Abstract
An air-independent propulsion system containing fuel cells is applied to improve the operational performance of underwater vehicles in an underwater environment. Fuel-reforming efficiently stores and supplies hydrogen required to operate fuel cells. In this study, the applicability of a fuel-reforming system using various fuels for underwater vehicles was analyzed by calculating the fuel and water consumptions, the amount of CO2 generated as a byproduct, and the amount of water required to dissolve the CO2 using aspen HYSYS (Aspen Technology, Inc., Bedford, MA, USA). In addition, the performance of the fuel-reforming system for methanol, which occupies the smallest volume in the system, was researched by analyzing performance indicators such as methanol conversion rate, hydrogen, yield and selectivity, and reforming efficiency under conditions at which pressure, temperature, steam-to-carbon ratio (SCR), and hydrogen separation efficiency vary. The highest reforming efficiency was 77.7–77.8% at 260 °C and 270 °C. At SCR 1.5, the reforming efficiency was the highest, which is 77.8%, and the CO2 generation amount was the lowest at 1.46 kmol/h. At high separation efficiency, the reforming efficiency increased due to the reduction of reactants, and a rate at which energy is consumed for endothermic reactions also decreased, resulting in a lower CO2 generation amount.
Highlights
Fuel cells generate electricity through the electrochemical reaction of oxygen and hydrogen.Hydrogen is separated into hydrogen ions and electrons at the anode, and the hydrogen ions move to the cathode and react with oxygen and electrons from the external circuit to generate water.The separated electrons move to the external circuit and form a current, generating electricity.Compared with the internal combustion engine, fuel cells are environment-friendly because they do not generate pollutants such as CO2, low noise because they do not have a driving unit, do not undertake explosions by combustion, and are highly efficient at electricity production by electrochemical reactions.Jen-Chieh Lee and Tony Shay [1] analyzed air-independent propulsion (AIP) systems containing fuel cells applied to underwater vehicles to enhance the underwater operational performance
The volume required for storing reactants and byproduct processing per unit unit of hydrogen production through steam reforming was analyzed for diesel, gasoline, ethanol, and of hydrogen production through steam reforming was analyzed for diesel, gasoline, ethanol, and methanol, which are applicable to underwater vehicles
Methanol, which are applicable to underwater vehicles
Summary
Fuel cells generate electricity through the electrochemical reaction of oxygen and hydrogen. Metal hydride has an advantage of high hydrogen storage density per volume, but has limitations in increasing the endurance of the underwater vehicles due to the low deployment flexibility of metal alloy and long-term hydrogen charge. Compression and a specific charging facility are necessary and safety requirements in terms of high pressure should be reinforced To overcome these limitations and drawbacks, studies on the application of fuel-reforming technology are underway. The fuels used in fuel reforming are based on hydrocarbon and alcohol and have advantages of high hydrogen storage density per unit mass and volume and ability to store hydrogen as liquid at room temperatures. Krummrich and Labres [17] developed a methanol reformer as a hydrogen supply system for next-generation fuel cell applications. Navantia in Spain built a S-80 equipped with an ethanol reformer
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