Cyclone sizing

When consistent units are used, the particle size will either be in meters or feet. The equation contains effects of cyclone size, velocity, viscosity, and density of solids. In practice, a design curve as given in Fig. 17-39 uses Dptk the size at which 50 percent of sohds of a given size are collected by the cyclone. The material entering the cyclone is divided into fractional sizes, and the collecdion efficiency for each size is determined. The total efficiency of coUection is the sum of the col-lecdion efficiencies of the cuts. 

Does the following calculations for a gas or air cyclone sizing, pressure drop, and fractional and overall efficiency. 

For a specific size of particle to be separated by the cyclone, a first rough estimate of the cyclone size may be obtained by estimating the particle drift vekx -ity in the cyclone. A large cyclone may be used if the particle drift velocity is large. If n is the number of the revolutions that the particle travels with the fluid in the cylindrical part of the cyclone, then the smallest particle of diameter d that can be separated by the cyclone may be approximated by (see Baturin )... 

The friction loss through cyclones may range from 1 to 20 inlet-velocity heads, depending on its geometric proportions. For a cyclone of specific geometric proportions, Fev and Apev. are essentially constant and independent of the actual cyclone size. 

The collection efficiency usually depends on the shape of the cyclone, size and density of the particles, and incoming tangential velocity. The collection efficiency of a... 

The effectiveness of a cyclone separator depends upon its size and the size of particles to be removed. The smaller the outer shell the more effective the separation conversely, the smaller the particle the greater the separating force required to move it from the air stream to the outer wall. The importance of cyclone size is evident from a consideration of the separation factor discussed in Chapter 2, Eq (2-46). If denotes the separation factor we have... 

The performance of a cyclone is often specified in terms of a cut size, which is the size of the particle collected with 50% efficiency. The cut size depends on the gas and particle properties, the cyclone size, and the operating conditions. It may be calculated from... 

Dry cyclone size based on an inlet gas velocity based on the particle loading for particle loadings of < 7 g/m use inlet gas velocity of 11 to 23 m/s to size inlet nozzle and then scale configuration from this dimension. 

The fonnulae proposed by Lynch et al. and Plitt have been applied to other cyclone sizes and slurries (see, for example, Aplyng et al. ), and neither model was found to be entirely successful it was necessary to change the constants to fit the predicted results to the experimental data. 

Similar design charts exist for some commercial cyclones, but as only a limited range of cyclone sizes are available from a given manufacturer, such charts are not continuous but merely show areas of cut size/capacity covered by the range of cyclone diameters. 

The conventional hydrocyclone design procedures have been based on a rather simplistic view of the hydrocyclone function the cyclone size is selected from the capacity and available pressure drop requirements, with the cut size not being a free choice but fixed by the former two requirements (reduction in cut size can only be achieved by using a greater number of smaller cyclones in parallel). This approach ignores completely the effect of the underflow orifice size on the cut size, and also on the solids concentration in the imderflow. The procedure based on the model in section 6.6.6 centres... 

This expression gives rise to the grade efficiency curve shown in Figure 9.6 for an a 5o cut size of 5gm. Very little is known how the shape of the grade efficiency curve is affected by operating pressure drop, cyclone size or design, and feed solids concentration. 

TABLE 7-6 Typical Cyclone Size versus Particle Cut... 

Fig. 1.3.2. A few examples of the variety of cyclone sizes and shapes used in commercial practice. Top photo courtesy of Ducon Technologies Inc., left photo courtesy of Fisher-Klostermann Inc., right photo courtesy of EGS Systems Inc.

Additionally, Eqs. (4.3.18) and (4.3.19) indicate that the Euler number and, therefore, the pressure drop, are independent of the cyclone size for geometrically similar cyclones or swirl tubes if the inlet velocity is kept constant. We can thus gain in efficiency without increasing pressme drop by splitting up the solid-laden process stream over two or more cyclones or swirl tubes and operating them in parallel. 

Choose the cyclone size giving the required cut size... 

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