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Old 07-24-2012, 04:40 AM   #1
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Default Kettle shroud for heat retention

So all of my awesome brew history has been lost in the years I have been gone. Life got tough (still is) and the days of turkey fryers, 20gal MLT's, 15 gallon batches, etc shall remain gone for awhile longer. But I can't stand not having access to tasty frothy homebrew, so I am getting back in, in a rather small way. I am doing stovetop boils on a really weak gas stove. I can't boil even 3 gallons as it is. So I am working on insulating strategies. Outside boils are not feasible in my apartment complex. Electric heating elements are out . I have to make it work with a weak gas burner.

The plan is to run a pair of 3 gallon kettles. As they sit, they don't get much above 185F on my stove. The first thing I did just now is take foam adhesive-backed foam and foil insulation and stick it on the lids. I know it would be hazardous to wrap the whole BK in this stuff, but I think it will be fine for the lids.

Next, I want to use some galvanized flashing to make a circular shroud that wraps around the BK and retains heat. I will use a mallet to bend the top of the shroud inward so that it rests atop the kettle (at the expense of a tightly fitting lid, but that's ok, I don't want to trap the DMS anyway). Some machine screws or a couple tiny bolts will be used to hold the contraption together. It will be open at the bottom, solid sheet wrapping around, and bent inwards at the top to rest on the kettle.

If I use galvanized, I think it should be fine since it shouldn't be coming into contact with the wort at all, except for very minor incidental splash contact perhaps.

Would others agree this is a reasonable approach? Galvanized flashing is very cheap. Or is the risk too great and I should seek out an alternative material?

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Old 07-24-2012, 07:11 AM   #2
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Originally Posted by Sir Humpsalot View Post
So all of my awesome brew history has been lost in the years I have been gone. Life got tough (still is) and the days of turkey fryers, 20gal MLT's, 15 gallon batches, etc shall remain gone for awhile longer. But I can't stand not having access to tasty frothy homebrew, so I am getting back in, in a rather small way. I am doing stovetop boils on a really weak gas stove. I can't boil even 3 gallons as it is. So I am working on insulating strategies. Outside boils are not feasible in my apartment complex. Electric heating elements are out . I have to make it work with a weak gas burner.

The plan is to run a pair of 3 gallon kettles. As they sit, they don't get much above 185F on my stove. The first thing I did just now is take foam adhesive-backed foam and foil insulation and stick it on the lids. I know it would be hazardous to wrap the whole BK in this stuff, but I think it will be fine for the lids.

Next, I want to use some galvanized flashing to make a circular shroud that wraps around the BK and retains heat. I will use a mallet to bend the top of the shroud inward so that it rests atop the kettle (at the expense of a tightly fitting lid, but that's ok, I don't want to trap the DMS anyway). Some machine screws or a couple tiny bolts will be used to hold the contraption together. It will be open at the bottom, solid sheet wrapping around, and bent inwards at the top to rest on the kettle.

If I use galvanized, I think it should be fine since it shouldn't be coming into contact with the wort at all, except for very minor incidental splash contact perhaps.

Would others agree this is a reasonable approach? Galvanized flashing is very cheap. Or is the risk too great and I should seek out an alternative material?
I would be more worried about the galvanized creating toxic fumes from being heated over a flame than I would contact with the wort. Aluminum flashing is just as readily available as galvanized in most areas, and is usually about the same price.
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Old 07-24-2012, 08:05 AM   #3
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I honestly did not recall that there was an issue with heating galvanized. As best as I remembered, it was just an issue of acidity and leaching of zinc... But that's why I asked first. :-)

I will look for aluminum flashing then. I am not into home building and whatnot so I honestly didnt know what else was out there beside the galvanized. But if I can find Aluminum, that should be perfect. I think this will be a very cost-effective and easy thing to make. It should help hold in quite a bit more heat, I should think.

