Control pannel for pot still

[DTL]

Hi guys.

I'm in the process of building a   new control panel with my control guys for a 750L still  electric heated element water/steam bain marie .I have acces to 600v 3 phases in the building .

I need to control 6 x   10kw 600v electric elements in the bain marie .

 

My question is : what is the best sequence to control these heting elements for a perfect control  on my  4 plate column ?

I try to figure  separate the elements in 3  so : 2 on a on/off switch  for preheating

                                                                                  2 on a variable heat dimmer 0 to 100% 

                                                                                  the last 2 on a SSR controled by PID with thermocouple on the top of the plate to maintain the temperature 

Does  it sound good ?? any feedback / recommendation will be welcome . 

 

 

[twalshact]

Just my 2 cents. I like the two elements on a on/off switch. How about the next two on a PID with a on/off switch. And the final 2 on a PID. Use zero cross SSR's. Great big heat sinks for the SSR.

Have a temperature sensor sound an alarm (which can be silenced) when you are 10-20 degrees (adjustable) below your starting point. 

[Southernhighlander]

First of all, you cannot pressurize the jacket for steam.  Water cannot exceed 212F if the jacket is not pressurized,  so if you are going to run water, proportional control is best and there is no reason to have a PID.  If you are going to run cooking oil or glycol all of your elements should be on the PID or you take the chance on having a huge problem.  Cooking oil can be heated to 350 F so cooking oil will give you a much faster heat up and run time than water.

From Twalshact's description, I think that he thinks that you have elements in the wash and did not understand the fact that you have baine marie.

Lastly, If you build the controller yourself you are not going to be able to get it passed your inspector, especially since you are in Canada.  i am guessing that you are in Canada because of your voltage. 

We build electric heating systems for stills everyday and we have hundreds of them out there in operation. 

 

[ViolentBlue]

if you jacket is capable of pressurization, then its not a problem to run above 212 degrees.

running 5psi in the jacket increases boiling point to appx 228 degrees

running 10psi in the jacket increases boiling point to appx 240 degrees

also keep in mind this is at a much higher heat density than oil is capable of, so you have a better heat transfer capability at a lower temperature than other heat transfer mediums.

if your jacket is capable/rated/certified for these pressures then water under pressure is your best option, if it is not rated for pressure, oil is your only option as it does not require pressure.

drop me a line, I'll talk you through setting up your controls for best result.

[Southernhighlander]

1 hour ago, ViolentBlue said:

if you jacket is capable of pressurization, then its not a problem to run above 212 degrees.

 

If a vessel has its own self contained heating system, such as electric over steam, then the complete system must have a UL device listing and the vessel must have an asme rating or you cannot pressurize the jacket, even if it would be operated at less than 15 psi. 

If a vessel has a jacket that operates at less than 15 psi and it is fired by a low pressure steam boiler that is ASME rated and UL listed, then the vessel itself does not need to have an ASME rating or a UL device listing.

  We are currently working on a baine marie still and baine marie mash tun designs with electric over steam that will have a UL device listing for the whole unit.  We should have these stills on the market sometime next year.  I don't know of any other vendors that have UL listed steam baine marie vessels that create their own steam. 

Anyway, if you pressurize the jacket on a baine marie that does not have a UL device listing, with it's own self contained heating system, you are breaking the law and also probably doing something that is very unsafe.

[bluestar]

On 9/24/2018 at 2:54 PM, Southernhighlander said:

If a vessel has its own self contained heating system, such as electric over steam, then the complete system must have a UL device listing and the vessel must have an asme rating or you cannot pressurize the jacket, even if it would be operated at less than 15 psi. 

If a vessel has a jacket that operates at less than 15 psi and it is fired by a low pressure steam boiler that is ASME rated and UL listed, then the vessel itself does not need to have an ASME rating or a UL device listing.

  We are currently working on a baine marie still and baine marie mash tun designs with electric over steam that will have a UL device listing for the whole unit.  We should have these stills on the market sometime next year.  I don't know of any other vendors that have UL listed steam baine marie vessels that create their own steam. 

