Page 194 - New Trends In Coal Conversion

Technologies for control of sulfur and nitrogen compounds and particulates 157

operating parameter, grinding the limestone finer resulted in further improvements in
the SO 2 removal by up to 2.6% (Wang et al., 2005). With respect to sorbent injection
technology, stream injections after desulfuration by limestone furnace injection have
also been proposed. Adding stream enhances the heterogeneous condensation of
fine particles, and they might be more easily removed from the flue gas using a
high-efficiency demister. This technique also reduces the need for the particulate con-
trol device downstream (Liu et al., 2011).
Most of the research on flue gas desulfuration has been focused on the development
of new adsorbents that can become competitive and marketable in midterm. Adsorbent
properties such as SO 2 affinity, fast kinetics, high specific surface, and elevated resis-
tance to multiple regenerations are desirable (Mathieu et al., 2013). Numerous adsor-
bents have been proposed in the literature. In addition to conventional magnesium and
calcium oxides, oxides supported by either carbonaceous materials or zeolites result in
promising SO x adsorbents (Gaudin et al., 2015; Rodríguez et al., 2011; Yu et al.,
2008).
Efforts have been driven toward the evaluation of simultaneous abatement of SO x
and NO x from flue gas derived from industrial processes. Novel sorbents and catalysts
such as activated coke, the use of microwave reactors with ammonium bicarbonate
combined with zeolites and electric corona discharge have been recently proposed
as promising alternatives for combined SO x and NO x removal (Onda et al., 1997;
Wei et al., 2009).

6.2.3 Particles removal technologies
6.2.3.1 What is particulate matter?

Particulate matter (PM) is a complex mixture of extremely small particles and liquid
droplets that get into the air. Once inhaled, these particles can affect the heart and lungs
and cause serious health effects (EPA, 2017).
The coal industry is facing stringent emission regulations to limit the release of par-
ticulate matter. PM can contain SO 2 ,NO x , or VOC chemical species or their com-
pounds, plus water and biogenic organic species. The chemical composition of PM
varies with coal type, power plant design and location, and also with ambient condi-
tions such as temperature and wind direction (Zhang, 2016). PM is usually classified
by particle size because of the wide variation and complexity of its chemical compo-
sition, which makes it complicated to elaborate a classification of it (Zhang, 2016):
• PM 1 particles less than 1 mm in diameter, known as ultrafine or submicron particles.
• PM 2.5 particles less than 2.5 mm in diameter, fine particles.
• PM 10 particles less than 10 mm in diameter, coarse particles.

6.2.3.2 PM formation
The largest particles, called the coarse particles, are mechanically produced by the
breakup of larger solid particles. These particles can include wind-blown dust from
agricultural processes, uncovered soil, unpaved roads, or mining operations. Traffic