Steam Kettle Idea

Hi all. I've been thinking about making a steam kettle out of Stainless Steel. I've had this idea in my head for a while now and I'm not sure whether or not it's worth pursuing.

The idea stemmed from a picture of a steam kettle I saw while flipping through some Google images of steam kettles like this one:


The design would be a hollow, "cylinder-in-cylinder" kettle with water on the inside. I think I read a while back that Brewpastor's kettles were similar to this. When the flame is put to the bottom of the kettle, the water inside would boile and create steam to condense on the inside (and outside) walls of the kettle and transfer heat to the sides instead of only to the bottom. A pressure relief valve could be used to maintain a constant pressure/temperature on the inside chamber and blow off any additional pressure for safety purposes. I'm assuming RO/distilled water would be best so it doesn't leave deposits on the side walls.

A further idea (not pictured) would be to add a coil from the inside wall to get the steam into the middle of the kettle. This would increase the surface area and the efficiency. I don't think a coil would be a good idea for a MLT but I'm not 100% on that.

I was thinking this could be a better kettle for more efficient use of propane or natural gas in rigs who use them. An electric version (as in the picture above) could be built by just adjusting the length of the outside cylinder to accommodate more water and installing a heating element through the side wall.

Some questions I have are:

1) How much water would need to be inside so that all the water doesn't evaporate. I'm assuming this would be a bad thing. I did some test calculations and got the inside and outside volumes of the cylinders. I did not calculate for surface area though.

2) What would the temperature response be for something like this? Once you cut the heat to the bottom, there would still be some steam in the chamber that could condense on the walls. I'm assuming the rise in temperature would be conditional upon the pressure/temperature in the steam chamber.

3) What gauge stainless should be used? More for outer wall and less for inner wall for better heat exchange to product?

I was thinking it could be ordered in pieces and then tig welded together and pressure tested. You'd have 4 main body pieces (not including a coil). 1) Outside Cylinder 2) Inside Cylinder with Flanged top 3) Cone bottom for Inside Cylinder 4) Flat Bottom for Outside Cylinder. All couplers for the thermometer and dip-tubes could be welded flush with both the inside and outside walls making for a cleaner look. A false bottom would sit nicely atop the cone bottom and wouldn't need to be hinged like on some keggles (unless there's something else to get in the way of installing it).

EDIT: I was thinking that 5-15 psi would be a reasonable operating range.

(Please forgive me for the horrible drawings )





Volumes, not including material thickness or coils:


I did a little research on Toledo Metal Spinning's website and found that all pieces could be manufactured on their "standard equipment". I haven't checked the pricing for such work and probably will in the near future.

Anyway, I wanted to get some thoughts/opinions on the design. Maybe I'll end up trying it out if it's not too expensive.

I think this could be extremely dangerous as even 1psi would create hundreds of pounds of force trying to rip the thing apart. you would ahve to have some good fabricators put it together and I would try to do a hydro-static test before you put any steam in it if you can. Unlike monti's steam generator, this isn't a narrow diameter pipe which can easily handle the pressure, this is a pot in a pot.

If you have some estimates on what sort of pressures you would be running it at, i can get you some minimum water volumes, but if you are using a relief valve to control your pressure, you are going to to through a bit of water as it gets hotter i would imagine as its pressure will have to increase for the same amount of heat transfer or you are going to be blowing off steam, which can also be dangerous

I would suggest some light reading before taking on such a project.

http://en.wikipedia.org/wiki/Pressure_vessel#List_of_standards

kerklein2 said:

I would suggest some light reading before taking on such a project.

http://en.wikipedia.org/wiki/Pressure_vessel#List_of_standards

Click to expand...

Great. Thanks for the link.

Mista_Sparkle said:

I think this could be extremely dangerous as even 1psi would create hundreds of pounds of force trying to rip the thing apart. you would ahve to have some good fabricators put it together and I would try to do a hydro-static test before you put any steam in it if you can. Unlike monti's steam generator, this isn't a narrow diameter pipe which can easily handle the pressure, this is a pot in a pot.

