: These columns are mostly used for one and done runs with a ferment as feed, but I did the calculations for a range of feed up to 40% ABS low wines. Here is the a graph of the pot watts at flooding for all three columns sizes over a 10% to 40% pot ABV range. The curves decrease because more vapor is boiled from the pot at higher pot ABVs, so less pot wattage must be used to have the bubble cap slot velocity at about 6 ft/sec.

image.png

Now, let's compare the estimated flooding and weeping points for a 4" reflux column using bubble caps vs sieve plates. I used a 7% open hole area for sieve plates in the comparison. Sieve plate flooding curves are in my previous posts. Here is the comparison graph, the solid line are for sieve plates, the dashed lines for bubble caps:

image.png

The operating range is the area between the respective flooding and weeping curves. At this 7% hole area sieve plate, the sieve flooding wattage is higher than the bubble caps and the operating range is also a little larger. If a sieve plate 4% hole area were used, the sieve plate flooding curves would be about the same as the bubble caps, and the bubble caps would then have a much larger operating range due to no weeping and also have a larger turndown ratio.

What is unexpected is that the bubble cap flooding wattage above 10% pot ABV is lower than 4500 watts. The take-off rate can range from 1 L/hr to almost 4 L/hr depending on the dephlegmater cooling and reflux rate. Since sieve plates have a higher flooding point wattage, they can be operated at higher take-off rates and run faster than bubble caps.

Here is the Excel sheet results for the Jersey Jerry post, which was at flooding conditions.
image.png
image.png
So, that is my information on bubble cap reflux columns. :D If anyone has run data to confirm or not confirm these results, please post it.
Thanks.
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Re: Plate Reflux Column Operating Characteristics

Post by haggy »

So far I have used the Excel program for Plate Reflux Column Operating Characteristics to show the results of several different runs. The first post included that Excel file, it has been updated for bubble cap plates. You need Office software to use the file.

I also have made a JavaScript html file of the same calculations including the bubble cap update. :clap: It can be run in a users browser or it can be put in the HD Calculator section for all to use. Html files are not allowed to be loaded in a post. When everyone is confident that the calculations are valid ( I think they are good now ), I will try to get it put into the HD Calculator section.

If you think the results and graphs in this thread are good and want this html file in the HD section now, let's pursue it with Uncle Jesse. :thumbup:

The html file calculates the operating characteristics for both sieve and bubble cap plates. Here is what that browser html file or HD Calculator output would look like:

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Input Your Plate Reflux Column Operating Data

Name Your Run -- Good Run Setpoints
Column Diameter 4 inch
Number of Plates plates 4
Plate Spacing 6 inch
Sieve Plate Hole Diam 0.0781 inch
Sieve Plate # of Holes 0 0=set by program

Potstill Charge 12 US gal
Alcohol Content 10% ABV
Initial Temperature 30 C
Power during Heat-up 5000 W
Power during Distillation 3400 W
Distillate rate initially 2.2 L/hr

Change any of these values and see the results in the boxes below ...

Results
Time to heat up potstill contents 38 min plus 20 min plate loading
Potstill temperature at start of boiling 94 C or 200 F
Column initial top plate temperature 78 C or 172 F

Initial Reflux Ratio 1.2
Initial Distillate rate 2.2 L/hr 4.65 pints/hr
Initial Distillate ABV - Sieves 93%
Initial Distillate ABV - Bubble 93%

Approx Run time until tails start 3.4 hr
Approx Total time that power is on 4.3 hr
Distillate ABV at tails start - Sieve 90.0 %
Distillate ABV at tails start - Bubble 90.0 %

Estimated Fores/Heads made 0.18 US gal or 0.7 Liter
Estimated Most Hearts made 1.00 US gal or 3.8 Liter
Estimated Hearts ABV - Sieve 92.5 %
Estimated Hearts ABV - Bubble 92.5 %

Flooding
Maximum column vapor velocity 32.5 in/sec
Initial column vapor velocity 4.2 in/sec
Percent of Flooding 12.8 %
Is column vapor velocity causing Flooding ? NO

