Definitions of biochar vary from charcoal used in soils to any 'blackened biomass' used for any purpose. I have decided to create a charcoal soil ammendment in an evironmentally- and economically-friendly manner, and I hope my project will serve as a model to the poor farmers of the region and small farmers all around the world.
My biochar is a charcoal produced from dried coconut husks through a method called pyrolysis. Pyrolysis is a thermochemical decomposition process that produces energy from biomass. After a slow-burning pyrolysis with complete or partial exclusion of oxygen (with temperatures in the 300*C to 500*C range) takes place, the biomass that remains is solid and carbon-rich. The design of our oven makes slow pyrolysis possible.
The coconut husks we use as biomass in the oven are ubiquitous and free in our area, and people tend to just toss them aside. They are by nature very porous, and after charring retain this porosity, which (with the help of a stable and purer presence of carbon) allows the nutrients in our soils to bind to the biochar (to prevent their washing-out as a result of the torrential tropical downpours), and also acts as a sponge for the humidity brought on by rain. It has been said that biochar also has the property of capturing atmospheric CO2. If our biochar does indeed do this, then the mitigation of climate change is a bonus feature of the biochar that enhances our soils and decreases local envioronmental pollution. By using coconut husks instead of wood, and heating our oven with methane gas rather than firewood, we are also working to curb deforestation, which is a major issue in the San Martín region and of course the Amazon as a whole. All these introductory points will be stretched thin in the coming posts, but first I would like to introduce the SachaChar biochar oven:
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The oven is based on a relatively simple and economically viable design which I altered to fit Centro Sachamama’s particular situation. Our oven uses a 200 liter metal drum as a retort, encased in a firebrick structure to house the external heat input and retain that heat. We use another 200 liter drum on top of the retort to act as an afterburner. We have connected our ‘biodigestor’ to our oven via gas tubing, and cleanly heat our retort with the methane from the nearby biodigestor (the pictures above are of our first firing with wood, before the biodigestor was hooked up…more pictures to come).The methane-fueled fire begins to heat up the drum and the dried coconut husks inside it, and the heat is drafted upward by the space between the drum and the brick enclosure, ensuring that the heat reaches the whole drum. Once pyrolysis temperatures are reached, the coconut husks will begin to char, and the exothermic pyrolysis process will begin to sustain itself. The gases are forced through a small hole in the top of the retort, and if combustible, flared off. The end product of the oxygen-restricted pyrolysis process is uniformly charred pieces of coconut husk. So in the end we are initiaing pyrolysis using recycled, clean-burning methane, and then using the product as a soil amendment that also serves to capture carbon from the atmosphere, a major problem in areas such as Lamas where deforestation is rampant.
