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My experience with a trench fire for biochar  RSS feed

 
Posts: 1826
Location: Kent, UK - Zone 8
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I mentioned in another thread that I was looking for a method that would let me process a large amount of material quickly, and that retort styles were too slow and labour intensive. I've wanted to try a cone kiln for a while, but getting one made up simply hasn't happened.  In the end I cracked out the spade and dug a trench, and had excellent results.


  • The material I am burning is long stems/branches of willow.
  • I wanted to minimise cutting of the lengths, so laying whole sections down the length of the trench was ideal
  • The material was cut in late winter and has had a few montsh to dry. The water content was down a fair bit already, so it burned nice and cleanly.


  • A few observations

    Most of the wood was too long for the trench, so the branches were suspended over the trench with excellent air flow. The fire was ferociously hot and consumed material rapidly. As soon as the wood had burned to lose structural integrity the charred sections fell into the pit, where they were effectively protected from burning any further by the flame front above.  After about two hours of burn time (we paused in the middle to have dinner and toast marshmallows and damper bread) the pit was full of char. I kicked all the ends in and left it for a few more minutes, before starting the quench.

    We didn't have access to a hose, so I was using buckets of water from the pond. Rather than pouring them into the trench - which in our soil would not hold water - I filled an old metal galvanized bathtub thing with water, and shoveled the char into it. This was quick and easy, and when finished the water was just lukewarm. This minimised the amount of water I had to haul.

    In that one burn I think I went through about 1/8th of the cut material we have sitting ready, and there is plenty more around the property. I'll be using this method again, quite happily. It is, for me, a perfect balance of low effort investment with good yield.
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    pollinator
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    I am surprised you did not get a reply on this, but I suppose it is because there was no real question to be answered, just an explanation of what worked.

    I am glad it did for you though. I tried this last year and failed miserably. In my case I think I tried to use too big of wood, and the wrong kind (White Pine). I had a good burn, but I either had ash, or charred wood blocks, nothing in between.

    I am glad it worked for you however.

    (Nice family and homestead by the way, you should be very proud)

     
    Michael Cox
    Posts: 1826
    Location: Kent, UK - Zone 8
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    Travis Johnson wrote:I am surprised you did not get a reply on this, but I suppose it is because there was no real question to be answered, just an explanation of what worked.

    I am glad it did for you though. I tried this last year and failed miserably. In my case I think I tried to use too big of wood, and the wrong kind (White Pine). I had a good burn, but I either had ash, or charred wood blocks, nothing in between.

    I am glad it worked for you however.

    (Nice family and homestead by the way, you should be very proud)



    Thanks Travis.

    We did another burn since then, using the same hole. I've got it down to a pretty slick process now. I can get the trench filled with char in about 2 hours. Shoveling out to quench has worked well for me - it saves a lot of water, and if the trench is full I can empty it and immediately carry on burning.

    And yes, the family are pretty awesome. I just wish we had the time to really do a "homestead". Life is settling down a bit though, and some projects are progressing.
     
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