Anyway, if you pressurize the jacket on a baine marie that does not have a UL device listing, with it's own self contained heating system, you are breaking the law and also probably doing something that is very unsafe.

Paul is correct. Ours was from Vendome, the heating element system is UL listed, and their design is certified. And as I mentioned, it has pressure relief at less than 1psi.

[bluestar]

Even with water and proportional control, you still might want a PID or some means to have temperature sensitive safety limit cutoff. We have two PIDs, one for temperature control, one for safety limits.

[Southernhighlander]

bluestar is correct.  PID, set point temp controls, are best for jacketed stills.  Using proportional control on jacketed stills with oil is extremely dangerous.  Proportional control is best for direct fire electric.  

[SilverSwede]

Here are my two cents from experience with PID controlled electric heating processes. It is often easiest and  cheapest to use on off control. You can still have a sophisticated controller that control your temperature very precisely by pulses. Your heating element will be on or off but your controller will modulate the length of the on/off times. Some of the simple controllers use a pulse of fixed time and they work well but you may experience unstable building voltage depending on your service (flickering lights) if you frequently turn 6kW on and off.

The other option that i think would work very well is to split range the six heaters into 16.67% increments with a simple PLC and three relays. one for one one heater (16.67% one for two heaters 33.33% and one for three heaters 50%) A normal PID loop would then pull in the relays that were in demand depending on the controllers output.

Also for safety put a second independent  high temperature switch in the bath so if something fails and your oil or water gets over a predetermined temperature an alarm will sound and the system will require manual reset and restart. 

[bluestar]

I am going to half agree and half disagree, I think, with both @SilverSwede and @Southernhighlander. In our case, the limit (protection) PID is operating simple on-off using relays, and in fact not only protects the still and its elements, but also the SSRs that are used for temperature control. Note that you really should not use mechanical relays for temperature control, since they are rated for limited cycles that can easily be exceeded for still operation in far less than one year. On the other hand, the temperature control PID can be flexible enough to operate in different ways, including cycling in fixed % power or feedback with dampening to temperature set point. The main advantages of the SSR is that they can cycle many times (long lifetime) before failure compared to mechanical relays, and they can cycle much faster. The latter is useful to avoid surging in the still, where the rate at which product is vaporized can vary as the elements cycle on and off. We see this effect sometimes all the way down to a few seconds cycling. While the effect is more pronounced in direct heating with elements, we also observe it with the use of a bain marie, especially when operated near boiling point of water (for the bath). This is because the cycling of the power on and off is resulting in surges in vapor production in the space above the bath, which transfers heat to the pot contents by condensation, essentially an internal steam source in the surrounding boiler. So, in that case, cycling the power on and off while heating the bath is equivalent to opening and closing a valve to a steam source.

@Southernhighlander is correct that you have to be concerned for a larger still (ours is 40KW) that cycling can cause variations in voltage on the circuits in common with the still power. Really, you should be sure to wire up your facility so that it will not occur. In our case, the key is both to use balanced 3-phase supply and to pull an independent panel sourced all the way back to the main building transformer for powering the stills.

Finally, if you can obtain and afford the necessary type of PID and SSRs, you can do pulse control of the supply, where the waveform is chopped instead of cycling the time, or the number of cycles on and off is chopped. This can result in an effectively equivalent to a proportional control of the supply. Generally, since this means variations in power draw that are a fraction of a second or even a fraction of a 60-hertz cycle, the inherent inductive impedance of the wiring in the building will smooth out the power draw and minimize the affect of the power fluctuations seen elsewhere in the building. An isolation transformer can even further mitigate this effect if necessary.

