Calculating reflux ratios

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BDF
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Re: Calculating reflux ratios

Post by BDF »

Most of those questions were posed to set the stage for why I wanted to get around having to deal with them.
I don't believe we need to since we are working in moles and the LHV (heat of vaporization)for water/ethanol on a per mole basis is extremely close
They're pretty close, Ethanol (38560 joule/mol) and Water (40680 joule/mol), but when one is 5.5% higher than another that can add up with other unknowns.
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Re: Calculating reflux ratios

Post by flyingdutchman »

True :D
Its a ballpark estimate. The temperature model would be a lot more accurate IMHO.


There's always the low tech LM method. Drain the collection well then open the collection valve all the way for 1 minute and see what you get for 0% reflux.
measure twice cut once and if that dont work get a bigger hammer!
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Re: Calculating reflux ratios

Post by Undies »

Slightly off question, but still on topic... I have a VM still. My question is also about measuring the RR.

The coolant water starts 'cold', then enters the product condensor, leaves 'warm', then enters the reflux condensor, and finally leaves 'hot'.

I measure the temperature of the coolant water at the 'cold', 'warm', and 'hot' stages.

If my valve is closed, the temperature of the 'cold' and 'warm' are the same, but 'hot' is high - 100% reflux. If I were to (hypothetically) block the reflux condensor, the 'warm' and 'hot' would be the same temp, IE 0% reflux.

So, my question is, is it feasible to calculate the RR based on these three coolant temps?
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Re: Calculating reflux ratios

Post by Yummyrum »

Good question Undies :thumbup:
Nice thinking
I'm sure there is some correlation between them . I have mine set up like yours but my PC is so efficient , it barely changes the temp of the water for the small amount of product that goes through it compared to the RC which is cooling a high proportion of reflux vapour . But having the water feeds in series adds some complexity to analyzing as well .

I guess if I /we had an identical condenser for both the two vapour splits ( reflux and product) feed off a common supply rather than in series , it would be an interesting comparison as the temp changes should be exactly proportional to RR.

Not saying that your method is not doable but rather it would be difficult to correlate the data .
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Re: Calculating reflux ratios

Post by OtisT »

I believe you can. Power in equals power out. If you ignore all the heat loss inherent in the rest of the system, it should be close.

This kind of thinking last year led me to switch all my cooling for my VM to from serial to parallel, with independent control valves for each condenser. Before doing this I could not turn down my reflux low enough for some operations. Like you, I reverse engineered my way into concluding there was too much reflux due to the coolant temps. Months later I bought a sight glass and confirmed my thoughts on this.
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Re: Calculating reflux ratios

Post by Undies »

Thanks for the feedback guys! I've just calibrated my thermistors for the cold, warm and hot measurements. I use an Arduino to display the results and calculate the reflux ratio. Uncalibrated it appeared to work for my last run, so hopefully my next run will yield some accurate results. Thanks again, and I'll keep you posted.
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Re: Calculating reflux ratios

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Undies wrote:Thanks for the feedback guys! I've just calibrated my thermistors for the cold, warm and hot measurements. I use an Arduino to display the results and calculate the reflux ratio. Uncalibrated it appeared to work for my last run, so hopefully my next run will yield some accurate results. Thanks again, and I'll keep you posted.
Undies, you are my kind of nerd. Combining Stillin' and Arduino in the same post. ;-)

A year or more back I played a bit with Arduino MPCs and temp sensors on my still to monitor/control cooling. It was a great learning experience, but before I mastered the final solution I came to the conclusion that it was way overkill and there was no need for it. I could see this kind of automation helping large distilleries, especially alarms when tolerances are hit, but for my hobby needs it introduced complexity where it was not needed.

I'm not trying to talk you out of it. Just sharing my own brush with automation. I would love to see your final device and hear how it impacts your stillin.

