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Centrifuges for Sludge Treatment
Published in Saravanamuthu Vigneswaran, Roger Ben Aim, Water, Wastewater, and Sludge Filtration, 2020
Manufacturers of low-speed decanters prefer, obviously, the length to diameter ratio of 2 to 3, while in high speed decanters a ratio of 4 or more is used. Moreover, the geometry of the bowl varies with the length of the cylindrical section (i.e., the section with constant diameter) and the steepness of the conical section. The significance of the beach angle was discussed earlier. The length of the cylindrical section has an influence on the clarity of the effluent; for example, an increase of the length increases the retention time of the settling solids in the bowl and thus facilitates the deposition of slowly settling particles. Therefore, a saving on flocculants can be achieved, in practice, with the longer bowl. The longer bowl will also produce, in general, a comparatively higher throughput when the separation efficiency is held constant. These factors induced a recent supply of longer bowls with a length-to-diameter ratio of more than 5.
Sludge treatment and disposal
Published in Nick F. Gray, Water Science and Technology: An Introduction, 2017
Vacuum filtration and centrifugation are also used for dewatering sludges, although their use is largely restricted to industrial wastewaters. In vacuum filtration, water is sucked from the sludge under vacuum through a filter cloth that is carried on a slowly revolving drum partly immersed in the sludge (Figure 15.11). Centrifuges consist of a rotating bowl into which sludge and polyelectrolytes are added. Centrifugal forces enhance the settling rates of the particles causing solids to separate out at its periphery from where it is removed (Figure 15.12). Often called decanters, in order to operate continuously they need a mechanism to scrape the centrifugally deposited solids from the cylinder walls and convey them to a discharge point. This is done using a scroll running coaxially with the main bowl that acts as a screw conveyor.
Solid—Fluid Systems
Published in Enrique Ortega-Rivas, Unit Operations of Particulate Solids, 2016
In order to handle concentrated suspensions, basket centrifuges, screening centrifuges, and decanter centrifuges, among others, have been employed. Decanter or scroll centrifuges are conventionally used for the continuous separation of solids from liquids. They consist of a solid horizontal bowl tapered at one end and enclosed within a cylinder (Figure 10.32). Thick slurry is pumped into the bowl along the central axis, and it is projected against the cylinder wall near the tapered section. A screw, revolving at a higher speed close to the bowl wall, conveys the solids along the tapered surface to the point of discharge and allows the inner layer of liquid to be drained out through a second discharge channel.
Advances in dewatering and drying in mineral processing
Published in Drying Technology, 2021
Benitta A. Chaedir, Jundika C. Kurnia, Agus P. Sasmito, Arun S. Mujumdar
Beside hydrocyclones, there are also many industrial centrifuges types that play a key role in solid-liquid separation processes. While they are significantly more expensive and complex, centrifuges offer better separation performance and greater flexibility than hydrocyclones.[3] One type of these centrifuges that is frequently used is decanter centrifuge. This centrifuge consists of two distinctive components; i.e., solid wall enclosure (the bowl) and the conveyor scroll inside to drive and segregate the mineral slurry, as shown in Figure 3. The cylindrical-conical bowl shell revolves at a high speed to induce centrifugal force required for separation process. Typically, the bowl diameter ranges from 0.2 m to 1.4 m depending on the separation capacity required. A conveyor scroll is contained inside the bowl for continuous discharge and it rotates at a speed relative to the speed of the enclosure. The feed slurry is fed via the center tube of the rotating screw conveyor and is subjected to a high centrifugal force, pushing the solids to settle at the outer section. These separated solids are pushed by the conveyor scroll out of the liquid and discharged at the solid outlet.[3] Throughputs of the centrifuge vary depending on feed concentration, which varies in the range from 0.5% to 70% solids, with 5–20% of water content in the solid product. An advantage of the decanter centrifuge is its continuous process and its capability to segregate suspension that contains small amount of liquid and high concentration of solid material.[17] However, decanter centrifuge possess lower G-forces than tubular and disk centrifuges and it has smaller surface area than disk centrifuges. In designing a decanter centrifuge for specific applications, critical parameters that are critical to its performance such as length-diameter ratio, vibrations, and temperature must be considered.