And I know I am not the only one with this issue. So if it works, maybe it'll help some other people as well.

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Old 07-28-2012, 09:21 PM   #4
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Alright. I got 14" aluminum flashing, cut it in half length-wise to 7 inches and made a shroud with simple angles at the top to help retain heat. I have the foam foil on the lid and I am running the stove now with 3 gallons of water. Let's see how it does...

forumrunner_20120728_162043.jpg

Tools needed: heavy duty scissors, yardstick, sharpie, drill (or a nail and hammer would work) and a pair of nuts and bolts. Total time was about 2 hours including some head scratching.

As the kettle is heating up, my first observation is... Wow, that aluminum foil and foam top sure traps a LOT of heat. It's not even hot to the touch! If I went electric, I think my kettles would be wrapped in that stuff.

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Old 07-28-2012, 09:36 PM   #5
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Ladies and Gentlemen!

It has been 18 minutes since I turned on the stove and... I have a 3 gallon boil!!!!!

Wait. I hear something happening. OMG YES IT IS!!!! 20 minutes to a full rolling boil!!!!

Lid off and.... The boil is being maintained with just the shroud.

Success!!!!!

Hmmm I am even maintaining the boil with the lid off and the heat turned down quite a bit... This means I can scale up my heat shroud to fit my 5 gallon kettle and see if I can get that to boil as well.

Ok. So I am back in brewing business after 3 or 4 years off. It's only extract brewing for the moment, but with a full rolling boil and a pair of 3 gallon kettles, I am in business!!!!

First thing I'm gonna do though is chill this water and do a partial boil. I'm just getting my feet wet again here.

Thanks, Juan!

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Old 07-28-2012, 10:52 PM   #6
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I had a bit of oil splash on my stove from when I fried up some dumplings last night. The stove now looks like $%/t. That shroud really kept the heat in and around the pot.

I have to recommend this to any brewer who is trying to save on energy costs.

My total expense for this project was about twenty bucks, and I have enough to do 2 to 4 kettles, depending on size.

It probably cuts your time to boil in half. And whereas I couldn't even boil 2 gallons before, I can now maintain a boil using the burner set just a little more than halfway.

Very nice energy savings. Should pay for itself within just a couple of brew sessions.

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Old 08-11-2012, 12:16 AM   #7
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Originally Posted by Sir Humpsalot View Post
Alright. I got 14" aluminum flashing, cut it in half length-wise to 7 inches and made a shroud with simple angles at the top to help retain heat. I have the foam foil on the lid and I am running the stove now with 3 gallons of water. Let's see how it does...

Attachment 69972

Tools needed: heavy duty scissors, yardstick, sharpie, drill (or a nail and hammer would work) and a pair of nuts and bolts. Total time was about 2 hours including some head scratching.

As the kettle is heating up, my first observation is... Wow, that aluminum foil and foam top sure traps a LOT of heat. It's not even hot to the touch! If I went electric, I think my kettles would be wrapped in that stuff.
Thanks for the informative posts. Since I just went electric and am looking for some kettle insulation, would you mind posting a bit more detail on the foam/aluminum foil you used on your lid?

Much appreciate
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Old 08-11-2012, 05:06 AM   #8
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Thanks for the informative posts. Since I just went electric and am looking for some kettle insulation, would you mind posting a bit more detail on the foam/aluminum foil you used on your lid?

Much appreciate
How about a pic of the package it comes in? It's duct insulation. I've used about half of it so far to wrap a corny keg and cover 2 lids. This should give you all the detail you need. I got mine at Home Depot.

Cheers!
20120810_235035.jpg  
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Old 01-19-2013, 06:13 PM   #9
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Sir Humpsalot, this is a great idea thanks for posting your success and boil times.

I frequently brew during the winter months and it takes quite a while to bring 11+ gallons to a boil not to mention the amount of propane used.

