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The scope of this paper is to examine proposed e-fuels (e-hydrogen, e-ammonia, e-methanol) as alternative maritime fuels. A techno-economic analysis is conducted considering the current energy demand of the shipping sector, the solutions for decarbonisation that are based on e-fuels, and the projections and scenarios regarding the energy mix towards 2050, to meet the IMO targets. According to the current preliminary study, apart from the barriers related to technological maturity levels, applicability and safety, there are barriers related to (a) the Well-to-Wake characteristics of e-H2, e-NH3, and e-CH3OH, (b) the existing infrastructure that utilises Renewable Energy Sources and the current and projected percentage of RES in the global energy mix, and (c) the availability of resources required for the development of the infrastructure to support e-fuels’ utilisation. Estimated fuel prices in 2050 that include production and distribution costs, indicate that alternative fuels are expected to be uncompetitive. Though they become relatively competitive when carbon-price is added to production and distribution costs of fossil fuels, the Well-to-Wake Analysis of biofuels and e-fuels proves that a significant RES rump-up is required, which further requires huge capital investment costs and raw materials. Ultimately, a re-prioritisation is proposed targeting decarbonisation of “easier-to-abate” sectors before decarbonising “hard-to-abate” sectors such as shipping and aviation.

In the present study, energy and exergy analyses of a simple supercritical, a split supercritical and a cascade supercritical CO2 cycle are conducted. The bottoming cycles are coupled with the main two-stroke diesel engine of a 6800 TEU container ship. An economic analysis is carried out to calculate the total capital cost of these installations. The functional parameters of these cycles are optimized to minimize the electricity production cost (EPC) using a genetic algorithm. Exergo-economic and exergo-environmental analyses are conducted to calculate the cost of the exergetic streams and various exergo-environmental parameters. A parametric analysis is performed for the optimum bottoming cycle to investigate the impact of ambient conditions on the energetic, exergetic, exergo-economic and exergo-environmental key performance indicators. The theoretical results of the integrated analysis showed that the installation and operation of a waste heat recovery optimized split supercritical CO2 cycle in a 6800 TEU container ship can generate almost 2 MW of additional electric power with a thermal efficiency of 14%, leading to high fuel and CO2 emission savings from auxiliary diesel generators and contributing to economically viable shipping decarbonization. [ABSTRACT FROM AUTHOR]

In the present work, the contemporary exhaust gas treatment systems (EGTS) used for SOx, PM, and NOx emission mitigation from shipping are reviewed. Specifically, after-treatment technologies such as wet scrubbers with seawater and freshwater solution with NaOH, hybrid wet scrubbers, wet scrubbers integrated in exhaust gas recirculation (EGR) installations, dry scrubbers, inert gas wet scrubbers and selective catalytic reduction (SCR) systems are analyzed. The operational principles and the construction specifications, the performance characteristics and the investment and operation of the reviewed shipping EGTS are thoroughly elaborated. The SCR technology is comparatively evaluated with alternative techniques such as LNG, internal engine modifications (IEM), direct water injection (DWI) and humid air motor (HAM) to assess the individual NOx emission reduction potential of each technology. Detailed real data for the time several cargo vessels spent in shipyards for seawater scrubber installation, and actual data for the purchase cost and the installation cost of seawater scrubbers in shipyards are demonstrated. From the examination of the constructional, operational, environmental and economic parameters of the examined EGTS, it can be concluded that the most effective SOx emission abatement system is the closed-loop wet scrubbers with NaOH solution which can practically eliminate ship SOx emissions, whereas the most effective NOx emission mitigation system is the SCR which cannot only offer compliance of a vessel with the IMO Tier III limits but can also practically eliminate ship NOx emissions. [ABSTRACT FROM AUTHOR]