Hybrid Scrubber

medium 4 models total

A hybrid scrubber can run open-loop on seawater alkalinity or switch to closed-loop with caustic dosing and a holding tank, letting a vessel keep burning higher-sulphur fuel wherever open-loop discharge is restricted or banned.

Read more — Hybrid Scrubber explained ▾

What Makes a Scrubber "Hybrid"

A hybrid scrubber can run in open-loop mode, using seawater alkalinity to neutralise sulphur oxides and discharging the wash water overboard after treatment, or switch to closed-loop mode, dosing the wash water with caustic soda and recirculating it through an onboard process tank so nothing is discharged in that mode except a small bleed-off. A pure open-loop unit cannot operate where overboard discharge is restricted; a pure closed-loop unit carries the running cost of continuous caustic dosing. The hybrid design lets the vessel switch modes as it crosses between open water and the growing list of ports, estuaries and emission control areas that restrict or ban open-loop discharge.

Main Components

Scrubber tower

A vertical vessel fitted in the exhaust uptake where seawater or dosed fresh water is sprayed countercurrent to the exhaust gas flow, stripping sulphur oxides and particulate matter before the gas exits the funnel.

Seawater supply and overboard discharge system

Pumps drawing raw seawater for open-loop operation, with a dedicated overboard discharge line fitted with monitoring for pH, PAH (polycyclic aromatic hydrocarbons) and turbidity before the water leaves the ship.

Caustic soda dosing and process tank

A storage tank for sodium hydroxide solution and a dosing system that maintains process water alkalinity in closed-loop mode, feeding a smaller recirculation tank rather than the sea.

Sludge and residue handling

Closed-loop operation generates a sludge that must be collected and landed ashore as waste rather than discharged, requiring a dedicated holding tank and manifold connection.

Bypass and mode-change dampers

Ducting and dampers that let exhaust gas be routed around the scrubber during maintenance or, on some installations, switch between parallel scrubber units.

Selection Criteria

Sizing follows engine exhaust flow at full load, the sulphur content of the fuel actually being burned, wash water flow rate needed to hit the required SOx reduction, and closed-loop tank capacity against the trading pattern's time spent in discharge-restricted waters. A vessel trading mostly deep-sea with occasional restricted port calls has different tank sizing needs than one running short coastal legs where closed-loop operation dominates.

Regulations and Class

Scrubbers are approved as an equivalent means of compliance with the MARPOL Annex VI sulphur limit, under the IMO scheme that lets a vessel burn higher-sulphur fuel provided the exhaust gas cleaning system brings SOx emissions down to the equivalent of compliant fuel. Wash water discharge criteria for pH, PAH, turbidity and nitrate are set out in the IMO 2015 Guidelines for exhaust gas cleaning systems, and increasingly by individual port and coastal state bans on open-loop discharge that go beyond the IMO baseline. Class surveys the scrubber under the vessel's approved EGC system certificate, with continuous monitoring records checked at survey.

Typical Faults

Wash water monitoring sensor fouling gives false pH or PAH readings and risks an out-of-specification discharge going unnoticed, or a compliant discharge being wrongly flagged.
Spray nozzle blockage or erosion reduces SOx removal efficiency below the required level without an obvious alarm.
Caustic dosing pump failure in closed-loop mode lets process water alkalinity fall, cutting scrubbing efficiency.
Corrosion of the scrubber tower and ducting is a recurring maintenance cost, since the wash water is acidic and erosive.

What to Look for in a Supplier

Wash water treatment and monitoring package proven to meet the discharge criteria in the trading area actually planned, not just a generic IMO-compliant claim.
Materials specification for the tower and ducting suited to continuous exposure to acidic wash water.
Support for the port state documentation increasingly demanded for open-loop discharge, including access to discharge water quality records.

Do not assume open-loop mode is always the cheaper default: track which ports and coastal states on the vessel's actual routes restrict it, because switching to closed-loop too late costs more than the caustic soda ever would.

