Automating flow rate through condenser based on output temp.

[rumbo]

I've got an idea which might make life a bit easier for me and would like some feedback. I'm almost finished with my 2" copper pot still build. Condenser is a 40" Liebig. I'm planning on using a recirculation system with a 200L drum of water and a 12v submersible pump running off my 12v battery charger in power supply mode.

I was thinking of rigging up a microprocessor (arduino) based control for the pump speed based on output water temperature. I could adjust the output temp to a particular value and the arduino would adjust the pump speed through pulse width modulation (PWM) until output temp matches the preset temp. I could then increase or decrease the output temp in small increments (less than 1 degree if I want to) and it will change the pump speed accordingly. Only particular pumps are suited to being controlled this way. This would be particularly useful for a recirculation system as the input temp will slowly increase throughout the run and the speed of the pump would automatically increase to compensate for this. Also removes the need for a tap to control flow manually and allows for much finer adjustment.

As a noob to distilling, i'm guessing that there is no set output water temp to aim for during a run? Probably a lot of variables would affect this such as heat input into boiler, ABV of wash, design and size of condenser etc etc.

Has anyone else tried this?

Note: For those that are not into electronics, it is quite simple to build this but you need basic computer programming skills. It would cost under $20 to build.

PS I realise that the important part of running a pot still is in making the right cuts. I'm not talking about automating the still at all, just making it easier to adjust until I get the flavour right and then maintaining it like that for the rest of the run.

[Kegg_jam]

I say go for it. I'm curious as to what you come up with.

You probably should get the hang of manually adjusting your coolant flow first though.

[humbledore]

I had an idea something like this the other day. My take on it was an electrically controlled valve driven off of the output temp that could open or close more as needed. And yes, in my system and a few others here, 120F is a good output temp to shoot for. That may vary according to your system. But in mine if I could shoot for 120F it is a good balance of water use and cooling. When you crank the power up, you need more water. lower power, less flow. It is a good idea. Would love to see it.

[still_stirrin]

I hope you have enough control of the hysterisis so you don't cycle the pump divergently from your set temperature. With an efficiently designed condenser, your water flowrate will be low.

Keep data as you progress. I'm interested on the design.
ss

[Maritimer]

This would be particularly useful for a recirculation system as the input temp will slowly increase throughout the run and the speed of the pump would automatically increase to compensate for this. Also removes the need for a tap to control flow manually and allows for much finer adjustment.

I only use a pot still for stripping runs, so I can't really comment on cuts from a pot still. Technically, though, what you are proposing would mean that the gradient (temperature difference over the length of the liebig) would be getting smaller as the coolant in the reservoir warmed up. A constant flow rate would keep the gradient constant (the coolant temperature difference would be the same), although the outlet temperature would gradually rise over the course of the run. Maybe someone could comment on this.

M

[Twinrivers]

Pump speed has nothing to do with it. Most chilled water systems work from constant pressure from a pump. The cooling water is modulated at the cooling coils by a control valve to achieve a set output air temp. Your condenser is basically the same concept. If you had a 24 volt pump, a 24 volt high temp thermostat and a 24 volt control valve you could easily set up your condenser to govern it's self. Remember, control valve always goes on the output side of a coil.

[dstaines]

I agree with Twinrivers, setting your arduino up to manipulate a control valve sounds more straightforward and inexpensive than changing the pump speed. There are variable speed pool heater pumps that are designed to do what you're proposing, but they cost a lot more than $20.

[Twinrivers]

You can pick up control valves on eBay from time to time. I'm not saying that you couldn't do it with the speed of the pump. Don't get me wrong, it may work just fine. This is just the way I see it done in commercial applications at work.

[Twinrivers]

It won't be long and one of our engineering types will probably chime in with a confusing dissertation on how the given size of your cooling water tank will heat up at the same rate weather you are pushing 1 gallon a blah blah blah or... Over my head but very interesting in the same. Wait for it......

[Maritimer]

Oh yeah, it doesn't matter what the coolant flow rate is. Think of the boiler and condenser as a heat transfer device. The heat in the boiler gets transformed into steam. The steam loses its heat to the coolant. If there were a difference in the rate at which the reservoir warmed up, that would contradict the law of conservation of energy. In effect, you are putting the heater into the reservoir tank.

Always happy to chime in.

M

[humbledore]

With a pot still and a reservoir maybe the flow rate doesn't matter. If you are not recirculating and it's going down the drain then minimizing the use of water is a good goal in my book.

