Shipping is a relatively clean transport method with low emissions per ton-mile compared with road transport. However, harmful emissions emitted in coastal areas are a concern, as these affect local air quality and health. To reduce sulphur oxide (SOX ) emissions, the International Maritime Organization (IMO) implemented a global sulphur cap of 0.5 wt% and the 0.1 wt% limit in emission control areas (ECAs). Ship owners can opt for either low sulphur fuels or wet scrubber systems. Wet scrubber systems are a reliable method for reducing SOX emissions with capture rates of up to 98%. These systems may use seawater alkalinity or caustic soda (e.g. closed-loop systems) to neutralise the SOX emissions. However, the dynamic loading of engines can cause large fluctuations in the exhaust flow conditions, and it is unknown how these affect the effectiveness of the scrubber. This study explores the impact of dynamic loads on the SOX removal efficiency of closed-loop wet scrubbers. A dynamic model of a closed-loop wet scrubber utilising fresh water and caustic soda is developed and verified using publicly available data. The model applies the two-film theory to model the gas-liquid interface. Billet and Schultes liquid hold-up theory is used to model the liquid film thickness in the packed bed. Maintaining scrubber efficiency with large load fluctuations or high-frequency fluctuations requires an increased liquid flow. The scrubber control system used a set-point of 75% of the equivalent compliance limit to ensure compliance with the 0.1% ECA limit during load fluctuations. The model and results can be used to develop a more advanced control system for improved scrubber operation and integration with a selective catalytic reduction (SCR) system to demonstrate compliance with the IMO NOX Tier III limit when using high-sulphur heavy fuel oil (HFO).

Dredging operations result in severe load changes, and the transient capability of natural gas-fuelled dual fuel engines in gas mode is not sufficient to cope with them. An energy storage system may compensate the difference depending on the system size and control strategy. Previously developed component models are adapted and expanded with natural gas combustion and a kinetic energy storage system. The dual fuel engine's performance and transient behaviour in gas mode is validated with data from a factory acceptance test. Both the effect of increasing the available engine power and increasing the power of the energy storage system are investigated. The simulation results show the trade-off between the transient capability and lower harmful emissions on one side, and the operational costs and system efficiency on the other side. Increasing the available engine power, enhances the drive system's transient capability by reducing load change experienced by each engine, but it also increases the fuel energy consumption and global warming potential. A kinetic energy storage system increases the average engine load and fuel energy consumption slightly. The higher engine load results in a lower methane slip and does, therefore, not result in a net increase of the global warming potential.