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Wartsila: To scrub or not to scrub

Scrubbers can make a positive impact not only on the environment, but also on a company’s bottom line, it says.
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The following ‘To scrub or not to scrub’ article was first published on the Wärtsilä magazine Twentyfour 7 in April 2019:

One way or another, ship owners are soon going to have to make big, and in some cases expensive, changes to meet compliance. New International Maritime Organization (IMO) regulations coming into force at the start of 2020 will slash the allowed concentration of sulphur oxides in fuel from the current 3.5% to just 0.5%. While strict sulphur limits had already been a fact of life for operators sailing in Emission Control Areas in Europe and North America, these new caps will now apply everywhere around the globe.

The options available to ship owners include switching from heavy fuel oil (HFO) to a compliant (and costlier) marine gas oil, converting to LNG, or using an exhaust gas cleaning system (EGCS) better known as a scrubber. Since LNG is currently available only in certain ports and reasonable only for certain ships, the vast majority of owners are left pondering the question: to scrub or not to scrub.

Heidi MJ Paulsrud, Director of Sales & Marketing at Wärtsilä's Exhaust Gas Cleaning division, points out that the answer mainly comes down to this.  Weighing the cost of the scrubber and its installation against potential savings that come from using a cheaper fuel. The more fuel you typically burn, the bigger that savings will be.

“If you look at the price differential between gas oil and HFO, even today when the differential isn't that big, the payback time for scrubbers is fairly short, especially if you install a simpler type of scrubber system,” Paulsrud explains.

The simplest type of scrubbing is done through the open-loop system, which works by spraying seawater on the exhaust to convert the sulphur oxide to sulphuric acid, then releasing the wash water back into the ocean where the acid is neutralised by the seawater's natural alkalinity. The more complex closed-loop scrubbing system is used in areas where the water's alkalinity is too low to be effective. This system then relies on caustic soda to get the job done and a system of tanks to clean and hold the wash water until it can be safely discharged. A hybrid scrubber system allows switching from open-loop to closed-loop as needed to meet compliance.

“The benefit of the open-loop system is that it's simpler. And you don't need chemicals – you basically just use seawater to scrub the exhaust. The operation and maintenance of the system are much cheaper,” Paulsrud explains.

And, fortunately, the open-loop option fits with most operating profiles. Closed-loop scrubbers, on the other hand, are intended for ships that spend much of their time on fresh water or in specific zones where discharge is prohibited. Ships that spend most of their time at sea can always opt for open-loop scrubbers and then switch to a compliant fuel when entering a problematic area.

Critical reactions

When delving into recent discussions surrounding open-loop scrubbing and its environmental impact, Paulsrud notes that there are many misconceptions surrounding the issue.

“People say you're just taking something out of the air and putting it into the sea, but actually that's not the case, at all,” she says. The difference, she explains, is that the seawater is a medium where chemical reactions are taking place. The alkaline seawater quickly converts the sulphur in the wash water into sulphates, which are a natural part of the ocean chemistry.

Recent bans on open-loop scrubbing in Singapore and China, which are based on fears that too much wash water released in high traffic areas will cause a build-up of acidity, have also cast the technology in a negative light.

28 of the 174 European Union countries have recently submitted a paper to the IMO saying the use of open loop scrubbers was “expected to lead to a degradation of the marine environment due to the toxicity of water discharges.” The paper also mentioned that it wanted to see “harmonization of rules and guidance.”

Paulsrud and other insiders, the IMO included, point out that IMO regulations for scrubber design already take these concerns into account. In other words, any MARPOL-certified scrubber on the market is efficient enough to make the concern a non-issue. Additional studies conducted in Denmark and Japan have both backed up the assertion.

In any case, such bans haven't been a big worry for scrubber owners and operators, Paulsrud says. They can always turn off the scrubber and switch fuels when needed.

Particulates matter

An added benefit in scrubbing with Wärtsilä's open-loop system is its ability to cleanse the exhaust of particulate matter (PM) – which is both a pollutant and an eyesore. Per today’s date PM capture is not addressed and/or controlled in regulations. 

“One thing people using open-loop scrubbers worry about is the particulate matter you capture in the seawater, which makes the discharged water look dirty. Of course, if you're running a vessel without a scrubber, you're still discharging it into sea, since the particulate matter from the exhaust will fall into the sea. But in the scrubber wash water you can see it more clearly,” Paulsrud explains.

