Exhaust gas cleaning – solutions for sulphur oxide emission reduction

Clipper Quito and Clipper Victory (Solvang) Clipper Quito and Clipper Victory (Solvang)
Industry Database

With tighter SOx regulations in ECAs coming into effect in 2015, shipowners and operators must decide within the next few months on how to reduce SOx emissions; Leonardo Sonzio, director retrofit, Wärtsilä Ship Power environmental solutions, explains that there are two main options, exhaust gas cleaning systems or switching to lower sulphur content fuel.

By the end of 2013, Wärtsilä had 41 vessels contracted for a total of 88 exhaust gas cleaning (scrubber) systems, for both newbuild and retrofit projects. Wärtsilä has accrued about 70,000–80,000 running hours with its open loop scrubber system, and around 6,000 running hours with its closed loop scrubber. The majority of the running hours have been accumulated at sea as well as at the Wärtsilä test facility in Moss, Norway.

Wartsila considers that this experience puts it in an informed position to share practical insights into the pros and cons of investing in such a system.


Wärtsilä calculates that if, for example, a large vessel sails roughly 50% of its time in ECAs, investment in an exhaust gas cleaning system is a solid business case. In the case of a vessel with large installed power, there is a positive business case even if the vessel sails less than half of its time in ECAs. The best return on investment is usually achieved in a ro-ro or ferry operating in ECA. Ro-ros and ferries typically have high engine power and hence, rather high absolute annual fuel oil consumption. In addition, they are used in short sea shipping, which means they are operating within an ECA practically 100% of the time – if located in the ECA.

In addition, bulkers, tankers and containers operating 30% to 40% of their time in ECAs benefit from an exhaust gas cleaning system because they also consume vast amounts of fuel oil. Wärtsilä says that bulkers, tankers and smaller containers are quite straightforward from a retrofit point of view and, hence, less costly. This improves the total economics of the investment.

In the end, the return on investment depends on various factors, such as total installation time and downtime, operating costs of the exhaust gas cleaning system, and expectations of future fuel prices.

According to Wärtsilä, the biggest cost factors in exhaust gas cleaning retrofits are the equipment, the installation, operations and material. Generally, the cost of the equipment varies depending on the type and size of the ship. The installation cost depends on the extent of modifications to the existing ship, and the time needed at the dry dock.

“Usually, equipment and installation each represent 40% of the total price for a turnkey retrofit; the remaining 20% is related to engineering, project management, site management, logistics and class approval costs,” says Mr Sonzio.

An alternative to installing exhaust gas cleaning systems would be switching to lower sulphur content fuel such as MGO or LNG. Wärtsilä estimates that because of growing demand for marine gas oil caused by SOx regulation, the price difference of MGO and HFO would be expected to increase in 2015. So, the true expense of using MGO versus HFO in the future is uncertain. The other low sulphur option is LNG which is said to be the cleanest fossil fuel and is currently the fastest growing fuel type in the world. However, switching to LNG requires changing the engine.


Wärtsilä has delivered exhaust gas cleaning systems to many companies who have already made repeat orders after initial experience with their first systems installations. Some of those companies include Solvang, Wilh. Wilhelmsen and Ignazio Messina.

Norwegian operator Solvang considered an exhaust gas cleaning system the only realistic option for its environmentally friendly LPG carriers, such as Clipper Quito and Clipper Posh. MGO, with the market price and indirect changeover costs, was seen as a rather expensive alternative. LNG is not, for the time being, an option for Solvang’s existing fleet due to lack of infrastructure and regular sailing patterns.

Tor Øyvind Ask, fleet director of Solvang ASA explained: “Given a total evaluation including environmental performance and operational cost and flexibility, exhaust gas cleaning is the best solution for us. HFO is available all over the world, which gives us maximum fuel capacity and operational flexibility. Clipper Posh is on a long term time charter and will sail in and out of the ECAs. The cost reduction inside those areas is estimated to be around US$20,000 per day.”

Solvang now has four operational scrubber systems in two vessels. The company has ordered exhaust gas cleaning systems from Wärtsilä for six further vessels. The first delivery was in 2013 when a Solvang’s newbuilding was fitted with two open loop scrubber systems.

“Our two vessels with Wärtsilä’s exhaust gas cleaning systems have been in normal operation; Clipper Quito since July and Clipper Posh since December. Both vessels have been sailing inside and outside of ECAs. We have now accumulated about 2,000 running hours with good experiences,” says Mr Ask.

According to Solvang, scrubber system installations have been technically quite unproblematic. Getting the required class approvals, on the other hand, has taken longer than expected with testing and reports. After the paperwork was completed for Clipper Quito, subsequent approvals became easier. Clipper Posh was the first ship in the world to obtain a full term IAPP (International Air Pollution Prevention) certificate on exhaust gas cleaning.

“We believe that exhaust gas cleaning brings us competitive edge. Our LPG carriers are cheaper to operate in ECAs due to lower fuel cost; the scrubber systems are one of many actions, which are carried out to improve our environmental performance and reduce fuel consumption. We see exhaust gas cleaning as a way forward to us,” Mr Ask concludes.


There is a possibility that ECAs might expand at some point. Therefore, reduced sulphur emissions are on the agenda for shipowners planning to build new vessels. Provision for exhaust gas cleaning system fitting at the ship design phase should save cost compared with retrofitting.

Retrofitting scrubber systems may pose some challenges, but they can be overcome. “In retrofit cases, finding space for the system is the most common challenge. Sometimes there is a need to make changes in the funnel shape or rethink the use of spaces in the vessel to create more room for scrubber systems. So far, we have not come across any project in which retrofitting would not be technically possible. It is just a matter of identifying the best solution or compromise with the shipowner,” Mr Sonzio explains.

The Wärtsilä portfolio of exhaust gas cleaning systems includes three configurations for removing sulphur content from the exhaust gas: open loop scrubbers, closed loop scrubbers, and hybrid scrubber systems. All three configurations include a wash water treatment plant to clean the effluents before discharge into the sea with no risk of harm to the environment. In addition, the closed loop scrubber and hybrid scrubber can be operated in a zero effluent discharge mode for a certain period of time, if required.

The closed loop system uses freshwater and a reagent, typically caustic soda (NaOH), and works best in seas with low alkalinity and for operators looking for zero discharge. The open loop system, on the other hand, is the preferred option for ocean-going ships because it uses seawater, and neither freshwater nor caustic soda is needed. The hybrid scrubber systems operate on either open loop or closed loop by using sea water, and sea water and caustic soda respectively. This allows for full flexibility of operations. The hybrid systems sail both in seas with low alkalinity as well as in open oceans. It is also possible to first install an open loop system and, if needed later, modify it for hybrid operation.

“Factors affecting the choice of an exhaust gas cleaning system – or not choosing one – are mainly the ship type and size, its absolute annual fuel consumption and the vessel’s geographical operating area. Choosing an open loop or closed loop scrubber system depends on where the vessel sails in. Some vessels require full flexibility due to their vast sailing range. Equipped with an exhaust gas cleaning system, a vessel can operate on HFO inside and outside of ECAs. Hybrid technology increases flexibility even more,” Mr Sonzio concludes.



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