A closed-loop scrubber utilizes alkaline-dosed seawater to neutralize sulfur oxide gasses from marine exhaust streams. Using alkali, such as sodium hydroxide (NaOH), also known as caustic soda, or magnesium hydroxide (MgOH), acids can be removed due to chemical reactions.
Sulfur oxide (SOx)
Sulfur oxides (SOx) consist of small compounds of sulfur and oxygen molecules. Sulfur oxides are damaging to human health as they can lead to respiratory symptoms and lung diseases. In the atmosphere, sulfur oxides can cause acid rain, which will ultimately harm crops, forests, infrastructure, and buildings, as well as aquatic species by acidifying the world’s oceans. And these are some of the main reasons for the IMO 2020 as limiting SOx emissions from the shipping industry is key in order to protect the environment and ensure a sustainable future. Fortunately, closed-loop scrubbers are very effective in removing sulfur oxide. As much as 98 % of sulfur oxide from exhaust streams can be removed. Once the sulfur is treated, it is turned into sulfur-based salt such as Na2SO4, which is harmless to the environment.
Nitrogen oxide (NOx)
Nitrogen oxides (NOx) consist of small compounds of nitric oxide (NO) and nitrogen dioxide (NO2), which represent gases produced by the heavy fuel combustion process in the vessel’s engine. NOx is highly acidic and corrosive and damages the environment as well as human health. High levels of NOx can cause respiratory infections, asthma, and chronic lung diseases. Moreover, NOx smog leads to poor air quality and harms vegetation. Approximately 5-10 % of NOx is removed. NOx cleaning technologies such as Exhaust Gas Recirculation (EGR) or Selective Catalytic Reduction (SCR) can be employed to reduce NOx by more than 80 %, which will ultimately deliver IMO Tier III compliance.
Particulate Matter (PM)
Particulate matter (PM) is an airborne substance consisting of hundreds of different hazardous solid particles and liquid droplets. Therefore, PM is often referred to as particle pollution. PM can include organic and inorganic particles, including soot, smoke, dust, and liquid droplets. The particles of PM can take different forms, compositions, and origins. Some can be seen with the naked eye, while others are so microscopic that they can only be seen with a microscope.
Some PM stems from a direct source, such as when fuel is burned. Yet, the majority of PM takes form in the atmosphere when chemicals meet each other and form complex reactions. This is often the case with SOx and NOx emitted from industrial operations, power plants, vehicles, and vessels.
PM constitutes a major health risk, as it can easily be inhaled. The smallest particles constitute the most severe health risk as they can enter deep into the human lungs and bloodstream. Fortunately, as the exhaust gas is scrubbed, around 60-80 % of the PM can be removed. Yet, some of the PM is absorbed by the wash water, which ultimately calls for effective water treatment. Learn more about what a water treatment unit removes here.
Want to learn more?
Visit our Marine Knowledge site to learn everything worth knowing about marine scrubbers, wash water treatment, and how to comply with the IMO 2020 sulfur cap.