Investigation of selective catalytic reduction (SCR) systems used in marine diesel engines in terms of design and performance

Restrictions have been introduced by the international maritime organization (IMO) to reduce NOX emissions from ships. Selective Catalytic Reduction (SCR) systems are one of the most effective methods used to meet these restrictions. In this study, SCR system design and performance parameters for two different marine diesel engines, two-stroke and four-stroke, were investigated numerically. Numerical analysis studies were carried out with the finite volume method, steady-state, and the boundary conditions were verified with the literature data. Parametric studies were carried out at 85% load condition to determine the optimum values of SCR length, SCR system diameter, catalyst activation energy, and mixing chamber length and location. SCR system performance was evaluated for 1200 mm SCR length, 760 mm SCR system diameter and 4000 mm mixing chamber length, which are the most suitable design parameters obtained. The amount of Urea-Water Solution (UWS), which meets the emission restrictions determined by IMO for variable engine loads, and the NOX reduction performance and ammonia slip for these amounts were determined. In addition, the effect of SCR Bypass Valve (RBV) opening on system NOX, ammonia slip and pressure drop against any NOX emission restriction was evaluated. Parametric studies were carried out for variable exhaust flow rates and inlet NOX rates for the same flow rate throughout the SCR system. As a result of the study, the UWS injection amounts, which meet the IMO Tier III limitation for each load condition, were determined as 103 l/h, 91 l/h, 85 l/h, 62 l/h and 38 l/h, respectively. Both NOX emissions and ammonia slip increase exponentially at rates greater than 20% RBV opening ratio