Inspector Mode Show All 4 total

4 manufacturers · 4 models

Alfa Laval

PureSOx Hybrid

variable · Exhaust Gas Treatment · Hybrid exhaust gas scrubber

Type

hybrid

Marpol

Technical Specifications

Sox-abscheidung: >98% Removal mit Partikelfiltration
Betriebsweisen: Open-Loop, Closed-Loop, Hybrid, mit optionalem Energy Reduction Mode
Wasser-reinigungseinheit: Centrifugal-Separator (PureSOx H2O), 6 m² Grundfläche, modulare 3-Skid-Konstruktion
Installationen: 100+ Schiffe weltweit, 200+ Retrofit-Projekte abgeschlossen
Service-Verfügbarkeit: 24/7 Global Support, 24-Stunden-Ersatzteilversand, Dry Dock Services, Crew-Training

Product Lines

PureSOx U-Design
PureSOx I-Design (Inline)
PureSOx Express
PureSOx Hybrid
PureSOx Closed-Loop
PureSOx Open-Loop

Common Failures & Inspection Points

Area: Düsen- und Sprühsystem-Verschleiß: Nozzles können durch Erosion, Verschlammung oder Mineralabsatz verstopfen/beschädigt werden, was Sprühmuster beeinträchtigt u
Check: Visuelle Inspektion der Spray-Nozzles auf Verschleiß, Risse, Ablagerungen; Funktionalitäts-Test des Sprühmusters; Verwendung echte Ersatz-Nozzles via Alfa Laval Sprayer Replacement Programme mit Hersteller-Kalibrierung
Area: pH und PAH Sensor-Kalibrierung: Sensoren (PAH, Trübung) müssen 2-jährlich werkseitig kalibriert werden (MEPC-Standard). Ungenaue Messungen führen zu Compliance-
Check: Überprüfung Kalibrierungs-Datum (sollte nicht älter als 2 Jahre sein); Sensor-Austausch via Alfa Laval Exchange Programme; Dokumentation der Kalibrierungs-Zertifikate und Mess-Logs (aktueller Standard: Logging alle ~90 Sekunden)
Area: Absorber-Korrosion: Das Absorber-Modul (separat vom Jet-Modul durch natürliche Water Trap) ist Salzwasser/Säure-Umgebung ausgesetzt und kann korrodieren; Korros
Check: Trockendock-Condition Assessment durchführen (idealerweise 6 Monate vor Dock geplant); visuelle Inspektion auf Korrosions-Flecken, Materialverlust an Wänden/Böden; Messung der Wanddicke (kritische Bereiche); Dokumentation und Reparaturempfehlungen
Area: Wash Water Monitoring und Leck-Detektion: Im Closed-Loop/Hybrid-Betrieb entsteht Schmutzwasser mit Ruß, Mineralien und Öl; unzureichendes Monitoring oder Leck i
Check: Prüfung der Wasser-Reinigungs-Einheit (PureSOx H2O Zentrifugal-Separator) auf Verschleiß/Verschlammung; Überprüfung pH/PAH/Trübungs-Messungen und Aufzeichnungen (Kontinuierliches Logging gefordert); Sichtprüfung auf Leckagen an Rohrleitungen und Armaturen; Validierung, dass Trübung <25 FTU bleibt
Area: Jet- und Absorber-Modul-Verrohrung und Damper-Ventile: U-Design oder Inline-Design nutzen komplexe interne Rohrsysteme; Ablagerungen, Korrosion oder Ventil-Vers
Check: Dry Dock Inspektion: Sichtprüfung internaler Rohre (Endoskop nutzen wenn nötig) auf Ablagerungen/Korrosion; Funktionsprüfung von Damper-Ventilen und Pumpen; Inspizieren von kritischen Komponenten gemäß Alfa Laval Dry Dock Service Kit (Damper Valves, Pumps, Sensors); Austausch verschlissener Teile mit Original-Ersatzteilen
Area: Discharge Water Testing und Compliance-Dokumentation: IMO MEPC fordert Labor-Tests des Ablaufwassers nach Commissioning und vor jeder Schiffsbesichtigung; Tests
Check: Prüfung der Discharge-Water-Test-Zertifikate (Labor-bestätigt) und deren Datum; Vergleich Messwerte gegen Grenzwerte (pH ≥6,5, PAH ≤50 µg/L, Trübung ≤25 FNU, Temperatur ≤60°C); in US-Gewässern: mindestens 2 Tests im 1. Jahr, dann jährlich 1x; in anderen Regionen evtl. häufiger; Dokumentation im Schiffs-Compliance-Logbuch

Typ-universelle Inspektions-/Wartungspunkte fuer Exhaust Gas Cleaning (Alfa Laval, Mega-Schwarm 2026-06). Per-Modell-Specs nicht auto-gefuellt.

