To malcolmf,
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In a traditional method like yours, the energy must come from the combustion of some of the feedstock. You could easily waste a third of your feedstock if it is not dried.
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What I do in my small (20 gallon) garbage can is get a good little fire going at the bottom, then put in some medium size pieces of wood, then on top of that 2 or 3 large pieces of wood or left over large pieces that didn't char the first time. This takes up 1/2 to 3/4 of the can and separates the heat source from what I want to char.
Living in the Black Hills of South Dakota one thing I don't have to worry about is starter material. We have dead wood everywhere! In fact the Forest Service pays to thin the forest and they leave these large piles of wood in tepee shapes. They sometimes even burn them. We also have lots of logging so when ever I need some fresh pine needle I just go and get their wastes.
Why I am trying to char pine needles is that I am soon moving to Colorado and in talking to a Colorado State University soil professor he was concerned that any process that raised the ph of the soil was not good because most of the soils on the Front Range are already too alkaline. In my reading on pine needles they are acidic and do lower the ph when mulched in/on soil. But not much and for not long. Also they do not degrade very fast. My idea is to find out if charring the needles will eliminate these 3 problems by the stability of the char and its ability for some to decompose quickly (kind of a contradiction but isn't that what fresh charcoal does?). My one concern is that the charring may drive off the acidic compounds that I am trying to get but until I do that I won't know. If adding a certain amount of pine needle char can control the ph level of the charcoal then we can use charcoal for both acidic and akaline soils.
In getting back to the Forest Service/logging wastes. All my life I always thought of what we could do with all the pine forest we have here in the west? Can we sustainiably use them to provide charcoal and other soil amendments? Right now every year we have massive forest fires that turn pine into CO2. Can we capture that through sustainable efforts and turn in into char? This is what I call a "pie in the sky" idea but again I already see the Forest Service/loggers thinning the forest so how much more effort would it take to turn some of their wastes to charcoal?
Another idea I think we should pursue (and I think one of your earlier posts mentioned this) is how can we amend a particular local soil by the parent stock of the char, charring temperatures, and by composting it with certain organic materials. I have read numerous composting articles and the information says you can design your compost to match your soil. All we do with the Terra Preta idea is use the physical and chemical properties of carbon to create a sustainable soil with all the benefits we know Terra Preta has. I firmly believe that many of Terra Preta benefits come from partial biochar of all kinds of organic wastes. One person posted the idea that we currently look mainly at first order effect when we do something to our soils. What about 2nd, 3rd, and 4th order affects that may happen 1, 2, 3, 4 years down the road. Example: I plan to use bone meal in some of my Terra Preta in place of the calcium/phosphorous that the Amazonian Indians had via their "fish residues and turtle shells". We know bone meal is a good fertilizer and the NPK amounts are listed on the box. That’s a first order effect. But what happens to the physical structure of bone meal a year later? 5 years later? What we put in the soil stays there and who know what a certain microbe might use 3 year old bone meal (or whatever is left or whatever it became) for?
Terra Preta is very complicated and we have lots of things to try.
RB
