Farm visit: pictures, lots of work done, rotary sifters

Tons of work got done during the 3 weeks there, including:

  • Took down and partly processed 6 very large cypress trees above the tea field
  • Started new long-term compost pile
  • Planted several dozen new tea plants, mostly Y/Y cultivars
  • Lots of wood moving and splitting
  • Re-built the char pit with real firebrick, which should last forever
  • Several burns of the char pit.

Lots of thinking about how to make the process easier, mostly in the sifting-crushing-sorting.  Right now i am thinking about building a low-tech Rotary Sifter, something like this. Combined with some kind of crushing phase, with gravity to assist in moving char through the process, i think this would radically increase the amount of finished fine char per hour of work.

Update: it turns out that what i’d like to build is called a Trommel.

Farm visit fall 2012

I’ll be back on the island from August 24 – September 15 – to work on the farm, plant tea plants, split firewood, make compost, make biochar, and experiment with lots of cool stuff like making native bricks and larger and better biochar production techniques. I’ve also just bought a GoPro and Steadicam so i hope to make some videos about all of the above. Stay tuned!

More on Tea & Biochar in Sri Lanka

More about growing tea with biochar in Sri Lanka, from an eariler comment on this blog.

1. “Biochar: Can it put the tea industry back in the black?”, Dr. J.C. Krishnaratne, http://www.sundaytimes.lk/120624/business-times/biochar-can-it-put-the-tea-industry-back-in-the-black-3850.html
In summary, it says that the Sri Lanka tea fields are in bad shape due to erosion and long-term overuse of chemical fertilizers, that biochar can and should help, and that char could be made out of the Gliricidia trees that are already quite widespread and grow well in that region.

2. A response to the above article by Hemal de Silva, http://dl.dropbox.com/u/52700813/Biochar.pdf
In summary, he says that while biochar is certainly good for tea soils and yields, the economic situation is more complicated, lack of re-investment money means biochar may not be sufficient to solve the industry’s money-losing problems, by itself. He suggests that looking at particular tree species, Pentadesma butyracea and Garcinia indica (Kokum) might provide a better economic result.

I was unaware of the economic picture and have never heard of these tree species, so it’s very interesting.

Biochar and Tea

I spent the month of September 2011 back on the farm, getting it into shape and making batches of biochar.  At the end of the month i took a truckload of the char down to Josiah’s biochar operation in Puna, where it was inoculated and ground up.  Back at the farm, the living char was spread all over, especially in the tea field.

To date, there has only been two studies of biochar on tea that i know of: some Japanese work back in 1997-2003, and my own postings on this blog.  Today, i heard of a third study: Using Biochar to Improve Soil Health and Leaf Production at Tea Plantations in Sri Lanka.  It’s early, but very positive, just as with the studies here and in Japan.

Farm biochar flowchart

How does biochar fits into our farm?  I scribbled a flowchart onto paper, and today put it into the computer; it looks like this:

Ideally, it’s a continuously flowing cycle; there is no “waste” and no need for unsustainable inputs; that’s the goal.  The chickens provide meat and eggs to the humans, and poop to the compost cycle; the biochar stabilizes the nutrients in the urine and compost, making them plant-available longer.  You can see how the compost pile is the engine in the middle of everything.

Biochar: from kiln to pit

Those of you following the biochar-hawaii list know that i’ve stopped using my kiln, and am now focused on making biochar in a pit. This is both for reasons of scalability and wear; my 55-gal steel drum kiln/retort could only make ~23-gal of char, and the surrounding kiln blocks cracked from repeated heating.

Hence, a pit. Mine is lined with blocks for clean char and easy unloading. Continuously fed wood, pyrolysis occurs at the air-starved bottom of the pile, gradually the pit fills up, then i cover and let it cool for a day, before opening and scooping out the finished char:

That first small pit worked well, so i made it bigger and sure enough, it scales well:

Width Length Depth Gallons Cubic feet # of blocks Gallons of Char
24 32 16 53.2 7.11 33 16.5
32 48 16 106.4 14.22 48 34
32 48 24 159.6 21.33 60 68
32 48 24 On second burn: 82

That 82-gallon operation took 2.5 hours to do the burn, then 2.25 hours the next day to unload, crush, sort, sift, and load into buckets. That’s 82/4.75 = 17.25 gallons of char per hour of work. That’s not bad, given that i’m working with some cheap concrete blocks, a piece of old corrugated roofing, and a shovel. With more money and technology, like a continuous pyrolysis machine, you could certainly get vastly more char per hour of labor, but those machines start at $100,000. I’m feeling quite happy about my pit. The Biochar2010 album has all the pictures.