[Twinrivers]

I have often thought about this and in fact a started a thread the other day about conserving water. I constantly check the outlet temp of my condenser as well as the temp of my product for two reasons. #1 I believe that a higher outlet temp is solid proof that I have eliminated shock cooling and #2 conserve water. Thank you Maritimer for backing me up on the engineering end of things. I wish my brain worked as good as my hands....

[Maritimer]

Just a thought. If the gradient is important, and you wanted to reproduce your pot still runs, you would need to keep the input and output temperatures of the coolant to the liebig constant. As rumba suggests, controlling the flow rate could be used to control the output temperature of the coolant. He seems to want to use a large reservoir rather than a fan and radiator. But if he were to use a radiator, he could use a much smaller reservoir and also control the temperature of the reservoir by turning the fan on and off.

If the temperature of the reservoir rises above a pre-set level, the fan turn on until the reservoir temperature falls below the level. Admittedly, there would be a slight variation, but that would apply to the coolant flow regulation, too. But overall, the inlet and outlet temperatures of the liebig would always be the same.

As I said, I don't use a pot still. This is just a technical idea.

M

[Twinrivers]

You could use it to heat your shine shack this time of year

[rumbo]

Thanks to everyone. I believe that I can use PWM on a 12v brushless motor quite effectively. I have a 300l/h pond pump with max lift height 2.5m (but it is from china - might be grossly exaggerated) which cost $4.90. I'll do a little bit of testing with it. If it looks like working I will post some detailed info and pics. Cheers.

[Windy City]

[quote="Twinrivers"]Pump speed has nothing to do with it. Most chilled water systems work from constant pressure from a pump. The cooling water is modulated at the cooling coils by a control valve to achieve a set output air temp. Your condenser is basically the same concept. If you had a 24 volt pump, a 24 volt high temp thermostat and a 24 volt control valve you could easily set up your condenser to govern it's self. Remember, control valve always goes on the output side of a coil.[/quote

I have just returned home from the International Air-Conditioning, Heating, Refrigerating Exposition - AHR Expo at McCormick Place in Chicago.
In the past we used mixing valves at our heat/cooling output to control temps but that has become very old school. The trend for the last few years (or longer) has been to use VFD's to control temp. I had some long talks with engineers from Grundfos and Bell & Gossett that came to the conclusion that in another 5 years or so a on/off pump will be the exception instead of the norm. The expo was bursting with new pumps, vfd's and controllers. With VFD pumps you can control delta T or delta P, with a host of other inputs and with much better efficiency and control.
I understand we are not building a high rise here but the experiment is valid and should work.
I say go for it and report back on your progress.

[Saltbush Bill]

As a noob to distilling, i'm guessing that there is no set output water temp to aim for during a run?

A Liebig works best if you have a temperature gradient (cold/ cool at the bottom, warmish to hot at the top)

Probably a lot of variables would affect this such as heat input into boiler, ABV of wash, design and size of condenser etc etc.

Correct
Personally I think the idea is a waste of time and money. Maybe its just me but I like to keep things as simple as possible and get a feel for how my stills work, not let some electronic gadget do it for me. Learning to run a pot still well using your your senses of smell, touch,taste and sight will allow you to run any other still on earth well without any fancy gadgets.
A Liebig is a pretty forgiving condenser and I doubt a few degrees one way or the other is going to make a great deal of difference.

[Yummyrum]

Hi rumbo ....you sound like a man after my own heart .... also being of the electronic type I tend to spend huge amounts of time thinking about automating various parts of the brewing and distillation process.....its something you do while spending time watching the drips and trickles . So after over four years of fantasizing and creating quite elaborate brain farts I still twiddle knobs by hand

Building a controller is great because it really makes you think about the process that's going on .

Being the controller is even better ...especially with the aid of those extra sensors Salty mentions

[bellybuster]

Glad some one chimed in on the nay side, I've been reading this thinking.."it's a pot still!!!"

I'm all for automation, but only if it improves the process or the product. I see only added expense here.

Different strokes for different folks though, I'd for sure watch the build

[still_stirrin]

My concern is about the hysterisis of the controller.

Fore example, as you control the "speed" of the pump (flowrate) it takes more or less heat out of the exchanger. As you take less heat (wider pulse width), the temperature rises at the outlet. Compensating for this, your controller speeds up the pump. This pulls more heat out and the temperature again cycles lower.

