Over 80% of international cargos trade is transported over the sea, making maritime transport the most energy-efficient route of cargo transportation (Zis et al., 2020)(R. Li et al., 2022). Maritime transport is essential for global trade and significantly contributes to sustainable development worldwide (Wang et al., 2020). The shipping transportation is necessary for decarbonization, which is at the top of the domestic and international policy agenda (Xing et al., 2021). The International Maritime Organization (IMO) has launched numerous regulations and guidelines to regulate airborne pollutants and restrict greenhouse gas emissions (GHGs) such as the IMO Initial Strategy, MARPOL, etc. The strategy includes a commitment to minimize CO₂ emissions per transport work by over 40% by 2030 and reduce total GHG emissions from maritime transportation by over 50% from 2008 levels by 2050 (International Maritime Organzation)(Hansson et al., 2020). To assist reducing GHG emissions from shipping, it is necessary to switch to alternative low-and/or zero-carbon fuels because technical and operational efficiency measures alone will not be able to achieve the desired emissions reduction (Ashrafi et al., 2022). Several prospective decarbonization marine fuel alternatives, including liquefied natural gas (LNG), hydrogen, ammonia, biofuel, and methanol, are available to the shipping industry to assist in the reduction of emissions. Among them, methanol is prospective and promising as a hydrogen fuel source with a high hydrogen content. It is also a potential and promising maritime fuel for lowering SOx and CO₂ emissions, resulting in minimal climatic changes and green shipping strategies (Valera-Medina et al., 2021).

Methanol (CH₃OH) is a colorless, clear substance that is flammable, unstable, and has an alcoholic odor. Methanol is a polar organic solvent that is well known for being toxic. According to Adamson et al. (Adamson and Pearson, 2000) methanol is still advised, nevertheless, because it is extremely safe compared to other hydrogen transporters and fuels. The liquid form of methanol is simple to handle and has a boiling point of 64.7 °C, high energy density, high octane rating (Wang et al., 2019), and it is environmentally friendly(Kulikovsky, 2008). Methanol is also safe to handle at normal temperatures and pressures, is convenient to store, and easy to refuel (Atacan et al., 2017)(Calabriso et al., 2015). As a result, methanol is a suitable fuel option for fuel cells as well as other nautical applications such as internal combustion engines, gas turbines (Alias et al., 2020).

Researchers and manufacturers are looking at methanol coupled with fuel cells because of its advantages over internal combustion engines, including high efficiency, less noise, less air pollution, and higher thermodynamic performance. Methanol can be either directly or indirectly delivered to fuel cells depending on the kind and operating temperature of the fuel cells. The SOFC and PEMFC are the two most popular fuel cells designs that can be used with methanol systems. The limitation experimental findings have been published for other types of fuel cells, such as using alkaline and alkaline membranes (Hansson et al., 2020). Methanol can be reformed at a lower temperature (about 250 °C) than other fuel sources because of its molecular properties ((Zhao et al., 2022). PEMFCs indirectly use methanol by reforming (Sankar et al., 2017)(Chen et al., 2011), whereas SOFCs directly use methanol (Kim et al., 2007)(Bicer and Khalid, 2020). There have been several studies on methanol as a fuel and its use in maritime fuel cells due to its enormous potential to be paired with SOFC and PEMFC.

