World Cement - November 2018

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according to local regulations and in accordance with best
practices for dust disposal. Where sorbents are employed
to reduce mercury emissions, these can be shuttled with
filter dust and managed in the same way.
Dust shuttling is most effective when the kiln filter gas
is kept below 140°C. In the raw-mill-on operation, the gas
temperature is typically 90° – 120°C. In raw-mill-off, it may
be significantly higher, which greatly reduces the amount
of adsorption of mercury onto particles.
As described above, dust removal and the use of
sorbents can help lower mercury emissions. However,
other pollution abatement techniques can also assist. For
example, selective catalytic reduction catalysts can also
oxidise elemental mercury in the gas stream; oxidised
mercury is more likely to be collected in the filter system
(and by sorbents). Similarly, wet scrubbers can also help
because, while gaseous elemental mercury is insoluble in
water, gaseous compounds of oxidised mercury are water
soluble and will therefore be absorbed by the aqueous
slurry of a wet scrubber system.
Emissions monitoring
Globally, stricter monitoring requirements are being
imposed on an enormous variety of combustion processes,
including domestic heaters, motor vehicles, shipping,
industrial processes, cement plants, and power plants. As
a consequence, technology providers need to continually
develop their products to ensure that they are able to
meet the required levels of performance. The Volkswagen
scandal highlighted the importance of accurate, trustworthy
monitoring data. In industrial process monitoring, this is
underpinned by approved certification schemes that test
and verify instrument performance (such as the MCERTS
scheme in the UK and TÜV scheme in Germany).
The growing number of parameters that have to
be monitored means that the operators of regulated
processes have to employ multiparameter technologies,
such as FTIR, or purchase a number of analysers to meet
the requirements. However, mercury necessitates a specific
measurement technology: since the emission limits are so
low, it is necessary for this technology to have performance
certification at these levels.
In most regions of the world, emission limits form part
of a regulatory framework that protects the environment.
However, individual countries or states generally have
the opportunity to set specific limits and monitoring
requirements that fit within this framework, while meeting
domestic needs. Individual states may set stricter limits or
individual plants may implement more rigorous monitoring
and abatement technology, in order to demonstrate
good environmental performance. In most cases, this is
undertaken as part of a corporate responsibility strategy, in
response to demands from stakeholders, or in anticipation
of tighter future regulatory requirements.
Mercury emissions regulations
In Europe, the requirements of the Industrial Emissions
Directive (2010/75/EU) for both emissions reduction and
monitoring are provided in sector-specific Best Available
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