Reflux control guide

[Bigadz]

G'day from Australia!

I've messaged a few people on various forums but thought it may be worthwhile to ask the question here for others in the same boat as me to gain any insights. 

First up, I wanted to say a huge thank you to everyone that has gone before me and left a tonne of valuable knowledge through comments and posts on the forum. I have learnt so much from everyone.

I am in the development/tuning stages of my distillation process and trying to drive repeatability and consistency in my product as I get ready to launch here in Australia, for me, until I can do this without fail I don't want to open the doors. I make my own spirit for Gin primarily, but also some brandies, with an intention of whisky down the track.

I have been reading up on RC/Deph control and have been umming and ahhing on one of the Danfoss setups or building a PID controller. I'm technical enough to do it and have some experience with automation, but the more I read the more I'm getting confused, and I'm not sure if there is a "definitive" way or a best method to go about setting up a pid or a danfoss. I am looking for a method that requires minimal manual intervention as I firmly believe there has to be a better way than tweaking needle valves.

My current coolant source is municipal water into a surge tank with pump into the condensers. The pump feeds into a Y split that goes to PC and RC cooling inputs with a needle valve on each condenser input and then both outputs are plumbed together and drained off. At this stage the water is not recirculated. I have 2 stills setup in this fashion, a 230L steam jacketed boiler with a 6" 8 plate column, and a smaller 4" plated column that I run on either a 110L milk can boiler or 35L pot boiler for testing. All are Dephlegmator for reflux and shot gun for PC.

With all of the reading it seems a few things are common for PID:

• A PID with proportional control

• A proportional ball valve controls either input or output flow

• Temperature is taken from either the Deph coolant output or from the deph housing itself around mid to 2/3 the way up

In the Danfoss setup, apparently it's as simple as water input plumbed to PC, Danfoss valve measures and sets water temp going into deph and thats pretty much it.

From what I've read many use PID and/or a danfoss? Are there any resources around the best way to build or some general best practise stuff that I should be looking at to weigh up my options?

The Danfoss set up is desirable I supposed from a "simplicity" and potentially a safety point of view, but I imagine a PID would be better for setting a program and getting the most out of a system.

Really appreciate any input, and if I haven't been clear enough or need to add some information please let me know!

Cheers!

[DrDistillation]

Let me throw out a couple of links you might want to do a quick read through for ideas.  It might have you answer or lead you to a solution of give you more questions to ask here.

These should give you some ideas on types of control instruments to use and how/where to monitor temps.

http://adiforums.com/topic/8069-dephlegmator-control/

https://www.stilldragon.org/discussion/1450/my-pid-experiments

Let me know if this was helpful or just left you hanging and really wasn't the type of info you were looking for and we can pick it up from this? 

If this is roughly the type of info you were looking for BEFORE starting to purchase things for a test still, do some measurements of you coolant water temp and how much you are currently using.  IE you'll use more coolant for NGS then if you were distilling a 151 proof rum most likely so it's good to know the typical water volume flow rate you will need to size things properly to get in the ballpark.

 

[Bigadz]

Many thanks @DrDistillation.

I have read the adi link you posted but not the stilldragon link, I will read that and come back with more.

I'll see what I can do for coolant temp measurements, as we are on city water and in Melbourne it's particularly cold at the moment the water temps are quite low, however Melbourne on a good day can swing temperature quite significantly so if there's a compensatory control for that it would be interesting.

I guess one immediate thing I'm thinking of for a proportional valve is what kind of Cv I should be looking for? This is something that confuses me a bit.

Really appreciate the response!

[kleclerc77]

The thing that caught my eye was the temp control on the water going IN to the deph. Wouldn't the temp of the water OUT of the deph be the better place to control it? The temp of the water coming out will be indicative of the temp being held in the deph, where water temp going in can/will fluctuate because it's city water. 

[DrDistillation]

Yes out temp over input temp but probably best to put a probe right in the middle of the condenser.