(Laosiripojana and Assabumrungrat, 2007) experimented with a direct methanol SOFC system over Ni/YSZ anode at an operating temperature from 900 - 975 °C. The research shown that methanol can be efficiently supplied to SOFC without any carbon formation. The methanol reformation rate was obtained at 100% if the operating temperature of the SOFC close to 900 °C. (Kim et al., 2007) investigated the stability and performance of direct methanol SOFC with Cu-ceria-YSZ and carbon-ceria-YSZ as anode and demonstrated that methanol is more effectively oxidized in compared with H₂ over tested anodes materials. The findings shown that, even at very low temperatures, species within SOFC electrodes can be highly migratory. (Zhang et al., 2022) experimented with the effects of the catalyst layer on the operation of a direct methanol SOFC system. The enhanced electrochemical performance proves that the integrated catalyst layer is helpful in catalytic the methanol fuel for Ni-YSZ anode-supported SOFCs. The reforming ability of the integrated catalyst layer for methanol is studied by analyzing the microstructural and composition of the anode and catalyst layer after the stability test. The integrated catalysts layer shows a 55.2% reduction in polarization resistance and 42.32% increase in peak power density at 800 °C after the inclusion of the integrated catalyst layer. (Y. Li et al., 2022) analyzed the performance of indirect methanol high temperature proton exchange membrane fuel cells (HT-PEMFC) and revealed that methanol is thought to be an ideal fuel for PEMFC due to its high hydrogen to carbon ratio and lack of carbon-to-carbon (C-C) bonds. The developed model could achieve an 8.8% exergy utilization factor, a 47.24% trigeneration primary energy saving, and a 66.3% energy efficiency. The conversion of CH₃OH and the hydrogen production are more than 95% in the acceptable temperature range when the H₂O/CH₃OH mole ratio is greater than 1.2. (Özcan and Akın, 2019) optimized the methanol steam reforming process for the indirect methanol HT-PEMFC system. The appropriate temperature, pressure, and H₂O/MeOH ratio to produce hydrogen for HT-PEMFC were determined to be 246 oC, 1 atm, and 5.6, respectively. Additionally, at these ideal conditions, carbon monoxide production in all three scenarios is extremely minimal, between 30 and 1700 ppm, and is therefore acceptable to the anode catalysts of HT-PEMFC systems. The SOFC combined system for marine application was studied by ((Duong et al., 2022b). The study showed that the energy and exergy efficiencies of combined system can be obtained 64.53% and 61.14%, respectively. The waste heat recovery systems increased 20.73% energy efficiency in comparison to the SOFC stand-alone system. However, because SOFC operated at high temperatures (from 700 to 1000 °C), it was unsuitable for marine vessels that required rapid response of the propulsion system and electric power during start-up and maneuvering.

It would be excellent if hydrogen could be extracted from methanol utilizing waste heat from SOFC and pressure swing adsorption (PSA) and supply to the PEMFC. This would boost the fuel cells system's overall energy efficiency. It denotes the usage of a methanol SOFC as the system's main power source, with the waste heat from its exhaust gas being repurposed as a heat source for a system that transforms and purifies methanol to produce more hydrogen for a PEMFC. The hydrogen storage and PEMFC system will instantly produce power for the propulsion plant thanks to the low working temperature of PEMFC, whilst SOFC, which runs at a higher temperature, will largely be used under stable seagoing circumstances. The methanol used as a marine fuel in this study is a proposed and assessed innovative combined SOFC-GT-PEMFC system. The main contributions of current research are listed below:

A general cargo vessel with an electric propulsion system of 3800 kW was targeted to application. The vessel operates on the Yellow Sea, is 130 m long and has 3800 gross tonnage.

The propulsion plant's main power source is referred to as the SOFC. The core idea behind the phrase “integrated system” is the utilization of waste heat from SOFCs to generate useful work (electricity). A PEMFC is an auxiliary power source that gives the system surplus power, especially during maneuvering and loading/unloading. The high-temperature exhaust heat of SOFC will be reused in turn by three regenerators and a methanol dissociation unit (MDU). The HT-PEMFC is selected in this system to produce extra energy from pure hydrogen. For HT-PEMFC, triethylene glycol is used as the cooling oil. The organic Rankine cycle (ORC) transfers heat from the HT-PEMFC's oil used for cooling to its operating fluid. Their expander devices provide electricity for these procedures.

