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Research Papers

Combination of Biological Processes and Fuel Cells to Harvest Solar Energy

[+] Author and Article Information
Dieter F. Ihrig

 University of Applied Sciences Suedwestfalen, 58644 Iserlohn, Germany

H. Michael Heise, Ruediger Kuckuk

 Institute for Analytical Sciences (ISAS) at Dortmund University of Technology, 44139 Dortmund, Germany

Ulrich Brunert

 University of Applied Sciences Suedwestfalen, 58644 Iserlohn, Germany; Institute for Analytical Sciences (ISAS) at Dortmund University of Technology, 44139 Dortmund, Germany

Martin Poschmann, Klaus Stadtlander

 University of Applied Sciences Suedwestfalen, 58644 Iserlohn, Germany

J. Fuel Cell Sci. Technol 5(3), 031001 (May 09, 2008) (5 pages) doi:10.1115/1.2889031 History: Received November 30, 2005; Revised February 20, 2007; Published May 09, 2008

Biomass production by micro-algae is by a factor of 10 more efficient than by plants, by which an economic process of solar energy harvesting can be established. Owing to the very low dry mass content of algal suspensions, the most promising way of their conversion to a high exoergic and transportable form of energy is the anaerobic production of biogas. On account of this, we are developing such processes including a micro-algal reactor, methods for micro-algal cell separation and biomass treatment, and a subsequent two-stage anaerobic fermentation process. First results from parts of this development work are shown. The continuous feeding of the anaerobic process over several weeks using micro-algal biomass is discussed in more details. The biogas is composed of methane, higher hydrocarbons, carbon dioxide, and hydrogen sulphide. Using steam reforming, it can be converted to a mixture of carbon dioxide and hydrogen. These gases can be separated using membrane technology. It is possible to form a closed carbon cycle by recycling the carbon dioxide to the micro-algal process. The transportable and storable hydrogen product is a valuable energy source and can be converted to electrical energy and heat using fuel cells. The simulation of such a process will be explicated.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Principle of a biological solar energy generator. Energy is collected by micro-algae and converted into biomass. After settlement and cell rupture, which both are not shown in this figure, the biomass is transferred to an anaerobic process. The biogas will be purified (not shown) and methane will be converted to hydrogen and carbon dioxide using steam reforming. Hydrogen will be recovered using membrane separation and delivered to fuel cells, respectively, households. Carbon dioxide will be removed as a fertilizer for the micro-algal process.

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Figure 2

Assessment of economics. The rate of increase of expenses for energy suppliers is given in %.

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Figure 3

Laboratory models of flat PMMA reactors to produce micro-algal biomass. It is possible to simulate daylight using fluorescent tubes (not mounted here), which are under computer control.

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Figure 4

Growth curve of micro-algal biomass monitored by photometry. The absorbance of chlorophyll at 440nm and 680nm has been used as a parameter for cell density.

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Figure 5

Distribution of cell size of micro-algae before and after enrichment using cross-flow ultrafiltration

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Figure 6

DOC concentration of substrate solution, first stage and second stage of an anaerobic reactor as well as the rate of DOC decomposition. During this experiment, the anaerobic reactor was supplied with micro-algal biomass.

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Figure 7

Loading rate and gas production (refer also to Fig. 6)

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Figure 8

Correlation of carboxylic acids measured by HPLC and IR spectroscopy. The data shown were obtained for the first and second stages of the anaerobic fermentation reactor during successful operation.

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