Agricultural Biogas Plant as a Thermodynamic System: A Study of Efficiency in the Transformation from Primary to Secondary Energy
Type
Journal article
Language
English
Date issued
2023
Author
Faculty
Wydział Inżynierii Środowiska i Inżynierii Mechanicznej
Journal
Preprints.org
Pages from-to
art. 2023091455
Abstract (EN)
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
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 substrates was estimated in laboratory conditions by measuring the heat of combustion in a ballistic
bomb calorimeter (17,760 MWh·year‐1), and in the case of pig slurry, biochemical methane potential (BMP,
(201.88±3.21 m3
·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 amount of biogas produced at the plant, 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, biomass conversion efficiency was determined as a ratio of chemical energy
in methane to (primary) energy in substrates, which was 59.87%, as well as electricity production efficiency, as
a ratio of electricity produced (4,913 MWh·year‐1) to primary energy, with a 35% cogeneration system
efficiency. 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.
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
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 substrates was estimated in laboratory conditions by measuring the heat of combustion in a ballistic
bomb calorimeter (17,760 MWh·year‐1), and in the case of pig slurry, biochemical methane potential (BMP,
(201.88±3.21 m3
·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 amount of biogas produced at the plant, 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, biomass conversion efficiency was determined as a ratio of chemical energy
in methane to (primary) energy in substrates, which was 59.87%, as well as electricity production efficiency, as
a ratio of electricity produced (4,913 MWh·year‐1) to primary energy, with a 35% cogeneration system
efficiency. 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.
License
CC-BY - Attribution
CC-BY - Attribution Open access date
September 21, 2023