<abstract xmlns="http://www.w3.org/1999/xhtml">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.</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.

Evaluation Criteria and Benefit Analysis of Mixing Process in Anaerobic Digesters of Biogas Plants

Institute of new Energy Systems, Technische Hochschule Ingolstadt

Environmental and Climate Technologies

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

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...

Evaluation Criteria and Benefit Analysis of Mixing Process in Anaerobic Digesters of Biogas Plants

Published Online: Dec 14, 2020

Page range: 305 - 317

DOI: https://doi.org/10.2478/rtuect-2020-0105

Keywords
Anaerobic digester, biomass, computational fluid dynamics (CFD), Cost-Benefit Analysis (CBA), evaluation criteria, flow velocity, full scale biogas digester, mixing, propeller

© 2020 Fosca Conti et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Evaluation Criteria and Benefit Analysis of Mixing Process in Anaerobic Digesters of Biogas Plants

Published Online: Dec 14, 2020

Page range: 305 - 317

DOI: https://doi.org/10.2478/rtuect-2020-0105

KeywordsAnaerobic digester, biomass, computational fluid dynamics (CFD), Cost-Benefit Analysis (CBA), evaluation criteria, flow velocity, full scale biogas digester, mixing, propeller

© 2020 Fosca Conti et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Keywords
Anaerobic digester, biomass, computational fluid dynamics (CFD), Cost-Benefit Analysis (CBA), evaluation criteria, flow velocity, full scale biogas digester, mixing, propeller