I built mine slightly different as I brew in a keggle and outside. The shroud is two pieces of aluminum flashing riveted together to get the height I needed. I just bent it approximately 1/2", cut the bend about every inch so it would wrap around the keggle without kinking too much. When I curled it around the keggle the cuts opened up slightly in a spiral which is enough to vent the exhaust gasses. If it needs more or less flow I can always open/close the tabs with a screw driver. Since the aluminum is so thin I did use some standoffs around the base.



It definitely does cut the time it takes to bring the wort to a boil.
Thanks again
Bob

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Old 01-20-2013, 05:34 AM   #10
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Good thinking, Sir Humpalot,

The princple you are using is identical to that used in Rocket Stoves (aka Turbo Stoves). Check em out on YouTube, Wikipedia etc.

These stoves are used in poor developing countries where fuel is scarce and expensive. They are amazingly energy efficient. You can boil a big pot of food with a just a handful of twigs. The combustion chamber is designed to fully combust all the gases, so they are smokeless and can be used indoors without presenting a health hazard to the inhabitants (think of mothers with babies strapped to their backs cooking over smokey fires).

You are using town gas supply to heat your pot (not twigs) but like rocket stoves you have thought up the idea of using a 'shroud' around the outside to keep the hot combustion gases against the wall of the vessel as they rise into space. Brilliant. In rocket stove terminology this shroud is called a 'skirt'. Most homebrewers who use gas firing and want a better boil have traditionally taken the dumbo path and simply increased the amount of gas burned during the boil (bigger, mightier burners). Very Tim-the Toolman (urg, urg urg) but stupid.

There are two main ways of getting a quicker, stronger boil - increasing the temperature (ie. burn more fuel), and increase the surface area being heated. This is what your shroud (skirt) is doing. You are directed the still hot combustion gases to flow against the outer wall of the pot, instead of just the bottom. The area of the walls is vastly bigger than the bottom. By just heating the bottom all the still hot combustion gases just drift off into space - what a waste!

To tweak your design even further you could look into rocket stove construction and see that super efficiency comes when you insulate the skirt. As it is you are still losing a lot of heat from the wall of the skirt. You wrap another skirt around the first skirt and fill the cavity with non-combutable insulation material like crushed pumice rock or easily available vermiculite clay (a very light clay mineral you can get from garden centres -
I think its used as potting material by orchid growers). What this does is keep the rising combustion gases at higher temperature as they flow up past, and in contact with, the walls of your pot.

The need to bend over the top of the skirt (as in a pic above) to 'trap' in the heat is unnessesary if the gap distance between the inner and outer skirt is correct. There is a mathematical calculation that will determine the best gap in the the 'Worksheet (Excel 700K)' at http://www.rocketstove.org/index.php...link-from-menu . The maths is beyond me, but basically there is a direct relationship between your pot diameter and the optimum gap between the two skirts.

Couple of safety issues worth mentioning:
If using any mineral insulation material, do not inhale the dust when crushing or pouring it in. Wear an appropiate particulate face mask (its not poisonous, but all minerals are silicon based and inhaling silicon dust can caused silicosis which is like asbestosis - very bad).
Realise that in a kitchen stove situation you are effectively venting the hot gases higher up than if you were using the gas burner normally - perhaps too close to cupboards etc above. The safe distance is specified in building regulations which vary from place to place but is usually a distance of 500mm (about half a yard) between gas burner and anything (including fume extrator fan) above. In other words - be careful, don't leave the room, and don't burn you apartment down!
Think about the high temp gases and how they might affect your ball valve and fittings. A silicone o-ring on the outside of the pot might degrade in the high heat and cause a catastrophic and sudden leak that cannot be stopped easily. Even an internal o-ring might be in jeopardy, depending of the set up-up. A welded fitting should be ok.

I'd love top see someone implement a full rocket stove outdoor wood burner boil kettle for home brew. And on a handful of sticks!

Congrats again on a brilliant solution.

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