Biogas fuel cell delivers heat and power: the world's cleanest and most efficient energy system?

A milestone development in Germany is taking us towards what is probably the most efficient and cleanest energy system imaginable: biogas powered fuel cells.

In Europe, biogas is being developed on a large scale for the production of fuels for stationary power generation (to be used in natural gas plants), as well as for the transport sector (earlier post). It is being fed into the natural gas grid on a large scale (earlier post) or in dedicated pipelines supplying cities (earlier post), while some are creating real biorefineries around it that deliver green specialty chemicals, fuels and power (earlier post). The green gas can be made by the anaerobic fermentation of biomass, either obtained from dedicated energy crops (such as specially bred grass species or biogas maize), or from industrial, municipal or agricultural waste-streams. Of all biofuels, biogas delivers most energy per hectare of crops. It is also the least carbon intensive production path, with some biogas pathways actually delivering carbon negative bioenergy (earlier post). In Germany, some project the potential for biogas to be so high that it might replace all natural gas imports from Russia (earlier post).

Meanwhile, new fuel cells are being developed that do not require hydrogen to function, but that work on all common types of biofuels, from biomass-based syngas to ethanol and biogas. The latter fuel path is far more feasible for large-scale power generation than hydrogen, the production of which is inefficient, very costly and not very clean (if derived from fossil fuels; in case the hydrogen is made from biogenic processes and biomass, it is renewable and carbon-neutral, but currently, biohydrogen production is not very efficient). Now combine the efficiency of these fuel cells - which is far higher than power plants using combustion engines - and the low carbon footprint and efficiency of biogas production based on organic waste, and we have what is probably the cleanest and most efficient large-scale energy system currently in operation on earth.

In a world's first, innovative German fuel cell company MTU CFC has made this revolutionary system work on a large and practical scale: a high temperature molten carbonate fuel cell (MCFC) is coupled to a biogas digester and delivers electricity and heat to the District of Böblingen in Leonberg.

"It fits with the innovative Böblingen approach to use our commitment to intensify development of fuel cell technology and stimulate pioneering projects for utilising renewable energy. With this high-tech system, we have created an exemplary combination of ecology and economy and made an active contribution to climate protection" - Böblingen district administrator Berhard Maier.

Biological waste can now be converted into energy with maximum efficiency and minimum environmental impact thanks to modern utilisation of biogas in the Leonberg digestion plant. Its key innovative element, the high-temperature fuel cell or "Hot Module", was officially dedicated on 2 October 2006. The fuel cell in the Leonberg digestion plant has been in operation since August. It is already operating with more than 200 kW output in the current trial operation phase, and it has accumulated 500 operating hours. A total of 30 megawatt-hours of electricity were fed into the electrical grid during the first weeks of operation. The estimated annual electrical energy production is 1,400,000 kilowatt-hours.

The technical specifications of the innovative system look as follows:

• Digestion plant quantity flows (maximum)
• Incoming biological waste: 29,900 tonnes per year
• Amount of generated biogas: approx. 3,700,000 cubic metres per year
• Total electricity production: approx. 8,200,000 kilowatt-hours per year
• Fuel oil savings: approx. 770,000 litres per year

MCFC fuel cell technical data:

• Biogas supply: approx. 120 cubic metres per hour
• Electrical capacity: up to 250 kW
• Thermal capacity: approx. 120 kW
• Operating temperature: 650 °C
• Electrical energy generation: approx. 1,400,000 kilowatt-hours per year
• Electrical efficiency: approx. 47 %
• Thermal efficiency: approx. 23 %
• Maximum overall efficiency: approx. 70 %

Since early 2005, biological waste generated in the district of Böblingen – amounting to nearly 30,000 tonnes per year – has been prepared and processed in the modern Leonberg digestion plant, which was constructed by remodelling the former composting facility. In a fermentation unit with a height of 25 metres, the biomass is digested to produce a biogas that is utilised by two cogeneration units to produce electricity and heat. In addition to these two cogeneration units, the Waste Management Corporation commissioned installation of a molten carbonate fuel cell (MCFC) in early 2006 along with auxiliary generating units, with the specific objective of increasing the electricity yield by more than 25% thanks to increased electrical efficiency:
biomass :: bioenergy :: biofuels :: energy :: sustainability :: waste management :: municipal waste :: biogas :: molten carbonate fuel cell :: MCFC :: fuel cell :: combined heat-and-power :: climate change :: carbon dioxide :: carbon negative :: Germany ::

"Utilising biomass to produce energy by digestion and a fuel cell not only improves energy efficiency, but also protects the climate and points the way to the future", as district administrator Maier said in praise of this intelligent and exemplary approach to municipal energy projects. The overall efficiency of the fuel cell for generating electricity and heat is 70%, which is accompanied by a dramatic reduction in emissions of harmful substances. These values cannot yet be achieved using other approaches.

