Why you need a controller and what kind. (Electric heat)

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Why you need a controller and what kind. (Electric heat)

Postby Prairiepiss » Wed Nov 06, 2013 10:00 am

There is always a lot of confusion about the need for a controller when an electric element is used to heat a still boiler and or an electric heat source like a hot plate. So I would like to clear things up a bit with this post. It's not about which controller is best to use. There are plenty of threads about the different types of controllers. This thread is about why you need one. And what that controller needs to do for you.

Since you are reading this I am assuming you have already researched and learned the basic theory of distilling, if you have not, you should do so before getting too deep into this subject, otherwise you won't fully understand what is being said here.

Basic distilling:
You need to boil the liquid in the still boiler to produce alcohol vapors that can be recondensed into a higher ABV distilled spirit. The temperature that that liquid will boil at is dictated by the ABV of that liquid since it is a mixture of alcohol and water. It will be somewhere between 173f/78c (boiling point of 100% alcohol) and 212f/100c (boiling point of water). The higher the ABV the lower or closer to 173f/78c the boil point will be. The lower the ABV the closer to 212f/100c the boiling point will be. There are charts available to figure exactly what that boiling point will be.
Alcohol content of Wash

Just remember. You cannot control the temp of the boil the amount of alcohol does this.

This now leads me to why you need a controller for your electric heated still.

You need to be able to adjust how fast the liquid is boiled off. This controls how much vapor is produced. Less heat makes for a slower boil. And will make lower amounts of vapors produced. More heat will make the liquid boil faster. Producing more vapors. You need to be able to adjust the amount of heat. That you put into the still boiler. So you can adjust the amount of vapors produced and sent into the still head. I will give you a couple of examples.

Pot Still
On a pot still you control the takeoff rate not temps. To do this you need to control the amount of vapors that are sent to the condenser. Again The slower the boil less vapors are made. So you get a slow takeoff speed on a properly configured system. A steady takeoff rate of drips per second should be achievable. In the lower heat settings when you crank the heat up the amount of vapors created by the faster boil increases, thus more vapors are sent to the condenser and the takeoff rate increases. Do not exceed the condenser limitations. Allowing alcohol vapors to be pumped into the air. The top speed you can take product off is limited by the product condenser being used in your still. But a good takeoff speed for a pot still is somewhere between a steady broken stream and a steady twisted stream. You can only achieve that by adjusting the amount of heat put into the boiler to get the liquid to boil off at the correct rate to produce the right amount of vapors. If you don't have control over the heat it will either be to slow of a takeoff speed or to fast of a takeoff speed. Vary seldom can you achieve the correct takeoff speed without a controller. Keep in mind that the ABV of the liquid in the boiler will affect the amount of heat needed. So a 10% wash will take more heat to get the correct takeoff speed than a 40% low wines still charge. So you need to be able to compensate for this by being able to adjust the amount of heat. A setting that works for a 10% wash will be too much for a 40% low wines so the takeoff speed would be too fast. As the run progresses the ABV in the boiler goes down thus the heat needed to maintain the same takeoff speed will increase.

Reflux Stills
There are many different types of reflux stills but the same basic rules apply to all of them.
On a reflux still you want the proper amount of vapor sent to the column to produce the proper amount of reflux for the still to work at an optimum level. Too little heat results in too little vapors and reflux giving you poor results and shows up as higher temps on the columns thermometer. This results in a lower ABV product because not enough reflux is returning to the column for the packing to work properly. Not having the proper amount of reflux returning to the column will not allow the needed column temp gradient to be achieved, more hot vapors than cooler returning reflux showing a higher temp than wanted. Now a too high of a heat input creating to many vapors will more than likely flood the column where there is too much reflux returning to the column and to much vapors coming from the boiler causing the vapors to hold the reflux in the column not allowing it to return to the boiler. This will cause a safety problem and poor performance. You need to be able to adjust the heat input to achieve the correct amount of vapors to achieve the correct amount of returning reflux and rising vapors in the column. This is different for every still. And as above the ABV of the boiler charge will also change this so it needs to be adjusted for your particular still setup. There isn't a one size fits all type heat setting it's all as per still.

Now on to the kind of controller like I said this is not about the best controller. It's about what that controller needs to be able to do for you. The controller needs to be able to adjust the amount of heat being put into the boiler. In a steady variable amount you want the heat to be as steady as possible. You do not want it cycling on and off wildly. If cycle times are more than say one time a second. It's more than likely not a good choice because every time it cycles on more vapors are created. Then when it cycles off no vapors are created and you get surging. It would be like if you were trying to use a hose and your kid was around the corner pinching off the hose and laughing at you because the hose sprays then shuts off, then sprays and shuts off again. This variance in vapor amounts can and will wreak havoc on the still operation causing surging which in turn will cause smearing of the heads hearts and tails and it can give you false readings on a thermometer in a reflux column.

The other thing you do not want is a controller that works off of temps. A thermostat controller or PID controller (without manual mode) are examples. First off we can't control a still by boiler temp. As it will be ever changing and these types of controllers cycle very widely. They reach the set temp while at full power then shut off all power till the temp drops below the lower setting which is usually a long time span. Since it’s trying to control temps and you are trying to control amounts of vapor produced the temp settings usually get set high so you get really long surges of full power heat. All this creates bad surging within the still and the same holds true as stated above about the surging.

There are many types of good controllers out there. And many good threads on all those types of controllers. Please do your own research as to which one of those will be best for your situation. As long as it does what I mentioned above it will serve you well.
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