Could you use distillate flow rate as the monitored variable for feedback to the controller?

Indeed and that would be perfect. I fear that flow control measurement is a little expensive.

 

Re PID,
yes in this case it uses temperature,

At the simplest, a temperature controller could be "on" till a set temperature , then "off"
this works in say a house,

The "problem" is to do with steps.
The simple controller, if you use a small heater, it can take ages to reach temperature, but it will over shoot the temperature very little.
Alternatively, to speed up how soon you reach temperature, you use a bigger heater, but that will tend to over shot the required temperature,

A PID controller, takes the current temperature, and calculates how fast the approach to the real temperature is and how fast the acceleration to the real temperature is.
The PID, then sets its output such that when a long way away, it puts out lots of power, and as it gets closer, lowers the power,
such that the output has minimal if any overshoot, but moves as fast as possible.

https://en.wikipedia.org/wiki/PID_controller

 

The problem with the boiling point is a function of the solution (liquid) which is a combination of many components each with a different boiling point. As these components are driven off the boiling point of the solution intrinsically alters.

When you set water on a stove in a pot at 1kw and it will boil at 94°C (well certainly where I am from), if raise the power to 2kW the water will still boil at 94°C but there will be more steam due to the increased power. The increased steam for us is increased volume output. So you can control the output of water vapour by simply applying more power.

If you put a pot of alcohol wash on the stove and set it to maintain the solutions boiling point, 78°C. The lower BP components will boil off as the their BP is reached which in turn alters the BP of the solution. As the lower BP components have boiled off the average BP now increases. However the stove is set to 78°C and will maintain that temperature. The result is that the process has now stalled as any substance with a BP of say 80°C will not be able to evaporate. So one now needs to lift the temperature to say 81°C, and the cycle repeats.

If one was to say set the PID to reach 94°C to avoid all these adjustments then the amount of energy required would increase the output past the pencil lead trickle, the condenser would not have sufficient capacity to cool the distillate and the alcohol % would reduce. All undesirable attributes.

It is for this reason that some argue that controlling the power into the still is better than controlling temperature. The PID lads insists that PID's are best but they are not technical enough to explain it to me who probably would not understand.

You're describing latent heat. You can put a pot of pure water on the world's hottest stove, an acetylene-powered monster stove, and the temperature of the water won't go over 100C. Latent heat is the phenomenon that occurs at the temperature where a given substance changes state from solid to liquid or liquid to gas, or back again.

If the alcohol you want evaporates at 80 C then you can set your still for 80C and simply discard anything that evaporates prior to that.

 

Do you have a p/n for this 4kW thyristor controller?

 

https://www.ebay.com/itm/Eurotherm-...-/192559079565?_trksid=p2349624.m46890.l49292

 

Set temperature limiter at 95 °C and control vapor pressure:


ADDED:

The problem with a calibrated hole is that you have a pressure vessel with a finite hole, filled with highly volatile liquids, in short you have a bomb.

Bomb? Really?
Even in hermetic vessel, filled with pure ethanol, vapor pressure will 1200 mm Hg @ 95°C.
So manometric pressure will 1200-760=440 mm Hg only.
With mix water/ethanol and existing output hole vapor pressure will much lower.

Log10 of ethanol vapor pressure vs. temperature. Uses formula:

For hundreds of years distillers have been using boiling a kettle with a simple fire beneath and then condensing the vapour to make alcohol, it is deceptively simple

How about technological progress?

 

Do you have a p/n for this 4kW thyristor controller?

5000w ac 220v high power electronic regulator scr voltage regulator module Sale - Banggood.com

I call it 4000W as I think that is a safe limit. I did open the unit to check on the SCR rating but cannot remember the component number but the maximum output was 20A. I am running a nominal 3000W element (measured max 2 700W) when up to temp will be cut back to around the 1 100W range.

 

Set temperature limiter at 95 °C and control vapor pressure:

View attachment 231618

For hundreds of years distillers have been using boiling a kettle with a simple fire beneath and then condensing the vapour to make alcohol, it is deceptively simple. The problem with a calibrated hole is that you have a pressure vessel with a finite hole, filled with highly volatile liquids, in short you have a bomb. Now one would have to fit a pressure release valve. I distill purely for home consumption and make a couple of bottles of Gin every now and then. So I am mindful of the the cost vs. benefit factor.

