Flue gas treatment system

A method for cleaning a gas stream containing carbon dioxide and sulfur dioxide, said method including removing, at least partly, carbon dioxide from the gas stream in a carbon dioxide removal step by bringing the gas stream into contact with a liquid comprising ammonia such that the gas stream is depleted in carbon dioxide and enriched in ammonia, said method comprising the steps of:

• a) bringing the gas stream into direct contact with a liquid stream in a first upstream gas-liquid contacting device upstream of the carbon dioxide removal step, cooling the gas stream, and absorbing into the liquid at least a part of the sulfur dioxide of the gas stream such that the gas stream is depleted in sulfur dioxide and said liquid stream is enriched in sulfate,
• b) bringing the gas stream depleted in sulfur dioxide into direct contact with a liquid stream in a second upstream gas-liquid contacting device upstream of the carbon dioxide removal step, cooling the gas stream, and absorbing into the liquid at least a part of the sulfur dioxide of the gas stream such that the gas stream is depleted in sulfur dioxide and said liquid stream is enriched in sulfate,
• c) removing, at least partly, carbon dioxide from the gas stream by bringing the gas stream depleted in sulfur dioxide into contact with a liquid comprising ammonia such that the gas stream is depleted in carbon dioxide,
• d) bringing the gas stream depleted in carbon dioxide into contact with a liquid stream enriched in sulfate in a first downstream gas-liquid contacting device downstream of the carbon dioxide removal step, cooling the liquid stream, and absorbing into the liquid at least a part of the ammonia of the gas stream such that the gas stream is depleted in ammonia and said liquid stream is enriched in ammonia,
• e) bringing the gas stream depleted in ammonia into contact with a liquid stream enriched in sulfate in a second downstream gas-liquid contacting device downstream of the carbon dioxide removal step, cooling the liquid stream, and absorbing into the liquid at least a part of the ammonia of the gas stream such that the gas stream is depleted in ammonia and said liquid stream is enriched in ammonia,
• f) withdrawing at least a portion of the liquid stream used in the second upstream gas-liquid contacting device and reusing the withdrawn liquid in a downstream gas-liquid contacting device, or withdrawing at least a portion of the liquid stream used in the second downstream gas-liquid contacting device and reusing the withdrawn liquid in an upstream gas-liquid contacting device;
• and
• further comprising the steps of:
• b1) bringing the gas stream depleted in sulfur dioxide from step b) into direct contact with a liquid stream in a third upstream gas-liquid contacting device upstream of the carbon dioxide removal, cooling the gas stream, and absorbing into the liquid at least a part of the sulfur dioxide of the gas stream such that the gas stream is depleted in sulfur dioxide and said liquid stream is enriched in sulfate, and
• e1) bringing the gas stream depleted in ammonia from step e) into contact with a liquid stream enriched in sulfate in a third downstream gas-liquid contacting device downstream of the carbon dioxide removal, cooling the liquid stream, and absorbing into the liquid at least a part of the ammonia of the gas stream such that the gas stream is depleted in ammonia and said liquid stream is enriched in ammonia;
• and
• wherein in step f) a major portion of the liquid stream used in the second upstream gas-liquid contacting device is withdrawn and reused in the second downstream gas-liquid contacting device and a minor portion of the liquid stream used in the upstream second gas-liquid contacting device is reused in the first upstream gas-liquid contacting device, and a major portion of the liquid stream used in the second downstream gas-liquid contacting device is withdrawn and reused in the second upstream gas-liquid contacting device and a minor portion of the liquid stream used in the second downstream gas-liquid contacting device is reused in the first downstream gas-liquid contacting device.