(558f) A Systems Approach for Renewable Fuels and Innovations for the Shipping Industry

Maritime transport, although one of the most energy-efficient modes of transport, is also a large and growing source of greenhouse gas emissions. Hence, the EU has established a new regulation for reducing GHG emissions, which came into effect from January 2024, to achieve the reduction targets. Consequently, the shipping industry faces escalating pressure to decarbonize and alleviate its environmental footprint. Meeting the ambitious sustainability goals and regulations set for the industry necessitates a sophisticated portfolio of tailored technological solutions, meticulously developed and implemented.

Alternative fuel options considered in the study include LNG, methanol, ammonia, and hydrogen, alongside biocrude oil as a direct substitute for marine diesel. Additionally, bio-based production routes, according to the available state-of the art technologies, are also examined for all alternatives to assess their impact on the ship’s environmental performance. The advantages and disadvantages of each option are summarized in Table 1.

Table 1 Pros and cons of different fuel options

The paper outlines a systematic and holistic approach that combines the LCA-based environmental impact and techno-economic feasibility assessment for the use of conventional and alternative marine fuel options, along with energy efficiency, integration, and on-board CO₂ capture technologies.

Methodologically a case study approach for specific vessel type and route configurations was employed for the simulation and flowsheeting of the available options. The process and energy integration, encompassing heat recovery, cogeneration, and cryogenic integration of low boiling fuels, was conducted to assess their potential application onboard. Additionally, an environmental impact assessment based on Life Cycle Assessment (LCA) using the ReCiPe 2016 Hierarchist (End point) method, along with the Global Warming assessment method, was utilized to evaluate the comparative impact of various ship operation scenarios on its environmental performance. Finally, the technoeconomic constraints of applying the available options to the existing ships, through retrofitting, was investigated.

Energy integration: Indicative shifted composite curves for each of the five alternative fuel options applied in the engine simulation model are presented in Figure 1. The major energy needs, in the case of marine diesel use are for heating, and the pinch point value in this case is quite low, therefore heat exchange is expected to be beneficial only above the pinch temperature, where the heat exchange potential is larger; when LNG is considered high fuel preheating requirements arise, due to low storage temperatures, therefore the cooling needs are fully covered for any of the examined operation modes. It is noteworthy that despite the reduced comparative need for carbon dioxide separation from the other components of the flue gas, due to the lower emissions for the same energy production by LNG in comparison with marine diesel, the heating needs cannot be fully satisfied by the integration. This is due to the corresponding reduced heat recovery from the flue gas and the additional heating requirements for fuel preheating; the heating requirements for methanol are particularly high, as it can be observed in the respective diagram of Figure 1, and only under energy integration assumptions it can be considered feasible. The scenario without carbon dioxide capture seems to be more realistic; however, the feasibility of its implementation will depend on the environmental impacts which should be studied further; the thermal needs of the system for the use of ammonia can be fully satisfied with the implementation of a network of heat exchangers based on energy integration. The maximum possible heat recovery from the generated flue gases is significantly greater than the required heat supply. Consequently, it is considered that full heat recovery from the flue gases will not be achieved; the thermal requirements for hydrogen have been fully matched as well, with the difference lying in the ratio of actual to maximum heat recovery. Overall, the degree of integration is satisfactory, and minimum heat supply requirements are negligible.

Figure 1: Energy integration – Shifted composite curves for multiple fuel options, MCR 75% and Carbon Capture (except NH₃ and H₂)

Table 2 summarizes the examined scenarios for the operation of the main engine under different fuel, MCR and Carbon capture assumptions, as well as the expected impact of energy integration on the overall efficiency of ship energy consumption. The energy integration benefits are in the range of 8-20% in the case of marine diesel oil; 17-18% for the use of Methanol; 9-12% for LNG; 12-14% for ammonia and 10-12% for Hydrogen; depending on the selected operation mode for each fuel type.

Table 2: Fuel consumption before and after energy integration, for multiple fuel, MCR and Carbon Capture combinations (MDO: Marine Diesel Oil, MET: Methanol, AMM: Ammonia, HYD: Hydrogen)

LCA based environmental impact assessment

The environmental impact of the most promising operation scenarios for the specific ship and route considered in the case study, is presented in Figure 2. As it can be easily observed the fuel with the lowest impact is renewable hydrogen where up to 90% of the base case emissions (i.e. MDO without CC) can be achieved. For fuels where carbon dioxide is produced during combustion, biofuel options dominate within each category. More specifically the use of bio-oil results in 33%; biomethane 70%; bio-methanol 75% reduction of GHG emissions. The use of NH₃ can also produce benefits of up to 60% reduction of GHG emissions; but only under the condition its production follows a biological pathway.

It should be noted that the use of carbon capture technologies has a very significant impact on the GHG emission potentials of examined ship operation scenarios; i.e. 55% reduction can be achieved in the case of MDO, and 50% for the use of LNG, if assessed on a Well-to-Wake basis. Given the limited resource availability for the production of significant amounts of bio-based fuels to meet the demand of marine sector, the paper pointed to the CO₂ capture on board as the most realistic technology option to meet the targets set for the GHG emissions reduction.

Figure 2. Indicative LCA based, cradle-to-grave environmental impact of different fuel origins, use and carbon capture technologies for the case study ship and route scenarios