Question

(a) Describe, with the aid of a sketch, an open loop system for reducing SOx emissions from engine exhaust gas, explaining how the system operates whilst the vessel is in open waters. (6)

(b) Describe, with the aid of a sketch, a closed loop scrubber system for removing SOx from engine exhaust gas, explaining the operation of this unit and stating when it would be used. (10)

Answer 1

Part (a)

The open loop scrubber system uses seawater to lower the sulphur content of the exhaust gasses to an equivalent of 0.1%. The process water is discharged overboard in compliance with IMO 2020 regulations. Open loop systems are primarily used for vessels that operate mainly at open sea.

Exhaust gases enter via the bottom side of the scrubber tower
Seawater is sprayed at the top of the scrubber through spraying nozzles
This results in an equally divided spray pattern throughout the scrubber
Sulphur particles in the exhaust gas attach to the water droplets under the right temperature and process conditions
Cleaned exhaust gas leaves via the top of the scrubber tower
The seawater leaves* via the bottom and is discharged overboard.
pH, turbidity and PAH are continuously monitored in accordance with IMO regulations, MARPOL Annex VI resolution.

Part (b)

The closed loop system uses sodium hydroxide or caustic soda with Fresh water to wash the sulphur content of the exhaust gasses to an equivalent of 0.1%. In compliance with IMO regulations Fresh water used in the process is continuously re-circulated.

Closed loop systems are primarily used for vessels that operate in ports and sailing areas where overboard discharge is prohibited.
Exhaust gasses enter via the bottom side of the scrubber tower
Fresh water is inserted at the top of the scrubber through spraying nozzles
This results in an equally divided spray pattern throughout the scrubber
Sulphur particles in the exhaust gas attach to the water droplets under the right temperature and process conditions
Process water is led to the circulation tank
NaOH is added to the process water to neutralise acidity
Cleaned process water is pumped upwards again to the top
Polluted water is drained and led through a separator
Solids and oil are removed from the polluted water forming sludge
Sludge is pumped to the sludge storage tank on the ship

✓ Verified Model Answer (Text Solution)

The open loop scrubber system uses seawater to lower the sulphur content of the exhaust gasses to an equivalent of 0.1%. The process water is discharged overboard in compliance with IMO 2020 regulations. Open loop systems are primarily used for vessels that operate mainly at open sea.

The closed loop system uses sodium hydroxide or caustic soda with Fresh water to wash the sulphur content of the exhaust gasses to an equivalent of 0.1%. In compliance with IMO regulations Fresh water used in the process is continuously re-circulated.