According to MEPC.259(68) the pH discharge criteria of scrubber systems can be approved by computational fluid dynamics or other equally scientifically established empirical formulae. Conmecs provides the calculation and documentation according to these requirements. If desired, conmecs can also take over the communication with the associated class society.

In 1997, a new annex was added to the International Convention for the Prevention of Pollution from Ships (MARPOL). The regulations for the Prevention of Air Pollution from Ships (Annex VI) seek to minimize airborne emissions from ships (SOx, NOx, ODS, VOC shipboard incineration) and their contribution to local and global air pollution and environmental problems.

In 2008, the Marine Environment Protection Committee (MEPC) revised MARPOL Annex VI with tightened emissions limits in light of technological improvements and implementation experience.

The main changes to MARPOL Annex VI are a progressive reduction globally in emissions of SOx, NOx and particulate matter and the introduction of emission control areas (ECAs) to reduce emissions of those air pollutants further in designated sea areas.

Due to these regulations, new exhaust gas cleaning systems entered the maritime market. These systems, can be divided according to their used main working principles into closed and open-loop scrubber systems. Open loop exhaust gas systems are based on the use of seawater as wash-water medium. Sulphur oxides are absorbed in the seawater to form sulphites, which in turn reach equilibrium with seawater species. The equilibrium is held at lower acidity levels (pH values of about 2.5-3.5) compared to the typical seawater pH (~8.2 – 8.8).

According to MEPC.259(68), this acid wash water has to be diluted up to a minimum of pH 6.5 in a distance of 4m from the ship hull. The easiest way to show compliance for this requirement is to dilute the wash water inside the ship and measure the pH value at the discharge. For this procedure, a lot of  additional installations and extra liquids to mix the wash water, e.g. caustic soda (NaOH), is needed. Alternatively, ship owners can show compliance to the regulations by measurements under defined condtions or by fluid dynamic calculations.

For this purpose, conmecs provides calculations and documentations according to class society requirements.

computed mass fraction of scrubber wash water outflow
mass fraction of scrubber wash water outflow; black line equals pH-value of 6.5
proof of MEPC.259(68) compliance

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