Efficiency of cyclones

The collection efficiency of cyclones varies as a function of particle size and cyclone design. Cyclone efficiency generally increases with (1) particle size and/or density, (2) inlet duct velocity, (3) cyclone body length, (4) number of gas revolutions in the cyclone, (5) ratio of cyclone body diameter to gas exit diameter, (6) dust loading, and (7) smoothness of the cyclone inner wall. Cyclone efficiency will decrease with increases in (1) gas viscosity, (2) body diameter, (3) gas exit diameter, (4) gas inlet duct area, and (5) gas density. A common factor contributing to decreased control efficiencies in cyclones is leakage of air into the dust outlet (EPA, 1998). 

A series of theoretical analyses of the fluid and particle collection efficiency of cyclones were performed in the 1970s by Bloor and Ingham " and they have been found to be in good agreement with the experimental data. 

Dietz, P.W., 1981. Collection efficiency of cyclone separators. American Institution of Chemical Engineers Journal, 27(6), 888. 

Hoekstra, A. J., Gas flow field and collection efficiency of cyclone separators , Ph.D. Thesis, Delft University of Technology, Delft, Netherlands (2000). 

Leith, D. and Licht, W. (1972). The Collection Efficiency of Cyclone Type Particle Collectors A New Theoretical Approach. AlChE. Symp. Ser., 68(126), 196. 

D. Laith and W, Licht, The Collection Efficiency of Cyclone Typa Particle Collectors—A New... 

From the principle of the cyclone function it follows that smaller particles may be separated in cyclones with smaller diameters. The separation efficiency of cyclones depends on a number of factors, the most important of them being defined by the relationship... 

The separation efficiency of cyclones is further dependent on temperature it decreases by 1 to 5% with increasing temperature. This effect is more marked in the case of particles of smaller diameters. 

The theory of particle removal by cyclones is well developed and equipment dimension ratios are well established, making it possible to design cyclones to remove particles of a known size range with reasonable estimates of particle collection efficiency as a function of particle size. However, the efficiency of cyclones is greater for the larger particles. Smaller particles can only be removed with cyclones of small diameter. Pressure drops in cyclones can be substantial and often limit the smallest particle size that can be removed. Multiple cyclones are sometimes used in series or parallel. 

The efficiency of cyclones (or other gas-solids separation devices where applicable) may greatly aflcct the overall process performance. 

As compared to the efficiency of cyclone n° 1, the efficiency of the cyclone n° 2 is poor. This is explained by its axial entry, which provides a tangential entry of 10 m/s for about 700 m3/h instead of 280 m3/h for cell n° 1. Thus, the residence time being shorter, the collection is worse. However for high dust loading, efficiencies of more than 90% were... 

Figure 7.3.16. Comparison between theory and eiqperiment for the second-stage cyclone at Exxon s miniplant (assumed m = 0.7). Reprinted, with permission, from P.W. Dietz, Collection efficiency of cyclones," AlChE]., 27(6), 888(1981). Copyriffit [1981] American Institute of Chemical Engineers (AIChE).

Predicting the separation efficiency of cyclones involves predicting how particles behave in the separation space. In order to do this, we need to know the velocity distribution of the gas. Some researchers have made all-embracing models for both gas flow pattern and separation efficiency others have concentrated on one or the other. We look at the two issues separately here. 

The strong influence of the vortex finder diameter, Dx, on the efficiency of cyclones is not directly evident in the reasoning behind the time-of-flight models. For the Rosin-Rammler-Intelmann model, Zenz (2001) argued that... 

When determining the efficiency of cyclones and swirl tubes, samples can be taken at three positions the inlet, the gas outlet and the dust outlet (see Figure 10.4.1). 

Hoekstra A J 2000 Gas Flow Field and Collection Efficiency of Cyclone Separators PhD thesis Delft University of Technology. 

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