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  • The basic system is a seawater pump, two pipes and an exhaust gas cleaning tower.
  • Seawater is pumped to the tower, which replaces the engine exhaust silencer.
  • Seawater is sprayed into the tower, where it cleans the exhaust from the ship’s engines, removing SOx, mainly SO2.
  • The seawater drains from the tower and (in port) through a filter before discharge.
  • Any remaining SO2 is measured by a gas analyzer above the tower.
  • The seawater used is measured continuously for pH, turbidity, and PAH (oil content) in three locations (inlet, after tower, and before discharge).
  • The Advanced Air Quality Systems remove sulfur (SOx) from the air emissions, preventing the airborne part of the sulfur cycle.
  • The Advanced Air Quality Systems also remove a high percentage of particulate matter (PM) with good effectiveness against the 10- and 2.5-micron particles and superfines.
  • Diesel particulate filters and catalytic oxidation reactors (together known as “dry filters”) also reduce PM, with particular effectiveness in reducing PAH.
  • Advanced Air Quality Systems with HFO have produced overall better air emissions than MGO.
  • Advanced Air Quality Systems with HFO have typically lower sulfur (SO2) emission levels, fewer ultrafine PMs, lower NOx and fewer PAHs than MGO.
  • MGO has a higher greenhouse gas emissions (GHG) penalty in production, as MGO is a distilled product requiring more refining.
  • Advanced Air Quality Systems release miniscule amounts of material in the water, which is not harmful, and in the case of sulfur, it is naturally occurring in the ocean.
  • The human health concern from sulfur and PM/PAHs is from airborne impact.
  • The sea is the planet’s natural reservoir for sulfur and there is no environmental impact from discharging sulfates.
  • The small amount of soot discharged contains trace amounts of PAHs and metals, which are measured in ppb (parts per billion) and are within all major water discharge standards. This means negligible environmental impact.
  • Typically, this is not smoke but a “white plume,” which when environmental conditions are right is a condensation of the water vapor entrained in the exhaust from the scrubbing process. This normally dissipates a few meters beyond the stack.
  • Occasionally we also see some “blue plume,” which can be more persistent. This is from light effects on a few remaining compounds in the exhaust, and we are working to further reduce this as well.
  • This is mainly air bubbles, which can create foam like any other agitation of sea water, such as waves at the beach. Our general term for these increasingly rare events is “surface effects.”
  • The same effect may often be from the engine cooling water discharge.
  • In addition to a few bubbles there may occasionally also be a light film at the edge of the agitated area, which is left from the breakdown of the bubbles or foam; repeated sampling of this has never shown up any oil content.
  • When running Advanced Air Quality Systems in ports, especially with buffering water, normally a longer discharge plume two to three meters beneath the surface may be seen, or a small cloud of microbubbles.
  • High organic content in the water (e.g., algae) may lead to a brown or black foam appearance. This is most common in in northern climates in mid-to-late summer as water temperatures warm up.
  • Lab tests of these discolored “surface effects” have typically shown zero or only trace evidence of oil, but often have high organic content.
  • Open loop brings in seawater for “scrubbing” the exhaust and discharges it immediately back to sea, filtered or unfiltered.
  • Closed loop recirculates the seawater, adding chemicals as the seawater alkalinity becomes saturated. Some seawater is bled off to a storage tank, where it is filtered and dewatered for later discharge at sea or sludge offload to designated facilities.
  • The most common closed-loop chemical is caustic soda, which is highly toxic and requires careful storage and handling by trained personnel.
  • Closed loop exhaust plume is usually much more visible than open loop.

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