Thursday, September 29, 2016

Biochar Kilns

"We tell the government officials that we can provide more power than they need, at a tenth of the cost of the oil, and we can do it from feedstocks they consider wastes, and we can use processes that net sequester greenhouse gases at each step, with a lifecycle cost that is high in the black, low capital outlay and quick return on investment. Oh, and it arrests global warming, deepens soils, saves water and increases biodiversity.

Naturally, they are incredulous.

Surely we are trying to sell them snake oil, what we propose is illegal, or there is some neglected externality in our calculus that makes our proposal fall apart once exposed to serious scrutiny.”  -- Albert Bates, "The Biochar Moment"

Biochar is a win-win-win, for energy, for environment, for economy.

"But as I've studied biochar, it's the only thing I've seen with no downside. Nothing! And that's very exciting to me."
  --Doris Hamill, NASA Langley Research Center

Biochar is pure natural charcoal made exclusively from above ground biomass resources with no added ingredients.  Biomass is wood, straw, stalks, stems, cobs, husks, hulls, pits, etc.  When biomass is heated to a point where all that remains is the black carbon that previously formed the main structure of the biomass, bingo, charcoal.  When this natural charcoal is  applied into the soil for soil improvement and carbon sequestration it officially becomes "biochar".

Dr. Karl Frogner of the Ulaanbaatar Biochar Initiative estimates almost a ton per acre of excess biomass from mixed maize, rice and agroforestry small farms (7-10 acres).  After deducting the energy stored in biochar produced, the btu equivalent of about 100 gallons of propane per acre is available as current carbon cycle, non-fossil energy.  As the biochar is soil applied, about a half ton per acre of atmospheric carbon is sequestered for hundreds to thousands of years.

This pure natural charcoal has no resemblance to most commercial bagged charcoal for grilling.  Never apply bagged charcoal briquettes to the soil!  They are not even similar products.

Pure natural charcoal has many uses besides soil improvement, with centuries of traditional use in medicinal, veterinary, odor control, liquids filtration and de-contamination applications.  Hans-Peter Schmidt writing for the ithaka journal describes 55 modern and past uses.

Pure natural charcoal has also been "gasified" in onboard "producer gas" systems for vehicle power, most notably in WWII Europe during petroleum fuel shortages.

Natural charcoal can be obtained as easily as scraping the black chunks off partially burnt pieces of wood - right on up to as complex as anyone can dream up

Charcoal kilns have been developed over the years at various scales and purpose.  A fairly recent innovation is micro-gasification cookstoves.  These devices, use only the energy already contained in the biomass, to make smoke, burn the smoke and save the charcoal.  More detailed info on the concepts and applications are in the book "Make Smoke, Burn Smoke".

In the early days of small scale biochar production, a fellow "stover" (clean cook stove builder) opined that "biochar kilns are a lot like snowflakes, no two alike".  Kilns were fashioned mostly from "obtainium" by those knowledgeable in the basic engineering principles.

For simple micro-gasifiers, the "feedstock", the biomass to be charred, drives the design.  Beyond that usability, and making use of the "waste heat" are additional considerations.  The simplest tool that will do the job is THE design pattern in brushape circles.

Listed in chronological order, from earliest to latest designs.

AnthroSoil Grassifier
Natural charcoal is not all created equal.  Various biomass feedstocks have varying pore spaces and shapes.  Grass/straw/stalks generally do not char well in kilns designed for charcoal production from wood.  A University of Hiroshima study discovered that bamboo charcoal holds almost 5 times as much water as hardwood charcoal. "..bamboo is in a class by itself in the charcoal world - its ability to store water is tremendous"

The anthrosoil was developed to convert grassy feedstocks into biochar.  It works well across a variety of grasses including wheat straw, switchgrass, corn stalks and bamboo.  In real world use it has even been used to char 2x4 wood scraps by a knowledgeable user.

The shiny thing near the chimney is a skillet. Cooking supper while charring switchgrass, delicious.

