Effect of mixing of waste biomass in anaerobic digesters for production of biogas

Conti, Fosca; Wiedemann, Leonhard; Saidi, Abdessamad; Goldbrunner, Markus

doi:10.1088/1757-899x/446/1/012011

Cited by 6 publications

(7 citation statements)

References 10 publications

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“…The fluid velocity was mapped in the whole volume using an acoustic velocimeter, based on the Doppler Effect, and a particle image velocimetry (PIV) spectrometer, based on the photoexcitation of seeding particles. More details regarding the velocity measurements can be obtained in [19], [24].…”

Section: Methods Of Mixing In Scaled-down Laboratory Digestermentioning

confidence: 99%

CFD Modelling of Biomass Mixing in Anaerobic Digesters of Biogas Plants

Conti

Saidi

Goldbrunner

2019

Environmental and Climate Technologies

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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.

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Section: Methods Of Mixing In Scaled-down Laboratory Digestermentioning

confidence: 99%

CFD Modelling of Biomass Mixing in Anaerobic Digesters of Biogas Plants

Conti

Saidi

Goldbrunner

2019

Environmental and Climate Technologies

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“…Digester substrates are classified as non-Newtonian fluids because of the shear-dependent behaviour of the viscosity [12]- [14]. In the present study, the Oswald-de Waele power-law model was selected for the simulation of a fluid with a density of 1090 kg/m 3 [15].…”

Section: Modelling Procedures and Cfd Settingmentioning

confidence: 99%

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

Conti

Saidi

Goldbrunner

2020

Environmental and Climate Technologies

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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.

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“…On the walls and bottom surface layers of the tank no‐slip conditions were adopted, whereas the fluid surface on the top (transition to gas) was modeled with slip conditions. To improve the convergence of the simulations, the segregated flow solver was preferred to the coupled solver .…”

Section: Methodsmentioning

confidence: 99%

“…was modeled with slip conditions. To improve the convergence of the simulations, the segregated flow solver was preferred to the coupled solver [32]. There is no theorem directly relating Re to turbulence.…”

Section: Meshing Of Geometry and Simulation Processmentioning

confidence: 99%

Numeric Simulation‐Based Analysis of the Mixing Process in Anaerobic Digesters of Biogas Plants

2020

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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-e turbulence model and the standard k-w 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.

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Effect of mixing of waste biomass in anaerobic digesters for production of biogas

Cited by 6 publications

References 10 publications

CFD Modelling of Biomass Mixing in Anaerobic Digesters of Biogas Plants

CFD Modelling of Biomass Mixing in Anaerobic Digesters of Biogas Plants

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

Numeric Simulation‐Based Analysis of the Mixing Process in Anaerobic Digesters of Biogas Plants

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