Optimizing thermal integration for onboard carbon capture: A techno-economic perspective

Carbon capture onboard ships could play a key role in decarbonizing the shipping sector, particularly if renewable fuels remain scarce in the near future. Various carbon capture technologies exist, with chemical absorption being the most advanced concept in terms of technology readiness. In this approach carbon dioxide is removed from the ship engine’s exhaust gas using a liquid solvent and subsequent solvent regeneration. However, regeneration has a significant heat requirement. Supplying this extra energy on board can lead to high additional fuel consumption, particularly at high carbon capture rates. Fuel consumption can be reduced by recovering and utilizing the engine’s exhaust heat. However, most existing ship energy systems have not been optimized for this purpose. This paper explores several strategies for improving the thermal integration of the carbon capture unit by taking a systemic approach. A case study on a 10,000 twenty-foot equivalent unit (TEU) container ship demonstrates that a combination of measures can significantly reduce fuel penalties. These measures include the introduction of a main engine turbine bypass, a reduction in steam working pressure and the implementation of a waste heat recovery system for the auxiliary engines. In the example case, it is possible to reduce the additional fuel consumption from 55% to 23%, while increasing the avoided carbon dioxide rate from 76% to 81%. Onboard carbon capture might thus enable a significant reduction in carbon dioxide emissions from ships at acceptable abatement costs.