Bench-Scale Fluidized-Bed Pyrolysis of Switchgrass for Bio-Oil Production

TLDR

The U.S. biomass initiative seeks to increase biofuel production from lignocellulosic feedstocks, but fermentation challenges have prompted exploration of alternative conversion methods. The study evaluates fast pyrolysis as a method for converting switchgrass and other agricultural residues into bio‑oil. A 2.5‑kg/h fast pyrolyzer was built and tested on switchgrass to assess process performance.

Abstract

The U.S. biomass initiative is counting on lignocellulosic conversion to boost the quantities of biofuels currently produced from starches in order to achieve much needed energy security in the future. However, with current challenges in fermentation of lignocellulosic material to ethanol, other methods of converting biomass to usable energy have received consideration nationally. One thermochemical technique, fast pyrolysis, is being considered by the Agricultural Research Service (ARS) researchers of the USDA for processing energy crops such as switchgrass and other agricultural residues, e.g., barley hulls and alfalfa stems for bio-oil (pyrolysis oil or pyrolysis liquids) production. A 2.5 kg/h biomass fast pyrolyzer has been developed at ARS and tested for switchgrass conversion. The unit has provided useful data such as energy requirements and product yields that can be used as design parameters for larger systems based on the processing of perennial energy crops. Bio-oil yields greater than 60% by mass have been demonstrated for switchgrass, with energy conversion efficiencies ranging from 52 to 81%. The results show that char yielded would suffice in providing all the energy required for the endothermic pyrolysis reaction process. The composition of the noncondensable gas produced has been initially characterized. Initial mass and energy balances have been calculated based on this system, yielding useful parameters for future economic and design studies.