Environmental Engineering Reference
In-Depth Information
emissions by stages up to 70 per cent by 2003—
will be met in large part by the installation of
FGD equipment (Park 1991).
Flue gas desulphurization is thus one of the
most common methods of SO
2
removal, in part
because of the high efficiencies possible, but for
other reasons also. Scrubbers are technically
quite simple, and can be added to existing
power plants relatively easily. Retrofitting
existing plants in this way is less expensive than
building entirely new ones, and in some systems
the recovery of sulphuric acid for sale can help
to offset the cost.
None of the FGD systems described works
well to reduce emissions of NO
X
from power
plants. The best results for NO
X
control—up to
80 per cent reduction—have been obtained
using a selective catalytic reduction process
(SCR), which breaks the NO
X
down into the
original N and O, but the price is high. To
retrofit an existing thermal power station would
cost an estimated $10,000 for every 1,000 kg of
NO
X
removed, and maintenance costs would be
substantial because the life of the catalyst is
short (Ellis
et al.
1990). Difficulties also exist
with emission reductions from automobile
exhausts. The development of technology that
can produce a cooler burning internal
combustion engine, or perhaps replace it
completely, may be required before emissions of
NO
X
from that source are reduced significantly
(Park 1987).
It is now technically possible to reduce SO
2
emissions to very low levels. However, as is
common with many environmental problems,
technology is only one of the elements involved.
In many cases, economics and politics have
retarded the implementation of technical solutions
Figure 4.13
Technologies
and trade-offs in
power station
emission control
Source:
From Ridley
(1993)
