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Thermodynamic analysis of a novel power-hydrogen cogeneration system

Gargari, Saeed Ghavami, Rahimi, Mostafa, Ghaebi, Hadi
Energy conversion and management 2018 v.171 pp. 1093-1105
biogas, carbon, carbon dioxide, clean energy, energy efficiency, exergy, helium, hydrogen, methane, steam, temperature, thermodynamic models
In recent decades, hydrogen is considered as a secondary clean energy source, commonly referred to as an energy carrier. Hydrogen can be used to move, store and deliver energy in a form that can be easily used along with many other applications. Due to the significant role of hydrogen, a novel combined system for cogeneration of power and hydrogen is proposed in this paper. The proposed system is integrated from a Gas Turbine-Modular Helium Reactor (GT-MHR) and a biogas steam reforming (BSR) system to produce power and hydrogen, simultaneously. Biogas mixture consists of a considerable amount of methane and carbon dioxide as well as negligible amounts of other gases. A comprehensive thermodynamic modeling (i.e., energy and exergy analysis) of the proposed combined system is carried out. It is found that the proposed combined GT-MHR/BSR system can produce hydrogen and net output power of 0.217 kg/s and 260.13 MW, respectively. In this case, the overall exergy destruction rate, energy efficiency, and exergy efficiency of the combined GT-MHR/BSR system are calculated 329.31 MW, 47.69%, and 51.08%, respectively, showing a considerable enhancement in the efficiency of the basic system (GT-MHR cycle) from first and second laws of thermodynamics viewpoints. Moreover, the results of exergy analysis indicated that among all components, reactor core is accountable for the highest exergy destruction through the system (57.64%). To better understand the effect of various parameters on the performance of system, a comprehensive parametric study of some key thermodynamic parameters on performance criteria is performed. It is concluded that a higher energy and exergy efficiencies can be obtained by increasing the turbine inlet temperature, steam to carbon molar ratio, and turbine pressure ratio or decreasing the carbon dioxide to methane molar ratio and compressor pressure ratio. Last but not the least, it is demonstrated that the performance of the proposed integrated system can be maximized based on the reformer temperature.