Float-sink tank

Another common method is sorting by density in a float-sink tank or hydrocyclone. This method is, however, difficult for polyolefins as these have very similar density. Air classification uses a combination of density and shape to achieve the separation, e.g. for separating plastic films and paper residues. 

Microsorting of plastics is commonly practiced for separation of lighter-than-water from heavier-than-water plastics. While such separation can be done in a simple float-sink tank, hydrocyclones are often used because of their advantages in size and throughput. Application of density-based separation for mixtures of plastics that are all heavier or all lighter than water is relatively rare. 

At the plastics processor, the baled HDPE containers are usually shredded, washed, and sent through either a float-sink tank or a hydrocyclone to separate heavy contaminants. Air classification may be done prior to washing. The clean materials are dried and then usually pelletized in an extruder equipped with a melt filter to remove residual nonplastic contaminants. If mixed colors are processed, the result from typical curbside or drop-off programs is a grayish-green color, which is most often combined with a black color concentrate to produce black products. 

Open floating-roof tanks Rim seal fire Overfill ground fire Obstructed full liquid surface fire Unobstructed full surface fire Application of fire water to the roof area should be carefully controlled to prevent overloading and sinking the roof when fighting a rim seal fire. 

After the wash, the material moves to the separation stage. Two most common methods for separating plastics by resin type are float-sink and hydrocyclone. The float-sink method is less costly but requires a relatively large tank size in order to realize volume effectiveness. A hydrocyclone is more costly, but uses less water, has no moving parts, and generally takes up less space than the older float-sink method. 

Zinc and lead usually occur together in nature as sulfides. Earlier separation processes involved the fine grinding of the combined sulfides and then treating the particles with chemical reagents to cause one sulfide to be preferentially wetted and rhns the two sulfides separated by the froth flotation process. In a first stage, the lead sulfide is floated while the zinc sulfide sinks to the bottom of the tank. In the second stage, the process is reversed and the zinc sulfide is floated. Gangue and other nonmetals collect at the bottom of the tank. The separated sulfides are dewatered to a 6-7% moisture content and are referred to as the zinc concentrate and the lead concentrate. 

FIGURE 21.3 The flota- tion process for concentrating metal sulfide ores. Mineral particles float to the top of the tank along with the soapy air bubbles, while the gangue sinks to the bottom. 

The food to be fried is carried into and through the oil tank by an appropriate conveyor. Food can also be fed by slow-moving paddles and it either sinks to the submerged conveyor or, if it floats, is held below the surface by a second conveyor. The conveyor speed controls the frying time. The fried food is removed from the fryer by an inclined conveyor and excess oil is drained back into the tank. 

To surface, air Is blown Into the blast tank of a submarine to push water out of the tank to make the submarine lighter-the submarine floats to surface. To dive, the blast tank is opened to let water in and to push out the air. The submarine sinks below the surface. The diving and surfacing of the submarine demonstrate the relationship between the weight of the submarine and the buoyancy force acting on it... 

Sink-float tanks have been extensively evaluated for the separation of plastics from end-of-life durables [49, 73, 79, 80]. Engineering plastics from end-of-life durable goods cover an exceptionally broad range of densities (less than 0.9 g/cm to greater than 1.7 g/cm ). There are many factors that influence the actual density of the compounded plastic besides the density of the base resin. Several of these are listed here ... 

Hydrocyclone System Centrifuge System Sink-Float Tanks... 

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