Science Forums 2

[Philip Small]

The Pilot-Scale Retort: Simple and Fun

In pursuit of soil science's Holy Grail, Terra Preta Nova, I made some char last summer using a small retort on the BBQ. My retort was along the lines of what I had learned when Making Char Cloth as needed for Flint and Steel Fire Making but my retort was bigger to accommodate wood and such. I made it from a soda cracker tin, and used wood scraps and maple tree self-prunings from around the yard. One thing I learned is that charcoal making with this approach works far better when the temperature outside is hot. If you must play with making charcoal on a mild day, do it before the wind picks up in the afternoon! Wind can be amazingly effective at sucking off the heat needed to complete the process.

An Intermediate Compost Stage Inoculates the Char

Next step, I soaked the char bits in a dilute solution of Miracle Grow, somewhat along the lines suggested by DD over at eprida.com. Then I worked them into my soil-inoculated maple leaf and kitchen scraps compost pile, where they sit to this day. I have a good feeling about this compost finishing approach. For one, the kiss of MG nicely goosed the compost process. I figure this intermediate compost stage will inoculate the charcoal with a wide variety of aerobic fungi, archaea, and bacteria prior to moving it the garden.

A Wood-gas Stove Would Be Better Than A Retort

I highly recommend the BBQ/Hibachi sized retort as a first step in experimenting with making char for your garden. However, with the retort, the precious wood gas gets wasted in the process. Not something I want to promote as a final solution. I think a wood-gas cooking stove is my next step. These are gasifiers that produce gas from wood and then burn the gas, leaving the charcoal. According to Wood fires that fit - Appropriate technology: Journey to Forever, they are reputed to be "...clean, fast and efficient. They burn small pieces of wood, sticks, wood chips, corncobs or nutshells, producing a clean, blue flame and no smoke. A lot of cunning engineering has gone into the development of these stoves, and yet they're easily made from locally available materials -- even tin cans. ..."

Note: I had intended this post to include links, but, apparently, until I get 10 posts, I can't do that. I'll post this with links to nscss.org/forum.