The "wet scrubber solution" has been operating successfully for many years and complies with the current regulations of IMO MARPOL Annex VI, however this solution involves significant energy consumption, and discharge of the wash water back into the sea could also be an issue in certain regions.

ANDRITZ is proud to offer an additional solution in the field of the maritime exhaust gas cleaning. Based on its in-depth and long-term experience gathered from land-based applications, ANDRITZ can offer two dry filtration solutions in addition to the well-known wet scrubber variations (SeaSOx Scrubber, formerly known as SeaSOxwet) already available.

Depending on the customer's needs or requirements, it is possible to install SeaSOx Dual Filtration or SeaSOx Multi Filtration in order to be prepared for compliance with additional emission guidelines. SeaSOx Dual Filtration is used for the abatement of sulphur oxides (SOx) and particulates. SeaSOx Multi Filtration additionally removes nitrogen oxides (NOx).

ANDRITZ has identified specific target markets for this system in the shipping segments where stricter emission guidelines will be soon required. These are ferries, RoRo, RoPax, feeder vessels, coastal liners, inland waterway shipping, but also cruise ships during a stay in port or any other vessels entering an area where particulate or NOx removal is required.

The ANDRITZ SeaSOx filtration solution can remove SOx, particulates and NOx, which is comparable to or exceeds the performance of a diesel engine equipped with an SCR and DPF system. This cleaning efficiency (for SOx and particulates) has already been demonstrated and issued with a DNV GL certificate for the 10 MW installation on the RoPax ferry “Piana”, operated by La Méridionale between Marseille and Corsica in France.

ANDRITZ specializes in working directly with customers to develop an optimized solution for each company, ship or operating profile and in response to customers’ individual needs.

That is why different vessels will require different solutions. In-depth discussions with the client to find the right solution for every vessel is essential in good collaboration to achieve the best-performing exhaust gas cleaning system. As filtration is a new technology in the maritime sector, the following table provides a general comparison of a SeaSOx Scrubber (Hybrid) and a SeaSOx Dual/Multi Filtration system.

Parameter Unit SeaSOx Scrubber (hybrid) SeaSOx Dual/
Multi Filtration
SOx removal performance %S 0.1% 0.1 %
Particulate removal performance (mass reduction) % Up to 75% max. (not certified) > 99.5% (certified)
Ultra-fine particulate removal (< 1µm) performance (number reduction) % None – cannot remove particulates < 3µm > 99.5%, including PM10 and PM 2.5, PM 1 (certified)
NOx removal performance Not possible, requires an SCR system Available with the Multi Filtration option (no extra space required)
Main absorption media Sea water NaHCO3 (sodium bicarbonate powder)
Consumption of additional media Various options possible for closed loop operation: NaOH, MgO, Mg(OH)2, Na2CO3, NaHCO3 Compressed air
Main scrubber/filter material Alloy 31, SMO 254 and Super Duplex Carbon steel
Zero water discharge Yes, in closed loop with sea water and sludge storage in tanks Yes, no water used for absorption


A serious comparison between these two solutions is only possible if all parameters are considered. So the total system weight, the necessary space, the additional benefits of the filtration technology, and the question of installation must also be considered. A comparison of the filtration system with an open loop scrubber is not useful as these technologies are used for different requirements. Wherever only SO2 removal is required and water discharge is allowed, an open loop scrubber will be the most competitive system. That is why ANDRITZ offers all solutions and finds the best one for each vessel.

Whenever more stringent emission limits are required, the filtration system offers clear advantages (the additional and perhaps not immediately obvious benefits of the dry system are mentioned below):

- Less power consumption (approx. 1/10 of that of a wet scrubber)

- No dry dock needed (no sea chests or overboard installations)

- No wash (or waste) water discharge

- No circulating fluids

- No harmful sorbents

- No plume

- Less equipment overall


To provide a real comparison of a scrubber and a filtration system, the following showcase offers technical information for a cruise ship. The table compares the data for a closed loop SeaSOx Scrubber with those of a SeaSOx Dual Filtration system during a stay in port when only one main engine is in operation to generate electricity. The additional benefit of the filtration system in this case is the removal of particulate, a facility that is very important on passenger ships. Due to the fact that wash water discharge from open loop scrubbers is often forbidden in port, the comparison is made between a hybrid system in closed loop, zero-discharge mode and dry operation.

Parameter Unit SeaSOx Scrubber SeaSOx Dual Filtration
Engine type 4-stroke diesel engine
Engine model WÄRTSILÄ 12V46F
Connected power kW 12,750 (1 x 85% ME)
Main media flow rate      
Recirculation water flow m3/h 1,150 None
Cooling water flow to heat exchanger m3/h 1,000 None
Compressed air Nm3/h Instrument air only 300 Nm³/h
Wash water segregation m3/h 4 None
Sludge/residue produced kg/h 70 380
Caustic mass flow kg/h


270 (NaOH 50% solution) 460 (NaHCO3 powder)
Scrubber/filter dimensions (LxWxH) mm 3,000 x 5,000 x 9,700 5,200 x 7,450 x 11,000
Total operating weight kg 70,000

10,000 scrubber

5,000 GRP piping

10,000 aux. equipment

45,000 circulating fluids


35,000 filter

3,000 steel piping

10,000 aux. equipment

1,000 circulating powder

Required tanks/additional space
Process tank m3 21 None
Caustic tank (1 week) m3 30 (NaOH 50% solution) 95 (NaHCO3 powder)
Segregation tank (1 week) m3 670 None
Wet sludge tank (1 week) m3 7 None
Dry residue tank (1 week) m3 None 80
Energy requirement

(at design load)

kW 270 35
Fuel consumption increase kg/day 1,170 165


Showcasing of the cruise vessel shows good capabilities by the filtration system, especially when taking additional port restrictions into account (e.g. particulate emission, water discharge). This solution has its clear benefits for certain of the aforementioned vessels operating in specific areas. Nevertheless, ANDRITZ also offers the entire portfolio of wet scrubber solutions (as open loop, closed loop or hybrid, I-type (inline) or U-type (bypass), round or rectangular) for all other types of vessel.

This showcase is merely an example that illustrates the need to discuss the requirements and special circumstances of the vessel in detail with the shipowner before installing an exhaust gas cleaning system. As ANDRITZ is the only supplier in the world to offer all of the different technologies, SeaSOx is the right choice for every type of vessel.


The views expressed in this article are solely those of the author and do not necessarily represent those of SAFETY4SEA and are for information sharing and discussion  purposes only.


Marco Dierico (Area Sales & Proposal Manager): [email protected] / Tel.: +43 676 82 248 2050 or




René Schöberl (Area Sales & Proposal Manager): [email protected] / Tel.: +43 316 501 2895