Analysis of an integrated PEMFC/ORC power system using ammonia for hydrogen storage

The present work deals with a high temperature proton exchange membrane (SPEEK-type) fuel cell (HT-PEMFC) energy system fuelled with hydrogen obtained by reforming of ammonia (NH3) and coupled with a bottoming Organic Rankine Cycle (ORC) energy system. This system was designed for distributed electric power generation, mainly for production of electric power systems with potential future applications in smart-grid. The use of ammonia as hydrogen rich gas source allows to avoid hydrogen tanking with metal hydrides, giving the opportunity to lighten and simplify the storage section of the system with respect to the pure hydrogen fed systems. The hybrid fuel cell/ORC configuration allows to increase the efficiency of standard power generation technologies. In other words, the ORC subset represents the most appropriate solution, in terms of sustainability, for extracting the excess heat produced during the H-2 combustion maintaining the PEMFC working temperature at 120 degrees C and for reducing the temperature of the exhausts. The objective of the work is to optimize the electric output of the system (PEMFC + ORC), thus improving the overall efficiency. To this end, a numerical model is implemented and tested. A validation of the numerical scheme is carried out comparing the prediction of the reforming phase with experimental results obtained by the authors. The thermal and electrical energy balance is also assessed. Furthermore, the operation conditions of the reformer are studied in detail to determine the settlements leading to a proper ammonia cracking to produce nitrogen and hydrogen. Furthermore, the calculations take into account also the auxiliary equipments such as pumps, compressors and heat exchangers.