RC efficiency controlled by coolant temp

[Blackened]

Hello all,

After a few successful runs through my new reflux column I thought I'd post here regarding the end result. Hopefully I'm not telling people something they already know! Sorry if that's the case. The reason I chose this path is because I intend to automate the rig, and temperature control seemed simpler than accurately measuring flow, and being able to accurately adjust the flow. This is my second attempt at this type of device, the first was ok, but the internal tubes of my previous RC we too large and too few.

My RC is overkill by normal standards, in order to get a smaller variation in vapour escaping per coolant degreeC. Its 400mm long, 3" jacket with 6 x 1/2" internal tubes.

I run a recirculated coolant via pump and radiator, controlled via a simple thermostat accurate to 1C. IE: it over/undershoots by about 1C from the target, but sometimes a little more. This turned out to be a bit less than ideal. I got some surging on the output, and increments of 1C weren't incremental enough. 40C virtually no flow, to 43C decent flow but not quite right. It worked ok, but I'd like more gradual control. So to that end I'm upgrading the thermostat to PWM power control of a 12v thermofan on the radiator. I'm using the micro-controller that will be used for the entire rig so it's no extra expense. Just a bit of programming to get the algorithm sorted.

I'll report back on the effectiveness of the new temperature controller when I run it again. Hopefully it will be accurate to 0.1 of target.

Cheers all

[woodduck]

That's some high tech stuff there. Good luck with it hope it all turns out well for ya.

[Blackened]

That's some high tech stuff there. Good luck with it hope it all turns out well for ya.

Thanks man. :smile: I don't have room for a large water reservoir, so I already had the coolant recirculation system, and the micro-controller so I figure, why not hey?

[1 2many]

What is type of micro controller are you running :-B

[Blackened]

A Maximite clone called a Duinomite. I've got it set up in an enclosure with assorted SSRs and a bus for temperature probes. I built it for controlling a RIMS setup, and it's uses have expanded lol. Just waiting on some bit's n bob's from China for the PWM power output.

[1 2many]

Do you have any pics you would like to share, :whistle:

[Whiskyaugogo]

Do you have any pics you would like to share, :whistle:

:text-+1:

[Blackened]

I'm at work right now so I'm afraid I can't take any pics. I'll have to take and upload a couple tomorrow morning if I have time.

[Brendan]

Don't know if it helps you, but I've read from commercial distilleries that 77 degrees Celsius is the optimum that they aim to run their dephlegmators at...

[Blackened]

Interesting. I guess my condenser isn't efficient enough then. A pure water run required a coolant temp of around >85C, but the alcohol vastly reduces the required temp. I'm just glad I don't need a refrigeration unit instead of a fan blown radiator lol I'm guessing hotter coolant = warmer reflux. Requiring less heat to re-vaporise.

[Brendan]

I'm guessing hotter coolant = warmer reflux. Requiring less heat to re-vaporise.

Yeah I think so too. I think it's the whole temperature gradient thing of just crossing back to liquid and re-vaporising many times over, with as little change in temp as possible :think:

[Stoney]

been controlling mine by monitoring rise in coolant temp.
seems to work fine.

[Blackened]

been controlling mine by monitoring rise in coolant temp.
seems to work fine.

Hi Stoney, can you expand on that a bit?

[Blackened]

Pictures as requested. It's dismantled though so I can't show the entire rig running at the moment.

RC.JPG

Fan.JPG

Controller.JPG

The controller has all the 240V outputs and temperature/usb input sockets on the bottom. The entire thing is sealed against the odd splash so there's no holes on the top,sides or back. The LCD screen on the front is the weakest link but I figure it wasn't worth messing around mounting it inside with a perspex cover, because the screen itself has buttons that would be inaccessible. Ignore the label on the front panel. I stuck it on when it was just my RIMS controller.

The radiator/fan thingy is actually an old compressed air drier. I ripped off the 240V fan just recently in favour of this much larger automotive 12V one. There's two water pumps. One is higher pressure/high head 400W and really only required to blast all the air out of the lines, then I switch over to a pissy little washing machine drain pump. The drain pump is gutless, but it's also silent and very low watts, maybe 25w or something. It can't pump up to the RC but easily maintains the flow once the air is purged. There's a lag of 5 to 10 seconds before the temperature reading in the tank reflects the state of the fan. So keeping the coolant volume low helps reduce that lag. I think it's around 10L if you include all the lines etc... but I haven't measured.

The RC was a custom build. I work for a Laser Cutting firm so I designed and cut all the tube and flanges, but a mate TIG welded it all together for me. 400ml long, with 6 internal 1/2" tubes. 3" external. Just a pitty I couldn't get hold of thin wall tube for the internals, as I think that would have made a noticeable difference in efficiency. The boiler adapter, column, RC, and cap cost around $200 - $250. With all of the external fittings scavenged from previous incarnations and my junk box.

[Stoney]

been controlling mine by monitoring rise in coolant temp.
seems to work fine.

Hi Stoney, can you expand on that a bit?

I have a thread .. the 1 3/8 nixon stone one with details and code.
it seemed to me that by far most of the excess energy going into the boiler ends up heating the cooling water if the still isnt venting.
the boiler temperature barely increases, the column temp barely increases. the cooling system temperature rise is pretty much proportional to the amount of reflux occuring.
so i set mine to give me 6c temp rise, if i turn it up flat out, i get about 7.5C temp rise as it starts to vent a little.
once set, i can maintain a constant take off rate throughout the run. pretty much set it to 5 drips a second i guess, i measured with a scale to about 12g a minute, which is about 16ml i guess without doing the math. my 1800W element is cycling at around 1000-1200W. i preheat with gas and then run the element flat out to collect the last of the tails till column hits 94 or so.
its not a fast still but its pretty pure, which is what i wanted, the best neutral i could get relatively easily. takes me around 2.5 hours to pull 1500ml from a 3kg/20l wash plus 200ml or so feints, including initial heating and so far as I can tell its usually around 95.2% what I keep.