Scrubbers at a glance

Exhaust gas cleaning systems (EGCS), or scrubbers, are becoming a more frequently used technology for ships to achieve compliance with the 2020 sulphur cap. A scrubber sprays seawater or fresh water mixed with a caustic chemical into the exhaust gas stream in several stages. The pollutant – mainly sulphur dioxide – reacts with the alkaline water, forming sulphuric acid. In the case of an open-loop system, the resulting wash water is discharged back into the sea.

In areas and ports where open-loop scrubbing is prohibited, ships can use closed-loop systems and collect the accumulated sludge on board for subsequent disposal at a suitable in-port facility.

Hybrid scrubber systems can operate either in closed-loop or in open-loop mode, offering more flexibility. A multi-inlet scrubber can treat the exhaust gas from several engines, whereas a single-inlet scrubber serves one engine only. It is important to weigh all options for a given ship and trading pattern carefully to ensure the economic sustainability of the chosen solution

Closed-loop scrubbers

Closed-loop systems add chemicals, such as caustic soda, to the wash water to boost its alkalinity. The wash water is then recirculated through the system and partially purged.

Open-loop scrubbers

Open-loop systems use seawater, which is alkaline by nature, to wash the SO_X out of the exhaust. The resulting discharge water must meet MARPOL requirements before being discharged.

Growing demand

Time is pressing; the 2020 sulphur cap forces shipowners and operators to act. There are currently almost 1,300 ships with confirmed scrubber projects.

The current market

The majority of the recently signed projects are for bulk and oil/chemical vessels. Open-loop scrubbers are the most popular. But for the vessels operating inside areas where wash water discharge to sea is restricted, closed-loop or hybrid systems are required.