Service: Hybrid operation — closed loop in restricted waters, open in open sea.

Spare Parts: Alfa Laval: Spezialteile per Hersteller. Lead time: 4-8 Wochen. Gasdetektions-Sensoren an Bord.

Strengths

>98 % SOx removal meeting MARPOL Annex VI requirements
Hybrid flexibility – can run open‑loop in open sea, closed‑loop or energy‑reduction mode in restricted waters
Modular 3‑skid design (≈6 m²) simplifies installation and retrofits
Integrated PureSOx H2O centrifugal separator reduces wash‑water treatment footprint
24/7 global support, spare‑part logistics and crew training from Alfa Laval

Weaknesses

Higher capital cost and deck space requirement compared with single‑mode open‑loop scrubbers
Complex maintenance – regular inspection of spray nozzles, pH/PAH sensors and absorber corrosion needed
Wash‑water handling system adds weight and requires continuous monitoring for leaks
Energy‑reduction mode still consumes power; overall fuel penalty can be 1–3 % depending on operating profile
Requires skilled crew training to manage mode changes and compliance documentation

Typical Vessels: Crude oil tankerProduct tankerLNG carrierContainer shipBulk carrierRo‑Ro / ferry operating in emission control areas

Certifications: IMO Type Approval (MEPC.73(78))DNV GL ApprovedABS ApprovedLR Approved

Decision Guide: Choose if the vessel operates both in open sea and in ECAs or inland waterways where closed‑loop capability is mandatory, when retrofit space is limited and modularity is valued, or when a single system must cover all operating modes. Avoid if budget constraints preclude higher upfront cost, deck area is severely restricted, or the operator prefers a simpler open‑loop only solution with lower maintenance complexity.

Use Cases: The PureSOx Hybrid is deployed on more than 100 ships worldwide—including crude and product tankers, LNG carriers and container vessels—to meet strict SOx limits in emission control areas, inland waterways and ports. It is also the preferred choice for retrofit projects where flexibility between open‑loop and closed‑loop operation reduces wash‑water discharge constraints while maintaining compliance.

Manufacturer Datasheet

Datasheet

EcoSpray (Saacke)

EcoSpray Marine Scrubber

variable · Exhaust Gas Treatment · Hybrid exhaust gas scrubber

Type

hybrid

Marpol

Origin

Italy

Common Failures & Inspection Points

Tower corrosion
Pump seal failure
Control system error

Service: Italian manufacturer. ECA-compliant.

Spare Parts: EcoSpray (Saacke): Spezialteile per Hersteller. Lead time: 4-8 Wochen. Gasdetektions-Sensoren an Bord.

Strengths

ECA‑compliant with flexible open‑/closed‑loop modes for varied water quality conditions
Reduced freshwater consumption compared with pure open‑loop designs
Compact installation footprint suitable for retrofits on existing vessels
Integrated control system enables automated mode switching and monitoring
Italian engineering reputation for robust mechanical design

Weaknesses

Reported tower corrosion issues requiring regular inspection and protective coating maintenance
Pump seal failures have been noted, increasing spare‑part inventory needs
Control system errors can lead to temporary non‑compliance if not promptly addressed
Higher upfront capital cost than basic open‑loop scrubbers
Requires onboard waste‑water handling infrastructure for closed‑loop operation

Typical Vessels: TankerContainer shipBulk carrierGeneral cargo vesselCruise liner

Decision Guide: Choose if the vessel operates frequently in Emission Control Areas and needs the flexibility to switch between open‑ and closed‑loop modes without installing separate systems. Avoid if budget constraints preclude higher capital outlay, or if the ship lacks adequate waste‑water treatment capacity for closed‑loop operation.

