Print Email Facebook Twitter Optimising flow and mixing in a full-scale gas-mixed anaerobic digester by integrating sludge rheological data using computational fluid dynamics Title Optimising flow and mixing in a full-scale gas-mixed anaerobic digester by integrating sludge rheological data using computational fluid dynamics Author Wei, P. (TU Delft Sanitary Engineering; TU Delft ChemE/Transport Phenomena) Uijttewaal, W.S.J. (TU Delft Environmental Fluid Mechanics) Spanjers, H. (TU Delft Sanitary Engineering) van Lier, J.B. (TU Delft Sanitary Engineering) de Kreuk, M.K. (TU Delft Water Management) Department Water Management Date 2023 Abstract Gas-mixing is commonly applied in anaerobic digesters, yet the resulting flow and hydraulic mixing are difficult to evaluate because of limited full-scale experimental data and uncertainties in integrating sludge rheological data. This study used computational fluid dynamics (CFD) to assess the impact of treated sludge rheology on flow and mixing characterisation in a full-scale biogas-mixed digester. The CFD model, which was firstly validated using a lab-scale setup, showed that flow and mixing predictions depended on the rheological properties, especially at low shear rates. The predicted dominant shear rate was out of the effective shear-rate range of the Ostwald model, leading to flow and mixing performance overestimation. The results indicated that there are limitations in applying the Ostwald model and the conventional approaches for determining dead-zone. The Herschel-Bulkley model was more appropriate for the prevailing low shear rates and predicted large viscosity gradients in the digester, indicating two distinct compartments with different flow and mixing behaviour based on the gas-sparging height: a plug-flow compartment with dominant vertical convection above, and a dead-zone compartment with considerable segregation below. The results showed that the applied gas-sparging induced insufficient flow and mixing, but contributed to the well-functioning of the digester. To correctly assess flow and mixing, the applied rheological data should be in agreement with the type of sludge that is treated in the digester. Our results indicate that the shear rate in the digester must be increased and various options for achieving this are proposed. Subject Anaerobic digestionCFDFlow and mixingGas-mixingOptimisationSludge rheology To reference this document use: http://resolver.tudelft.nl/uuid:0be9845b-2a6e-4e19-b0c8-656b409ad3b5 DOI https://doi.org/10.1016/j.cej.2023.143647 ISSN 1385-8947 Source Chemical Engineering Journal, 468 Part of collection Institutional Repository Document type journal article Rights © 2023 P. Wei, W.S.J. Uijttewaal, H. Spanjers, J.B. van Lier, M.K. de Kreuk Files PDF 1_s2.0_S1385894723023781_main.pdf 9.84 MB Close viewer /islandora/object/uuid:0be9845b-2a6e-4e19-b0c8-656b409ad3b5/datastream/OBJ/view