Fatboy V2 Gasifier

I have finally finished and tested my Fatboy V2 Gasifier over 50 times and it’s on it’s way to a new home. I thought I would share some pics of the unit as I have refined many areas of the unit since my Fatboy V1.
The inner 75 litre chamber came of a stainless steel pool filter which also included a brass inlet which was modified creating the primary air which can be controlled from outside the unit, this also allows the capture of quench water. The large pin the the centre of the inlet is tried to the grate with string and when the hot char burns the string it drops the pin with a clang indicating the unit has finished and is ready for quenching.

This was the first version, the plans at the top of the page still represent how the unit works. Fatboy V1>>>> 

Some quick data.
75 litre chamber produces 30 litres of Biochar.
45 minutes processing time on mixed dry green waste. (25min with larger flue design)
15-20 litre of water for quenching
Can process 35mm dia branches mixed into wood chips.
Easy start, start smoke to clear to 15 seconds. (every time without added liquid fuels)

Tesco flue analyser, 15min after start up from the top of the flue
696 NOx mgm2
2.46 CO2%
305.5c Flue Temp
61 H2 ppm
60 NO ppm
17.61 O2%
519 CO pmm

This unit runs super hot, the condenser ‘hat’ surface temperature ranges from 550 (green waste) to 900 deg (macadamia nuts shells).  When you quench the unit, full coverage of skin with non flammable clothing and good quality welding gloves are required, the image of a metre of flame is what you will commonly have to deal with. Always avoid the quench stream as this contains some carbon monoxide.

Development of the Fatboy continues (see green tank at the bottom of this page), next version will hopefully include a simple thermal oxidiser which should improve emissions. This unit has been developed as a open source style of project please feel free to copy any part of the unit and share your development ideas.
Note: This unit has not produced any Biochar product of Black Earth Products.

All Biochar produced from this unit has been used in my own permaculture food forest and is always layered through my compost bins or blended with composts prior to application.

9 thoughts on “Fatboy V2 Gasifier”

  1. Thanks for sharing. Cool design. How are you quenching? Just spraying water on top?

    Also this looks like natural draft but I was confused with your description of primary. Ae you using a blower of some sort to get the temps that high?

  2. Quenching is with a hose on a wide spray. Natural draft is correct but the design develops high controllable air flow more so than any other natural draft unit I have seen.

  3. Very nice looking unit, you have many design features that I like a lot. But I do have a few questions you could answer to help me with the functioning of the unit. Can you describe the quench indicator in more detail? I do not understand how this is used during the process, can you turn the quench from underneath the stove like a dampener or have I missed it completely?

    The vortex slot, is that cut on a slight angle to start a swirling effect on the gasses that are being emitted from the burn? In the picture showing the primary air inlets, are there holes drilled into the bottom of the barrel or is that residue from a burn?

    We are looking at various stove designs to be used for the Master Gardeners and also for my own backyard food forest. Any assistance you can provide would be appreciated.


  4. Hi Vince

    The quench indicator is a simple way to let you know when the inner chamber is ready to be quenched as the limited oxygen hot coals travelling down have reached the bottom grate, once this occurs the biochar will have access to oxygen and with start to burn, you can lose 50-70% of a batch in 10 minutes if you do not quench the biochar and take the heat out of it. The quench indicator is as simple as a bolt tried to the bottom of the grate, the hot coals burn the string and the bolt drops making an audible noise letting you know it’s ready. Just a reminder stay out of the steam when you quench as it contains some carbon monoxide.

    You can reduce the incoming air from the bottom, but not the top, when you apply quenching water the steam vapour will increase the porous structure as the stream jets through the chamber. This creates a better quality biochar. Always remember the smoke produced is highly flammable, think petrol flammable so you always want a flame burning the gases so you do not create an explosion which I have seen happen with a retort.

    The vortex slot is not angled and does not need to be.

    The outer drum has slots at the bottom, keep them at the bottom as this will help create air pressure at the top of the chamber forcing air into the secondary burn which is the main burn of the volatile gases. Think air fuel mix, air coming up the gap between the inner chamber and outer drum. It heated and forced through a small gap which speeds up the flow, the fuel is the volatile smoke gases coming from the inner chambers hot coals burning down through the biomass, as the hot coals are travelling down they create an oxygen-less environment above in the newly create char.

    You can slow down the units rate of production by limiting the inner chambers air flow, don’t try limiting the outer.

  5. Barry,

    How much of an air gap is there between the inner barrel and the lid on the 55 gallon barrel? Do you have any images of the barrels with materials ready to ignite, I assume you are still adding burnable materials between the outer barrel and the inner barrel to ignite?


  6. 1-3mm is the gap from the inner drum and the condenser hat, so the outer drum is 1-3mm higher as this is what the condenser hat sits one.

    No material is added to the gap between the inner chamber and outer drum. See the Fatboy V1 page to see how this style of unit is loaded and how it was lit. If you add material in this gap it will create smoke and interfere with the air needed for the correct air fuel mix. The units volatile smoke will not burn if you do not allow for a clean air source which creates the correct air fuel mix.

  7. I have several blocks of highly fire resistant building material I got from a friend.They are 2′ X1′ X 6″. I also have about 8′ of 12″ diameter pipe and a top with a screen around it to catch hot debris, both from our old fireplace. Everything in excelent condition stainless and double layered. After seeing your set-up I’ve resolved to make biochar for my garden..When I took down a few trees that were blocking garden sunlight I chipped up all the branches that were under 8 inch diam. (turned the rest into lumber). I have a woodworking shop and always have small pieces that usually go to friends for kindling.
    Question #1: Is there a reason for not blocking the air flow from the draft apertures and the point where the stovepipe meets the unit and then turning on a spray of water from pipes already installed inside? Are we looking at an explosion?.If so The chimney can be made to swivel away from the top of the unit, rather than doing it manually. Right???
    Question #2 Are you saving the drain water for any particular reason? Thank you

  8. Hi, thanks for the description of a great looking device. Can you please let me know what the inner drum is made of and where you got it as it doesn’t appear to be commonly available?

    Also – could you avoid the need for water quenching by modifying the quench indicator to drop a plug and close off the primary air rather than just making a noise?

  9. The inner drum of the Fatboy 1 was a small pressure tank and Fatboy 2 was from a pool pumps filter housing. It all comes down to what you can find in stainless steel for the inner chamber. I have thought a stainless beer keg could work well.

    I water quench for a couple of reasons. One, it increases the porous structure and surface area of the biochar. Two, it makes the biochar hydrophilic as dry biochar can repel moisture. 3, it stops any chance of the biochar igniting and burning to ash.

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