In a study of a Danish wastewater treatment plant, Computational Fluid Dynamics (CFD) simulations showed a potential for energy savings of more than 50% for mixing of horizontal flow systems. For submersible mixing in an activated sludge tank this can be realised by changing from medium speed, small diameter propeller mixers to slow speed, large diameter propeller flowmakers without altering the flow field in the tank.
Process tanks with unrestricted flow could potentially find easy and economically justified energy savings of up to 50% by using low speed, large diameter propeller flowmakers.
The study was based on an analysis of velocity flow fields using Computational Fluid Dynamics. The payback time for implementing the change in flowmakers will vary from plant to plant, and for the Drøsbo wastewater treatment plant in Denmark, the payback time was shown to be around four years. Furthermore, optimising the flowmakers reduces CO2 emissions by a substantial amount, reducing the burden on the environment.
Based on findings in this study, process tanks with unrestricted flow could potentially find easy and economically justified energy savings by using low speed large diameter propeller flowmakers compared to medium speed small diameter propeller mixers, despite the higher initial cost of a flowmaker.
PHOTO: Velocity contour flow fields 0.3 m above the bottom of the tank.