METHOD AND APPARATUS FOR LOW-TEMPERATURE SEPARATION OF A GAS CONTAINING CO2 TO PRODUCE A CO2-RICH FLUID

Abstract

The invention relates to a method for the low-temperature separation of a gas containing CO.sub.2 in order to produce a CO.sub.2-rich fluid, in which method a gas containing CO.sub.2 and at least one component lighter than CO.sub.2 is compressed in a compressor comprising at least two stages, the gas being cooled downstream of at least one of the stages in a cooler and by exchanging heat with air and then being cooled in a first heat exchanger, the gas cooled in the first heat exchanger is separated at low temperature by partial condensation and/or distillation in order to produce a fluid rich in CO.sub.2 and depleted in the component lighter than CO.sub.2 and a gas depleted in CO.sub.2 and enriched in the component lighter than CO.sub.2. The gas depleted in CO.sub.2 is first heated in the first heat exchanger and then in the cooler before being expanded in a turbine.

Claims

1-15. (canceled)

16. A process for the low-temperature separation of a gas containing CO.sub.2 to produce a CO.sub.2-rich fluid, the process comprising the steps of: compressing a gas containing CO.sub.2 and at least one component lighter than CO.sub.2 in a compressor comprising at least two stages to form a compressed gas, cooling the compressed gas to form a cooled gas, wherein the step of cooling the compressed gas further comprises cooling the compressed gas in a first cooler, a second cooler that is configured to exchange heat with water, and a first heat exchanger to form the cooled gas; separating the cooled gas at low temperature by partial condensation to produce a liquid and a gas, wherein the liquid is enriched in CO.sub.2 and depleted in the component lighter than CO.sub.2, wherein the gas is depleted in CO.sub.2 and enriched in the component lighter than CO.sub.2, heating the gas depleted in CO.sub.2 in the first heat exchanger and subsequently in the first cooler before being expanded in a turbine; and separating the liquid enriched in CO.sub.2 by distillation to form at least one CO.sub.2-rich fluid.

17. The process as claimed in claim 16, wherein the at least one CO.sub.2-rich fluid is a liquid and at least a part of the CO.sub.2-rich fluid is vaporized in the first heat exchanger.

18. The process as claimed in claim 17, wherein the at least one vaporized CO.sub.2-rich fluid is compressed in a compressor driven by the turbine.

19. The process as claimed in claim 17, wherein the liquid enriched in CO.sub.2 is expanded and sent to the top of a stripping column and the at least one CO.sub.2-rich fluid is a bottom liquid from the stripping column.

20. The process as claimed in claim 16, wherein the liquid enriched in CO.sub.2 is fed to the top of a scrubbing column and the liquid from the scrubbing column feeds a distillation column.

21. The process as claimed in claim 20, wherein a top gas from the distillation column is compressed in a compressor driven by the turbine.

22. The process as claimed in claim 16, wherein the gas depleted in CO.sub.2 goes into the cooler at a temperature greater than ambient temperature, for example greater than 30 C.

23. The process as claimed in claim 16, wherein the gas to be separated is separated by partial condensation to produce the gas depleted in CO.sub.2 and also a liquid; the liquid is separated by distillation in a distillation column to produce the CO.sub.2-rich fluid, which is preferably a CO.sub.2-rich liquid.

24. The process as claimed in claim 16, wherein at least a part of the cold is provided by a closed refrigeration cycle comprising at least one cycle compressor driven by the turbine.

25. The process as claimed in claim 16, wherein at least one CO.sub.2-rich fluid is a gas which is heated in the first heat exchanger E before being compressed.

26. An apparatus for the low-temperature separation of a gas containing CO.sub.2 to produce a CO.sub.2-rich fluid comprising: a compressor comprising at least two stages; a cooler in fluid communication with an outlet of the compressor, such that the cooler is configured to receive a compressed gas from the outlet of the compressor; a water cooler in fluid communication with an outlet of the cooler, such that the water cooler is configured to receive gas from the outlet of the cooler; a first heat exchanger in fluid communication with an outlet of the water cooler, such that the first heat exchanger is configured to receive gas from the outlet of the water cooler and to at least partially condense the gas to form a dual phase fluid; a phase separator in fluid communication with the first heat exchanger, wherein the phase separator is configured to receive the dual phase fluid from the first heat exchanger and separate the dual phase fluid into a gas and a liquid, wherein the liquid is enriched in CO.sub.2 and depleted in the component lighter than CO.sub.2, wherein the gas is depleted in CO.sub.2 and enriched in the component lighter than CO.sub.2; at least one distillation column configured to receive the liquid enriched in CO.sub.2, wherein the at least one distillation column is configured to produce at least one CO.sub.2-rich fluid; means for sending the gas depleted in CO.sub.2 to be heated first in the first heat exchanger and subsequently in the cooler, thereby forming a hot gas depleted in CO.sub.2; and a turbine configured to receive the hot gas depleted in CO.sub.2 from the cooler and expand the hot gas depleted in CO.sub.2 to form an expanded gas;

27. The apparatus as claimed in claim 26, further comprising a cycle compressor coupled to the turbine.

28. The apparatus as claimed in claim 26, further comprising a CO.sub.2-rich product compressor coupled to the turbine.

29. The apparatus as claimed in claim 28, further comprising means for liquefying a part of the gas compressed in the CO.sub.2-rich product compressor and means for sending the liquefied gas to the at least one distillation column as reflux.

