Thermo-environmental multi-aspect study and optimization of cascade waste heat recovery for a high-temperature fuel cell using an efficient trigeneration process

Abstract

This study suggests a novel cascade waste heat recovery process for a solid oxide fuel cell power plant. The present process utilizes a trigeneration model producing electricity, cooling, and hydrogen using the energetic stream exiting the upper power plant. This model consists of a two-stage steam Rankine cycle, an ejector refrigeration cycle, a thermoelectric generator, and a low-temperature electrolyzer. After precise thermal and electrochemical simulations, a multi-aspect sensitivity analysis is regarded from the thermo-environmental point of view. Afterward, a multi-objective optimization procedure is applied through the non-dominated sorting genetic algorithm-II. The main difference between the present model and those evaluated in the literature review is its combined cooling and power cycle, which significantly increases the overall performance. According to the sensitivity analysis, the fuel cell operating temperature is the most crucial parameter affecting the studied variables. From the optimization, the optimum objective functions, i.e., exergy efficiency and carbon dioxide emission, are found to be 58.02 % and 252.5 kg/MWh, respectively. In addition, the optimum net generated power, cooling output, and hydrogen production rate are computed to be 508.8 kW, 161.9 kW, and 0.6 kg/h, respectively. Besides, the optimum energy efficiency and exergoenvironmental impact index are equal to 68.2 % and 0.7, respectively.