Scrubber technology: What you should know about exhaust gas scrubbing on ships.

Sulphur oxide: A problem for people and the environment

Ships on which fossil fuels (such as heavy fuel oil and marine diesel) are burned emit a large number of air pollutants, especially sulphur oxides. Sulphur oxides are strong respiratory poisons. Even in low concentration in the air they can lead to coughing, breathing difficulties, or inflammation of the respiratory tracts. It is estimated that in 2018 alone the emission of sulphur oxides by ships worldwide caused about 400,000 people to die prematurely and approximately 14 million children to develop asthma. Equally as disastrous are the effects of sulphur oxides on the environment as they may alter plant growth and destroy ecosystems. In the atmosphere sulphur oxides can convert to sulphuric acid, which may be deposited on the ground and in vegetation. This is a major factor in the acidification and impoverishment of our natural environment.

To counteract these loads, the sulphur content in ship fuel has been limited to 0.1 percent in Europe since January 2015 in the so-called emission control areas (ECAs). The North Sea and Baltic Sea are among the emission control areas, for example. Since early 2020 a maximum sulphur content of 0.5 percent in ship fuel applies worldwide to lower the air pollution caused by ships effectively and sustainably. 

The easiest and fastest solution to reduce sulphur emissions is the use of fuels that contain less sulphur. But there is another solution: Thanks to scrubber technology.

The scrubber technology: Desulphurisation as an alternative to fuels with a low sulphur content

As an alternative to sulphur-reduced fuels the international regulations on reducing sulphur emissions in maritime transport explicitly allow the desulphurisation of exhaust gases. This is realised with the aid of so-called exhaust gas cleaning systems (EGCS) or in brief: scrubbers. The international classification society DNV (called DNV GL until March 2021) estimated that in 2019 already 3,756 vessels that were either in use or being built had a desulphurisation scrubber fitted on board. 

What exactly is a scrubber and how does it work? In simple words: A scrubber is an apparatus in process engineering that is fitted on board a vessel to filter or scrub the sulphur out of the exhaust air to prevent the sulphur from being blown into the atmosphere. In most cases "wet scrubbers" are used, which scrub the exhaust gas with seawater. In this process, seawater is drawn in by pumps and then sprayed onto the stream of exhaust gas. The water absorbs the pollutants (such as sulphur oxides) from the exhaust gas and turns into scrubber water.

Depending on the scrubber system used, the scrubber water is then either discharged back into the ocean (open loop system) or it is collected on board, where it is chemically or physically treated and disposed of in the next port (closed loop system). Next to these two wet processes, dry scrubber systems can be employed. They are based on a lime slurry that has to be completely disposed of in the port after use. 

Environmental impacts of scrubber systems

Scrubbing technology divides the shipping industry worldwide: Some are for gas scrubbing and some are against. The opponents favour the new, low-sulphur fuels. As a matter of fact, scrubbers filter many other pollutants out of the exhaust gases in addition to sulphur oxides. However, they are not the final solution for reducing pollutants overall.

The largest problem with scrubbing: The composition of scrubber water is highly complex and varies depending on the quality of the fuel used, the machinery output, the completeness of combustion, the preload of the seawater collected and the performance of the scrubber itself. Limits for the scrubber water have been stipulated by the Marine Environment Protection Committee (MPEC), regulating the pH, turbidity, nitrate and PAHs (polycyclic aromatic hydrocarbons) contents of the waste water produced in the scrubbing process. But does the shipping industry observe these regulations? 

In 2021 the German Environment Agency published a recent assessment of environmental impacts of scrubber systems in a comprehensive study. The market analysis contained in this study showed that more than 3,000 ships, accounting for 16.8 percent of the world fleet's deadweight tonnage, are currently fitted with scrubbers. On many of these ships, significant breaches of the EGCS guidelines stipulated by the IMO (International Maritime Organization) regarding the waste water quality criteria were detected. The German Environment Agency's investigations to date have revealed that many scrubber waters are too acidic and contain several pollutants such as heavy metals and polycyclic aromatic hydrocarbons. In addition, many EGCS waste waters showed oil residues and nitrate in relevant concentrations. 

Another disadvantage of the scrubber technology: The installation on board requires space, additional technical equipment and significant investments in the medium to high single-digit million euro range. However, the investments pay back quickly when the price difference between the HFO (heavy fuel oil) and the costly low-sulphur blends is high and storage costs are compared to charter income. Richard von Berlepsch, Managing Director of Hapag-Lloyd's Fleet Management comments on the scrubber technology: "From our point of view scrubbers are not the technology of the future. They are only an interim solution." 

KSB is your partner for all questions on scrubber technology and alternative fuels

Depending on the process and manufacturer technology used, the individual treatment circuits and fluids to be pumped in the scrubber technology differ. All process stages therefore have to be closely examined in terms of temperature, pH, chloride/sodium contents, solids, oil, sulphur and other additives as well as their oxygen content. In the first stage, the interactions of the individual substances and their critical temperatures can cause pitting and crevice corrosion at metal components as well as at pumps and valves. This can be avoided by adjusting them specifically to the process.

Opt for KSB as your partner who has been a major player and actively involved in scrubber technology and alternative fuel developments for many years. KSB has even designed a complete product portfolio for the scrubber technology. Many open loop and closed loop systems today are fitted with reliable KBS pumps, such as vertical ILN and ILNC centrifugal pumps or single-stage Etabloc volute casing pumps. Other KSB products found on board many vessels in the world, helping to make the shipping industry greener, are Movitec high-pressure in-line pumps as well as ISORIA and KE centred-disc butterfly valves.

Don't hesitate to contact us: As a single-source supplier, KSB has detailed knowledge of the production, transport and storage of new alternative fuels and alternative energy sources. We look forward to hearing from you. Please contactus.