A gas cleaning system (8) for cleaning a carbon dioxide rich flue gas containing sulphur dioxide generated in a boiler (2) comprises a first gas cleaning device (10) being operative for removing at least 80% of the sulphur dioxide content of the flue gas generated in the boiler (2), thereby generating a partly cleaned carbon dioxide rich flue gas, and a second gas cleaning device (12), being separate from the first gas cleaning device (10) and being operative for receiving at least a portion of the partly cleaned carbon dioxide rich flue gas that passed through the first gas cleaning device (10). The second gas cleaning device (12) is operative for removing at least a portion of the water content of the partly cleaned carbon dioxide rich flue gas by means of cooling the partly cleaned carbon dioxide rich flue gas to condense water there from.