NEFCO’s CFD Study
The study was originally conceived to evaluate the performance of the NEFCO Stamford Baffle design and several variations on that design to better understand the parameters that affected baffle performance. To that end, the plan was straightforward. The first step was the simulation of a 70-ft diameter clarifier. This clarifier would serve as the test bed to calculate the predicted effectiveness of each design in reducing effluent solids. As these first steps were completed, however, the simulations produced a number of results that raised more questions and caused us to broaden our effort in some cases and explore more deeply in others.
The simulations in the 70-foot clarifier highlighted the performance of the NEFCO Stamford Baffle as well as two other configurations, one with a more shallow (30 degrees as measured from the horizontal) inclination angle and the other with a longer horizontal projection. These three configurations then became the focus of the baffle portion of the study. The initial results also provided insights into the relationship between clarifier flow, density current formation and baffle performance.
The baffle simulation effort was scaled up to a 100-foot diameter test bed clarifier and used to predict the performance of the several baffle configurations across a range of flow rates. Detailed analysis of simulated baffle flow patterns enabled us to examine the effect of inclination angle and baffle projection. The relationship of baffle to blanket distance was also examined and attempt was made to define an optimum baffle mounting location.
Finally, by combining the 30-degree inclination angle with a longer horizontal projection, a new baffle configuration was produced that was consistently 30% to 50% more effective than the original Stamford Density Current Baffle. This new baffle, which we call Stamford Baffle 2.0, represents the first major improvement in baffle performance in thirty years. The performance of Stamford Baffle 2.0 was confirmed at the Monclova, Mexico WWTP, where it reduced effluent TSS by almost 70%
Inspired by simulated density current flow patterns generated during earlier work, NEFCO engineers began to explore alternative baffle configurations that might utilize the energy contained in this flow to improve baffle effectiveness even more. The result of that effort is the Dual Surface Density Current Baffle, a new design that is predicted to reduce effluent solids by as much as 75% in larger clarifiers operating at very high flow rates.