[Bigadz]

Really appreciating the comments!

The input temp going into the dephleg was something I picked up from @Southernhighlander and I think @clearwaterbrewer with the use of a Danfoss thermostatic valve and I am lead to believe from reading up on it that it's how some of the big still manufacturers control control there stills.

Danfoss valve on PC cooling input, thermoprobe on PC output, PC output to dephleg input.

I supposed the idea would generating another constant in the cooling equation and altering the variables like reflux ratio that way, but I'm any sort of expert on this stuff and may have misunderstood.

[Southernhighlander]

We experimented a lot figuring out the best control point, using a thermostatic valve for coolant control.  We tried every scenario we could think of.  We found that if we plumbed the system so that the coolant from the final condenser goes to the last dephleg in line then from the last dephleg to the 2nd to last dephleg in line and so on, this worked best.  We found that the best placement for the Danfoss probe is at the coolant output of the final condenser and the best place for the valve was at the coolant input of the final condenser.  Also we found that you need to have just a little bypass at the valve to make things work smoothly.  We tried every other possible position and this worked best.  We have used this method to operate up to four dephlegmators and the final condenser on one danfoss valve.  We found that we get a much steadier output than using a PID with non proportional on off solenoid valve.  The first thing we tried was having the probe of the thermostatic valve at the coolant output of the dephleg and the valve at the input of the dephleg and this did not work well at all.  We also tried plumbing the dephlegs separately and the final condenser separately using multiple danfoss valves and this did not work well either.  We also tried putting the probe in the vapor path and that caused a very irregular output.  The input temp going into the last dephlg in line is the best control point.

 

[JustAndy]

4 hours ago, Southernhighlander said:

We found that the best placement for the Danfoss probe is at the coolant output of the final condenser and the best place for the valve was at the coolant input of the final condenser.  Also we found that you need to have just a little bypass at the valve to make things work smoothly. 

This is exactly how our 3 plate Kothe still is setup. The manual bypass valve is important, as you need to be able to flow water to make sure the water retained in the dephleg is starting out cold and not hot from a previous run. 

[Bigadz]

On 6/15/2020 at 10:50 PM, Southernhighlander said:

We experimented a lot figuring out the best control point, using a thermostatic valve for coolant control.  We tried every scenario we could think of.  We found that if we plumbed the system so that the coolant from the final condenser goes to the last dephleg in line then from the last dephleg to the 2nd to last dephleg in line and so on, this worked best.  We found that the best placement for the Danfoss probe is at the coolant output of the final condenser and the best place for the valve was at the coolant input of the final condenser.  Also we found that you need to have just a little bypass at the valve to make things work smoothly.  We tried every other possible position and this worked best.  We have used this method to operate up to four dephlegmators and the final condenser on one danfoss valve.  We found that we get a much steadier output than using a PID with non proportional on off solenoid valve.  The first thing we tried was having the probe of the thermostatic valve at the coolant output of the dephleg and the valve at the input of the dephleg and this did not work well at all.  We also tried plumbing the dephlegs separately and the final condenser separately using multiple danfoss valves and this did not work well either.  We also tried putting the probe in the vapor path and that caused a very irregular output.  The input temp going into the last dephlg in line is the best control point.

 

Does there need to be any temperature control on the water supply at the beginning? if I go straight from my reservoir to the final condenser the water is pretty cold in the cooler months. So I assume you bypass the danfoss valve for loading plates, then when they are stacked you enable the danfoss valve, but the water going in to the final condenser wont start heating up until vapour is aloud to pass. How do you manage that or have I missed something?

[JustAndy]

On our still the thermal mass of the water in the depleg at the start of the run is enough to condense all the vapor, load the plates, and cause the still to run in total reflux for about 5-10 minutes. If I wanted to stay in reflux, I would need to use the manual bypass valve but that's not usually what I want. There are instances where having separate inputs for the depleg and product condenser would be nice, but having used stills setup that way they are much fussier to get adjusted and keep consistent.