Minimum residence time for no Downcomer Backup Flooding - 3.5 sec
Downcomer residence time - Sieve 12.3 sec Backup Flooding? NO
Downcomer residence time - Bub Cap 17.8 sec Backup Flooding? NO

Maximum Hole velocity for no Sieve Downcomer Backup Flooding - 11 ft/sec
Sieve Plate Hole velocity initially 4.7 ft/sec Is Sieve Plate Flooding Likely ? NO
Maximum Hole velocity for no Bubble Downcomer Backup Flooding - 5.9 ft/sec
Bubble Cap Hole velocity initially 4.6 ft/sec Is Bubble Cap Plate Flooding Likely ? NO

Entrainment
Entrainment Sieve 0.01 lb/lb liq
Entrainment Bubble 0.01 lb/lb liq
Sieve Plate Efficiency 72 %
Bubble Plate Efficiency 72 %

Weeping
Sieve Plate Minimum hole velocity 3.0 ft/sec for Weeping

Sieve Plates with 180 holes at 0.0781 in diam Sieve Plates have 7.3 % hole area
Hole velocity initially 4.7 ft/sec
Hole velocity at tails start 1.6 ft/sec If 2X Power 2.4 ft/sec
Is Sieve Plate Weeping Likely ? NO

Bubble Caps with 5 caps per plate each at 1" diam giving 9.2 % slot area
Bubble Cap Slot velocity initially 3.8 ft/sec
Bubble Cap Slot velocity at tails start 1.3 ft/sec If 2X Power 1.9 ft/sec

A good power setting may be at about 1.8 times the Weeping conditions.
For Sieve Plates try this power setting 4178 W with this distillate rate 2.77 L/hr
For Bubble Caps try this power setting 3438 W with this distillate rate 2.13 L/hr
The run time may be longer here, but the run should be at the best plate efficiency.

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

So,
If you think the results and graphs in this thread are good and want this html file in the HD section now, let's pursue it with Uncle Jesse. :thumbup:
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Re: Plate Reflux Column Operating Characteristics

Post by Hügelwilli »

haggy,

you could attach the html file as a txt file. Instead of for example refluxcolumn.html simply name it refluxcolumn.txt. Or perhaps refluxcolumn.zip or perhaps even refluxcolumn.jpg. Try out what works. It depends on the settings of the forum.
Then everyone can download it, and after renaming it back to refluxcolumn.html can try it out.

Or post the complete code into a code-box:

Code: Select all

Here is the html code
Then everyone can select all and copy it into a file, which gets the ending .html

Here member hefezelle attached even an exe-file here at hd by putting it into a zip folder:
viewtopic.php?p=7574409&hilit=abvfromabw#p7574409
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Re: Plate Reflux Column Operating Characteristics

Post by haggy »

Thanks for that info Hugelwilli.

I loaded the html code and made it a different file type and tried to attach six or seven different file types and none worked, all were rejected by the forum. Not familiar with the code-box, could not do that right away. I will look into it.

We probably will have to wait and hope to put this html file in the HD Calculator.

haggy
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Re: Plate Reflux Column Operating Characteristics

Post by haggy »

Here is the final chapter on estimating flooding limits of plate reflux columns.

There is something different when using 2 or 3 plates in a reflux column.

Yes, the distillate is lower in ABV, about 80% and 86%, but other things happen because of this. More water is in the plate vapor and water vapor has a density three times less than ethanol vapor. So, the volumetric vapor flow from the top plate of 2 or 3 plate columns is higher than that of a 4 plate column for the same pot wattage.

The upshot of this is the slot or hole velocity of 2 or 3 plates will be higher at the same pot heating vs the 4 plate column. Therefore, the pot wattage for flooding in 2 or 3 plates is lower than that for 4 plates.

I used the calculator to estimate the flooding point watts for 2 and 3 plates and came up with these rules of thumb that apply to both sieve or bubble cap plates:

Rule of Thumb #7: :D
First:
See the flooding point watts for 4 plate sieve reflux columns in the haggy posts on October 13 for 4" columns and October 20 for 3" columns. See the post on October 29 for 4 plate bubble cap column flooding point watts.


