Affinity Laws for Decanter Centrifuges: Impacts of G force on dewatering centrifuge capacity and performance. An explanation of the G-volume scaling methodology.

Introduction Affinity Laws for pumps and fans are commonly known but why aren't they commonly known for decanter centrifuges? Dewatering performance has a large impact on overall wastewater treatment operations and understanding how modern decanter centrifuge technology has evolved is critical to selecting the correctly sized equipment. The optimized selection of a decanter centrifuge and its performance plays an important role in the cost of returned solids (solids recovery) and the cost of disposal (dryness of solids). The scaling methodology (Affinity Laws for Decanter Centrifuges) of capacity and performance becomes a crucial activity. The inner diameter of the bowl has historically been one of the main criteria for comparing decanter centrifuges. However, this approach has not been sufficiently accurate for the prediction of capacity or performance. The holding volume, geometry, and operating speeds all need to be compared. For this purpose, GEA has developed and validated a theoretical model by performing side-by-side field trials. The validation of the G x Volume affinity law (See Figure 1) demonstrates that G force combined with volume are reliable criteria for the scaling of capacity and performance of decanter centrifuges for dewatering in wastewater treatment plants. Hypotheses 1. Comparing geometrically similar decanter centrifuges with an equivalent volume with a higher G force would result in either a higher cake dryness or a greater capacity. See figure 2 2. Comparing decanters with a different bowl diameter but with the same G volume, the performance and capacity would be the same. See figure 3 Methodology 1. Side-by-side operation with two equivalent bowl diameter decanter centrifuges with different G-volume was performed at WWTP Langenberg, Germany, keeping other parameters such as sludge characteristics, concentration of infeed sludge and solids recovery identical. 2. Side-by-side operation with two different bowl diameter decanter centrifuges with an equivalent G volume was performed at WWTP Oldenburg, Germany, keeping other parameters like sludge characteristics, concentration of infeed sludge and solids recovery identical. 3. In both trials, the services of KBKopp (Dr. Julia Kopp) were utilized to determine the maximum sludge dewaterability. See figure 4 for photos of the test equipment and site Results The research establishes that centrifuges with an equivalent bowl geometry, but having different G volume owing to rotational speeds, will have an equivalent capacity at the same performance level or a different performance at the same capacity. The capacity and performance is directly proportional to the G volume difference, and only indirectly related to the bowl diameter. See figures 5, 6, 7 Implications The study brings forward 'G x Volume' as reliable criteria for scaling and selection of decanter centrifuges in wastewater treatment plant design and also brings a paradigm shift from conventional wisdom of bowl diameter as the comparative driver. The research helps in selection of centrifuges that get higher capacity per square meter space or significant reduction in cost of operation (disposal and polymer consumption) per cubic meter of sludge handled. In either of the cases, 'G x Volume' based selection drives towards optimized scaling for reduction in CO2 footprint and an efficient circular economy. The Future The development and use of Affinity Laws for Decanter Centrifuges is on-going and is expected to result in more economically efficient and environmentally friendly operations.