Biochar

How can a waste stream become part of a cyclical system?
Make biochar, a soil amendment, by making and using a model top light updraft (TLUD) pyrolysis kiln or oven.

Lessons

  • Top light, updraft (TLUD) pyrolysis kiln or oven

    Construct a TLUD pyrolysis kiln or oven to make biochar.

    building-a-tlud.pdf

Teacher background

For centuries, farmers have been utilizing methods to try and minimize water loss and reduce the cost and loss of fertilizer due to runoff. Farmers know how important it is to keep costs low and production yields high. Two large costs that can result in profit/losses are fertilizers and water, if improperly managed. Biochar, or pyrolized plant material, represents an ancient, but effective, soil amendment that is capable of reducing both water and fertilizer loss. Additionally, biochar represents an underutilized carbon sink for the mitigation of carbon dioxide induced climate change.

Biochar’s value as a soil amendment has historical precedence and is continually being verified through community groups, organic farming collectives, and the scientific research community. Biochar, or activated charcoal, has a unique, microscopically porous structure that allows each granule to hold water and fertilizer until biological needs for each arise. By adding a percentage of biochar to existing soils farmers are able to increase their retention of both fertilizer and water and thereby increase yields and profits. Biochar has the additional feature of never degrading and therefore remaining as part of the soil structure in perpetuity. This means that a farmer does not need to add more to his field once the desired percentage of soil has been met. Additionally, since the carbon in the biochar can be considered a carbon sink, it represents an offset for carbon in the atmosphere.

Biochar is the product of pyrolisizing any biological fiber. Pyrolysis is the process of “burning” a substance in the absence of oxygen, which results in the material being turned into pure carbon instead of ash, as in an oxygenated fire. Therefore, the biomass (the carbohydrates, the lignin, and the hemicelluloses) is thermally degraded. Most commonly students will recognize this as the way charcoal is produced. Biochar can be produced on very small scales (as small as an 8 oz. soup can) up to large industrial sized production facilities (think Kingsford Charcoal). The key to understanding biochar is to independently analyze its production and its value as a soil amendment.

In these classroom examples, combustible gases and oils can be separated from the biochar by creating a top light, updraft (TLUD) pyrolysis kiln or oven. This oven does a great job of drawing a huge amount of air through the main gasification chamber and therefore isolating the combustible wood gas from feedstock being gasified. Therefore there is no direct combustion of the feedstock and biochar remains.

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