Scrubbers are the ultimate immediate compliance solutions that the shipowners are looking into. Although the skepticism and ban on open-loop scrubbers have made some adverse effect on this decision yet there is considerable goodwill in the favor of EGCS. While most people are bothered about the scrubber water discharge very few pays heed to the quality of the water that goes into the scrubber.
So, here we are answering the most pertinent question of the time – what exactly are the qualities of water supplied to a scrubber.
Water Used to Wash Exhaust Gases
The driving factor for sulphur acid neutralization, and therefore SO2 reduction, is the alkalinity of water used to ‘wash’ the exhaust gases, rather than its salinity.
- Such alkalinity is available in seawater, which of course is also saline, but it can also be added artificially in the form of an alkaline chemical.
- Alkalinity does not refer simply to pH, but to the ability of water to resist changes in pH.
- Buffering materials are primarily bicarbonate and carbonate, but about 4.0% of the neutralization is provided by borates and other ions in low concentrations.
- Total alkalinity, is the sum of all these.
- Salinity describes the salt content of water.
- The salinity of ocean water is approximately 3.5%-weight.
- Some waters can have high alkalinity and zero salinity depending on the calcium concentration.
The Alkalinity of Ports and Coastal Areas
- Open ocean alkalinity is usually constant and high at approximately 2200-2300 μmol/l.
- Alkalinity in some coastal areas, ports, rivers and estuaries can be affected by the different drainage areas of the inflowing rivers, resulting in large variations in the chemistry.
- Rivers running through soil rich in carbonates will be high in alkalinity. For example, the northern rivers of the Baltic Sea run through granite bedrock resulting in low alkalinity at approximately 800-1300 μmol/l, whereas the southern rivers run through calcite bedrock resulting in high carbonate concentrations with consequently high alkalinity of approximately 1650 -1950 μmol/l.
- In general, the alkalinity in the Baltic Sea is lower than open sea areas because of the minimal exchange of water through the Danish straits.
- At low alkalinity levels the seawater scrubber can still operate, but in some cases cleaning efficiency may be reduced .
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