Experimental analysis of mixing-processes in biogas plants

Annas, Sven; Elfering, Michael; Jantzen, Hans-Arno; Scholz, Jürgen; Janoske, Uwe

doi:10.1016/j.ces.2022.117767

Cited by 6 publications

(12 citation statements)

References 29 publications

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“…Nowadays a growing need to lower the dependency on fossil fuel for energy production is driven by both environmental and geopolitical reasons. The fermentation of bio-substrate may represent a reliable and sustainable energy production route, providing more controllable and dependable alternatives than solar and wind farms …”

Section: Introductionmentioning

confidence: 99%

“…14 Among the different techniques highlighted by Li et al, 14 characterizing the fluid dynamics of stirred digesters. PIV is adopted to determine the local flow fields 1,13,15 from which the local shear rate and the velocity distribution in the volume can be calculated. The homogenization dynamics of a tracer in the system can be followed with the PLIF technique, thus determining the mixing time.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Consequently, relatively high viscosities are found in digesters, with large inhomogeneities due to the fluid shear-thinning properties. These aspects lead to stirring systems designs based on “trial and errors” driven by power inputs criteria, often leading to suboptimal designs . In fact, a better design approach should consider different design criteria, such as the formation of caverns around the impellers, evolving rheology, sedimentation of the feedstock, and presence of dead zones to name a few.…”

Section: Introductionmentioning

confidence: 99%

“…Among the different techniques highlighted by Li et al, particle image velocimetry (PIV), planar laser-induced fluorescence (PLIF), and electrical resistance tomography (ERT) techniques are especially valuable in characterizing the fluid dynamics of stirred digesters. PIV is adopted to determine the local flow fields ,, from which the local shear rate and the velocity distribution in the volume can be calculated. The homogenization dynamics of a tracer in the system can be followed with the PLIF technique, thus determining the mixing time. − The analysis of the feedstock sedimentation can be performed with the ERT technique, simultaneously tracking the feedstock/medium mass transfer and the additives injection dynamics .…”

Section: Introductionmentioning

confidence: 99%

“…The fermentation of bio-substrate may represent a reliable and sustainable energy production route, providing more controllable and dependable alternatives than solar and wind farms. 1 The challenges posed by this technology stem, among others, from integrating different fields of knowledge, 2 the need for flexible systems treating varying feedstock compositions, 3 and the relatively high operative costs, especially related to mixing. 4 Concerning this last aspect, several studies analyze the effect of different mixing devices and modes, as well as different operative strategies, and a review can be found in Lindmark et al 5 The characterization of the state of mixing of the digester usually relies on the determination of two key parameters: the bioreactor hydrodynamics and the medium rheological behavior.…”

Section: ■ Introductionmentioning

confidence: 99%

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Power Consumption and Fluid Mixing in a Scale-Down Geometry of a Stirred Digester for Biogas Production

et al. 2023

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A unconventional stirred tank of geometry typically adopted for the production of biogas is experimentally investigated with pseudo-plastic model fluids. The apparent viscosities of the fluids, based on the Metzner–Otto method, are in the range of 39–264 mPa·s, resulting in a range of rotational Reynolds number equal to 17–648. The power consumption of the three top-entering agitators is measured by a strain gauge technique, and the power number curve is obtained in the full range of flow regimes, going from laminar to fully turbulent conditions. The flow field measured by particle image velocimetry allows us to observe the fluid circulation patterns and their variations in different operative conditions. The measurements reveal relatively low axial and radial velocities, especially toward the bottom of the tank, that may hinder solid feedstock suspension and subsequent biogas production. Significant changes in the flow patterns are observed with small variations in the impeller speed and the mixture viscosity. The homogenization dynamics of a tracer obtained by planar laser-induced fluorescence leads us to estimate the dimensionless mixing time, a trend similar to that observed for conventional stirred vessel geometries. The detailed fluid dynamics information collected by a combination of different techniques can contribute to optimize the energy requirement and to avoid failure of the biogas production due to poor fluid mixing.

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Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Power Consumption and Fluid Mixing in a Scale-Down Geometry of a Stirred Digester for Biogas Production

et al. 2023

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Lift characteristics of an airfoil at low Reynolds numbers for Newtonian and shear-thinning Carreau fluids

Raj,

Roy

2023

Physics of Fluids

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In the present study, we have numerically investigated Carreau and Newtonian fluid flow over a stationary National Advisory Committee for Aeronautics 0012 airfoil using a sharp interface immersed boundary method. We have explained the mean lift behavior and stall phenomena by identifying different vortex formation patterns over the airfoil surface for different angles of attack. We found that not all but some shear-thinning fluids avoid stall altogether at high angles of attack. It is observed that the lift behavior is strongly related to the frequency of vortex departure from the suction surface. We have correlated fluctuating energies with mean lift characteristics, which is one of the novelties of our work. We have also used time-averaged vorticity transport rate analysis to explain the effect of non-linear viscosity distribution in the departure of vortices at high angles of attack. It is observed that the apparent viscosity dominates the transport of vorticity, and the effect of shear straining is negligible at high angles of attack.

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Orientation resolved measurements of accelerations with sensor particles in bioreactors

Buntkiel,

Ma,

Reinecke

et al. 2023

Tm - Technisches Messen

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The measurement of the spatially distributed flow field in large industrial vessels, e.g. biogas fermenters, is not possible with commercially available measurement equipment. Therefore the concept of flow following sensor particles has been developed. They act as data loggers within the vessel. The sensor particles are equipped with a pressure sensor and an inertial measurement unit to measure their motion. The measurements are taken in the coordinate frame of the sensor particle and need to be transformed into the vessel’s coordinate frame to analyze the flow field. This is done by an error-state Kalman filter which estimates the orientation of the sensor particle with respect to the vessel based on the direction of the gravitational acceleration and the local magnetic field. Since no other aiding sensors are available or usable within an industrial vessel, particular emphasis was given to the inertial sensors’ stochastic modelling and the accelerometer’s calibration. Based on the orientation estimation, the measured acceleration is transformed into the vessel frame. We performed two experiments in a 1.4 m3 lab reactor to qualify this approach. The results show, that the transformed acceleration is in good qualitative agreement with the known flow field inside the lab reactor.

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Experimental analysis of mixing-processes in biogas plants

Cited by 6 publications

References 29 publications

Power Consumption and Fluid Mixing in a Scale-Down Geometry of a Stirred Digester for Biogas Production

Power Consumption and Fluid Mixing in a Scale-Down Geometry of a Stirred Digester for Biogas Production

Lift characteristics of an airfoil at low Reynolds numbers for Newtonian and shear-thinning Carreau fluids

Orientation resolved measurements of accelerations with sensor particles in bioreactors

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