I think that I will simply stick with my voltage controller, it works. KISS probably is best at my knowledge level.

 

I fear that flow control measurement is a little expensive.

Not for a home-made gauge. A simple gauge operating on the tipping-bucket principle would suffice for moderate flow rates. Or if the flow rate is low then an opto-sensor could be used to count drops of distillate.

 

I think that I will simply stick with my voltage controller, it works. KISS probably is best at my knowledge level.

This is frustrating. Frustrating to know exactly the solution to someone's problem and spell it out over and over, only to have them throw their hands up in defeat as you hadn't said anything at all. It's like trying to convince a woman to leave an abusive relationship.

Not your fault. Or at least, more my fault than yours. Maybe if I had explained things better. Oh well, maybe next time.

 

Hello there

Maybe if I had explained things better. Oh well, maybe next time.

The only time you should never fail is the last time you try. Besides with that information I think I'll start a microbrewery I mean in-house for personal consumption thank you sir.

 

strantor, on the contrary. You assisted in clarifying things for me. So the control variable I have realised is NOT temperature but volume. An azeotrope does not give off substance A at 60, then substance B at 65 and so on. It gives off an ever changing composition of chemical substances. As it does this the boiling point lifts as the low boiling point substances are removed. So with a moving variable, which you are unaware of, is difficult to control.

However when you observe a solid stream of circa 2mm diameter, this delivers product in the range that is desirable. Maintaining this stream is the golden rule for the home distiller with 30 - 50l boilers, it is how you maintain that stream which is hotly debated.

You cannot control it by temperature as the components in the azeotrope will boil off at their rated boiling point. Set the controller to 80 and substance A will only boil of at 60. Can't change that fact. You may have 10 components with 10 BP's, which do you control? The average? But the average is moving and you don't know what the average is.

However by applying more energy one can have the liquid simmer which will result in a drip drip or vigorously boil which will result in a sold stream. The components will still boil off at their relative BP's.

It is counterintuitive and the crowd that tries temperature control as a means of control will for the most part migrate to power control except for some diehards will defend the indefensible.

So maybe you can turn the PID into a power controller, bit why? Buy another PID one with analogue inputs, buy another SSR with analogue inputs, go through some fancy settings and experimentation, and possibly force a PID out of its comfort zone. Why not just take a power controller from the beginning, when the stream moves alters every now and then simply tweak an analogue know and you are back on track. It may well be visual control be home distillers rarely leave the stills for safety reasons. So while there you may as well become your own PID.

If we could use the flow meter as a variable for the PID then a different story but now the cost of control moves past the average home distiller budget.

 

If we could use the flow meter as a variable for the PID then a different story, but now the cost of control moves past the average home distiller budget.

I don't see why. Did you read post #29?

 

I don't see why. Did you read post #29?

I did I have been googling flow meters and PID's tonight to see if they are cost effective.

 

Can you make your own flow-meter? A micro-tipping-bucket type would be low-cost.

 

Can you make your own flow-meter? A micro-tipping-bucket type would be low-cost.

A digital rainfall gauge perhaps

 

What sort of flow-rate are we talking about? 1drop/sec, 1ml/sec, 1litre/min .... ?

 

Probably anything from a drop per second to 5 litres per hour.

 

However when you observe a solid stream of circa 2mm diameter, this delivers product in the range that is desirable.

Control liquid flow:

For stream 2 mm diameter, calibrating hole should be 2mm diameter too.
Or use valve instead of calibrated hole, then you can set desirable diameter of stream manually.

ADDED:
LDR: Light Dependent Resistor NSL 4960, 1 MOhm, 500 mW, 320 V, 550 nm (peak).
It should be connected directly to SCR regulator, instead of variable resistor (control knob).

LED: Super-Green LED (GaInN/GaN) RL5-G5023 3.5 V, 20 mA, 5000 mcd, 524 nm (peak).

 

Control liquid flow:
View attachment 231990
For stream 2 mm diameter calibrating hole should be 2mm diameter too.
Or use valve instead calibrated hole, then you can set desirable diameter of stream manually.

Mmm that's rather elegant, mmm gonna muse on this one,