"Positioning of a measuring system for determination of mixing quality in biogas digesters"

Various measurement methods are available for determining mixing quality in biogas digesters, most of which provide a point-by-point reading. These include ion-selective electrodes, in-line viscometers, force sensors, magnetic-inductive sensors or ultrasonic sensors.

Flow Fields
Figure 4. Flow fields: propeller at 80mm distance from bottom, 1750 min–1, and different measurement layers (80, 200, 320, 440mm from bottom) labeled E080, E200, E320, E440. CMC/water mixture: 0.8 %. (© TUMCS / Regenerative Energiesysteme; publ. by: Huber et al)

The measurement of global properties of the mixing or the flow field is associated with considerable difficulties due to the size of the plant and the opacity of the fermenter contents. Therefore, the question arises as to the optimal positioning of local velocity sensors in order to achieve an optimal correlation of the measured value and a global parameter for the flow field.

Within the scope of experiments on a model digester, flow fields of different agitators in biogas plants were measured with a 2D PIV system. The data evaluation of these flow fields provides particularly suitable positions for the installation of velocity sensors at the periphery of biogas plants in order to infer a global parameter of the flow field from the local measured value. The resulting angular positions can be directly transferred to the real plant due to the dimensional analytical design of the experiment.

The publication on the topic can be found here: