Scrubbers: Scheme B - real time monitoring data
7th July 2015 11:39 GMT

In a recent Bunkerworld article, a German environmental group questioned the long-term effectiveness of using scrubbers as a compliance tool to meet Emission Control Area (ECA) rules. The Association for the Protection of the German North Sea Coast (Schutzgemeinschaft Deutsche Nordseeküste) stated the following in its rationale:

•    The use of scrubbers requires increased monitoring because its efficiency is difficult to control during a vessel's journey
•    Ship operators may not be willing to do so be due to the high costs involved
•    Failure to monitor scrubber performance could lead to a potential residual build-up in the unit, which may be released into the air or sea.

Firstly, it is important to remember that scrubber guidelines (MEPC 184(59)) allow for only two methods of approval, Scheme A or Scheme B.

Scheme A demands initial certification of performance followed by periodic survey with continuous operating parameters and daily emission checks to confirm performance in service.

Scheme B requires performance confirmation by continuous monitoring of emissions with daily operating parameter checks. The vast majority of scrubbers being installed are adopting 'Scheme B' - the continuous monitoring of sulphur emissions. This means that scrubber performance is being continuously monitored, providing real time data that not only demonstrates compliance, but also that a scrubber is working efficiently, thus eliminating any potential for residual build-up in the unit. It also removes any concerns over cost, as it's part of the scrubber solution itself.

A recent consultation by the UK's Maritime and Coastguard Agency suggested that it could prove hard for port state control (PSC) authorities to check if a vessel with a scrubber onboard was actually using it. This prompted Meindert Vink, senior policy advisor, Netherlands Shipping Inspectorate to state that he had faith in scrubber technology, especially if combined with tamper-proof continuous monitoring technology. He noted that this would make it straightforward for PSC to simply check the record on paper.

Indeed continuous emissions monitoring systems (CEMS) have the ability to monitor gases from the combustion of residual and distillate fuels such as SO2, CO2 and NOx. By transmitting this information ashore combined with identity, position and port calls obtained from the AIS (Automatic Identification System), PSC can easily confirm compliance in port, in ECAs and in international waters.

The Scheme B approach mitigates against any technical concerns, as it gives complete and ongoing assurance of emissions at exit from ship, whereas Scheme A does not. In addition, if CEMS are not fitted there is a potential risk that the indirect Scheme A method of monitoring system parameters could result in non-compliant emissions being undetected between daily emission spot checks - particularly undesirable in port and in ECAs.

Continuous monitoring of exhaust gas emissions is the only way to provide complete reassurance, no matter the type of scrubber system installed.  Furthermore, any port state control inspection will be able to readily confirm emissions are compliant under Scheme B using MEPC 184(59) Table 1, whereas under Scheme A, cross reference of unfamiliar operating parameters will need to be made with those in the EGCS technical manual (ETM-A).

With regard to applicability of analysers, whilst CEMS for Scheme B must be approved according to MEPC 184(59), the daily spot checks required under Scheme A risk use of unapproved portable analysers that are neither ranged appropriately for a very low level of SO2 emissions (less than 20 ppm), nor meet the performance specifications appropriate for the application. Due to the manual method of obtaining an emissions reading using a portable analyser, there is risk of an inconsistent and non-representative result, not to mention the associated safety risks if an access point to a hot flowing exhaust needs to be opened and a hand held probe inserted.

Using Scheme B to confirm compliance will simplify matters for operators of ocean going vessels as it ensures the same methodology regardless of the vessel location. Simplicity really is key. At a time when crew members are being asked to undertake increasing responsibility to meet changing legislation; only robust, reliable tools and technology that need minimal maintenance and resourcing are viable.

Unlike portable analysers, CEMS for SO2 and CO2 are a reliable and mature technology, with a number of commercially available marine systems approved according to MEPC 184 (59). To ensure ongoing emissions compliance, CEMS must be ranged appropriately to measure the low levels of SO2 that will be found in the exhaust stream. The measured concentration should also fall between 15% and 100% of the measurement range used. This will ensure future-proofed accurate monitoring and simplifies matters for ship operators, providing reassurance that the analyser will meet regulatory requirements regardless of where vessel is located.

Scrubber technology is only one solution to ECA compliance. However, some industry experts including oil and bunker industry expert Dr. Rudy Kassinger have been quoted as saying that scrubbing technology will be a necessity once a global 0.50 percent sulphur cap comes into force. With increasing numbers of ship owners installing scrubbers, cost effective continuous emissions monitoring will be essential in demonstrating both compliance and performance.


Chris Daw,
7th July 2015 11:39 GMT

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