Analysis of Retrofit SCR System for Small-Sized Ship Diesel Engines Using Numerical Methods

Tier III is being implemented to regulate the nitrogen oxides (NOx) emitted from ships, and selective catalytic reduction (SCR) systems are installed in ships to comply with this regulation. However, it is difficult to apply an SCR system to small or remodeled ships, because the engine room has limited space. Moreover, an SCR system should be installed in the consideration of the back-pressure of the engine exhaust gas, and the pressure should be less than the allowable back-pressure (less than 150 mmH₂O) downstream of the turbocharger. The purpose of this study was to identify the design parameters to install a retrofitted SCR system in the limited space inside the engine room. A performance test was performed to develop the retrofitted SCR system applicable to small and size ships. A CFD analysis was performed by varying the exhaust gas velocity (6–12 m/s) and the porosity of honeycomb (60–90%) after a verification of CFD analysis and experiment results, obtained from an actual SCR system in a small-size ship. It was confirmed that when the exhaust gas velocity decreased, the back-pressure downstream of the turbocharger was reduced. In addition, the pressure variation was minimal when the catalyst porosity was 70% or more at the constant 8 m/s gas velocity. The results of the current study can guide the design of the retrofitted SCR system in small-size ship that has limited engine room space.