On the 1st of January 2020, the IMO adopted a stringent SOx emission cap with the aim to improve air quality for a more sustainable future. If a ship does not comply with these new regulations, severe sanctions are involved. Sanctions can be debunking all non-compliant fuel oil, fines, or even imprisonment of the vessel's captain. As a ship's oil tank is designed to receive oil, it is not easy to pump it out. Thus, debunking a ship's oil tank is both complex and time-consuming, and it may cause significant delays and obstruct your operation.

To comply with the IMO 2020 sulfur restrictions, the shipping industry has two options. 

Option 1:

Switch to a compliant fuel containing a lower amount of sulfur or alternative fuel with no sulfur

Option 2:

Implement a marine scrubber to lower the SOx output and continue to operate on heavy fuel oil (HFO)

A scrubber, also known as an exhaust gas cleaning system (EGCS), is an air pollution control device that can reduce the SOx output in exhaust gases from 3.5 % to less than 0.1 %, allowing a ship to operate everywhere in the world, including the Emission Control Areas (ECA). Simultaneously, a scrubber allows ships to legally use HFO. HFO is, in most cases, much cheaper than low sulfur fuels. Thus, a scrubber delivers returns in the form of fuel cost savings. This secures low OPEX, which can quickly justify the CAPEX.

Whether a marine scrubber is a good investment highly depends on the fuel price spread. The price spread may easily be triple-digit per metric ton (mt). S&P Global Platts estimated a peak in the price spread between 0.5% and 3.5% fuel oil on the 3rd of January, 2020, at $321.5/mt on a FOB Rotterdam barges basis. Yet, the gap constantly changes. When the gap peaked in January 2020, a scrubber had a return on investment (ROI) in less than 6 months. Yet, a conservative return on investment is typically 1-3 years, which still ensures a prosperous financial outlook for scrubbers. You can calculate whether a scrubber is a good investment for your operation based on your fuel consumption and the fuel price spread. You can get an overview of the fuel price spread in real-time here. 

The open-loop, closed-loop and hybrid scrubbers can thereby secure both sustainable and financial growth. Closed-loop and hybrid scrubber technology is a market-proven and environmentally sound solution. The research and analyst firm CE Delft has conducted a study called Comparison of CO2 emissions of MARPOL Annex VI Options in 2020 in where they compare CO2 emissions from producing and installing scrubbers with CO2 emissions from producing and burning refined marine fuel. To this, CE Delft concluded that scrubbers lead to a 1.5-3 % rise in CO2 emissions for a variety of relevant ships. Meanwhile, using low sulfur fuel leads to a 1-25 % rise in CO2 emissions. Thus, scrubbers have a significantly lower carbon footprint than alternative fuel options.

Learn more about the differences between open-loop scrubbers and closed-loop scrubbers here.

And the development is clear. A substantial number of vessels implement or retrofit to a hybrid scrubber or a closed-loop scrubber to maintain low OPEX by operating on cheaper heavy fuel oil. As of today, more than 4,000 ships have installed or ordered a scrubber in order to avoid expensive low-sulfur fuels. Approximately 16 % of all vessels globally, corresponding to 36 % of all container carrying capacity, operate with scrubbers.

Figure: Number of ships with scrubbers installed or ordered

Marine scrubber installations

Source: DNV GL Alternative Fuels Insights Platform

A marine scrubber can either be installed from new, or you can convert your open-loop scrubber to a hybrid or closed-loop scrubber. Yet, most often the conversion is from open-loop to hybrid. Open-loop to hybrid or closed-loop conversion is essential for the marine industry as many countries have banned open-loop scrubbers as this method discharges large amounts of sulfuric wash water effluent into the oceans causing ocean acidification.

Marine deposition - wash water and exhaust emissions - LiqTech

This is avoided with a closed-loop scrubber as this solution has an integrated alkali tank to neutralize the pH of the sulfuric scrubber wash water. The alkali tank will automatically dose the right amount of alkali to maintain a balanced pH. To do so, sodium hydroxide (NaOH) or magnesium hydroxide (MgOH) is employed. pH adjustment is a significant advantage for the marine environment as it helps prevent ocean acidification. 

A closed-loop scrubber requires a water treatment unit (WTU) as a small bleed flow of the process water is extracted for water treatment to remove sludge and harmful elements such as Polycyclic aromatic hydrocarbons (PAH) and particulate matter (PM). Based on more than 20 years of experience in the filtration industry, LiqTech has developed an innovative, state-of-the-art water treatment unit based on patented membrane technology. This solution has been employed by various scrubber manufacturers and marine industry leaders. 

Our WTU is a flexible solution that merely requires a small footprint. This enables you to utilize your capacity to the fullest. Additionally, multiple units can be installed to accommodate your specific needs. The mechanical separation process delivers high-quality water. The sludge can be disposed of in port for a small fee. This ensures that all scrubber waste is handled correctly and sustainably, enabling you to comply with current and future regulations while the solution is designed to match your specific operation.

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Want to learn more?

Visit our Marine Knowledge site to learn everything worth knowing about marine scrubbers, wash water treatment, and how to comply with the IMO 2020 sulfur cap.


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On the 1st of January 2020, the IMO adopted a stringent SOx emission cap with the aim to improve air quality for a more ...