Biochar processor simulation

This series of photographs was taken over the course of about an hour.  The smoke shown here above the flower pot is coming from a quart of wood pellets in a 3" copper pipe that had one end open (on the left just above the flower pot) and the other end (capped with an aluminum foil cover near the mid-right side of the fire pit).  The "smoke" had just started and would not ignite. It is composed of low temperature volatile compounds including;  water vapor, methanol, CO2, methane, acetic and other acids. The next picture will show the stable flame that is supported when the "smoke" has more flammable components.  In a normal biochar processor system these low temperature volatiles could be either collected or cracked for later use.

It took about 10 minutes for the steam to clear out and the flame to stay lit.  The flame burned for another half an hour.  When it went out I pulled off the cap shown next.  At this point the process could have been continued by pushing the previously heated material in the tube towards the middle of the tube from the covered end and additional feedstock could be added to fill the tube and the cover replaced.  Since the volume of the feedstock is reduced by the charring process there might not have been any charred material that was moved out of the tube.  Eventually charred pellets would drop into the flower pot when the tube was completely full at the end of a charring cycle.  See the Biochar Systems page for a discussion of some experimental designs.  Note that some of these are not truly pyrolyzers because some use added air to cause the heating.
The pyrolysis had proceeded all the way through the tube.  The finished char filled two and 1/4 flower pots.  The last pellets (those near the end cap) were not quite fully charred.  These are still somewhat brown as shown in the next shot.
The smoke is coming from the partially charred section you may see that there are slightly brown pellets on the right side of the two piles.  These remained very hot and it took about a quart of water to cool them off to stop the pyrolysis.

Pyrolysis begins by raising the the temperature of the feed stock, in the absence of air, to the point where volatile compounds in the feedstock are turned to vapor.  The water both free and chemically bound and other low temperature volatile compounds are released before other higher temperature compounds begin to be oxidized.  The feedstock temperature can be raised either by combustion of an external fuel after which some redirected gasified flammable feedstock components can replace the external fuel after an initial heating period .  Eventually a threshold is reached when the oxygen bound to carbohydrates can react with some of the remaining carbon and hydrogen and the reaction puts out enough heat to continue the pyrolysis until all the available oxygen has been reacted.  This situation maximizes the amount of carbon that can be recovered as char.  The hot fully charred stock must be cooled so that contact with external oxygen does not cause continued combustion.