Dephlegmator With 3 x Inputs And 3 x Outputs - How To Plumb It?

Smaug

Just be careful that the second stage doesn't get out run by the first stage. Doing so will cause heavy surging.

needmorstuff

Hi All, I now have the 100L still for this dephleg, it is a jacketed boiler with 2 x 5.5kw elements. I'm running 20 plates for vodka.

The control box does have a PID and a temp sensor. The sensor default location seems to be in the belly of the boiler.

Is this the best place to control the still? because it seems like a glorified on/off switch.

In this thread people talk about PID control in the dephleg, on another site someone's saying to put the probe under the dephleg - which i think isnt great because reflux liquid will make it jump all over the place.

The hole in my dephleg is in the jacket/water, not in the vapour path.

So my question is, what is the best use of what I have to make vodka?

I could add a thermowell probe to any stage of the column of course.

Smaug

The only way I would leave the probe in the jacket and use the PID to drive your elements is if you decide to use oil as your heating media.

Hopefully your PID will allow you to run with variable control and just use the probe as a basic temp station.

needmorstuff

@Smaug said: The only way I would leave the probe in the jacket and use the PID to drive your elements is if you decide to use oil as your heating media.

Hopefully your PID will allow you to run with variable control and just use the probe as a basic temp station.

I had a wiring fault on the probe to start and the elements wouldn't even fire. I'm having a hard time understanding the control box if I'm honest. I'm not sure if I can bypass the probe/pid interaction and just use the probe for reporting temp.

I hadn't planned on using oil as the heating medium.

The instructions for the control box are quite terrible in my opinion, I've attached them.

So regards running the elements with PID on vapour temp, that's not recommended? Even if I add a thermowell after the dephleg?

needmorstuff

Control box manual (PDF)

grim

@needmorstuff said: In this thread people talk about PID control in the dephleg, on another site someone's saying to put the probe under the dephleg - which i think isnt great because reflux liquid will make it jump all over the place.

The problem with controlling the dephleg water flow using the reflux temperature as the input, is that reflux temperature is a bit of a moving target. The reality is the reflux temperature is constantly increasing through the run - it's highly correlated with output proof. While the pid can control SOME, it's going to hit a point where the still goes into 100% reflux. Making neutral, it's not a problem, with something like whiskey, it's a bit of target chasing.

Using reflux coolant output temperature isn't really ideal either.

needmorstuff

I'm going to control dephleg water flow manually with a needle valve using output abv at the parrot (temp corrected)

Just unsure of the best use of the pid and probe

grim

Nothing wrong with manual control on the dephleg.

Hell, even the German stills that use thermostatic valves to control dephleg temperature don't necessarily put the control knob in a place where you'd imagine it would be used regularly during operation (many of these stills were kind of designed as set and forget).

Smaug

@needmorstuff said: So regards running the elements with PID on vapour temp, that's not recommended?

@grim said: Using reflux coolant output temperature isn't really ideal either.

Yeah the best way if you don't have a giant, knarly chiller is to monitor the vapor temp above the defleg and use that set point to control cooling flow with an automatic proportional valve. But that's not what you have.

needmorstuff

so the pid isn't that useful for me, I either use oil and the probe in the boiler (not sure of the reasoning) - or use water and set the high to more than 100c so it just always stays on, like 120c, then just control everything manually?

Smaug

Well your PID may allow for variable input based on a percentage. You should confirm if it has that capability.

Using the PID to monitor oil temps in the jacket works well because the oil does a nice job of marinating heat. Even when the PID shuts off power to the element. This is very efficient but you will loose adjustment flexibility. Not a problem if you are running exactly the same way every day, day after day.

Additionally the boiling point of the oil will always remain the same. The boiling point of the kettle charge on the other hand will continue to change as the alcohol is rendered out