Rule of Thumb #8: :D
For 3 plate reflux columns, the flooding point watts are about 90% of the 4 plate column watts.
For 2 plate reflux columns, the flooding point watts are about 70% to 77% of the 4 plate column watts.
The 70% is at a 10% pot ABV and the 77% is at a 40% pot ABV.


Rule of Thumb #9: :D
In a similar manner, the wattage at the weeping point will be lower for 2 and 3 plate sieve columns, about the same amount as Rule #7. That is a good result.


An example of a 2 plate column flooding run is the 4" reflux column standard bubble cap run data of bluefish. See the Table of Bubble Cap Posted Runs in my October 29 post. Here is the Excel program results for that run showing the flooding point ( at a 6.0 ft/sec hole velocity ) at 4000 watts, lower than the two other run flooding watts.

image.png
image.png

Here is the current, updated Excel program incorporating the new bubble cap flooding calculations and other improvements.
Attachments
platerefluxcolumn - Update.xlsx
(50.87 KiB) Downloaded 58 times
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Re: Plate Reflux Column Operating Characteristics

Post by haggy »

Here is:
An example of what could have been done by fruit fly in October 2019 if this calculator Excel file or the browser file were available then.

He had a question about his new 3" bubble cap column, it was well answered by LWTCS but he could have gotten some more information from the calculator.
3" bubble cap column questions
Post by fruit fly » Tue Oct 08, 2019 4:05 pm
I bought today a 3 plates 3" bubble plate column. (modulaire)
I want to make whiskey and rum.
Are 3 plate enough for this ?
and how many liters an hour can I expect with my 2000 Watt boiler ?
and do I also do a strip run in this column, or in my pot still ?
Re: 3" bubble cap column questions
Post by LWTCS » Tue Oct 08, 2019 4:15 pm
1. Yes.
2. Depends on RR, plate design as well as heat input. Perhaps 1.5 to 2.5 LPH? 4 inchers seem to do best at about 3 LPH (+ or -)but can go to 5 LPH (+ or -)
3. You should try both ways to help develop your own point of view. Either way is fine though either way will affect the outcome.
So,
The calculator results would show more information including the RR when run at several L/hr rate at 2000 watts. He could find the range of takeoff speeds and the run time for each. Also, he could see what running 10% to 40% ABV in the pot would be like. Flooding conditions could be found and avoided.

Here is one of the cases giving input data and run result information for his 3" 3 plate column at 2000 watts.

image.png
image.png
Running other cases at 2000 watts and 10% ABV would show that 1 to 2.5 L/hr are ok with the RR ranging from 2 to 0.2 as rate increases. The 2.5 L/hr would be a maximum. Run time would range from about 8 hours down to 4 hours. The estimated pot heatup time and likely column start vapor temperatures and the amount and %ABV made could help guide the first run.

If 40% ABV low wines in the pot were used at a 2 L/hr take-off rate, the pot should be run at 1300 watts maximum, higher watts could lead to flooding.

So,
The initial screening of a new plate reflux column with this calculator can help a user understand his process and know the operating limitations of a run.
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RC Al
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Re: Plate Reflux Column Operating Characteristics

Post by RC Al »

I have 3x pro caps in a 4" 3 plater
The downcommers easily exceeds the flow characteristics of the riser/cap
I can only flow 8lph through the 3x3 caps with reflux off vs 15 as a pot still

Edit, pouring a jug from the top of the column would be in litres per minute not hour
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Re: Plate Reflux Column Operating Characteristics

Post by haggy »

RC Al,

Thanks for sharing your take-off rate data, it will be a good test of my calculations.

