Large portable wood gasifier stove

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*New* video of large gasifier operation HERE

Poor man's large gasifier Instructible

MIDGE small tin can gasifier Instructible


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This is the documentation of my largest gasifier experiment so far.
This unit costs about $50 to make.

After building a MIDGE stove, I wanted to design something with bigger,better performance.
It also needed to be a design that could be copied easily. All parts must be commonly available. Tools should be kept to a minimum.

This gasifier can be built in two quality levels. The prototype is identical to this silver aluminum model but is made from a large popcorn can using no power tools.

The output of this stove is very high. A very rough estimate might be 30-40,000 BTU. Don't quote me on that though. It can boil 5 gallons of water in 30 minutes. I've also mounted it under a 30 gallon gas water heater. After an hour and a half of runtime the water inside reached 150 deg. F

The stove will run for 1 hour without "in flight refueling". Wood pellets are the preferred fuel but literally anything "woody" can be burned in the stove. This stove burns material from the top down.
If burning wood scraps like 2x4 and pallet chunks, pack the wood in tight and cover with a layer of wood pellets. The top layer of pellets will create the initial layer of coals you need for nice combustion.

Much more can be said about stove operation. I will document some of this as I go on. Once you build the stove and run a few times on wood pellets, the operation becomes more obvious. When operated correctly there should be NO SMOKE emitted.
There are somewhat dangerous fumes produced by this size stove so don't use it indoors. Treat this device like a literal "campfire in a can".

TLUD stoves such as this are very safe in operation for the most part. The top ring of the burn pot gets incredibly hot (230 deg. +) but the sides stay cool (100 deg. or so) for the rest of the burn.

My stove uses a regular common computer fan for air supply. A centrifugal blower style fan is preferred but an axial fan can be used successfully if you make a straight duct and attach to the outer pot. Blower fans can be found surplus or can also be found in some Dell tower computers.

Improvise and adapt!

Now on to the plans........

Step 1: Gather tools and parts

Tools needed:

- Dremel tool with fiberglass cutoff wheel
- Corded or cordless drill
- DeWalt 1/8 or 9/64th titanium drill bit

Components needed:

- 12 quart aluminum stock pot (buy quality restaurant grade with thick lid)
- 4 quart stainless steam table pot with "inset" top (Libertyware IP04 or Vollrath?)
- 6 quart stainless steam table pot bain marie(Libertyware BM06 or Vollrath ?)
- 12 sheet metal screws (pref. stainless)

Libertyware website w/part numbers:

http://www.libertywareusa.com/products/i/ip04.aspx
http://www.libertywareusa.com/products/b/bm06.aspx


Optional (if you can't cut the main hole perfect):

- wood stove cement
- high temperature RTV sealant
- Thermo Steel high heat putty


Optional tools for cutting main holes:

- Makita die grinder GD0601 
http://www.toolbarn.com/makita-gd0601.html?ref=base

- Clesco M-3 wheel mandrel set (Holder for 3" stainless cutting discs. Can be used with Makita or  corded drill)
http://www.drillspot.com/products/62526/Clesco_M-3_Screw_Type_Cut_Off_Wheel_Mandrel

- 3" fiberglass cut off wheels (Any brand with these specs will do. 3/8" center hole preferred)
http://www.lehighvalleyabrasives.com/servlet/the-99/3%22-X-1-fdsh-16%22thk.-X/Detail

These pots should be bought from a real restaurant supply store (or come from a restaurant).
I used Libertyware (Indian made), but Vollrath (USA) should work also. The Vollrath "inset" 4  quart is shaped differently I believe. Test fit before buying.
The burn pots are stainless, this is the only durable way to go. Use DeWalt or equivalent drill bit that is capable of drilling stainless. The point angle of the drill bit really matters. A Rigid brand cryo cobalt bit did NOTHING. It literally melted trying to drill the thin stainless. DeWalt titanium went through like drilling butter. It was a night and day difference. Will give part number of drill bit later. It's common at any Home Depot.

Comments

[thexmark]

Thanks for the instructable. I plan on having a go at this in the next couple weeks. I have the stock pot with lid and am ordering the other SS pots. Could you shed some light on how exactly to cut the hold in the lid for the 6inch pot? What is the best method to start the cut and then to actually make the round cut? What tool(s)?

