Inclined tube settling

Pearce(11) studied the effect of a downward-facing surface by considering an inclined tube as shown in Figure 5.5. Starting with a suspension reaching a level AA, if the sludge line falls to a new level BB, then material will tend to settle out from the whole of the... 

Finally, we make mention of a settling method that employs the fact that particles when settling in an inclined tube do so faster than if the tube is vertical. This effect is termed the Boycott effect, after the physician A.E. Boycott, who in 1920 made this observation in connection with the sedimentation of blood cells in a tube. A picture of batch sedimentation in an inclined channel is shown in Fig. 5.4.8. The clarified liquid, suspension, and sediment are modeled as three distinct regions separated by kinematic shocks, as in vertical settling. 

Fig, 19.19 Methods of achieving high yeast concentrations in continuous fermentation by (a) Centrifuge (b) Settling tank (c) Inclined tube (d) Concentric tubes (e) Riser tube. 

The units are cost-effective for many applications, even though the inclined tubes or plates add appreciably to the equipment cost. These settling units are best for discrete sohds setthng where detention time is not a significant factor. 

Settling-rate data obtained [122] in inclined tubes showed a maximum at an angle of about 50° from the vertical, with typical results being given in Fig. 4-20. The spread in the data is largely due to the difficulty in dis-.cerning an interface due to supemate rushing upward as the thoria settles out. 

Sedimentation of particles follows the principle outlined above [Eq. (1)] in which particles in the Stokes regime of flow have attained terminal settling velocity. In the airways this phenomenon occurs under the influence of gravity. The angle of inclination, t /, of the tube of radius R, on which particles might impact, must be considered in any theoretical assessment of sedimentation [14,19]. Landahl s expression for the probability, S, of deposition by sedimentation took the form ... 

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. 

The bottom of the fluidized bed has an incline of about 15° and carries the bent gas-inlet tubes. These tubes are movable vertically so that their distance from the bottom of the fluidized bed can be varied. With this arrangement, there is a variable settling zone for small metal pieces and stones which occur as impurities of the plastic waste. 

We found that an inclined overflow tube would allow most of the cellulose to settle back so that clarified liquid could be passed through an analytical system. When the dilution rate was too slow to provide sufficient sample, the sample stream plus small amounts of salt (formed from neutralization in the analytical system) could be recycled to the bioreactor. Cellulose was withdrawn separately with a smaller tube that allowed no settling. Independent removal of clarified liquid and cellulose slurry could be controlled to hold a setpoint for cellulose concentration, but we have not used this other than to carry out some manual adjustments. 

Tube and plate settlers have been used for many years as sedimentation units. There are a variety of designs, but basically all of them use submerged inclined surfaces with relatively close spacing that increases the separation surface area in a vessel that is smaller than conventional sedimentation units (Fig. 3.6). The water to be treated is passed between the surfaces at velocities which permit suspended sohds to settle and to coalesce on the lower tube or plate surface. The angle of inclination (45° or more) enables the settled sohds to slide downward into a sludge-concentration compartment located at the bottom of the treatment unit. 

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. 

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