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Fuel Oil Sulphur Limits

Fuel Oil Sulphur Limits As ships use heavy fuel oils that contain up to 3.5% sulphur, exhaust gases from their diesel engines contain sulphur oxides (SOx) that are known to be a cause of air pollution and acid rain.
Regulation 14 of MARPOL Annex VI (International Convention for the Prevention of Pollution from Ships) stipulates that the amount of sulphur in fuel oil shall be gradually reduced.

Sulphur Limit for Ship’s Fuel Oil

Regulatory Overview

In SOx emission control areas (ECA: Emission Control Areas) such as the North Sea and the Baltic Sea in Europe and coastal areas in North America, the use of fuel oil containing no more than 0.1% sulphur was already mandatory, but from 1 January 2020, the use of fuel oil containing no more than 0.5% sulphur has also become mandatory in general sea areas outside ECA.

  • MRegulation 14 of MARPOL 73/78 Annex VI
    Gradual regulation of sulphur content in fuel oil used on ships

Regulation 14. 1 General Requirements (general sea areas)
The sulphur content in fuel oil used on ships operating in general sea areas (not ECA) shall not exceed the following:

  1. 4.50% m/m (up to 1 January 2012)
  2. 3.50% m/m (from 1 January 2012)
  3. 0.50% m/m (from 1 January 2020)

Regulation 14. 4 Requirements within emission control areas (SOx Emission Control Areas: ECA)
The sulphur content in fuel oil used on ships operating in ECA shall not exceed the following:

  1. 1.50% m/m (up to 1 July 2010)
  2. 1.00% m/m (from 1 July 2010)
  3. 0.10% m/m (from 1 January 2015)

Requirements of Exhaust Gas Cleaning System (EGCS)

According to Regulation 4 of MARPOL Annex VI, the use of conventional heavy fuel oil is permitted by installing an exhaust gas cleaning system (EGCS: Exhaust Gas Cleaning System) capable of reducing the SOx in exhaust gas to below the regulation value.
This exhaust gas cleaning system is a scrubber system that enables the continuous use of conventional heavy fuel oil with low cost and stable quality.

SOx concentration in exhaust gases

The SO2/CO2 ratio must meet the specified value to be equivalent to low-sulpfur fuel. To be equivalent to fuel oil with a 0.5% sulpfur content, SO2/CO2 must be 21.7 or less, and to be equivalent to fuel oil with a 0.1% sulpfur content, SO2/CO2 must be 4.3 or less.

SOx removal rate of scrubber

If common heavy fuel oil containing 3.5% sulphur is used, the following SOx removal rate must be achieved.
Equivalent to fuel oil with 0.5% sulpfur content: removal rate must be 85.7%(=(151.7-21.7)/151.7)
Equivalent to fuel oil with 0.1% sulphur content: removal rate must be 97.2%(=(151.7-4.3)/151.7).

Sulphur concentration in fuel oil
(% m/m)
SO₂/CO₂ emission ratio
(ppm)/(% v/v)
4.50 195.0
3.50 151.7
1.50 65.0
1.00 43.3
0.50 21.7
0.10 4.3

Discharge water of scrubber

Potential of hydrogen (pH), polycyclic aromatic hydrocarbon (PAH), and turbidity/suspended particulate matter (SPM) must be continuously monitored and recorded.

For nitrates, analytical data on emissions must be submitted at the initial and renewal inspections Note 1).

  • A discharge water sample is collected and analyzed at least 3 months prior to a renewal inspection.
Discharge water regulation value
pH Min. pH 6.5 at 4 meters from the overboard discharge point
PAH The PAH concentration difference between wash water and discharge water should not be greater than 50 ug/L PAHphe at 45 t/MWh of sea water flow.(In case the flow rate of sea water increases or decreases, the flow rate x concentration should not be greater than 45 t/MWh x 50 ug/L PAHphe.)
SPM The maximum continuous turbidity of discharge water should not be greater than 25 FNU or 25 NTU compared to the turbidity of wash water.
Nitrates Either 12% of NOx emissions in the exhaust gas or a nitrate concentration of 60 mg/L in 45 t/MWh equivalent sea water is not exceeded, whichever is greater.
(In case the flow rate of sea water increases or decreases, flow x concentration should not be greater than 45 t/MWh x 60 mg/L.)

What is "DIA-SOx®" ?

We have developed a distinctive SOx scrubber by integrating Mitsubishi Shipbuilding's marine engineering capabilities with the technologies possessed by Mitsubishi Hitachi Power Systems and Mitsubishi Kakoki Kaisha. This product is "DIA-SOx®".



With this phrase in mind, Mitsubishi Shipbuilding is striving to develop and promote marine solutions such as "DIA-SOx®", to contribute to further development of marine logistics and a reduction of environmental impacts that are expanding on a global scale.

DIA-SOx® Product Lineup

DIA-SOx® has two types of towers. A wide range of engine outputs is supported.

Mitsubishi Shipbuilding’s Role


Large design impact SOx scrubber

The SOx scrubber system reduces the sulphur oxides (SOx) contained in the exhaust gases from main engines and generator engines installed on board ships. The layout of the engine room of ships has changed over the years, with the use of electronically controlled engines and the mandatory installation of local fire extinguishers and ballast water treatment systems. The SOx scrubber system is one of onboard auxiliary systems with a large impact in the last 20 years. The installation of a scrubber not only changes the engine room, but also greatly affects the ship's overall basic plan, including the ship's appearance, stability, vertical strength, and equipment number.

Very important thing to note regarding SOx scrubber installation

A scrubber system does not function by itself; for example, the scrubber tower is integrated into the engine exhaust line, scrubber pumps are connected to the seawater line, and scrubber monitoring and recording systems are connected to GPS and engine control systems to receive and use the relevant signals.
Therefore, unlike other marine auxiliaries, this system requires careful preparation for installation while adjusting to match the onboard piping and electrical systems.


Mitsubishi Shipbuilding’s Role

Through joint development with Mitsubishi Hitachi Power Systems and Mitsubishi Kakoki, Mitsubishi Shipbuilding’s role is to commercialize a scrubber system with high safety and reliability that is easy to apply to existing engine plants, and to provide various services for enabling faster, easier and more reliable installation of this system by shipowners and shipyards.

DIA-SOx® Value Chain

The excellent technology of our development partners has been reborn as a marine SOx scrubber with high safety and reliability that can be easily applied to existing engine plants through a rigorous verification process.

We use the global supply chain of the MHI Group not only to ensure quality, but also to meet the demands of quick delivery and multiple lot orders.

We develop the system requirements and design concept based on the customer's views, actual ship operational data, and the results of analyzing installations on various ship types.
Based on the requirements and concepts, we utilize the knowledge each partner has developed to realize the scrubber system.
Using our long experience of shipbuilding, we review the design from the perspective of shipyards that actually carry out installation of the scrubber system.
We continue to make improvements to detailed points such as customizing land-use equipment and improving ease of installation as well as complying with classification rules and international regulations.
The concepts of "DREaM PaC" and "ACTIVE FUNNEL" were born out of this marinize review.
We are working to reduce costs of common parts by joint purchasing, developing a local supply chain for overseas production, and building a stable supply scheme for products.
We propose the optimum system for the planned ships.
In the case of retrofit, we also support requests for package orders including engineering and installation work at our dockyard and so on.
We also support requests such as dispatching supervisor when carrying out installation work at overseas yards, etc.
  • We share jointly developed technologies with Mitsubishi Kakoki Kaisha, Ltd. and manufacture and sell them under our own brand names.

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