Study on CO₂ sequestration via fly ash mineralization in underground coal gasification cavities

Abstract:

To address the dual challenges of global carbon emissions and industrial solid waste disposal， this study proposes an integrated "carbon sequestration-solid waste disposal-abandoned cavity utilization" three-in-one engineering scheme. This scheme combines abandoned cavities from Underground Coal Gasification （UCG） with fly ash mineralization for CO₂ sequestration. Using CMG-STARS software， a 3D， three-phase， five-component coupled model was developed to simulate the thermodynamic and mineralization behaviors during the injection of fly ash slurry and CO₂. The study focused on the effects of different CO₂ injection rates on temperature field evolution and sequestration efficiency. The results indicate that increasing the CO₂ injection rate significantly enhances the intensity and spatial uniformity of the mineralization reaction. For the same total injection volume， increasing the rate from 20000 m3/d to 60000 m3/d improves the sequestration efficiency by approximately 15%. While the injection of low-temperature CO₂ initially causes a cooling effect， the exothermic nature of the mineralization reaction gradually reverses this trend， stabilizing the temperature at approximately 250 ℃. This study provides a theoretical basis and parameter optimization strategies for the development of this integrated engineering technology.