This first post is not the bigger more fancy setup I am working on, it is simply about a 20 minute quicky I built yesterday to prove to someone it works.

This is very basic. Take a 55gal drum with removable lid. Remove any plastic caps or plugs in the lid, they will melt. Fill holes by threading in a pipe cap of the correct size or simply weld metal over the holes air tight. For this one I just happend to have the correct sized plug handy for the small hole, the large hole I had a metal cap from a different type of barrel. Remove the rubber gasket in the rim of the barrels lid, it will melt and leak. For this one I left it in just to see, it did melt and I had some small leaks burning around the edges. Replace the gasket with gasket material for wood burning stove doors. That works well, also I will test it, but I think a high tempature gasket silicone would work but not sure yet.
I made the frame from sections of a couple metal floor lamps. I have alot of those junk 300/500 watt halogen floor lamps, can't give them away. That was the posts for the frame. Each section was the corrct lenght, I simply used 4 as legs standing up right, 2 go side to side under the barrel, the other two go front to back along side the barrel. Just a cheap simple self standing four legged frame which I can sit the barrel into, it worked fine.
Lay barrel on side in frame, cut about a 2" hole in top, weld on 2" pipe. I had a junk section of exhaust pipe from some vehicle handy, I used that.

I have a small pit here, I am building a fancy model of this and it will be in the pit. You don't have to have a pit. You do need to hold the heat to the barrel though. In the above picture I have filled the barrel with junk wood from dead trees that have fallen over around here. It has been raining alot so everything is wet, notice the water on top of the barrels in the first picture. Well this worked anyway!
Would have been better with normal dry woods though, but wet worked fine.
For my enclosure to hold heat to the barrel I used 3 sheets of metal siding/roofing.
The one is bent in a U shape making the sides and back. The wind blew it acrossed the roof and bent one side for me the other day when it hit my fireplace chiminey so I only had to bend the other side, wasn't that nice. I just had my daughter stand on it and I lifted the end and we bent it. The 2 pieces on top are just laid there of course, supported by the sides of the pit.
We filled under the barrel with dead wet wood, around the sides also, then lit it.
After awhile we had a hot fire burning and wood gas coming out the top.

