Coking or 'woodgas' stove

[alcul8r]

Though not technically a woodgas stove, this does do some woodgas

conversion as it burns.  In reality it charcoals first, burning the

vapors produced in a secondary burn below the grate.  Though there

is bound to be some producer gas after it heats up and charcoals, my

primary aim is just an efficient, controllable stove which will burn

small wood scraps.






It is efficient, and can do a nine-hour burn putting out good heat

the entire time.  It also does a great job burning the small scraps,

ranging from 12" 2x4s down to 2x2x1.

What I do not have is control.  Enough air to get it started is

enough to turn the entire stove orange as the outgassing starts.  

Even less is required once the wood is charred through and we are

burning charcoal.  Part of the problem has been caused by using a

flat piece of stainless for the cover.  If fire gets into the fuel

magazine it tends to warp the stainless, giving way too much oxygen

in the wrong place.  The whole stove has turned orange a couple of

times, which seems to distress my wife almost as much as the charred

spot on the floor.






Primary air is two 3/8" standpipes teed about 4" above the burn

grate.  They come up from a 2" piece of exhaust tubing with 28 1/4"

holes drilled into it for the secondary air supply.  Regulation is

via a snug-fitting aluminum can with 2 Vs from the open end.  Moving

can out exposes more of the Vs to let in more air.

Observation so far says I should increase the primary vent sizes.  

Also, there is a good possibility that the door gap lets in enough

air to fulfill secondary needs so I could plug more of the holes in

the exhaust tubing.  I tried to make it fairly tight, but even a

1/8" gap all the way around would be 5 square inches of vent.

My biggest problem has been the top warping.  My brother is bringing

me some disks off of farm implements which are dome-shaped and will

not have the warp problem flat metal presents.  The disks will be

given a lip, an inner collar, and a stove gasket, which should

pretty much eliminate the leaks.

This is a batch stove, although the lid may be lifted to add fuel

either while there is still plenty in there or after the charcoal is

almost gone.

Sorry for the long post, wanted to include as much information as I

could.  If you have suggestions I'd be glad to hear them.

This same question will be posted to the Yahoo Woodgas group for the purpose of eliciting suggestions.

Rex

[whatsnext]

How much ash comes out of this thing? I have an almost unlimited supply of oak sawdust and would love to use it in a way that did not require pelletization.

John......

[chux0r]

Use a bimetallic strip to open and close an air intake, just like in a regular wood furnace.  It can be full open when it's cold, and close down at higher temperatures to control the heat.

[TomW]

A draft control can be rigged up from an old style carburetor choke with the bimetallic spring reversed. Used one of these years ago on a woodstove I built. Just need the upper body and choke assembly from the carburetor.

Just one junkyard method that worked quite well for me in the 70's.

Cheers.

TomW

[alcul8r]

We were discussing burning sawdust just yesterday.  I think it will require a funnel-shaped magazine or perhaps a blower.  Going to try it someday.  That's why I designed this one.  A friend works where they pay to have lots of small pieces hauled off.

Not a lot of ashes.  I burned half a dozen loads (22 gal each) of wood and only had one small can of ashes.

[tecker]

 

  I've used wood chips and sawdust by rolling a log up in several layers of paper

 and a shaker grate in the woodgas gen in up draft configuration. Mix the sawdust with the wood chips and it works well the sawdust makes a bond with the chips as they heat to temperature . As long as the chamber can heatup .The gas is very thick. Pine is really hard to manage with out running the burner with a little excess gas from the generator . I ended up with the exahust from my gas engine ducted to the bottom of the gas chamber that worked well.

[nothing to lose]

Nice setup.

 I have been testing various things here also.

I think what you need is to seal the system so it only draws air from where you want it to. You mentioned all those gaps and leaks, you can't control those so get rid of them. Then it should be as simple as venting in a little air and controlling it with a choke.

 You may need more than one vent though. You need air for the wood to burn to turn to charcoal and air to burn the gas. First you need to get the wood hot enough to produce gas, that takes air to burn a fire. BUT, when you get gas that needs air to burn also. If you burn both you have a hotter fire than needed and make gas faster than needed.

So it would seem, burn feul (wood or charcaol) to bake the wood hot enough to produce gas. Light the gas to burn and make heat. Choke out the wood so it cannot burn, only heat to porduce the gas that is baking it. The gas will keep the fire hot enough to produce gas untill there is no more let to bake out of the wood. Then you have charcaol, so either save it for latter or something else or close the air intake to the gas chamber and open the one to the charcoal chamber. Supply air to the charcoal while still hot and the gas has just went out and it will burn well now. Control the charcoal rate of burn by how much air you let in.

May sound confusing but very simple. Basically you just have to control how hot the wood gets to control how fast you get the gas out. And once the gas is burning you need no other heat source for baking the wood, this will be a self feuling proccess once started.

 Alittle different than what I am doing. Your trying to make charcaol, burn the gas, burn the charcoal it seems, but I am making the charcoal to have charcoal so I do not have to control it's burn rate at all since it does not burn for me. I only have to get it hot enough to produce gas, then burn the gas to keep it that hot untill the gas stops being produced, let it cool and I have the best charcoal for any use.

So we are sort of doing the same things for different reasons. If you bake the wood fast enough (and start with good dry wood), you can get both enough gas to keep the fire burning and store some gas for latter use too. This is part of my goal for a total system. Use a little charcoal to start the process (the first heat), use gas to keep it going. Use extra gas produced for a gas gennie after filtering also store some for latter. Once the process is compleated and cooled I have charcoal to start the next batch, charcoal for blacksmithing, aluminum casting, heat, and use some charcoal as a filter in a barrel to run the gas produced though it before the gas engine or storing. Can burn the dirty charcoal filter as the fual to start a new batch of charcoal when you change out the filter

 All the heat created in doing all this can be used for other things also, the heat is a byproduct so it still heats oil or water to circulate for house heating, runs a stirling, Steam engine or anything else.

Course most of mine will be a total outdoor system when done. I have even decided I should be able to use the heat from burning charcoal for casting aluminum to start a new batch of charcoal. This is why mine is not done, I work at it a little, but so many things to do and figure out for the best ways for everything, then I decide to do it different anyway

But it all does work great for each section and job, only building one sytem to do it all at once is the hard part, each little part is easy itself.

[rotornuts]

Nice idea Tom, I hadn't considered an old choke control before but they would work great I assume.

[TomW]

nuts;

Well I think it originated in The Mother Earth News  and I just tried it and it worked quite well.

As I recall it was a GM carb and I used that plastic  cap on the side thats for adjusting the choke setting as the way to set the flap.

It could not completely shut off the air but a tuna can fit it perfectly to use as a cap to kill all airflow. It worked pretty well for regulating the stove based on heat output.

Hope it helps someone.

T