Exhaust Gas Scrubbers
- Admin
- Oct 7
- 3 min read
Since the introduction of IMO 2020 sulphur regulations, “scrubber” has become a familiar word for every mariner — but not everyone fully understands what it does, how it works, or when it must be used.
Let’s break it down in simple and practical terms 👇
1. What Is a Scrubber?
A scrubber (Exhaust Gas Cleaning System, EGCS) is a device installed in a ship’s exhaust system to remove sulphur oxides (SOₓ) from the exhaust gases before they are released into the atmosphere.
It allows ships to continue using high-sulphur fuel oil (HSFO) while still complying with the IMO limit of 0.50% sulphur content in emissions.
In short:
A scrubber “washes” the exhaust gases — cleaning them from sulphur and other particles before discharge.
2. Why Do We Need Scrubbers?
Sulphur oxides from ship exhaust contribute to acid rain, air pollution, and health problems near coastal areas.
To reduce these emissions, the IMO (MARPOL Annex VI) established global and regional limits on sulphur content in fuel.
Since 1 January 2020:
Global sulphur limit: 0.50%
ECA (Emission Control Area) limit: 0.10%
Ships without scrubbers must burn low-sulphur fuels (VLSFO, MGO).Ships equipped with scrubbers can use HSFO (typically 3.5% S) while keeping emissions equivalent to burning low-sulphur fuel.
3. What Are ECA Zones?
ECA (Emission Control Areas) are specific sea regions where stricter limits for sulphur and other pollutants apply.
As of now, the main ECAs are:
Baltic Sea
North Sea
North American Coast
US Caribbean Sea
When your vessel enters an ECA zone:
Sulphur content in emissions must not exceed 0.10%, or
The scrubber system must be in full operation and properly monitored.
4. How Does a Scrubber Work?
A scrubber uses water (sea water or fresh water with alkali) to wash the exhaust gas.
There are three main types:
Type | Description | Typical Use |
Open-Loop | Uses seawater’s natural alkalinity to neutralize SOₓ. Wash water is discharged back to sea. | Common in open ocean; restricted in some ports. |
Closed-Loop | Uses freshwater with chemicals (e.g. caustic soda). Water is recirculated, and residues are stored on board. | Used where discharge is restricted. |
Hybrid | Can operate in both open and closed modes. | Most flexible, modern installations. |
Inside the scrubber tower, exhaust gas passes through spray nozzles or packed beds, where sulphur reacts with water and is converted to harmless compounds (mainly sulphates).
5. When and How to Use Exhaust Gas Scrubber?
Scrubber must be started before entering ECA zones, allowing time to stabilize operation.
The exhaust gas monitoring system continuously records SO₂/CO₂ ratio, proving compliance.
Crew must log all mode changes (fuel switching, open/closed mode, malfunctions) in the EGCS Record Book or Oil Record Book Part I.
Washwater discharge, pH, and turbidity are also logged as per MARPOL requirements.
If the system fails inside an ECA, you must:
Report immediately to the flag and port state authority, and
Change over to compliant fuel as soon as possible.
6. Scrubber Residues and Environmental Issues
Residues from closed-loop systems are stored on board and must be land-disposed ashore as waste. Many ports have restrictions on open-loop discharge, especially in:
Singapore
China
European ECAs
U.S. coastal waters
Before arrival, always check port circulars or Notices to Mariners regarding scrubber discharge bans.
7. Key Takeaways for Deck and Engine Officers
-Understand when the scrubber must be running (ECA entry/exit points).
-Monitor and record all operational parameters.
-Keep EGCS manuals, certificates, and records ready for PSC inspection.
-Check local regulations on washwater discharge.
-Always follow the manufacturer’s start-up/shutdown sequence — improper operation can damage the unit.
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