I gave a biochar talk to the Kona Coffee Grower’s Association on June 2. 10 minutes of that talk got uploaded to YouTube. I then addressed the Hawaii Tropical Fruit Growers on July 19, that time with a fancy presentation with charts and pictures. Next will probably be an evening talk in Waimea on August 8, and then a 1-day workshop on making and using biochar here at our farm, date TBA.

Biochar kiln progress

I recently did a second and third burn in my biochar kiln, tweaking each time. The story is best told in pictures:


Upon detailed inspection, the April test burn actually gave good results. Four white buckets are completely charred material, two orange buckets incomplete, one mixed and one of material from the surrounding fire.


Completely charred wood from retort, and the incompletely charred – only a small amount, and generally from the bottom of the barrel, perhaps due to a lower temperature there.


Preparing for burn #2, using smaller wood and some changes to the kiln.


Added a layer of firebrick at the base. Ideally, it should enclose the whole chamber, but that would take a lot of actual masonry.


More air inlets, allowing air into all four corners.


The ‘chimney’ is formed by the blocks themselves.


Smaller wood scraps for burn #2.


Opening the kiln after burn #2.


As before, the material at the bottom of the barrel (top, when inverted like this) is less charred, but everything above (below) it is completely charred


Much of the sticks that look brownish on the outside are actually completely charred black on the inside


Burn #3


Got the fire real hot this time, you can clearly hear the “whoosh” of the pyrolysis gasses from the barrel joining the fire


Sifting/crushing/sorting the result. Some 1/2″-minus has direct uses. The rest will soak in nutrients to charge it, then goes through the chipper-shredder to make “charged fines” – biochar fertilizer.

UBI biochar

biocharAs a followup to my last biochar post, i was sent the following document from Karl Frogner of UBI. Karl asked me to make it available, so i’ve put it here: Biochar Ovens, until UBI has a place for it on their own site.

It describes experiments conducted in Mongolia on making biochar in a steel drum where the combustion occurs in a metal center tube. Innovative and fascinating! I want to try it here on my farm, but i’ll have to somehow locate some heavy large-diameter metal pipe, and be able to make holes in it.

Biochar retort, experimental design, first trial run

My friends Josiah and Jay down in Puna are producing biochar using a classic pit method, which seems to work well. I may end up making char that way as well, but there is some criticism on the biochar list of open burns, saying that emissions aren’t fully combusted and carbon yield is low, recommending a kiln or even better, a retort (closed “cooking vessel”). So, i looked at plans online and found two approaches, the two-drum and the Twin Oaks, particularly as built by Kelpie in Oregon. The first approach is too small a batch and requires multiple drum sizes, the second requires expensive metalwork including pipes and welding. I came up with a hybrid of the two approaches which should be cheap, simple and high yield.

I did my first trial fire-up yesterday. The trial results are from this picture onwards.

Results were promising, but need tuning. I learned a lot from this trial run. Some indications:

  1. The kiln fire needs to be strong and hot and heat up fast.  My kiln burned moderately, for a long time, so it didn’t fully cook the retort.
  2. More air inputs.  I was hoping to limit openings to focus the heat inside.  I put vents on the left and right and front, but the fire seemed to want more air.
  3. A round barrel in a square box isn’t great geometry for a fire, which tends to burn separately in the four corner “zones”.  I could try stacking the blocks in a more circular arrangement, like a hexagon/octagon.  If i stay with this arrangement, i’ll need air vents specifically pointing into each corner.
  4. Chimney.  I figured a simple rectangular hole at the back should suffice, since it worked for Kelpie.  But mine didn’t seem to draw well. Charcoal kilns for a thousand years have had proper chimneys.  I’ll probably need one too.
  5. Insulation.  I used regular CMUs because they’re cheap and available.  No doubt better insulation would result from using firebrick, thereby focusing more heat inside.  I could also fill/bury the hollow tile walls, even if they’re dry-stacked.

The half-charred results of this trial aren’t useless; they could still be used for a less-smoky cook fire, or dropped through my shredder to make mulch with a more stable carbon content.  However, the goal remains easy, cheap, reliable full pyrolysis.  If it doesn’t pan out with this design, i could always switch to a pit, or hybrid brick-lined pit, or other ideas.