Numerical Evaluation of High-Pressure Supercritical CO2 Effect on the Axial Turboexpander Blades Natural Frequencies, A Case Study

Abstract In addition to the global effort and focus on using renewable energy sources, climate models that incorporate carbon capture and sequestration represents a broader portfolio of opportunities to meet climate change targets. The Allam Cycle contributes to sustainable energy by utilizing hydrocarbon energy reserves in a process that captures CO2 from combustion for sequestration or reuse. The cycle reduces emissions by employing oxy-combustion and a high-pressure supercritical CO2 working fluid in a highly recuperated cycle, which can utilize a wide variety of hydrocarbon fuels. As the Allam cycle is going to be soon demonstrated using a pilot plant, a numerical study has been developed to investigate the effect of the high-pressure supercritical CO2 on the natural frequencies of axial Turboexpander blades. This is crucial to accurately predict the blades natural frequency and avoid resonances in operating range. The study first compares the variation of natural frequency of a simplified plate-like structure model due to the effect of the fluid environment considering Air, Water and supercritical CO2. This allows to understand the acoustic fluid-structure interaction combined with the effect of different fluid/structure volumes ratios. Once investigated the plate-like simple structure, a more realistic case of turboexpander bladed disc is considered. This allows to evaluate the effect of the fluid volume surrounding only the blade or the complete bladed disc sector. The results indicates that the density values of supercritical CO2 at the turboexpander stages inlet conditions do not significantly impact the blades natural frequencies for a combined effect of density values and structure stiffness.