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Re: Calculating reflux ratios

Post by Undies »

Thanks for the replies and support. I can deny it all I like, but using an Arduino for these purposes certainly makes me a nerd. :D

I could certainly use the Arduino to control runs, but I use it for monitoring purposes only. The temps of various things like keg, vapour, etc., are shown on a computer screen so I can keep an eye on progress. My palate is not good enough to test the product as I go, so I supplement that with feedback from data. It seems to work for me until I can learn to taste a bit better.
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Re: Calculating reflux ratios

Post by Yummyrum »

Well undies . You get a super Nerd wedgie from me too :D
Best of luck with your data logging and analysis . I'm sure you will find some corelataion between the two .
If anyone can , sounds like you're the man :thumbup:
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Re: Calculating reflux ratios

Post by OtisT »

Undies wrote: I could certainly use the Arduino to control runs, but I use it for monitoring purposes only. The temps of various things like keg, vapour, etc., are shown on a computer screen so I can keep an eye on progress. My palate is not good enough to test the product as I go, so I supplement that with feedback from data. It seems to work for me until I can learn to taste a bit better.
One idea on my list of to-dos was to line my tall column with temp sensors every few inches, bottom to top, to see the temp gradients durring fractioning. Would tell you if you need to slow down or can speed up a fraction run. As opposed to a screen, use multi-color LEDs to represent each sensor, and you could light your column like those "Christmas tree" starting lights at the drag track. Instant visual satisfaction........ Sorry. I'm a dreamer. :-)

Have fun. Otis
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Re: Calculating reflux ratios

Post by Undies »

Otis, can you feel us slowly walking backwards away from you? Oooooooo-kay... :)

But seriously, how much fractioning is going on in the column? I always imagined that once we were into hearts, the top X% was what we wanted, and everything below (100-X)% was junk we don't want? Or is it broken up into more fractions than that? Is your plan to have green LED's at the top, a small bar of orange, and red below that? The aim would be to keep orange close to the top, but below collection? That would be great to watch AND informative.
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Re: Calculating reflux ratios

Post by Kareltje »

I would like a paint that changes colour with temperature. I have seen liquid crystal displays for between 15 and 25 dgr C, but would like to see some between 75 and 100 dgr.
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Re: Calculating reflux ratios

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Undies wrote:Otis, can you feel us slowly walking backwards away from you? Oooooooo-kay... :)

But seriously, how much fractioning is going on in the column? I always imagined that once we were into hearts, the top X% was what we wanted, and everything below (100-X)% was junk we don't want? Or is it broken up into more fractions than that? Is your plan to have green LED's at the top, a small bar of orange, and red below that? The aim would be to keep orange close to the top, but below collection? That would be great to watch AND informative.
I feel that way too some days when I look in the mirror. ;-)

I may be all wet but you asked, so here was my reasoning at the time.... If each section of the column were at the same temp, then all the LEDs would be the same color. Use the current max temp as one end of the color spectrum, and the gradient will need to be a small range from that so you can easily tell apart 1 degree differences. You may need to adjust the resolution, depending on normal delta temps in your column during operation.

When you reach equilibrium, all one color or possibly a slight gradeient should be the normal state (regardless, a pattern will be present.) If, however, you start to pull product too fast you would see a temp change creeping up your column and you would know when you need to slow it down before going too far. After reaching Equilibrium, you could continue opening your VM valve until just before the creeping temp gets close to the takeoff point.

Oh, and forgot the mention the sensors likely should be inside the column to react in a timely fashion.

Who knows if it would work, because I gave up on it when I learned how to still. ;-)
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Re: Calculating reflux ratios

Post by Undies »

That sounds great, but a big project. I hope you get it going. Post some pics for us if you get it running. How are you going to measure temps? I use thermistors, but they seem to report back too inconsistently for such a sensitive temp range - even after exhaustive calibration. Maybe that's on me. :?
Last edited by Undies on Sat Aug 19, 2017 1:01 pm, edited 1 time in total.
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Re: Calculating reflux ratios

Post by Yummyrum »

Check these out Undies
http://www.hobbytronics.co.uk/ds18b20-arduino" onclick="window.open(this.href);return false;" rel="nofollow

Never tried it myself but Ive read as each one has its unique address you can have many of them connected and read them individually .
Sure they are plastic but easily housed in a metal tube with heatconductive paste
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Re: Calculating reflux ratios

Post by Undies »

Small update with this. I managed to get it all up and running, albeit with some dodgy reading from the thermistors (my fault). However, it did work very well. I could close the valve and watch the RR for to 100%, the open it all the way and watch it go to around 30%.

