Solid Oxide Fuel Cell for Use in the Hydrogen Liquefaction Cycle

The increasing use of fossil fuels for energy has put the world at risk of environmental pollution as well as the depletion of fossil fuels. Following human efforts to find energy sources with these properties, hydrogen has found its place among clean and renewable energy sources. In this paper, an integrated structure for liquid hydrogen production using solid oxide fuel cells and renewable energies is developed. Liquid air, after compression and recovery of refrigeration, uses the waste energy of the refrigeration cycle and the waste energy of the solid oxide fuel cell output for heating, and after generating power in gas turbines, it enters the solid oxide fuel cell. The output current of the fuel cell is used to supply heat to the power generation cycle and to preheat the inlet currents to the fuel cell. This integrated structure produces ۱۰۲۸ kg/h of liquid hydrogen. Also, the efficiency of solid oxide fuel cell is ۶۲.۹۶%.Hydrogen is a clean and renewable fuel that can be replaced with conventional fossil fuels, but due to its very low density, its use as a fuel creates problems in transportation and storage [۱]. Hydrogen liquefaction is the best way to make this fuel denser and reduce the problems caused by its low density [۲]. In this paper an integrated structure for liquid hydrogen production using a solid oxide fuel cell is developed. Aspen HYSYS software and MATLAB programming were used to simulate the integrated structure developed.In this paper, an integrated structure for liquid hydrogen production using liquid-air refrigeration recovery for pre-cooling and six cycles of compression refrigeration with hydrogen and helium refrigerants are used for liquefaction. After recovering refrigeration and reheating, the compressed liquid air enters the gas turbines and solid oxide fuel cells, respectively. Then, the hot output current of the fuel cell is used to supply the heating cycle of carbon dioxide power generation and preheating the input currents to the fuel cell and gas turbine. Figure ۱ shows the block flow diagram of the integrated structure of hydrogen liquefaction.In this paper, in order to liquefy hydrogen, the cooling energy of liquid air is recycled for pre-cooling and six cycles of compression refrigeration with hydrogen and helium refrigerants are used for liquefaction. The use of liquid air cooling energy recycling for pre-cooling instead of the multi-component refrigerant cycle reduces the specific energy consumption by ۲۲.۵۶% and eliminates the multi-component refrigerant cycle part for pre-cooling. Compressed liquid air after heat recovery can enter the power generation cycles after heating by the heat dissipation of the compression refrigeration cycle with hydrogen and helium refrigerants and the waste heat from the fuel cell and provide part of the power of the developed integrated structure. Compressed air with water and natural gas then enters the solid oxide fuel cell and produces ۵۱۷.۷ kW of power. The waste stream of the fuel cell is used to supply heat to the solid oxide power generation cycle, to preheat the fuel cell and to preheat the compressed air before entering the gas turbines. The efficiency of solid oxide fuel cell is ۶۲.۹۶%. Figure ۲ shows the solid oxide fuel cell performance diagram in terms of mean current density, obtained based on the fuel cell surface and temperature.