Open loop scrubber

An open-loop scrubber sprays seawater into the exhaust stream, using the natural alkalinity of seawater to neutralize SO2, then discharges the acidified washwater overboard after monitoring against the EGCS washwater criteria in MEPC.340(77). It needs no caustic soda and little tankage, which makes it cheap to run, but it cannot operate where local rules ban open-loop discharge, including parts of China, Singapore, and several US and European ports. Many such ships are hybrids able to switch to closed-loop in restricted waters.