It is the cycle time between rising outlet temperatures and controller (and pump flowrate adjustments) which will be very flexible and unstable. A finer control on your outlet temperature will help, but I still suspect fluctuations will occur. If the pump speed (flowrate) can't react fast enough to the temperature changes, you could experience a diverging control condition.

That's what I'm interested in.
ss

[Maritimer]

Fore example, as you control the "speed" of the pump (flowrate) it takes more or less heat out of the exchanger. As you take less heat (wider pulse width), the temperature rises at the outlet. Compensating for this, your controller speeds up the pump. This pulls more heat out and the temperature again cycles lower.

This is where the I in PID comes in. I means integrate. Instead of reacting instantaneously, which is what the P (proportional) does, the I holds a constant value that the error works around.

So, the I value will ramp up, driven by the temperature error. The I value sets the PWM ratio and deviations in the temperature from the set point will nudge the I value slowly to increase or decrease the PWM ratio. In the end, the PWM will be quite constant. The period of the PWM is another matter, which depends on the capability of the motor.

Go for it, rumbo. We are all on tenterhooks!

M

[Kegg_jam]

So i was pondering this idea. Since we're talking recirculating. Would it be better to try to control the temp of the coolant in the reservoir instead of coolant flow?

I mean I like the idea of controlling coolant flow (not necessarily for pot stilling) but for say reflux temp.

It just seems at some point the pump will be at max flow but since the temp in the reservoir is increasing it wont make any difference. (Depending on size of cooling tank of course).

[Maritimer]

I'm writing code to automate my still at this moment. One of the ideas I was playing with, before this thread, was controlling the temperature of the reservoir by turning the fans on and off on the radiator. This was prompted by the large temperature range I get in my reservoir. In the winter, I keep the shop at 40*F, and in the summer, the coolant can start at 80*F. So the plan was to bring the coolant to, say, 90*F and keep it there. Just one more parameter that can be set, trying making every run the same. My reservoir is a 5 gal bucket, but it doesn't need to hold 5 gallons. Two gallons would work fine.

Again, I don't use a pot still, except for stripping. But I would imagine that keeping this parameter the same from run to run would result in improved consistency.

M

[Twinrivers]

wouldnt it be nice if I didn't have to constantly screw with my deflag water to achieve the constant output temp that I'm looking for. That would give me more time during a run to sit back, take a sip, and post on HD. You guys really have my gears turning here.

[Jacksonbrown]

I’m looking at doing something similar but slightly different with a CM.

I picked up a few small magflow meters for $70 each and a proportional solenoid valve too.
If I monitor the inlet and outlet temp of my reflux condenser along with the flow rate I can get the Watts being taken away.
If I compare that to the Watts going into the element I have the RR (adjusting for heat losses of course).
I can use the proportional valve with the flow meter signal via a PID function to control the flow rate and thus the Watts being taken away.

With a few PID functions I can do all sorts of cool things.

For my flavoured runs I could just set a fixed RR and it will dynamically adjust to any outside influences and give a rock solid RR through the run unless I decide differantly.
I could also control the RR with a PID function to maintain a set vapour temp and maximise neutral output too. A CM E-ARC.
There are all kinds of cool avenues to explore once you’ve got good monitoring and control of flow.
I want to minimise water usage too.
One benefit of minimising the flow rate in a recirc system is you can get away with a smaller pump and when you want to get the heat back out of the loop you have a much higher delta T to work with so you can get away with a much less efficient heat exchanger.

I’m in the middle of Arduino programing now for another project so we’ll see how that goes before I take on too much else.

ABV.jpg

I’m not sure why people go with monitoring condenser outlet temps. It just seems like a very indirect and inconstant way of looking at RR. In a pot it seems all but pointless (other than the delta T mentioned above).
Happy to be enlightened though Are there other benefits that I’m missing?


Hey WC, could you explain attemperation (spelling??) loops? When, where & why?
I’m guessing a fixed, high flow rate is better for heat transmission?? Perhaps a lower Delta T offers better control too??

We’ve used a combination of both in the past and different industries seem to have different preferences.
In a cooling loop through an entire plant that has many different loads we would use the supply pump to supply pressure, not flow.
A pressure transmitter on the line would control the pump via VSD to provide a set pressure to the line regardless of how many take offs on it are open.
Those different take offs would probably have controls valves though. Possibly feeding attemperation loops that have fixed speed recirc pumps.

In this instance we only have one load on the system so I guess we can treat it differently. To control the flow we have to control the pressure either via the pump or a restriction (valve/orifice). Different means to the same ends I suppose.


