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170 New Trends in Coal Conversion

6.4 Concluding remarks

Clean coal technologies have been developed and deployed to reduce the environ-
mental impact of coal utilization. The focus has been on mainly reducing emissions
of particulates and sulfur and nitrogen compounds. Environmental concerns will prob-
ably be the most significant influence on future coal use in the world, and requirements
to reduce the environmental and health risks of flue gas from coal technology are ex-
pected to grow more stringent. This issue will determine the acceptability of coal-
based systems. As a result of this, recently, the focus on clean coal technologies has
moved to the development of low and near-zero GHG emission technologies.
Clean coal technologies comprise a variety of pollutant abatement techniques,
which have emerged in recent decades in response to the environmental problems
of coal and other fossil fuel burning.
• Increased efficiency of plant in supercritical and ultrasupercritical cycles (up to 46% thermal
efficiency now and 50% expected in future) means that newer plants produce less emission
per kWh than older ones.
• Coal cleaning by “washing” has been standard practice to reduce emissions of ash and sulfur
dioxide.
• Electrostatic precipitators and FFs can remove more than 99.9% of the fly ash from the flue
gases.
• Flue gas desulfuration reduces the emissions of sulfur dioxide to the atmosphere by up to
97%, the task depending on the level of sulfur in the coal and the extent of the reduction.
• Low-NO x burners allow coal-fired plants to reduce nitrogen oxide emissions by up to 40%.
Coupled with reburning techniques NO x can be reduced to 70% and selective catalytic reduc-
tion can clean up 90% of NO x emissions.
• Advanced technologies such as IGCC enable higher thermal efficiencies still up to 50% in
the future.
New challenges in PCC are related to the improvement of pollutant removal effi-
ciencies and cost reductions as well as the integration of gas cleaning trains for
CCS-ready coal-fired power plants.
In coal gasification, new challenges for IGCC are focused on hot cleaning tech-
niques and the development of new dry sorbents and catal-sorbents.

References

Amick, P., 2017. Integrated Gasification Combined Cycle (IGCC) Technologies. Chapter 18.
Case Study: Wabash River Coal Gasification Repowering Project, USA. Elsevier Ltd.,
ISBN 9780081001851, pp. 699e714. https://doi.org/10.1016/B978-0-08-100167-7.
00017-2
Annamalai, K., Puri, I.K., 2007. Combustion Science and Engineering. CRC Press, Taylor &
Francis Group, 775 pp.
Atsonios, K., Panopoulos, K., Grammelis, P., Kakaras, E., 2016. Exergetic comparison of CO 2
capture techniques from solid fossil fuel power plants. International Journal of Greenhouse
Gas Control 45, 106e117.