The partners in the project are MTU CFC Solutions GmbH in Ottobrunn, which developed and supplied the fuel cell; RWE Fuel Cells GmbH in Essen, which acted as prime contractor for the overall fuel cell system; the Waste Management Corporation of the District of Böblingen, which is the end user; and EnBW Energie Baden-Württemberg. The Waste Management Corporation established a subsidiary named Biogas-Brennstoffzellen GmbH for construction and operation of the fuel cell. The latter organisation implemented the entire project.

The total cost of this world-premiere pilot project was approximately 3 million euros. As it is regarded as a demonstration project, more than 80% of the total cost was financed by the Federal Republic of Germany, the State of Baden-Württemberg, EnBW Energie Baden-Württemberg, RWE Fuel Cells GmbH, and DaimlerChrysler AG. In addition, consultation support was provided by the Wirtschaftsförderung („Economic Development Corporation“) of the Stuttgart Region, the Kompetenz- und Innovationszentrum Brennstoffzelle („Fuel Cell Competence and Innovation Centre“), and the German Aerospace Centre. The remainder of the investment cost of the project, amounting to somewhat more than 500,000 euros, were borne by the Waste Management Corporation. This amount includes a cost share of approximately 250,000 euros for the fuel cell and expenditures on installation of the fuel cell in the digestion plant and the operational infrastructure.

Baden-Württemberg is committed to utilisation of renewable resources and enhanced use of future technologies. Examples such as the Leonberg digestion plant demonstrate the innovation-friendly climate of this region and the technology leadership of the region in the fuel cell sector. Minister-President Günther H. Oettinger praised the environmentally friendly fuel-cell technology, which is now being operated using biogas for the first time in the world. With the objective of giving public recognition to outstanding developments in fuel cell technology and stimulating further development, the Environment Ministry of Baden-Württemberg and Wirtschaftsförderung Region Stuttgart GmbH joined forces with EnBW Energie Baden-Württemberg to issue the „f-cell“ award founded by the State of Baden-Württemberg. This award is given in recognition of practically oriented developments in the innovative sector of fuel cells. The commitment of the Waste Management Corporation was honoured a few days ago with the third-place f-cell Bronze award, which is accompanied by a prize of 5000 euros. District administrator Maier expressed his pleasure with national recognition of the innovative spirit of the District of Böblingen, which he underlined by saying, „For the District of Böblingen, installation of the Hot Module can also act as a stimulus for an experimental centre for fuel cells with regenerative energy gasses, with all the associated benefits for the Leonberg site and the Stuttgart region. In this way, the Waste Management Corporation contributes to ensuring the future of the site, including creating future high-skill jobs.“

The aim of EnBW Energie Baden-Württemberg, which contributed 500.000 euros to the financing of the fuel cell project, is to foster research and development that generates new, climate-protecting technologies for energy supply systems of the future. This includes fuel cells, since they can generate electricity and heat very efficiently and can do so using renewable energy sources. „In the fifth year of our field trial with fuel cells operating with natural gas, we are now tackling the next technological challenge: the transition to biogas. We are pleased to have this opportunity, thanks to this cooperative project with the District of Böblingen, to try out the first large biogas fuel cell in the world. A fuel cell of this type at Michelin in Karlsruhe has been successfully generating electricity for three years now, and we are especially interested in learning more about the technical and economic aspects of operation using biogenic gases“, remarked Professor Thomas Hartkopf, Engineering Director of EnBW Energie Baden-Württemberg. Fuel cells are one of the innovation focuses of EnBW. The energy company has installed eighteen fuel-cell heating systems in private houses since 2001, along with medium-sized systems for municipal and industrial applications. Various types of systems are in operation, with electrical power capacities ranging from 1 kW to 250 kW. In addition, EnBW is working with Siemens Power Generation and other partners to develop a hybrid fuel cell generating unit in the megawatt class, which will be able to convert up to 70% of the fuel energy into electrical energy. Modern gas-turbine and steam-turbine generating units achieve a maximum efficiency of just under 60%.

