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Hybrid Scrubbers

The merchant marine industry is catching up to comply with the coming deadline of Sulphur Cap of 2020. The specified conditions laid down by the International Maritime Organization (IMO) restrict sulfur content in fuels to 0.50% globally and to 0.10 in certain areas to reduce the harmful effects sulphur oxides in ship exhaust gases have on the environment. In terms of planning and strategy, the industry has already provided a working alternative for compliance compared to switching to costly low-sulphur fuel oil (LSFO). Exhaust gas cleaning systems i.e. scrubbers or hybrid scrubbers system have been widely accepted as a cost-efficient alternative. However, this alternative would lead to a higher CAPEX investment and adding machinery onboard.

Scrubbers may prove to be the right option for merchant’s vessels in terms of ROI depending on the vessel size, age, and trading pattern. They are competitive compared to the LSFO prices and the yearly fuel savings may be in millions.

Exhaust gas desulphurization processes include several different applications where sulphur oxides are removed from exhaust gases by absorbing them into different alkaline sorbents such as sodium hydroxide or normal seawater. This blog will help you to access the large benefits of various scrubber systems for ships.

Choosing the Right Scrubber for Your Ship

Scrubbers systems for ships widely come in three types i.e. Open Loop, Closed Loop Systems, and Hybrid Systems. These are integrated as per the scope of the budget and requirements of the scrubber vessels. Some of the vessels demand a hybrid version of these scrubbers to ensure smooth operation in zero discharge areas where the open-loop scrubber systems are mostly prohibited but allow the vessel to operate in cost-effective open loop mode at open seas.

Open Loop Scrubbers

Open Loop Scrubbers are widely accepted as a good alternative to LSFO and other scrubber systems due to its fast ROI. Open-loop scrubbers utilize the natural properties of seawater to neutralise the acidic water produced in the reactions between exhaust gas sulphur oxides and seawater. The inherent seawater properties that facilitate the scrubbing process are its alkalinity and salinity. (Behrends and Liebezeit, 2003)

The buffering components of seawater neutralize the increased acidity caused by sulphur dioxide and trioxide reacting with water. The buffering components of seawater are mainly bicarbonate (HCO3-) and carbonate (CO32-).

Seawater contains calcium and sodium carbonates in solution and is therefore naturally alkaline. The alkaline salts are continuously regenerated by contact with marine and coastal deposits of alkaline sediments and by addition from rivers. (Pipitone and Bolland, 2008)

The downsides of using open-loop scrubbers are that the scrubbing process is strongly dependent on the alkalinity and the temperature of the seawater. At higher temperatures and low alkalinities, the use of seawater scrubber may not be feasible, as the cleaning process is more efficient at low temperatures and high alkalinities.

Open-loop scrubbing also needs large volumes of seawater, which indicates that the pumping costs will be higher. (Vidal Barrero et al., 2007; Vidal Barrero et al., 2009) A large pump will be required onboard, which will consume a proportion of the power generated in the ship.

Advantages of Open Loop Scrubbers

One of the benefits of using open-loop seawater scrubbing processes is that no additives are needed, as the inherent alkalinity of seawater is used as sorbent.

Another benefit is that little byproducts are produced except for some sludge and a slight increase in the natural concentration of sulphate in seawater. (Andreasen and Mayer, 2007) This increase is within the naturally occurring variations in seawater. The difference from the background level is not normally detectable within even a short distance from the point of discharge. (Srivastava, 2000) Furthermore, the absence of bulk chemicals opens up a possibility for simpler process design.

Using open-loop scrubbers would reduce both capital and operational costs compared to other methods. (Vidal Barrero and Ollero, 2001) Open-loop scrubbers are easier to maintain than closed-loop scrubbers as they have fewer moving parts. The return on investment may be as fast as 6 months to 1.5 years.

Closed Loop Scrubbers

The closed-loop scrubbers use a similar process as open-loop scrubbers but in the case of closed-loop scrubbers, the process water is re-circulated instead of discharging it directly into the open sea. In this case, chemical additives such as sodium hydroxide or magnesium hydroxide are required to replenish the scrubbing water alkalinity.

It is quite a better option for the scrubber vessels operating in the Baltic and other regions where the water is not highly alkaline. This is a useful operating system for zero discharge areas.

Why choose closed-loop scrubbers?

The closed-loop scrubbers are fully compliant in all areas especially when vessels are operating in zero discharge areas as it doesn’t need to discharge washwater back into the sea.

Closed-loop scrubbers have more moving parts such as advanced water treatment and alkali addition systems, which will require regular maintenance. If the vessel does not operate frequently in zero discharge or low alkalinity areas it is recommended to have an open-loop scrubber.

Hybrid Scrubbers

The hybrid scrubber systems use state of the art remote-controlled equipment to offer easy switch between the open and closed-loop scrubber operating modes as per the need and requirement of the vessel. This type of technology helps vessels to run smoothly over the zero discharge areas without worrying about compliance.

The hybrid scrubbers might cost more than the open and closed-loop scrubber systems, but they are more cost-effective on OPEX. One of the biggest advantages of this system is that high sulphur fuel can be used in all areas and the engine can be optimized to use a single fuel type.

As the deadline of 2020 is approaching, many shipowners are taking a stance to install scrubbers rather paying a high OPEX on low sulfur fuels. The installation of scrubbers is a one-time investment that offers great rates of return for a longer period.


Marine transportation produces a large portion of the global sulphur oxide emissions as a consequence of operating with high sulphur fuel. Corrosive and toxic sulphur oxide gases may cause respiratory illnesses as well as damage to different materials. International Maritime Organization and European Union have set strict sulphur oxide limits, which are already partly implemented and will be implemented on a large scale internationally in January 2020. By using scrubbers to comply with the new limits, shipowners can continue to use more cost-effective high sulphur fuels.

With Kamelia Cleantech scrubbers, scrubbers can be installed while on-voyage (with a maximum 7-day downtime at quayside). Kamelia Cleantech offers I- line (Inline Scrubbers), U-line (Traditional Scrubbers), U-type scrubber, I-Line Hybrid Systems, I-Line Open Loop Systems, U-Line Hybrid Systems, U-Line Open Loop Systems, and U-Line Hybrid Ready Systems.

To know more about Kamelia Cleantech scrubbers, its benefits, costs, and installation procedures, send us an email and our Scrubber Experts will be more than happy to assist you.

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