Why does PID control work?

[dmachura]

After introducing myself in the new to distillation and stating that I use PID control to run my still I was informed (more than once)that it is impossible to control a still using vapor temperature at the top of the still. But yet after following George Duncan's instructions I can get an excellent neutral spirit at 185 proof.

So my question is why does it work for me? Am I doing something so wrong that its right?

[bluefish_dist]

I don’t think people say that it’s impossible to control a still by still head temp. They say it’s impossible to control by boiler temp. Big difference. I have often thought of automating the control of my reflux with a controller.

[LWTCS]

Thermostatic control can still put vapor into suspension,,,,obviously.

Let me ask you:
Have you only ever used your PID control for heat input to your boiler?
Have you not read through the various explanations as to why PID controlled heat input is not optimal?

After all of the explanations on all of the recent "PID" threads by multiple qualified members I can only assume you don't yet understand or you are trolling?
Are you trolling?

[OtisT]

High ABV and good separation (compression) of your fractions are two different things. The better your compression, the larger your hearts cut can be because you got more of your heads in fewer jars and more of your tails in fewer jars, so there is more volume of your hearts in between.

If you run your fractioning column way to hot, you will get a high ABV output that is stacked like a pot still run (no compression).

My understanding of the issue with a PID controlling your boiler is that the PID will cycle your element on/of, like an electric burner on a stove. This means your boiler produces more vapor when the element is on, and less when it is off. Changing the amount of vapor changes the speed of that vapor in your column, and there in lies the rub.

There is a fine balance between heating (vapor) and reflux cooling that you need to achieve to stack your fractions and get good separation/compression. If your vapor speed is continually changing, it is hard to achieve/maintain that balance. The taller your column, the more forgiving it would be dealing with vapor that speeds up and slows down.

You can affect vapor temp at the head, within a range, by making adjustments to heating/cooling. Better separation will result in lowerIng vapor temp at the head.

Hope this helps you understand why PIDs are not the right tool for the job when it comes to boiler control.

Otis

[StillerBoy]

But yet after following George Duncan's instructions I can get an excellent neutral spirit at 185 proof.

A 185 proof is just an average efficiency for a 2" x 40" reflux column setup, which is only a 92.5 % abv.. that can be achieve wide range of setting or precision setting is not all that critical..

Now try this.. using your PID and and your unit, and work at achieving a 190 proof or 95 % abv.. 185 proof is relatively easy to achieve, but 190 proof, requires understand of how vapors work within a packed column and in relationship with the RC..

PID will allow you to produce product, as you have experience and many of the other who use PID's, but not very useful for achieving 95%.. reason is that the column vapors need to be in a state of equilibrium, and the vapors need to be maintain / held in a very steady state of equilibrium.. and that can only be made to happen by a steady power input and a constant water temp at the RC..

A slight variation of either one and the column vapors fall out of equilibrium.. to fully learn about the equilibrium in a column, install a sight glass at the bottom of the column and one at the very top.. then watch the cascading effect in the packing.. it's very interesting to see the different with only a 1/4 amp change with do within a few minutes..

Mars

[Expat]

I can't believe we need to keep having this same conversation.

You can probably eat soup with a fork, but why would you?!

George is a hack.

[acfixer69]

After introducing myself in the new to distillation and stating that I use PID control to run my still I was informed (more than once)that it is impossible to control a still using vapor temperature at the top of the still. But yet after following George Duncan's instructions I can get an excellent neutral spirit at 185 proof.

So my question is why does it work for me? Am I doing something so wrong that its right?

So why don't you post the run sequence that you do to make your numbers with a PID.

[StillerBoy]

I can't believe we need to keep having this same conversation.

Cause the newbie is an instrumentation engineer who's giving himself a hard time at learning the art of distillation, plus he's a fan of George.. which by the way, distillation is not about instruments but about learning vapor behavior, which is what George fails to understand also..

Mars

[acfixer69]

I can't believe we need to keep having this same conversation.

Cause the newbie is an instrumentation engineer who's giving himself a hard time at learning the art of distillation, plus he's a fan of George.. which by the way, distillation is not about instruments but about learning vapor behavior, which is what George fails to understand also..

Mars

Chill man Heehehee

[shadylane]

I don’t think people say that it’s impossible to control a still by still head temp. They say it’s impossible to control by boiler temp. Big difference. I have often thought of automating the control of my reflux with a controller.

I have also
Having a PLC with enough inputs and control of the process could get the job done.
IMHO, the best use of a PID would be for temperature control.
A PID is very good at learning how much power is needed to heat something up, without over heating it.

[Saltbush Bill]

I can't believe we need to keep having this same conversation.

