Update: I have finished my second version of my Fatboy design, photos and information can be seen here >>>>
This is my second major gasifier project and it is now at a point where I have run it successful over 30 times with only a few minor tweaks required. The FatBoy gasifier has been developed as a grass roots or back yard style of project using recycled materials sourced from tip shops and friends junk piles. The cost of my FatBoy Gasifier is approx $15-20 plus welding sticks and cutting/grinding disks. The basic design is a straight forward top lit up-draft gasifier with some tweaks to increase air flow, reduce emissions and improve ease of lighting. This design is more than suitable for a large suburban gardener interested in engineering and producing their own Biochar.
The FatBoy is designed to process dead dry wood chips and optionally topped of with dead dry branches up to 30mm. It will process 12-14 litres of biomass into approx 6-8 litres of Biochar in 15 minutes. The system is scalable in theory and development of a larger 150 litre version is currently in the design phase. This is an open source style of project which I’m happy to share and develop with others. If you have IP issues with this design please contact me directly by message at the bottom of this page.
Now onto the fun stuff. =) All the plans and photos are click-able to full sized images.
The above plan was based on the materials I sourced for this project, if you follow the basic principles and ideas you should be able to knock out a working version in a weekend. I have not focused on connection points like the feet or the flue holding system as that will depend on the material you source.
Please read this warning: This system runs extremely hot and it produces toxic gases which need to be avoided, do not work directly in the path of the flue gases. The system is not compatible with children in any way, some of the surfaces will reach more than 700°C, this type of heat will instantly burn and remove any skin that comes into contact with hot areas of the system . Any contact with the system has to be with good quality welding gloves and strong grips. If you are in a fire prone area a spark arrester would need to be added to the top of the flue. You need to stay with the system during operation and access to a water hose. I accept NO responsibility for any damage you or your system creates.
Following is a series of photos showing close ups of the system apart and being put together, filled, lighting and quenching the final Biochar.
This is the bottom of the outer chamber, having the system off the ground allows for good air flow. Both the inner and outer air inlets can be seen here. The system sits in the weather and the constant use creates some surface rust, Painting up the outer chamber with black high temp paint would clean up the look of the system if that was an issue for you.
Next is a top view of the outer chamber, you can clearly see both the air inlets, the three small rectangles hold the inner chamber in place, I also included a ring around the inner air inlet pipe to create a better seal.
I used stainless steel for the inner chamber as it’s light to handle and does not rust as constant heating, cooling and quenching in a water bath would rust out mild steel quite quickly. The grate was made from two different galvanised square wire meshes I had on site which I cut with bolt cutter to shape and used alloy fence clips to hold them together. The second shot shows how the grate has bent due to exposed heat. The bolt is a simple trick I developed as a quench indicator, when the hot coals hit the bottom of the inner chamber they burn the string and the bolt drops out the bottom of the system onto a piece of steel indicating it’s time to lift the inner chamber into my quench bath. I do this to increase the Biochar yield and reduce ash content. The lid photo shows the flue holder, it holds the flue 30mm above the pipe, this creates a good air inlet for secondary smoke burning and also gives you a nice view of what is happening inside the unit.
Loading the inner chamber with sun dried wood chips to approx 80mm from the top, next I add a couple of layers of small dead dry branches up to 30mm. Newspaper is ripped finely and some small sticks are added to hold it in place, the lid is put in place and more small sticks up to 10mm are added. Newspaper is ripped finely and fine sticks 0.5-2mm are added. Lighting the gasifier is easy as the good natural air flow will quickly increase the flame. Soon as you see the flame take hold, add the flue as this will increase the air flow to the flame, the unit is now fully started. If you have any issues with early smoke, make a small ball of newspaper and drop it into the gap, this will re-ignite the gas burning flame and draw more air up through the system. If your feedstock feels damp don’t use it, the feed stock needs to be bone dry as the moisture coming off biomass in a gasifier is not very flammable and the unit will just smoke and you will lose the gasification flame which in turn lets all the un-burnt smoke out the flue which is no fun to deal with, all you can do to stop the process is by taking off the lid and dropping the inner chamber in the quench bath. Avoid breathing the white smoke as much as possible.
The small gap between the lid and flue allows you to keep an eye on the process. I have found it gives you a better idea of the gasification process, the flame has a mild audible roar as the air flow works well. The close up of the flame from the inner chamber shows the air flow drawing in and burning on the left of the image, you can simply lift the lid an inch (carefully with gloves) and take a sneak peak inside the inner chamber. As soon as the string burns and the bolt drops out the bottom it’s ready to quench. This is the dangerous part, carefully lift the hot lid and flue off, placing on to an area that will not catch fire as the lid and flue is really hot. As the gasification process has finished the Biochar is now burning because of all the heat and incoming oxygen, you need to stop this process as quickly as possible. Using a good sized pair of grips lift out the inner chamber and drop it into the quench bath, water will push up the air inlet hole and you will need to stir the Biochar getting it all under water. The top of the inner chamber will stay hot for quite some time, after a few minutes lift the inner chamber out of the bath, the grate will stop most of the Biochar flowing out the bottom and tip it into a bucket. You can break up the Biochar with a hammer and it’s ready to add to your compost. You could quench the Biochar with a hose directly into the unit but you will get a lot of boiling hot stream jetting back at you. I have found it easier to just drop it into a bath, which was the other half of the cylinder I cut in half to make the outer chamber.
I intend to add some handles to the lid and flue making the quenching process safer, When lifting the inner chamber out be careful as you are dealing with open flames and hot surfaces, wear long welding gloves and a long sleeved cotton shirt.
If you have any questions or issues feel free to ask.