I don’t think hysteresis should be a concern. I agree that on/off control is a stupid idea but your PWM output can be proportional so why not control it with a PID function (as mentioned)?

[Jacksonbrown]

Remember, control valve always goes on the output side of a coil.

Could you elaborate on that?
I know with pneumatic systems it's a good idea to throttle the outlet side to minimise flutter but why so on a hard piped, incompressible fluid? (genuine question )
It's just I've seen it done both ways and never got a good answer.

[Twinrivers]

Jackson, before you take my word for anything I will remind you that I'm not an engineer, just a lowly Pipefitter. With that said it is common industry practice to pipe cooling and heating coils in the bottom and out the top. Why?? Because that is what has been drilled into my head since I was a first year apprentice in 1996. As mentioned before a lot of chilled water systems are run with a vsd pump that maintains pressure on the supply side. So by putting the control valve for every. VAV and AHU coil on the return outlet of the coil you will have your coils included in the supply side of the system and the pressure cut(or flow cut whatever) will be constant at every coil in the system. I have learned from work experience that "in the bottom out the top" is not always correct however. We did a 5 story office building wih 5 AHU's and I've 400 VAVs and the balancer guys couldn't get the cooling coil in the one of the air handlers to work right. It wasn't cooling the air to specs (actually air conditioning doesn't cool air it removes heat but that's a totally different story) the coil in that air handler was fabricated so that the inlet nozzle ( on the bottom) was on the air Inlet side of the coil. When we switched the piping around so that the chilled water supply went in the top which also happened to be the air outlet side of the coil(after about an hour of friendly pipefitter/superintendent/customer/engineer head banging session) low and behold it balanced and worked properly. Moral of he story.... My dephlagmator is piped in the top out the bottom because that is the most efficient way to remove heat from the vapor that is going in the opposite direction. Sorry for the lengthy explanation and bad typing.

[Jacksonbrown]

The pipe fitters I know all have tons more practical experience than any engineers. You can probably rattle off all kinds of rules of thumb, steam pipe expansion rates??
As a piping designer I think I picked up a lot more than most engineers I worked with too.
They just did the selling and the shopping, I did the design work and you guys did all the building (and fixing).


We might be talking about a few different things here.

In the bottom out the top is just to flush out all the air I believe. I’ve seen fitters do it the other way on tank jacketing only to have to cut it out and re do it. Just the same as condensers, like you mentioned. The interior piping arrangements (like a Jackson cross flow) or an air bled system or even high flow rates might allow otherwise but normally you will just trap air.

Counter current flow gives you the highest Delta T which gives you the greatest efficiency heat exchange but you may have your water flowing in the top and out the bottom to achieve that. That might give you have a big air trap and a heat exchange not performing right, like in your story)
The solution is to always have the water flowing up hill and if that results in concurrent flow just over size the condenser to account for the reduced efficiency.
Most of our condensers are all oversized anyway.

I haven’t done much HVAC but VAV sounds like what Maritimer is doing with his fan control. From what I just read it seems like control valves would be more on CAV systems??

I've seen control valves on inlets to plate heat exchanges, I think to protect them from main line pressure, same with tank jacketing. Proper pressure reduction would probably be a better idea.
It sounds like your trying to give the control valve a larger delta P or pressure drop to work with by putting it on the outlet side, which still doesn’t seem right to me.
The pressure drop over the coil will be there regardless. Maybe someone can spell it out.

I’m hardly an expert either, I know just enough to get myself in trouble
So much to learn so little time.

[rumbo]

Hi everyone,
Just an update to this. I found that the first cheap pump that I bought was about half of the quoted flow rate. Beware of this if you are looking at them. I ended up buying a DC40-1250.If has a much better flow rate. It also responds to PWM really well. Next step is to set up the temp sensor and see how it behaves.

One thing I did notice when using my pot still for the first time today was that the output temp seemed to fluctuate. It would fell warm then cool, warm then cool. It was alos huffing a bit and I need to sort that out - not sure if this is linked to the fluctuating out temp.

Will keep you posted.

[bellybuster]

the huffing isn't related to the output temp fluctuating, its the other way around. the output fluctuates because its huffing.
Huffing can be caused bty many things, too fast coolant rate is a big one. Too shallow angle on your liebig. etc etc.
What are you running for a heat source.

Gentlemen, the OP is running a pot still, not a reflux, totally different world