@article{ContiSaidiGoldbrunner2020, author = {Conti, Fosca and Saidi, Abdessamad and Goldbrunner, Markus}, title = {Evaluation Criteria and Benefit Analysis of Mixing Process in Anaerobic Digesters of Biogas Plants}, volume = {24}, journal = {Environmental and Climate Technologies}, number = {3}, publisher = {De Gruyter Poland}, address = {Warsaw}, issn = {2255-8837}, doi = {https://doi.org/10.2478/rtuect-2020-0105}, pages = {305 -- 317}, year = {2020}, abstract = {A valid method to evaluate decisions of a project proposal is the so-called cost-benefit analysis. Criteria are selected and properly weighted to determine if the project is effective and feasible. The present research study is focused on methodical selection of design parameters to install two propeller mixers inside anaerobic digesters of biogas plants. A cylindrical tank of 1400 m3 was considered. For the model-based optimisation, the substrate was considered as a non-Newtonian fluid with a density of 1090 kg/m3. The Oswald-de Waele power-law model was selected to account for the rheological behaviour of the fluid. Installation parameters of the mixers were rotational angles and heights of the shafts of the two propellers. A computational model was developed to simulate the fluid dynamics depending on the mixing process inside the tank. Several configurations were analysed according to evaluating criteria such as the value of the fluid velocity, its distribution along the three spatial dimensions, and the power consumption to rotate the mixers. The maximum fluid velocity and minimum power consumption were observed when the propellers are located at intermediate height inside the tank and with the shafts perpendicular to the tank radius. With this configuration, the fluid reaches a maximum velocity of 0.28 m/s. According to the investigation, it is evident that mixing systems with propeller shafts deep-seated and parallel to the tank radius should be avoided, both in term of efficiency of the fluid mixing distribution and in term of power consumption.}, language = {en} } @article{ContiSaidiGoldbrunner2020, author = {Conti, Fosca and Saidi, Abdessamad and Goldbrunner, Markus}, title = {Numeric Simulation-Based Analysis of the Mixing Process in Anaerobic Digesters of Biogas Plants}, volume = {43}, journal = {Chemical Engineering \& Technology}, number = {8}, publisher = {Wiley}, address = {Weinheim}, issn = {1521-4125}, doi = {https://doi.org/10.1002/ceat.201900650}, pages = {1522 -- 1529}, year = {2020}, abstract = {Stirring systems with two rotational three-bladed propellers were analyzed using computational fluid dynamics. The propellers are located at three heights and seven angles in a tank with 9 m radius. The fluid was characterized by non-Newtonian rheology and simulated by applying the k-ε turbulence model and the standard k-ω model. Reynolds numbers were estimated. High fluid speeds were obtained with the propellers located at a height of 2 m and oriented at 90° with respect to the tank radius. In the top regions of the tank, the fluid velocity was generally less intense and less affected by the angle setting. The configurations identified as good mixing systems showed power consumptions broadly distributed around 30 kW.}, language = {en} } @article{ContiSaidiGoldbrunner2019, author = {Conti, Fosca and Saidi, Abdessamad and Goldbrunner, Markus}, title = {CFD Modelling of Biomass Mixing in Anaerobic Digesters of Biogas Plants}, volume = {23}, journal = {Environmental and Climate Technologies}, number = {3}, publisher = {RTU Press}, address = {Riga}, issn = {2255-8837}, doi = {https://doi.org/10.2478/rtuect-2019-0079}, pages = {57 -- 69}, year = {2019}, abstract = {Cut in greenhouse gas emissions, increment of energy from renewables and improvement in energy efficiency represent the three key targets for future energy systems. Among the available bioenergy technologies, biogas production via biodegradation and anaerobic digestion is a widely applied approach, not only to produce biofuels but also to manage industrial and domestic organic waste. Within the biogas production, a sufficient mixing of the organic mass is a crucial step to ensure high biogas yields by bacteria and enzymes. Measurements of the electric power consumption of biogas plants revealed that the electrical energy demand of the stirrer system has a high share of the total electricity consumption of a biogas plant. Investigations on real biogas digesters to optimize the mixing process are cost and time intensive. Therefore, laboratory prototypes and computational simulations represent promising alternatives to analyse and improve the efficiency of mixing systems. In this paper, a computational fluid dynamics (CFD) model is presented, which is applied to commercial stirring systems. The case of two propeller stirrers, located in diametrically opposite positions in a tank filled with ca. 1400 m3 of substrate is described in detail. For the simulation, the rheology of the fluid is adapted to a biomass with 12 wt \% dry matter content and obeying the non-Newtonian generalized Ostwald-de Waele power law. The developed simulation procedure considers the rotation angle of each propeller and its height. A total of 441 mixing configurations are calculated and evaluated in terms of the technical benefit. The investigation reveals that locations of the rotors far away from the bottom and high rotational angles cause advantageous fluid dynamics.