Wet air scrubbers, which use seawater or fresh water as cleaning media for sulfur dioxide, are progressively used by shipping companies to comply with emissions regulations. Nowadays shipping emissions are likely to increase significantly, alongside increasing emphasis on the sustainability and environmental impacts of the maritime transport sector. Emissions of gases and particulates to the atmosphere affect the surface ocean directly and indirectly through deposition and dissolution of gases, as well as radiative forcing effects on the climate. A close collaboration between natural scientists and social scientists is crucial for progress toward sustainable shipping and protection of the marine environment. In the last decades, global and regional efforts to reduce the environmental impact of ship emissions have been made.
Wet scrubbers are low-cost and, therefore, preferred alternatives to high-cost, low-sulfur fuel. Scrubber technology primarily removes SOx (SO, SO₂, SO₃, S₆O₂, S₂O₂), NOx (NO, NO₂), and particles to some degree, but not CO₂.
Wet air scrubbers use seawater or fresh water as cleaning media for sulfur dioxide (SOx) producing sulfurous acid, sulfuric acid, and calcium sulfate. In contact with finely dispersed water, SO₂ dissolves and is removed from the exhaust gas. Three types of wet scrubbers are commonly used:
- Open loop scrubbing systems
In open loop scrubbers, the water flow rate into the scrubber depends on the alkalinity in the sea water. A higher flow rate is necessary for an effective scrubbing in areas with low pH buffering capacity (for example, in the Baltic Sea). Water temperature also has an impact on the efficiency of open loop scrubbers, as higher temperatures reduce the solubility of SO₂.
- Closed loop scrubbing systems
Closed loop scrubbers use fresh water in a circuit supplemented with sodium hydroxide. Such scrubbing systems can operate for short periods without any discharge.
- Hybrid systems
Such systems can switch between the open and closed wet system modes of operation.
The use of wet air scrubbers in the shipping industry has benefited the environment by significantly reducing the release of pollutants to the atmosphere. However, it should be noted, there is an incomplete understanding of the impact of scrubber wash water discharge and the associated marine biological impacts. Thus the direct emission monitoring on ships, it is crucial to improving spatial and temporal measurements of pollutants along shipping lanes and in ports to gain a comprehensive understanding of shipping-related pollution and the effect of emission reduction technologies.
Being a new type of wet air scrubber, multi-vortex wet air scrubber provides improved air treatment quality and can be used for both particles matter and gas collection. The treatment quality of multi-vortex wet air scrubber is generally 99.95-99.99% for both types of pollutants. Besides high efficiency, multi-vortex wet air scrubber possesses a number of advantages over conventional wet scrubbers – multi-vortex wet air scrubber is compact, omnivorous, eco-friendly, economical, and low-maintenance.