Simulation and economic evaluation of NOx removal in wet scrubbers of low-speed two-stroke vessels using H₂O₂ as a replacement for conventional EGR

NOx is one of the major pollutants present in the exhaust gas of marine diesel engines. Normally, NOx is difficult to remove using scrubbers because NO, which accounts for 90 % of NOx, has very low water solubility. However, if NO is oxidized to other highly soluble nitrogen oxides, the removal efficiency of NOx in a wet scrubber can be greatly improved. In this study, we estimated the efficiency of NOx removal from the exhaust gas of a 50 MW diesel engine using H₂O₂ solution. Then, we compared the results with the removal efficiency of a conventional exhaust gas recirculation (EGR) system. The amount of H₂O₂ consumption varied from 0 to 760.30 kg/h to satisfy emission regulations, depending on the amount of NOx input in the scrubber. In this study, we conducted an economic evaluation of the operation costs of NOx removal using H₂O₂, considering other parameters affecting the operation cost and by comparing the results with that of the conventional EGR system. The results of the economic evaluation show that the use of EGR in ECAs was 2.307 M$/y, which is more economical than that of H₂O₂, and the use of H₂O₂ in non-ECAs was 1.044 M$/y, more economical than that of EGR. If the ECA ratio is less than 31.5%, the operation cost of using H₂O₂ is lower than using EGR.