Multiphysics simulation and optimization of microwave-assisted regeneration of spent activated carbon for enhanced...

Microwave (MW) heating at the molecular level represents a promising alternative to conventional thermal processing methods. However, its industrial application is hindered by localized overheating due to uneven electromagnetic field distributions within MW cavities. Traditional temperature measurement approaches fail to capture comprehensive temperature profiles, and research exploring MW applications at 915 MHz remains limited. This study employs a coupled multiphysics modeling approach to optimize MW regeneration processes for activated carbon (AC) at frequencies of 2450 MHz and 915 MHz. The effects of waveguide mode, relative phase difference, spatial configurations of AC columns, loading height, and power input strategies on MW energy utilization, temperature distribution, and contaminant removal were investigated. Comparative analyses between 2450 MHz and 915 MHz revealed distinct frequency-dependent heating behaviors. The results demonstrate that dual-waveguide mode outperforms single-waveguide operation, achieving 93.9 % MW utilization efficiency, elevating AC temperatures to 662.5 °C, and reducing per-fluoropentanoic acid (PFPA) decomposition time by 35 %. Dynamic phase-shifting enabled thermal redistribution, suppressing localized overheating and enhancing energy efficiency. Intermittent power input strategies improved heating uniformity compared to constant power input. A centralized placement of AC improved MW utilization from 68 % to 97 %. Loading height critically influences temperature distribution, with AC column heights of ≥5.1 cm achieving MW utilization efficiencies above 90 %. Frequency comparisons showed that 915 MHz provides superior heating uniformity for larger-scale systems (>10.2 cm), whereas 2450 MHz was more effective in smaller-scale setups (<10.2 cm). These findings offer critical insights into optimizing the MW regeneration of materials, providing a theoretical basis for scaling up industrial MW-assisted AC regeneration.