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Combining complementary strengths to meet global environmental requirements

The complementary strengths of industry leaders Hamworthy and Wärtsilä combine exhaust gas scrubbing technology and marine engineering expertise with entrepreneurial resources to provide a strong platform for future development, and to meet the growing environmental focus of customers around the world.


There is a growing environmental awareness and concern around the world. Authorities are applying ever tougher legislation, while market players are using all their R&D efforts to meet the growing demand for “green” products. For Wärtsilä also, the environment is an area of focus offering growth possibilities, with emissions abatement as an obvious example.

Background – new regulations introduced

Emission standards have long been applied for land based industries, and limits have become increasingly stringent. The outcome is that in some areas, the shipping industry is now the major source of SOx and PM (particulate matter)emissions. Even though sea transportation is the most environmentally friendly means of transport, there is still room for improvements. The first SOx regulations were introduced in 2005, with a gradual tightening to allow owners time to adapt.

Initially the IMO regulations cover two emission control areas; the Baltic and North Sea, and a 200 nautical mile zone off the North American coast. Here the current maximum fuel sulphur content is 1%, with that limit being reduced to 0,1% from 2015, effectively forcingowners of  all vessels operating in these areas to take action. The IMO and EU regulations, as well as some more stringent local rules, are being implemented.

Thousands of vessels sailing within or to Europe and North America will have to adapt, with a change of fuel or the installation of abatement equipment being the only options. Changing to MGO (Marine Gas Oil) fuel is one, albeit a costly solution, and fuel switching can be risky. As the demand for residual fuels disappears, the price differential between HFO (Heavy Fuel Oil)  and MGO will grow even greater in the future, while LNG is becoming a viable fuel alternative for fixed sailing routes. Currently, the availability of LNG is limited, and the capex requirement and retrofit complexity will eliminate some players. There are also alternative fuels, but the overall fuel demand for shipping is still expected to grow going forward, and availability is a potential challenge. Installing abatement equipment is the most financially viable solution. There is still a capex required, but the payback time is very attractive. This alternative is also the least intrusive.

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Fig. 1 – The MARPOL Annex VI fuel oil sulphur limits.
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Fig. 2 – The MV Tarago will be fitted with a Wärtsilä Hybrid Exhaust Gas System design to clean both main and auxiliary engines.

The Technology

A typical requirement of the evolving regulations is 97% SOX removal, with a 3,5% fuel sulphur content of the fuel.

Using sea water to scrub and remove SOx and particulates is a well-known process. The first installations were done on land almost 100 years ago, and it is the same principles that have been used in Hamworthy Inert Gas scrubbers for 50 years. Wärtsilä’s extensive background and expertise in marine engineering and equipment supply, combined with Hamworthy’s 50 years of experience with scrubbers onboard ships, provides a unique platform. The resulting offering is a full range of systems based on customer requirements and the operational profiles of their vessels. This includes open loop sea water systems, zero-discharge fresh water systems, and single and multi-inlet integrated systems capable of scrubbing the exhaust from engines from 100 kW to 100 MW, while complying with all current and proposed legislation.

The Wärtsilä open loop system utilizes seawater to remove SOx from the exhaust. The sulphur oxide in the exhaust reacts with water and forms sulphuric acid. There is no need for chemicals since the natural alkalinity of seawater neutralizes the acid. The system is being kept as simple and robust as possible, with few moving parts. The environment inside the scrubber is of course very corrosive, so only high-grade stainless steel is used in the scrubber body. Exhaust gas enters the scrubber through a venturi section and is sprayed with seawater in three different stages. The wash water is taken from the sea chest and pumped to the scrubber using standard sea water pumps before being distributed to the different scrubber sections. To improve the PM capture, it is possible to install an additional booster pump for increasing the pressure in the venturi. From the scrubber, the wash water first enters a settling tank before entering a hydro cyclone for filtration. Prior to being discharged overboard, the water is diluted so as to raise the discharge pH to approximately 5.5. This dilution is only needed for in-port operations, as the mixing effect of the wake that you get when sailing provides a much better dilution effect.

The residue is collected in sludge tanks. Although the sludge is legislatively considered non-hazardous, it cannot be incinerated on board and has to be disposed of ashore in conjunction with rules relating 
to the discharge of a vessel’s waste oils and sludge. To avoid condensation, dry air is then pulled in from the casing to increase the temperature above the saturation point, thereby avoiding the creation of a steam plume. If the available back pressure is insufficient, an ID fan (for induce draught which force the exhaust gas up the stack )may be installed at the scrubber outlet.

The exhaust gas is continuously monitored for SO2 and CO2. The wash water is monitored for pH, PAH (Polycyclic aromatic hydrocarbons), and turbidity (the cloudiness of a fluid caused by individual invisible particles, similar to smoke in air) at both the inlet and outlet to make sure it is in line with the discharge criteria of MEPC (Marine Environment Protection Comitee) 184(59) before being discharged into the sea with no harm whatsoever to the environment. This data coupled with the ships GPS signal is logged in a secure data-logger, which is used for proving regulation compliance.

