HX Fluids For Bain-Marie Boilers

Smaug

@grim said: Smaug your comment above is important. I was not aware of what you described until I looked at some of the prints again.

Yes. It is the vapor occupying the head space that does all of the heavy lifting.

TheMechWarrior

A couple of great posts there from @jacksonbrown & @Myles =D>

Atmospheric and efficient transfer medium = WINNING

BP TRANSCAL N Heat Transfer Oil is a heating medium I saw being used in a plant near Hobart earlier this year. It will do the trick @Ryno

Not sure how it compares in price to the glycol variants.

Here's the MSDS: BP Transcal N - Heat Transfer Oil (PDF)

grim

Nearly all of the high-end HX are extremely pure mineral oils.

Myles

In an open unpressurised system I really wouldn't consider using water at all. I WOULD consider using atmospheric pressure steam. However, you need some mechanism to vent the surplus steam and if you are distilling indoors it is a real PITA.

Your other big option - and to me it really does make sense, is to INJECT steam directly into the wash.

When you consider that an open system running a HX fluid is operating with a much higher temperature gradient than you can get with water it makes sense.

If you are able to use steam in a jacketed boiler it makes sense to do so. However not everyone can, which is where HX fluids come in - at a price.

When you try to heat a container of water by sitting it in a liquid bath that is just a bit hotter, it takes a VERY long time.

I can't imagine that anyone with a HX fluid jacketed boiler would try to run it with the glycol (or any other HX fluid) set to less than 100°C. Far more typical is 115°C to 121°C. Even higher if you have the buffers in the fluid to extend the life of the fluid.

Smaug

I'm a bit confused here?

Are we talking recreational theory for the sake of discussion or practice here?

A cap on one nipple and a 15 psi PRV on the other nipple and there is no discharge of steam.

At 7 or 8 psi internal jacket temps will be 230 to 233 degrees F. so long as there is head room for the vapor to occupy the space. It works like a charm.

Myles

@Smaug I agree with the scenario you just put up and for me that is an excelent example of use of low pressure steam. That temperature is a nice useable one that is much better than 100 degC and you get the boost from latent heat.

The earlier suggestion though was to use just hot liquid (water) which i have tried to show is no good. If you must use liquid only then you need to increase the temperature. Running an open system with steam escaping is also very slow.

Your suggestion is good and it is quite popular in Europe.

jacksonbrown

What kg rating are those 15 psi PRV's?

grim

I'd imagine you need some sort of pressure control on the jacket, no? The PRV is not being used as a regulator...

grim

BTW - If we had heavy power, I think we'd have gone this route. For me, installing steam was easier than pulling all that expensive copper.. :)

SDeurope

Here in Austria the usual still for farmers, who do not need a license to distill, can have a boiler up to 150L and it's pretty much always a bain-marie used with plain water to the max allowed pressure of 0.5 bar ~ 7.25 psi. As far as I can see, it's as easy as filling the bain-marie jacket up to half of the sight glass, adding a pressure gauge and safety relieve valve to the two inlets and you are good to go.

Interestingly the Austrian Alcohol Tax Law also mentions an oil bath without max pressure value, but we have never seen a still using oil as HX fluid around here.

jacksonbrown

@SDeurope said: the max allowed pressure of 0.5 bar ~ 7.25 psi. As far as I can see, it's as easy as filling the bain-marie jacket up to half of the sight glass...

Hmm... How about an open but pressureised BM?
0.5bar should get you over 110° I think, which is enough.
If you have the space in the barn then a 5m over flow/breather will have the jacket at 0.5 bar even though the system is still open to atmosphere. Just have the level switch at the top of the 'breather' to keep a 5 metre column of water there.
That might be a nice loop hole for some regs too.

jbierling

I don't think the PRV is ever really used as a regulator as typically how it works is that the pressure mostly doesn't get high enough to need it. The inefficiency of the heat transfer from jacket to boiler requires the pressure increase for everything to work, but 15 psi seems enough headroom in most cases.