[KoffeeKommando]

Ok, first you need to use something to draw the hole. The hole needs to be the exact diameter of the 6 quart pot sides. Not the lip on top of course.

You can measure the bottom of the pot diameter, then use a circle drawing tool to mark the hole.

I had an MSR 4 quart (I think) stainless camping cook pot. It happened to be the exact size. You see this in the first pic. I just set it on top and traced around it.

Next step is cutting the hole. I used a dremel with reinforced fiberglass cutoff wheel. Pic 2 of this step. Dremel and fiberglass cutting wheels are available at Wal Mart/Home Depot etc.

You hold the dremel just like in pic 2, then let the spinning wheel "sink" into the lid. Move the dremel in a circular path along your marked line (hold with both hands very steady). Think of it like a "can opener" action with you moving, not the can.

Of course make sure the pot/lid is held down to the workbench securely. I did mine freehand but you have to have some skill with a dremel. And wear eye/face protection. The fiberglass wheels disintegrate easily while cutting. Stainless metal shards will also fly everywhere. Don't breathe any of the dust in.

Hope this helps clarify!

[thexmark]

KK

Thanks for the detailed reply. I have a clear idea of what to do now.

One quick note, you mention stainless metal shards but the stock pot you and I are using is actually aluminum, correct?

Thanks,

tXm

[KoffeeKommando]

Yes, the stock pot is aluminum. I was just fixated on my memory of stainless flying in my face from cutting the hole in the bottom of the 6 quart pot ;)

In both cases you have to watch out. Cutting with any fiberglass cutting wheel is messy and somewhat dangerous.

Oh, cutting the hole in the bottom of the 6 quart pot is done the same way.
I made it square cause I ran out of small cutting discs. All I had was a corded drill with mandrel and 3" cutting disc. The corded drill was not high rpm enough to cleanly do the circle. I just did straight lines instead.

I'll update the main instructable with some alternate cutting tool info. Will show a Makita die grinder and the mandrel that holds 3" cutting discs.

[thexmark]

I've got similar fans laying around. Looking at the image of the mounted fan, did you insert the short output duct into the out pot until the fan sat flush? And, if so, how did you secure the fan to the outer pot and did it withstand the heat after several burns?

-tXm

[KoffeeKommando]

Yes, the output duct is just slipped in. Then I put two short screws into the duct part (inside the pot) to keep the fan from popping back out.

I cut the duct opening very tight. It holds the fan pretty tight all by itself.

The fan does just fine. Not hot at all. This is due to the double burn pot configuration. The outer burn pot keeps the heat concentrated on the inner pot for the most part. The large outer pot only reaches around 100 deg down near the bottom. This is the beauty of the multi pot solution.

[KoffeeKommando]

Automotive header/exhaust manifold tape would be a great addition to the 6 quart pot:

http://www.summitracing.com/parts/THE-11002/

It would keep the heat contained in the burn area. The entire stove would probably be cooler on the outside surfaces.

[thexmark]

I've also seen "concentrator" lids used to focus flame/heat output. Would you recommend one for this gasifier or have you tried using one?

[KoffeeKommando]

I played around with different odd concentrators and got wildly different things to happen. This Instructable was mainly for people to just get something up and running right off the bat.

Experiment away though!

If you come up with something that works, I'll add it to the Instructable with credit.

[stoveman88]

Based off of this idea, I made this bushbuddy style stove. I also use a double wall as well but no fan. Same idea...I made mine the size of a roll of toilet paper.

[KoffeeKommando]

Very nice! Looks like a stainless vacuum mug?

[stoveman88]

You can check out an explanation of the stove and see it working here: http://www.youtube.com/user/solostove

[jemor143]

Tought I'd share some pics of my stove. Made with a 22 oz coffee can (6,5’’ x 5’’) and a 5" x 4,25" can for the burn pot. For use with twigs ans scraps I'll extend the burn pot to 6'' X 4,25". For the same burn time, twigs take a lot more space than wood pellets. The 5 volt fan is power here by a home made solar battery: the Mighty minty boost (see the Instructables by Honus).