Use Cases: The EcoSpray Marine Scrubber is commonly installed on mid‑size tankers and container ships transiting North Sea and US Gulf ECAs, as well as cruise vessels that require rapid mode changes when entering ports with strict water discharge regulations.

Datasheet

Wärtsilä

Wartsila Hybrid Scrubber

variable · Exhaust Gas Treatment · Hybrid SOx scrubber

Type

hybrid

Marpol

Technical Specifications

Sox-reduktion: 98% Schwefeldioxid-Entfernung
Operationsmodi: Open Loop, Closed Loop, Hybrid
Seewasser-Alkalinität erforderlich: 2300 µmol/l zur Reduktion von 3,5% auf 0,1% Schwefelgehalt
Abwasser-pH Entladung: Minimum 6,5, Maximum Temperatur 60°C, max. 2 pH-Einheiten Differenz Inlet-Overboard
Überwachungsparameter: pH, PAH (Polyzyklische aromatische Kohlenwasserstoffe), Trübung, Temperatur
Entschwefeleinsätze: Venturi-Absorber mit 3-stufiger Wasserzerstäubung, Hochleistungs-Edelstahl

Product Lines

Conventional Quench and Venturi Design
Inline Scrubber Design
IQ Series Scrubber (compact, 25% weniger Platz, 30% leichter)
Hybrid Scrubber (Open/Closed Loop kombinierbar)

Common Failures & Inspection Points

Area: Absorber/Venturi-Erosion und Verschleiß
Check: Halbjährliche Sichtprüfung des Absorbers auf Erosions- und Korrosionszeichen; Drucktest der Sprühköpfe (niedriger Druck = Erosion); Überprüfung auf Verschleiß an Venturi-Wänden und Umlenkblechen
Area: Sprühdüsen-Verstopfung und -Erosion
Check: Wöchentliche Überprüfung der Sprühköpfe und Header auf Verstopfung oder Erosion; Überprüfung der Flüssigkeitsdruckmanometer zur Erkennung abnormal niedriger Drücke (Indikator für Erosion); Halbjährliche interne Inspektionen auf verstopfte oder erodierte Düsen
Area: Abwassersensorik und pH-Sonde Kalibrierung
Check: Jährliche Vollservice- und Kalibrierung aller Sensoren durch zertifizierte Techniker; Regelmäßige Überprüfung auf Sondenverschmutzung und Sensorempfindlichkeit; CEMS und Wasserüberwachungssysteme kalibrieren gemäß Herstellervorgaben
Area: Abwasserqualität: pH, PAH, Trübung, Temperatur Monitoring
Check: Kontinuierliche Überwachung von Inlet- und Outlet-Wasserqualität; Dokumentation von pH (min. 6,5), PAH, Trübung, Temperatur (max. 60°C); Jährliche Probenahmen spätestens nach dem ersten Betriebsjahr durchführen; 3-Jahres-Aufbewahrung aller Testergebnisse
Area: Korrosion an Abwasserrohren und Ableitungsleitungen
Check: Dickenmessungen aller Abwasserrohre und Überbord-Leitungen bei jeder jährlichen Hauptbesichtigung durchführen (DNV-Anforderung); Visuelle Inspektionen auf Korrosions- und Erosionszeichen; Überprüfung der Integrität von Rohrbefestigungen und Schweißnähten; Besonders Aufmerksamkeit auf Säurekorrosion vor Seewasser-Verdünnung
Area: Nebel-Abscheider (Mist Eliminator) Verschmutzung und Blockade
Check: Halbjährliche innere Inspektionen des Nebel-Abscheiders auf Verschmutzung, Verstopfung und Korrosion; Überprüfung auf Feststoffansammlung im Abscheider; Funktionsprüfung der Washdown-Systeme des Abscheiders; Reinigung oder Austausch bei Beschädigungen durchführen

Typ-universelle Inspektions-/Wartungspunkte fuer Exhaust Gas Cleaning (Wärtsilä, Mega-Schwarm 2026-06). Per-Modell-Specs nicht auto-gefuellt.

