Wet Scrubbers for Emission Control - Mathematics and Statistics for the Environment - page 532

where
N Reo = Reynolds number for the liquid droplet at the throat inlet (dimensionless).
v gt = Gas velocity in the throat (cm/s).
d d = Droplet diameter (cm).
v g = Gas kinematic viscosity (cm 2 /s).

d pg = d ps ( C f × p p ) 0.5 (18.13)

where
d pg = Particle aerodynamic geometric mean diameter (µmA, where A has units of (g/cm 3 ) 0.5 ).
d ps = Particle physical or Stokes' diameter (µm).
C f = Cunningham slip correction factor (dimensionless).
p p = Particle density (g/cm 3 ).

The Cunningham slip correction factor ( C f ) can be found by solving Equation 18.14:

( )

− 4

62110 . × T

C =+ 1 (18.14)

f

d

pg

where
C f = Cunningham slip correction factor (dimensionless).
T = Absolute temperature (K).
d ps = Particle physical or Stokes' diameter (µm).

Example 18.1 illustrates how to use the infinite throat model to predict the performance of a
Venturi scrubber. When using the equations given in the model, make sure that the units for each
equation are consistent.

■ EXAMPLE 18.1
Problem: Cheeps Disposal, Inc., is planning to install a hazardous-waste incinerator that will burn
both liquid and solid waste materials. The exhaust gas from the incinerator will pass through a
quench spray and then into a Venturi scrubber and finally though a packed bed scrubber. Caustic
will be added to the scrubbing liquor to remove any HCl from the flue gas and to control the pH of
the scrubbing liquor. The uncontrolled particulate emissions leaving the incinerator are estimated
to be 1100 kg/hr (maximum average). The local air pollution regulation states that particulate emis-
sions must not exceed 10 kg/hr. Using the following data, estimate the particulate collection effi-
ciency of the Venturi scrubber (USEPA, 1984c, p. 9-8).

Given:
d ps = Mass-median particle size (physical) = 9.0 µm
σ gm = Geometric standard deviation = 2.5
p p = Particle density = 1.9 g/cm 3
µ g = Gas viscosity = 2.0 × 10 -4 g/cm-s
v g = Gas kinematic viscosity = 0.2 cm 2 /s
p g = Gas density = 1.0 kg/m 3
Q G = Gas flow rate = 15 m 3 /s
v gt = Gas velocity in Venturi throat = 9000 cm/s
T g = Gas temperature (in Venturi) = 80°C
T Tl = Water temperature = 30°C