Stopping Climate Change One Tiny Farm at a Time

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The Trench: Best biochar technology for the poor

We are mesmerized by the new and the high-tech – proven or not. Sure, social media took off really fast, but it is the exception. As a rule, new technologies take a long time to bring to scale. Our climate is at the tipping point; we do not have a lot of time. We need to change our thinking. Forget the cool. It is time to make our mantra: Scale up what is already working!

And what is already working?

Biochar.

And where is there unexplored room to scale? In the poorest corners of the world where 300 gigatons of crop waste are burned annually – but could be converted into biochar.

What is the least expensive, most practical biochar making machine for the poor who live there that is especially good for charring awkward stuff like bamboo, corn stalk and rice straw?

A hole in the ground.

Really.

Let’s start with the four big problems confronting would-be biochar makers at the poor, rural fringe of the developing world: cost, weight, lack of water and awkward feed stocks.

Cost: The gold standard of poor man’s biochar tech is the 200-liter drum TLUD. It’s ugly, but it’s simple, efficient and foolproof. The TLUD, however, has limits in the lands of the truly poor. (1) 200 l. drums are prized and, where available, are costly. (2) You can make a TLUD without a power drill or cutter, but I can tell you personally that it is hard work. (You try pounding all those holes in a drum’s bottom with a piece of sharpened re-bar and a big rock.) (3) Although you can smother a TLUD, it takes hours. If you can afford just one, production is limited to two burns per day. (4) Why not quench with water? Because few poor people have any in their fields or enough at home to waste.

Weight: TLUDs are a pain to carry up steep slopes, but nowhere near as hard as the next best biochar technology – the trough/Kon-Tiki/flame cap kiln. Troughs are great for charring all the stuff that won’t go in a TLUD – stalks, branches, bamboo, straw. But like TLUDs, troughs have limits. (1) A trough tough enough to take into the field is made of steel. You can cut costs by scavenging recyclers’ yards, but you must still pay a welder. (2) Even if farmers can manage the cost, the weight of troughs often defeats them. Dragging a trough up and down a steep mountain cornfield or even through a hillside orchard is hard work. (3) Troughs can be smothered, but it takes even more work than smothering a TLUD.

Lack of water: Much of the densely populated developing world experiences a weather cycle of three months rain, nine months dry. Crops get planted with the rains and harvested early in the dry season. If the dry season starts slowly enough, farmers may squeeze in a second crop before the ground dries hard. Most places, however, no second crop is possible. Water may run out by March or April and is at a premium. Whatever the potential benefits of biochar, quenching it with water during the dry season is out of the question.

Awkward feedstocks: TLUDs eat corncobs and love any form of neatly chunked feedstock that does not pack densely. (Anything from pinecones to big, dry wood chips work great, but beware coffee hulls and rice husks!) Unfortunately, most char-able stuff just won’t go in a TLUD without a lot of work. The poor, however, lack the time or energy to pack corn stalk into a TLUD, let alone cut dry bamboo to length. Low density feed stocks such as straw and high density, naturally long ones like bamboo and branches require an “open mouth” char technology – that isn’t a costly, heavy, water-dependent trough.

What to do?

Dig a hole.

Why?

Cheap.

Weighs nothing.

Requires no water.

Great for awkward feedstocks.

Trench of millet stalk biochar open with roofing sheet at side



Learn how easy it is to do:

Instructions for Making Char in a Trench

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