Method and apparatus for liquefying a CO2-rich gas

A process for the separation of a flow containing at least 95 mol % of carbon dioxide and also at least one impurity lighter than carbon dioxide by distillation, wherein according to a first and a second mode of operation:

• cooling the flow in a heat exchanger (20) and separated in a distillation column (30) or a separator vessel;
• ii) withdrawing a liquid flow containing at least 99 mol % of carbon dioxide at the bottom of the column or vessel;
• and
• iii) sending at least a portion (12) of the liquid flow to be cooled in the heat exchanger to form a subcooled liquid (3);
• iv) expanding at least a portion of the subcooled liquid to produce a two-phase flow;
• v) the two-phase flow is separated to form a gas (16) and a liquid (8, 14) and at least a portion (14) of the liquid is sent to be heated in the heat exchanger by indirect heat exchange with at least a portion of the flow that is to be separated and with the at least a portion of the liquid that is to be subcooled, the at least a portion of the liquid vaporizing in the heat exchanger;
• and
• vi) wherein
• a) according to the first mode of operation,
• a′) a portion of the liquid from step v) is taken as first liquid product (4), or
• b′) a portion of the subcooled liquid is taken as first liquid product and
• b) according to the second mode of operation, a portion (5) of the bottom liquid is taken as second liquid product without subcooling it in the heat exchanger, no portion of the liquid from step v) is taken as first liquid product, all of the liquid from step v) being vaporized in the heat exchanger, and no portion of the subcooled liquid is taken as the first liquid product.

An apparatus for the separation of a flow containing at least 95 mol % of carbon dioxide and also at least one impurity lighter than carbon dioxide by distillation comprising:

• a heat exchanger (20);
• a distillation column (30) or a separator vessel;
• expansion means (V3);
• means for sending the flow to be cooled in the heat exchanger;
• means for sending the cooled flow to be separated in the distillation column or in the vessel;
• means for withdrawing at the bottom of the column or vessel a liquid flow containing at least 99 mol % of carbon dioxide;
• means for sending at least a portion (12) of the liquid flow to be cooled in the heat exchanger to form a subcooled liquid (3);
• means for sending at least a portion of the subcooled liquid to the expansion means to produce a two-phase flow;
• a phase separator (40) for separating the two-phase flow to form a gas and a liquid;
• means for sending at least a portion (14) of the liquid from the phase separator to be heated in the heat exchanger by indirect heat exchange with at least a portion of the flow that is to be separated and with the at least a portion of the liquid that is to be subcooled;
• means for taking a portion (4) of the liquid from the phase separator or of the subcooled liquid as liquid product at a first pressure;
• and
• means for supplying liquid that has not been subcooled as liquid product at a second pressure connected to the means for withdrawing a liquid flow at the bottom of the column or vessel.