Heating with Induction Hotplates

DonMateo

This is just a question to the Forum, is anyone using induction heaters to heat the vessel, rather than heating elements. I am sourcing equipment for my distillery and I came across some induction heaters of various sizes from 8 to 12 kw. That are made for heating Steel woks for chinese kitchens. I was thinking these things would be great to used under a flat bottom kettle depending on the size. I have been thinking about doing some wheat whisky runs with distillation on the grain and these things would be a great. I also found a couple of smaller, 1800 to 3 kw versions single induction hotplates on Amazon that are reasonably cheap, that you could put under a flat bottom milk can boiler and your away. For those that dont know induction heaters use strong magnetic fields to heat the vessel, pot or pan, rather than applying direct heat. Anyway Just a question to see if anyone is using these things of have used them ?

grim

Make sure it has enough power level variation to be useful, I've seen large units with only 5 power settings, at high power this may be too crude to fine tune vapor speeds.

Make sure it does not work based on measuring the temperature near the cooking surface, or by trying to estimate a temperature through some kind of on/off modulation. You need to control power level.

In fact, more importantly, it would be ideal if it did not work through any kind of on/off modulation, and if it did use modulation to manage the power levels, it needs to be fast enough so that you don't have noticeable wavering in your output flow. Imagine if it ran with something like 5 seconds on, 5 seconds off, the surging would drive you nuts.

Lastly, make sure there is no cooking time limitation - I know of some units on the market that will only stay on for 99 minutes.

The metal surfaces near the induction cooktop will be just as hot as with gas. There is no difference. Gas works by heating the metal surface, induction works by heating the metal surface. I can get my induction cooktop over 500F for searing steaks. If you scorch with gas, you'll scorch with induction, it is not in any way "more gentle or lower temperature". Induction cooktops can cause hotspots just the same. If the induction element isn't perfectly in alignment with the bottom of the vessel (I mean the coil, not the cooktop surface), you'll see a big difference in temps. Another good test is to boil water on it with an open top, once you are on the cusp of boil you can see the bubbles forming at the bottom, you'll see the hotspots.

I have a 3.6kw 12" induction cooktop in my kitchen and it's got brutal power. It makes my 20k BTU dual ring gas cooktop look like a toy. It will burn anything with the best of them.

Really though, much too small surface area for a commercial operation. The element sizes are going to significantly limit the vessel size. Going to be difficult to put anything more than a 100 liter vessel on a typical element.

Those small desktop hobs they sell, just asking for you to knock your still over when it's perched on that thing.

CothermanDistilling

I would like to find one that worked for my 2L glass lab still, I can just cut a steel plate to set it on...

grim

Doesn't @Sadi use one?

DonMateo

That is what I was thinking for a large boiler. Put it under a 1 inch steel plate to distribute the heat.
I was thinking of using a flat bottom still on leg but with an arrangement to elevate the induction heaters under the still. An alternative I was thinking of us doing a bain marie type of still with the induction heaters heating the bottom of the bain marie section and probably the bottom of the still as well. Anyway just making suggestions and asking if people have tried this.

DonMateo

Just to make another comment. THe commercial one I saw was about 40 cm diameter which would fit nicely under a 150l 44 gallon drum. But thats 8kw goign into 150l with a very high efficiency.

Sunshine

we have 30L stove top boilers that are working with induction stoves. They are good value for the money.

30L Stove Top Boiler Induction @ StillDragon Europe

For bigger sizes I suspect they would be really expensive, since the bottom has to be extremely even. I don't see how this could beat a cheap heating element in a single wall boiler or in a bain-marie. In the end it all comes down to the price.

grim

Why not give it a shot and let us know how it goes? Worst case you end up needing to separate solids prior to distilling.

But I'll emphasize, my induction heater can burn chili with the best of 'em. Even in a very heavy cast iron pot (don't ask me how I know). It's a matter of watt density and the temperature of the surface necessary to transmit the energy.

For example, a steam jacket kettle with a big-ass boiler (120kw), only requires a watt density of something like 5 watts per square inch, with a max temperature of 250f/121c. Incredibly gentle.

Ultra low watt density elements (wavy style) are still upwards of 50 watts per square inch - with very high surface temperatures.

I've never seen an 18" induction element, most are 12" max, and closer to 11" is typical. The surface of the hob might be 18". Who knows, could be wrong.

With 11" and 8kw, you are talking about a watt density of around 21 watts per inch. Better than the wavy element, but still high. You could easily get this equivalent by simply running two elements at half the rated wattage.

If you did have a full 18", realize that in order to match the gentle watt density of a hemispherical jacket, you are at best limited to about 5k, way too small for 200l. In a commercial op, you'd probably want 15-20kw in a 200l.

grim

We should start a poor-mans-jacket discovery thread to share some ideas. I agree, there has got to be a way to make a cost effective electrical jacket.

I came across these things a few weeks ago:

6"X36" 1200W 220V Guitar Side Bending Silicone Heat Blanket w/ Controller 0~200C @ eBay

Silicone heat blankets. You can find larger ones, but they are expensive. It might be feasible to use a half dozen of the 1200 watt units to hit a decent power input level. At about $100usd per 1200w, it's still expensive, but it's not terrible.

CothermanDistilling

how about a bunch of stainless balls, what would happen in a boiler using induction?

