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IMO2020 Sulphur Cap Regulations


Per the first of January 2020 the IMO202 Sulphur Cap has been in place. This article give you answers to most questions you can have about the regulations and requirements of the IMO2020 SULPHUR CAP.


The Marine Environment Protection Committee (MEPC) of IMO adopted the 1997 Protocol to the MARPOL Convention, which added Annex VI, Regulations for the Prevention of Air Pollution from Ships. This Annex entered into force on May 19, 2005. To reduce the harmful effects of SOx emissions on human health and the environment, Regulation 14 to Annex VI introduced a worldwide limit on the sulfur content of 4.5 percent to marine fuels and a limit of 1.5 percent in designated SOx emission control areas (SECA). The Baltic Sea was the inaugural SECA adopted under the Annex and was followed by the North Sea/English Channel SECA (see Figure 1) on November 22, 2007.

IMO2020 Sulphur Cap

In October 2008 the 58th IMO MEPC session adopted significant changes to Annex VI under Resolution MEPC.176 (58). A global sulfur fuel limit of 3.5 percent became effective January 1, 2012, and introduced further reductions in the fuel sulfur limits within SECAs, with a limit of 1.0 percent applicable from July 1, 2010, and 0.1 percent from January 1, 2015. In the 70th MEPC session, held in October 2016, member states agreed that a 0.5 percent global sulfur cap on marine fuel would be implemented in 2020 based on the studies that identified the availability of compliant fuel (0.5%S).

What are the IMO2020 fuel oil Sulphur limits?

See Table 1 for IMO fuel oil sulfur limits.

Date Sulfur % Date Sulfur %
Initial limits 4.5 Initial limits 1.5
Jan 1, 2012 3.5 Jan 1, 2010 1.0
Jan 1, 2020 0.5 Jan 1, 2015 0.1

Table 1: IMO fuel oil sulfur limits

The revised Annex VI included a change to the terminology and regulations associated with the coastal air emission control areas with the revision from SECAs to ECAs. This added the provision to designate the areas as SOx, NOx and PM Emission Control Areas. Currently IMO does not define PM limits, but PM is significantly reduced through the reduction of the sulfate portion of the PM by the use of low-sulfur fuels or other technological means such as exhaust gas cleaning system (EGCS). IMO Resolution MEPC.190 (60) and IMO Resolution MEPC.202 (62) added two new ECAs, the North American ECA and the U.S. Caribbean waters, including Puerto Rico and the U.S. Virgin Islands ECA


The IMO Guidelines are based on wet scrubbing technologies and therefore are not applicable to other abatement techniques.

The development of EGCS for use on board of ships has been driven by the aforementioned IMO, national, and local regulations. These EGCS were envisaged by the original Regulation 14.4 (b) to MARPOL Annex VI, whereby SOx emissions were limited to 6.0g/kWh for systems that met the requirements in the subsequently developed guidelines of IMO2020 Resolutions MEPC.130 (53), MEPC.170 (57), MEPC.184 (59) 2009 and MEPC.259 (68) 2015 Guidelines for Exhaust Gas Cleaning Systems (adopted on May 15, 2015, and hereafter referred to as the ‘2015 Guidelines’). These provide guidance for the monitoring of the SO2/CO2 content of the exhaust gases for varying sulfur contents of the fuel (see Table 3) to provide equivalency to the prescribed specific SOx emission limits as stipulated in Regulations 14.1 and 14.4.

The 2008 revision to MARPOL Annex VI removed the specific reference to EGCS from Regulation 14, and approval of an EGCS is now undertaken in accordance with the requirements under Regulation 4 of the Annex as an ‘equivalent’. Flag Administrations must take into account any relevant guidelines developed by IMO2020 when assessing the equipment and notify IMO2020 (for circulation to all Administration parties) of the details of that assessment. It is important to note that the 2015 Guidelines are not regulations. However, it is understood that EGCS installations meeting these guidelines will be accepted as equivalent by the Administrations. This equivalence needs to be confirmed by the flag Administration of each vessel onto which the equipment is to be installed on a case-by-case basis. The 2015 Guidelines identify the method of determination of the pH value from the discharge washwater. The pH can be determined either by direct measurement or by using a calculation-based methodology (computational fluid dynamics or other equally scientifically established empirical formulae) to be left to the approval by the Administration.

