Scrubbing technology; proven, market ready and evolving to meet operators’ needs

Wärtsilä hybrid scrubber Wärtsilä hybrid scrubber
Industry Database

Sigurd Jenssen, director EGC of Wärtsilä Environmental Solutions, looks at the current state of the exhaust gas cleaning systems market and its application to ships required to comply with very low sulphur emissions regulations.

A recent study from maritime consultant and analyst IHS has found that around 140 scrubbing units have been ordered or fitted so far. Wärtsilä alone has now signed contracts for more than 50 ship sets, totaling in excess of 100 scrubber units. This level of uptake clearly demonstrates that the market now understands the operational capability and economic viability of scrubbing systems.

This trend is only set to continue. Investment in onboard scrubbing facilities is predicted to reach US$25 billion over the next 15 years according to recent research and analysis from Marine and Energy Consulting. New Outlook for Marine Bunkers and Fuel Oil to 2035 Study, which was released in September 2014, anticipates that the post-ECA environment will rapidly establish the economic viability of this technology.

As the market moves out of its infancy and towards maturity, the challenge facing manufacturers is no longer in proving the economic and regulatory viability of scrubbing; these factors are now self-evident in a technology that is actively being used in the market. The most pressing challenges for owners, operators and scrubber manufacturers alike now include leveraging dry docking schedules for installation, unlocking the finance to fund the investment and finding or developing systems to suit all operating profiles.


Given the variance in the size and type of vessels, operational divergence and regulatory jurisdictions – there is no single ‘one size fits all’ solution. This is why Wärtsilä has developed ‘closed’ loop, ‘open’ loop, hybrid and new ‘inline’ units.

The history of exhaust gas cleaning lies with open loop technology. As the name may suggest the system operates in an open loop, using seawater as scrubbing water; water is taken from the sea, led through the scrubber and a water treatment system, and then released back into the sea. It remains the simplest solution with the lowest installation and operational costs. However, it will not match the needs of every operator, which is why alternative solutions have been developed.

The Wärtsilä closed loop system was developed for operation in areas of low alkalinity – for example The Great Lakes. It is not dependent on taking in alkaline seawater from the surroundings and instead is filled with water, which is then recirculated with addition of an alkaline solution. It can operate in zero discharge mode when necessary and store the cleaned wash water (effluent) for discharge at a later date.

The third alternative is a hybrid solution. This option continues to grow in popularity and has seen the most take-up over the past year. Wärtsilä’s hybrid scrubber uses seawater to neutralise the sulphur compounds and is also able to operate in closed loop mode using NaOH when required, for instance whilst in port and during manoeuvring. With the ability to operate in both open and closed loop, a hybrid approach enables flexibility of operation. Wärtsilä’s open loop scrubbers are available in a ‘hybrid ready’ configuration. This means that should future regulation come into force regarding wash water disposal, the systems could be upgraded to closed loop scrubbing.

Of course some operators face further considerations beyond regulation and environment. On the face of it, scrubber units have a relatively short payback given the current variance in fuel costs between HFO and distillate fuel. However, some operators will have to take into consideration in the cost-benefit calculation the potential loss of revenue due to lost capacity. As a result of this concern being raised with Wärtsilä in the past, the company has recently launched an ‘inline’ scrubber intended to overcome this challenge and reduce the space impact of scrubber installation.

The inline unit, which operates as an open loop scrubber, has a significant size advantage largely derived from pumping more flow through a smaller diameter at a higher velocity. It has additional water spray, but no packing inside, meaning there is no requirement for a bypass. The end result is easier to install and offers a more flexible operational profile since the design often enables space to install a dedicated scrubber unit for each engine.

With just one compact scrubber per engine, installation is faster and easier, which consequently reduces the out-of-service time for the vessel. The inline scrubber’s smaller footprint makes it easier to install in the funnel or casing or alternatively, the silencing effect of the scrubber means it can replace the vessel’s silencer.