The Hot Module used in the Leonberg digestion plant is made by MTU CFC Solutions GmbH, a joint venture of MTU Friedrichshafen and RWE Fuel Cells GmbH. It operates in the 250-kW class and generates electricity and heat from methane gas produced by digestion of compostable waste. Carbon nitrate fuel cells use molten carbonate as an electrolyte and operate in the high-temperature region at 650° C. The Hot Module consists of a cylindrical steel enclosure with a horizontally configured stack of fuel cells, an upstream gas preparation stage, and a downstream electricity feedin stage. The fuel cell is quiet and environmentally friendly in operation. It is energy-efficient and highly flexible in use. With a net electrical efficiency of 47%, it is more than 25% more efficient than modern cogeneration units. It also has excellent overall efficiency and practically no harmful emissions, since the waste gas from the fuel cell contains only air, carbon dioxide and water vapour. The cogeneration product of the system is hot exhaust air at approximately 370° C, which is also utilised effectively via a heat exchanger system used to dry the digestion residues from the biogas generator so they can be used afterward as fertilisers.

The fuel cell in the Leonberg digestion plant has been in operation since August. It is already operating with more than 200 kW output in the current trial operation phase, and it has accumulated 500 operating hours. A total of 30 megawatt-hours of electricity were fed into the electrical grid during the first weeks of operation. The estimated annual electrical energy production is 1,400,000 kilowatt-hours. The highly promising advanced technology emphasised by Managing Director Michael Bode with the words, „We are exceptionally pleased that with this innovative concept of biogas utilisation using our Hot Module fuel cell system, we can demonstrate that our technology is especially suitable for high-efficiency conversion of renewable fuels into electricity and heat. This project is a significant milestone in the implementation of our product and marketing strategy of placing more emphasis on regenerative fuels for carbon-dioxide-neutral generation of energy.“

For the District of Böblingen, the environmental aspect and utilisation of renewable energy were the key considerations for selecting the fuel cell solution, since they enable it to make a decisive contribution to reducing global warming gasses because the biogas is obtained from biological waste arising from renewable resources. When energy is obtained from biogas, the amount of carbon dioxide that is released is the same as the amount absorbed by the plants while they are growing. This sustainability makes the pilot project very attractive from the ecological viewpoint as well as the economic viewpoint. All partners in the project are interested in demonstrating the potential and feasibility of high-efficiency carbonate fuel cells operating using biogas as a fuel, in order to act as pioneers in promoting further use of this extremely environmentally friendly form of energy generation.

MTU CFC Solutions was jointly managed by MTU Friedrichshafen GmbH (a Tognum subsidiary) and RWE Fuel Cells GmbH from 2003 onwards. It is domiciled in Ottobrunn near Munich, currently employs 85 persons, and is one of the world's leading specialists for high-temperature fuel cells for the environment-friendly generation of electricity and heat.

MTU CFC Solutions has so far installed more than 40 plants worldwide, together with its license partner Fuel Cell Energy (FCE). Just a few weeks ago, MTU CFC Solutions delivered the world's first large-scale biogas fuel-cell plant, which generates up to 1.4 million kilowatt-hours of CO2-neutral electricity per annum in Leonberg near Stuttgart, using biogas created from fermented organic waste.

High-temperature fuel cells typically generate up to 245 kilowatts of electricity and a maximum of 180 kilowatts of heat simultaneously (power-heat coupling). They are superior to block-type thermal power stations using engines: Their good electrical efficiency of nearly 50% is higher than with conventional technology, and their quiet operation is an advantage, particularly in urban applications.

The plants have demonstrated a high degree of technological maturity, having already produced more than 140,000 megawatt-hours of electrical energy. For the future, the construction of power plants with an electrical output of up to two megawatts is planned, either as power-heat coupling or in the combination of power, heat and cooling.

More information:
MTU Friedrichshaven: Fuel Cells for Biogas [*.pdf].
MTU Friedrichshaven: Molten carbonate fuel cells - overview.