}, language = {en} } @article{WiedemannContiSaidietal.2018, author = {Wiedemann, Leonhard and Conti, Fosca and Saidi, Abdessamad and Sonnleitner, Matthias and Goldbrunner, Markus}, title = {Modeling Mixing in Anaerobic Digesters with Computational Fluid Dynamics Validated by Experiments}, volume = {41}, journal = {Chemical Engineering \& Technology}, number = {11}, publisher = {Wiley}, address = {Weinheim}, issn = {1521-4125}, doi = {https://doi.org/10.1002/ceat.201800083}, pages = {2101 -- 2110}, year = {2018}, language = {en} } @article{ContiWiedemannSonnleitneretal.2018, author = {Conti, Fosca and Wiedemann, Leonhard and Sonnleitner, Matthias and Saidi, Abdessamad and Goldbrunner, Markus}, title = {Monitoring the mixing of an artificial model substrate in a scale-down laboratory digester}, volume = {2019}, journal = {Renewable Energy}, number = {132}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0960-1481}, doi = {https://doi.org/10.1016/j.renene.2018.08.013}, pages = {351 -- 362}, year = {2018}, language = {en} } @article{SaidiTrinklContietal.2018, author = {Saidi, Abdessamad and Trinkl, Christoph and Conti, Fosca and Goldbrunner, Markus and Karl, J{\"u}rgen}, title = {Partially Upgraded Biogas: Potential forDecentralized Utilization in AgriculturalMachinery}, volume = {41}, journal = {Chemical Engineering \& Technology}, number = {11}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1521-4125}, doi = {https://doi.org/10.1002/ceat.201800100}, pages = {2111 -- 2119}, year = {2018}, language = {en} } @article{ContiWiedemannSonnleitneretal.2017, author = {Conti, Fosca and Wiedemann, Leonhard and Sonnleitner, Matthias and Goldbrunner, Markus}, title = {Thermal behaviour of viscosity of aqueous cellulose solutions to emulate biomass in anaerobic digesters}, volume = {42}, journal = {New Journal of Chemistry}, number = {2}, publisher = {RSC}, address = {London}, issn = {1369-9261}, doi = {https://doi.org/10.1039/C7NJ03199H}, pages = {1099 -- 1104}, year = {2017}, language = {en} } @article{SaidiContiSonnleitneretal.2018, author = {Saidi, Abdessamad and Conti, Fosca and Sonnleitner, Matthias and Goldbrunner, Markus}, title = {Membrane separation process for small scaled partial biogas upgrading}, volume = {2018}, pages = {012012}, journal = {IOP Conference Series: Materials Science and Engineering}, number = {446}, publisher = {IOP Publishing}, address = {London}, issn = {1757-899X}, doi = {https://doi.org/10.1088/1757-899X/446/1/012012}, year = {2018}, abstract = {Biogas upgrading is actually limited to the production of biomethane as natural gas substitute. To realize the according gas quality a cost intensive methane enrichment is required, wherefore biogas upgrading is actually merely cost-efficient in case of high production rates. Since the energy and cost effort disproportionately increases with the required product gas purity partial biogas upgrading for decentralized utilization represents a promising utilization approach for farm based applications. Among the available technologies for CO2-separation the gas permeable membrane has high potential for small scaled biogas upgrading. Within the present study a model based analysis to determine the savings potential of a membrane based upgrading system is performed.}, language = {en} } @article{ContiWiedemannSaidietal.2018, author = {Conti, Fosca and Wiedemann, Leonhard and Saidi, Abdessamad and Goldbrunner, Markus}, title = {Effect of mixing of waste biomass in anaerobic digesters for production of biogas}, volume = {2018}, pages = {012011}, journal = {IOP Conference Series: Materials Science and Engineering}, number = {446}, publisher = {IOP Publishing}, address = {London}, issn = {1757-899X}, doi = {https://doi.org/10.1088/1757-899X/446/1/012011}, year = {2018}, abstract = {Biogas technology is an important renewable bioenergy producer. The biogas generating process needs to be optimized to minimise the energy consumption due to the stirring of biomass slurry. Numerical simulations and laboratory experiments are economically and practically preferred over investigations of industrial scale biogas plants. Additionally, a strategic approach to model the reality in scientific laboratories is to use a rheological valid artificial chemical substrate to replace real biomass. The proposes of this study were (i) to investigate the mixing process in a 1:12 scaled-down home-made laboratory digester filled with a 0.3 wt\% water-cellulose solution, (ii) to simulate the mixing process in the laboratory-scale digester using a computational fluid dynamics model, (iii) to validate the model by comparison of the simulation with laboratory experiments results obtained on the laboratory digester. Optical and acoustic measurements on the flow velocity inside the digester during the mixing process of the water-cellulose solutions indicate that the model based on computational fluid dynamics is valid. The data are presented and discussed in the paper.