NOx Abatement Technique for Marine Diesel Engines - Improved Marine SCR Systems

Doctoral thesis, 2014

Growing awareness of the environmental implications of nitrogen oxide (NOX) emissions, 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 the International Maritime Organization (IMO). The most stringent IMO legislation, i.e., Tier III, represents an NOX reduction of approximately 80% compared with today’s engines, but only applies in certain emission control areas (ECAs). Several NOX abatement technologies are available on the market, of which one of the most effective technologies is selective catalytic reduction (SCR). However, little research has been conducted into marine SCR. Therefore, the objective of this thesis is to study fundamental aspects of vanadium based urea-SCR for marine applications and to assess the applicability of the SCR technique for shipping. NOX emissions from international sea transport in the EU are projected to increase by 67% between 2000 and 2020, and could thereby exceed the total of all land-based sources in the EU-27 by 2020 unless further action is taken. It has also been suggested that approximately 15% of all global anthropogenic NOX emissions originate from vessels. Moreover, approximately 70% of all emissions occur within 400 km of land, which may indicate that NOX emissions from vessels are important. Hence, in an attempt to fulfil the objective of this thesis a multi-disciplinary approach was considered to be an appropriate strategy, which comprises four interconnected research tracks: synthetic gas flow reactor experiments, human-machine aspects of SCR installations in practice, compilation of exhaust gas measurement reports from existing marine SCR installations in combination with an approach to potential ECA regulation compliance strategies and the design and experimental validation of a marine part flow urea-SCR system. As a final conclusion of this thesis, it may be concluded that the marine SCR system has reached a certain technical maturity and is a highly efficient NOX abatement technology that can meet Tier III and potentially even more stringent NOX regulations in the future. However, certain risks are related to different types of deactivation. In particular, the specific deactivation by the formation of ammonia sulfates and ammonia nitrates may be avoided to a certain extent by the careful design and operation of the SCR system, e.g., by monitoring exhaust gas temperatures, space velocity and sulfur concentrations. However, there may also be other types of catalytic deactivation due to possible additives and/or impurities in marine fuels, lube oils and different urea water solutions. Therefore, conducting complementary deactivation studies in a synthetic gas flow reactor and a part flow urea-SCR may prove valuable. However, the overall performance of marine SCR systems may never reach its full potential if crew members and managers are not provided with appropriate and sufficient knowledge of how the system works and what the prerequisites are for achieving successful SCR operation, i.e., the investigation of technical issues is a necessity but it is not necessarily sufficient to obtain safe, efficient and sustainable operation of marine SCR systems.