EGCS (scrubbers) are fitted as an equivalent method under MARPOL Annex VI to meet sulphur emission limits while burning high sulphur fuel oil.

1. Open Loop Scrubber

• Uses seawater as the scrubbing medium.
• Natural alkalinity of seawater neutralizes SOx in exhaust gas.
• Wash water is treated/monitored and then discharged overboard.
• Simple and low chemical requirement.
• Limited in ports/estuaries where discharge may be restricted.

2. Closed Loop Scrubber

• Uses fresh water mixed with alkali (usually NaOH).
• Wash water is recirculated after cooling and treatment.
• Small bleed-off/sludge is retained in holding tank for shore disposal.
• Suitable in areas where overboard discharge is prohibited.
• More complex and higher operating cost.

3. Hybrid Scrubber

• Can operate in both open loop and closed loop modes.
• Open sea: usually open loop.
• Port/restricted waters: closed loop.
• Most flexible system but highest installation and maintenance cost.

When EGCS is operating, monitoring and recording must demonstrate compliance with IMO EGCS guidelines and MARPOL Annex VI. IMO washwater monitoring requires continuous recording of key discharge parameters, especially in ports/harbours/estuaries.

1. Exhaust gas compliance data

• SO₂ / CO₂ ratio (or equivalent emission value) to prove sulphur compliance.
• Continuous monitoring where fitted.

2. Scrubber operating parameters

• Exhaust gas temperature before and after EGCS
• Exhaust gas pressure / pressure drop across scrubber
• Engine/boiler load
• Wash water flow rate
• Pump running status
• NaOH dosing rate / circulation status (for closed loop)

Older IMO EGCS guidance specifically lists parameters such as washwater inlet/outlet pH, exhaust pressure drop, combustion equipment load, and exhaust temperature before/after the unit for recording.

3. Wash water discharge quality (continuous)

• pH
• PAH (oil content / polycyclic aromatic hydrocarbons)
• Turbidity
• Temperature
• These are specifically required to be continuously monitored/recorded when discharging, especially in ports, harbours, estuaries, or from temporary storage.

4. Residue / sludge handling

• Quantity of sludge / residue generated
• Storage tank level
• Date, time, location of transfer to reception facility
• Record in EGC log / record book

IMO requires residues to be delivered ashore and the storage/disposal to be recorded in an EGC log; residues must not be discharged to sea or incinerated on board.

5. Record books / documents

• EGC Record Book / electronic logger
• Alarm and fault history
• Maintenance and calibration records
• Port restrictions / mode changeover entries
• Non-compliance or malfunction entries

If the scrubber fails, immediate action is required to prevent violation of MARPOL Annex VI sulphur limits.

1. Inform and report immediately

• Inform Chief Engineer and Master
• Record time, position, engine load, fuel in use, and nature of fault

2. Check if safe restart is possible

• Check alarms/trips on:
  • scrubber pumps
  • wash water flow
  • fan/demister blockage
  • NaOH dosing (closed loop)
  • sensors / PLC faults
  • overboard valve / recirculation valve
  • sludge tank high level
• Attempt restart as per maker’s manual / OMM

3. Change over to compliant fuel immediately

• If EGCS cannot be restored quickly:
  • change from HSFO to compliant low sulphur fuel oil
  • Ensure service tank, settling tank, heaters, viscosity adjustment and purifier line are arranged properly
• This is the most important compliance action.

4. Stop overboard discharge if required

• If wash water monitoring or treatment fails:
  • stop discharge
  • shift to closed loop / zero discharge mode if available
  • or stop EGCS completely

  5. Enter full details in records

  • Enter in:
    • Engine room log book
    • EGCS record book
    • Planned maintenance / defect log
    • Alarm history
  • Record:
    • failure time
    • corrective action
    • fuel changeover time
    • repair time

    6. Repair and verify before reuse

    • Rectify fault (pump, sensor, dosing unit, valve, blockage, automation, calibration)
    • Test system
    • Confirm:
      • proper wash water flow
      • normal pH/PAH/turbidity
      • acceptable SO₂/CO₂ ratio
    • Only then return to normal EGCS operation

    7. If entering/inside ECA or restricted port

    • Must not continue on HSFO without a functioning EGCS
    • Use compliant fuel only
    • If required, notify company/flag/port as per shipboard procedures and SECA compliance plan