Performance analysis and optimization of combined heat and power system based on PEM fuel cell and [formula omitted] type Stirling engine

Abstract

In this study, a new arrangement of a combined heat and power (CHP) system is proposed, which is designed based on a dual-prime mover of proton exchange membrane (PEM) fuel cell and β type Stirling engine. By using this CHP system based on Stirling engine and fuel cell in hybrid form, the potential of performance improbvement of the system can be analyzed and the appropriate operation condition compared to using the CHP system based on one prime mover can be achieved.Also, two suitable thermodynamic models have been used for modeling the fuel cell and Stirling engine from energy, environmental and economic issues. In addition, the effects of Stirling engine speed, temperature, and fuel cell current density on power, electrical efficiency, CHP efficiency, fuel cost savings, the amount of annual CO2 emission reduction (ACO2ER) and payback period have been investigated for the CHP system. Then, an optimization method has been performed with the help of a two-objective genetic algorithm and the TOPSIS methods, and several optimal cases from different viewpoints of the CHP system are presented. The modeling results showed that to increase the CHP system's efficiency, the engine speed should be in the range of 1500 rpm and to increase the system's capacity, a higher engine speed should be used. Also, based on the payback period analysis, the system has higher economic performance at a higher rotational speed.I addition, increasing the fuel cell's temperature increases the system's power and electrical efficiency. The system's capacity increases with the current density, but the system's efficiency decreases. The optimization results showed that the engine speed, the fuel cell temperature, and the current density are recommended to be 3000 rpm, 94.5 °C, and 0.67 A cm−2, respectively. Suppose the main goal is to maximize the CHP efficiency and ACO2ER simultaneously, the CHP system should be started with a slightly lower engine speed of around 2126 rpm, a lower temperature of around 70.11 °C and a higher current density of around 0.93 A cm−2.