Environmental and energy efficiency assessments of offshore hydrogen supply chains utilizing compressed gaseous hydrogen, liquefied hydrogen, liquid organic hydrogen carriers and ammonia

Abstract

Hydrogen has emerged as an eco-friendly energy to replace fossil fuels. But, it is difficult to store large capacity and to transport long distance due to a low volumetric energy density. In order to overcome the disadvantages of hydrogen, hydrogen supply chains are being widely studied and reported to compare which chains are better to be deployed. However, few studies have reported in terms of an environmental impact assessment. Therefore, in this study, an environmental impact is analyzed using a life cycle assessment (LCA) for offshore hydrogen supply chains linked to offshore wind farms, as well as an energy efficiency. The hydrogen supply chains include all stages of converting hydrogen produced on an offshore platform into compressed gaseous hydrogen (CGH2), liquefied hydrogen (LH2), liquid organic hydrogen carriers (LOHC), or ammonia (NH3), transporting them to an onshore plant and storing as CGH2. In particular, in order to calculate the amount of fuel consumed in ship transportation, the weight of cargo is estimated accordingly. The results vary depending on the electrical energy sources used and the transport distance. In almost all stages except for transport, electrical energy sources have a significant impact on the environmental load. The global warming potential (GWP), which is an alternate value of greenhouse gas emissions, is in the range of 1.15–10.11 kg CO2 eq when the national electricity grid and the offshore wind power (W + G) are used together. On the other hand, it shows a much lower value as 1.15–2.05 kg CO2 eq when using only offshore wind power (W). As the transport distance increased, it is significantly affected in some impact categories, i.e. GWP, acidification potential (AP), and eutrophication potential (EP). The contribution of transport gradually increased, and at 10,000 km, the value was 25.32–35.42 kg CO2 eq for W + G and 24.88–27.49 kg CO2 eq for W. Comparing the efficiency, CGH2 is the highest at all transport distances, followed by NH3, LOHC, and LH2. Considering that CGH2 is typically unfeasible for ship transport, hydrogen transport using NH3 can be the most attractive option. Finally, it is found that the longer the transport distance, the greater the effect on chain efficiency. Accordingly, the efficiency of the chains sharply decreases as the transport distance increases.