You can probably eat soup with a fork, but why would you?!

You and me both Expat, Explaining this BS over and over again to Newbie George fans is wearing thin fast.

[cranky]

dmachura, I'd like to know specifications on your still, how you are running it and how long it takes.

Edit: I see from your welcome thread you say you are running a 40" x 2" reflux column but that doesn't really tell us much. What type of reflux column?

[NZChris]

So my question is why does it work for me?

It works well enough because you have low expectations. The only time I've run my similar sized Bokakob at those low abvs was to make hand sanitizer out of my feints. It normally sits on azeo until the boiler runs out of alcohol.

[Setsumi]

I run a 5plate flute on propane, my take off sits at 92%. so no worries there from me.. but i do help actively guys in my community to understand stilling. most that run electric start with a PID, so i try to understand.

a PID learns to control a set temp. it does not learn how to deliver constand power, with constand power your head temp will naturally increase during your run since the abv in the boiler will diminish. yes on a reflux column that increase will be small... but there lies the problem. the smaller the difference between heads, harts and tails the bigger the challenge for good seperation.

[StillerBoy]

a PID learns to control a set temp. it does not learn how to deliver constand power, with constand power your head temp will naturally increase during your run since the abv in the boiler will diminish. yes on a reflux column that increase will be small... but there lies the problem. the smaller the difference between heads, harts and tails the bigger the challenge for good seperation.

And here's another issue with chasing temp.. it is never constant from one run to the other... why... because most people don't pay attention to the boiler load amount and the boiler load abv.. a variation in either one will give different vapor temp at the base of the column, which will require different management setting in power and water flow, which will be required to achieve the end result wanting..

I've been running for yrs a reflux concentric column unit setup on an electric controller with temp probes meters and sensors.. I know from experience, just how critical a slight adjustment of power or water flow will affect the column vapors equilibrium.. and if you start a run without knowledge of that info, one will be constantly making adjustment or chasing a temp number..

Mars

[StillerBoy]

Chill man Heehehee

Yeah.. those PID and George followers..

Thanks

Mars

[bluefish_dist]

And here's another issue with chasing temp.. it is never constant from one run to the other... why... because most people don't pay attention to the boiler load amount and the boiler load abv.. a variation in either one will give different vapor temp at the base of the column, which will require different management setting in power and water flow, which will be required to achieve the end result wanting..

I've been running for yrs a reflux concentric column unit setup on an electric controller with temp probes meters and sensors.. I know from experience, just how critical a slight adjustment of power or water flow will affect the column vapors equilibrium.. and if you start a run without knowledge of that info, one will be constantly making adjustment or chasing a temp number..

Mars

I felt that head temp run to run when adjusted for air pressure was quite repeatable. Yes, it could require different settings to achieve the same temperature, ie more or less reflux depending on boiler loading. In the end I could and did run the same temperatures run to run. Vodka was the only challenge as air pressure could cause up to a 1 deg temperature change. Usually not a big deal unless a front came through and the abv to temperature changed.

[StillerBoy]

I felt that head temp run to run when adjusted for air pressure was quite repeatable.

I like the use of words such as "felt" and "quite".. you are correct on both count as that has also been my experience..

Vodka was the only challenge as air pressure could cause up to a 1 deg temperature change.

Both air pressure and temperature do have a influence on the top temp.. I'm also notice the different between running in the winter vera summer..

Mars

[Setsumi]

a PID learns to control a set temp. it does not learn how to deliver constand power, with constand power your head temp will naturally increase during your run since the abv in the boiler will diminish. yes on a reflux column that increase will be small... but there lies the problem. the smaller the difference between heads, harts and tails the bigger the challenge for good seperation.

And here's another issue with chasing temp.. it is never constant from one run to the other... why... because most people don't pay attention to the boiler load amount and the boiler load abv.. a variation in either one will give different vapor temp at the base of the column, which will require different management setting in power and water flow, which will be required to achieve the end result wanting..

I've been running for yrs a reflux concentric column unit setup on an electric controller with temp probes meters and sensors.. I know from experience, just how critical a slight adjustment of power or water flow will affect the column vapors equilibrium.. and if you start a run without knowledge of that info, one will be constantly making adjustment or chasing a temp number..

Mars

yip, was going to post that as well, boiler volume and abv even on the same mash will differ and change your boiling temp, on a constand heat input no worries. on temp management, good luck.

[NZChris]

Dmachura's thermocouple is at the top of a reflux still, so I don't know that talk of temperatures in the boiler, or lower in the column, are relevant to his question.

[dmachura]

I don't know why pid control brings such vitriol from some members, the technique produces an acceptable product (okay for me) so it obviously works.

