Fluidized Bed Dry Scrubbers for Marine Emissions Control: Opportunities and Challenges

While the maritime sector continues to generate notable emissions of SOX, NOX, particulate matter (PM), and approximately 3% of global CO2, the International Maritime Organization’s robust regulatory framework provides stringent oversight and is steadily steering the shipping industry toward cleaner, more efficient, and more sustainable operations. This review examines exhaust gas cleaning options, emphasizing dry scrubbing technologies, and particularly marinized fluidized bed dry scrubbers. It covers reactor hydrodynamic behavior under roll/pitch disturbances, ship integration, and the potential coupling with selective catalytic reduction and onboard CO2 capture. Although wet scrubbers are traditionally the most common solution for sulfur oxide (SOX) control, the discharge of contaminated wash water caused by gas–liquid pollution transfer is subject to extra environmental monitoring and regulation due to the handling of contaminated effluents and sludge and ecotoxic effects. Dry systems, on the contrary, avoid liquid effluents and, in fluidized bed configurations, provide efficient gas–solid contact, high SOX and PM removal, and solid residues that can potentially be valorized, provided impurity levels are controlled. Experimental and numerical studies demonstrate that, with proper codesign of geometry, internals, particle properties, and control strategies, circulating and bubbling fluidized beds can operate stably at sea. This enables compact, modular reactors that can house sulfur sorbents, NOX catalysts, and CO2 adsorbents within a single, dry-based architecture. Key challenges include sorbent storage and logistics, pellet attrition and regeneration under marine cycling, motion-aware scale-up, and port-side handling of solid residues. These aspects remain at an early development stage for marine deployment and should be interpreted as research gaps rather than performance claims validated under field conditions. Meanwhile, opportunities exist for process intensification using fluidized bed scrubbers as multifunctional exhaust units by combining SOX and NOX abatement, particulate control, carbon management, and waste heat recovery to achieve low-impact shipping, which motivates further work on materials, reactor modeling and simulations, and system-level deployment.