Introduction: A Homemade Wood Gasifier to Keep You With Power After the Grid Fails
After the April 27, 2011 outbreak of tornadoes in the state of Alabama, half a million TVA customers were without electric power for up to five days. I have lived in the region for most of my life, and this was by far the longest period of time without power that I've ever experienced. We squeaked by with a 350 watt inverter hooked up to my car battery and a propane grill to cook on. Ever since that experience, I have studied ways to prepare for another disaster, natural or man-made. One thing I wanted to be sure of was that we never went without power again! I eventually came across information about a centuries-old technology that promised to produce fuel to run any internal combustion engine, provide light or heating a home.
Wood gas has been used for lighting, heat and engine fuel since the 1790s. Gasification uses natural forces to obtain otherwise wasted elements for more efficient use of woodburning. When you burn firewood in your fireplace, the smoke you see rising up the chimney is in fact burnable gases, mostly methane, hydrogen and carbon monoxide. The gasification process draws off these byproducts to make a gas that can run an engine such as a generator, lawnmower or even an automobile! This instructable will show you how I built my first portable wood gasifier to run a 1350 watt generator. If this is successful, I will upgrade to a 4000 watt generator and attempt to run the basic needs of my house. In an emergency situation, this could keep your compound or your bug-in location with electrical power when the rest of the world is plunging into darkness!
WARNING! Working with flammable materials and gases can be very dangerous! Please use all precautions to protect yourself and others from fire and toxic fumes! Do NOT attempt to operate one of these indoors! I will NOT be held responsible in any way, legally or otherwise, if you do anything that brings harm to yourself or others trying to follow the instructions herein. So please don't do anything stupid!
Step 1: First, Do Some Homework
I studied this subject for at least two years in my spare time before I began to gather materials for my gasifier project. I watched dozens of Youtube videos, I read dozens of websites and asked question after question and studied every different individual design to get as much detail as I could about the design and building process before I started my project. I was interested in making my gasifier as simple and inexpensive as I could while still getting a machine that would work decently. My goal was to get it up and running with as little modification and adjustment as I could get away with.
There are several basic designs for a wood gasifier, whereas the variety is mostly in terms of scale and available materials. The two most frequently used basic designs are the Fema and the Imbert. I won't go into any detail about the differences in the two, or debate the pros and cons of each. I chose the Fema design because it's simpler to build. I suggest, however, you should go read up about both designs and decide for yourself which would serve your purposes better.
My design ended up being an amalgamation of all the similar gasifiers I studied in a more compact scale to set on a metal cart to make it portable and use mostly materials I either had on-hand or could easily buy at the hardware store. I made two purchases through eBay, one of which was the 20-gallon metal barrel with locking lid that I will use for my burn chamber, the other an inline marine bilge air blower. I bought several pieces of hardware as I needed them to complete my setup, but the major components were things I already had in my possession. As you will see, I made every effort to reuse items I already had in interesting ways for this project.
Step 2: Gather Your Parts and Materials
Once I knew about how I wanted to build my gasifier, I made a list of the parts I would need. The first major hurtle was a large metal container for the burn chamber. I wanted to keep a smaller scale than most of the designs I studied, while still being able to use certain items. The "hopper" to supply the wood to be burned into the burn area was made from an old, rather large steel funnel my father left me. I've had this thing nearly 20 years without having a real use for it, but now I know what to do with it. I chose to buy a 20-gallon metal barrel with a locking lid because the size suited my purposes and the funnel fir very nicely in the lid once I made an opening for it to set in.
I also needed something to make a 'cyclone filter' out of. This is the first chamber the smoke is drawn into from the burn chamber. The idea is to have the smoke drop down to the bottom as it cools and let the liquids (tars) run out the bottom. I chose to use a balloon inflator tank I had. Once the tars are removed, the gases then go into the next container for filtering out any solid impurities, such as creosote. At first, I was going to use an ammo can I recently bought, but then I spotted an old galvanized 5-gallon gas in the shed. I will be putting some kind of media that will be easy to pour or out of the top for the purpose of capturing the remaining impurities as the gases rise from the bottom and out the top.
After the filtering process, the gases should constitute a relatively clean-burning fuel. They will rise through PVC pipes, through a ball valve and up to a burner. They will be drawn through by the action of the inline marine air blower mounted inline in the PVC pipe. This acts as a substitute for the vacuum action of an engine pulling the vapors into the combustion chamber until the gasifier warms up enough to produce burnable fuel.
So, a brief list of things I used are as follows:
20-gallon metal barrel
Balloon inflation tank
5-gallon galvanized gas can
Inline marine air blower
3/4" galvanized floor flanges
3/4" black steel nipples, various lengths
old galvanized pipes, elbows
1" PVC pipe
1 1/2" PVC pipe
2" PVC pipe
2" x 1 1/2" PVC reducers
3" x 1 1/2" PVC reducer
1/4" x 1" bolts and nuts
Ball canning jar with lid
Step 3: The Burn Chamber and the Cyclone Filter
I needed to fit the funnel in the lid of the barrel, so I cut a 12" circle in the lid and dropped the nozzle end of the funnel through the opening. It fit fine. The leftover metal will go back onto the opening of the funnel. A 3/4" floor flange is attached to the side of the barrel. It gets adapted up to a 1" nipple than runs over to the side of the balloon tank and enters it at a tangential angle. This would send the smoke spiraling down to the bottom so the tars would drip into a Ball jar mounted beneath. Another floor flange is mounted in the bottom of the tank and a 3/4" nipple drops down to the lid of the canning jar. I put a galvanized adapter under the lid to secure the pipe. A second pipe comes out of the tank at a steep angle for the smoke to be pulled into the next chamber.
