(278f) Enhancing Carbon Capture Efficiencies in Natural Gas Power Plants through Magnetic Stabilization of Fluidized Beds

Despite the increase of renewables for power generation, fossil fuels such as natural gas remain crucial in meeting our growing energy needs. However, fossil resources release significant amounts of CO₂, the primary greenhouse gas driving the pressing global issue of climate change. This underscores the urgent requirement to develop CO₂ capture technologies, including efficient CO₂ capture materials and reactor technologies for Natural Gas Combined Cycle (NGCC) power plants. The objective of this study is to improve the carbon capture efficiency of the NGCC process by employing a magnetic field-supported fluidized bed.

The work employs solid sorbent-based approaches for CO₂ capture, which are less energy-intensive and have wider operating temperature ranges compared to solvent-based or membrane-based methods. Specifically, solid sorbents based on potassium carbonate are not only cost-effective and possess high CO₂ sorption capacities but are also well-suited for post-combustion CO₂ capture due to their tolerance towards moisture in the flue gas. While several studies have focused on sorbent material design, there has been insufficient attention paid to reactor design for enhancing carbon capture efficiency. Traditionally, fixed bed reactors are used for CO₂ capture due to their operational simplicity. However, they suffer from poor heat and mass transfer characteristics, leading to high pressure drops when processing high flue gas flow rates. These limitations could be mitigated by fluidizing the bed, which improves heat transfer but may not necessarily enhance mass transfer due to bubble formation. Implementing a magnetically stabilized fluidized bed (MSFB) shows promise in increasing carbon capture efficiency by suppressing bubble formation, thereby enhancing gas-solid contact. This approach also reduces pressure drop across the bed, prevents sorbent carry-over at high flow rates, and minimizes sorbent attrition.

A magnetic bed setup was designed, utilizing a current-carrying coil cage simulated using COMSOL to generate a uniform magnetic field within the bed. The setup was fabricated, and hydrodynamic testing was conducted using sorbent material K₂CO₃ supported on Al₂O₃, impregnated with magnetic iron (Fe). Energy Dispersive Spectroscopy (EDS) confirmed the uniform dispersion of Fe on K₂CO₃-Al₂O₃. The magnetic susceptibility of the sorbent was determined using a superconducting quantum interference device (SQUID), quantifying the amount of magnetic field required to stabilize the bed. The hydrodynamic study investigated the effect of magnetic field strength, Fe loading, and gas velocities on bed pressure profiles. Results showed decreased pressure fluctuations when the bed entered the stabilized regime compared to when no magnetic field was applied, validating bubble suppression and enhancing gas-solid contact. Additionally, a decrease in pressure drop across the bed was observed when applying the magnetic field, contributing to potential cost savings on compressor operations in large-scale applications.

Following this, CO₂ capture from flue gas streams using K₂CO₃-Al₂O₃-Fe sorbent was evaluated across various reactor configurations - fixed bed, fluidized bed, and MSFB - at the same weight hourly space velocity (flue gas flow rate to weight of K₂CO₃). Characterization techniques such as X-Ray Diffraction (XRD) confirmed the formation of desired sorbent phases post-adsorption (KHCO₃) and post-regeneration (K₂CO₃). Performance across the different configurations was assessed based on carbon capture capacity and CO₂ removal fraction. The MSFB reactor demonstrated higher carbon capture capacities due to the improved gas-solid contact achieved by suppressing bubbles, as also observed in prior hydrodynamic testing. Compared to conventional fluidized beds, MSFBs also exhibited superior CO₂ removal fractions.

This study helps confirm the benefits of magnetic stabilization in fluidized beds, with potential applications in industrial processes requiring effective gas-solid contact. Insights gained from material and reactor design could also advance other CO₂ capture technologies vital for addressing climate change, such as direct air capture, which is currently a prominent area of research.