Exhaust gas scrubbers have high efficiency in limiting SOx emissions

Exhaust Gas Scrubbers are becoming a topic of significant importance in the marine industry, especially in the context of current and future regulations entering into force.

Developments in environmental research highlight the impact ships have on the quality of the air we breathe. Vessels that don’t already operate on low-sulphur marine fuel are faced with two variants: installation of new machinery or conversion of existing ones, in order to run on more expensive low-sulphur fuel, such as LNG, or retrofitting of Exhaust Gas Cleaning Systems.

Marine exhaust gas scrubbers enable the ship operator to run on cost-efficient high-sulphur fuel and still be compliant with the 0.1% SOx cap in ECA. In time, this means that the capital expenditure for the scrubber installation will return in the form of fuel cost savings.

How to choose the right Scrubber?

Ship operators need to consider several facts regarding choosing the right exhaust gas scrubber for their operations. Wet scrubbers have been widely accepted in the industry, for their increased efficiency, compared to dry scrubbers. The challenge in determining the right type of wet scrubber is choosing between the three available systems: open loop, closed loop and hybrid. The major factor that needs to be taken into consideration is the operating route. Water scrubbing technology relies on the natural alkalinity of the seawater. The liquid is sprayed on the exhaust gasses in order to neutralize the sulphur oxides and remove some of the particulate matters.

In high alkaline waters, open loop system scrubbers use seawater as scrubbing liquid, due to its high alkalinity. The waste stream is treated and discharged into the sea, leading to further removal of the particulates and heavy metals from the exhaust gas. In closed loop scrubbers, the scrubbing is generally performed with freshwater treated with additives that increase its alkalinity. The liquid is recycled back into the scrubber after each passing through the tower and, occasionally, additives and freshwater/ seawater are added to maintain efficiency levels and correct chemical composition. For ships that operate along routes with variable alkalinity, the safe choice would be using a hybrid type scrubber that can switch between the two operating modes.

Operating costs will vary according to the type of system used, as they each require different resources. Factors such as seawater recirculation that increase the power consumption of the pumps, the use of additives in the freshwater, additional equipments such as pumps, tanks, dosing equipments, maintenance operations due to wear, make the case for one or the other.

The infographic below aims to explain the context in which exhaust gas cleaning systems are proving to be an increasingly popular option among ship operators.

Exhaust Gas Scrubbers


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