The shipping industry has been in a search of alternative low-sulfur fuels and greener shipping technologies in an effort to reduce air pollution. The aim is to cut down on the sulfur oxide emissions that can negatively impact the environment. This is why most ships are equipped with an exhaust gas cleaning system, better known as a scrubber. They are useful in removing harmful gases, like sulfur oxide and nitrogen oxide, from the exhaust gases that are generated by the marine engine’s combustion process. If you have been thinking about investing in cruise ships for sale, now would be a good time to learn more about the various scrubber systems installed in a marine vessel. Below, we take a closer look.
Dry Scrubbers
Water has no use under this dry scrubbing technique and here, hydrated lime prills are used as scrubbers to remove the sulfur.
Dry scrubbers are used at a higher temperature, than wet scrubbers. This enables the scrubber to burn oily residues and soot in the system. The calcium in the caustic lime granulates present in the exhaust gas chemically reacts with sulphur dioxide and forms calcium sulphite. This calcium sulphite is then, air-oxidized to form calcium sulphate dehydrate, which after reacting with water forms gypsum. The prills after use are stored and are released at the ports. These discharged prills which are in form of Gypsum are used as fertilizer materials and construction material and thus, not wasted.
In contrast, to wet scrubbers, the dry scrubber method uses less power than wet systems, as they can work without a circulation pump. In case of weight, a dry scrubber weighs more than, wet scrubber system.
Wet Scrubbers
The scrubbing liquids that are used inside a wet scrubber can be fresh water-induced with additives or seawater. Among the additives that are used, the most common is caustic soda (NaOH) and Limestone (CaCO3).
In this technique, the sulphur oxides are sent through a stream of water, which reacts with the water and becomes sulphuric acid, which is then passed through exhaust gas, so that, it gets removed from the system. Sulphuric acid is an acclaimed corrosive element, however, when treated with a lot of alkaline seawater becomes neutralized, diluted, and loses the harmful effect and before getting discharged in the open sea it gets treated in the separator for removing the sludge.
The different types of wet scrubbers are as follows:
- Open Loop Scrubbers: Seawater is specially used in this open-loop scrubber as a scrubbing medium and no other chemicals are used in this system. Here, the exhaust gas which is emitted by the engine or boilers is passed through the scrubber where it gets treated with seawater. This system is limited in its function because this system works effectively only when the seawater has high alkalinity and can eliminate the sulfur from the system.
- Closed Loop Scrubbers: The working principle is similar to the open-loop system. However, in the close-loop system, sodium hydroxide treated freshwater is used as the scrubbing medium. Here, SOx from the exhausted gas stream is converted to sodium sulphate which is not corrosive and harmful. Here, the process tank is where the wash water passes into before getting recirculated, unlike an open-loop system where; the flow-through method is used.
- Hybrid Scrubbers: Hybrid scrubber system is a combination of both open and closed-loop scrubber systems. It offers great advantages in minimizing, the sulfur oxide emission effectively as it operates as an open-loop scrubber when the water conditions match the open-loop scrubbing system to work effectively. At other times, it works as a closed-loop scrubber system when the same factors match the closed-loop scrubbing system to work efficiently, thus, proving it can work in any condition without limitation.
Conclusion
Here we read about the different types of scrubber systems that are used in ships to minimize sulphur oxide emissions considerably helping to create a pollution-free environment. If you are wondering about purchasing a cruise ship for sale then go ahead, now that you know, the marine industry is taking initiatives to balance the pollution level across the world.
