rocket or TLUD stove

[David M]

I'm interested in trying to build a decent sized rocket or gasifier stove for outdoor cooking.

Ideally something around the size of a beer keg (probably, made from a beer keg ;)

The TLUD designs bug me because it doesnt seem like you can refuel it while its going like you can a rocket stove. You fuel it, fire it up, cook for a while, then it goes out. Maybe this is just a necessary evil so that you can remove the charcoal to make room for more fuel.

There are a number of designs out there- I do like the carbon-negative ones that produce charcoal, but one restriction I have is that it can't require power for a blower fan.

So far most of the designs ive seen instructions for are camping-sized light-duty ones, made from paint cans or the like, or perhaps brick.

Finalyl Id like it to be semi-portable, so maybe a beer keg on wheels, like a smoker.

Anyone else have any experience or interest in this? I have modest welding skills, but am a little short on understanding the theory of operation quite well enough to design this "carbon negative passive-air inflight-refuelable" stove.

How about a fuel magazine like a drawer with two fuel chambers - when one runs low you light up the other and pull the drawer to switch over?

regards
David

[Matt C.M.]

I have created impromptu furnaces that work like this using a 55 gallon drum with both the top and bottom cut out and a screen in the bottom, with it up on concrete blocks for air flow.  The problem with the larger design is that it produces WAY TOO MUCH heat to cook anything, its going to immediately char the outside, then burn it up.  The reason the stoves are small is because of the high burn rate.  They are sized to produce enough heat to use a pan over, you can't roast anything over them because they burn too hot.  You must use a pot or pan to spread the heat out over a large area.  Its like trying to cook on a propane torch, the heat is too point source, and scaling up, you just end up with a 10' cone of 1000 degree flame.  Totally not suitable for a barbecue grill.

[Matt C.M.]

These design's high efficiency is due to the high burn rate and temperature, they are designed for maximum heat extraction, and minimum emissions, which is not ideal for cooking on.  Frankly, these are crappy stoves because of that, most people don't cook with their stove on HIGH all the time, but for people camping, or those in poor communities, there are bigger concerns than making sure your steak is medium rare and not medium well.

[Paul Bonser]

You could heat something up and then use the thermal mass of that thing to do your cooking...

Like, a thick steel plate with a cast iron pan sitting on top of it, perhaps.

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[David M]

Here are two that I thought looked interesting:

"char-b-que"

http://biochar.bioenergylists.org/content/dont-barbecue-char-bq

"experimental downdraft bbq"

http://www.stoves.bioenergylists.org/stovesdoc/PVerhaart/DowndraftBarbecue/DDB.htm

[Robert Ristroph]

I have interest in gasification, and have done quite a bit of research
on it. All from the point of view of fueling an internal combustion
engine, not for cooking, but I'd be interested in helping with this.

I second Paul's suggestion of using thermal mass to disperse the heat.
Note that thermal mass doesn't have to be heavy, and some types of
firebricks disperse heat radiently might work as well (like the light
foamy firebrick in old-fasioned wall mount gas heaters).

Matt is right that a large furnance of this type will burn up with
it's own heat. It you moderate it by reducing air you can still
produce a lot of carbon monoxide which is bad if not burned in the
flame.

I suggest building a shell that is appropriate for your BBQing goals,
with brick lined interior or whatever, and testing with a propane
burner; when that works, try to replace the propane burner with a
small paint-can style TLUD furnance, which will last a short amount of
time before burning out, but prove the setup; then, as the final
stage, let's build a small screw feed that will take the high temps
and feed in sawdust or pelletized fuel to run it continuously.

--Rob

http://rgr.freeshell.org/

[Paul Bonser]

Ah, yes! An auger would be a great way to feed fuel in.

My dad works as a pipefitter and told me a process for making augers which involves cutting circles out of metal, cutting a circle out of the center and a notch from the outside to the circle, then just stretching one side up and one side down to force it into a spiral.

Something like this: http://www.millerwelds.com/resources/communities/mboard/showthread.php?22359-Laying-out-auger-flighting

You then just make a bunch of those and weld them onto a shaft to make your auger.

[Robert Ristroph]

That's a pretty cool way to make a feed screw. I am anticipating
problems making a feed auger that will not jam on the variety of fuel
types you might send through it. I was thinking of starting by
looking at what is available for automatic animal feeders at one of
the agricultural supply places.

--Rob

[Martin Bogomolni]

What kind of fuel do these setups normally use?

-M

[Marshall Peck]

Gabi and I had a similar idea for making bio char. We figured a keg was good because they're stainless steel. 55 gal drum barrels seemed to rust out after only a few fires.

We weren't thinking advanced enough to auto feed the fuel but we did want to power the unit with it's own gases. Say start with propane then switch over to wood gas. What we would need is to install a large enough port to supply and remove the fuel (wood chips most likely) and a brass pipe from the top of the keg to a valve or regulator so the flue gases can be used to heat the wood chips. There would never be any direct flame on the fuel just ample heat to release the wood gas aka syngas and produce bio char to our liking that would be "cooking" at lower temperatures relatively speaking for longer periods of time. We were hoping that would result in more char and less ash.

As for semi continuous feed we think we could dump small bits from the bottom and load from the top while keeping most of the char hot and producing gas.

We were stuck at how much wood chips does it take to keep wood chips "cooking" and can you do this without direct flame on the fuel? Is there enough wood gas produced to run on it's own?

Interested in this project.

[Robert Ristroph]

I'm not sure for BBQing.

A gasification stove for home heat would use pelletized wood waste, or
corn - search on "wood pellet stove" or "corn stove".

Gasification for other alternative energy use is often based on the
premise that it uses some type of agricultural bio-mass that is
essentially free, or waste newspaper or other garbage.

--Rob

[David M]

Thanks for all the feedback so far!

To clarify, cooking was my primary goal - biochar generation is only a secondary desire to satisfy my inner nerd and make things a little more challenging - not a firm requirement. I think Marshall was hinting about this, that you'd need some way to empty out the charcoal bits while the fire is still going. The incoming wood charge would have to be pre-heated so it doesn't go in cold. I still kind of like my idea of a drawer with two fire boxes, but i'm not quite sure how it would work - its not quite the same as re-fueling a fire while it's burning, more like swapping out a dying fire with a fresh one.

I already have a smoker, so I'm flexible over whether or not smoke is insulated from the cooking surface.

Wood pellets and an auger feed is intriguing, but maybe a bit more complicated than I was planning on. I'd love to see someone else make one like that though.

I also would prefer to have something I can burn any old (nontoxic) wood in, there's always lots of fallen hardwood branches available in my yard, and bits and pieces of firewood.

Is that enough requirements yet? ;) ;)

regards
David

[Hans L]

I wasn't really familiar with rocket stoves so i looked it up and found this video.
http://www.youtube.com/watch?v=aOZ7gJaqdtQ

Seems like a decent and simple design.  This guy uses 80/20 perlite/concrete mix for insulation.  I think this would be a good choice for insulator since you mentioned the desire for portability, and the mostly-perlite insulation should be reasonably lightweight even if scaled up a bit larger.