Comparative Life-Cycle Assessment of Biochar Activated Carbon and Synthesis Gas Electricity with Commercially Available Alternatives

This report presents a compilation of research conducted on the life-cycle assessment analysis for processing raw material woody biomass into biochar activated carbon (AC) and synthesis gas (syngas) for electricity production. The study was part of the United States Department of Agriculture Biomass Research and Development Initiative project with a broader goal of an integrated assessment of biomass feedstock production, logistics, conversion, distribution, and end use focused on a novel thermochemical conversion system using woody biomass feedstocks. Cradle-to-grave analysis of the syngas electricity supply chain included upstream processes of the feedstock procurement and preparation life-cycle stages, core process of the thermochemical conversion (woody biomass carbonization) stage, and then downstream processes with syngas storage and combustion (use) at the generator for electricity production. Cradle-to-gate analysis of the biochar AC supply chain included upstream processes of feedstock procurement and preparation, the core process of thermochemical conversion (woody biomass carbonization), and then the downstream process of steam activation of the biochar into high-grade AC. The results of the comparative analysis revealed that a notable decrease in the global warming impact can be achieved through substitution of coal AC with biochar AC. Greenhouse gas (GHG) emissions were 39% lower for the biochar AC system compared with the coal AC system. However, GHG emissions were higher for syngas electricity than for electricity from natural gas when biochar sequestration effect was not accounted for, but this was reversed when the sequestration effect was accounted for. The primary driver of GHG emissions for both bioproducts was the thermochemical conversion stage (the core process) because carbonization required propane to fuel the endothermic reaction. The second greatest source of GHG emissions for biochar AC was the steam activation process. An alternative scenario using low-energy syngas generated from the carbonization stage (not currently being done) showed that displacing propane decreased GHG emissions substantially. Therefore, optimization of the supply chain would probably improve all environmental impacts for the two bioproducts analyzed.