Ecological and economic costs and benefits of the use of pyrolysis as a climate change mitigation technique in the neotropical developing world
Snyder, Brian Francis
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One of the most promising technologies for net atmospheric carbon removal is biomass pyrolysis. Biomass pyrolysis is the thermal decomposition of organic material in the absence of oxygen. It is generally endothermic but it results in high energy syngas, a liquid bio-oil and biochar, a carbonaceous material which when added to soil stimulates plant growth. Here, the economic potential of small-scale pyrolysis in the neo-tropical developing world is investigated using a net present value framework. Biomass costs are estimated using waste biomass, jaragua grass, short-rotation woody crops, and biomass from artificial wetland systems in Costa Rica. Costs are computed with and without consideration of the environmental services associated with the modeled systems. When environmental services are appropriately valued, the costs of biomass from artificial wetland systems becomes negative; that is, operators of artificial wetlands used for water services would be expected to pay for biomass harvesting. Using the computed biomass costs, pyrolysis system costs are computed for fast and slow pyrolysis and compared to gasification. Fast and slow pyrolysis systems break even at carbon credit prices exceeding 0-5 $/ton, but gasification systems do not break even under most realistic assumption sets. The emergetic costs of pyrolysis systems are also evaluated. Emergy is a measure of the energy and resources required to produce a product, and can be considered a theoretical alternative monetary or accounting system that allows for a more holistic valuation of goods and services than either an exchange (money) or value (exergy) system. The results indicate that the transformities (or emergetic efficiency) of pyrolysis production systems using waste biomass are similar or less than those of geochemical hydrocarbon production systems. Since geologic fossil fuel production is emergetically efficient, this result is promising and suggests that unlike other biomass based alternative energy systems (e.g. ethanol), pyrolysis may be ecologically beneficial when measured holistically. Pyrolysis is a carbon negative technology (i.e. it creates a long term carbon sink) which creates the potential for a cap and trade system in which there is differentiation between carbon neutral and carbon negative credits. The economics of such a system are discussed.