Statistical and Thermodynamic Evaluation of CO2-Plume Geothermal Power Generation

Abstract In light of the 1.1% rise in global CO2 emissions in 2023, reaching 37.4 Gt, deploying carbon capture, utilization, and storage (CCUS) technologies is imperative to decarbonize the energy sector. This study investigates power generation using a CO2-Plume Geothermal (CPG) system. A thermodynamic process simulation model was developed to analyze turbine performance under varying wellhead conditions, including mass flow rate (50-250 kg/s), temperature (50-110 °C), pressure (65-215 bar), and CO2 mass fraction (0.8-1). Two fixed turbine pressure ratios (0.3 and 0.5) were evaluated to understand the influence of pressure drop on power output. The simulation incorporated isentropic turbine expansion, phase separation, and heat rejection, with emphasis on turbine output power. A natural log Box-Cox transformation (λ = 0) was applied to minimize variance and enable regression modeling. Two-way ANOVA and response surface regression were conducted with pressure ratios between 0.3 and 0.7 to identify statistically significant effects and interactions. Diagnostic tools, including residual plots and Pareto charts, confirmed the model’s robustness, with an R2 > 0.99 and low standard error. Results revealed that mass flow rate and temperature influence power output, while pressure and CO2 fraction exhibit complex, nonlinear interactions, especially at lower CO2 purities. The presence of water was found to enhance expansion work under specific conditions but may introduce operational challenges. The findings provide critical insights for optimizing CPG systems and guide design strategies under variable subsurface and operational constraints.