If you have some estimates on what sort of pressures you would be running it at, i can get you some minimum water volumes, but if you are using a relief valve to control your pressure, you are going to to through a bit of water as it gets hotter i would imagine as its pressure will have to increase for the same amount of heat transfer or you are going to be blowing off steam, which can also be dangerous

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I'm thinking a "resonable" pressure range would be anywhere from 5-15 psi in the steam chamber. From what I've read, 15 psi would give you ~250 deg F. Is that right?

I was also thinking about using either a thermometer or a pressure sensor as input for a PID loop to maintain the pressure/temperature in the chamber with the burner or heating element being cycled on/off as needed. I could then set the pressure relief valve to a value just higher than the pressure I'm trying to maintain.

Just think about this: If your pot is 15in diameter, at 5psi, you will have almost 900lbs of force on the bottom alone.

Please don't build a bomb.

Take a look at GreenMontis boiling method with copper coils on the flash boiler thread, that is a DIY possible build and should be quite safe with minimal pressurized components.

Thanks kladue. I've been following that thread religiously (as well as some of your builds). It's getting good .



For sake of argument, lets say that the pressurization is not a problem. Are there any suggestions regarding material gauge, operating pressure or anything else???

doing some quick crunching, if your inner pot is entirely jacketed and you are using 12ga stainless you only need a 2º temp differential to dissipate 4kW, and 4º at half a jacket. 4kW will boil off about a gallon and a half an hour if you insulate it well. To get that temp increase, you only need 1.2psig.

Granted, this is just on an ideal heat transfer analysis of your stainless neglecting convection and mixing and temperature gradients in your wort.

The higher the pressure you use, the higher your temperature differential, however, until you are approaching the boiling point, you will have sufficient heat transfer without the elevated pressures as you can fully condense the vapor at lower pressure and lower temp. Your operating pressure will rise as your wort temp rises.

Your required gauge will depend on many factors most importantly your width and your shape. A rounded bottom will be much safer if you can do that as it will reduce your stresses at your joints.

I would also recommend doing this as in the original design with an electric element as if done properly, this kettle will be extremely efficient and a gas flame could cause more unexpected thermal stresses as well as more heat and pressure than your pot can handle.

edit edit: if you were to go electric, i think a temp sensor would go a long way as you could use it to monitor your temps and pressures. You could also easily incorporate an additional overtemp shutoff as well.

I second the round bottom design kettles, most seem to be about 12 Ga. material and usually operate at 5-8 PSI. The average 30 gallon kettles had about 20-30KW boiler attached, and others were connected to heating plant steam. You might consider a shrouded kettle with gas burner like some of the kettles had, it eliminates the steam hassles.

Great info. Thanks everyone. The round bottom suggestion got me thinking "kegs have round bottoms". I'll think another option would be to get a wide, deep cup and weld it into an already cut keggle. It would cut down on the usable capacity of the keggle, but might be easier than fabricating the whole thing from scratch. The kegs are built to hold pressure anyway. Although I'm not sure how much.

ebay may be your friend on this one.
http://cgi.ebay.com/Garland-Dual-HU...ZBI_Steam_Cooking_Warming?hash=item2a0480bf4d

I just talked a buddy out of doing a 50 gallon build on something like this. kegs hold pressure from the inside and are affected differently when the pressure comes from outside. if you go through with this you will need a good welder, good tight joints, a relief valve and a tight temp controller.

I agree with what has already been said about the weldor. Find a good one, and I mean none of this he is OK stuff. Make sure the guy knows how to weld.

I agree too. A good welder is key. If I decide to move forward, I have a friend who has been welding since he was 10 years old . I just talked to him and he says he said it should be no problem and that he does a lot of stainless work. He even asked me if I wanted him to roll the steel to make the cylinders ourselves. That makes me feel a little better. He's in Michigan and I'm going up there in a few weeks. I'm thinking about small version as a test piece. That way we can pressurize it and put a burner under it until it fails and see what fails first.