I wanted the burn chamber and the cyclone filter to be permanently mounted to the dolly, so I used some lengths of slotted angle to make legs for the barrel and the tank, then bolted the legs to the sidewalls at one end of the dolly. This helped me to visualize where to connect the two together near the top.
Step 4: The Solids Filter
A length of PVC pipe drops down into the spout of the galvanized gas can and to the bottom of the interior. Inside the can will be some kind of filter media, probably wood pellets. As the smoke rises through the media, tars and creosote are caught in the media, making the smoke cleaner and much closer to being a burnable gas. It also protects the rest of the system from gumming up.
Step 5: Coming Out of the Filter
A 1 1/2" x 2" reducer is attached to the screw-on cap of the gas can. A 1 1/2" PVC pipe rises out of the reducer, attaches to the tee, then goes up to a PVC ball valve then runs up to a marine inline air blower, which is used for creating a vacuum and pulling the gases through the system. I will have a burner mounted atop this stack so I can check if the gases are ready to light and to check the quality and color of the flame. If the system is working properly, not only should I be able to light the burner, the resulting flare should approach being blue in color. This is considered a sign that the gases emitted are free of impurities and under the proper amount of pressure.
Once I'm satisfied that the system is running right, I will close the ball valve, uncap the line going to the generator, fit the elbow into the gas tank, sending the gas to the generator. Once the generator starts and runs, it will draw the gas through like the air blower did, feeding fuel to itself.
Step 6: Sealing the System
I dry-fitted everything to work out where each section would set on the dolly. I then loosened or removed, as the case may be, each connection along the way and squirted some fire sealant underneath to seal that connection. The worst problems with a gasifier are as a result of leaks in the system. I decided on fire sealant because it claims to be able to withstand heat for several hours. Every point where there is a floor flange got a generous portion of sealant. Where the galvanized pipe meets the PVC on the way to the filter I wrapped with duct tape to close the gap. At that point, I figure the smoke will be cool enough not to be a problem for the PVC.
Step 7: Some Finishing Touches Before First Test
I added a strainer plate near the bottom of the funnel to keep the burning media from clogging the neck. A stainless steel bowl went into the bottom of the barrel to catch any hot ash that dropped from the burn area. I also mounted a length of flat metal across the lid of the barrel to hold it in place because of the need to severely limit oxygen flow through the burn area. I then capped an opening in the center of the lid to complete the sealing of the system.
Step 8: Preparing for the First Test
The beauty of the wood gasifier is that you can use just about any kind of wood related product as fuel. You can burn leaves, acorns, twigs, wood chunks, wood chips, pellets etc. There is reportedly a wide variety of materials that can be used in the filter to trap the tars and creosote. I will be using wood pellets at first because the size of nuggets make it very easily pourable into the gas can/filter can and just as easily removable for replacement. They also provide plenty of area for the impurities to be captured.
I have nearby to my location a tree service which gives away wood chips for free, so I gather up 5 gallon buckets and fill them up with chips for fuel. There are many sources of free fuel if you just look around. Every time I drive through my neighborhood when people have been trimming trees, I see not piles of branches and twigs by the side of the road but piles of free fuel! So, I have several buckets full of test fuel and a promise of a continuing supply.
Taking the cap off the filter can, I pour in wood pellets (you can buy 40 lb. bags of grilling type wood pellets at Lowe's) and fill the can about 3/4 full. I then fill my burn chamber almost to the top with wood chips and replace the lid, leaving the small opening in the center. I plug in the air blower to start the downdraft and apply flame from a butane torch to the opening to start the fire. The wood should catch quickly and start to burn fast and hot. We want the fire to burn as hot as possible so the process of pyrolysis (look it up) will give us plenty of good clean fuel.
It takes a few minutes even with the best designed system to get up to temperature and become ready to light a flare. Smoke will rise out of the stack, and you can try to light it until it actually begins to burn. You'll know then that you have fuel just about ready to run your generator!
With my design, when I want to switch over to the generator, I would take a cap off the tee'd off 2" pipe, add the 90 degree angle and attach it to the gas tank of the generator. Then I would close the ball valve and try to start the generator. If it starts and runs, then I know I was successful. Once I am sure it will continue to run on the wood gas, all I will have to do is make sure I always have wood chips in the burn chamber burning. And as long as there is wood or wood related products available to burn, I will never be without power!
Step 9: Tweaking and Improving
As with any homemade project, improvements and tweaks are practically inevitable. I plan to fiddle with parts and methods to make this a better more efficient machine. The fun is in the journey, not just the destination. It's my hope that you, dear reader, have your interest in this tried and true, almost-forgotten technology piqued and that you'll go and study its interesting history for yourself and find your own reason to reach for self-sufficiency!
Here are a few resources to get you started if you're interested:
Go to www.youtube.com and type in the search bar: "Wood Gas" or "Gasifier"
PLEASE study these materials carefully and PLEASE be careful when designing, building and operating one of these machines! They produce flammable and toxic gases and should NEVER be operated indoors! As the old saying goes: Safety first! Thanks for reading!