Whichever solution is chosen, Wärtsilä considers that its involvement since the very inception of the exhaust gas cleaning sector not only ensures compliance with current regulations, but also that upgrades and modular add-on features will meet any future updates to guidelines.


Scrubbers have been used in land-based applications for over 80 years and it is not a new technology for ships either. Wärtsilä has been installing this sort of technology onto vessels for more than 50 years, albeit on a slightly smaller scale and for a different application - inert gas systems.

As far as chemical processes go it is a simple process and well understood from its years of use on land. Scrubbers spray alkaline seawater into exhaust gasses, which reacts with the SOx and traps much of the PM material in the gases, ensuring regulatory compliance.

The mechanical system by which this is achieved is also relatively simple. The only moving parts in a Wärtsilä scrubber are pumps and valves, components that crews already understand, and are well versed in their effective maintenance. This, combined with the fact that a central design criteria for Wärtsilä scrubbers was that they last for the lifespan of the vessel, means that the units, once installed, should not add a significant load to existing pump maintenance processes. There are typically six to 10 pumps in a system and two-thirds of pumps can be standard marine pumps as they deal only with the intake of seawater.

The key element for the training of crews is in the bunkering of caustic soda, for use in the treatment of wastewater, and the disposal of the waste ‘sludge’ produced by the scrubber. Wärtsilä can offer both classroom training and hands-on training at its testing facility to offer crews the skills they need when handling these corrosive products.

Indeed, the corrosive nature of wastewater and sludge is something that has been considered end-to-end in the design and preparation of scrubbing technology, materials, installation and training. Pumps that come into contact with the wastewater are made from corrosion resistant ‘super duplex’ steel. There are provided as standard elements in the company’s scrubbing systems - and have been since the first Wärtsilä scrubbers went into operational use in 2010. Because Wärtsilä incorporates only high performance pumps that are made in-house the company believes it can can ensure that pumps are assembled and tested to the highest quality, and meet every requirement of the scrubber system.

Disposal of sludge is also a key issue, not just in ensuring crews can effectively manage the disposal but also in ensuring that disposal sites are in place at ports. Wärtsilä has been in discussion with a number of key ports across Europe on the issue of sludge disposal and each has indicated that it will be prepared to receive scrubber sludge. The costs involved vary from port to port, but the quantity of sludge produced by scrubbers is significantly smaller compared to engine sludge – which must be disposed of separately – and so this should not affect the savings offered by the ability to continue burning HSFO.


With 2015 rapidly approaching, owners and operators must avoid leaping to any last minute installation decisions which could result in choosing a ‘second choice’ technology – potentially one that is not actually suitable for future operations. There is not a single ‘plug and play’ solution available. No two ships are the same and these systems need to be custom engineered and fine-tuned. Ship stability checks, engine room space and layout, the design of the exhaust funnel all have a significant impacts on the design of each individual scrubber, alongside choosing the most appropriate scrubber type and assuring training and scheduling is in place. Therefore a close cooperation between the ship owner and scrubber manufacturer is vital to ensuring reliable and efficient operation. For that reason Wärtsilä can offer a full turnkey solution if required.

A collaborative and planned approach will ensure that cost savings are realised by maximising the utilisation of periods in dry dock and avoiding unscheduled downtime. Wärtsilä has found that most installations can incorporate ride-on crews or quayside work to minimise the time a vessel spends out of service. Of course, the time to plan an installation can often take well over six months, even without drydock scheduling being factored in. Owners considering scrubbing now must budget for the increased operational costs they will face by burning distillates throughout the period between the ECAs coming into force and the date they will be able to install scrubbers on each vessel.

All shipowners really want is clarity, assurance and reliability. From survey, design, equipment procurement, delivery and installation, to automisation, data and documentation updates, training and maintenance of the system, the assurance of experienced project management provides insight into best value. This enables shipowners to make confident, informed decisions to meet compliance targets, both now and into the future.


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