Dr. Shigeki Sawayama, Senior Research Scientist in the Biomass Research Group at the Institute for Energy Utilization, a division of the National Institute of Advanced Industrial Science and Technology (AIST; an independent administrative institution), in cooperation with Aisin Seiki Co., Ltd. (Aisin Seiki), has made improvements to the production model of a compact, highly efficient, city gas-powered 6-kW gas engine cogeneration system manufactured by Aisin Seiki, resulting in the successful operation of the 6-kW gas engine cogeneration system fueled by low-calorific-value biogas derived from livestock waste and other biomass waste material.
This system is being viewed as a new means of establishing small-scale biogas-powered plants at livestock farms, sewage treatment plants, and similar sites.
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Gas Engine Cogenerator Specifications |
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Engine Type |
Vertical, Water-Cooled, 4-Cycle, 3-Cylinder, Overhead Cam Engine |
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Engine Displacement |
952cc |
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External Dimensions |
W: 1100mm / D: 660mm / H: 1500mm |
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Weight |
465kg |
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Total Efficiency |
86.0% (Reference value when used with municipal gas) |
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Power-Generating Efficiency |
26.5% (Reference value when used with municipal gas) |
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Waste Heat Recovery Efficiency |
59.5% (Reference value when used with municipal gas) |
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Overview of Biogas-Powered Gas Engine Cogeneration System |
Much attention is being paid to methane fermentation (anaerobic digestion) technology as a means of dealing with the problems of global warming and as a tool aiding the formation of a recycling-based society. Methane fermentation technology enables the production of biogas (comprising roughly 60%-65% methane and 35%-40% carbon dioxide) and organic fertilizers from food scraps, livestock manure, organic sludge, and other forms of biomass waste. The energy from the biogas thus obtained can then be utilized in a system of recirculation, returning organic wastes to the farmlands from which they originate. This has resulted in increased construction of biogas plants capable of treating food scraps and livestock waste material in recent years. Additionally, a "Biomass Japan General Strategy" initiative launched last year calls for promoting the spread of methane fermentation technology.
Methane fermentation presents issues concerning utilization and processing of fermenting liquids as well as the matter of energy efficiency and economics in using biogas effectively. Although the use of biogas is being considered for gas engines, micro gas turbines (MGTs), and fuel cells and similar technologies, other relatively larger systems generating power in the area of 30kW are already available, as are numerous power generating systems specifically tailored to run on biogas. The resulting limits on potential sales of biogas systems leads to the problem of increased manufacturing costs.
Therefore, in February of 2002, AIST's Institute for Energy Utilization and Aisin Seiki began joint research and development of a biogas-compatible cogeneration system based on a "6-kW gas engine cogeneration system" fueled by municipal gas (or propane gas) that Aisin Seiki had put on the market. The base system is compact and highly energy-efficient (with a total energy efficiency level of 86% when used with municipal gas), and further offers an excellent economic advantage in that it based on a model already in mass production (incidentally, calculations show that the energy required to power a 6 kW cogenerator can be supplied by a dairy farm with 100 head of cattle). However, since biogas has a lower concentration of methane and lower calorific value than municipal gas, biogas-powered gas engines do not operate as well as conventional municipal gas-powered units. Therefore, trials were conducted to adjust the fuel-air ratio using low-calorie model biogas, as this resulted in the successful operation of a gas engine cogenerator using a mixture of 60% methane and 40% carbon dioxide. These results demonstrate the promise of developing a cogeneration system featuring a biogas-powered gas engine cogenerator capable of generating 6kW of electricity and further utilizing waste heat.