I will explain my procedure, but I'm sure most of you already have watched Georges videos know. My column is 2" x 40" copper tube packed with about 20 inches of stainless steel scrubbers. I use birdwatchers sugar wash recipe to make 23 litres which is 10 to 12 percent ABV.

I let my still heat up using the pid to 80F at the top of the column, of course when vapor breaks through the temp rises to over 100F. At that point the pid turns off the power and the temperature drops I then increase the setpoint as the temp drops 10 to 15 degrees at a time until the overshoot gets to about a 150F. at that point I let the pid and column stabilize. I will say at this time my pid controller is tuned so it holds the temperature exactly after a minute or two. I will then increase the setpoint slowly to 170F At this point there will be a slow drip from my condenser of about 1 to 2 drops per second. I leave it here until I collect 50ml of condensate. I throw away the condensate and slowly increase the setpoint to 175 or 178 until I get a steady drip. I leave the temperature unchanged and collect one quart of 180-185 proof liquid it takes about 90 minutes. I then slowly increase the temp to 185F and collect another quart of 170- 175 proof liquid in about 90 minutes. Then I increase the setpoint to 190 and collect another quart at about 100-110 proof in another 90 minutes. Then I shut the still off.

I will also note that my pid uses a ssr and not a scr so I cannot put the controller in manual but it is tuned so it does not cycle the temperature at the measurement point, at the top of the still.

[acfixer69]

Dmachura's thermocouple is at the top of a reflux still, so I don't know that talk of temperatures in the boiler, or lower in the column, are relevant to his question.

He said nothing of reflux still. He has no reflux condenser only tall pot with some packing stuffed in it. That temperature means nothing to running a pot still.

[Tummydoc]

Dmachura's thermocouple is at the top of a reflux still, so I don't know that talk of temperatures in the boiler, or lower in the column, are relevant to his question.

He said nothing of reflux still. He has no reflux condenser only tall pot with some packing stuffed in it. That temperature means nothing to running a pot still.

In his intro, he clearly states he is using a reflux still and hitting 175 proof. Above he says 185.

[acfixer69]

He doesn't here witch would have been helpful information. His proof was too high for a pot still but since he uses a PID for a controller I didn't trust those as accurate either.

[LWTCS]

Vitriol? Wrong adjective.
If 185 is where you reckon your best neutral lives then good for you.
I85 in the real world is a no man's land.
Too proofy for flavored spirits and clearly not clean enough for premium vodka.

Course it only needs to be good enough for you. Congratulations on your shed worthy spirits.

[NZChris]

After doing a lot of research I've built myself a 40 x 2 inch reflux still, using pid control works like a charm. I've now made 10 batches of neutral spirits at 175% using bird watches excellent sugar wash recipe. Thanks to bird watcher, odin, and george from Barley and Hops videos.

[LWTCS]

After doing a lot of research I've built myself a 40 x 2 inch reflux still, using pid control works like a charm. I've now made 10 batches of neutral spirits at 175% using bird watches excellent sugar wash recipe. Thanks to bird watcher, odin, and george from Barley and Hops videos.

I stand corrected.
175 is even deeper into no man's land for a neutral. 175 for neutral says you? Excellant says you? Sure. What ever you say.

[StillerBoy]

He said nothing of reflux still. He has no reflux condenser only tall pot with some packing stuffed in it. That temperature means nothing to running a pot still.

I'm in agreement with the above statement..

His description of the method of operating his unit is a pot mode method.. even with 20" of ss scrubbies in a 40" column doesn't make it a reflux column.. no reflux condenser.. pot still..

And he's all over the map with his lack of understanding vapor behaviors and style of still designs..

Congratulations on your shed worthy spirits

Plus no cuts.. Yeah as Larry stated,

Mars

dmachura.. Post a picture of your unit with the reflux condenser attached..

[Tummydoc]

Mars, he says its a reflux still in his intro. And if he's hitting 90% ABV, its not likely to be in pot mode. I agree I'd like more details on his still, VM, LM, CM, CCVM? Also boiler size: since he's only collecting 3 quarts, I would guess the boiler is under 5 gallons.

[Saltbush Bill]

clearly states he is using a reflux stil

He doesn't here witch would have been helpful

Easy mistake to make AC......people don't make it easy at times
170 proof = .85% abv. That's pretty poor preformance from a reflux still.
My guess is the lack of power to the boiler is retarding the amount of reflux.....hence low abv.
Most are here to do things the right way and make excellent booze. Others it seems are happy to settle for mediocer booze and less than mediocre methods of making it.
Can lead a horse to water......but can't make em drink.