Life-Cycle Inventory Analysis of Bioproducts from a Modular Advanced Biomass Pyrolysis System

Abstract

Expanding bioenergy production has the potential to reduce net greenhouse gas (GHG) emissions and improve energy security. Science-based assessments of new bioenergy technologies are essential tools for policy makers dealing with expanding renewable energy production. Using life cycle inventory (LCI) analysis, this study evaluated a 200-kW_e modular advanced biomass pyrolysis system, referred to as the Tucker renewable natural gas (RNG) unit. Similar to pyrolysis systems except no bio-oil is produced, the Tucker RNG unit converts forest and woody residues at high temperatures in an extremely low oxygen environment to synthesis gas (syngas) and biochar. Mass and energy balances, cumulative energy consumption, and LCI flows including environmental outputs were determined. Feedstock consumption for the Tucker RNG unit was estimated at 263 kg/h of whole-tree coniferous micro-chips at 8% moisture content. A 1-h system run test was done to collect production data and sample products. The Tucker RNG unit showed a net energy gain of 12.0 MJ/kg of dry chips from the system when excluding chip transportation. Consequentially, the system had a positive (over 1.0) fossil energy replacement ratio (FERR) of 2.54, which means 2.54 MJ of bioenergy products (syngas and biochar) were produced for every 1 MJ of fossil energy consumed in the system. Including chip transportation of 4,000 km, emission data summarized from the LCI flows through SimaPro modeling showed biomass and fossil CO₂ emissions of 0.43 g and 734 g, respectively, per kilogram of chips processed. The fossil CO₂ emission contributions were as follows: wood chip transportation (48.7%), propane combustion (50.2%) and electricity use (1.1%). A FERR of 2.54 shows, from a life cycle perspective, that the Tucker RNG unit has a net energy gain. Additionally, co-locating the Tucker RNG unit and the wood chip source would substantially lower GHG emissions while saving energy.

Citation

Bergman, Richard; Gu, Hongmei. 2014. Life-Cycle Inventory Analysis of Bioproducts from a Modular Advanced Biomass Pyrolysis System. In: Proceedings, Society of Wood Science and Technology 57th International Convention. June 23-27, 2014. Zvolen, Slovakia: 2014; pp. 405-415.