Sea Water Scrubbing FAQ's

1. Can sea water scrubbing be used to reduce emissions by as much as using low sulphur heavy fuel oil, (HFO)?
2. Can sea water scrubbing be used where the heavy fuel oil has a sulphur content of the maximum allowed under IMO Marpol Annnxe VI, namely 4.5% sulphur content?
3. What are the main pollutant emissions from the combustion of high sulphur heavy fuel (HSFO), on board ship?
4. What are the main applications for sea water scrubbing on board merchant ships?
5. Has sea water scrubbing technology been used on ships before?
6. How can the ship’s Officers be sure that the sea water scrubbing system is working efficiently?

1. Can sea water scrubbing be used to reduce emissions by as much as using low sulphur heavy fuel oil, (HFO)?

In fact sea water scrubbing is so effective at the removal of SO2 from exhaust gases, that it can achieve emissions reductions equivalent to using 0.1%S diesel oil. Sea water scrubbing is also effective at removing soot, unburnt oil, and ash, resulting in a clean exhaust emission, by trapping these in some cases harmful components in the scrubbing water. The scrubbing process even ensures the elimination of the dark exhaust plumes seen when marine diesel engines start up or when there are quite large dynamic load changes due to a step increase in power demand.

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2. Can sea water scrubbing be used where the heavy fuel oil has a sulphur content of the maximum allowed under IMO Marpol Annnxe VI, namely 4.5% sulphur content?

The number of fuel deliveries exceeding 3.5% sulphur is less than 5% of all marine bunker deliveries globally. Krystallon sea water scrubbing system is designed for up to 3.5% sulphur fuel to achieve maximum scrubbing efficiency. When using marine bunker fuel with higher sulphur content there will be a slight increase in emissions of SO2 after scrubbing. However the scrubbed exhaust emissions from a 4.5% sulphur marine bunker fuel would still be less than the unscrubbed exhaust emission from a 0.5% sulphur fuel oil or diesel fuel.

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3. What are the main pollutant emissions from the combustion of high sulphur heavy fuel (HSFO), on board ship?

• The main pollutant emissions from the combustion of high sulphur marine bunker fuels consist;
• Sulphur dioxide, (SO2) often simply called SOx, (pronounced “socks”).
• Oxides of nitrogen, NO, NO2, N2O) often simply called NOx, (pronounced “Knocks”). The oxide NO predominates at around about 95% of the NOx components.

Incombustibles or ash, such as metals typically found in the marine bunker fuels, (nickel and vanadium), and metals from refinery processing, (aluminium) and metals used in the lubrication oils, (typically calcium). Other ash components consist of partly burnt hydrocarbons and unburnt fuel oil and lubricant.

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4. What are the main applications for sea water scrubbing on board merchant ships?

The main applications for sea water scrubbing on board merchant ships are for main engines, auxiliary engines, and boilers. It is not normally economic to apply sea water scrubbing to combustion plant using distillate fuel, (diesel), or plant which only consumes small quantities of high sulphur marine bunker fuel and where a switch to distillate fuel is more economic.

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5. Has sea water scrubbing technology been used on ships before?

Sea water scrubbing was introduced on board oil tankers from about the 1960s. After a series of explosions caused by the ignition of the potentially explosive mixture of hydrocarbon gases and air found in the space above the crude oil cargoes, sea water scrubbing was introduced on board tankers. The exhaust gases from the tanker’s boiler plant was scrubbed to clean the gas providing an inert gas, (deficient in oxygen) to blanket crude oils and prevent explosive gas/air mixtures occurring. All oil tankers are now fitted with inert gas systems, and most use sea water scrubbing to clean the exhaust gas of their boilers to produce the inert gas.

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6. How can the ship’s Officers be sure that the sea water scrubbing system is working efficiently?

The IMO sea water scrubbing guidelines define two methods for approving sea water scrubbing systems. Krystallon utilises Method B which requires the continuous monitoring of the exhaust gas. Continuous Emissions Monitoring, known as CEMs has been used on land based plant for many years. Krystallon utilises state of the art pulsed laser technology to provide a highly reliable and accurate measurement of exhaust gases passing the probe, (which is situated in the gas stream). The gases NO, NO2, SO2 and CO are reported to a console in the Engine Control Room for ship’s Officers to inspect. The data is also recorded to a secure recording system which also records other parameters such as the ship’s position, for the purposes of demonstrating compliance in the event of Port State inspection.

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