What does a scrubber remove?

A scrubber is an exhaust gas cleaning system that employs liquid to wash away unwanted pollutants from exhaust gas streams generated by combustion processes in the vessel engine. It can remove sulfur and other harmful elements. Let us dive into what a scrubber removes and why this is essential to remove.

A closed-loop scrubber utilizes alkaline-dosed seawater to neutralize sulfur oxide gasses from marine exhaust streams. Acids can be removed due to chemical reactions by using alkalies, such as sodium hydroxide (NaOH), also known as caustic soda, or magnesium hydroxide (MgOH).

Sulfur oxide (SOx)

SOx, short for sulfur oxide, consists of small sulfur and oxygen molecules compounds. Sulfur oxides are damaging to human health as they can cause respiratory symptoms and lung diseases. In the atmosphere, sulfur oxides can cause acid rain, which will ultimately harm crops, forests, infrastructure, buildings, and aquatic species by acidifying the world’s oceans. These are some of the main reasons for the IMO 2020, as limiting SOx emissions from the shipping industry is vital to protect the environment and ensure a sustainable future. Fortunately, closed-loop scrubbers are very efficient in removing sulfur oxide. As much as 98% of sulfur oxide from exhaust streams can be removed. Once the sulfur is treated, it turns into sulfur-based salts, such as Na2SO4, which is harmless to the environment.

Nitrogen oxide (NOx)

Nitrogen oxide (NOx consists of small compounds of nitric oxide (NO) and nitrogen dioxide (NO2). These compounds represent gases produced by the heavy fuel combustion process in the vessel’s engine. NOx is highly acidic and corrosive. Furthermore, NOx damages the environment and 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 hazardous solid particles and liquid droplets. Therefore, PM is often referred to as particle pollution. PM can include organic and inorganic particles, including shoot, 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 burning fuel. Yet, most PM forms in the atmosphere when chemicals meet each other and from complex reactions. This is often the case with the case SOx and NOx emitted from industrial operations, power plants, vehicles, and vessels.

PM constitutes a significant 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, the wash water absorbs some of the PM, which ultimately calls for effective water treatment. Learn more about what a water treatment unit removes here.