Page 509 - Air Pollution Control Engineering

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Emerging Pollution Control Technologies 481

Table 5
Parameters Affecting the HEPA Filter Efficiency and Lifetime
Parameter Comments
Moisture Moisture will blind the filter. The blinding will increase
the pressure drop across the filter, which will eventually
lead to filter failure because of excessive resistance.
PM As the PM loading increases, the filter life decreases.
Additionally, the change in pressure drop across the filters
will be accelerated. As velocity increases across the filter,
the PM control efficiency decreases. The higher the
pressure drops across the filter, the shorter the filter life.

disadvantages when treating point sources of air pollution for VOC control. Figures 16
and 17 further illustrate the operating ranges (in terms of initial VOC concentrations of
the influent air emission streams), the process removal efficiencies (RE), and relative
cost-effectiveness of both emerging and conventional technologies for point-source
VOC controls. From Tables 6 and 7 and Figs. 16 and 17, it appears that the two emerg-
ing technologies (ICEs and UV process) are excellent for point-source VOC controls.
The RE of both ICEs and UV processes are higher than or equal to the RE of any con-
ventional technologies, within their operating ranges (Fig. 16). The internal combustion
engine technology is cost-effective only when the influent VOC concentration is
extremely high (7000–100000+ ppmv), whereas the UV process is cost-effective only
when the influent VOC concentration is in the moderate narrow range of 100–1000
ppmv (Fig. 17).
10.2.2. PM and Heavy Metal Removal
Table 7 compares a selected emerging technology (HEPA filters) with conventional
technologies (fabric filtration, electrostatic precipitation, and scrubbing/absorption) in
terms of their advantages and disadvantages when treating point sources of air pollution
for PM control.
A further comparison between the same emerging technology (HEPA filters) and the
same conventional technologies (fabric filtration, electrostatic precipitation, and scrub-
bing/absorption) in terms of their RE for point-source PM controls is presented in Table
8. The RE of HEPA filters for removal of PM (10 µm size) is greater than any other
conventional technologies under evaluation. However, HEPA filters cannot remove acid
from polluted gas streams (see Table 8).
The estimated RE for controlling toxic metals by various technologies is introduced
in Table 9. HEPA filters are not recommended for toxic metals control because of lack
of an established RE.

10.3. Evaluation of Fuel-Cell-Powered Vehicles for Air Emission Reduction
The US Department of Energy introduces how a fuel cell functions. In an electro-
chemical reaction with oxygen, hydrogen generates electricity and water inside a fuel
cell. Electrical energy is generated by the fuel cell in three steps: (1) Hydrogen is fed