Biochar researcher John McDonald-Wharry put out a call for char samples a few months ago. I was curious about my cone kiln char, so I shipped a small bit of char out to New Zealand, and John ran it through his Raman Spectroscopy analyzer (see how casually I mentioned that, as if I know what the heck that is!). Here is the note he sent me today, with the results of his analysis:
I have attached the provisional Raman results for the char sample you sent in. I am in the process of writing a paper on the around 40 samples which were contributed to this Raman survey.
Your sample was well-carbonised in the top 3 of 40 in terms of our measurements of nanostructural development with results similar to our laboratory produced chars at HTTs between 700 and 1000 degrees C. I am impressed with how consistently well-carbonised this sample was with the results indicating a low level of variability with the sample.
I will send out copies of the paper manuscript once it is near completion to the contributors which should help with interpreting results and allow comparisons with a wide range of other chars (and a few other carbonaceous materials).
This result is very interesting to me. I don't own any thermocouples, so my only way of measuring the temperature of my cone kiln was to use a cheap infrared thermometer on the side of the kiln. I knew it must be hotter than the 350 degrees C I could measure on the outside metal of the kiln, but I had no idea it could get up to between 700 and 1000 degrees C! Time to get some thermocouples and check it out.
The other surprise is what John said about consistency in the sample. I took the sample - just a few grams - from a barrel of char that was made in the pyramid kiln. The char had gone through the leaf shredder, so it was pretty well mixed. Maybe it was just luck, but I am surprised that it was so uniform.
If you have been around biochar for awhile, you know that there are many types of biochar with very different characteristics. Biochar characteristics differ depending on the feedstock used, processing temperature and exposure to oxygen. Things to look for in biochar properties are pH, surface area and porosity, ash content, volatile matter content, and the "fixed" carbon content. Fixed carbon refers to the degree that the carbon has been converted to stable benzene rings that do not degrade easily.
Biochar made in the cone kiln from pine, black locust and bamboo, compared favorably with biochar made at fairly high temperatures (600 C) in a retort placed inside a laboratory oven. The cone kiln biochar has as much fixed carbon and surface area as the retort char. The cone kiln char had higher pore volume than the retort chars, and superior water holding capacity. The reason for the difference is that the cone kiln char carbonized more quickly than the retort char (the heat is transferred more quickly since it does not have to pass through a metal retort wall), shrinking less in the process, and maintaining more pore spaces inside.
Other findings from the paper include the efficiency of the cone kiln process: For red pine, about 14% of the feedstock mass (dry basis) was converted to biochar, with about 24% of the carbon retained. Values were higher for black locust and bamboo. The pH was higher in the cone kiln biochar because of the ash produced. This can be altered by rinsing the biochar, or composting with other materials if the high pH is not desired.
The researchers concluded that the cone kiln biochar is "suitable for amendment that would enhance water-holding capacity of soil and neutralize acidic soil."
Backyard Biochar This site has descriptions of my experiments with Flame Cap Kilns. I also report on work by others.
US Biochar Initiative I am on the advisory board of the USBI. We are sponsoring the 5th North American Biochar Symposium in Corvallis, Oregon - August 22-25, 2016
Illinois Valley Forest Collaborative I've been involved with the group in my hometown for several years. We are working with the US Forest Service on hazardous fuels and small diameter timber sales. Biochar is a part of what we do.
Umpqua Biochar Education Team (UBET) I am working with UBET on a Conservation Innovation Grant from the USDA-NRCS. We are helping small farmers learn how to make biochar and use it to manage manure and make premium compost.