To mitigate the dirt and bad optics, Wärtsilä offers a water treatment unit for its open-loop systems. “Our scrubber is designed so we can change the inlet to capture more particulates from the exhaust if we want to, and we can capture it in the water treatment later on. So we can actually adapt our scrubber to focus on more than just sulphur,” she says.

Any way to reduce stress on the environment is, of course, a step worth taking – even more so when it provides a money-saving path to regulatory compliance. In the grand matchup between Exhaust Gas Cleaning and sticking with distillates, the combined benefits of scrubbing make it the clear winner.

Photo credit and source: Wartsila
Published: 13 May, 2019
 

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Ammonia

AM Green plans to build green ammonia plant at Indian port

Initiative also includes development of green ammonia handling, storage and bunkering infrastructure, pilot bunkering operations, safety procedures and training programmes, says VOC Port Authority.

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22 hours ago

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June 3, 2026

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VO Chidambaranar (VOC) Port Authority on Friday (29 May) said it has signed a Memorandum of Understanding (MoU) with India’s ammonia producer AM Green Ammonia to collaborate in the development of a green ammonia production plant.

The plant will have a capacity of one million tonnes per annum (MTPA) at Tuticorin.

The initiative also includes development of green ammonia handling, storage and bunkering infrastructure, pilot bunkering operations, safety procedures and training programmes. 

The project is expected to support the development of green fuel corridors connecting VOC Port with major ports in Europe and Asia, thereby strengthening India’s position in the global green fuels value chain.

VOC Port also signed a Memorandum of Understanding (MoU) with Bureau Veritas (India) Pvt. Ltd., to collaborate on Green Port certification, emissions accounting, ESG reporting, safety validation, development of green bunkering practices, and establishment of a Centre of Excellence for green fuels and sustainability.

The port also plans for an upcoming 750 m³ green methanol bunkering facility.

 

Photo credit: Naveed Ahmed on Unsplash
Published: 3 June, 2026

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Port & Regulatory

Study: Major drop in ship sulphur emissions confirmed following IMO regulations

National Centre for Atmospheric Science study found that the average sulphur content in ship fuel dropped nearly tenfold in open ocean areas following IMO’s 2020 regulation.
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6 months ago

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December 8, 2025

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Recent global regulations have significantly reduced sulphur emissions from ships, helping to improve air quality in coastal regions – confirmed by a recent international study led by researchers at the National Centre for Atmospheric Science. 

The research, published in Environmental Science: Atmospheres, used aircraft and ground-based instruments to measure sulphur dioxide and nitrogen oxides emitted by ships in the North-East Atlantic and European coastal waters between 2019 and 2023.

The team found that the average sulphur content in ship fuel dropped nearly tenfold in open ocean areas following the International Maritime Organization’s 2020 regulation, which capped sulphur content in marine fuel at 0.5%. 

Before the change, many ships exceeded the previous 3.5% limit. After 2020, only a small number of ships were found to breach the new standard.

In European sulphur Emission Control Areas (SECAs), such as the English Channel and the Port of Tyne, sulphur levels were even lower – well below the stricter 0.1% limit. Interestingly, ports outside these zones, like Valencia in Spain, also showed low sulphur levels, likely due to EU rules requiring cleaner fuel when ships are docked for extended periods.

This is the first study to use aircraft-based measurements and predictions from the Ship Traffic Emission Assessment Model (STEAM3) to assess ship emissions outside of sulphur control zones since the 2020 regulation came into effect. The findings support the widely held view that ships now emit around seven times less sulphur than before the rule change – an important step toward cleaner air and healthier coastal environments.

Note: The research, titled ‘SO2 and NOx emissions from ships in North-East Atlantic waters: in situ measurements and comparison with an emission model’ can be found here. 

 

Photo credit: shraga kopstein on Unsplash
Published: 8 December, 2025

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Interview

IBIA Annual Convention 2025: ‘Exciting times’ for post IMO 2020 bunker suppliers, states Equatorial

Choong Sheen Mao, Chief Operating Officer, Equatorial, describes to Manifold Times the pre/post IMO 2020 challenges and evolution of bunker suppliers.
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7 months ago

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October 31, 2025

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Sheen Mao MT

The International Bunkering Industry Association (IBIA) will be hosting its flagship Annual Convention in Hong Kong at the Hong Kong Convention Exhibition & Convention Centre between 18 to 20 November 2025, as part of Hong Kong Maritime Week.

