According to Wärtsilä the new inline scrubber system design that has been developed by the Company lowers cost, saves space, and eases installation.
Wärtsilä’s inline scrubber system is designed to offer notable benefits over conventional exhaust gas cleaning systems. Namely some of its advantages are:
- Compact form that saves considerable space. This is particularly important in smaller vessels.
- Lower cost structure of the new design offers CAPEX advantages.
- Installation is faster and easier with just one scrubber system per engine. Consequently the out-of-service time for the vessel is being reduced.
- Operational flexibility is improved.
The inline scrubber system operates as a conventional Wärtsilä open loop scrubber system. 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 difference of the new inline scrubber system design is that it has three water inlets in the main body of the scrubber, as opposed to two in the conventional system. The exhaust flows enter from the bottom and exits at the top, with water being sprayed in three stages in a counter flow to the exhaust. A Wärtsilä designed water trap prevents the scrubbing water from entering the engine. The inline configuration can be offered on the hybrid scrubber system as well.
The first vessel to utilise the new Wärtsilä inline scrubber system will be Color Line’s SuperSpeed 2. The contract was signed in June 2013 and the installation will take place in March 2014 at FaYard in Denmark. This high speed ferry sails twice a day between Larvik in Norway and Hirtshals in Denmark and has limitations on the available space in the funnel. The inline system thus offers a practical solution for overcoming this restriction. In September 2013 contracts were signed for the fitting of the Wärtsilä inline scrubber system to three other Color Line vessels.
Source: Wärtsilä
Officer of the Watch 
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