The proposed integrated SOFC-GT-PEMFC-ORC system is shown in Fig 1. The fuel gas supplies system (FGSS) supply the SOFC combined system with methanol. Due to different operating temperatures and working characteristics, methanol is directly supplied to SOFC, whereas indirect supply to PEMFC via H₂ generation system that includes methanol reforming system (MR) and pressure swing adsorption (PSA). The main electrochemical reaction will be taken in the SOFC. After that, the exhaust gas is delivered to the afterburner to finish the combustion process. The temperature of the exhaust gas increased because of the significant amount of heat produced. The exhaust gas is subsequently used to generate extra energy in regenerative and gas turbines (GT). As a result, a number of regenerators use and transport SOFC waste heat. The fundamental elements and guiding principles of the cycles are described below:

SOFC: The two heat exchangers pre-heat methanol and compressed air in sequence using the SOFC's exhaust gas. By this way, the compressed air and methanol can be obtained at the SOFCs' needed input temperature. In the SOFC, reforming and electrochemical reactions take place after preheating. These reactions produce a significant amount of heat and electrical energy (resulting from converting chemical energy to electrical energy). The ship's propulsion system then receives the AC electricity that was first converted from DC.

H₂ generation system: Using a suitable catalyst in the reformer, a methanol-water mixture can be transformed into reformate gas. The CuZn-base, which is highly active at low temperatures and reasonably priced, is taken into consideration as a catalyst in this study. The production gas, which is created by reforming methanol and consists of water vapor, carbon dioxide, hydrogen, and carbon monoxide, is then fed to the PSA, where pure hydrogen is separated from the other produced gases.

PEMFC system: The separated pure hydrogen (stream 24) is provided to the HT-PEMFC after being reduced in pressure by expander 1 to the working pressure of the HT-PEMFC. The electrochemical reaction will take place in cathode of HT-PEMFC. Those reaction produce electricity and heats. Heat is supplied to the ORC which transfers heat from the cooling oil of the HT-PEMFC via HEX-7. Heat from cooling oil in the evaporator vaporizes the organic working fluid. The expander is powered to produce energy by the superheated steam that enters it from the organic working fluid (stream 37). The organic working fluid's steam condenses in the condenser before going into the ORC pump (HEX-8). The ORC Pump supplies the working fluid to obtain the required pressure prior to starting the cycle.

Methanol was proposed to be the fuel for the SOFC-GT-PEMFC-ORC system, and ASPEN-HYSYS V12.1 (Aspen Tech, USA), which offers reliable methodology and a sizable database for computing physical attributes, was used to model the system. The Aspen Physical Property System REFPROP function was used in the simulation. The thermodynamic characteristics of the stream compositions and operating circumstances for the SOFC-GT-PEMFC-ORC integrated system's components were estimated by participating in the the Peng-Robinson (PR) equation of states

The boundary condition is demonstrated in Table 2 (Ezzat and Dincer, 2020)

Table 3 presents the modelling results of the designed model with methanol as the fuel, which were calculated using this study's proposal and results from the literature ((Duong et al., 2022a). The estimated values correspond to the data from the literature, and the difference between the current simulation data and the literature data is kept within a reasonable range.

The suggested system has the capacity to concurrently power the propulsion system and other electrical devices while also producing hot water for shipboard crew members. Subsystem is required because the subsystem generates 33.32% of the total power of the integrated system.

Methanol is used as the primary fuel in a system that incorporates SOFC-GT-PEMFC-ORC to provide electricity for the ship’s primary propulsion system and harvest high-temperature exhaust heat from SOFCs to generate surplus electricity for start-up, maneuvering, and accommodating seafarers. The designated multigenerational energy system intends to provide marine vessels with alternative, environmentally sound options by utilizing renewable, sulfur-free, and low-carbon fuels in power plants. Energy and exergy assessments as well as thorough parametric research were carried out to evaluate the proposed system's performance and energy harvesting. The following are some of the study's most crucial conclusions: