Biomass fuels such as wood, herbaceous materials and agricultural by-products are the world’s third largest primary energy resource, behind coal and oil. At best, conventional biomass to energy is considered to be carbon neutral. Harvesting biomass to produce energy may not be sustainable because it can result in reduced soil productivity by depletion of carbon and nutrients. Biomass pyrolysis addresses this dilemma, because it can utilize waste products and about half of the original carbon can be returned to the soil (Lehmann, 2007).
In a recent paper published by the Ecological Society of America, Johnannes Lehmann of Cornell University discussed the basics of biomass pyrolysis (excerpts from: Lehmann, 20007, Bioenergy in the Black, available as a PDF).
Dr. Lehmann also explains that
“Comparable ratios for ethanol currently amount to 0.7–2.2 kg C (kg C)-1 (Pimentel and Patzek 2005; Metzger 2006) and, for biomass burning, to 10–13 kg C (kgC)-1 (willow; Keoleian and Volk 2005), with the caveat that the latter produces only heat, not liquid fuel.”
Therefore Dr. Lehmann concludes that: