Closed-Loop Scrubber (EGCS)
Exhaust gas cleaning system that uses caustic soda (NaOH) in a closed water loop to remove SOx; sludge stored aboard for shore disposal.
In practice
Used in waters that prohibit open-loop discharge. Caustic dosing rate set by exhaust SOx; the engineer monitors fresh-water makeup and effluent settling tank level. Sludge handled as MARPOL Annex I oily residue.
Regulatory detail & full definition
A closed-loop scrubber is an exhaust-gas-cleaning system that removes sulphur oxides using a recirculated wash water dosed with caustic soda (NaOH) rather than seawater's natural alkalinity, so that little or no wash water is discharged overboard. Because the water is treated and recirculated - passing through hydrocyclones and a sludge tank, with the sludge stored on board for shore disposal - it can be operated in ports and other zero-discharge waters where open-loop discharge is banned. The trade-off is higher operating cost from NaOH consumption and the need to land sludge ashore.
Authoritative source: IMO Resolutions Index ↗
Related
Source: MEPC.259(68); MEPC.184(59)
High confidence
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