Asheville – The City of Asheville has recently completed a pilot program with CharBoss, a piece of heavy machinery that can be transported to various locations to convert wood into biochar, a carbon-dense solid produced by quenching material that would otherwise turn to ash. Biochar is sterile and is often used as a soil amendment.
Clearing brush is part of the city’s public works, sanitation, and parks and recreation activities. Following Helene, the council received numerous comments from constituents regarding deadwood. The pilot program, a collaboration between the city and the Southern Research Station of the US Forest Service, was initiated partly to address ongoing threats to public health and safety posed by materials that could attract rodents and harmful molds or ignite wildfires.
The CharBoss was developed through a joint venture between the USFS and Air Burners, Inc. Biochar is typically produced by thermally degrading woody debris in an oxygen-free environment, a process known as pyrolysis. Air Burners created a proprietary technology for degradation that occurs in an open-top bin, where high temperatures are maintained and oxygen levels are kept low through continuous blasts of hot air over the wood.
Members of the forest service loaned a CharBoss to the city and trained staff to operate it. Over ten days, 16 truckloads of woody debris, collected from the daily operations of the Public Works and Parks and Recreation departments, were loaded into the CharBoss. This material was then thermally degraded to less than 5% of its original mass.
This process met the city’s interest from a proof-of-concept perspective. However, the CharBoss proved inadequate for the city’s needs, as the Sanitation Division alone collects 1,635 truckloads of woody debris each year.
Consequently, the city would only consider adding biochar production to its operations if it could acquire a larger-capacity machine. One system under consideration is Air Burners’ TigerCat 6040. While the CharBoss can pyrolyze woody debris at a rate of 1 ton per hour, the TigerCat can process 15-20 times that amount per hour. With either system, the city anticipates needing three dedicated employees to operate the machinery and cut the wood.
The city is also exploring pyrolysis reactor systems from other companies, such as ARTi or CO2Sync. These systems would be more versatile, capable of pyrolyzing even water treatment sludge, and their biochar would be denser in carbon. They would require only one operator, although additional staff might be needed to prepare materials for input. These machines can also operate continuously, 24/7.
The city could utilize the biochar for its own landscaping or stormwater management needs. One of the next steps for the pilot program is to “organize biochar use trials.” It was suggested that the city conduct side-by-side experiments with plants to compare growth with and without biochar as a soil amendment. Additionally, it could assess how effectively biochar reduces harmful stormwater runoff. A third option would involve collaborating with the North Carolina State Agricultural Extension to evaluate biochar’s potential for rehabilitating farm soil.
Financially, a larger machine could reduce annual municipal tipping fees by $130,000, and hazard mitigation grants might also be applicable. If the city invests in a reactor, it would have further options for capturing heat from the reaction for power generation.
The city could also earn carbon credits for using one of these machines. These credits would be for the carbon that is not released into the atmosphere by compacting raw materials through a process that retains carbon in the solid end product. While it is too early to determine how much revenue the city could generate from selling biochar and carbon credits, preliminary annual estimates range from $21,000 to $80,000 for biochar and $70,000 to $276,000 for carbon credits.
The city estimated that the annual costs of operating a CharBoss would be $368,000. In April, the purchase price of a CharBoss was $153,000. In May, the upfront cost of a TigerCat was $800,000, with estimated annual operating costs of $90,600.