What is a Marine Scrubber?

Stay Compliant With Marine Scrubbers

As the International Maritime Organization (IMO) applied a global limit on sulfur in ships’ exhaust gases on January 1st, 2020, marine exhaust gas cleaning systems (EGCS), also called scrubbers, have become even more vital to stay compliant.

With the current focus on sustainability, more regulations are expected to enter into force to secure a cleaner shipping industry and a cleaner environment. Let us dive into what marine scrubbers are and why they are essential.

What Is Open Loop To Closed Loop Scrubber Conversion

What Is a Marine Scrubber?

A scrubber is an exhaust gas cleaning system that removes particulate matter and harmful substances, such as sulfur oxide (SOx) and nitrogen oxide (NOx), from exhaust gas streams emitted by ships.

Before the shipping industry started to adopt exhaust gas cleaning systems, all the exhaust went directly into the atmosphere, causing great harm to our planet and human health. But by utilizing scrubbers, up to 98% of the SOx emissions are eliminated.

There are three kinds of scrubbers: open-loop scrubbers, hybrid scrubbers, and closed-loop scrubbers. Open-loop scrubbers have previously been preferred due to low installation and operational costs. Still, this method does not deliver full compliance as many countries have already prohibited open-loop scrubbers and the discharge of scrubber wash water to prevent ocean acidification. Many ports around the world are soon expected to join the ban. Learn more about which countries have adopted a ban on open-loop scrubbers and scrubber wash water discharge. Therefore, we focus on closed-loop and hybrid scrubbers as these are the methods for compliance and a sustainable future.

A closed-loop scrubber typically has three basic components:

  1. A scrubber tower to treat exhaust gas
  2. A scrubber wash water treatment unit (WTU)
  3. A sludge handling facility

1. The Scrubber Tower

A vessel generates an exhaust gas stream containing harmful particles as the engine is operates due to combustion processes in the engine. The SOx emissions are eliminated as the exhaust moves through the scrubber tower, where the gases are scrubbed with water. A closed-loop scrubber typically employs seawater with added alkalies such as sodium hydroxide (NaOH), also known as caustic soda, or magnesium hydroxide (MgOH), to scrub the exhaust gas. Yet, a closed-loop scrubber can also utilize seawater. The scrubbing process will turn the SOx from the exhaust gas into sulfates such as Na2SO4, which are harmless to the environment. A scrubber tower is typically placed high up in the ship or close to the funnel area due to available space and easy access.

Marine Scrubber Water Treatment Liqtech (1)
Marine Scrubber Water Treatment System

2. The Scrubber Water Treatment Unit (WTU)

Although exhaust gas cleaning systems significantly decrease SOx emission, they generate dirty scrubber wash water. To treat this, closed-loop scrubbers require a water treatment unit (WTU). A water treatment unit treats the wash water bleed-flow, complying with the present scrubber water discharge limits on turbidity, pH, temperature, and PAH. Read more about the discharge limits for scrubber wash water here.

Marine scrubber water treatment can remove harmful particulate matter, such as unburned fuel oil, soot particles, ash, PAH, and heavy metals from the scrubber wash water. These elements do not end in the ocean. Closed-loop scrubbers recirculate the wash water between the scrubber tower and a process tank. A continuous bleed-flow from the process tank is treated and filtered. This process ensures that no polluted scrubber wash water is discharged into the oceans.

A water treatment unit can be installed on new scrubbers or retrofitted onto existing ones.

Based on more than 20 years in the filtration industry, LiqTech has developed an innovative and efficient water treatment unit based on patented membrane technology. The LiqTech marine scrubber water treatment unit (WTU) is compact, meaning it solely takes up a small footprint of your vessel. Add to this; the design is modular to secure a flexible installation that matches your needs. The WTU is highly efficient, which provides efficient and high-quality scrubber water treatment in compliance with current and future discharge limits set by the IMO and local authorities.

See our marine water treatment unit

3. The Sludge Handling Facility

Closed-loop scrubbers retain the scrubber sludge for safe onshore disposal. Therefore, it is essential to have adequate sludge handling facilities onboard a ship. The sludge of concentrated pollutants is stored separately, where it can be further dewatered into a dry cake of up to 80% dry matter with a filter press before it is discharged in port. A filter press is acknowledged as one of the most efficient and cost-effective tools to dewater sludge. When sludge is dewatered, its weight is reduced significantly, ultimately leading to lowering handling costs.


Why Use Scrubbers?

The simple answer is: To comply with the significantly lower limits for sulfur in ships’ exhaust gas.

According to the Exhaust Gas Cleaning Association, approximately 10% of sulfur oxide (SOx) emissions stemming from human activities are caused by the global shipping industry. To lower this emission significantly, the International Maritime Organization (IMO) has implemented an international sulfur cap, which reduces the exhaust gas limit from 3.5% m/m to 0.5% m/m. Thus, the exhaust must be lower or equivalent to using fuel with 0.1-0.5% sulfur.

The IMO sulfur cap does not affect the Emission Control Areas (ECA). ECA is defined by the Annex VI of the International Convention for the Prevention of Pollution from Ships (MARPOL) Protocol. ECA represents peculiar sensitive waters, such as the Baltic Sea, the North Sea, most of the US, including the Caribbean, and Canada. Here, the upper limit for sulfur in exhaust gas is 0.1% m/m. With the IMO 2020 regulation, the amount of harmful sulfur oxide (SOx) emissions emitted from ships and vessels are thereby, reduced by as much as 77%. It corresponds to an annual drop of approximately 8.5 million metric tons of SOx. This reduction benefits the environment and human health, especially for people living in port cities and coastal areas of Asia-Pacific, Africa, and Latin America.

You can dive into the details about the IMO sulfur cap here.

Marine Knowlegde Ebook Download

Marine Knowledge E-book

If you want to learn more about the marine industry, you can download our Marine Industry Knowledge e-book.

Learn everything worth knowing about marine scrubbers, wash water treatment, and how to comply with the IMO 2020 sulfur cap.

Read about emerging trends affecting the maritime industry, marine regulations, and how to stay compliant now and in the future. 

At LiqTech, our goal is to minimize the negative impacts of living an improved lifestyle. With innovative clean technology, we reduce the harmful effects caused by various polluting industries, including the marine industry, in line with current and emerging environmental regulations. We want to share our knowledge with you; therefore, we have created a universe full of marine knowledge.

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