Hybrid dimension-based analysis of the energy, exergy, and dynamic response of cross-flow SOFC-CHP system

Some of the solid oxide fuel cell (SOFC) poly-generation systems currently have the problem of high exergy destruction of the air-side heat exchangers, which exceeds that of SOFC. Meanwhile, there are fewer studies on the variable distribution of key components, especially the dynamic distribution characteristics. In this study, a combined heat and power (CHP) system integrating a cross-flow SOFC, an organic Rankine cycle (ORC), and a heating unit is proposed, and distributed parameter modeling is applied to develop a dynamic mechanism model for a two-dimensional cross-flow SOFC and a one-dimensional methane reformer. Then the steady state performance and dynamic response characteristics of the system and key components are comprehensively analyzed. The results show that the total exergy destruction of the air-side heat exchangers is always lower than that of the SOFC under each operating condition. The maximum temperature and current density of SOFC are located at nodes (8,8) and (5,8), respectively. With the increase in fuel utilization (FU), the total system efficiency increases and then decreases, peaking at 83.36 %. Increases in SOFC internal reforming rate and the decrease in inlet gas temperature exacerbate the SOFC temperature distribution non-uniformity. A step change in current causes rapid fluctuations in system performance and in the internal variables of the SOFC. A step change in air flow first changes the cathode oxygen concentration, causing voltage changes. The current density variation trends at each node of the SOFC are different depending on the reactant concentration and temperature.