In regards to the theory of the utility of the agitator to speed the heating of the boiler, I think its a good one. But the inefficiency of not using an agitator just means the jacket heats up a little more and thus increases the heat transfer on its own. The only real loss is additional heat to the environment which seems minimal. Its quite possible I suppose that your boiler just has way more power than elements in the jacket so your case might be completely different than mine. I have a gauge and I have watched it in the past for a change after turning the agitator on and off and I've never really seen one. The gauge might not be accurate enough I suppose, its 30psi max IIRC.

jacksonbrown

@jbierling said: In regards to the theory of the utility of the agitator to speed the heating of the boiler, I think its a good one. But the inefficiency of not using an agitator just means the jacket heats up a little more and thus increases the heat transfer on its own. The only real loss is additional heat to the environment which seems minimal.

That was my point but things are a bit different with grim as he's on steam.

I really like this idea of the presureised yet open to atmosphere system. I'm just trying to work out a good way to stop convection currents taking heat up the pressure column. A pigtail at the base or some sort of p trap might be OK but I'm concerned the boiler could be dry in some circumstances with the column still full of water.
Any 110° water let out will flash off too which could be a concern.
I'm sure there's an elegant solution, I just haven't thought of it yet.

TheMechWarrior

Can you see this liquid seal? It acts as a pressure relief. The tube enters the side of the still and follows the profile up the cone and into the vapour space of the tall horizontal cone. You just top it up with water or drain it as needed, it runs around half full of water normally.

The water level is easy to see thanks to the clear glass section.

jacksonbrown

That's kind of what I had in mind but I'm not sure it'll work with what I'm proposing. If that penetration was into the jacket and the sight glass was 5 meters high and full of water you could get the water temp in the jacket up to 110° without it boiling, just from the head pressure of the water column. Even though it is still technically an open system.

I don't think the way it is in that photo will give you liquid level in the tank jacket, only in the trap (and only one half of it, pressure differential will have both halves at different levels))

A level glass needs the penetration at the bottom and also at the top to balance pressure sometimes (if not ambient).

My concern is that gas build up in the jacket won't vent properly though. Two level switches could fix I guess. One at the top of the jacket and one at the top of the water column. They both have to be high (triggered) for the fill water valve to be off.

grim

Once you pressurize the jacket make sure you guys are using air vents, vacuum breakers, have a dual redundant means of controlling pressure, a gauge, a way to check level and add water, and a safety prv.

This is critical. You are making a steam boiler. Treat it as such.

jacksonbrown

Are you referring to my proposal? I was hoping the 5m open system could do away with all that yet still gain the high temp benefit.

Smaug

Based on the pics that TheMechWarrior posted, it would be no problem to incorporate a pressure gage at the top of the PRV/trap assembly with off the shelf parts. And would also be a snap to test.

And I like the fact that beyond a gigantic blob of fruit skins one might find in a true grappa charge/puke,,,,I don't see how that system could clog/fail.

grim

Nah just talking generally. If you are going to run the bain marie as a self-contained steam boiler, with pressure in the headspace, just add the additional gear to be safe. Most of this is standard steam train gear, and I bet you a decent plumber wouldn't have any problem.

In addition, performance.

Air is an insulator. Without an air vent to let non-condensible gasses escape, heat transfer in the jacket will be less efficient. This makes a big difference in the steam jacket and our hot water heat exchanger. If the air isn't vented, the system works 1/10th as well as it could.

Once you vent air, you need to be able to release vacuum, otherwise you'll crush your boiler like a beer can.

We use a Spirax VS-204 thermostatic air vent and a McDonnel Miller 26 Vacuum Breaker.

On startup, a large amount of air is pushed through the air vent, once the steam starts building, a small amount of steam escapes and the vent closes.

Pretty sure you'd have no problem using something like a Honeywell Pressuretrol 404 or similar to act as an electronic pressure limit switch. Set it to something like 10psi, have your PRV at 15psi. And wire it so that it cuts off your SCRs. Per code, our steam boiler has two parallel honeywell pressuretrols. If one dies, the other is the backup. Or, use two preset pressure switches that can handle steam, probably save $100 bucks.

Steam safely my friends.