Energy and exergy analysis of dry and steam external reformers for a power cycle based on biogas-fueled solid oxide fuel cell

Abstract

In the present research a cogeneration cycle based on a solid oxide fuel cell (SOFC), and Organic Rankine Cycle (ORC) is proposed. The cycle is fed with biogas in different molar ratios of carbon dioxide to methane (RCTC). In addition, the cycle is examined for both dry reforming (DR) and steam reforming (SR). A thermochemical model is presented for both cycles of SR–SOFC–ORC, and DR–SOFC–ORC. The model is coded in MATLAB coupled with Engineering Equation Solver software. The model was verified with both experimental and theoretical research and agreement was achieved. The energy and exergy performance of the cycle is presented and carbon deposition on the cathode due to different reactions of methane cracking, Boudouard reaction, and vapor formation are studied. The results show that for RCTC<1.2 steam reforming produces more hydrogen, while for RCTC>1.2 dry reforming is advantageous. At RCTC = 1.2 the DR and SR work the same. The overall thermal efficiency of DR-SOFC and SR-SOFC has reached 67 % and 70 %. Carbon deposition due to the Boudouard reaction, and vapor formation for both SR and DR are negligible while due to methane cracking is serious. The DR-SOFC deposits less carbon because of methane cracking due to higher operating temperatures.