Autonomous Sensor Concepts
The acquisition of spatially distributed parameters in the large-scale vessels is hampered by the limited access to the process itself in most industrial scale applications, where sensor mounting or cable connections are not feasible or desired. Therefore, state of the art instrumentation of such reactors is commonly limited to few spatial positions where it is doubtfully assumed that the measured parameters are representative for the whole reaction mixture. We developed the concept of instrumented flow followers (sensor particles) for the long-term measurement of spatially distributed process parameters in the chemically and mechanically harsh environments of agitated industrial vessels (Fig. 1a). Each sensor particle comprises of an onboard measurement electronics that logs the signals of measurement devices, namely temperature, absolute pressure (immersion depth, axial position) and 3D acceleration. The whole electronics is enclosed in a robust neutrally buoyant capsule (dp = 0.058 m), to allow free movement with the flow (Fig. 1b). Intended applications are in large-scale processes such as a stirred fermentation biogas reactor and activated sludge basins, but generally the sensor particle is not limited to these types of processes.
|Fig. 1: (a) Principle of application at a biogas fermentation plant||(b) mounted sensor particle|
Validation of the prototype sensor particles was carried out in a stirred vessel, a stirred fermentation reactor model, a draft-tube reactor and a bubble column (Fig. 2a). The analyzed data reveal the internal process conditions and particularly the flow conditions and in the vessels. Furthermore, axial parameter profiles can be extracted from the captured data of the sensor particles. Conclusions can be drawn on the mixing homogeneity, the axial distribution of solid fraction, the degree of suspension, the axial flow profile and the structure of large eddy flows. Moreover, model parameters of stirred vessels, such as the circulation number and the velocity head, and also parameters of dispersed flow models, such as the PECLÉT-number, can be estimated from the measured circulation time distributions (Fig. 2b).
|Fig. 2: (a) Stirred vessel during measurement with sensor particles||(b) extracted axial profiles of the mean circulation times for all set impeller speeds|
- S. Thiele, M. J. Da Silva, U Hampel, Autonomous sensor particle for parameter tracking in large vessels, Meas. Sci. Technol., vol. 21 (8), 2010.
- S. Reinecke, U. Hampel, Autonome Sensorpartikel zur Prozessdiagnose in Großbehältern, Tech. Mess., vol. 79 (10), 2010.
- S. Reinecke, et al., Flow following sensor particles - Validation and macro-mixing analysis in a stirred fermentation vessel with a highly viscous substrate, Biochem. Eng. J., 2012.
Studienstiftung des deutschen Volkes, Instrumented Flow Followers for Large Stirred Vessels, 2008 – 2011
- Fraunhofer Institute for Ceramic Technologies and Systems, Environmental Engineering and Bioenergy, Winterbergstrasse 28, 01277 Dresden, Germany
- Deutsches Biomasseforschungszentrum gGmbH (DBFZ), Biochemical Conversion Department, Torgauer Str. 116, 04347 Leipzig, Germany