I bend the top holes in order to have a nice swirling flame; I think it helps mixing the wood gas and the hot air and concentrates the flame in the center. It melted my aluminum pot stand right away!

Once started, it boils 2 cups of water in less than 3 minutes.

[KoffeeKommando]

And there you have it!

Now we just have to make a simple shroud for the fan to keep rain off.

Use metal wall studs from Home Depot to do ducts and boxes etc.
One stud can make tons of experimental ducts.
Cut with a good pair of tin snips. WalMart has yellow/black handled Stanley brand for cheap. They have serrated edges that helps the blades grab the metal.

I do like your aluminum box tubing as the duct.
What exact size is it?

Can you take a pic of the fan label up close?
And the air duct exit on the fan....

[jemor143]

It's the same fan you can see on my previous post (5v x 0,15A). The ouput of air is enough for the size of the stove.

I can't take picture right now (forgot the stove at camp for the winter), but the duct is made with 1" square aluminium tubing (1/16 thick). For now, it's just tape to the fan with electrical tape. I'll glue them together with something more tough and durable, maybe some Sugru. I insert the duct in a 1" x 1" hole on the side of stove. The fan and the duct can be stored in the burning pot when not in use.
Speaking of Sugru, I think I'll put some spot of this stuff on the side of the stove, so I can manipulate it when hot, without a separate handle. Tried it on my pot handle, and it works great as a heatproof coating.
I might also try to make the connection between the air duct and the stove really air tight with this stuff. But it's not really necessary.

[jemor143]

I thought of a fast and easy way for controlling the air flow in this type of stove, where a blower is mounted on the side. (Did'nt find an electronic speed controller for 5v blower yet... They all have 12v input.)

You could add an air duct between the blower and the side of the stove, where a slot would allow a door to partially close the duct at will. See the small sketch.

[KoffeeKommando]

You could also do a center pivot. Like a stovepipe damper.

The flap can fit really shoddy, cause you only need to slow the flow of air a little.

[jemor143]

Of course! Right on.

[jemor143]

I have a question regarding material for a potstand. I'm planning to make a pot stand like the one below. I only have aluminium strips laying around. KK talks about really high temperature on top... It may be a stupid question; would the aluminium be able to sustain the heat?

[KoffeeKommando]

Possibly. Just try it.

On my big stove? No. I used some heavy expanded metal as a grate while boiling 5 gal of water. It melted the steel and made it droop in a huge circle below the giant water pot.

[KoffeeKommando]

Oh...the expanded metal grate was 8" *above* the top of the stove.

That's an amazing amount of heat.

[jemor143]

I found and idea for the burn pot on another forum; http://www.randonner-leger.org/forum/viewtopic.php?id=351&p=3

It's in french, but the pictures are enough to understand.

The guy use a double wall stainless mug. There are a few 20 oz mug out there that would be fine for my need. I'd prefer a bigger stainless wine bucket, that is also double wall (about 4" x 9"). It's rugged, and all you have to do is drill holes and make a potstand. It's a bit more expensive than tin can, but will last way longer!
That's my next project!

[KoffeeKommando]

Yes, that's a great idea.

Here is something you need to do.

The inner burn pot needs holes around the bottom. Drill these by sticking a 1/8" drill bit *through* the outer bottom holes in your picture.

Then make a cowling to enclose the bottom holes and provide fan air into them.
It does not have to be airtight. It can be a base "unit" with circular hole that the pot shown above can slide down into. This can also protect the fan, making it rainproof. Would also provide a more stable base for the "pot"

Also his top holes are too large. A double row of 1/8" are all that is needed.

Actually all holes in the pot pictured can be round. Square is just extra dumb work.

Let me see if I can do a quick illustration in a bit. It's easy and would be worlds better than what he did.

