Thermoelectric Generators Improve Ship Energy Efficiency

Fuel consumption in the marine sector is directly connected to emissions in the atmosphere and the worldwide shipping fleet is considered to contribute considerably to greenhouse gas emissions. Due to increased energy consumption, efficiency is a key issue that must be addressed in the marine industry and across all industries.

Image Credit: Alex Marakhovets/Shutterstock.com

By conserving fuel and improving a ship’s energy efficiency, the amount of greenhouse gases released into the environment is reduced. Reduced fuel consumption in ship engines is a focus in the marine sector.

Energy-saving devices, innovative equipment technologies, and improving the fuel economy of ships in operation are just a few of the options available to increase vessel energy efficiency, decrease fuel consumption, and limit emissions. Reducing fuel use and introducing new solutions are both possible approaches.

Shipboard waste-heat recovery systems are a cost-effective way to improve the sustainability of marine transportation. It creates a safe working environment, helps to meet decarbonization goals, and reduces the maritime carbon footprint. It is also simple to connect with onboard power supply systems. The high-temperature potential exists in some areas, notably aboard ships.

Thermoelectric Generators (TEG) applications can reliably and practically help with energy conversion, and TEGs are considered one of the most potential energy technologies of the twenty-first century. Furthermore, in nations such as Japan, Germany, the United States, South Korea, and Canada, thermoelectricity technology is widely used for energy generation in vehicles, space, military, and other industries.

A thermoelectric material must have a high thermopower, high electrical conductivity, low thermal conductivity, and the basic characteristics of thermoelectric materials to optimize its thermoelectric value. On ships, thermoelectric generators may operate with great efficiency on a variety of surfaces.

Specific surfaces, such as the main engine, auxiliary generators, boilers, and the sites where the ship’s waste heat is extracted, can provide the temperature differential required for Peltier to produce electrical energy.

A study looked at the prospective surfaces on which the temperature differential on the ship may occur, as well as the alternative energy potential that could be generated with the assistance of a thermoelectric generator. As a result of the calculations, thermoelectric generators were demonstrated to be an alternative energy source at the point of waste recovery aboard.

Methodology

The IMO developed emission factors based on fuel types and data from the 2020 Fourth IMO Greenhouse Gas Study. Table 1 shows the emission factors.

Table 1. The emission factors. Source: Uyanik, et al., 2022

An oil/chemical tanker ship was investigated as part of the study, and the ship’s main engine exhaust gas output line and jacket cooling water heat exchanger were assessed in this context. Table 2 lists the characteristics of the vessel under investigation.

Table 2. Particulars of the ship. Source: Uyanik, et al., 2022

The next stage was to find TEGs with characteristics that could endure these temperatures. Figure 1 depicts the methods used in the research.

Figure 1. Methodology of the study. Image Credit: Uyanik, et al., 2022

Figure 2a shows the TEG design for the main engine exhaust outlet line surface under consideration, while Figure 2b shows the design for the jacket cooling water heat exchanger surface.

Figure 2. (a) Surface area for the TEG system designed on the ME exhaust outlet line; (b) Surface for the TEG system designed on the ME JCW heat exchanger. Image Credit: Uyanik, et al., 2022

Results

Data from the ship’s noon report, including FO consumption, generator loads, and temperature measurements, were evaluated to assess the environmental advantages of TEGs. The data from the research ship covers the voyage’s period, which was between 2020 and 2021, and assesses the effectiveness of TEGs.

Table 3 also displays the particular fuel consumptions of generators based on their different loads.

Table 3. SFOC values for aux. engines. Source: Uyanik, et al., 2022

Table 4 displays the total amount of fuel used by the ship’s main and auxiliary engines, as well as the costs associated with it.

Table 4. Fuel consumption and costs between 2020–2021. Source: Uyanik, et al., 2022

The inventory of emissions discharged into the atmosphere by the ship with specifics is shown in Table 5.

Table 5. Exhaust Emission Inventory for ship. Source: Uyanik, et al., 2022

A thermal camera was utilized to undertake a technical analysis of the ship’s temperature variations, and some examples are shown in Figure 3.

Figure 3. Thermal inspection of areas for the TEG applications. Image Credit: Uyanik, et al., 2022

Figure 4a shows the characteristics of the TEG to be utilized, as acquired from the manufacturer. Figure 4b shows the heat map of the second surface, which is regarded within the scope of the application.

Figure 4. (a) The characteristics of the TEG; (b) Heat map of ME JCW heat exchanger (°C). Image Credit: Uyanik, et al., 2022

The power requirements of the ship’s auxiliary machinery systems (shown in Figure 5) were studied to demonstrate the influence of the intended TEG system on the ship’s energy efficiency.

Figure 5. Power needs for the ship’s auxiliary machineries. Image Credit: Uyanik, et al., 2022

Figure 6 depicts the potential design for incorporating the TEG system into the ship’s microgrid.

Figure 6. The conceptual design for integrating the TEG system into the ship’s microgrid. Image Credit: Uyanik, et al., 2022

Table 6 shows the cost of the TEG system, the features of the inverters that connect the system to the ship’s microgrid, and the entire design’s yearly maintenance cost.

Table 6. System installation and maintenance cost (USD). Source: Uyanik, et al., 2022

Discussion

Solar energy, wind energy, and battery applications for marine microgrids have been the subject of several research and development projects aimed at enhancing efficiency and lowering emissions. This study offered a unique strategy for reducing fuel consumption and emissions aboard ships by employing thermoelectric generators as waste-heat recovery devices.

Furthermore, the actual data taken on board the ship were utilized to create heatmaps and an emission inventory. A mathematical model description of thermoelectric generating systems, on the other hand, was examined for the ship.

In this study, the TEG system was used to analyze existing waste-heat recovery in ships and determine its contribution to energy efficiency. Over the course of a year on the ship, TEG efficiency was measured by analyzing fuel consumption and average electrical energy produced by the generators.

Two zones on the ship were identified as having high heat efficiency, and heat maps were utilized to identify which regions were suitable for TEG installation. As a consequence of the research, critical findings for the use of TEGs on ships were acquired.

Installing TEG systems on the ship used in the case study resulted in a 2% increase in energy efficiency within a year; the increased energy efficiency would aid in the decrease of exhaust emissions as well as fuel savings, contributing to the marine industry’s long-term sustainability and green future goals.

Conclusion

The application of waste heat recovery TEG systems in the ship’s main engine exhaust gas output line and jacket cooling water heat exchanger is the subject of this study. The proposed method may be used on other parts of ships as well as different ship types, such as containers and cruise ships.

Furthermore, including additional energy-saving technologies into the suggested system, such as wind and solar, would improve energy efficiency. The development of hybrid systems, submission of a feasibility study, and cost analysis will all pique the attention of marine industry stakeholders in future research.

Journal Reference:

Uyanık, T., Ejder, E., Arslanoğlu, Y., Yalman, Y., Terriche, Y., Su, C.L. and Guerrero, J.M. (2022) Thermoelectric Generators as an Alternative Energy Source in Shipboard Microgrids. Energies, 15(12), p.4248. Available Online: https://www.mdpi.com/1996-1073/15/12/4248/htm.

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