Exhaust gas cleaning system and method for cleaning exhaust gas

Method for cleaning exhaust gas onboard a ship by means of an exhaust gas cleaning system, the method comprising

• washing the exhaust gas onboard the ship with a scrubber fluid that washes pollutants in the exhaust gas to clean the exhaust gas, the pollutants washed by the scrubber fluid including sulphur oxides and particulate matter, the washing of the exhaust gas occurring in a scrubber comprised in a scrubber unit,
• separating the scrubber fluid, after the washing, in a centrifugal separator, into a first and a second fraction, which second fraction is more polluted with the particulate matter than the first fraction;
• wherein the scrubber unit and the centrifugal separator are comprised in a first sub system of the exhaust gas cleaning system,
• the method further comprising
• passing the first fraction of the scrubber fluid through a membrane filter to separate it into a third and a fourth fraction, which fourth fraction is more polluted than the third fraction, wherein the membrane filter is comprised in a second sub system of the exhaust gas cleaning system, and
• feeding the first fraction of the scrubber fluid to the scrubber unit from the centrifugal separator.

Exhaust gas cleaning system for cleaning exhaust gas onboard a ship, which exhaust gas cleaning system comprises a first sub system including:

• a scrubber unit comprising a scrubber arranged to wash the exhaust gas with a scrubber fluid;
• a centrifugal separator arranged in communication with the scrubber unit for receiving the scrubber fluid after washing and separating it into a first and a second fraction, which second fraction is more polluted than the first fraction;
• the scrubber comprising an exhaust gas inlet for receiving the exhaust gas and an exhaust gas outlet for outputting the washed exhaust gas;
• the exhaust gas cleaning system further comprising a second sub system including a membrane filter arranged in communication with the centrifugal separator for receiving the first fraction output from the centrifugal separator and separating the first fraction into a third and a fourth fraction, which fourth fraction is more polluted than the third fraction;
• the centrifugal separator being in communication with the scrubber unit for feeding the first fraction of the scrubber fluid to the scrubber unit;
• the exhaust gas cleaning system further comprising
• a flocculation unit having an outlet and an inlet;
• and
• a chemical dosing unit, the chemical dosing unit being configured to supply a chemical substance that includes a flocculant and/or a coagulant to the scrubber fluid between the scrubber unit and the inlet of the flocculation unit;
• and
• the outlet of the flocculation unit being connected to the centrifugal separator.

Method for cleaning exhaust gas onboard a ship by means of an exhaust gas cleaning system, the method comprising

• washing the exhaust gas onboard the ship with a scrubber fluid in a scrubber comprised in a scrubber unit,
• conveying the scrubber fluid, after the washing, from the scrubber unit to an inlet of a flocculation unit and supplying a chemical substance that includes a flocculant and/or a coagulant to the scrubber fluid between the scrubber unit and the inlet of the flocculation unit;
• conveying the scrubber fluid from an outlet of the flocculation unit to a centrifugal separator;
• separating the scrubber fluid in the centrifugal separator into a first and a second fraction, which second fraction is more polluted than the first fraction, the scrubber unit and the centrifugal separator being comprised in a first sub system of the exhaust gas cleaning system;
• passing the first fraction of the scrubber fluid through a membrane filter to separate it into a third and a fourth fraction, which fourth fraction is more polluted than the third fraction, the membrane filter being comprised in a second sub system of the exhaust gas cleaning system;
• and
• feeding the first fraction of the scrubber fluid to the scrubber unit from the centrifugal separator.