A scrubber – or to give it its more correct name of Exhaust Gas Cleaning System is a device that removes sulphur oxides (SOx) from the exhaust gases of an engine or boiler using fuel with a sulphur content above that allowed under MARPOL Annex VI regulations.
The sulphur limits for fuels in place since 1 January 2020 are 0.1% sulphur by mass in ECAs and 0.5% sulphur by mass elsewhere.
It is possible for ships fitted with a scrubber to burn fuels with higher sulphur content as the scrubber will reduce the amount of SOx in the exhaust down to an equivalent or lower level of compliant fuels.
Why would an owner want to fit a scrubber?
Fuels containing higher levels of sulphur are cheaper to produce and are therefore cheaper to buy. This gives ships that can use such fuels a competitive edge over those that must use more expensive fuels. Before the current unusual situation with regard to over production of crude oil and the coronavirus impact, the premium for low sulphur fuels was typically between $200 and $300 per tonne. Presently it is closer to $50 to $60 per tonne.
A ship which burns 100 tonnes of fuel per day would therefore typically have the potential to save 100 x premium ($250) = $25,000 per day and based on 200 days per year at sea that equals $5 million per year.
Is my ship suitable for a scrubber?
The answer to this is a qualified yes. Scrubbers are typically large items of equipment that are installed mostly in the stack of a vessel. It used to be the case that ships below Handy/Handymax size were unsuitable. However, one Netherlands-based system maker has developed a smaller system that is a prefabricated, pre-installed, “plug and play” system in a road transportable casing. It comes in three sizes covering engines from 3MW to 9MW. This system can be easily switched between vessels if required.
How much does a scrubber cost?
This will depend upon the size of the ship and the type of scrubber fitted.
The cheapest scrubber type is known as the open-loop system which uses seawater to scrub the exhaust gas and after removal of oil and sludge, the washwater is discharged back into the sea. For large bulkers and VLCCs the cost of fitting an open loop scrubber in a newbuild ship is around $3m and for retrofitting a scrubber on an existing vessel around $4.5m.
More expensive systems are closed loop systems which retain the washwater on board for disposal ashore, and hybrid systems that can operate in either open or closed loop mode.
There are also some other technologies that use dry scrubbing methods and a catalyst to convert SOx into other chemical substances that are disposed of ashore.
Does a scrubber just move pollution from air to sea?
This is an emotive question and opponents of scrubbers do make this claim frequently. However, the answer is a qualified No. Firstly the chemistry of scrubbers means that sulphur enters the sea as sulphate which is a naturally occurring substance in seawater. On the other hand, it is recognised that a separate evaluation is necessary for environmental risks which may be caused by remaining substances such as the small amount of heavy metals contained in fuels or in their unburnt combustible content and Polycyclic Aromatic Hydrocarbons (PAHs).
These issues are under discussion and the IMO and it may be that some means of removing the substances from washwater needs to be developed. But it should be noted that these substances are also present in other fuels that do not contain sulphur so will enter the environment in any case. A scrubber will actually remove other atmospheric pollutants from the exhaust stream and as such are considered as being beneficial in reducing respiratory diseases due to shipping.
Is scrubber use unrestricted?
Unfortunately there have been a few port state regulations that have banned the use of open-loop scrubbers in some ports and restricted their use in others. However, these waters are usually limited in area and represent the final approaches of the ship to the port. For this short distance it is necessary to make use of 2020 compliant fuels instead of HFO but for ships making long voyages this inconvenience hardly affects the economic case for installing a scrubber.
Will a scrubber increase fuel consumption?
Up to a point yes. Power is needed to pump the water around the scrubber circuits and to operate the sludge separators. However, the savings in fuel cost permitted by the use of cheaper fuels more than offsets this negligible 1-2% increase in fuel use.
What happens if a scrubber breaks down?
Scrubbers, like any machinery are not infallible and if improperly maintained could fail. For such eventualities ships should carry a small supply of 2020 compliant fuel which can be used until the scrubber is repaired.
Scrubber makers will usually offer some service centres or have arrangements with engineering contractors but the equipment is mostly not proprietary and should be repairable by any competent engineering contractor.