I loaded the larger pro cap dimensions in my reflux column Excel program. Made a run at 5500 watts and 10% pot ABV. I varied the take-off rate until the reflux rate was zero. And :) that rate was 8 L/hr which fit your bubble cap plate column data. The hole velocity was 5.5 ft/sec - almost at the flood point. So, the calculations agree with your data, and we can be more certain of the bubble cap results. :thumbup:

Here is a copy of the Excel file input data and results.

image.png
image.png

The other information is that you get about 15 L/hr rate from a pot still. So I put that info into the Haggy's Pot-Thumper Calculator and checked that information. Here is the input data for the Pot:

Input your Pot still charge
Initial Volume of Wash 13 US gal
Alcohol Content 10 % by volume
Initial Temperature 30°C
Power during Pot and Thumper Heat-up 5500 W
Power during Distillation 5500 W
Riser Added Reflux 0 %

And the Pot section of the Results Table:

Time____Pot Power____Pot Temp_____Pot %ABV___Cuml%ABV____Pot Vapor
7 min___5500 watt____93.6 C________ 54 %_______54 %________ 1.85 L
14 min__5500 watt____94.6 C_________52 %_______53 %________3.65 L
25 min__5500 watt____96.3 C_________34 %_______48 %________6.21 L
37 min__5500 watt____97.4 C_________26 %_______43 %________8.55 L
48 min__5500 watt____98.2 C_________20 %_______38 %________10.73 L
60 min__5500 watt____98.8 C_________14 %_______35 %________12.79 L
71 min__5500 watt____99.2 C_________9 %________31 %________14.78 L
83 min__5500 watt____100 C__________6 %________28 %________16.72 L
94 min__5500 watt____99.7 C_________4 %________26 %________18.62 L
106 min_5500 watt____99.9 C_________2 %________24 %________20.50 L

So, the initial take-off rate at 14 min is 3.65*60/14 = 15.6 L/hr
Then at 25 min - 6.21*60/25 = 14.9 L/hr
Then at 37 min - 8.55*60/37 = 13.9 L/hr
etc

This agrees with your pot still take-off rate. :thumbup:
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Re: Plate Reflux Column Operating Characteristics

Post by haggy »

Here is a look at two very different sieve plate reflux column runs. First will be a run at close to neutral distillate ABV, second is a run making flavorful whiskey at low ABV (80%). Most of this information comes from studying many posts on these runs and including that information in my calculations.

The equipment for both is a 4" diameter sieve plate reflux column with deflagmater and product condenser and starting with 16 US gal at different %ABV in the potstill. Both have 7.3% open hole area in the plates.

High ( close to neutral ) 95% ABV run
The first run to make close to neutral 95% distillate is a slow spirit run starting with low wines in the pot at 40% ABV. Four plates ( or more ) are used and run at a high reflux ratio of 3 during the run. The Pot heat of 3000 watts stays constant and does not give flooding or weeping. A slow initial 2.2 L/hr take-off rate gives about a 13 hour run time. Input Data and Results are:

image.png
Next is the run time calculations for this run. Both distillate ABV and amount collected are given in the graphs. The ABV stays high for most all the run until tails start.

image.png
image.png

Flavorful Whiskey 80% ABV run
The second run to make a flavorful whiskey at 80% ABV distillate is a faster run starting with wash in the pot at 10% ABV. Only two plates are used at a very low constant reflux ratio of 0.4 . The constant Pot heat of 4000 watts does not give flooding or weeping. A faster 4.6 L/hr take-off rate gives about a 3 hour run time. Input Data and Results are:

image.png
Next is the run time calculations for this run. Both distillate ABV and amount collected are given in the graphs. The ABV gradually decreases during the run until tails start.

image.png
image.png

I hope this illustrates for you the input data and equipment settings needed to make these two different runs and what happens during the run. Of course, you have to know how to set your column deflagmater to achieve the take-off rate / reflux rate target.
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Re: Plate Reflux Column Operating Characteristics

Post by haggy »

Now let's look at the previous two very different runs using a bubble cap plate reflux column. The same close to neutral distillate run and an 80% Whiskey distillate run will be made as in the previous post for sieve plates. We can compare the bubble cap run settings with the sieve plate settings. Most of this information comes from studying many posts on these runs and including that information in my calculations.

The equipment here for both runs is a 4" diameter bubble plate reflux column with 5 bubble caps per plate and one cap down comer with deflagmater and product condenser. Each run starts with 16 US gal but at different %ABV in the potstill.