Service: NaOH (caustic soda) consumption monitoring. Sludge tank management.

Spare Parts: Wärtsilä: Spezialteile per Hersteller. Lead time: 4-8 Wochen. Gasdetektions-Sensoren an Bord.

Strengths

Very high SOx removal efficiency (≈98 %) meeting IMO Annex VI limits
Three operation modes (open loop, closed loop, hybrid) give flexibility for varying water quality and regulatory zones
Compact IQ series design reduces installation space by up to 25 % and weight by ~30 %
Wärtsilä lifecycle support includes integrated NaOH consumption monitoring and sludge‑tank management
Class‑approved and widely installed, providing proven reliability

Weaknesses

Requires seawater with alkalinity ≥2300 µmol/l for effective open‑loop operation; low‑alkalinity waters force closed‑loop mode
Closed‑loop mode needs continuous supply of caustic soda (NaOH) and handling of alkaline wash water
Higher capital cost compared with simple open‑loop scrubbers
Maintenance intensive – regular inspection of venturi, spray nozzles and pH sensors is mandatory
Discharge restrictions in zero‑discharge ECAs may limit use of the open‑loop mode

Typical Vessels: Oil tankerBulk carrierContainer shipCruise linerOffshore supply vessel

Certifications: IMO MARPOL Annex VI (SOx) complianceDNV GL approved marine scrubberABS class approval

Decision Guide: Choose if the vessel must meet the 0.1 % sulfur limit in ECAs, operates on routes with variable seawater alkalinity, or needs retrofit flexibility without sacrificing cargo space. Avoid if the ship is subject to strict zero‑discharge regulations, lacks storage for caustic soda, or cannot accommodate the additional maintenance regime.

Use Cases: Typically installed on existing vessels retrofitted after the 2020 IMO sulfur cap and on new builds destined for long‑haul trades where fuel flexibility is required. Hybrid mode is especially valuable for ships that alternate between high‑alkalinity open‑loop ports and inland or low‑alkalinity waters where closed‑loop operation is mandatory.

Manufacturer Datasheet

Datasheet

Yara Marine

Yara Marine SOx Scrubber

variable · Exhaust Gas Treatment · Hybrid exhaust gas cleaning system

Type

hybrid

Marpol

Origin

Norway

Common Failures & Inspection Points

Scrubber packing degradation
Chemical dosing system failure
Emission sensor malfunction

Service: Norwegian manufacturer. Hybrid capability.

Spare Parts: Yara Marine: Spezialteile per Hersteller. Lead time: 4-8 Wochen. Gasdetektions-Sensoren an Bord.

Strengths

Dual‑mode operation gives flexibility to meet regulations in both emission control areas and open ocean.
Reduced freshwater consumption compared with pure closed‑loop scrubbers because sea water can be used when permitted.
Proven Norwegian design with a compact footprint suitable for retrofits on existing vessels.
Integrated monitoring and automation reduces crew workload during mode changes.

Weaknesses

Higher capital cost than single‑mode (open‑ or closed‑loop) scrubbers.
Increased system complexity leads to more frequent maintenance (e.g., packing wear, dosing pump reliability).
Requires on‑board storage and handling of chemical reagents for closed‑loop operation.
Potential sensor failures can affect compliance if not promptly addressed.

Typical Vessels: TankerBulk CarrierContainer ShipGeneral Cargo VesselCruise Ship

Certifications: IMO Type ApprovalDNV GL Classification

Decision Guide: Choose if: the vessel operates in or frequently transits Emission Control Areas and needs flexibility between open‑loop and closed‑loop modes, or when a retrofit must meet Annex VI without extensive hull modifications. Avoid if: budget constraints prohibit higher upfront cost, or the operator lacks capacity for chemical handling and additional maintenance.

Use Cases: Commonly installed on newbuilds and retrofitted tankers, bulk carriers, and container ships that require global compliance with sulfur emission limits, especially those sailing between high‑sulfur fuel regions and ECAs where closed‑loop operation is mandatory in ports.

Datasheet