Build Your Own Wood Gas Generating Stove
What will you do when your fuel runs out, or your energy system fails? How about burning wood? I used to dismiss burning things for energy off-hand as a dirty and wasteful heating tool, nothing more - not a source of actual power or energy. However, learning what I have in the past few months has given me a new appreciation for this readily-available resource. My perspective was changed somewhat, and it was kind of a shock to me, because i'm pretty open-minded to alternative solutions. My mindset is this: until I have a wealth of food and supplies in storage, I can’t afford to ignore a resource – especially cheap and renewable ones. Can you? Even if you’re prepared for the long haul, it pays to have a couple contingency plans, and this could be one of them.
"Gasification" is the use of heat to transform solid biomass or other carbonaceous solids into a synthetic “natural gas like” flammable fuel. "woodgas" is the term usually applied to the fuel itself. The basic idea isn’t a new idea as much as it is an improvement on the basic principle of burning biomass for heat and light (like a fireplace); in fact, this has been around for more than 100 years. A “gasifier” is typically a multi-tank design that burns wood to create gas, cleans it, and cools it before it is used. And here's the clincher: when done properly, and routed to an engine or a storage container, the gasses can be used to power machinery and (drum roll please) your off-grid home power system.
The use of woodgas really became popular with the proliferation of the automobile, when inventors modified internal combustion engines to run off everything imaginable, including peanut oil, steam, and compressed air (a subject for another article). Gasification came into widespread use during the fuel crisis of WWII as well as during the OPEC fuel problems of a few decades ago, and the ever-increasing fuel prices make it just as relevant right now. There are a couple industrial power plants in places like Svenljunga, Sweden and Gussing, Austria, but this is a version that can be made small enough for personal use.
Building your own:
I’m going to stick to the details of my own experience, since that's more beneficial for you than simply sharing the research; you can find pictures and details online yourself, and you're welcome to email me for suggestions. Anyway, since my new goal is to convert everything of mine to run on woodgas(or a mixture of fuels), I decided to start small and work with a simple woodgas stove. The stove idea works like this, to give you an example:
Start with a small enclosed container, which could be cubed or round. I picked a barbecue propane tank, since they are easy to acquire and had the right size. The next major element is the flue and/or fuel inlet. (I picked 4'' steel stainless pipe). This I cut into 2 sections and welded into an "L" shape. The bottom emerges from the side, and the top emerges from the center of the tank. The third step would be to add a fuel tray, like in a fireplace. (I stuck with the barbeque theme and used part of a barbecue grill, cut to fit) This I inserted through the side (where you'll put your wood fuel) and tack welded in the center (little lower) of the pipe.
And that's pretty much all there was to it. I welded up the edges, where the pipe meet the container, and it worked like a charm.(Though in the absence of a welder you can get by just fine with a tube of high-temperature automotive caulk, like Gasket Goo) This is something that can be made in your garage or metal shop with a welder and a saw, although you don't have to follow my design - test models can be built out of soup cans or soda cans, with little or no fabrication.
You can imagine how it works, in principle; it’s quite similar to your chimney at home. This air flow is the same reason that campers will build a fire in a ‘tent’ shape. Once the fire is lit, hot air rises, drawing cold air into the vacuum. I made mine so that I could take it camping; the propane tank perfectly fits a small pan or pot on top, has a base for stability, and works almost as well as a gas-powered camp stove that you would buy at a retail camping supply outlet. In comparison to my simple stove, most gasifiers will utilize some kind of fan, in line, for two reasons: to help kick-start the process by improving air flow, and then to propel gasses thru the device and to the engine/container. At this scale, pressure and volume become an issue, and to standardize the process things like this become necessary; some users even use computerized controls to regulate burn and flow.
Most woodgas users produce it on-demand, which is preferable if you can afford to build a large (or efficient) enough system. Personally, I wanted to be sure I could save it, in some way, before I dumped any more time or money into this technology. With this in mind, I picked up a small air compressor and modified it to work with my camp stove. I routed a tube (flexible rubber automotive/compressor hose) from the top of the woodgas stove to the air intake on the compressor, so that as my compressor operates, it fills the tank with gas, instead of air. Using a regular tire style air fitting, I was able to fill an external compressor tank, from my compressor. I will use this method to fill similar tanks with a basic woodgas mixture, which I can use to run gas lanterns, a gas stove, or a basic propane-style camp stove. In the long run, I will store fuel in a much larger on-site container, but I chose these elements to fit my circumstances.
The woodgas stove or gasifier is not limited to wood. I have run my camp stove on the chaff from coffee husks, for example. I don’t have first hand experience with these, but here’s a list anyway, of other fuels, to get you thinking: walnut or peanut shells, charcoal, coal, sawdust, wood pellets, buffalo chips.... I think I'll continue to stick with cordwood as my main resource, though, even if it has to be chipped up to fit in a camp stove. I can find it for free all week long and in fairly large quantities. I have started scouting my local online classified ads for free woodpiles around town, and I've already filled one section of fence with cordwood. Of course, it needs to be relatively dry to work well, so it helps to live in a dry climate and have an out-of-the-way place to store materials. You may have access to other kinds of fuel in your area, so keep your eyes and ears peeled.
Camp stoves are easy; building actual gasifiers is a little more complex and actually requires some precision design work, so I'm going to need some expert assistance when I scale this system upward, to power a truck or a home generator. This doesn't require a huge systems change for me, since I had already started collecting the electrical supplies I would need to start going off-grid - just a change in the fuel supply. Rest assured that I will write again with the results of the next woodgas project, in greater detail. For those of you with construction experience (or if you’re just motivated, like me), there are schematics and drawings available online for a few different gasifier versions, one of which you can find by searching for “gasifier” on Wikipedia. If anyone's interested, I have found plans (complete with images) and instructions from a 1950s design, that was used to run a farm tractor. I don't have the original link to where this manual came from, but I'd be glad to forward on the information