Method and installation for liquefying flue gas from combustion installations

1. A method for producing liquid CO 2 product out of combustion flue gas, the method comprising:

partially condensing the flue gas in sequence through at least two separation stages to form a two phase mixture of an off gas to be vented and a liquid CO 2 stream;

separating the off gas to be vented from the liquid CO 2 stream in at least the last separation stage;

wherein the off gas to be vented and the liquid CO 2 stream are expanded and the at least two separation stages are cooled by the expanded off gas to be vented and the expanded liquid CO 2 ; and

wherein the expanded liquid CO 2 is further separated after having passed the last separation stage of the at least two separation stages in an additional separation drum; and

wherein the liquid CO 2 moving out of the additional separation drum is split into a part of the liquid CO 2 and a remainder of the liquid CO 2 ; and

wherein gaseous CO 2 moving out of the additional separation drum and the part of the liquid CO 2 moving out of the additional separation drum are expanded to a first pressure level for cooling the last separation stage; and

wherein the pressure of the remainder of the liquid CO 2 moving out of the additional separation drum is raised to a second pressure level and the remainder of the liquid CO 2 moving out of the additional separation drum is then expanded for cooling the CO 2 in the at least two separation stages and conveyed to a compression stage of a multistage compressor; and

wherein the gaseous CO 2 , the part of the liquid CO 2 moving out of the additional separation drum, and the remainder of the liquid CO 2 moving out of the additional separation drum are compressed with the multistage-compressor to produce liquid CO 2 .

2. The method according to claim 1 , wherein the remainder of the liquid CO 2 moving out of the additional separation drum is expanded to a pressure of approximately 15 bar to 25 bar.

3. The method according to claim 1 , wherein the liquid CO 2 from separation stage before the last separation stage is expanded to the pressure of the remainder of the liquid CO 2 moving out of the additional separation drum and the liquid CO 2 from the separation stage before the last separation stage and the remainder of the liquid CO 2 moving out of the additional separation drum are used for cooling purposes in the separation stage before the last separation stage.

4. The method according to claim 3 , wherein the liquid CO 2 from the separation stage before the last separation stage and the remainder of the liquid CO 2 moving out of the additional separation drum are fed to a second or third stage of a multistage-compressor.

5. The method according to claim 1 , wherein the flue gas is compressed in a first compressor, cooled in a first cooler and/or dried in a drier before entering a first separation stage of the at least two separation stages.

6. The method according to claim 1 , wherein offgas from the last separation stage of the at least two separation stages is expanded to approximately 17 bar and resulting in a temperature of approximately −54° C. before entering a heat exchanger of the last separation stage of the at least two separation stages.

7. The method according to claim 1 , wherein the offgas is superheated in a superheater after having passed all separation stages of the at least two separation stages and expanded in an expansion machine and subsequently fed again to a heat exchanger of the last separation stage of the at least two separation stages.

8. A plant for producing liquid CO 2 product out of combustion flue gas, comprising:

at least two separation stages where the flue gas is partially condensed and divided into off gas to be vented and liquid CO 2 at least in a last separation stage thereof;

pressure reducing valves configured to expand the off gas to be vented and the liquid CO 2 ; and

wherein the at least two separation stages are arranged to be passed through in sequence by the flue gas and are cooled by the expanded off gas to be vented and by the expanded liquid CO 2 ;

an additional separation drum configured and arranged to receive the expanded liquid CO 2 from the first expansion device and separate the expanded liquid CO 2 into liquid CO 2 and gaseous CO 2 ;

a splitter wherein the liquid CO 2 moving out of the additional separation drum is split into a part of the liquid CO 2 and a remainder of the liquid CO 2 , and wherein the gaseous CO 2 moving out of the additional separation drum and the part of the liquid CO 2 moving out of the additional separation drum are expanded to a first pressure level for cooling the last separation stage;

a pump and a pressure reducing valve, where the pressure of the remainder of the liquid CO 2 moving out of the additional separation drum is raised to a second pressure level and expanded for cooling the last separation stage of the at least two separation stages; and

a multistage compressor, wherein a stage of the multistage compressor is configured and arranged to compress the gaseous CO 2 moving out of the additional separation drum, the part of the liquid CO 2 moving out of the additional separation drum and the remainder of the liquid CO 2 moving out of the additional separation drum to produce liquid CO 2 .

9. The plant according to claim 8 , wherein each separation stage of the at least two separation stages comprises a heat exchanger and a separation drum for separating liquid CO 2 from gaseous CO 2 .

10. The plant according to claim 8 , further comprising at least one expansion machine and/or at least one offgas superheater.

11. The plant according to claim 8 , further comprising a first compressor, a first cooler, and a drier.