Origin of NOx emission from ships inside major bays in Japan

Abstract

The amount of NOx emission from ships inside the major bays in Japan, i.e., Tokyo Bay, Osaka Bay and Ise Bay, are analyzed and the strategies in the reduction of NOx emission are discussed. Normally each ship has three sources of NOx emission, i.e., main engine, auxiliary engine and auxiliary boiler. Since wide range of ships are in operation in these bays, each of the ships are categorized in 4 ranks by the size of each ships. The amounts of NOx emission from each source and each rank of ships are estimated separately and compared with each other to understand the origin of NOx emission inside these bays. From the systematic calculations, it was explored that more than half of the amount of NOx was emitted from the auxiliary engines during the anchorage period. Especially the influence of the NOx emission from auxiliary engines of larger sized ships of rank 4, the largest category, is the largest. This should be mainly due to the longer anchorage and cargo work time necessary for handling the larger amount of cargo of larger sized ships. On the other hand the NOx emission from main engines is mainly emitted from the small sized ships of rank 1. Same tendencies are obtained through the NOx emission calculations of three major bays in Japan. From these results, it is suggested that the usage of land electricity in larger sized ships is effective in the reduction of NOx emission in major bays.