Could some maths person let me know how I calculate the RR in a ratio? IE 1:1 or 1:2. Does 1:1 mean half the vapour is getting returned to the boiler, and half it being collected? Does 2:1 mean 2 units going back to the boiler, and 1 unit going to collection?
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Re: Calculating reflux ratios

Post by Yummyrum »

Undies wrote:
Does 1:1 mean half the vapour is getting returned to the boiler, and half it being collected? Does 2:1 mean 2 units going back to the boiler, and 1 unit going to collection?
Thats how I understand it :thumbup: .....but we both could be wrong
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Re: Calculating reflux ratios

Post by still_stirrin »

Reflux ratio is the ratio of the vapor condensed and returned down the column to the vapor advanced and collected at the product condenser: liquid refluxed down the column / liquid collected at the product outlet

When the collected product is shutoff, ie equal to zero....100% of the produced vapor is returned down the column (provided your RC can manage that) and the reflux ratio goes infinite (division by zero).

When running in a pure potstill mode, with no passive reflux, the reflux ratio goes to zero....all produced vapor goes to the output condenser.

Here’s a little helpful explanation: http://www.solvent--recycling.com/reflux%20ratio.html" onclick="window.open(this.href);return false;" rel="nofollow
ss
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Re: Calculating reflux ratios

Post by still_stirrin »

As an addendum, if you could measure the mass of the distillate vaporized per unit time and you could measure the mass of the product collected per unit time, then the mass of the vapor refluxed would be the difference.

Vapor produced - liquid collected = liquid refluxed (mass measurements, not volumes)

The challenge here is to measure the vapor production mass...I guess a volumetric flowrate and a density could calculate the mass flow. But bear in mind that the density changes continually with the product produced. And it is a funtion of temperature dynamically as well. But temperature is a scaler and can be easily measured. And density could be potentially measured as the reciprocal of pressure, which can be measured with a transducer.

How much you want to spend on your automation will come to a head with this challenge. Good luck.
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Re: Calculating reflux ratios

Post by Badmotivator »

I think I might be able to offer a couple of simple ways to calculate the reflux ratio on a nearly instantaneous basis.

The first method involves knowing your maximum full-power take-off rate in pot still mode, and then comparing that to the actual take off rate in reflux mode, making adjustments if needed to account for the lower wattage input. Hopefully you have a meter which gives you precise measurement of your power input or you run your reflux runs at full power.

The second method involves measuring reflux condenser water input temperature, reflux condenser water output temperature, and reflux condenser water flow rate. These three measurements will give you a number of watts that are being removed from the vapor stream so to speak. Then you compare that number with the number of watts put into the boiler.

Hope that helps.
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Re: Calculating reflux ratios

Post by Badmotivator »

Whoops. I did the research myself a while back and came up with an equation which helps with the second method. It describes the relationship between flow rate, power input, and temperature change in water. I forgot to share it. I think it looks like this:

flow rate(l/min) = 14*power input (kW)/temp rise (degree C)

Plug in your reflux condenser flow rate and reflux condenser water temperature change, solve for power input (kW). This tells you how many kilowatts have been taken out of the vapor stream. Put another way, this number is a measurement of the power you are putting into your boiler that is not getting to the product condenser. Those kilowatts must be making reflux. Therefore your reflux ratio is this number divided by the kilowatts you are putting into your boiler.
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Re: Calculating reflux ratios

Post by Badmotivator »

still_stirrin wrote:As an addendum, if you could measure the mass of the distillate vaporized per unit time and you could measure the mass of the product collected per unit time, then the mass of the vapor refluxed would be the difference.

Vapor produced - liquid collected = liquid refluxed (mass measurements, not volumes)

The challenge here is to measure the vapor production mass...
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Establish a benchmark maximum product takeoff rate for the two likely conditions: a low ABV wash in the boiler and a 40% ABV low wines charge. They'll be pretty similar, I expect. Set up your still in the most pot-still-ish way you can, start a run, get the fores out of the way, then measure the takeoff rate. There's your "vapor production mass". :)
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Re: Calculating reflux ratios

Post by The Baker »

I just throw some yeast in the wash and let it go. Sigh.

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