WPStrassburg said:

ebay may be your friend on this one.
http://cgi.ebay.com/Garland-Dual-HU...ZBI_Steam_Cooking_Warming?hash=item2a0480bf4d

I just talked a buddy out of doing a 50 gallon build on something like this. kegs hold pressure from the inside and are affected differently when the pressure comes from outside. if you go through with this you will need a good welder, good tight joints, a relief valve and a tight temp controller.

Click to expand...

Thanks for the link. I've been scouring Craigslist and eBay for some time now looking for kettles and vessels. Either they're too far away or way too much money. I'm going to keep looking though.

So I got a quote back yesterday from Toledo Metal Spinning. It seems that everything about the design can be done on their equipment without additional tooling except for the cone bottom for the inside cylinder. They want $2159 for the tooling to make a cone with my dimensions.

Quote:
Outside cylinders = $395.48 ea
Outside flat bottom = $121.93 ea
Outside cylinder and bottom welded together at factory = $639.85 total

Inside flanged cylinder = $262.62 ea
Inside cone bottom = $220.02 ea
Inside cone bottom tooling charge = $2159.00 tooling
$2159.00 / 3 = $719.67 ea

So...

Outside Total:
Welded at factory = $639.85 x 3 = $1919.55
Non-welded = ($395.48 + $121.93) x 3 = $1552.23

Inside Total:
$2159.00 + (($220.02 + $262.62) x 3) = $3606.92


Total:
Outside Welded = $5526.47, or $1842.16 per kettle
Non-welded = $5159.15, or $1719.72 per kettle


Wow! I guess eBay is going to be my friend on this one . Assuming I can find a suitable cone bottom without having to pay the tooling charge I'm looking at $990.05 per kettle just for the pieces.

I have some quotes out to some other companies to build everything, but I'm sure they won't be any lower than this quote just for materials. I don't think the advantages of this steam kettle are worth the cost at this point. I'm going to have to check with my friend in Michigan to see what he can do as far as fabricating and pricing.

Any ideas/suggestions?

P-Lay,

What's the advantage of your proposed design over a standard gas or electric heated system? What I see is added complexity and cost and a serious increase in risk of injury/accident. The steam heated systems I have seen/read about are heated with an external boiler that usually serves as the heat source for a number of vessels.

I think the advantages would be two fold. With a smaller amount of water in the chamber the burner would only be required to boil/evaporate that amount of water rather than the entire contents of the kettle, resulting in a decrease in fuel usage. The other would be an increase in surface area for heat transfer. With the water evaporating and then condensing on the inner jacket, the heat transfer should be more efficient than a regular gas burner applied to only the bottom of a regular kettle. Just how much more efficient? I really don't know.

It sounds like it is at the point of vanishing returns. You will be spending a lot of cash to save pennies.

P-Lay said:

I think the advantages would be two fold. With a smaller amount of water in the chamber the burner would only be required to boil/evaporate that amount of water rather than the entire contents of the kettle, resulting in a decrease in fuel usage.

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This is not correct. All you are doing is adding an intermediate step for the heating element. Instead of heat going from the burner to the kettle to the strike water/mash/wort, it's going from the burner, to some water, to the kettle, to the strike water/mash/wort.
Each transfer of energy has losses associated with it, so the more transfers, the more energy ultimately is used by the burner to increase the temperature of the contents of the kettle.
Your design will increase fuel consumption for any given volume in the kettle.

The other would be an increase in surface area for heat transfer. With the water evaporating and then condensing on the inner jacket, the heat transfer should be more efficient than a regular gas burner applied to only the bottom of a regular kettle. Just how much more efficient? I really don't know.

Click to expand...

You are confusing efficiency with an increase in the rate of temperature change.

Your design increases fuel consumption, complexity, cost, and safety risks. This is not a good design for making beer, where we can apply direct heat. The intended use of those boilers is to raise temperature evenly for something in which a temperature gradient could cause scorching, or it would be dangerous to apply direct heat (tar, certain plastics, etc).

