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Dimitris Poulos*: Deciding your route to SOx compliance


Vessel emissions – including those related to sulphur – are governed by MARPOL Annex VI, which first entered into force in May 2005.

IMO has adopted subsequent revisions of Annex VI to progressively reduce the maximum allowed sulphur content of marine fuels. However, IMO has also approved the use of higher-sulphur fuels with exhaust gas scrubbers that remove a corresponding amount of sulphur oxides, or SOx. This is referred to as an “equivalence” in IMO terminology. MARPOL Annex VI establishes the regulation of a global sulphur cap, as well as stricter regulation in Emission Control Areas (ECAs). Any party to MARPOL Annex VI can apply to become an ECA, with the time from application to enforce- ment taking about 18 months. As
of January 2015, the limit applicable in ECAs is 0.1%S. In October 2016, the IMO Marine Environment Protection Committee (MEPC) agreed to lower the existing Annex VI global cap from 3.5%S to 0.5%S as of January 2020. It is also worth noting that there are ports around the world that have chosen to establish their own sulphur limits outside of those set by MARPOL Annex VI. In some cases, these limits are even stricter than what is applicable for the global cap.
Will the fuel market change?
Fuel economy is the incentive for using anything other than low-sul- phur fuels to comply with MARPOL Annex VI. So long as there are cheaper fuel alternatives, those alternatives will have a strong business case. Of course, the future price of a given fuel is dif cult to predict. The price of LNG, for example, might become lower as the LNG infra- structure expands. Likewise, no one can anticipate the exact price of low-sulphur fuels and heavy fuel oil (HFO) in the coming years. However, a continued difference in price between low-sulphur fuels and HFO is likely. So long as it remains in common use worldwide, a residual fuel like HFO will always be a cheaper alternative. This price differential is what justi es the installation of a scrubber – and the sooner you can take advantage of it, the stronger the justi cation becomes. In other words: the earlier you choose a SOx scrubber as your route to compliance, the greater the potential for long-term savings.
The time to choose is now
A “wait-and-see” approach to SOx abatement – in the hopes of a drop in low-sulphur fuel prices or a sudden improvement in the LNG infrastruc- ture – is no doubt an option. What is certain, however, is that choosing to invest in a SOx scrubber means immediate payback in terms of fuel-related operating costs. The longer you delay your choice, the more dif cult it may be to implement when you make it. In addition to MARPOL Annex VI, other environmental regulations are necessitating new equipment on board. Shipyard availability, as well as the number of suppliers who can deliver a scrubber on time, may thus be limited in the future. By delaying your decision, you may be committing to expensive fuel for a long time to come.
PureSOx in overview
Alfa Laval PureSOx is a scrubber platform speci cally designed for marine SOx abatement. At sea
since 2009 and launched commer- cially in 2012, the platform has been continuously optimized and expand- ed over time. Its technological foundation, however, has always been the same.
Confirmed performance
PureSOx has been shown to reliably remove more than 98% of the SOx content in exhaust gas, as well as up to 80% of the particulate matter (PM). This exceeds both the global cap and ECA requirements set by IMO in MARPOL Annex VI. Even during periods of rapid change in engine load, SOx levels are kept well within ECA emission limits, as has been demonstrated during thousands of hours at sea.
Comprehensive flexibility
As a complete platform, PureSOx is much more than just a scrubber. With the many possibilities the platform offers, PureSOx can be fully tailored to your sailing pro le and the physical constraints of your vessel. Open-loop, closed-loop and hybrid arrangements are all avail- able, as well as scrubbers with a U- or an I-design. PureSOx also offers three different pro les designed to t your speci c compliance needs.
Extensive references
PureSOx has a substantial reference list, comprising more references than any other single SOx scrubber technology. Among them are the world’s largest scrubber installa- tions, a broad range of vessel types and repeat orders from satis ed major customers. All PureSOx systems ever supplied are still in use and operating in compliance with MARPOL Annex VI limits.
Comprehensive strengths
The PureSOx platform builds on Alfa Laval core expertise, including over 40 years of marine scrubber experience and world-leading strengths in centrifugal separation. PureSOx is also backed by
Alfa Laval’s global organization, which can provide service and support at any time, anywhere in the world. This chapter provides a complete introduction to the PureSOx platform, including a summary of the support, documentation and resources offered by Alfa Laval as a supplier.
PureSOx and ease of use
PureSOx requires little from the crew. The system is fully automated, which means starting it up, switch- ing between open-loop and closed- loop modes, and switching between 0.1%S and 0.5%S compliance modes can all be done at the push of a button. Even crews with no experience of scrubbers will be familiar with the majority of PureSOx components. Maintenance is limited, and the few points required can be performed while the engine is running. Sludge production in closed-loop operation is minimized by the ef cient water cleaning unit, and the sludge is disposed of on shore with the vessel’s other sludge streams. In the event of an emergency stoppage, the engine can be run independently. If the scrubber has a U-design, this is ensured by a “fail-safe open” function in the bypass valve. If the scrubber has an inline I-design, the exhaust gas will continue to pass through the scrubber in a so called “hot gas mode” with no water added.
The expertise behind PureSOx
The strengths of PureSOx as a system are tied to the strengths of Alfa Laval as a supplier. Alfa Laval is a world leader with a century of marine experience, including several decades of experience with marine scrubbers. Scrubbers are an integral component of inert gas production systems, which Alfa Laval has provided to oil, chemical and LNG carriers for over 40 years. Other Alfa Laval core technologies are also a part of PureSOx. These include high-speed centrifugal separation, which Alfa Laval pioneered and continues to push forward. Used for water cleaning during closed-loop operation, centrifugal separation is currently the only alternative that performs reliably in rough waters. The PureSOx water cleaning unit is a unique application of this technology, developed over the course of several years.
*Alfa Laval Regional Manager, Service and Equipment Marine & Diesel Power

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