Abstract

This study evaluates compact cogeneration technologies for urban areas with varying energy demands, focusing on renewable fuels such as hydrogen and biogas, compared to fossil fuels like methane. Among various options, proton exchange membrane fuel cells (PEM fuel cells) and recuperated micro-gas turbines (MGTs) are identified as the most promising technologies. Their performance under diverse scenarios, including control strategies, fuel choices, and operational conditions, is thoroughly modeled.
For PEM fuel cells, detailed electrochemical and thermal models simulate electricity and heat production, while for MGTs, a comprehensive model optimizes heat recovery and control strategies. The developed control strategy involves precise bypass valve adjustments to regulate mass flow distribution, improving efficiency. Heat management is further enhanced by coordinating bypass valve settings with storage tank cycles and auxiliary boiler transitions.
PEM fuel cells are shown to excel in high-efficiency cogeneration due to their direct conversion of chemical to electrical energy at low operational temperatures, minimizing heat loss and optimizing hydrogen utilization. MGT systems, on the other hand, benefit from hydrogen combustion’s higher flame temperatures, boosting power generation. Parametric analysis reveals that increasing rotational speed, pressure ratios, and working parameters in MGTs enhances power output, while higher cell counts and ambient temperatures improve PEM fuel cell efficiency and hydrogen consumption.
To reduce emissions from MGTs, a dual axial swirler combustor is proposed, ensuring uniform temperature distribution, minimizing hot spots, and enhancing fuel-air mixing. These features improve combustion efficiency and stability under partial loads, effectively lowering NOX and CO emissions. The emission characteristics are assessed using CFD simulations, an Equivalent Chemical Reactor Network (ECRN) model, and a custom mathematical model. Hydrogen combustion is associated with high NOX emissions due to its flame temperature, while methane and biogas show lower NOX concentrations. However, the inert CO2 in biogas presents challenges for efficiency.
In summary, this research provides a robust framework for evaluating renewable-fueled cogeneration systems, offering strategies to enhance efficiency and reduce emissions, supporting urban energy sustainability.