In line with the above discussed technology transfer, use of
scrubbers for SOx removal and urea-SCR for NOx removal has also
been addressed in the marine sector [15,16]. However, it must be
considered that to achieve IMO TIER III NOx target (Fig. 1), use of
urea-SCR technology is considered necessary [10,17]. This adds
complexity to the problem: both scrubber and urea-SCR reaction
should be placed at the engine outlet. Use of scrubbers for desulphurisation
is an assessed process with efficiencies over 90% [18,19].
However, use of urea-SCR for NOx abatement in exhausts with high
content (500–1000 ppm) of SOx is prone to difficulties due, inter
alia, to oxidation of SO2 and formation of ammonium sulphates,
particularly below 300 C [7]. An exception, cited with pleasure in
this dedicated volume, is the Haldor Topsøe ‘‘Sulphur and nitrogen
removal – SNOX™’’ process designed for stationary plants, which,
besides simultaneously removing all the pollutants, transforms
waste into a valuable product, that is sulphuric acid [20].