Appendix D Overview of the Sea Water Scrubber System - Holland ...

Water Intake through the Sea Chest
Water is taken aboard a vessel through a device called a sea chest. A sea chest is a rectangular steel
enclosure attached to the inside of a louvered or perforated section of the ship’s hull below the water
line. Water enters the sea chest, and when the valve is open, water passes into the pipe and through
the strainer into the ship, where it is delivered for its intended use. The strainer is cleaned periodically
to remove accumulated solid material (sea weed, twigs, etc). When the valve is closed, sea water does
not enter the ship.
The Sea Water Scrubber
Exhaust gas passes through the scrubber where it is mixed with raw seawater. There are no chemicals
added anywhere in this system. Several stages of seawater and gas mixing occur to ensure high levels of
scrubbing efficiency. The scrubbing cools the gas and entrains droplets of seawater. A “demister” was
installed in order to prevent these droplets of seawater from being carried out of the stack. As the
scrubber was not operated in port pending demonstration of the wash water technology, the demister
was subject to frequent dry operation which resulted in clogging. This clogging problem precluded use
of the demister during much of this demonstration project. To minimize generation of a vapor plume,
the wash water supply in the final scrubbing stage was switched off and it was then used as the
demister.
After scrubbing, the cooled exhaust gas is re‐heated using a hot air injection manifold to change the
relative humidity of the gas from 100% to less than 80%. This prevents a visible plume at the funnel
outlet.
Wash water (the effluent from the scrubber) flows out of the base of the scrubber unit to the
multicyclone below deck in the engine room.
The Multicyclone ‐ Wash Water Treatment Plant
After leaving the scrubber, the wash water passes through a high performance multicyclone, which
separates the particles from the wash water. The pH of the treated wash water is then raised to a near
neutral value by mixing with an essentially equal volume of “reaction water,” (see Figure 1 above)
delivered by a separate reaction water supply line before being discharged overboard to the sea.
This particulate removed by the multicyclone is collected in a chamber in the base of the unit (see Figure
2), from where it is batch ejected to a storage tank (see Figure 3).
Figure 2 ‐ The Multicyclone