Fermenters and fuel cells to produce bioenergy

The fermentation facility based in Leonberg near Stuttgart produces biogas from biological waste. Two combined heat and power plants (CHP), and now also a fuel cell, are converting biogas into electrical power and heat.

The ‘brown compost bin’ has become a successful model in Germany, also in Böblingen, where the amount of biological waste has been expanding over the years. It turned out that the capacity of the composting plant in Leonberg (district of Böblingen) was no longer sufficient. Approximately 5,000 tons of biological waste per year had to be disposed of at other locations. The local authorities were no longer satisfied with this solution and decided to construct a state-of-the-art fermentation plant.

Fermentation plant in Leonberg. (Photo: Waste company of the district of Böblingen)

The new plant was put into operation at the beginning of 2005 and has since been producing energy-rich biogas from up to 30,000 tones of biological waste per year. This gas is used to produce power and heat in two CHPs. The Renewable Energy Law guarantees consistent revenue for power produced from biomass. This is a major reason for the local authorities to decide in favour of the new fermentation plant. The supply of power provides the district of Böblingen with annual revenues of 700,000 euros. If operated to full capacity, the CHPs are able to generate 8.2 kilowatt hours of electrical power per year, which is enough to cater for the annual demand of 2,300 private households.

The heat produced by biogas combustion is also used effectively: it is used to heat the fermenter and the system used to dry the nearly 17,000 tons of fermentation waste per year. The fermentation waste is subsequently composted and used as fertiliser on local fields, thereby returning to the biomass cycle. It is this sustainability that makes this concept so attractive, both in ecological as well as economic terms.

Fuel cell improves degree of efficiency

The innovative district authorities were still not happy with this, sensing an even greater optimisation potential. Wolfgang Bagin, head of the district’s waste company and CEO of Biogas-Brennstoffzellen GmbH, describes how they ended up using fuel cells: “For us, fuel cells presented an attractive means to effectively use biomass, advance high-tech developments and act as a role model for future development. In addition, we also wanted to demonstrate the economic efficiency of the fuel cell technology. All in all, this was the beginning of our fuel cell.

Fuel cell with media supply (Photo: Waste company of the district of Böblingen)

Supported by WRS (Wirtschaftsförderung Region Stuttgart), Leonberg started a demonstration project that was unique in the world. The first facility was established and it enabled the transformation of biogas into power and heat using a molten carbonate fuel cell. In such a high-temperature fuel cell, molten carbonate functions as electrolyte for the electrochemical oxidation of hydrogen with which chemical energy is transformed into electrical energy.

From June 2006 onwards, the “HotModule” (name of this specific fuel cell) will improve efficiency even more. “The electrical degree of efficiency of gas engines in CHPs is approximately 38 percent; the degree of efficiency of fuel cells is approximately 48 percent,” explained Bagin. Another advantage of fuel cells is the drastically reduced emission of nitrous oxides, sulphur compounds, carbon monoxide and hydrocarbons. In addition, the fuel cell is very quiet compared to other types of power stations.

World premiere in Leonberg: biogas utilisation in the “HotModule”

Biogas processing and fermentation reactor in Leonberg

Only cutting-edge technology makes this biomass utilisation so effective. “Biogas technology has made considerable progress over the last few years; as has fuel technology,” said Bagin. The “HotModule” was developed and manufactured by MTU CFC Solutions GmbH in Ottobrunn, which is able to put information gained in this pilot project to good use in future developments. The fuel cell was installed by RWE Fuel Cells GmbH.

Growing restrictions in waste regulations and the finiteness of petrol and gas make the transformation of biomass into bioenergy more and more interesting. For this reason, the project in Leonberg is not only funded by the German (Kreditanstalt für Wiederaufbau (KfW)) and Baden-Württemberg governments, but also by the large energy producers EnBW and RWE as well as DaimlerChrysler AG.

We remain hopeful that the quality of the raw material stays as good as it is now. This depends largely on public awareness leading to responsible household practices. “Biomass originates largely from the ‘brown compost bins’ of private households and consists mainly of biological kitchen and garden waste. The proportion of rubbish is comparatively low. Coarse objects are detected by metal detectors and removed during biological waste collection and with metal separators prior to gas production. During the composting process of the fermented waste the fine preparation will do the rest.


leh - 19.05.06
© BIOPRO Baden-Württemberg GmbH

For further information, contact:
Biogas-Brennstoffzellen GmbH
Wolfgang Bagin (CEO)
Parkstr. 16
71034 Böblingen
Phone: [phone]
Fax: [phone]
E-mail: [e-mail]