Maximizing the Energy Output from Biogas Plants: Optimisation of the Thermal Consumption of Biogas Systems

Abstract

The majority of biogas systems uses block heat and power plants to utilize the biogas. The biogas is converted to heat and electric energy in these system parts. A part of both energy shares is necessary to operate the biogas system. Heat consumptions and feeding protocols of 4 agricultural systems spanning up to 10 years could be used for the study regarding the reduction of the infed heat quantity. Furthermore, the temperature of the fermentation substrate and the biogas were logged in 6 biogas systems in a weekly cycle over a period of 15 months. Aside from environment-related temperature fluctuations of the substrate, a not insignificant cooling of the silage could be determined in the reception bunkers and the screw conveyors. Heat quantities for the heating of the substrate were determined based on the temperature measured, which are maximally 81% of the infed heat in the winter months for liquid manure and up to 60% for maize. A heat transfer from the fermentation residues to the liquid manure can be easily implemented as both substrates can be pumped. Depending on the design of the heat exchanger, the heat necessary to achieve the process temperature can be reduced significantly for the liquid manure and no external heat would be necessary in an optimum case scenario. The cooling of the maize silage in the solid storage and in the screw conveyors can be reduced with coverings and insulation. Increasing the inlet temperature by 10 °C would reduce the heat requirement by 25%.