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A "scrubber" is a system for filtering exhaust gases from heavy-fueled ships' engines.

A "scrubber" under implementation on a vessel


Historically, in the merchant marine, the last clean energy to have been used was sailing, scientifically called sailing propulsion.

Sailing propulsion was replaced by a stable source of energy, coal, which when burning produced steam from water. The elevation of the pressure is used by a steam motor to transmit energy to the vessel propeller. We know today that the combustion of coal produces noxious fumes for man and his environment.

The coal was then replaced by diesel engines, which operates in the maritime heavy fuel oil, that is to say a fuel even less refined (less pure) than the diesel fuel of land vehicles. So even more polluting and illustrated on numbers of postcards, films and other images of the last century and the first two decades of the current century, by thick black smokes over the chimneys.


Faced with the growing imperative of finding so-called "clean" energies, all sectors of the economy are dedicated to finding alternative energy that is less polluting than those currently in place - in transportation in general and in the navy. in particular, the 3 main factors to be taken into account in this search for new energy are the immense distances to be covered (intercontinental journeys), the weight of the ship itself (several hundreds of thousands of tons) and the carrying capacity (number of passengers for the cruise, number of containers, weight or volume of the goods for the bulk, etc ...).

Unfortunately, the marine has not yet found propulsion energy that can equal the propulsive quota of carbon energy. Therefore, pending a more than hypothetical return to sailing propulsion, the vast majority of ships in service (99.7%) of the world fleet and frequenting waters with regulated air discharge (and running on heavy fuel) is seen obliged to have "scrubbers", a filtration system inserted between the exit of the exhaust pipes of the engine and the apparent chimneys of the ships. How does it work?



A "scrubber" is a chamber capable of withstanding a pressure of between 150 and 200 bar, in which several systems are simultaneously operating to "wash" the gases evolved by the combustion of the heavy fuel engine. This washing is done first with clear water and then with a glycol-based additive.

Discover how works a scrubber onboard merchant ships


The scrubbers are to be inserted in the exhaust line of the combustion gases, they are between the engine and the apparent outputs of the chimneys of a ship. Contrary to what one might think, a "scrubber" still weighs between 15 and 20 tons. And on passenger ships, there is no war of place other than the highest possible near the final exit of the chimneys. The installation of "scrubbers" has a significant impact on the stability of ships. When ships are equipped with an automatic calculation system, there is no option but a reconfiguration of it.


On a classic ferry, it is estimated that the "scrubbers" trap about 500 tons of CO² (carbon dioxide) year round. On a last-generation container ship, the same catch is estimated at more than 2,000 tonnes a year. A "scrubber" is therefore good for the environment, since it limits the emission of greenhouse gases. But it is also good for human health and not only, since it also traps:

- sulfur releases (SOx)

- releases of nitrogen oxide (NOx)

Hence the promulgation of laws at European level to protect human health in addition to the protection of the environment by establishing SECA zones. On this subject, read the article
"SECA" zone, what is it ?


The operation of laying scrubbers on a ferry in pictures

 Example of chimneys without scrubber

Before Scrubbers are put in place


To implement scrubber we have to remove a piece of bodywork

Removal of the "bodywork"


Thick black smokes become light and white once scrubbers are implemented

Smoke after setting up "scrubbers"


Related articles :

"SECA" zone, what is it ?

"Cold Ironing", what is this ?

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