Environmental Engineering Reference
In-Depth Information
(1 to 2 microns) is lower than for larger particles. Concern now focuses on the health
effects of these smaller particles, since they may be enriched with more toxic substances,
travel over long distances, and penetrate deeper into the human respiratory system. Also
the ESP process becomes less efi cient when low sulphur coal is combusted. A second con-
trol mechanism is the use of bag i lters which are particularly efi cient in collecting smaller
particles. However, bag i lters are more difi cult to operate, and more costly to maintain
than ESP. Removed particulates, either by ESP or bag i lters, are termed l y ash. By its
very nature, l y ash comprises i ne particles.
Emissions of organic compounds as polycyclic aromatic hydrocarbons (PAHs), which
have carcinogenic properties, have been signii cantly reduced by the increased use of large
coal combustors with highly efi cient l ue gas treatment controls.
Another environmental concern with coal combustion is the presence of trace metals in
coal. Trace metals are preferentially concentrated onto smaller ash particulates, the frac-
tion of particulate emissions, which are the most difi cult to arrest by control technology.
The quantities of trace metals emitted from power plants into the atmosphere depend on
the metal concentrations in the coal, boiler type, and installed l ue gas emission control
systems. Of particular interest are emissions of mercury from coal combustion. Coal com-
bustion has contributed a large portion of the mercury present in the atmosphere today.
While the natural component of the total atmospheric burden is difi cult to estimate, a
recent study (Munthe et al. 2001) suggests that anthropogenic activities have increased the
overall levels of mercury in the atmosphere by roughly a factor of three, some 70% of it
contributed by emissions from stationary combustion of fossil fuels, especially coal, and the
incineration of waste materials (UNEP 2002). As combustion of fossil fuels is increasing
in order to meet the growing energy demands of both developing and developed nations,
mercury emissions can be expected to increase. Today's l ue gas control technologies may
provide some level of mercury control, but when viewed at the global level, these controls
result in only a small reduction of total mercury emissions.
Trace metals are preferentially
concentrated onto smaller ash
particulates, the fraction of
particulate emissions, which are
the most diffi cult to arrest by
control technology.
CASE 13.11
Monash Energy Coal-to-Liquids and Carbon Capture and
Storage Project, Australia (Anglo Coal)
Anglo Coal's subsidiary Monash Energy has plans to convert
brown coal mined in Australia's Latrobe Valley to ultra-
clean diesel fuel. The process achieves low emissions to the
atmosphere by separating a concentrated stream of carbon
dioxide for transport by pipeline to injection wells for
injection and secure storage in deep underground geological
formations. The Monash Energy vision involves: a brown coal
mine; a coal drying and gasifi cation plant; a synthesis gas-
based, hydrogen production plant; a fuel synthesis plant for
converting gas to liquids; and an integrated waste heat and
off-gas power plant. The plant is planned to produce more
than 60,000 barrels per day of liquids - mainly ultra-clean
diesel fuel. The project, currently in its pre-feasibility stage,
is also acting as a catalyst for the development of
local carbon capture and storage infrastructure. Monash
Energy is investigating the technical and commercial
potential of the adjacent offshore section of the
Gippsland Basin as a site for the storage of carbon
dioxide. The project includes a community engagement
component to ensure the public has the necessary
confi dence in the technologies, and appreciates the
conceptual link between a carbon-constrained future
and the requirement for implementation of carbon
capture and storage.
Source: OECD/IEA 2006
 
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