Gee kinda looks like the gas pipe at an oil well doesn't it 
Ok, here I did not do much except make a little charcoal and burn off the gas. The only real reason I did this yesterday was I got tired of a skeptic telling me it doesn't work and how hard it is to build such things that do work ect... Now they will be quit, at least about this one.
In summery, you simply need a 4 legged stand to lay a barrel over sideways and a 2" pipe welded to the top (with hole cut in barrel to let out the gas). Fill barrel loosely with wood (not tight, heat needs to move around the wood and gas needs room to escape). Replace any plastic or rubber on barrel that will melt with something that does not melt, it needs to be air tight. Make a 3 sided and roofed enclosure to hold heat in. About anything that won't melt or blow away in the wind will do. Stack up some wood and get a hot fire going. First you get steam and smoke that won't burn, then in awhile you start getting the burning gas. How long that takes depends how wet your wood was and how hot your fire is ect..
Lite gas and watch it burn. Keep fire hot with more wood as needed untill gas stops, charcoal is done. Let cool over night before opening the barrel.
If you open the barrel while charcoal is too hot it will get oxygen and burn.
That's about it for a simple setup.
If you don't want the gas, make the pipe bend over from the top of the barrel down the back side and run along bottom of barrel to the front. Cap end shut and drill/cut holes, basically making a burner like a gas oven. When the flamable gas comes out it will ignite and burn from the fire under the barrel. Be aware though this will become a self fueling fire and can really produce large amounts of heat and flames, not dangerous really, but it can get wild and should not be done near anything the heat or flames could damage or set on fire. If you do it this way, then as I say it will become self feuling, in other words the gas comes out of the wood, burns under the barrel keeping it hot to produce more gas, and it runs till the gas stops, and that's when the charcaol is done. Word of caution, you never want to build up a high presure, if you use the self feuling proccess then be sure to make LOTS of holes! The dryer your wood, hotter the fire, and type of wood, will result in lots of gas and high heats which create lots more gas! I have had thin oak strips (1/4 thick X 4-6" wide) I could snap like toothpicks that burnt like they had been soaked in gasolene in my wood burner. That wood will make tons of gas, the hotter it is the faster it makes it. Something like that expect to end up with flames shooting out 3' in every direction if self feuling. Perfectly safe as long as no presure is created!
Now for fun!
Instead of burning off the gas for no reason, filter it, capture it, store it. That gas is useable for about everything you can use propane for including running an engine. My fancy setup will be storing the gas for other uses.
The heat, you are producing lots of heat here. Capture the heat for other uses also. Heat water for your hot water tank, winter heating for your house, anything else you want it for, maybe dry more wood for the next batch or heat a green house.
I will be doing that and more. Tomatoes are about $3 lb here, Hell with that, greenhouse time! I'll heat barrels of water and those will prevetn the green house from getting to cold at night. Also I will be building a small kiln to dry fresh lumber for a house, use this charcoal production heat to keep that hot also.
The heat from the fire to make charcoal is as good as the heat in your would burner or fireplace. Just don't use the fumes. The gas coming from the barrel of wood needs to be cooled and filterd anyway before storage, so pipe it through a heat exchanger and reclaim that heat also.
Charcoal itself serves many purposes, some that can be provided by plain wood and some that cannot be. Use it for cooking outdoors, this is the best you can get, far better than store bought brikets!! I'll use it for melting Aluminum and other metals in my small casting foundry I am also building. It's perfect for the forge for back smithing too. For both build the proper container, load charcoal, pump air, and you have the heat needed for the job.
As a filter charcoal is one of the best things you can use. After I get several batches made I will be using charcoal to filter the wood gas itself. First cool it to condense steam, then filter through charcoal before storing.
Filter water also. And I will be using a water tank as gas filtering, letting it bubble through water to cool and wash the gas. As the water gets dirty, simply filter through charcoal to clean and reuse. When the charcoal finally should be replaced, let dry in sun then burn for heat in the next batch, nothing is waisted. And the unwanted tars and resins are captured back into the charcoal filter and burned.
Charcoal can be sold, if you make more than you need yourself, like to get the gas and use the heat, sell the extra! People by that glued together dust and ground pieces type brickets every day, this is far better!
Use good woods for the charcoal, but you can use wood that will otherwise be wasted. I'll get most of mine from a lumber mill super cheap, it's scrap they burn off or just pile up and let rot away. Some haul it off to a charcoal plant to be made into brickets, but still it's cheap to buy it from them. I used that because the bark is removed, good for smithing or founderies. Cooking I wouldn't care.
For the fire, any garbage rotting tree pieces work well. I have acres of dead trees pieces. Many rot while growing and just fall over, break off half way up, or the limbs are falling off. Any of that wood is fine for the fire and dry it burns hot!
Free scrap for the asking often also, just looks around. Loggers want logs, limbs are just left behind to rot. Sometimes it's cut for firewood, most the time it's not.
Trees are RE.
Replanting of trees is not difficult or feul consuming or expensive. It just takes time for them to grow. The Texas paper mills do it all the time! Cut the trees to make paper, then hire planters. They just walk along getting fresh air hitting the ground with a pick, sticking in a tree (looks like a stick), stepping down to mash back the dirt and taking a step or two and doing it again. What they are planting is a pine that grows to size in about 10 years. But it can be done with any trees.
Well I had a 2 day break in the rain, Thanksgiving day was nice, but I was busy and couldn't do anything, yesterday I built this quickey and used it plus a little other stuff, today it is storming again so no work of this type for awhile I geuss.
Soon I will have an open building over that pit and be working on the real system in any type of weather, for now it's just a good day system.