Wet Scrubbers for Emission Control - Mathematics and Statistics for the Environment - page 535

dust dust

dust

−

in out

η required =

in

where
dust in = Dust concentration leading into the Venturi.
dust out = Dust concentration leaving the Venturi.

Thus,

dust dust

dust

− 1100 kg/hr 10 kg/hr

1100 kg/hr

−

in out

η required = = = 0 991 . = 99 1 . %

in

The estimated efficiency of the Venturi scrubber is slightly higher than the required efficiency.

18.2.5.3 Cut Power Method
The cut power method is an empirical correlation used to predict the collection efficiency of a scrub-
ber. In this method, penetration is a function of the cut diameter of the particles to be collected by
the scrubber. Recall that the cut diameter is the diameter of the particles that are collected by the
scrubber with at least 50% efficiency. Because scrubbers have limits to the size of particles they can
collect, knowledge of the cut diameter is useful in evaluating the scrubbing system (USEPA, 1984c,
p. 9-11). In the cut power method, penetration is a function of the particle diameter and is given as

P t = exp[- A cut d p ( B cut )] (18.15)

where
P t = Penetration.
A cut = Parameter characterizing the particle size distribution.
d p = Aerodynamic diameter of the particle.
B cut = Empirically determined constant, depending on the scrubber design.

Penetration, calculated by Equation 18.15, is given for only one particle size ( d p ). To obtain the
overall penetration, the equation can be integrated over the log-normal particle size distribution. By
mathematically integrating P t over a log-normal distribution of particles and by varying the geomet-
ric standard deviation (σ gm ) and the geometric mean particle diameter ( d pg ), the overall penetration
( P t * ) can be obtained.

■ EXAMPLE 18.2
Problem: Given similar conditions used in the example in the infinite throat section, estimate the
cut diameter for a Venturi scrubber. The data below are approximate (USEPA, 1984c, p. 9-12).

Given:
σ gm = Geometric standard deviation = 2.5
d pg = Particle aerodynamic geometric mean diameter = 12.6 µmA
η = Required efficiency = 99.1% or 0.991

Solution : For an efficiency of 99.1%, the overall penetration can be calculated from

P t * = 1 - η = 1 - 0.991 = 0.009