[Southernhighlander]

1 hour ago, bluestar said:

I am going to half agree and half disagree, I think, with both @SilverSwede and @Southernhighlander. In our case, the limit (protection) PID is operating simple on-off using relays, and in fact not only protects the still and its elements, but also the SSRs that are used for temperature control. Note that you really should not use mechanical relays for temperature control, since they are rated for limited cycles that can easily be exceeded for still operation in far less than one year. On the other hand, the temperature control PID can be flexible enough to operate in different ways, including cycling in fixed % power or feedback with dampening to temperature set point. The main advantages of the SSR is that they can cycle many times (long lifetime) before failure compared to mechanical relays, and they can cycle much faster. The latter is useful to avoid surging in the still, where the rate at which product is vaporized can vary as the elements cycle on and off. We see this effect sometimes all the way down to a few seconds cycling. While the effect is more pronounced in direct heating with elements, we also observe it with the use of a bain marie, especially when operated near boiling point of water (for the bath). This is because the cycling of the power on and off is resulting in surges in vapor production in the space above the bath, which transfers heat to the pot contents by condensation, essentially an internal steam source in the surrounding boiler. So, in that case, cycling the power on and off while heating the bath is equivalent to opening and closing a valve to a steam source.

@Southernhighlander is correct that you have to be concerned for a larger still (ours is 40KW) that cycling can cause variations in voltage on the circuits in common with the still power. Really, you should be sure to wire up your facility so that it will not occur. In our case, the key is both to use balanced 3-phase supply and to pull an independent panel sourced all the way back to the main building transformer for powering the stills.

Finally, if you can obtain and afford the necessary type of PID and SSRs, you can do pulse control of the supply, where the waveform is chopped instead of cycling the time, or the number of cycles on and off is chopped. This can result in an effectively equivalent to a proportional control of the supply. Generally, since this means variations in power draw that are a fraction of a second or even a fraction of a 60-hertz cycle, the inherent inductive impedance of the wiring in the building will smooth out the power draw and minimize the affect of the power fluctuations seen elsewhere in the building. An isolation transformer can even further mitigate this effect if necessary.

Just checked with my electrical department. We have been upgrading our panel designs every few months for years and I am not allways up to date on all of the specifics.

Our current panels have PID setpoint proportional control, meaning that they run full bore (if programmed that way) until a few degrees before the set point temp control is reached and then they work in a proportional manner.  He said that they also have pulse.  They can be programmed for on off control as well.  Even with on off control there is no surging with our baine marie stills because the elements are in the jacket.  Since the jacket temp is several degrees above the temp in the pot and the set point only has a 1 degree difference there is no chance of surging.  If on the other hand, the elements were in the mash and set point temp control was used, there would be so much surging that it would be impossible to run the still in a timely manner. 

Also, we improved our design several months ago by adding electromechanical relays.  So our panels have both electromechanical relays and SSRs on each element.  This provides an extra level of safety because sometimes an SSR can burn out and stick in the on position.    If that happens in our panels, the magnetic relay will still switch off the circuit.  I believe beyond a shadow of a doubt that currently our Baine Marie heating system controllers are some of the best in the industry.  Our panels currently meet the NEC 409 standard and in just a few short weeks they will have the 508 UL and cUL listing for NEMA4 panels, for the entire device, which only Vendome currently sells with their baine marie stills, as far as I know.

  Also, next year we will have  UL and cUL listings and ASME ratings for our entire baine marie stills, making them the only baine Marie stills that I know of that are legal to run 14psi steam in the jacket in a still with it's own self contained electric heating system.  Soon, certain municipalities will start requiring UL device listings for the entire baine marie still.  We have had a couple of municipalities ask for that already but since we currently sell the controller as a seperate device from the still we got around that.

  We have came a long way since I first posted that ugly 55 gallon barrel still on here a little less than 7 years ago.  Below is a pic of one of our stills,  As you can see she's really purty.

 

[bluestar]

Yes, the controller you describe sounds quite good, including essentially all the features we eventually incorporated into the unit we redesigned and built. Certainly, what the original vendor (not you) supplied was far from adequate. And from what we have seen from a number US vendors (other than you) have not been up to our standards, at least.

The only other thing I will add is that while you get LESS surging with the elements in the boiler (jacket), the effect I described was observed with the elements in the boiler (jacket). As I said, this is most noticeable when you get to the boiling point in the boiler (jacket), and steam production is a part of the thermal transfer (if the jacket has empty space for steam to fill above the water line). In this case, the on-off cycling will produce increased boil rates, which increases steam production. This is observable until you approach cycling rates of one second. You will not observe surge if you are well below boiling point of water, and/or if you have almost no space above the fill line in the jacket (since then there is little space or surface area for steam transfer).