Among other sections, the following provisions were retained:

The recommendation to IMO2020 Administrations to collect data on washwater discharges in accordance with Appendix 3 of the 2015 Guidelines enables this criterion to be subsequently reviewed by the IMO2020, taking into account any advice from the Joint Group of Experts on the Scientific Aspects of Marine Environmental Pollution (GESAMP).

Provision of two basic Schemes for compliance to be used for EGCS approval, Scheme A or Scheme B, at the choice of the equipment manufacturer. Approval is to be undertaken in accordance with the initial and ongoing survey requirements of the guidelines by, or on behalf of, a flag Administration, typically by a class society recognized by the Administration (as a Recognized Organization or RO). Refer to EGCS Approval for the approval process

The two EGCS schemes apply the following concepts:

  • Scheme A based on initial emission performance unit certification together with a continuous check of operating parameters and daily exhaust emission monitoring
  • Scheme B based on continuous exhaust emission monitoring together with a daily check of operating parameters

In both cases, the condition of discharged washwater used in the scrubbing process is to be monitored and recorded.


For Scheme A approvals, the EGCS must be certified as meeting the emission limit value specified by the manufacturer (the ‘certified value’) for continual operation with fuel oils of the manufacturer’s specified maximum sulfur content over the range of declared exhaust gas mass flow rates. Mechanisms are in place within the guidelines for the emissions testing to be reduced for ‘serially manufactured units’ of nominally similar designs where an agreed ‘conformity of production’ arrangement is in place.

Alternatively, it is possible for the manufacturer to obtain a ‘product range approval’ for the same scrubber design by undertaking emissions testing at the highest, intermediate and lowest capacity ratings. This certification can be undertaken prior to or after installation onboard and is approved by the issue of a serial number-based Sox Emissions Compliance Certificate (SECC) on behalf of the vessel’s flag Administration. The basis of the approval and the EGCS operating and maintenance parameters, together with survey procedures, are to be contained within the EGCS – Technical Manual for Scheme A (ETM-A), which is also to be approved by the Administration, or RO acting on its behalf.

The EGCS is to be surveyed after installation to confirm that the scrubber is installed in accordance with the ETM-A, and has the relevant SECC. This would enable the ship’s MARPOL Annex VI International Air Pollution Prevention (IAPP) Certificate to be amended and re-issued to reflect the EGCS installation. Subsequent surveys will be undertaken at the usual MARPOL Annex VI annual, intermediate and renewal survey intervals. Continual compliance is verified by continuous monitoring of EGCS operating parameters, daily checks of the exhaust emissions and continual monitoring of the washwater discharge. The shipowner is required to maintain an EGCS Record Book, in which the maintenance and service of the EGCS is to be recorded and made available for inspection at EGCS surveys. The form of this record book is to be approved by the Administration and may form part of the vessels planned maintenance record system.


The Scheme B EGCS does not require pre-certification to meet the emission limit value but must demonstrate compliance with the required equivalent emission values to the fuel sulfur content requirements 14.1 and 14.4 of MARPOL Annex VI Regulation 14 at any load point, including during transient operation, by verification of the SO2/CO2 ratio after the scrubber is in accordance with Table 2. This must be undertaken on a continual basis by the use of a continuous exhaust gas monitoring system that is approved by the Administration, and which records data at a rate of at least 0.0035 Hz.

Similar to Scheme A, Scheme B EGCS units are to be supplied with an approved EGC Technical Manual -B (ETM-B) detailing the EGCS operating parameters and limits. The EGCS is to be surveyed after installation and at the usual MARPOL Annex VI Annual, Intermediate and Renewal Survey intervals, in the same manner as Scheme A is surveyed for issue of the IAPP Certificate. Continual compliance is verified by continuous monitoring of the exhaust emissions, daily spot checks of the EGCS operating parameters and by continual monitoring of the washwater discharge. Scheme B ships should be supplied with an EGCS Record Book in the same manner as Scheme A.


