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Research Papers

Conversion of Syngas From Biomass in Solid Oxide Fuel Cells

[+] Author and Article Information
Jurgen Karl, Ulrich Hohenwarter

Institute of Thermal Engineering, Technical University of Graz, Inffelgasse 25∕B, A 8010 Graz, Austria

Nadine Frank, Mathilde Saule

Institute of Energy Systems, Technical University of Munich, Boltzmannstrasse 15, 85747 Garching, Germany

Sotirios Karellas1

Institute of Energy Systems, Technical University of Munich, Boltzmannstrasse 15, 85747 Garching, Germany

1

Present address: Laboratory of Steam Boilers and Thermal Plants, National Technical University of Athens, Heroon Polytechniou 9, 15780 Zografou, Athens, Greece.

J. Fuel Cell Sci. Technol 6(2), 021005 (Feb 23, 2009) (6 pages) doi:10.1115/1.2971172 History: Received May 14, 2007; Revised May 24, 2007; Published February 23, 2009

Conversion of biomass in syngas by means of indirect gasification offers the option to improve the economic situation of any fuel cell system due to lower costs for feedstock and higher power revenues in many European countries. The coupling of an indirect gasification of biomass and residues with highly efficient solid oxide fuel cell (SOFC) systems is therefore a promising technology for reaching economic feasibility of small decentralized combined heat and power production (CHP).The predicted efficiency of common high temperature fuel cell systems with integrated gasification of solid feedstock is usually significantly lower than the efficiency of fuel cells operated with hydrogen or methane. Additional system components like the gasifier as well as the gas cleaning reduce this efficiency. Hence common fuel cell systems with integrated gasification of biomass will hardly reach electrical efficiencies above 30%. An extraordinary efficient combination is achieved in case that the fuel cells waste heat is used in an indirect gasification system. A simple combination of a SOFC and an allothermal gasifier enables then electrical efficiencies above 50%. However, this system requires an innovative cooling concept for the fuel cell stack. Another significant question is the influence of impurities on the fuel cell degradation. The European Research Project “BioCellus” focuses on both questions—the influence of the biogenous syngas on the fuel cells and an innovative cooling concept based on liquid metal heat pipes. First experiments showed that, in particular, higher hydrocarbons—the so-called tars—do not have any significant influence on the performance of SOFC membranes. The innovative concept of the TopCycle comprises to heat an indirect gasifier with the exhaust heat of the fuel cell by means of liquid metal heat-pipes. Internal cooling of the stack and the recirculation of waste heat increases the system efficiency significantly. This concept promises electrical efficiencies of above 50% even for small-scale systems without any combined processes.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Natural gas resources in Europe (2)

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Figure 2

Electricity production costs for commonly discussed SOFC concepts (3)

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Figure 3

Composition and lower heating value of the wood gas during a 24h test

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Figure 4

Performance of a planar SOFC membrane with wood gas during a 24h test

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Figure 5

Total efficiency of CHP systems with different excess air ratios

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Figure 6

Dependence of the fuel cell temperature from the air ratio and the inlet air temperature

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Figure 7

Influence of the excess air ratio on the total efficiency

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Figure 8

Heat-pipe principle

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Figure 9

Simplified energy flow of common fuel cell systems with integrated gasification

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Figure 10

Simplified energy flow of the “TopCycle” system

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