Choong Sheen Mao, Chief Operating Officer, Equatorial Marine Fuel Management Services (Equatorial), speaks to bunkering publication Manifold Times about the challenges of a post IMO 2020 bunker supplier.

MT: How does Equatorial continue to offer customer assurance and maintenance of marine fuel quality to ISO8217 standards despite increasing complexity of bunker fuel blends?

We maintain our focus to provide compliant, quality and competitively priced products to our customers. There is no shortcut. We source our products from a wide range of cargo producers and suppliers. We continue to be strict and vigilant with our testing programme for our products before delivering them to our customers. Equatorial has deepened our engagement with the wider industry to have a better and up-to-date understanding of the existing and new marine fuels.

MT: Can you share the evolution of commercial marine fuel procurement, blending and trading strategies on the back of increasing fuel types (pre/post IMO 2020)?

Pre IMO 2020, the main types of marine fuel procured and consumed by vessels were high-sulphur fuel oil, marine diesel oil and marine gas oil. Trading strategies were therefore closely linked to that within the oil industry.

However, many of the new fuel types are from other industries. For example, biofuels, methanol and ammonia are mainly products from the chemical and agriculture industries. There are marked differences between these industries and the energy industry (in particular, the marine fuels industry). LNG is from the gas industry which is distinct from the oil industry.

Without an existing liquid paper market for many of these commodities (especially as a marine fuel), the price risk management is less straightforward. Furthermore, commodity prices are no longer the sole consideration for price itself. The price of compliance must be considered. This could range from guaranteeing the origin of the marine fuel, its sulphur properties as well as its carbon intensity. The list goes on.

MT: Operational wise, what are the changing role and responsibilities of a bunker supplier to date, compared to before IMO 2020?

The role and responsibility of a bunker supplier have evolved. Fundamentally, it has been about providing quality marine fuels at competitive prices. Quantity assurance has been a critical concern which led to the mandatory implementation of the mass flow meter system for bunkering in the Port of Singapore. Interestingly, due to the nature of credit terms in the bunker industry, bunker suppliers also performed the role of “bankers” by extending favourable credit terms to shipowners and charterers.

These days, post IMO 2020, things have become even more complicated. Today, a bunker supplier retains the abovementioned roles and responsibilities, and much more – it has to ensure compliance with a plethora of rules and regulations. Compliance not only with sulphur cap requirements, but with international and regional sanctions and restrictions unrelated to the quality of the marine fuel itself. In fact, especially with alternative low- and zero-carbon marine fuels, this means compliance with standards, rules and regulations on sustainability such as the European Renewable Energy Directive and/or International Sustainability and Carbon Certification. There is also the need to comply with increasingly stringent safety regulations on both conventional and alternative marine fuels.

In addition to the above, a post IMO 2020 bunker supplier is still expected to supply compliant and quality fuel at competitive prices.

MT: Equatorial is Singapore’s largest local-born supplier; what is the next big thing for the company?

Equatorial continues to adapt and improve with the times, while maintaining its core values – Integrity, Teamwork, Commitment, Proficiency and Quality, and Safety and Environment. The bunker industry is a highly competitive one, and it is our intention to keep our competitive edge and remain relevant. This means that we have had to step out of our comfort zone and embrace the two mega trends of our time – digitalisation and decarbonisation.

We have been early adopters and developers of the electronic bunkering note as part of our own digital bunkering efforts. We have diversified our product offering to include low carbon marine fuels and are proud to be one of the pioneers for bunkering B100 biofuels earlier this year. This was made possible by the arrival of our IMO Type II chemical and oil bunker tankers. These same bunker tankers are also capable for carrying and delivering methanol. Equatorial has invested in an LNG bunkering vessel (LBV) newbuilding that is set to be delivered in Q3 2027. We are also involved in a study to develop low- or zero-carbon ammonia bunkering in Singapore.

These are exciting times.

Note: Choong Sheen Mao is amongst panellists featured in ‘Session Three: Bunker Sellers Panel’ at the IBIA Annual Convention 2025.

Join the Conversation

With over 300 delegates expected, the IBIA Annual Convention 2025 is set to be a defining moment for the marine fuels industry. Registration is now open via the IBIA Annual Convention website.

 

Photo credit: Manifold Times
Published: 31 October 2025

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