The maritime sector CO2 emissions are one of the contributors to the increase of the concentration of this gas in the Earth's atmosphere. One of the proposed solutions for reducing these emissions is the implementation of carbon capture technologies onboard vessels. Carbon capture technologies work on the principle of apprehending the carbon dioxide resultant of any chemical process, avoiding the need to emit it into the atmosphere.
The goal of this study is to obtain a general solution to the technical challenge of implementing carbon capture technologies onboard ships. To do so, a general model is developed for the implementation of carbon capture onboard vessels regardless of their characteristics or operational profile. To test the model, two case studies are performed based on real vessels from the company Allseas where, using the developed model, a capture system design is proposed for each ship. With the input of one of these case studies and the developed model, the effect that the characteristics of the vessel's engines and the characteristics of the capture system have on the capture process is analysed.
The results from the case studies show that the proposed designs can reduce the CO2 emissions by 28% for the first case study and by 21% for the second case study. This reduction is enough to comply with the short-term objectives of the IMO in terms of CO2 emissions reduction.
The results of the characteristics analysis reveal that LNG is the preferred fuel to be used in combination with carbon capture. Small carbon capture systems have a higher performance in vessels with 2-stroke engines whereas larger carbon capture systems have a higher performance with 4-stroke engines. For the post-capture refrigeration cycles, a similar effect is observed. Small capture systems have a higher performance with absorption refrigeration cycles and large capture systems have a higher performance with vapour-compression refrigeration cycles. The reason for these results is the fact that the performance of the capture process mainly depends on the heat requirement of the capture system.
Thanks to the results of the analysis, it is found that, by combining the use of LNG and the implementation of carbon capture, a more significant reduction of the CO2 emissions for each case study can be achieved. This reduction is equal to 53% for the first case study and 46% for the second one.