Inclined-plate settling

Impingement Separator Inclined Plate Settling Increase of Volume upon Foaming... 

Rake The purpose of the rake is twofold direct the settled solids to the blowdown and to control the character of the sludge bed. High rake speed results in a fluffier bed while low speed hinders the contact between newly-formed floe (agglomerated suspended solids) and the bed. Note that most inclined-plate clarifiers do not have this feature. 

Inclined plate clarifiers, also known as Lamella clarifiers, use several inclined plates (or sometimes tubes) to maximize the settling area for a given floor area (Lamella is a registered trademark of Parkson Corporation, Ft. Lauderdale, FL). Figure 8.5 shows a diagram of an inclined-plate clarifier. 

Inclined plate clarification is a traditional separation technology that has been used for decades to remove suspended solids from a liquid stream in various types of systems including traditional precipitation [12]. In the semiconductor industry, the clarifier is commonly used in fluoride waste treatment systems where calcium fluoride precipitate is concentrated prior to dewatering in a press, or in assembly/test operations to separate silicon fines from backgrind operations. The clarifier will concentrate the solid phase of slurry like a UF, but unlike the UF or MF, the clarifier may require the addition of a chemical polymer to facilitate the agglomeration of the suspended solids so that they settle and concentrate. Polymer addition adds another level of complexity to the waste treatment system. The clarifier does not provide a physical barrier to prevent the transport of solids to downstream equipment, so it may be necessary to install a UF or MF downstream of the clarifier to capture extraneous particles or to protect the downstream equipment from clarifier upsets. 

Inclined-Plate Clarifiers Lamella or inclined-plate separators have achieved increased use for clarification. They contain a multiplicity of plates inchned at 45 to 60° from the horizontal. Various feed methods are employed so that the influent passes into each inclined channel. The geometry of the plates results in the solids having to settle only a short distance in each channel before sliding down the base to the collection zone beneath the plates. The clarified liquid passes in the opposite direction beneath the ceiling of each channel to the overflow connection. 

The total incoming flow of feed can be treated with air under pressure, but it is more usual to introduce the air into a recycle stream of cleaned liquid and to allow the bubbles to develop in the flotation chamber at the point where the recycle stream enters. The feed stream is pretreated with chemicals, if necessary, prior to its introduction to the flotation chamber where it meets the bubble blanket. The fine particles in the supension are captured by the bubbles and are floated up to the surface where they form a thick scum which is removed by a continuous mechanical scraper. Some solids will settle fi om most feed streams and it is usual to provide for the withdrawal of accumulated silt fiom the base of the chamber. Figure 7.13 shows a conventional diflused air flotation system housed in a rectangular tank and Figure 7.14 a DAF unit which incorporates an inclined plate settler to capture by sedimentation those particles that escape flotation. 

Clarifiers used for removal of settleable solids and readily floating oils and greases are either rectangular or circular basins (Figs. 4.73 and 4.74). Clarifiers are sized on the basis of settling rate (area) and detention time (volnme). Inclined plates can be inclnded to increase the effective settling area of a clarifier and rednce space reqnirements. 

The inclined plate (or tube) separator is widely used throughout industry, and is often combined with fine solids removal. The solids settle downwards between the plates, to be removed intermittently from the water tank at the base. 

A refinement of the gravity settler in Fig.1 is to place a baffle at the input end and inclined plates in the tank. This increases separation efficiency at the solid particles start from a better setting position and have a shorter distance to travel before reaching their point of settling. 

Lamella settlers are gravity settlers that use a large number of inclined flat plates, closely packed, so that the distance between the plates is small. The gravitational action makes the cells move in the direction of the lower surface of the individual separating space between two plates. Once settled, the particles slide down in a layer towards the plate periphery and then into the sludge hopper. For the same required sedimentation area, lamella settlers are much more compact than vertical ones. Theoretically, their total sedimentation area is the sum of the horizontally projected areas of all plates. In practice, however, only 50% of this total area is effective [137]. The main problem with inclined settlers is that the cells tend to adhere to the plates. Special coating of the plate surface and vibration of the whole lamella pack may alleviate this problem. 

A process for phase separation based on density differences. A commercial lamella settler for suspensions or emulsions comprises a stack of parallel plates spaced apart from each other and inclined from the horizontal. The space between each set of plates forms a separate settling zone. The feed is pumped into these spaces, at a point near the longitudinal middle of the plates. The less dense phases rise to the underside of the upper plates... 

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