A preliminary study of a multifunctional DOC/Wet-scrubber capable to reduce both chemical and acoustic emissions in marine field

The reduction of ship emissions (i.e., Nitrogen Oxides – NOx, Sulfur Oxides – SOx and Particulate Matter PM) are of paramount importance particularly when shipping in Emission Control Areas (ECAs) where restrictive limits on emissions are imposed by the International Maritime Organization (IMO). In such ECAs, which starting from 2025 will also include Mediterranean Sea, the use of Ultra Low Sulfur Fuel Oil (ULSFO – sulfur content ≤ 0.1 wt%) or, alternatively, an emission-equivalent Exhaust Gas Cleaning System (EGCS) is mandatory. The price of ULSFO is about twice that of the ordinary Heavy Fuel Oil, which heavily affects marine transport economics. Consequently, several EGCS concepts have been studied for the abatement of NOx, SOx and PM, yet they have big dimensions which preclude their installation on already existing ships and, therefore, making necessary the re-design of the whole propulsion system. In the presented study, the use of a Diesel Oxidation Catalyst (DOC) in series with a closed loop scrubber to reduce NOx, SOx, PM and acoustic emissions is studied with the aim to design a compact exhaust line, with multifunctional performances, that allow to be compliant with the IMO’s regulations. The role of the DOC is that of oxidizing the emitted NO to improve the solubility of the NOx species in the scrubber, besides hydrocarbons and PM abatement. It is shown that the oxidation activity and stability of the Pt-based catalysts can be significantly improved by doping with acidic oxides in comparison to a conventional Pt/Al2O3 catalyst. This allows to design a compact EGCS which, in addition to the chemical aspects, incorporates modification aimed at minimizing acoustic emissions as well, acting as a silencer. Preliminary results assessing the validity of the integrate system on a full engine-EGSC mockup are reported in the paper.