For ships intending to use an EGCS in part or in full to comply with Regulation 14 of MARPOL Annex VI, a SOx Emissions Compliance Plan (SECP) must be approved on behalf of the Administration and is required to detail the method of compliance for all fuel oil combustion machinery installed on board. Furthermore, an approved Onboard Monitoring Manual (OMM) is also to be retained on board the vessel for each installed EGCS.

The OMM should be approved by the flag State of the vessel and is to include the following parameters:

  • Data on the sensors used in the EGCS emissions and washwater monitoring system, including service, maintenance and calibration
  • Positions where the exhaust and washwater measurements are to be taken, together with any necessary supporting services or systems
  • Data on the analyzers to be used in the emissions and washwater systems, including operation, service and maintenance requirements
  • Procedures for analyzer zero and span checks
  • Other information and data needed to properly operate and maintain the monitoring systems
  • Details on how the monitoring systems are to be surveyed

Table 3 details the approved EGCS documentation that needs to be on board a ship utilizing EGCS under Scheme A

or B of the 2015 Guidelines.

Table 2: EGCS Sulfur Content Emission Equivalence

Fuel Oil Sulfur Content (% m/m) Ratio Emission
SO2 (ppm)/CO2 (% v/v)
4.5 195.0
3.5 151.7
1.5 65.0
1.0 43.3
0.5 21.7
0.1 4.3

Fuel Oil Sulfur Content (% m/m)

Document Schema A – Parameter Check Schema B – Continuous Monitoring
SOx Emissions Compliance Plan (SECP) X X
SOx Emissions Compliance Certificate (SECP) X
EGCS Technical Manual, Scheme A (ETM-A) X
EGCS Technical Manual, Scheme B (ETM-B) X
Onboard Monitoring Manual (OMM) X X
EGC Record Book or Electronic Logging System X X

SO2 (Table 3: List of Documents needed for Scheme A – Parameter Check and Scheme B – Continuous Monitoring


For EGCS operating on distillate and residual fuel oils, exhaust emission compliance with the equivalent fuel oil sulfur content is verified from the measured SO2/CO2 concentration ratio. Table 2 from the 2015 IMO Guidelines shows the required SO2/CO2 ratio in a diesel engine’s exhaust and the equivalent sulfur concentration in the fuel. If the exhaust from the scrubber has the same or lower SO2/CO2 ratio as that tabulated, for example less than 4.3 for a vessel operating in an ECA where fuel of a maximum of 0.1 percent sulfur is applicable, then the scrubber is considered to be providing equivalent effectiveness.

The verification through the SO2/CO2 ratio enables a much simpler verification of exhaust emissions. The derivation of this ratio and its applicability to typical marine fuels is given in Appendix 2 of the 2015 IMO2020 Guidelines and demonstrates the correspondence between the 6.0g/kWh prescribed by the original MARPOL Annex VI requirements based on a brake-specific fuel consumption of 200g/kWh. For those scrubbers where the exhaust gas cleaning process may affect the amount of CO2 in the exhaust gases, the CO2 concentration is to be measured before the scrubber, and the SO2 concentration after it, to calculate the ratio correctly.


The 2015 IMO2020 Guidelines specify the discharge washwater quality criteria and monitoring requirements for a number of parameters. Additional washwater limitations may be set by regional, federal or state regulations. Shipowners and vessel managers are encouraged to verify the requirements for each of the intended ports in a vessel’s voyage.


The 2015 IMO2020 Guidelines require a limit of pH 6.5 using one of the following two methods:

The pH of the washwater discharged from the scrubbing process at the overboard discharge should be no lower than 6.5 except during maneuvering or transit where the pH difference between the ship’s inlet and overboard discharge can be up to 2 pH units measured at the ship’s inlet and overboard discharge.

