The Magic of Pyrolysis


by James Sauer March 19, 2016

We owe the existence of biochar to the incredible chemical process called pyrolysis.  Under pyrolysis, organic matter is heated with little or no oxygen so that the carbon within the matter is left almost untouched.  A “skeleton” of the plant material is left in what used to be its cell walls, making for a myriad of microscopic carbon catacombs.

The word pyrolysis comes from the Greek terms “pyro” meaning “fire,” and “lysis” meaning “separation.” For our purposes of making biochar, heat causes a reaction in organic plant matter that separates carbon from tars, hydrogen and methane.   The Hydrogen and methane are forced out as what we call “syngas” or off-gasses, and burned as fuel creating more heat.  When the reaction is complete the biomass has been transformed into biochar with all its wonderful properties, almost like a caterpillar morphing into a butterfly. 

 

When biomass is heated it goes through a couple stages before turning into char:

  1. As the biomass heats up the moisture within begins to evaporate.   When the mass reaches its boiling point water escapes as steam and this continues until the mass reaches approximately 400 F. 
  2. The biomass is then "roasted" as chemical bonds start to break down within the matter.  This is the phase known as “torrefaction” and it happens in the temperature range of 400 to 600 F.  This phase could be compared to when you burn a cake in the oven. 
  3. When the temperatures increase to between 600 and 750 F the pyrolysis reaction approaches completion.  Syngas including hydrocarbons and tars are expelled from the biomass and burn while more chemical bonds within the mass are broken, leaving the carbon behind.  Additional residues in the mass can be driven off with additional heating of temperatures of 900 F and higher.  These higher temperatures serve to increase the purity content of the char. 

Pyrolysis naturally occurs in our environment and is partially responsible for the landscapes we are familiar with today.  Lightning has started fires on our planet for millions of years.  Those fires have indirectly distributed biochar into the soil over the years.  Anytime there is a forest or brush fire there is a small percentage of the combustible matter that burns incompletely without oxygen leaving char instead of ashes.  Parts of plant root structures can burn underground where voids of oxygen exist.  Or, burning matter can become buried by ash and other falling debris shutting off its access to oxygen.  Another example of this is when lava flows encrypt parts of trees and plants to burn without an oxygen supply.  In yet another scenario, rain could quench a forest fire, inhibiting the matter from transitioning from char to ash.  In all of these cases, pyrolysis occurs naturally when organic plant matter burns incompletely, creating biochar and enriching the soil.  Although forest fires are commonly known for death and destruction, they have indirectly played a large role in increasing the richness of our soils.  

Yes—naturally made biochar is a good thing!  Luckily, however, we don’t have to depend on forest fires to enrich our soil with biochar.  People are now able to make biochar in a controlled environment and apply it where it can do the most good.  We now have methods for making char efficiently while also using the heat released from the reaction.  For example, the BioCharlie produces heat and biochar on a small scale, giving off heat like the other logs in the fireplace while simultaneously making char. 
To sum it up in simple terms, pyrolysis is kind of like burning something only half way.  Black carbon is left behind instead of a small pile of ashes.  Further research is continuing throughout the world.  Better and more efficient ways of turning biomass into biochar are being developed.  It's exciting to see this simple and natural process used more in man-made applications to solve man-made problems.

Best,

Jim




James Sauer
James Sauer

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