Friday, May 23, 2008

New Gardening with Biochar FAQ

Note: Bio-char, agrichar, and charcoal are interchangeable terms when it comes to the intentional use of charcoal in the garden.

The argument for encouraging biochar use as a ubiquitous household practice is compelling: Improved garden soil will increase food production where it has the most impact on energy demand. Implementing charcoal manufacture at a household level draws in a supply of yard prunings and workbench scraps that otherwise would be lost to non-charcoal alternatives.

Unfortunately, finding even the most basic information on how to implement biochar use as a personal sustainability practice is discouragingly time consuming. In response I have started up a FAQ, a collaborative wiki, building on the efforts of the TP enthusiast community (1, 2, 3). Maybe you, the concerned gardening public, can help us thresh out the most important questions that need asking. Leave a comment here or at the FAQ. Here's my favorite bit from what has been posted so far:

2.05 What are some less smokey approaches to making charcoal for the gardener?

Choose your feedstock wisely. No matter what technique you use to make charcoal, choosing uniformly sized, dry woody material produces the highest yields. Uniformity is one reason that colliers will routinely use coppiced hardwoods.

Inverted Downdraft Gassification. For a cleaner burning configuration, consider a Top Lit Updraft (TLUD) technique, also referred to as an inverted downdraft gassification. The technique looks simple but in reality it involves some fairly sophisticated principles (PDF). That doesn't prevent success using common materials and dead simple design. Take that same open barrel configuration, tweak the design per the aforementioned sophisticated principles, and now light it from the top instead of the bottom. This takes a different skill set than lighting from the bottom but its also not that difficult to master. A little vaseline or ethanol on a cotton ball can work wonders for starting up. Once the fire gets going, the top layer of wood burns, creating charcoal, naturally. The heat from the top layer burning warms the wood below it releasing combustible and noncombustible gases which flow up into the charcoal layer. Glowingly hot charcoal has a wondrous ability to strip oxygen molecules from of anything that passes over it, so it converts the water into hydrogen, and the carbon dioxide into carbon monoxide. These two gases are flammable. They join with the other flammable gases released from the fuel. These ignite as they mix with air coming into the top of the open barrel above the charcoal layer. The result is a scrubbed gas-fed flame that is much more controlled, and which burns substantially cleaner and hotter than can be achieved with the bottom lit burn barrel. (Source). Insufficient oxygen below the combustion zone impedes loss of the charcoal despite the high temperature flame immediately above it. This allows charcoal to build up faster than it is consumed, at least until the pyrolysis zone reaches the bottom of the fuel column. The downside is that, while wondrously clean burning, a TLUD is challenged to achieve yields above 20% charcoal-to-fuel.

Folke Günther's simple TLUD-fired Retort. A retort works by restricting the air supply to the target feed stock for the duration of the burn. An outside heat source pyrolyzes the retort contents, small openings in the retort allow wood gas to escape, but restrict the flow of oxygen in. While retorts are capable of very high yield efficiency, the open flame used to fire the retort is not as clean as can be achieved with a gasifier. In small retorts, a further inefficiency is that wood gas generated from the retort can end up blowing by the combustion zone without being burned. Folke Günther's elegant solution is to combine a TLUD with a retort. This is easily the cleanest burning and highest yielding method we know of to make garden-sized batches of charcoal.



Nicola said...

My name is Nicola, I'm from Italy. That's why my english is quite "strange", it's been a long time since I wrote in your language... I rule a blog diary about my personal, and sometimes funny, experiences in "natural gardening" and home made permaculture.
I stumbled upon your wiki searching information about terra preta and find it very useful and interesting. I wuold be very pleased to translate your FAQ in order to publish it on my Blog (quoting your wiki, of course!), I can mail you back the translation (if it should be useful...).
Please let me know if there are problems about it.
Thank you for your great and interesting work!

Philip Small said...

Yes, please do. The courtesy of a simple attribution is always welcome, but I truly don't feel I "own" any part of it. Please feel free to interpret it and build on it and change it as fits best for your circumstances.

Anonymous said...

Two things in this BBC news item:

Lesotho gardens relieve food crisis

Depletion of soils:

"But they are terrible for farmers. . . . The already thin mountain soils have lost virtually all their productive nutrients."

Their solution so far:

"But Lesotho cannot wait . . . .They are now thriving on what have become known as "keyhole gardens". . . round gardens . . two metres in diameter and raised to waist-height . . . layered with tin cans, mulch and ash which together provide the nutrients to make the gardens extraordinarily productive. . . . They retain moisture far more effectively than land farmed by traditional farming methods, and they are compact enough to turn the tiniest plot of land into productive agriculture."

Is making and incorporating Biochar the next step they need?

Nicola said...

Thank you! I'm working on the translation, time to set the links up and it will be ready! I hope I haven't messed too much with tech terms!

WorldStove said...

Hello Phillip,
I just ran across Nicola's version of your FA(biochar)Q. He has done a super job (as have you)
Nat of WorldStove

new_biochar_land said...

You want to know all the secrets about biochar ?
This book will help !

Here practice and theory merge under a single cover of "The Biochar Revolution" and reveals hidden secrets of science called Biochar