The Pyrolysis Arts

Just as "biochar" sounds like something you don't want to have happen to your steak; "pyrolysis" sounds like something you don't want to catch. The connotations are unfortunate. Because "pyrolysis" of biomass is how "biochar" is made.

Pyrolysis is defined as thermal degradation in a restricted-oxygen atmosphere. When you pyrolyze biomass, you wind up with a mix of combustible gases, volatiles, and solid residue. The nature and relative proportion of these co-products depends on the pyrolysis environment and the type of biomass you started out with.

(There isn't yet universally accepted terminology in this field, so here's my take: The generic solid residue of pyrolysis can be referred to as "char". When this char is burned as fuel, as it has been for millennia, call it "charcoal". When we apply it as a carbon-sequestering soil amendment, call it "biochar". OK?)

The biomass, or "feedstock", is typically crop residue or agroforestry waste; but just about anything that was once living or derived from living material can be pyrolyzed, including sorted municipal waste and de-wetted sewage. As for the pyrolysis environment, that's all over the map--maximum temperature reached, heating rate, dwell time at different levels, presence of small amounts of oxygen, suffusing with certain gases, size of the biomass particle, etc. Larger scale engineered plants operate more like refineries, and the pyrolysis environment can be manipulated to maximize the yield of particular products; bio-oil for processing into biodiesel, combustible gases for resale or direct power production, and other commercially valuable products. Alchemy comes to mind. Given the huge range of inputs and variables and possible co-products, referring to the "Pyrolysis Arts" seems well justified.

Our interest is the solid stuff, the lowest common denominator. In the most basic char-making kilns, the gases and volatile compounds produced are consumed in the process, with the excess either released to the atmosphere or burned. Since many of these compounds can be potent greenhouse gases, atmospheric release is a no-no; if nothing else, we'll want to flare them off. Better still would be to capture some of the heat and use it (for drying more biomass, for example).

Many future posts will be devoted to experimentation with and optimization of char-making kilns.

Birth of an obsession

It was April 30, 2008. I know because it's stamped in my passport. Diane and I were driving back to Costa Rica's Osa Peninsula from the cool coffee highlands of Boquete, Panama where we'd gone on a "visa vacation" (non-residents are required to leave the country every 90 days). We took advantage of the hotel's high-speed internet for downloading and were plowing through a pile of Science Friday podcasts on the drive back, when Ira Flato's guest spoke of something he called "biochar", which he described as fertilizer made from pulverized charcoal. Whoa! Hang on a sec! We both had MS degrees in Botany. We know what fertilizer is; charcoal is NOT. Who was this crackpot, and how'd he get to be on this highly respected, nationally syndicated science program?!

Curious, I googled "biochar". What I learned blew me away. As a soil amendment, biochar is not only a potential source of plant nutrients, but it also improves water retention, reduces acidity, and changes soil surface properties to improve nutrient availability. It persists in the soil, so you only need to add it once. It reduces reliance on petrochemical fertilizers, improves groundwater quality, and reduces emissions of greenhouse gases common with traditional agricultural. As if that weren't enough, a co-product of making biochar in specially designed processing plants can be biofuel or electric power. And it's made from agricultural waste or timber slash, solving a waste disposal problem. Best of all, biochar persists in the soil for hundreds to thousands of years, sequestering CO2 and reversing the effects of global warming.

Is this possible? A potent and permanent soil amendment that improves environmental quality, is a non-fossil fuel energy source, solves waste disposal problems, and reverses global warming? Why didn't I know about this? Why doesn't everyone know about this?!

It's not even new. Turns out, there are areas in the Amazon basin know as Terra Preta (dark soil) where native peoples appear to have been practicing "char agriculture" for millennia. It was described in the soil science literature back in the '60s, but for some reason languished in relative obscurity until very recently. And while charcoal making is among the most ancient of the industrial arts, even modern "high tech" methods of simultaneously producing both char and power date back to WWII. Yet, despite its huge range of benefits and technical feasibility, nobody I talked to had even heard of biochar, and hardly anyone was actually practicing it.

Biochar embraces a constellation of disciplines that mirrors my personal interests, experiences, education, and aspirations; a "perfect storm" of environmental activism, plant science, technology development, sustainable agriculture; a chance to contribute, learn and grow. Plus, burning stuff is fun! Unbound by work or other hard commitments, and already dedicated to the principles of sustainable living, I decided to up the ante by making the advancement of biochar my personal mission.