High ( close to neutral ) 95% ABV run - bubble caps
The first run to make close to neutral 95% distillate is a slow spirit run starting with low wines in the pot at 40% ABV. Four plates ( or more ) are used and run at a reflux ratio of 2 during the run. The Pot heat of 2000 watts stays constant and does not give flooding or weeping. A slow initial 2 L/hr take-off rate gives about a 16 hour run time. These conditions are close to the flooding limit. Input Data and Results are:

image.png

So, for the close to neutral product, the bubble caps have to be run at lower heat ( 2000 watts vs 3000 watts ), not as high a reflux ratio and at a 10% lower take-off rate giving about 16 hour run time vs 13 hours for sieve plates.


Flavorful Whiskey 80% ABV run - bubble caps
The second run to make a flavorful whiskey at 80% ABV distillate is a faster run starting with wash in the pot at 10% ABV. Only two plates are used at a low constant reflux ratio of 0.5 . The constant Pot heat of 2800 watts is at about 90% of the flooding limit. A 3 L/hr take-off rate gives about a 4.5 hour run time. Input Data and Results are:

image.png

Again, the bubble caps have to be run at lower heat ( 2800 watts vs 4000 watts ), about the same low reflux ratio and at 3 L/hr vs 4.6 L/hr for sieve plates. Run time is longer, about 4.5 hours vs 3 hours for sieve plates.

The product ABV% should be fairly similar in both runs, but please refer to other HD posts for their product ABV% experience.
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Re: Plate Reflux Column Operating Characteristics

Post by haggy »

Yeasty Boyz has a post where he describes his 3" sieve plate reflux column build in good detail. The build had all the best dimensions of plate hole area and down comer size and defleg heat transfer area. He also discusses several runs he made, I would like to discuss two of these runs here. One run was at very low heat input (close to weeping ) and the other at very high heat input ( flooding ).

The build specifications are in this post, note the high 8.6% hole area in the plates:
The Yeasty Boyz wrote: Wed Sep 20, 2017 10:59 pm NChooch had dimensions on his build which was very helpful to me so I would like to do the same.

Here are the dimensions/specs of the build.

8pc Modular Flute

4 Plate Column:
Diameter: 3”
Length: 26"
Distance between plates: 5”
Plate Thickness: .07in
Number of holes/plate: 192ish
Diameter of holes in plates: 1/16”
Open Area of plate .588in2 = 8.6% open space/plate
Downcomer diameter .875 in
Downcomer cups diameter 1.25 in
Height of downcomer over plate .75 in
Plates not fixed, held by 1/4 20 SS rod/nuts
Sight glasses are 2.5” copper to SS ferrule both wrapped in tephlon/no gasket.

Packed Section:
Diameter: 3”
Length: 24”
Plate at both ends with 1/8” holes
Held together by 1/4 20 SS rod/nuts
Packs 165in3 or 2.7 Liters

Dephlegamator:
Diameter: 3”
Length: 8” (excess length to fit ferrules)
7 pc of .5” diameter tubes at 5” each
2pc .25” elbow sweat

Gin Basket:
Diameter 3”
Length: 8”
Sight glasse is 2.5” copper to SS ferrule both wrapped in tephlon/no gasket.
Later in the post, he describes a run where he probably had weeping:
Re: 3" Flute Build
Post by The Yeasty Boyz » Sun Oct 01, 2017 6:46 pm

Saltbush Bill wrote:
2400-2500ish is usually about right for most, a slower take off speed may have helped at 2000w.
I see all sorts of take off rates quoted for these stills but personally stick to 2-2.5L an hour. Each stills sweet spot will vary a little.
Good to know SaltbushBill. Im giving it another try with just the 2000w now. I just got it to flow. With only 2k w the plates are not (loading ) correctly. They are shallow and more uneven. Its putting out 170 proof as opposed to the 194 it hit with gas.