The Wärtsilä closed loop scrubber operates in a closed loop, i.e. the wash water is circulated within the scrubber itself. Exhaust gas enters the scrubber and is sprayed with fresh water mixed with caustic soda (NaOH) to increase the alkalinity. The sulphur oxides in the exhaust react with this mixture and are thereby neutralized. A small bleed-off is extracted from the closed loop and treated to fulfill the requirements stipulated by the IMO. The cleaned effluents can safely be discharged overboard with no harm to the environment. If operation with zero discharge is requested, the effluent can be led to a holding tank for scheduled and periodic discharge.

In addition to the closed and open loop systems, Wärtsilä also provides hybrid solutions. These solutions have the flexibility to operate in both open and closed loop modes. At sea, systems can be run in open loop mode, and when manoeuvering or in port they can be run in closed loop or even zero-discharge mode, with the separated discharge contained in a holding tank.

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Fig. 3 – Complete Wärtsilä Open Loop Scrubber System setup for both main and auxiliary engines.
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The aquavit story

Wilh. Wilhelmsen ASA, the global rolling cargo operator, will retrofit its vessel the ‘MV Tarago’ with a Wärtsilä Hamworthy hybrid Exhaust Gas Cleaning System. The vessel is a part of a long-standing liner trade. The vessel transports Norwegian aquavit world-wide in all sorts of environments and conditions and is designed for flexibility and optimal operational cost. This will also be the case for the Exhaust Gas Cleaning System. MV Tarago will be equipped with two scrubbers, capable of treating the exhaust from both the main and auxiliary engines with a combined engine power of 28 MW. This multi-stream scrubber system configuration provides extensive operational flexibility, by using the large scrubber for sea-going and the smaller scrubber for port operations. There is also a possibility to run the system in zero-discharge mode for a specified period. The installation will prepare the MV Tarago for the upcoming sulphur emissions regulations that come into force from January 2015, which mandates that vessels must burn fuel with a sulphur content of 0.1% when operating within Emissions Control Areas (ECAs). By using a scrubber to reduce sulphur and particulate matter emissions from its main engine as well as its auxiliaries, the MV Tarago will be able to operate in ECAs from 2015 on a ‘business as usual’ basis avoiding the $300 to $400 price differential that standard vessels will have to pay for the distillate fuels they will need to burn to remain compliant.

The technical and practical challenges are being solved by using well-proven technology and components combined with a genuine interest in cooperation from both the owner and the ship’s crew. The installation will be carried out during the vessel’s scheduled intermediate docking at Sembawang shipyard in the first quarter of 2013. Following the commissioning, a comprehensive third party measurement and verification program will be carried out over two and a half years, and is partly funded by the Research Council of Norway.

Reference list

Wärtsilä’s reference list is unprecedented. Having both the largest installed base of any marine scrubber supplier and a dedicated test laboratory, Wärtsilä has been able to optimize its products with regard to reliability, ease of operation, and installation simplicity.

The ‘Linea Messina’ has a Wärtsilä Hamworthy open loop system installed, and was the first vessel ever to operate commercially with a scrubber system. This enabled it to meet the 0.1% sulphur emission regulations in EU ports, as well as “future proofing” the vessel for the impending 0.1% Emission Control Area limit in 2015.

Wärtsilä was awarded the contract to supply the closed loop scrubber systems for a series of six, with an option for a further two, vessels built to transport bulk commodities on North America’s Great Lakes and the St. Lawrence Seaway for the Canadian owner, Algoma Central Corporation. The full propulsion system with an integrated closed loop scrubber lowers operating costs while reducing the vessel’s environmental footprint, since it allows the owners to use high sulphur fuels in Emission Control Areas (ECA) and still meet sulphur emission restrictions. With this contract Wärtsilä and Algoma Central Corporation will set new standards for environmentally sustainable shipping on the Great Lakes.
As mentioned earlier, Wilh. Wilhelmsen ASA, the global rolling cargo operator, will retrofit its vessel the ‘MV Tarago’ with a Hamworthy hybrid Exhaust Gas Cleaning System. This multi-stream scrubber system will remove sulphur and particulates, and manage the exhaust gases produced by the 38,486 dwt Mark IV RoRo vessel’s combined engine power of 28,000 kW.

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Fig. 4 – The MV Tarago will be fitted with a Wärtsilä Hybrid Exhaust Gas System design to clean both main and auxiliary engines.


Growing environmental awareness has resulted in legislation that puts a cap on sulphur content in fuels in Emission Control Areas (ECA). The combined effort of Hamworthy and Wärtsilä provides market leading solutions. The Wärtsilä Exhaust Gas Cleaning System provides a complete range of solutions, from open loop sea water systems to zero discharge fresh water systems. The hybrid system combines the benefits of both technologies. These systems comply with all current and proposed legislation.

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