Installation and characteristics of urea-selective catalytic reduction systems for nitrogen oxide reduction in marine diesel engine

Since 1 January 2016, the International Maritime Organization Tier III regulations concerning nitrogen oxides took effect. International Maritime Organization Tier III targets new ships weighing over 400 ton engaged in international sailing, especially those entering and leaving emission control areas. The number of emission control areas, including sulfur emission control areas, is forecasted to increase in Japanese seas and elsewhere; thus, all new ships intended for international sailing purposes must consider appropriate responses to these regulations. Currently, urea-selective catalytic reduction systems are frequently used to satisfy International Maritime Organization Tier III regulations in marine diesel engines, but these decrease ship engine performance due to increased engine exhaust gas pressure. Thus, following a study by Ryu et al., this research compares engine exhaust gas pressures at different engine loads (25%, 30%, 35%, 40%, 45%, and 50%) with the application of a thinner metal catalyst to a selective catalytic reduction reactor; metal catalyst thickness was reduced by 30% or more from the original sheet thickness of 0.1 t. Furthermore, 40% urea was injected into the exhaust gas line to conduct a comparative analysis of nitrogen oxide reduction. By changing the metal catalyst's sheet thickness, nitrogen oxide was reduced by more than 80%, while the engine exhaust gas pressure was lowered by approximately 13%-28%.