Dust collection performance curves

Figure 17-46 shows such a performance curve for the collection of coal fly ash by a pilot-plant venturi scrubber (Raben "Use of Scrubbers for Control of Emissions from Power Boilers, United States-U.S.S.R. Symposium on Control of Fine-Particulate Emissions from Industrial Sources, San Francisco, 1974). The scatter in the data reflects not merely experimental errors but actual variations in the particle-size characteristics of the dust. Because the characteristics of an industrial dust vary with time, the scrubber performance curve necessarily must represent an average material, and the scatter in the data is frequently greater than is shown in Fig. 17-46. For best definition, the curve should cover as wide a range of contacting power as possible. Obtaining the data thus requires pilot-plant equipment with the flexibility to operate over a wide range of conditions. Because scrubber performance is not greatly affected by the size of the unit, it is feasible to conduct the tests with a unit handling no more than 170 m3/h (100 ftVmin) of gas.

The proportion of each particle size fraction which is precipitated in a cyclone of particular shape and rating is called the fractional dust collection efficiency and is plotted as a percentage against the particle size diameter (in microns). The curve thus obtained is called a separation curve. It is an important criterion for comparing different cyclones with one another. Table6 indicates, by way of example, the overall collecting performance of a cyclone for dust with known particle size distribution. 

Example 7.1 In a test of the performance of a cyclone, a dust-laden gas with the particle mass flow rate of 600 kg/h is used. Given that the dust escape rate is 30 kg/h, what is the overall collection efficiency Plot the fractional efficiency curve to identify the cut-off size of this cyclone. The results of particle size analysis (by weight percentage [wt%]) at the inlet and outlet of the cyclone are given in Table E7.1. 

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