Individual cyclones

It is worth noting, however, that although failure had occurred on 25% of the individual cyclones, no significant performance mi-... 

The diameters of individual cyclones range from 10 mm to 2.5 m, cut sizes for most solids range from 2 to 250 microns, flow rates (capacities) of single units range from 0.1 to 7200 cubic metres per hour. The operating pressure drops vary from 0.34 to 6 bar, with smaller units usually operated at higher pressures than the large ones. 

It should be pointed out here that the scale-up procedure described here is specifically designed for separation or classification of fine particles. These are the particles predominantly used in the chemical industry and the approach, using dimensionless groups, is in common with the treatment of other unit operations in chemical engineering. The geometrical similarity concerns all internal dimensions of the individual cyclones except the size of the underflow orifice which is regarded here as an operational variable. 

Acceleration of Solids Pressure Drop. The solids entering the gas with the cyclone must be accelerated from a very low gas velocity in the freeboard of the fluidized bed to the inlet gas velocity of the cyclone. This term is generally the largest of the individual cyclone pressure drop terms listed here, and is given by... 

Multi-cyclones occupy less space on plan than multiple cyclones of equal performance. Besides, because of their small diameter the individual cyclones achieve more powerful centrifugal action and thus attain higher efficiencies. In... 

Cyclones in commercial service are often installed in parallel arrays or in series with other cyclones. Under such conditions, it is rarely possible to determine the performance of the individual cyclones. Thus, even after the data is collected, it is often a challenge to interpret it correctly. 

Before closing this discussion we wish to call attention to the fact that the liquid seal at the bottom of each cyclone causes their performance to be rather unaffected by flow imbalances of the type we just observed. This would not be the case had the cyclone underflows not been isolated from one another. In this case, any pressme imbalance that would exist between the cyclone underflows will cause gas to flow down some of the underflow openings and up other underflow openings. This, in turn can lead to a serious degradation of separation performance and is the reason why most multiclone systems do not perform as well as one of its individual cyclones tested in isolation. 

A true multicyclone is not only a parallel arrangement of cyclones, but also one wherein the individual cyclones are housed within a common casing that constitutes the inlet chamber. Furthermore, the dust (or liquid) discharge and the gas outlet pipes also report to their own common outlet plenum and hopper, respectively. Multicyclone systems of the type shown in Figs. 16.2.2 and 16.2.3 are usually comprised of numerous small diameter cyclones (typically under 250 mm in diameter) and this normally leads to excellent separation performance relative to fewer, larger units handling the same total volumetric flow. 

Returning now to the much smaller sized cyclones comprising most multicyclone installations, one of their advantages over an external array of parallel cyclones is that the individual cyclones do not have to be equipped with their own individual inlet pipes or ducts. A disadvantage is that, because the individual cyclones are fully enclosed, it is not normally possible to perform diagnostic or repair work on the individual cyclones while they are in service. On the other hand, it is sometimes possible to repair or patch up an... 

Individual cyclones can handle exceptionally large flow volumes. For the most part assemblies of hydrocyclones are less costly than other types of separator. Also,... 

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