ETD

• Allam cycle
• Dynamic analysis
• Operability

To mitigate climate change and global warming, the development of technologies capable of reducing pollutant emissions is crucial. Despite significant research on carbon capture technologies, their costs have not decreased as expected, while fossil fuels remain the dominant source for global power generation. This context highlights the need for power cycles that can utilise hydrocarbon fuels while avoiding CO2 emissions. The Allam cycle is an oxy-combustion, semi-closed, supercritical CO2 power cycle that inherently captures carbon dioxide while using methane or solid fuels such as coal. Its combustion process produces only water and CO2, the latter serving as the working fluid, a portion of which is extracted at high pressure for transport and storage. Although many aspects of the Allam cycle have been investigated, comprehensive analyses of its transient behaviour are still limited. Understanding its dynamic response is essential for assessing the system’s operability under real-world conditions, and for guiding the design of heat exchangers, turbomachinery, and control systems. This thesis presents the development of a simplified dynamic model of the Allam cycle. The model was then utilised to investigate the dynamic behaviour of the cycle under several conditions, including load variations under different control strategies, changes in ambient temperature and system turndown and ramp-up under hot conditions. The results showed that the temperature-based load control strategy provided the fastest and most accurate tracking of the setpoint compared to the inventory load control strategy, appearing much better suited for applications requiring rapid load modulation. An increase in ambient temperature resulted in improved cycle performance in the open-loop configuration, whereas in the closed-loop configuration, both load control strategies exhibited slow dynamics in restoring the equilibrium after a temperature disturbance. In the turndown-ramp-up analysis, important aspects related to the safe and stable operability of the cycle were identified. Notably, it was observed that during the deep load reduction, the system experienced substantial performance degradation, mainly due to the turbomachinery operating far from its design conditions. Ultimately, the obtained results provide useful insights for improving the Allam cycle transient stability, efficiency, and integration into flexible power systems.