[jemor143]

I totally agree. My previous stove had too much holes at the top (and too big) for the secondary burn. 1/8 seems enough. According to the various design I saw on the web, it's better to have 20 smal holes than 10 big ones. My favorite fan-assisted stove is this one, (the smaller version): http://www.woodgascampstove.com/ It only have a few tiny holes in the bottom of the pot burner (see picture), to slow down the first burn. the creator call this stage pyrolysis, the secondary burn at the top being the combustion)

Thanks for the idea. To drill the inner holes at the bottom, I was going to drill through the outer bottom, then block the outer holes with JB Weld. I'd drill a bigger hole to serve as an air intake for the blower, just like you did in your instructable.
I figure I'll be able to drill the top holes from the inside, drilling at an angle. You have experience with stainless: what do you think?

[KoffeeKommando]

JB Weld and all that stuff does not stick to stainless.

Stainless is very hard to drill. The drill tip has to be the correct angle.

DeWalt 1/8" gold titanium bits go through like butter.
That's what I used to do this instructable.

A Rigid 3/16" cryo treated bit literally melted in 20 sec.
It glowed cherry red and almost didn't make it through the stainless.

Illustration coming up...

[KoffeeKommando]

Here is the idea...

And when not in use, the base can store the batteries and solar panels you have. Just stick them inside the round hole.

The fan and stainless gasifier part have standoffs in bottom so water getting inside does not go in fan (and gasifier heat stays off the bottom of box).

[KoffeeKommando]

(removed by author or community request)

[jemor143]

Thanks! Nice sketch!
I'll consider building the base. Would be really heavy duty, and solve the weather problem (I'm in Canada... where weather often is a problem.)

[KoffeeKommando]

The box could be made from thin birch plywood. Make it in octagon shape (round off corners). Then waterproof the birch with rubbed oil coating?

Glue the box together with wood glue and also use tiny nails.

It should withstand the heat.

Bottom pot standoffs could be stainless screws with the tips ground flat.
Or stainless machine screws. Just predrill tight holes.

[KoffeeKommando]

Or...spray the box with duplicolor truck bed liner spray in a can. Its a waterproof thick vinyl coating when dry:

http://duplicolor.com/products/truckBedCoating/

[KoffeeKommando]

I redid the pic...

Plus, the stove wont sink into snow easily.

[KoffeeKommando]

Might want to mount fan vertical on the side of box, then drill holes to outside as air intake. Put some holes right at the bottom so they can be drain holes as well while the stove is in operation.

[KoffeeKommando]

Now...all our talk is for DIY people using old computer fans etc...

This is the winner in commercial stoves:
http://www.biolitestove.com/CampStove.html

It's self powered. The TEG inside powers the fan and can charge a cell phone too. No batteries or solar. The custom fan is the only moving part.

[jemor143]

I agree, the Biolite is the way to go. Correct me if I'm wrong, but I think we'll have to wait until next spring to buy it?

[KoffeeKommando]

Yes, it's at the link.

[jemor143]

Love what you did with the fan. I was inspired by your design, and solved my "problem".
Here is the setup iI settled for:
- a 5V blower fan
- two solar panel in parallel (1,715W) that can directly power the fan in sunlight.
- a 4 AA (NIMH) battery pack, that can be recharge by the solar panel.

On the picture, the fan is only powered by the solar panels, and it runs full speed. I'll be able to save batteries when it's sunny. Moreover, you can easily control the speed of the fan by covering/uncovering the panels!

[KoffeeKommando]

Cool! I like the USB plugs.

What is the model/part number of the fan?
Would like to see how many CFM it is.

[jemor143]

That's why I chose the 5V model, it allows more flexibility with the power.
It's a 5V x 0,15A and measures 50mm x 15 mm. It was listed as 15 cfm. Seems like enough power for the size of my stove, whick is a bit smaller than your. Anyway, I will try a bigger one: 5V/0,18A; 75 x 25 mm.

[KoffeeKommando]

Here is a big fan for $18 with USB end:

http://amzn.com/B005AKCNBY

[KoffeeKommando]

Where are you located?
Where did you buy those specific models of fan?
They sound about right CFM wise.

My 24 v fan runs very slow. It's not a blast furnace thing.

I have a 5v USB adapter for 12v cig. lighter socket. I could run 5v easily too.
There are also 12v laptop power supplies with an accessory 5v USB receptacle on them. I'm going to hook one to a Ryobi cordless tool batt pack. Having a USB jack is bonus.