I ( Yeasty ) did a run yesterday and it turned out that 2000 W was not enough to ( load )the plates (while collecting.) I was able to run the 5500 w element and ( load ) the plates but felt the heat should have been backed off so I ended up running both elements and doing a stripping run.
So, I ( haggy ) ran the 2000 watt case on the reflux plate calculator and got these results:
image.png
You see that the hole velocity is 3.3 ft/sec, very close to the 3.1 ft/sec weep point velocity, almost weeping and hard to load the plates. So, a good confirmation of the weeping point and agreement with the sieve plate weeping curves in my October 13, 2022 post.

Then there was a run at very high heat input, 7500 watts.
I (Yeasty ) am curious who has built larger or more intricate dephlegmators.... I found that mine could not handle all the vapor when I threw 7500 watts at it. The output water was warm but the vapor path was too short and direct to knock all of it down.
Here is the 7500 watt run calculator results :
image.png
You see that the hole velocity of 12.2 ft/sec is above the 11 ft/sec flooding maximum and he probably had flooding along with the dephlegmator limit point.


Finally, a good operating point for this sieve plate reflux column would be about 3000 watts and 2 to 2.5 L/hr take-off rate. Download the Excel file in my November 4 post and check it out.
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Re: Plate Reflux Column Operating Characteristics

Post by haggy »

New Subject ------------------------------------------DEPHLEGMATER ANALYSIS-----------------------------------------------------------

I did some heat transfer calculations on the dephlegmater ( reflux condenser, RC ) and have come up with some estimated gpm water cooling rates. First, we need to define the different types of reflux column operations and then see how the dephleg works and undestand the differences between them.

LM Operation
The LM reflux column has the reflux condenser above the liquid take-off point and totally condenses all the vapor coming off the last active plate. It can subcool the vapor also. The liquid drops down onto a collection plate and can go through an exit opening. A valve in the exit line controls the take-off rate D of the liquid product. A product condenser (PC) to cool the liquid product to the final exit temperature is optional. The vapor rate V to the LM is calculated as:
V lm = D * ( R + 1 )
where R is the reflux ratio. What is unique is that the vapor rate V is the same for different values of D. Vapor rates are higher in the LM vs the other operating modes, so a higher cooling water flow gpm is needed. Control of the liquid product D by the inline valve is not difficult. The reflux condenser can be a spiral coil with cooling water through the coils going down through the top of the column to condense the vapor.


VM Operation
The VM reflux column splits the vapor off before the reflux condenser. The rest of the vapor V goes to the RC and is totally condensed and subcooled and returned to the top plate. The vapor rate D that is split off is controlled by a valve in the exit line. The vapor rate to the dephleg RC is calculated as:
V vm = D * R
For the VM, the vapor rate to the dephleg does vary as the product rate D changes. Control of the vapor rate D through the in-line valve is not difficult. A spiral coil RC above the vapor take off point can also be used in the VM operation.


CM Operation
The CM operation has the dephleg directly above the top plate. The vapor V is only partially condensed and some vapor D goes through the dephleg without being condensed. The dephleg is usually a shotgun shell and tube condenser with water into the shell and vapor through the tubes. The rate D is controlled by the amount of cooling water through the shell of the dephleg. The vapor rate out the dephleg is:
V cm = D * R
the same as the Vvm rate but done by a different means. Both have less vapor condensed than the LM so the amount of cooling water gpm is much less. Since this is a partial condenser, any change is cooling water rate or inlet temperature will change the vapor rate D coming out the top of the dephleg. Usually, cooling water is fed into the bottom of the PC then comes out the top and then into the bottom of the dephleg and out the top. Different water flow methods are also possible. The exit vapor D goes to the final PC and is condensed and cooled there.

CCVM
There also is a Condenser Controlled VM where the spiral coil is moveable down the column into the vapor opening part way or all the way. I will consider this as a VM type.

Here are diagrams of the three operations taken from the following post:
VM, CM, and LM confusion
Post by BW Redneck » Wed Feb 20, 2008 9:28 pm
image.png
image.png
image.png
So, nothing new so far except how to determine the vapor rate V. I have integrated a calculation of the dephleg heat transfer into the calculations in the above Excel spreadsheet for plate reflux column characteristics. The input data includes the heating power watts, the pot ABV% and the distillate take-off rate D. From these inputs, we can find the reflux rate R and then calculate V for each operational mode ( LM, VM, CM ).

