MOTAT has partnered with SCION to test and roll out a new, low-carbon, artificial coal made from forestry slash. Slash is the woody debris waste product created during logging operations that is usually left on the ground. In dry weather slash can be a fire hazard and in wet weather can be washed away causing damage to infrastructure and farmland. SCION wanted to find a way to tackle the concurrent issues of finding commercial slash removal, making use of a waste product, and helping find a sustainable replacement solution for coal.
Untreated and unprocessed wood material can be burned as-is but it is problematic because it is high bulk but low mass, and furnaces would require extensive modification to make it work. BioCoal can be substituted within existing fire grates without needing remodelling. Additionally, BioCoal is a theoretically carbon neutral process if the trees are replanted. By using leftover/waste products, BioCoal means burning no additional carbon or other materials than the trees originally contained.
The slash is not just a simple pressed wood pellet but undergoes a torrefaction process – like pyrolysis but at lower temperatures. The slash is first dried in a kiln, with the heat coming from steps later in the process. Torrefaction then occurs in a closed reactor vessel in an oxygen-free environment, at around 200-300°C. The resulting dark powder is then pressed into brickettes with similar energy density to coal.
Presently, production of BioCoal is at quite a small scale. A couple of tests have happened at MOTAT in steam tram No. 100 under the supervision of Tony Messenger. The results so far are good. At the Tram Live Day 2023 passengers and other tram crew reported a more pleasant smoke, and the No. 100 crew reported less ash at the end of the day. Further, the ash wasn’t toxic like it would be with coal.
The next step for SCION will be to increase the production scale and extend testing. For MOTAT, this creates an opportunity to embrace innovative science and technology, as well as securing a low-carbon or carbon-neutral future fuel source for our steam-powered collections.
Words and photos by Scott Pilkington and Tony Messenger
