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218 Lawrence K. Wang et al.

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where D is the density (lb/ft ), P is the pressure of the emission stream (atm), M is the
molecular weight of the specific pollutant gas (lb/lb-mol), R is the gas constant (0.7302
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atm-ft /lb-mol °R), and T is the temperature of the gas (°R).
2.5.4. Venturi Scrubber Operation and Maintenance
The performance of a Venturi scrubber, when plotted, normally yields a logarithmic
curve. Such a curve relates collection efficiency in the Venturi scrubber to pressure drop
and particle size (3,19–21,23). Standard industry practice has been to plot pressure
drop versus mean particle diameter (D ) for a specific Venturi size. An example of such
p
a plot is given in Fig. 5. A Venturi vendor provided these data for a given removal effi-
ciency at various pressure drops. With D data from a polluted airstream, one can estimate
p
the removal efficiency possible for particulate matter from the airstream at various
pressure drops across this Venturi scrubber. Figure 5 is typical of data supplied by
Venturi scrubber system OEMs. Note that Fig. 5 is specific to one such OEM.
Also, because data are widely available from Venturi scrubber system OEM firms, it
is used for most design purposes for Venturi scrubber projects. A fundamental under-
standing of the design equations presented here assists in understanding the design
process for a Venturi scrubber; such equations, however, are generally not used by
environmental engineers on a daily basis. It is important to note that the removal
efficiency reported by OEM firms is a weighted average for each particle size in a
known particle size distribution. The actual particle size distribution being treated in a
polluted airstream may be, and most likely will be, different than the particle size dis-
tribution used by the Venturi scrubber OEM to generate Fig. 5 data. The D of the
p
design (OEM) and the actual (field air pollution project) particle size distributions
may also be the same or very similar, whereas the two particle size distributions are
actually quite different. Thus, the removal efficiencies reported in Fig. 5 should be taken
as approximations only.
Normal industry practice has been to use Venturi scrubbers that operate at pressure loss
from 10 up to 80 in. of water. Above pressure loss of 80 in. of water, it has generally been
found that particulate matter will not be removed efficiently within the Venturi scrubber.
A critical maintenance issue with any Venturi scrubber is that the spray nozzles
where the liquid (normally water) is injected into the scrubber must be kept open.
Routine inspection of nozzle openings and throat is good standard practice for any
Venturi scrubber system. These measures, combined with normal pump maintenance,
will help prevent both equipment failures as well as emission violations of a Venturi
scrubber system (24,25).
Pressure drops from a variety of air pollution control applications using the Venturi
principle are listed in Table 8 (9,18). These data are presented as typical of general
industry applications. Specific applications, therefore, may have a pressure drop outside
of this data range (9,18).
The capital expense of a Venturi scrubber system is straightforward. The system will
have an initial capital expense at time of purchase. Additionally, there will be direct and
indirect costs of site erection and commissioning of the scrubber system. Table 9 presents
capital cost factors for typical Venturi scrubber systems (26,27).