Because of the variety of parameters involved, accurately designing a scrubber for an installation without prior knowledge of scrubber performance at that or a similar installation is difficult. Factors such as air flow rate, scrubbing liquid flow rate, inlet gas temperature, scrubbing liquid temperature, relative humidity, concentration, size and size distribution of the aerosol in the incoming gas, scrubber droplet size and size distribution, and the type of scrubber can confound the design engineer and cloud the design process. Even so, some equations are available to make initial estimates for scrubber design.
Dust size distributions are often represented by log-normal distributions; that is, the particle frequency for a given diameter is distributed according to a normal curve when plotted against the logarithm of the particle diameter. Then, similar to the standard deviation of a normal distribution, the geometric standard deviation of a log-normal distribution measures the spread of the distribution. With a log-normal distribution having a geometric standard deviation of ig, 67% of all particles have diameters between the size ranges dg/ig and igdg. Equation 5.18(6) gives the form of the log-normal distribution:
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