In my past life, I did some complex heat transfer calculations for shell and tube exchangers, :thumbup: so I used those calcs in this work. Let us specify a typical 4" sieve plate column run and do the heat transfer calculations and get the cooling rates ( gpm ) required for each operation, LM and CM. Del T is the log mean temperature difference across the walls of the tubes. U is the overall heat transfer coefficient.

So, here is the input data for a run we will examine. Let us use the same reflux condenser for both the LM and the CM.
image.png
The shell and tube reflux condenser heat transfer calculation results for a LM operation is next:
image.png
The shell and tube dephlegmater heat transfer calculation results for a CM operation are next:
image.png
And, since R=1, the CM requires half as much cooling as the LM. The gpm required for the CM is much lower, only 0.075 gpm. If the gpm rate or inlet water temperature varies much, the take-off rate would be harder to keep constant. The cooling water rate and inlet temperature controls the D rate in a CM.

A VM operation is similar to the CM since both have the same V vapor rate to the reflux condenser. The main difference is that the VM reflux condenser could subcool all the vapor it sees. It is a total condenser, the CM dephleg is a partial condenser. So I do not include VM calculations here, they are close to the CM results. The cooling water rate does not control the D rate in a VM, a valve does this.

LM vs CM
The premise here is that the same heat exchanger is used in the comparison. Maybe I should use a spiral coil going down the top of the column for the LM. Maybe some other time I will do this.
Note the big difference in the heat transfer coefficient U between the LM and the CM. ( 70 vs 40 BTU/hr/ft^2/F). This is because the required water flow rate is much lower in the CM.

Where are we :econfused:
This post sets the premises for a dephlegmater analysis and shows that low water flow rates for the CM can lead to less than perfect control of the CM operation. Changes in flow rate or inlet water temperature can affect the operation.

In the next post, I will look at a range of power watts, several distillate rates, and 10% and 40% pot ABV and see the cooling rates required for the LM and CM modes of operation.
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Re: Plate Reflux Column Operating Characteristics

Post by haggy »

Here is a follow up on the dephlegmater analysis. I will try to define the operating range of dephleg cooling water gpm flow rates for a 4" x 4 plate reflux columns and offer some guidelines for distillation run set points. Both LM and CM cooling management operations are examined.

The LM cooling management option:
The vapor rate to the dephleg reflux condenser to be cooled will vary with the pot watts and the pot charge % ABV. Since all the vapor goes to the RC, changes in the reflux ratio and distillate will not affect the required cooling rate.

Pot watts were varied from a low weeping point (1600 watts at 5% hole area) to the high flooding condition ( 8000 watts at 8% hole area ) for a 10% pot ABV. Pot charges of 10% ABV and 40% ABV were evaluated. The results are applicable to both sieve plates and bubble cap plates, but weeping or flooding will occur at the low and high wattage points. See the previous graphs for the range of weeping and flooding for each type plate. The dephleg shotgun design used is given in the previous post. It has 0.69 ft^2 area for heat transfer. The vapor to the LM reflux condenser is totally condensed and subcooled.

LM Operation Cooling Water gpm for Pot with 10% ABV
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LM Operation Cooling Water gpm for Pot with 40% ABV
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The gpm flow is much higher for the LM operation than the other operations. Changes in the liquid distillate takeoff rate are done by the valve setting and do not affect the cooling rate. The LM operation is stable.

The CM cooling management option.
This analysis is more complex because the cooling water gpm rate also depends on D the distillate take-off rate in addition to depending on the watts used and the pot % ABV. The entering vapor is only partially condensed in the CM operation and the vapor distillate D exits out the top of the dephleg. A VM operation will result in very similar gpm cooling rates as the CM, less vapor is condensed since it is taken off below the VM reflux condenser. The vapor is totally condensed in the VM reflux condenser.

