Solid Oxide Fuel Cell Hybrid Systems for Dynamic Rail Applications
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Solid Oxide Fuel Cell Hybrid Systems for Dynamic Rail Applications

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The world’s railway system is responsible for approximately 1% of the total anthropogenic carbon emissions [1]. Fuel cell hybrid systems can theoretically meet the power and dynamic operating requirements of locomotives and provide an efficient, low emission and potentially affordable way to decarbonize rail. In this work, different ways of hybridizing Solid Oxide Fuel Cells (SOFCs) are analyzed to determine the best way to power trains in the future. CO2First, the development of a Solid Oxide Fuel Cell-Reciprocating Engine (SOFC-RE) hybrid system model on MATLAB Simulink is reported. The steady state system efficiency while operating on natural gas is 68.8% compared to 66.1% for a stand-alone SOFC. The cell voltage in the SOFC is 0.802 V with a current density of 0.623 A/cm2. The SOFC-RE outperforms a stand-alone SOFC, but not an SOFC-Gas Turbine (SOFC-GT) hybrid system, which has an efficiency of up to 72.2%. The model and results can be used to predict the performance and aid in design of hybrid systems of this kind for both stationary and transportation applications. Second, the simulation of a Solid Oxide Fuel Cell-Gas Turbine (SOFC-GT) hybrid system for a locomotive application is presented. Using MATLAB Simulink, a 2.8 MW SOFC system was combined with a 500 kW GT and simulated to travel the route from Bakersfield to Mojave in California. Elevation data was imported using the Google Application Programming Interface (API) and smoothed to calculate the dynamic power demand for the SOFC-GT system, assuming 480 tons of freight per 120-ton locomotive traveling at an average speed of 45 mph. The SOFC-GT system model follows this demand without causing a significant disruption to the speed of the locomotive. A lithium-ion battery was included into the system model to improve the net system efficiency with regenerative braking and make the operation smooth enough for the highly dynamic route power demands. The overall efficiency along the simulated route has been estimated as 57% operating on partially pre-reformed compressed natural gas (CNG) fuel. These results suggest that SOFC-GT systems are promising for the future of freight rail transportation throughout the United States. CO2 and particulate matter emissions are significantly reduced compared to current diesel-electric locomotives and it is also possible to operate the system on hydrogen to make it completely emission-free. Third, different scenarios for how to the use of a renewable hydrogen-powered hybrid SOFC-GT system used in both freight and passenger trains are considered. A techno-economic analysis is performed to evaluate the potential emission reductions and the direct costs associated with this conversion. The corresponding reduction in carbon dioxide emissions ranges from 1.07% to 3.05% of global carbon emissions and the expected demand for renewable hydrogen is annually between 30 and 50 million metric tons, with future costs ranging from $45-75 billion. Moreover, this technology offers the potential to reduce global carbon emissions by up to 15%, if more aggressive adoption occurs. A case study for the U.S. in which the necessary renewable energy infrastructure is designed. It is shown that in order to decarbonize the transportation sector, zero-emission hydrogen-powered trains are both essential and viable in terms of technical, economic, and practical feasibility.

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