Harry

What about this little gem... Drum Heaters (PDF)

TheMechWarrior

@Harry, a supplier I'm working with at the moment sent me exactly the same drum heater info, including some Ex rated gear. All too low a wattage for what I'm looking for though. There's some novel heating solutions out there, that's for sure.

jacksonbrown

I think those belts designs are aimed more for liquefying drums of fats/waxes etc. Might be OK for fermentor control but not so much for boiling.

grim

Yeah I thought the silicone blankets were interesting because they had higher power levels than anything I've ever seen in a drum heater.

Explosion proof band heaters will always be low power in comparison, as most of the classification systems dictate maximum surface temperature limits. Lower power, lower maximum temp.

Want to see something cool? Check out fluoropolymer heating cable. Imagine how easy it would be to just wind the cable around whatever vessel you have, cut to length, and fire it up? There are even immersible elements with an incredibly low watt density of 10w per square inch.

Multi-Element Fluoropolymer (PTFE) Heaters @ Process Technology

Spiral Fluoropolymer (PTFE) Immersion Heaters @ Process Technology

The cost is astronomical though.

jacksonbrown

I've refereed to it as heat tracing in the past.
Not much call for it in this industry though. Maybe cip concentrate lines or liquid sugar lines, can't think of anything else. Jacketing is probably an easier alternative in most cases.

Harry

@TheMechWarrior That NZ mob are engineers in heating bars. They'll build anything you like to your specs. Elec ovens, you name it. Give em a call. Can't hurt.

TheMechWarrior

Cheers @Harry, will do, thanks.

DonMateo

The reason why I was thinking of using induction heaters was I want to distill wheat on grain and not have to use gas burners inside a small distillery, at least for the stripping run. Obvious for the spirit runs heating elements are the way to go and when I do whiskey runs with a clean wort then that will go in a still with heating elements.

grim

On-Grain = Really, Really Low Watt Density

Like 5-10 watts per square inch density, 5 assuming no agitator, maybe 10 with an agitator. Watt density doesn't only apply to immersion elements, apply to it the vessel surface being heated to understand if it's going to be hot enough to burn.

Anyone who has tried to mash corn over flame knows it's really easy to burn it on the bottom, even when it looks like it's boiling nicely, even when the flame is low. The mash settles, it sticks, the viscosity thickens at the bottom. It burns.

Just plugging numbers in (5-10watts/sq.in.), based on the circular bottom of a vessel...

16" Diameter = 1105-2011 watts

18" Diameter = 1272-2545 watts

20" Diameter = 1571-3142 watts

22" Diameter = 1901-3801 watts

24" Diameter = 2262-4524 watts (approximately a 55 gallon drum)

You can see that it's difficult to push a high amount of wattage into a such a small surface area. That's why steam tank jackets tend encase the bulk of the liquid holding area of a tank, surface area rules when you need to keep watt density low.

Sure, maybe you could deal with the lower wattages for run power, but heat up power? On the 24" diameter vessel you are talking about nearly 6 hours heat up time at the low watt density, and 3 hours at the high watt density. Brutally slow.

CothermanDistilling

reminds me of a learning experience.... A Hoegaarden clone Witbier I made in 2008 that I shut the flame off below a keggle and kept the drill paddle going for about 30 seconds.. it was a multistep mash with rests at 111, 130, 140, and 155, with mashout at 165... made it through most steps just fine, but the bottom ring was basically red-hot after each step, even with low heat, and transferred that heat and made the mash burn... we noticed when emptying the mash tun, but we continued with the beer anyway, but it tasted like an ashtray... so we smoked some habeneros on the grill and threw them in... I have a few bottles left of it, it is a really nice pepper beer, a bit oxidized and sherry like now, you would not notice the scorch unless told... then you could pick it up...

Moral of the story - keep stirring for a long time after you turn off the flame!

Sadi

@grim said: Doesn't Sadi use one?

yep I do. :) I now have one like yours 3.6kw and agree with all you said about it. My measuring device says it pulls off 2.3kw maximum probably because that is the limit at my house wiring. However, I am able to get 6lt/hour with my 4"CD with it. :-bd

@DonMateo as you mentioned, in order to use it, I made a framework to carry the boiler and I slide the owen under it. I put a few milimeters of insulation at the sides and the owen does not touch the boiler which keeps it very cool. In order to elevate the owen, I used springs at its legs which turned out to be a very good solution. Sorry did not take any pictures yet.

The boiler has a proper bottom suitable for induction, which I think helps a lot by helping distribute the heat more evenly.

As for distilling on the grain, although I have not tried it, I think it might work... I respect what grim has said, and maybe a small scale experiment by putting some grains in a small pot and heating it with induction may give us some idea.

Cheers.

Sadi

Here are some pictures, @DonMateo

Cheers

DonMateo

Wow thats great. So someone is actually doing it and I am not coming up with hairbrained ideas, again. I was thinking putting two of those things under a 150l boiler with a wide base. I will have to get the boiler made up so I will probably get thicker steel for heat distibution. I respect everything that Grim says. I am about 4 weeks from starting to buy stuff for my distillery and I think I will get a couple of these smaller ones before I get an 8 kw boiler. Thanks for the photos. Your a winner Sadi.

grim

For extra fun, try a high rye bourbon mash bill.