Coupled multiphase flow and heat-mass transfer mechanisms during spray calcination of high-level liquid waste

Spray calcination of high-level liquid waste involves complex phase-change heat transfer and intense turbulence, which often promotes wall scaling. A three‑dimensional unsteady Euler–Lagrange model incorporating droplet breakup and species transport was developed and validated against pilot‑scale data (relative error <10%). Simulations reveal a dual‑vortex structure that largely governs temperature distribution, while intense evaporation generates a pronounced “thermal cold core” that may retard local drying kinetics. Fine particles (<30 µm) tend to follow gas streamlines, whereas larger particles (>70 µm) are more likely to cross trajectories and contribute to wall deposition. Maintaining a core temperature of approximately 460 °C at 4 L/h feed would require a wall heat flux on the order of 4933 W/m2, which delineates an operating window for achieving final moisture below 1%. These findings offer mechanistic criteria that can inform the design and scale‑up of high‑temperature spray calcination processes.