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Title: Lifecycle assessment of microalgae to biofuel: Comparison of thermochemical processing pathways

Microalgae are currently being investigated as a renewable transportation fuel feedstock based on various advantages that include high annual yields, utilization of poor quality land, does not compete with food, and can be integrated with various waste streams. This study focuses on directly assessing the impact of two different thermochemical conversion technologies on the microalgae to biofuel process through life cycle assessment. A system boundary of a “well to pump” (WTP) is defined and includes sub-process models of the growth, dewatering, thermochemical bio-oil recovery, bio-oil stabilization, conversion to renewable diesel, and transport to the pump. Models were validated with experimental and literature data and are representative of an industrial-scale microalgae to biofuel process. Two different thermochemical bio-oil conversion systems are modeled and compared on a systems level, hydrothermal liquefaction (HTL) and pyrolysis. The environmental impact of the two pathways were quantified on the metrics of net energy ratio (NER), defined here as energy consumed over energy produced, and greenhouse gas (GHG) emissions. Results for WTP biofuel production through the HTL pathway were determined to be 1.23 for the NER and GHG emissions of -11.4 g CO2-eq (MJ renewable diesel)-1. WTP biofuel production through the pyrolysis pathway results in a NERmore » of 2.27 and GHG emissions of 210 g CO2 eq (MJ renewable diesel)-1. The large environmental impact associated with the pyrolysis pathway is attributed to feedstock drying requirements and combustion of co-products to improve system energetics. Discussion focuses on a detailed breakdown of the overall process energetics and GHGs, impact of modeling at laboratory- scale compared to industrial-scale, environmental impact sensitivity to engineering systems input parameters for future focused research and development and a comparison of results to literature.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [1]
  1. Utah State Univ., Logan, UT (United States). Mechanical and Aerospace Engineering
  2. Idaho National Lab. (INL), Idaho Falls, ID (United States). Biological and Chemical Processing Dept.
  3. CF Technologies, Hyde Park, MA (United States)
  4. Utah State Univ., Logan, UT (United States). Biological Engineering
Publication Date:
OSTI Identifier:
1177612
Report Number(s):
INL/JOU--14-32120
Journal ID: ISSN 0306-2619; PII: S0306261914012586
Grant/Contract Number:
AC07-05ID14517
Type:
Accepted Manuscript
Journal Name:
Applied Energy
Additional Journal Information:
Journal Volume: 154; Journal ID: ISSN 0306-2619
Publisher:
Elsevier
Research Org:
Idaho National Lab. (INL), Idaho Falls, ID (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Bioenergy Technologies Office (EE-3B)
Country of Publication:
United States
Language:
English
Subject:
09 BIOMASS FUELS Microalgae, supercritical fluids, pyrolysis, Hydro