}, language = {en} } @article{FlachContiBayraktaretal.2022, author = {Flach, Charley and Conti, Fosca and Bayraktar, Ahmet and Goldbrunner, Markus}, title = {Direct Methanation and Storage Concepts for the Flexibilization of Biogas Plants}, volume = {46}, journal = {Chemical Engineering \& Technology}, number = {3}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1521-4125}, doi = {https://doi.org/10.1002/ceat.202200239}, pages = {579 -- 586}, year = {2022}, abstract = {Enrichment of the methane fraction in a biogas mixture is an innovative possibility to make existing biogas plants more flexible by using excess power. In the described concept, the CO2 in the biogas is directly catalytically converted into CH4 with H2. The CH4-enriched biogas is again fed into the digester to save energy for later use in the combined heat-and-power unit. Additionally, the fed heat gas can mix and heat the substrate. A heat pipe injector system was therefore developed for cooling the hot biogas stream after methanation and to prevent damage to the microbial consortia during the biomass mixing. The concept was proven at a laboratory-scale biogas plant.}, language = {en} } @article{AhmedContiBayeretal.2022, author = {Ahmed, Arslan and Conti, Fosca and Bayer, Peter and Goldbrunner, Markus}, title = {Hydronic Road-Heating Systems}, volume = {26}, journal = {Environmental and Climate Technologies}, subtitle = {Environmental Performance and the Case of Ingolstadt Ramps}, number = {1}, publisher = {De Gruyter Poland}, address = {Warsaw}, issn = {2255-8837}, doi = {https://doi.org/10.2478/rtuect-2022-0078}, pages = {1044 -- 1054}, year = {2022}, abstract = {Snowfall and ice formation on road surface significantly impact the safety of driving conditions. To resolve this, every year salt and de-icing chemicals are sprinkled on roads. However, use of salts and snow ploughing have environmental as well as economical disadvantages. To resolve these problems, hydronic road heating systems are valid alternatives. Heat transfer fluid, i.e. mixture of ethanol and water, is pumped into a tubular circulation system under the asphalt. By this technology, the road and pavements shall stay ice-free even in times of snowfall and temperatures below the freezing point. The system can also be used to cool the asphalt in case of extreme heat, which - besides the heating effect - could also prevent road from damages in extreme summers. This study aims to compare the environmental impact of use of salts and road-heating system in terms of GHG emissions. To assess the environmental impact, an operational road heating system for a ramp in Ingolstadt, Germany, is considered. A cradle-to-grave analysis technique is used to determine the environmental effects based on a life-cycle assessment (LCA) framework. The analysis includes nine components solemnly responsible for hydronic heating of asphalt surface such as local heating pipe, insulation, pumps, and heat meters. Comparison is performed in terms of relative and total impact over 50-year lifetime of three heated ramps having 1989 m2 surface area in total. The results show that the asphalt and heating-circuit causes the major fraction (65 \%) of overall GHG emissions, with total life-time emissions of 28.10 kg CO2 eq./m2 of heated surface. During an operational life of 50 years, road heating systems emit 18 \% less CO2 eq./m2 as compared to the use of salts.}, language = {en} } @article{AhmedContiSchiesslWideraetal.2023, author = {Ahmed, Arslan and Conti, Fosca and Schießl-Widera, Michael and Goldbrunner, Markus}, title = {CFD-Based Sensitivity-Analysis and Performance Investigation of a Hydronic Road-Heating System}, volume = {16}, pages = {2173}, journal = {Energies}, number = {5}, publisher = {MDPI}, address = {Basel}, issn = {1996-1073}, doi = {https://doi.org/10.3390/en16052173}, year = {2023}, abstract = {To minimize the impact of snowfall and ice formation on safety of transportation, salt is sprinkled on the asphalt every winter. However, the use of salt has economical as well as ecological disadvantages. To resolve these problems, road heating systems are used in the northern regions of Europe and America. Despite their widespread usage, considerable potential of the operational optimization is evident. The current systems are controlled under predefined weather conditions such as start of operation at 5 °C air temperature, even when snowfall is absent. Consequently, loss of energy input to heat the system is caused. To avoid unnecessary financial and energetic expense, this study presents CFD-based performance investigation as a basis for a novel predictive controller to increase the operational efficiency of hydronic road heating systems (HRS). The simulation model was developed based on a real operational HRS located in Ingolstadt and composed of bridges and ramps for a total surface of 1989 m2. Climate data of the years 2019-2020 from local weather stations were implemented in the simulation model for performance prediction on extreme climate conditions. This investigation identified that up to 70\% of operational hours in terms of energy input can be saved by using a hypothetical predictive controller, thus making the HRS a more economically efficient and environmentally attractive alternate to conventional de-icing techniques.}, language = {en} } @article{ElhausKolbMuelleretal.2023, author = {Elhaus, Nora and Kolb, Sebastian and M{\"u}ller, Jakob and Goldbrunner, Markus and Karl, J{\"u}rgen and Herkendell, Katharina}, title = {Environmental assessment of anaerobic digestion and biological methanation in power-to-methane systems}, volume = {2023}, pages = {139509}, journal = {Journal of Cleaner Production}, number = {429}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1879-1786}, doi = {https://doi.org/10.1016/j.jclepro.2023.139509}, year = {2023}, language = {en} }