The overboard pH discharge limit applicable to the overboard discharge monitoring position can be determined either by means of direct measurement or by using a calculation- based methodology (computational fluid dynamics or other equally scientifically established empirical formulae) subject to the approval of the Administration to achieve with the ship stationary a pH of 6.5 at a distance of 4 m from the overboard discharge point, and in accordance with the following conditions to be recorded in the ETM-A or ETM-B:

1. EGC units connected to the same outlets and operating at their full loads, (or highest practicable load) and with the fuel oil of a maximum sulfur content for which the units are to be certified (Scheme A), or used with (Scheme B)

2. If a lower sulfur content test fuel and/or test load lower than maximum sufficient for demonstrating the behavior of the washwater plume is used, the plume’s mixing ratio must be established based on the titration curve of seawater. The mixing ratio would be used to demonstrate the behavior of the washwater plume and that the overboard pH discharge limit has been met if the EGCS is operated at the highest fuel sulfur content and load for which the EGCS is certified (Scheme A) or used with (Scheme B)

3. Where the washwater flow rate is varied in accordance with the EGCS gas flow rate, the implications of this for the part load performance should also be evaluated to confirm that the overboard pH discharge limit is met under any load

4. Reference should be made to a seawater alkalinity of 2,200 mol/litre and pH 8.2; an amended titration curve should be applied where the testing conditions differ from the reference seawater, as agreed by the Administration

5. If a calculation-based methodology is to be used, details to allow its verification such as, but not limited to, supporting scientific formulae, discharge point specification, washwater discharge flow rates, designed pH values (at both the discharge and 4 m location), titration, and dilution data should be submitted The pH is to be continuously monitored with a pH electrode and meter having a resolution of 0.1 pH units and temperature compensation, with both electrode and meter meeting the standards referenced by the Guidelines.

The washwater discharge may be diluted by mixing with other sources of seawater, such as cooling water discharges, to achieve the required pH level. Furthermore, the pH at the washwater discharge may be adjusted by controlling the flow of reactive water to the EGC unit. For those EGC units using chemicals or additives to meet the pH, or any other washwater criteria, the washwater is required to be further assessed for those agents, taking into account IMO guidance for ballast water management systems that make use of active substances (G9 under MEPC.169 (57)).


The washwater discharge is also to be monitored for polycyclic aromatic hydrocarbons (PAH), whereby the maximum continuous PAH concentration is not to be greater than 50μg/L PAHphe (phenanthrene equivalence) above the inlet water PAH concentration. The PAH concentration should be measured downstream of the water treatment equipment (i.e. after any water treatment equipment), but upstream of any washwater dilution or other reactant dosing unit, if used, prior to discharge. This limit value is applicable to EGCS washwater flow rates normalized to 45t/MWh, where MW refers to the maximum continuous rating (MCR) or 80 percent of the power rating of the fuel oil combustion unit. This limit may be adjusted up or down in accordance with Table 4 for

different flow rates.

Table 4: PAH Discharge Concentration Limits

Flow Rate (t/MWh) Discharge Concentration limit (µg/L PAHphe equivalents) Measurement Technology
0- 1 2,250 Ultraviolet Light
2.5 900 Ultraviolet Light
5 450 Fluorescence*
11.25 200 Fluorescence
22.5 100 Fluorescence
45 50 Fluorescence
90 25 Fluorescence

* For any flow rate greater than 2.5 t/MWh fluorescence technology should be used.

The 2015 IMO2020 Guidelines permit a 15-minute deviation of up to 100 percent of this limit value, in any 12-hour period, to account for EGCS startup. The PAH discharge is to be continuously monitored and the monitoring equipment must be capable of monitoring PAH in a range twice that given to the applicable limit value as shown in Table 4, using either the permitted ultraviolet or fluorescence measuring techniques. The monitoring equipment must not deviate by more than 5 percent within the working range of the application.


The turbidity of the EGCS washwater should not exceed 25 FNU (formazin nephlometric units) or 25 NTU (nephlometric turbidity units) above the inlet water turbidity. This should be measured continuously using equipment meeting the requirements of the standards referenced by the 2015 IMO2020 Guidelines. During periods of high turbidity, the time lapse between inlet and outlet measurements may be such that the acceptable limiting difference may be unreliable. Therefore, all turbidity readings must be a rolling average over a 15-minute period to a maximum of 25 FNU.

The turbidity in the washwater must be measured downstream of any water treatment equipment, but upstream of washwater dilution (or other reactant dosing) prior to discharge. The treatment system should be designed to minimize suspended particle matter such as ash and heavy metals. Similar to the criteria for PAH, the Guidelines permit a 15-minute deviation of up to 20 percent in any 12-hour period.


