Friday, June 13, 2008

Backyard Smoke: What to do with the biogas from making char

Philip Small
Thinking Join Date: Jan 2007
Location: Spokane, WA
Posts: 78
Blog Entries: 1

Backyard Smoke: What to do with the biogas from making char


Making char produces biogas. It is flammable and contains a prodigious amount of energy. In an industrial setting char-making strategies often rely on the value of that energy, using it to produce hydrogen, etc.

It appears to me that the commercial value of the released biogas approaches the commercial value of the char produced. We who frequent this forum should not be letting this value slip away, allowing it to contribute to greenhouse gases, without some attention to the potential for recovery.

In the typical backyard/rural lot setting of the terra preta tinkerer, reasonable options for using the heat and smoke produced are below the metaphorical horizon or a "back burner" issue at best. Hopefully this thread will help stimulate some initial discussion in this area.

To date, I have found two technologies that offer some reason to hope that solutions could be developed at the individual household level:

1) The inverted downdraft gasifier. Developed to make more efficient use of wood for cooking in developing countries, it is undergoing continuing refinement. Many DIY-type folks are trying their hand at various configurations (The Garlington, the Magh smoke burner stove. The MIDGE (pdf). The James Butler MIDGE). It is a small batch process. It is highly efficient: a handful of twigs will boil a cup of water. The process is shut down about halfway through the burn sequence in order to retain the char.

2) At the high tech - glimmer-in the eye end of the visualization spectrum: The Stirling engine. A highly efficient, fairly simple, external combustion engine, the Stirling engine is far safer than the steam engine. The Strirling being applied to generating electricity from industrial waste heat, to generating electricity from solar heat, to cogeneration of household heat and electricity, and to service as a wood stove top circulating fan. A demo stirling can be made from tin cans and plywood, but a machinist in the family could be quite handy.

Look forward to seeing folks build on this theme of using the smoke and the heat generated in some beneficial way.

Last edited by Philip Small; 05-04-2007 at 10:18 AM. Reason: add JB MIDGE link

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