The biomeiler I built in the summer of 2022 has been disassembled and I can soon begin building the 2024 version.
The new version will have three significant changes. First, it will be 12’ in diameter, which is bigger than the 10’-diameter of the 2022 version. Second, it will have an aeration system, rather than rely on air to infiltrate naturally from the surfaces. And, third, the heat extraction tubes will be in two concentric vertical cylinders, rather than in layers of horizontal spirals.
The purpose of the aeration system is to keep the oxygen level of the pile high enough to maintain aerobic decomposition. The previous versions used anaerobic decomposition. It worked well enough, but there should be more heat available for extraction if the aeration system is sufficient for the pile to remain aerobic.
Arranging the heat extraction pipes in concentric cylinders is mostly for the ease of construction and deconstruction. I don’t think there is any particular advantage to the geometry in terms of heat extraction.
When disassembling the pile, it was a pain to have to scrape out the material layer by layer. Pushing a shovel vertically into the pile would have been more convent, but would have risked damaging the heat extraction pipes.
If the pipes are, instead, coiled around the walls of vertical cylinders, most of the pile could be shoveled away, rather than scraped away.
