6.1 SOX scrubber technologies
Currently there are two main types of SOX scrubber:
• wet scrubbers (section 6.2) that use water (seawater or fresh) as the scrubbing medium; and
• dry scrubbers (section 6.7) that use a dry chemical.
Wet systems are further divided into:
• ‘open loop’ systems (section 6.3) that use seawater
• ‘closed loop’ systems (section 6.4) that use fresh water with the addition of an alkaline chemical; and
• ‘hybrid’ systems (section 6.5), which can operate in both open loop and closed loop modes.
7. NOX-reducing devices
As the largest component of NOX is formed through the Thermal NO(X) mechanism, it is not possible to effectively reduce NOX emissions by controlling the fuel consumed. NOX reduction is therefore achieved by reducing thermal NO(X) by one of the following:
• primary NOX control, which reduces the formation of thermal NO(X); and
• post-combustion abatement in which the exhaust gas is treated to remove NOX.
Subject to an imminent IMO review of available technologies, Tier III NOX limits will apply to all ships constructed on or after 1 January, 2016, with engines over 130kW that operate inside an ECA-NOX. Unlike the sulphur limits in Regulation 14 of MARPOL Annex VI, the Tier III NOX limits will not retrospectively apply to ships constructed before 1 January, 2016 (except in the case of additional or non-identical replacement engines installed on or after 1 January, 2016).