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........

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.

Measure or find something that will give you the EXACT size of the 6 quart pot. Cut this size hole in the 12 quart stock pot lid. Take your time and get this PERFECT. It is the most critical part of the project. This gap must be almost airtight. If you cut perfect, the screws bolting the pots together will make sealing unnecessary. You want the stainless pot lip to sit perfectly flush on the stock pot lid.

I had some Dremel trouble and my fit was not exact. Don't freak out, it can be fixed by a little stove cement or high temp sealant. The stove will still work in any case. You may get a little air leakage and see some gas ignite in the wrong spot. This will not harm anything.

Just go slow and make it PERFECT. It CAN be done and you will have great results.

Mark the side of the 12 quart stock pot. Cut opening for your fan/blower near bottom. Get it as close as possible to the bottom. Heat from the burn will eventually migrate down. A cheap fan might melt from the 100 deg. temp. A small short duct made from a steel building stud or sheet metal cut and bent into box is helpful.

This part is up to you the builder. There are many ways to do it depending on your fan/blower.

Cut one large center hole in the outer 6 quart stainless pot with Dremel.

Square or round, your choice. 3 inch or so diameter.

This is where the fan/blowers primary air enters initially. This outer pot also insulates the small inner burn pot somewhat. It keeps the extreme inner heat from heating the outer 12 quart pot to dangerous temps.

This is the tricky part. Get ready to do some stainless drilling!
Mark holes first with a sharpie marker or metal punch.

If marked with sharpie marker just go slow with drill at first. Make sure the drill is biting into the metal, then go full speed and punch the hole quickly. Too slow and the bit will never make it through. The stainless gets heated by the bit and odd things happen. You have a "window of opportunity" of just a few seconds. DeWalt bits make it pretty easy. I was able to get into a fast hole punching motion easily.

Refer to the pics for the hole configuration. These are CRITICAL.

Lower holes are in the most optimal configuration ( I believe). The stagger allows for a nice secondary burn when the pellets get low.

The top "afterburner" holes are offset somewhat to give a little "swirl" to the burning gases.
Single holes can work fine too. Larger holes work well also. They are very hard to drill in stainless though. Some more work and testing on top hole configuration is needed.

IMPORTANT NOTE:

See the 4 screws spaced evenly in the pot below the top air holes?
These center the inner burn pot inside the outer 6 quart pot. Makes things line up perfect when you drop the small pot into the larger one. You will see these screws better in the next step.
It's just a little trick to save time and ease alignment. You can cut the sharp heads off with Dremel if you like.

At this point everything should just drop in. Carefully line all pots up for the next step.

Mark holes for screws. Drill  holes so the screw heads overlap slightly and hold inner burn pot.

This is a two for one. The screws bolt the 6 quart air cowling pot to main casing, and also hold inner burn pot in place.

Slick.....

A tip on fan wiring. Use Radio Shack high grade 9 volt battery snap leads.

Wire the 9 volt snap connector properly at the fan end.

Wire the other 9 volt snap to a 12 volt cigarette lighter plug. Do this one reverse polarity. Backwards.

This allows you to run the fan off a jumper pack or car, then also connect up a Radio Shack 8AA battery holder. You can then use 8 AA rechargeable batts to power fan at 10 volts. With a small solar charger you can power the fan anywhere.

Using a jumper pack to run the fan makes better sense. A small solar panel can charge the jumper pack for really long runtimes. Plus you have a jumper pack to charge a cell phone etc.

There are many ways to hook up a fan to do this job. I can't list them all.

My fan is a Japan Servo 24 volt. I can run it off 24 volt, 12 volt, and 10 volts from the 8AA pack. The stove runs pretty well at all power settings.

Here is a link to purchase the correct fan:

Japan Servo 12 VDC 23 CFM BLOWER model FBDC12H7P
https://www.surpluscenter.com/item.asp?item=16-1358&catname=electric

The speed of the blower determines how long your burn time and flame quality will be. Too slow of a blower/fan will make large yellow tarry flame. The right speed will give you nice blue flames.

Make sure you can get about 45 minutes to 1 hour burn time. Closer to 1 hour is best. After 40 or so minutes you will have hot glowing coals in the burn pot. There will still be a huge amount of heat.

If you reload small amounts of pellets starting at the 30 minute mark, you can keep a nice burn going for longer than an hour. You will have to experiment with this.

The stove is now complete. Get a battery pack and fire it up!

Fill the burn pot up to the "bell" line. I loaded partially to show you the line.

Always load the burn pot at least halfway. You need a good mass of pellets/wood to get the "reaction" going.

ALWAYS keep pellets/wood below the top air holes! This keeps smoke from leaving the stove.

When stove is operated correctly, there is NO SMOKE generated from start to finish.

To get pellets lit in an easy manner use a "combustible" fluid. About a shot glass full.

Pellet stove gel, lamp oil, diesel fuel, JP-8 jet fuel, and some alcohols work great.

Don't use gasoline, Coleman white gas or other volatile starters unless you know what you are doing. This stove collects the vapors and will blow the top off in your face possibly.
We are talking mini fireball mushroom cloud.

I add the fluid, let it soak about a minute, then toss a lit ball of toilet paper into the top.
You can use a barbecue lighter or mini torch directly on the fluid if you like.

Wait another minute or so then switch fan on.

As always, use caution.  Don't be stupid. If you blow your eyebrows off it's not my problem.

With the blower going this stove is not affected by wind really. There is enough heat to probably deep fry a turkey. I'm not joking. This stove will boil LARGE pots of water. Might even be able to melt some metals.

Have fun! 

Please discuss and comment. I will constantly refine this instructable.
If you want to collaborate locally, please message me:

koffeekommando at gmail.com

One of my goals is to see these stoves in use everywhere they are needed. Build a few for the homeless near you, no matter where in the world you live. Build some for Haiti. Keep one of these and a jumper pack in your car in case you get stranded. It will save your life.

Show others how to make these. It's important. They are very efficient. No need to chop down trees wholesale to keep warm or cook anymore!


For more information about biomass stoves:

http://www.bioenergylists.org/