Lori's Terra Preta Authentica Clay Kiln
Had been looking for someone to build a biochar kiln in clay.  Lori, a local art teacher made one for me, one for her, and had her entire class make them as an art project.  She said the ugliest one in the class burned the cleanest.  (Engineers don't make the best art students?)  Her design not only looked beautiful, but made a very interesting thin line of flame and ran plenty clean enough for space heat in her drafty garage/art studio.  The clay throws wonderful radiant heat.

KeySTove LX
The KeySTove LX design was publicly released to instructables and won the "instructables of the month" award in December 2011.  The name came from discussion with a fellow stover as the Keystone XL pipeline tar sands plumbing project was in the news.  He said "you know they will probably waste more energy clearing and burning the right of way than the net energy that will ever come out of it".  Tar sands have an incredibly low rate of energy return on energy invested (EROEI), requiring $100 per barrel oil to turn a profit.

Besides open sourcing the design to instructables, also built several hundred of these for friends and eventually for sale.  "The vortex swirl" was fun to watch, and creates turbulence.  The three T's of clean combustion are time, temperature and turbulence.  With the small combustion chamber, the time was not much, but insulation and swirl made up for it in a very clean stove that saved "biochar".

The KeySTove LX had an operating time of about 90 minutes on small twigs, with enough power to cook a meal or boil a pot of water.  A larger version dubbed KeySTove GH (GreenHouse version) reliably operated at about 50% greater output for 8 hours on 10 pounds of hardwood pellets.  Perfect combustion releases mostly carbon dioxide (the same thing animals breathe out) and water, both great for greenhouse plants. 

"Just Another Kiln Experiment" and the first name of the fabricator that supplied the stainless steel tubes.  The tubes were being made for chimney vent pipes.  The kiln is produced in 1foot, 2 foot and 3 foot versions that all operate at the same power.  The one footer runs 4 hours, 2 footer 8 hours, and 3 footer 12 hours on a charge of hardwood pellets.  The output besides heat is beautifully uniform charred pellets.  A full load in the two footer is about 10 pounds.  The one foot version is my current personal choice for a clean char making stove/heater.  It is small enough to pack easily, has plenty of output to cook and heat.

2 foot JAKE

Jake replaced his wood burning stove with a JAKE char maker for one heating season in his office where doors to the outside and into the shop were frequently opened.  While he liked the heat and the char, his white metal ceiling acquired a patina of black soot.  Soot collector/burner caps were then designed and used on the higher end pyramid kilns.  See below.

Pyramid Kilns

Not long after we started building these, a professional grower relayed a bit of wisdom.  The term pyramid literally means "fire in the middle".

The pyramid shape in limited testing seems to have amazing potential.  In one test in a humid greenhouse setting the chimney began to roar and turned bright red.  A kid walking by asked "what are you burning in that thing, rocket fuel?"  The most logical explanation is that with the high humidity in the greenhouse getting higher as the kiln ran, some kind of dissociation of water into hydrogen and oxygen was happening in the humid environment.  Then the molecules re-combined in the flare.  Anyone who has cut metal with an oxygen torch can relate.

We have built and tested a few of these, but not nearly enough to explore the potential.  A noticeable side effect was that when soot collection was added, the temperature in the soot collector chamber (1950F) was higher than in the combustion chamber (1350F).  The stainless steel soot collector immediately "blued".

Blued collector right, new build left

Pyramid kiln with soot collector (on top) and char dump can (on bottom)

In the pyramid shape, time, a key design element for clean combustion, becomes an ally.  Both residence time in the combustion chamber, and residence time in the even higher temperature of the soot collector aid the the other two T's of combustion, temperature and turbulence.

Back to Practical
In parallel time frame of pyramid kilns, an aquaponics client asked for an inexpensive long duration kiln with high btu output.  55 gallon (200 liter) drums were used for the fuel cell, with a housing built around them.  Over 100,000 btuh output and they ran mostly smoke free across a wide range of "waste" biomass feedstocks.

Fun with Kilns
Some folks are looking for commercial products.  Brushapes just have fun fabricating innovative biochar kilns.  The clean heat and biochar are a bonus.

In a win-win-win scenario, all is a gain.

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