Method and apparatus for liquefying a gas rich in carbon dioxide
A method for liquefying a CO2-rich gas flow containing at least 90 mol % of CO2 involves the following steps: compressing the CO2-rich gas flow, liquefying and separating in order to produce a first liquid flow at a first pressure MP and a first temperature T1. Extracting part of the first liquid flow at the first pressure and the first temperature by way of first product, supercooling part of the first liquid flow down to a temperature below the first temperature by indirect exchange of heat in a heat exchanger, expanding the liquid supercooled down to the second temperature T2 until it reaches a second pressure lower than the first pressure, the second pressure being equal to or greater than the equilibrium pressure of the expanded liquid, and extracting part of the expanded liquid by way of second product and evaporating another part of the liquid in the heat exchanger by exchange of heat with the part of the first flow in order to produce a vaporized liquid.
1 . A method for liquefying a gas flow rich in CO 2 containing at least 90 mol % of CO 2 comprising the following steps:
a) compressing and drying of the gas flow rich in CO 2 in a compressor,
b) liquefying and separating by at least one of distillation or phase separation to produce a first liquid flow at a first pressure and a first temperature;
c) extracting of a portion of the first liquid flow as a first liquid product;
d) subcooling another portion of the first liquid flow to a temperature below the first temperature by indirect heat exchange in a heat exchanger to produce a subcooled liquid;
e) splitting the subcooled liquid into a second product portion and a refrigerant portion;
f) expanding the second product portion to a second pressure below the first pressure to form a second liquid product; and
g) expanding the refrigerant portion to a third pressure and vaporizing the expanded refrigerant portion in the heat exchanger by heat exchange with said another portion of the first liquid flow to produce a vaporized liquid.
2 . The method as claimed in claim 1 , wherein the first pressure is greater than 14 bar.
3 . The method as claimed in claim 1 , wherein the first temperature is up to 5° C. less than the equilibrium temperature or equal to the equilibrium temperature.
4 . The method as claimed in claim 1 , wherein the second pressure is equal to or less than 10 bar.
5 . The method as claimed in claim 1 , wherein the second temperature is up to 5° C. less than the equilibrium temperature or equal to the equilibrium temperature.
6 . The method as claimed in claim 1 , wherein vaporized gas in the heat exchanger transfers cold to the gas flow rich in CO 2 .
7 . The method as claimed in claim 1 , wherein the heat exchanger exchanges heat between the expanded liquid and the portion of the first liquid flow only.
8 . The method as claimed in claim 1 , wherein the compressor compresses the flow rich in CO 2 to at least 60 bar, the flow at at least 60 bar is cooled in a second heat exchanger to a temperature below 35° C. before being liquefied.
9 . The method as claimed in claim 1 , wherein vaporized gas in the heat exchanger is conveyed to a point upstream of the liquefaction of the gas flow, for example an inter-stage point of the compressor, which performs the compression step.
10 . The method as claimed in claim 1 , wherein the third pressure is less than the second pressure.
11 . The method as claimed in claim 10 , wherein the third pressure is between 5 and 6 bar.
12 . The method as claimed in claim 1 , further comprising h) recycling at least a portion of the vaporized liquid flow to step a).
13 . The method of claim 1 , wherein the first liquid flow from step (b) is directed to an intermediate storage unit ( 100 ), and wherein the first liquid product is extracted from the intermediate storage unit.
14 . The method of claim 13 , further comprising conveying a vapor phase ( 22 ) from the intermediate storage unit ( 100 ) to the heat exchanger to be cooled and liquefied.
15 . The method of claim 1 , wherein the vaporized liquid in step (h) is compressed in a dedicated compressor before being recycled to step a).
16 . A method for modifying an apparatus for liquefying a gas flow rich in CO 2 containing at least 90 mol % of CO 2 , wherein the apparatus comprises:
a) a compressor and means for conveying the gas flow rich in CO 2 to the compressor
b) liquefying means connected to the compressor to liquefy the gas flow rich in CO 2 and means of separation by distillation and/or phase separation to separate the liquefied gas flow to produce a first liquid flow as an end product at a first pressure MP and a first temperature T1;
wherein the method comprises the steps of:
adding the following components to the apparatus:
a heat exchanger,
means for conveying a portion of the first liquid flow to cool in the heat exchanger,
means for expanding a first portion of the first liquid cooled in the heat exchanger and for outputting said expanded liquid as a second end product, and
means for expanding a second portion of the first cooled liquid, separately from the first portion of the first liquid, connected to the heat exchanger to enable a heat exchange between the first liquid and the portion of the first expanded liquid.
17 . The method as claimed in claim 16 , wherein the step of adding the following components to the apparatus includes adding means for conveying at least some of the portion of the heated expanded first liquid in the heat exchanger to the compressor or to another compressor to be compressed.
18 . The method as claimed in claim 16 , wherein a dedicated compressor compresses the heated expanded first liquid.
19 . An apparatus for liquefying a gas flow rich in CO 2 , the apparatus comprising:
a compressor configured to compress the gas flow;
a liquefaction unit fluidly connected to an outlet of the compressor, the liquefaction unit configured to produce a first liquid flow;
a first product line configured to extract a portion of the first liquid flow as a first product;
a heat exchanger;
a fluid conduit configured to convey another portion of the first liquid flow to the heat exchanger to be subcooled, thereby producing a subcooled liquid;
a splitter fluidly connected to an outlet of the heat exchanger, the splitter configured to separate the subcooled liquid into a second product portion and a refrigerant portion;
a second product line including a first expansion valve, the second product line configured to expand the second product portion to form a second product; and
a refrigerant loop including a second expansion valve, the refrigerant loop configured to expand the refrigerant portion and route the expanded refrigerant portion through the heat exchanger to be vaporized and subsequently recycled to the compressor.