In the 2008 amendments to the International Convention for the Prevention of Pollution from Ships (MARPOL) Annex VI, the IMO agreed in Regulation 14 to reduce the maximum allowable sulphur content of marine fuels from 4.5% to 3.5% in 2012, and then to 0.5% in 2020, except in sulphur Emission Control Areas (SECAs), where the maximum sulphur content was limited to 1.0% in July 2010 and 0.1% in January 2015. The IMO agreed to implement the 0.50% sulphur limit in 2020 based on research showing that sufficient quantities of compliant, low-sulphur-content fuel would be available in 2020 (Faber et al., 2016) and that doing so would prevent tens of thousands of premature deaths each year by reducing air pollution (Sofiev et al., 2018). Compliance with Regulation 14 can be achieved either by replacing the High Sulphur Fuel Oil (HSFO) commonly used in shipping with low-sulphur content fuel, or by using a scrubber instead, which is permitted under MARPOL Annex VI Regulation 4, which deals with ‘equivalents’ as long as the scrubbers are at least as effective at reducing emissions. Chelsea’s Sea Sentry is an instrument installed on ships for monitoring wash water.

Scrubbers have been installed on ships since the 1990s. At first, scrubbers were used only within SECAs, where limits on sulphur emissions were more stringent than the global limit. For SECAs, unless a scrubber was used, the maximum allowable fuel sulphur limit was 1.5% before July 1, 2010, 1.0% from July 1, 2010, to December 31, 2014, and then 0.10% beginning January 1, 2015. It was only in 2020 with the implementation of a stricter global regulation that ships started routinely using scrubbers outside of SECAs. Scrubbers have historically not been tightly regulated and, until recently, have not been widely used. But according to DNV GL (2020), 4,341 ships were expected to be outfitted with scrubbers by the end of 2020, which is 83% more than in 2018.

The number of scrubber-fitted container ships rose to 850 by 20 December 2022, an increase of 150 ships compared to the start of the year, according to shipping database Alphaliner. Ship-owners investing in scrubbers are currently enjoying discounts due to a supply glut, buying high-sulphur fuel oil at a discount of more than $500 a ton in Asia compared with cleaner varieties. The collapse in HSFO prices has been partially driven by increased Russian flows, according to traders. The cost of very-low sulphur fuel oil, meanwhile, has surged as more of its feedstock gets refined into gasoline. About 8% of the global shipping fleet currently use scrubbers according to Drewry Maritime Services. Some 19% of container ships are fitted with scrubbers, the highest proportion among different types of vessels, followed by tankers and bulk carriers at around 13%, according to Drewry. While the current savings may prompt some vessel owners to consider putting in scrubbers — which costs $3 million to $4 million for supertankers and $2 million or less for medium-size product tankers — uncertainties around whether the price trend will last, and the long-term transition to cleaner fuels may complicate their decisions.

What are scrubbers?

Vessel scrubbers, also called Exhaust Gas Cleaning Systems (EGCS) allow vessels to burn HSFO fuels without emitting sulphur exhaust that is in excess of the IMO 2020 sulphur cap. Scrubbers function by introducing alkaline water into the vessel’s exhaust which removes sulphur along with other unwanted chemicals. This process allows for the use of HSFO while still remaining compliant.

Scrubbers are categorized as open-loop, closed-loop, or hybrid, with hybrid scrubbers able to alternate between open- and closed-loop modes. Open-loop scrubbers take up seawater, use it to capture sulphur oxides (SOx) in exhaust, and then release the discharge water, or washwater, back into the ocean. Open-loop scrubbers have been shown to release hot, acidic washwater containing, in varying concentrations, PAHs, particulate matter, nitrates, nitrites, and heavy metals including nickel, lead, copper and mercury (Boer & ‘t Hoen, 2015; Comer et al., 2020; Kjølholt, Aakre, Jürgensen, & Lauridsen, 2012; Teuchies, Cox, Van Itterbeeck, Meysman, & Blust, 2020).

Unlike open-loop systems, closed-loop systems collect contaminated scrubber sludge on board and store it for on-land disposal. Closed-loop scrubbers also add caustic soda to the water to neutralize some of the acidity, but they are not waste-free, as they produce highly concentrated “bleed-off” water (Magnusson, Thor, & Granberg,
2018; Winnes, Moldanová, Anderson, & Fridell, 2016). Open-loop scrubbers are the most common type installed on ships because they are less expensive, dump any sludge they generate overboard, and do not require adding chemical additives to increase alkalinity. As of 2020, open-loop scrubbers accounted for 85% of installations; 14% were hybrid systems and the remaining 1% were closed loop.

Monitoring Wash Water with Sea Sentry

Given their high cost, the way to ensure confidence in the future return of a scrubber installation is to use an accurate, maximum range wash water monitoring solution as an integrated part of the scrubber system design. Ensuring scrubber compliance requires a monitoring system that can be trusted and operated easily by crew. Chelsea Technologies’ Sea Sentry is designed with this in mind; the highly adaptable system embeds unique technologies to ensure its adaptability, reliability, and ease of management at sea. The monitoring system contains self-maintaining features, including an integrated air purge antifouling system, automatic monitoring of the optical sensor window, automatic PAH measurement adjustments for turbidity, UV absorbance and temperature, and an integrated pump, de-bubbler, pressure relief system and flow metering.

MEPC 340 (77) Compliant Sea Sentry: Features & Applications

• Fully integrated turnkey solution for monitoring wash water and meet IMO regulations
• DNV Type Approved, DNV-GL and Class NK in compliance with IMO MEPC 259(68) and new regulations from January 2023 MEPC 340(77)
• Suitable for retro fit and new installation of open, closed loop and hybrid scrubber system
• Full PAH Range – Full 0 – 4,500µg/L PAHphe measurement which provides full compatibility with all scrubber system flow rates
• Two year calibration intervals on the PAH+ and Turbidity sensors allowing for uninterrupted monitoring
• Easy to use onboard sensor check – the new Chelsea solid standards kit allows you to verify the sensor calibration onsite with easy to operate, robust and stable solid standards as part of the commissioning process, without the need for liquids or chemicals
• Chelsea designed sensors and cabinet– as designers and manufacturers of both the sensors and complete system, Chelsea knows the science and the technology
• Confirms wash water from ship exhaust gas cleaning systems is within regulatory limits
• Suitable for both new ship and retrofit installations
• Compatible with Open Loop, Closed Loop and Hybrid systems