We began the process by feeding the shells into a delivery auger which drops material into a hopper. The pyrolysis auger then moves the material from the hopper along the bottom of the pyrolysis zone where it is heated. The heated material carbonises and gases bound up in the material are released. These gases are mixed with introduced air and combusted, creating heat which is sufficient to maintain the process, with excess heat vented up the flue. The carbonised material (biochar) is removed, quenched and collected.
It did take us some time to “learn” how to char the shells. Initially, because uncharred shells were coming out through the feed-out auger we were feeding any unprocessed shells back through the process.
We achieved process temperature by moving the shells through the machine slowly, using the diesel burner to heat the chamber. Once gasification was established along the length of the kiln and we were confident the temperatures could be maintained, we turned the burner off and the process was self-sustaining.
There are 6 thermocouples which monitor process temperatures at key locations in the kiln. During the process, a record was kept of the temperatures at 5 minute intervals. Process temperature is controlled by using water jets inside the kiln.
Initially, the shells caused a lot of noise in the feed-in, pyrolysis and feed-out augers and seemed to make the machine “work” very hard. However, as the time of processing increased, the noise level dropped. We suspect that the fact the kiln had not been used for a few weeks, the insides of the augers were rusty and needed some time to settle in. Once this problem was resolved, there were no significant handing issues.
Macadamia shell biochar discharged from the kiln was immediately quenched using fresh water. This is critical to avoid the hot biochar from igniting when it contacts the air. It also aids with handling of the biochar post discharge.