An Agricultural Biogas Plant as a Thermodynamic System: A Study of Efficiency in the Transformation from Primary to Secondary Energy

Krzysztof Pilarski (), Agnieszka A. Pilarska (), Alicja Kolasa-Więcek and Dariusz Suszanowicz
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Krzysztof Pilarski: Department of Biosystems Engineering, Poznań University of Life Sciences, Wojska Polskiego 50, 60-627 Poznań, Poland
Agnieszka A. Pilarska: Department of Hydraulic and Sanitary Engineering, Poznań University of Life Sciences, ul. Piątkowska 94A, 60-649 Poznań, Poland
Alicja Kolasa-Więcek: Institute of Environmental Engineering and Biotechnology, Faculty of Natural Sciences and Technology, University of Opole, Kominka 6, 46-020 Opole, Poland
Dariusz Suszanowicz: Institute of Environmental Engineering and Biotechnology, Faculty of Natural Sciences and Technology, University of Opole, Kominka 6, 46-020 Opole, Poland

Energies, 2023, vol. 16, issue 21, 1-15

Abstract: Using a wide range of organic substrates in the methane fermentation process enables efficient biogas production. Nonetheless, in many cases, the efficiency of electricity generation in biogas plant cogeneration systems is much lower than expected, close to the calorific value of the applied feedstock. This paper analyses the energy conversion efficiency in a 1 MWel agricultural biogas plant fed with corn silage or vegetable waste and pig slurry as a feedstock dilution agent, depending on the season and availability. Biomass conversion studies were carried out for 12 months, during which substrate samples were taken once a month. The total primary energy in the substrates was estimated in laboratory conditions by measuring the released heat (17,760 MWh·year −1 ), and, in the case of pig slurry, biochemical methane potential (BMP, (201.88 ± 3.21 m 3 ·Mg VS −1 ). Further, the substrates were analysed in terms of their chemical composition, from protein, sugar and fat content to mineral matter determination, among other things. The results obtained during the study were averaged. Based on such things as the volume of the biogas, the amount of chemical (secondary) energy contained in methane as a product of biomass conversion (10,633 MWh·year −1 ) was calculated. Considering the results obtained from the analyses, as well as the calculated values of the relevant parameters, the biomass conversion efficiency was determined as the ratio of the chemical energy in methane to the (primary) energy in the substrates, which was 59.87%, as well as the electricity production efficiency, as the ratio of the electricity produced (4913 MWh·year −1 ) to the primary energy, with a 35% cogeneration system efficiency. The full energy conversion efficiency, related to electricity production, reached a low value of 27.66%. This article provides an insightful, unique analysis of energy conversion in an active biogas plant as an open thermodynamic system.

Keywords: calorific value; biomass conversion; biogas production; chemical energy; energy efficiency; cogeneration (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (1)

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