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Research Papers: Energy Systems Analysis

Mass Balance, Energy, and Exergy Analysis of Bio-Oil Production by Fast Pyrolysis

[+] Author and Article Information
Akwasi A. Boateng

e-mail: akwasi.boateng@ars.usda.gov

Charles A. Mullen

Eastern Regional Research Center,
Agricultural Research Service,
U.S. Department of Agriculture,
600 E. Mermaid Lane,
Wyndmoor, PA 19038

Nelson Macken

Department of Engineering,
Swarthmore College,
Swarthmore, PA 19081

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the Journal of Energy Resources Technology. Manuscript received August 25, 2011; final manuscript received July 12, 2012; published online October 19, 2012. Assoc. Editor: Gunnar Tamm.

J. Energy Resour. Technol 134(4), 042001 (Oct 19, 2012) (9 pages) doi:10.1115/1.4007659 History: Received August 25, 2011; Revised July 12, 2012

Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture (USDA). USDA is an equal opportunity provider and employer. Mass, energy, and exergy balances are analyzed for bio-oil production in a bench-scale fast pyrolysis system developed by the USDA’s Agricultural Research Service (ARS) for the processing of commodity crops to fuel intermediates. Because mass balance closure is difficult to achieve due, in part, to the system’s small size and complexity a linear programming optimization model is developed to improve closure of elemental balances without losing the overall representation of the pyrolysis products. The model results provide an opportunity to analyze true energy and exergy balances for the system. While energy comparisons are based on heating values, exergy flows are computed using statistical relationships and other standard techniques. Comparisons were made for a variety of biomass feedstocks including energy crops and various byproducts of agriculture and bioenergy industry. The mass model allows for proper accounting of sources of mass loss and suggestions for improved system performance. Energy recovery and exergetic efficiency are compared for a variety of pyrolysis product utilization scenarios including use of biochar and noncondensable gases as heat sources. Exergetic efficiencies show high potential for energy utilization when all the pyrolysis product streams can be recycled to recuperate their internal energy. The exergy analysis can be beneficial to developing exergetic life cycle assessments (ELCA) for the fast pyrolysis process as sustainable technology for advanced biofuels production.

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Figures

Grahic Jump Location
Fig. 1

USDA-ARS bench-scale fast pyrolysis system. (a) Gas preheater, (b) feed hopper, (c) injection screw, (d) fluidized-bed reactor, (e) cyclone, (f) condenser train, (g) electrostatic preceptor (ESP), and (h) exhaust (NCG to GC).

Grahic Jump Location
Fig. 2

Energy and exergy flows for the system

Grahic Jump Location
Fig. 3

Comparison of measured and model yields for fast pyrolysis of selected biomass

Grahic Jump Location
Fig. 4

Comparison of exegetic efficiency for fast pyrolysis of various biomass. In this case, all pyrolysis products (bio-oil, biochar, noncondensable gases are considered useful products).

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