As global and regional sulphur emission regulations continue to evolve, shipowners need solutions that are not only compliant — but also evolutive, adapted to their routes, to their fuel strategies, and onboard constraints.

LAB offers three operating modes for its DeepBlueLAB SOx system to ensure full compliance with IMO MARPOL Annex VI, including the 0.5% global sulphur cap and the 0.1% sulphur limit in SECA zones.

Open Loop Mode

In Open Loop mode, the scrubber uses seawater and its natural alkalinity to wash exhaust gases and neutralize sulphur oxides. The liquid is then analyzed online and discharged back into the sea, meeting regulatory water quality limits.

Advantages:

• Simple design, no need for chemical additives
• Lower CAPEX and OPEX
• Ideal for vessels operating primarily in open waters
• Fully compliant with IMO discharge criteria (where allowed)

Limitations:

• Not permitted in ports or regions where water discharge is restricted
• Dependent on water salinity and temperature

Closed Loop Mode

In Closed Loop mode, the system recirculates water and uses an alkaline additive (magnesia milk and caustic soda) to treat the exhaust gas. This configuration allows to operate with a reduced and treated effluent discharged in conformity with the MARPOL requirements. Minimal effluent is discharged; most of it is reused.

Advantages:

• Can be used in zero-discharge zones (e.g., ports, fjords)
• Less sensitive to seawater properties
• Full control over water quality and compliance

Considerations:

• Requires chemical supply and management
• Slightly higher operational complexity

The extreme configuration called zero discharge mode is based on the close loop configuration. But instead of discharging the treated effluent, it is stored on board on a specific tank. This restriction is required in some areas in the world like in the Norwegian fjord for example.

Hybrid Mode

The Hybrid system combines both Open and Closed Loop capabilities, allowing the ship to switch modes based on operational context and geographic location.

Advantages:

• Maximum flexibility and route coverage with an optimum operational cost
• Automatic switching based on GPS and environmental conditions
• Optimized compliance with SECA zones, harbor rules, and fjord-specific discharge bans

System design and integration

LAB’s DeepBlueLAB SOx systems in all three configurations are:

• Modular and compact, suitable for retrofit or newbuild
• Built with corrosion-resistant materials (GRP or 254SMO)
• Available with ATEX-certified components for hazardous environments
• Fully automated with remote monitoring and control

Each system is tailored to your vessel’s profile — number of engines, space availability, discharge policies along routes, and crew preferences.

Choosing the right mode

The decision depends on several factors:(the decision is driven by the following key factors

• Route type (oceanic vs coastal / SECA)
• Port stop frequency
• Water discharge restrictions
• Fuel strategy (HSFO vs LSFO)
• Availability of chemicals and crew familiarity

LAB’s teams can perform a feasibility and compliance analysis to define the most cost-effective and reliable solution for your fleet.

Not sure which mode is best for your vessel?