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NUCLEAR TECHNOLOGIES AND METHODS 111
PROCESS ENGINEERING
SULPHUR ISOTOPE RATIO δ 34 S
IN THE DESULPHURIZATION PROCESSES
Małgorzata Derda, Andrzej G. Chmielewski, Janusz Licki
Major environmental impact of atmospheric sulphur
compounds is related to rain acidity, human health,
climate, visibility and material corrosion. Very important
is the evaluation of economic responsibility
for emitted pollution. Therefore, scientists look
for a suitable marker which could be used as environmental
tracer.
A literature review shows that there are a few
data on sulphur isotope ratio in Polish coals and
on fractionation of sulphur isotopes in process of
coal combustion. Results of preliminary investigations
concerning characteristics of the Polish
coals are presented [1].
On the basis of this study an investigation was
performed for desulphurization process in the
Electric Power Station (EPS) Bełchatów [2]. The
study concluded that the phenomena which occur
during desulphurization process play a major role
in the change of sulphur isotopic composition in
the outlet gases. This confirms that during the desulphurization
process, a fractionation of sulphur
isotopes occurs. The sulphur in the outlet gases is
depleted in the heavy isotope and the by-product
from this process is enriched in the isotope 34 S
(fractionation factor is lower than 1). This fractionation
may suggest that the main process runs
in heterogenic conditions (gas-liquid). Therefore,
most likely the equilibrium and kinetic processes
are responsible for the sulphur isotope fractionation.
The condensed phase (liquid, solid) is enriched
in the heavier isotope 34 S [3].
The desulphurization process was tested at an
electron beam/ammonia experimental installation.
Sulphur dioxide from the outlet gas was absorbed
in hydrogen peroxide solution:
HO 2
SO + H O ⎯⎯→H SO ⎯⎯⎯→ H SO
2(gas) 2 2 3 2 4
The sulphate ions produced in this way were quantitatively
recovered as barium sulphate by precipitation
with barium chloride solution [4].
The product is a mixture of sulphates and nitrogen
from ammonium with fly ash. This mixture
has been formed as a consequence of irradiation
of outlet gases. The product is removed as by-product
in the desulphurization process. The obtained
results are presented in Table.
Table. Sylphate sulphur in flue gas and the product from
desulphurization process [‰].
The sulphur from the outlet gas was also absorbed
to determine sulphur isotope fractionation
in the desulphurization process. The sulphates
from outlet gases are enriched in the light isotope
32
S in comparison to coal which is the fuel in the
studied power plants. However, in the case of solid
products from the investigated process (gypsum
and ammonium sulphate), 34 S is enriched in this
phase in both desulphurization processes. This
method may also be applied to investigate different
air pollution control technologies, for example,
the method can be used to establish further fate
of the by-products e.g. elution of gypsum from landfill
waste, monitoring of water and investigation
of ash leaching.
However, introduction of desulphurization
units has changed the isotopic ratio of sulphur in
the outlet gas streams. Normally, sulphur dioxide
retained in this flue gas is depleted in the heavy
isotope 34. These phenomena should be taken into
account during the preparation of sulphur balance
for the country and region.
References
[1]. Chmielewski A.G., Wierzchnicki R., Derda M., Mikołajczuk
A.: Nukleonika, 47, 67-68 (2002).
[2]. Derda M., Chmielewski A.G.: Determination of sulfur
isotope ratio in coal combustion process. In: INCT
Annual Report 2004. Institute of Nuclear Chemistry
and Technology, Warszawa 2005, pp.120-121.
[3]. Chmielewski A.G., Wierzchnicki R., Mikołajczuk A.,
Derda M.: Nukleonika, 47, 69-70 (2002).
[4]. Hałas S., Wolacewicz W.D.: Anal. Chem., 53, 686
(1981).