I swear I did not mean to sound like such a buzzkill!

i have been steam cleaning carpet and tile for 8 years now and 4 of the machines i have used have held 1000 psi at 250 degrees with no risk of explosion so as long as you use the corect materials you can easily do this without making "a bomb" pressure relief valves work very well and as long as you have two (always one for back up) incorporated into your design this is very doable. now the heat exchangers on our machines run from $800 to $2000 so i am in the opinon that this is a huge investment for what you are trying to acheive. i try to keep my diy investmentsin home brewing in ones that improve my homebrew and i dont believe a steam kettle will make your homebrew better or save you the time for the money invested. just my 2 cents. good luck if you try it.

reminder 2 pressure relief valves

250F steam at 1000PSI..not a chance. What P-Lay is proposing is not a trivial application of physics. It's not something an amateur should be attempting.

maskednegator said:

This is not correct. All you are doing is adding an intermediate step for the heating element. Instead of heat going from the burner to the kettle to the strike water/mash/wort, it's going from the burner, to some water, to the kettle, to the strike water/mash/wort.
Each transfer of energy has losses associated with it, so the more transfers, the more energy ultimately is used by the burner to increase the temperature of the contents of the kettle.
Your design will increase fuel consumption for any given volume in the kettle.

You are confusing efficiency with an increase in the rate of temperature change.

Your design increases fuel consumption, complexity, cost, and safety risks. This is not a good design for making beer, where we can apply direct heat. The intended use of those boilers is to raise temperature evenly for something in which a temperature gradient could cause scorching, or it would be dangerous to apply direct heat (tar, certain plastics, etc).

Click to expand...

I see what you're saying. My thinking is that if water vapor gives up 100% of the energy it took to create it, then this "intermediate step" is negligible. As is the extra layer of SS. So maybe this isn't more efficient.

I think a lot of products increase fuel consumption, complexity, cost and safety risks. Who here wouldn't want a Ferrari?

maskednegator said:

I swear I did not mean to sound like such a buzzkill!

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No worries. I asked for input. Thank you for yours. I admit, though, when I read through that the first time, I felt like my coach was yelling at me.

GNBrews said:

250F steam at 1000PSI..not a chance. What P-Lay is proposing is not a trivial application of physics. It's not something an amateur should be attempting.

Click to expand...

I'm not going to be welding this thing myself - no way in hell. I have friend who I trust and is a professional welder that can handle that for me.

I probably won't pursue this due to the cost, but would if the cost were lower. If naysayers ran the world, we'd all still be living in grass huts flinging our poop at each other.

I wondered about efficiency after I was able to boil using my flash boiler. Now I am sorry for the vagueness here but it is the best I can do. When I direct fire my keegle it takes 2 too just over 2 full turns on my burner control to achieve a boil. With my flash boiler in action, "WITH" an uninsulated steam line, "IN" 50* weather, I was able to boil on 2 full turns, "AND" I brought 50* water to a boil faster then the electric folks can claim. Now I ask where did I loose??

I now have a boiling kettle and I am assured to never ever get above 225* on any surface in or on the kettle. Doesn't seem like a bad deal to me considering sugar scorches at 300*ish. I do have a little more complexity to the setup then most, yes. I would chalk that up to, what ever floats your boat. Everyone spends money frivolously...its just a matter of what's frivolous to you. Some like gas, some like electric, and some like steam.

Here is a left field idea, how about doing a dry fired kettle that with a jet burner in a tube under the kettle and a shroud to hold hot gasses around kettle like some of the commercial direct gas fired kettles. One of the cast burners for ceramic kilns and a 14 gauge inner and 20 gauge outer heat shield tube to heat air to run around kettle might work, and the shroud could be carbon steel liner with KaoWool insulation and an galvinized outer jacket. Kettle would drop in and seal around top edge, gasses would vent on backside, not as sexy as a steam unit but within the DIY realm. An example might be the Wearever aluminum direct gas fired kettles that were around a while back.

P-Lay said:

If naysayers ran the world, we'd all still be living in grass huts flinging our poop at each other.

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If engineers never ran the numbers, bridges would collapse every day.

We just dont want you to melt your face off, because we care