Washwater discharge samples are to be taken within three months of an EGC unit renewal survey and analyzed for nitrate discharge data. The analysis certificate is to be retained as part of the EGC Record Book for the purpose of verifying that the washwater treatment system prevents the discharge of nitrates beyond a level equivalent to 12 percent removal of NOx from the exhaust, or 60 mg/l normalized for a discharge flow rate 45t/MWh. The Guidelines require that all EGCS be tested for nitrates in the discharge water and, if typical levels are above 80 percent of the upper limit, they should be recorded in the ETM-A or ETM-B.


The 2015 IMO2020 Guidelines require that data recording devices are provided as part of any EGCS installation. The following details some of the basic system data that is to be continuously monitored and recorded automatically against Universal Coordinated Time (UTC) and vessel position by Global Navigational Satellite System (GNSS):

  • Washwater pressure and flow rate at the at the EGC unit’s inlet connection
  • Exhaust gas pressure before and pressure drop across the EGC unit
  • Engine and/or boiler load(s)
  • Exhaust temperature before and after the EGC unit
  • Exhaust gas SO2 (ppm) and CO2 (%)
  • Washwater pH, PAH and turbidity
  • Temperature
Monitoring Scrubber emmisions

The data recording device should be robust, tamper-proof, read-only and able to record at a rate of at least 0.0035 Hz. It should be capable of preparing reports over specified time periods and the data should be retained for a period of at least 18 months from the date of recording. If the unit is changed during that time period, the shipowner should ensure that the required data is retained onboard and available as may be required. The device should be able to download a copy of the recorded data and reports in a readily usable format. The copy of the data and reports should be made available to the flag Administration or Port State

Control (PSC) authorities upon request. The emission and discharge measurement are summarized as follows.

Table 5

Design Requirements Measurement Method
  • CO2 analyser is to be operating on non-dispersive infared (NDIR) principle
  • SO2 analyser is to be operating on non-dispersive infrared (NDIR) or non-dispersive ultraviolet(NDUV) principle
  • Sampling probe is to be at least 10 pipe diameters downstream of the EGC unit, and 0.5 m or 3 pipe diameters, whichever is greater, upstream of the exit exhaust gas system
  • Temperature at the sample gas probe is to be at least 70 deg C. Alternative sampe probe location is subject to approval by Administration
  • The pH electrode and pH meter are to have a resolution of 0.1pH units and temperature compensastion
  • The electrode is to meet requirements in BS 2586 or equivalent
  • The meter is to meet the requirements in BS EN ISO 60746-2:2003 or equivalent
the overboard pH discharge limit can be determined by the following means:
  • direct measurement at overboard discharge monitoring position is to be a minimum of 6.5 pH units), or
  • calculation-based methodology (computational fluid dynamics or other scientifically established empirical formula). This involves the use of calculations or modeling to simulate the dilution and neutralisation of the acidic washwater when it is discharged into the sea. The minimum pH value that will be required at the overboard monitoring discharge limit of 6.5 pH at 4 m from the discharge point with the ship stationary, can then be determined. Such calculations are to be based on sea water alkalinity of 2200 µmol/lite and pH of 8.2
  • PAH measurement is to use ultraviolet light tehcnology for washwater flow rates not greater than 2.5 t/MWh
  • For washwater flow rates greater than 2.5 t/MWh, fluorescence technology is to be used
to be measured downstream of the water treatment equipment, but upstream of any washwater dilution or other reactant dosing unit, if udes, prior to discharge.
Turbidty Turbidty monitoring equipment is to meet requirements in ISO 7027:1999 or USEPA 180.1 to be measured downstream of the water treatment equipment but upstream of washwater dilution (or other reactant dosing) prior to discharge
Nitrates Anlysis of nitrates is to be based on metogs of seawater analysis by Klaus Grasshoff, et al The washwater sample for analysis of nitrate concentration is to be taken downstream of the water treatment equipment, but upstream of any washwater dilution or other reactant dosing unit, if used, prior to discharge

read more about how our Value Maritime scrubber can help your vessel comply with the IMO2020 Sulphur cap regulations