Using renewable methanol, PEM fuel cells and on-board carbon capture to reduce well-to-propeller ship emissions

This paper gives an overview of research that was carried out with the purpose of gaining insight whether renewable methanol, fuel cells and on-board carbon capture can be used to reduce the CO2 emissions of part of a fleet consisting of various (governmental) work ships, using methanol produced from waste biomass, excess wind energy and recycled CO2. Since CO2 is a by-product from steam reforming methanol to hydrogen, this can be captured, liquefied, and stored on board for later use in methanol production. Integrating the necessary systems seemed possible for larger ships using dimensions of currently available systems, although suitable carbon capture systems are not yet available. Using system parameters and operational profile as input, a MATLAB-Simulink model was constructed to calculate the tank-to-propeller emissions, as well as providing insight in required tank dimensions (both methanol and CO2). In general, the total energy stored on board of larger ships is reduced when using methanol instead of traditional fuel oils, but the reviewed ships are still able to achieve their original operational profile. Smaller vessels require various advancements in order to fit the required systems whilst still being able to store enough fuel for at least a single trip. These advancements can include more compact reformer and fuel cell systems, or class rule changes regarding the dimensions of cofferdams that are to be fitted around methanol tanks. Assuming these advancements are possible in the near future, the total emissions could be reduced significantly, by up to 82% in the originally reviewed case. This means that the net CO2 emissions are still positive and subsequently a gap in CO2 supply for methanol production occurs. However, both problems can be tackled simultaneously with further advancements: either by capturing more CO2 during the various well-to-propeller stages, or by introducing an additional carbon-negative CO2 source. It could therefore be possible to operate a fleet with net zero CO2 emissions in the future by using renewable methanol, fuel cells and on-board carbon capture, if feedstock availability is high enough and technological advancements are made.