NOx Abatement Technique for Marine Applications - Improved SCR Systems

Licentiate thesis, 2011

Growing awareness of the environmental implications of emissions of nitrogen oxides (NOX), such as eutrophication and acidification on land and at sea, has contributed to the development of more stringent international NOx legislations within the framework of IMO, with the most stringent legislation, Tier III, representing a NOx reduction of approximately 80% compared with today’s engines. Several NOx abatement technologies are available on the market, the most effective of which may be Selective Catalytic Reduction (SCR). Little research has been conducted into marine SCR however. The NOx emissions from the international sea transport in the EU are projected to increase by 67% between 2000 and 2020, thereby exceeding the total of all land-based sources in the EU-25 by 2020 unless further action is taken. It has also been suggested that approximately 15% of all anthropogenic NOx emissions originates from vessels, and, combined with this, about 70% of all emissions take place less than 400 km from land, which may indicate that NOx emissions from vessels are important. Hence, the purpose of this thesis was to investigate and present certain parameters and aspects that may need to be considered in the pursuit of installing and successfully operating a urea-SCR system for marine applications with high overall NOx reduction efficiency. The thesis therefore considers two tracks: catalytic flow reactor experiments and human-machine aspects of practical experiences of SCR installations. As a final conclusion of this thesis, it may be argued that SCR is a highly efficient NOx abatement technology. There are some risks of different types of deactivation, however, of which the specific deactivation by the formation of ammonia sulfates may, to a certain extent, be avoided by careful design and operation of SCR, e.g. monitoring exhaust gas temperature, exhaust gas flow and sulfur concentrations. The overall efficiency of the marine SCR systems may never reach its full potential, however, if the crew members and managers are not provided with appropriate and sufficient knowledge of how the system works and what the prerequisites are to achieve successful SCR operation, i.e. the investigation of technical issues is a necessity but not necessarily sufficient for the safe, efficient and sustainable operation of SCR. Suggestions for further work may include flow reactor experiments to investigate the potential effects of different types of marine urea and marine fuels.