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Research Papers: Hydrogen Energy

System Analysis of Thermochemical-Based Biorefineries for Coproduction of Hydrogen and Electricity

[+] Author and Article Information
Robert J. Braun, Luke G. Hanzon, Jered H. Dean

Department of Engineering, Colorado School of Mines, Golden, CO 80401

J. Energy Resour. Technol 133(1), 012601 (Mar 29, 2011) (12 pages) doi:10.1115/1.4003541 History: Received August 04, 2010; Revised January 19, 2011; Published March 29, 2011; Online March 29, 2011

Fuels derived from biomass feedstocks are a particularly attractive energy resource pathway given their inherent advantages of energy security via domestic fuel crop production and their renewable status. However, there are numerous questions regarding how to optimally produce, distribute, and utilize biofuels such that they are economically, energetically, and environmentally sustainable. Comparative analyses of two conceptual 2000 tons/day thermochemical-based biorefineries are performed to explore the effects of emerging technologies on process efficiencies. System models of the biorefineries, created using ASPEN Plus® , include all primary process steps required to convert a biomass feedstock into hydrogen, including gasification, gas cleanup and conditioning, hydrogen purification, and thermal integration. The biorefinery concepts studied herein are representative of “near-term” (approximately 2015) and “future” (approximately 2025) plants. The near-term plant design serves as a baseline concept and incorporates currently available commercial technologies for all nongasifier processes. Gasifier technology employed in these analyses is centered on directly heated, oxygen-blown, fluidized-bed systems that are pressurized to nearly 25 bars. The future plant design employs emerging gas cleaning and conditioning technologies for both tar and sulfur removal unit operations. A 25% increase in electric power production is observed for the future case over the baseline configuration due to the improved thermal integration while realizing an overall plant efficiency improvement of 2 percentage points. Exergy analysis reveals that the largest inefficiencies are associated with the (i) gasification, (ii) steam and power production, and (iii) gas cleanup and purification processes. Additional suggestions for improvements in the biorefinery plant for hydrogen production are given.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Biorefinery process flow diagram

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Figure 2

Baseline-case biorefinery process flow diagram

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Figure 3

Future-case process flow diagram

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Figure 4

Baseline-case exergy/exergy flow diagram

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Figure 5

Gasifier exergy/energy flow detail

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Figure 6

Exergy/energy flow diagram of PSA unit

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Figure 7

Exergy/Energy flow diagram for steam-power generation process

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Figure 8

Exergy/energy flow diagram for ASU

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Figure 9

Exergy/energy flows for future-case plant

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Figure 10

Exergy/energy flows for future-case steam-power generation process

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