CM Cooling Water gpm for Pot with 10% ABV
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CM Cooling Water gpm for Pot with 40% ABV
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Water Temperature Changes
When the cooling water inlet temperature changes, the temperature difference ( Del T ) across the tube walls changes. This causes more or less heat transfer ( U*A*Del T) and can change the take off rate of a CM reflux column. It affects the CM operation, but is not a big effect on a LM or VM operation.


What guidelines can we get from this analysis:
Most HD distillers do not have flowmeters on their water lines. But, maybe this will encourage some to add a flowmeter and find the best set points and see how things change when water flow or water temperature changes.

The LM and VM modes of operation are the most stable and have less difficulty. The distillate take-off rate is not affected very much by changes in the cooling water flow rate or temperature.

The charts do show the conditions where you may have trouble in a CM operation. Those are the conditions where the dephleg cooling water flow rate is low, say less than 0.1 gpm. From the CM charts at 10% pot ABV, 1.5 L/hr is a more stable rate above 2200 watts power, at 2.2 L/hr above 3000 watts is not too bad, at 3 L/hr run above 4000 watts and at 4 L/hr run above 4500 watts. To be more conservative, run at the conditions ( watts and L/hr ) above 0.2 gpm deph cooling water rate.

At a given pot wattage, decreasing the take-off rate will give higher dephleg cooling water gpm and should improve the stability of the operation. High pot heating watts require higher water gpm. For sieve plates, runs above 4000 watts and 3 L/hr or less may be best CM operation. But watch out for flooding conditions. Check the previous charts for the watts flooding limits.

Bubble cap columns will flood at lower pot watts than sieve plates. So they are run at lower pot watts and the dephleg cooling water is at a lower gpm. Bubble cap columns probably are more sensitive to dephleg cooling water changes than sieve plates. Check the previous charts for the bubble cap watts flooding limits.

For runs at 40% pot ABV, dephleg water flow gpm is most always above 0.1 gpm , so CM operations are more stable at 40% pot ABV. So strip and spirit runs should be more stable operations with a CM reflux column.

I hope these guidelines help you find the sweet spot for your operation.

haggy
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higgins
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Re: Plate Reflux Column Operating Characteristics

Post by higgins »

haggy,

your spreadsheet has helped me tremendously with learning to run my 4" sieve plate column. I appreciate all the hard work you've done to develop this, and the feedback on my run data.

If your HTML version is ready to use, I highly recommend that it be added to the HD Calculators section.
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Re: Plate Reflux Column Operating Characteristics

Post by tjsc5f »

haggy wrote: Fri Dec 16, 2022 9:16 pm I have integrated a calculation of the dephleg heat transfer into the calculations in the above Excel spreadsheet for plate reflux column characteristics.
Hi Haggy, could you post up the most recent version of your calculator that includes these heat transfer calcs?
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Re: Plate Reflux Column Operating Characteristics

Post by haggy »

tjsc5f,

Thanks for your interest in the heat exchanger calculator. I have Excel spread sheets for three of them.

1. Deflag RC Shotgun
2. Deflag RC Coil Dimroth
3. Shotgun PC

They are not tried and true ( have not had much data to confirm them), but use the best established heat transfer coefficient correlations that I can find. I did test the RC Coil Deflag heat exchanger with Higgins run data and it seemed to work well. See my June 23 post in "Higgins 4" 3 sieve plate column build" for that example.

I am reluctant to post the heat exchanger Excel spreadsheet files. The user has to interact with the calcs and find the cooling water (cw) flow rate that matches the heat load of the vapor with the heat load of the cooling water. The results are very sensitive to the input conditions. Vapor ABV% , Pot ABV% Pot watts strongly influence the cw rate needed. Wrong answers can easily be obtained if these input conditions are off. Sometimes, you get an error message.

So,
I am working on JavaScript browser versions that find the best cw flow rate for you. They could go in the HD Calculator Section in the future if they are accurate enough and the moderators want them. Almost done with them, more real run data is needed to confirm them.

Here is an example of the browser version of the RC Coil for that post for Higgins.
image.png
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However, if you want, send me a PM with your email address.
I can send you one of the heat ex calculator files.

haggy
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