30. The apparatus as claimed in claim 26, wherein the at least one distillation column comprises a first distillation column and a second distillation column, wherein the first distillation column is fed with the liquid enriched in CO.sub.2 coming from the phase separator, and the second distillation column is fed with a bottom liquid from the first distillation column, wherein the second distillation column is configured to remove NOX.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

[0025] FIG. 1 diagrammatically represents a process according to the invention.

[0026] FIG. 2 diagrammatically represents a process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0027] FIG. 1 diagrammatically represents a process using a single distillation column to remove a component lighter than CO.sub.2 in a first column.

[0028] A gas flow 1 is compressed in a multistage compressor, in this instance having four stages C1, C2, C3, C4, in this instance with a cooler R1, R2, R3 between each pair of stages and two coolers R4, R5 downstream of the last stage. This flow 1 can, for example, be the waste from an H.sub.2 or CO.sub.2 PSA and can be compressed up to at least 35 bar abs in the stages of the compressor C1 to C4. The coolers R1 to R3 are cooled solely by cooling water CW, just like cooler R5.

[0029] The gas flow 1 contains CO.sub.2 and at least one lighter component which can be hydrogen, carbon monoxide, nitrogen or oxygen. In this example, the gas flow is rich in nitrogen. Preferably, the gas flow 1 contains less than 1 mol % of methane.

[0030] The gas flow cooled in the two coolers R4, R5 downstream of the last stage is cooled down to a temperature of less than 50 C. in a first heat exchanger E by heat exchange with at least one fluid resulting from the cold separation. This exchanger E can be of plate and fin type made of brazed aluminum.

[0031] The gas flow 1 is partially condensed in the first heat exchanger E and the two-phase flow formed is separated in a phase separator S, forming a gas 3 enriched in the at least one lighter component, in this instance at least nitrogen. This gas is heated in the first exchanger E up to a temperature greater than ambient temperature, for example greater than 30 C., and is subsequently heated in the first cooler R4 directly following the last stage C4 of the compressor from a temperature of 30 C. up to a temperature of 100 C., being the only cooling fluid sent to this first cooler R4. Subsequently, the gas cooled in the first cooler R4 is cooled in a second cooler R5 against cooling water CW to an ambient temperature of less than 40 C., indeed even of less than 30 C.

[0032] Alternatively, the gas flow 3 enriched in the at least one light component can cool the compressed gas in the second cooler R5, the first being cooled by water.

[0033] Alternatively or in addition, the flow enriched in the at least one light component can cool the compressed gas in a cooler R1, R2, R3 between two stages of the compressor.

[0034] Thus, the gas 3 to be expanded in a turbine T is preheated against the gas compressed in the compressor C1 to C4, so that the heat of compression makes it possible to produce more energy in the turbine.

[0035] The gas flow 3 enriched in light component heated in the first cooler R4 is at 8 bar and is expanded in the turbine T from this pressure down to approximately atmospheric pressure. The gas flow enriched in light component 3 can subsequently be used to regenerate adsorbents for drying the gas feeding the PSA to produce the flow 1.

[0036] The liquid 5 from the phase separator S is expanded and subsequently sent to the top of a distillation column C which is a stripping column from which a liquid 9 enriched in CO.sub.2 and depleted in the at least one light component is withdrawn at the bottom. This liquid can form at least a part of the product of the process. At least a part of the liquid is pressurized by a pump P and can be sent to be vaporized in the first heat exchanger E, a part 11 of the vaporized liquid optionally being sent to the bottom of the column C as reboiling. At least a part 13 of the vaporized liquid can be compressed in a product compressor C5 driven by the turbine T to produce a CO.sub.2-rich gas. The gas is subsequently compressed by other compression stages C6, C7, with a water cooler CW between each pair of stages (R6 between C5 and C6), and a last cooler downstream of stage C7. The gas compressed in C7 constitutes the CO.sub.2-rich gaseous product in this example.

[0037] The top gas 7 from the column C is heated in the first exchanger E.

[0038] The exchanger E, the phase separator S and the column C are inside a thermally insulated chamber CB.

[0039] Two means of cold production are used: [0040] A closed cycle in which CO.sub.2 is compressed in a cycle compressor CC and returned to the first heat exchanger, where it is cooled, liquefied, separated and expanded in two different valves to form two flows at 5.5 and 9.5 bar abs. These two flows are heated in the first heat exchanger E to provide cold and are then returned to the cycle compressor CC. [0041] Vaporization of the liquid 9 in the exchanger E.

[0042] Obviously, the system may comprise several phase separators, in series and/or in parallel and upstream of the distillation, and also at least one distillation column.

[0043] If the system does not comprise a column separator, the gas expanded in the turbine will be taken at the top of the distillation column.

[0044] FIG. 2 diagrammatically represents a process using two columns to remove a component lighter than CO.sub.2 in a first column and a component heavier than CO.sub.2 in a second column.

[0045] A gas flow 1 is compressed in a multistage compressor, in this instance having four stages C1, C2, C3, C4, in this instance with a cooler R1, R2, R3 between each pair of stages and two coolers R4, R5 downstream of the last stage. This flow 1 can, for example, be the waste from an H.sub.2 or CO.sub.2 PSA and can be compressed up to at least 35 bar abs in the stages of the compressor C1 to C4. The coolers R1 to R3 are cooled solely by cooling water CW, just like cooler R5.

[0046] The gas flow 1 contains CO.sub.2 and at least one lighter component which can be hydrogen, carbon monoxide, nitrogen or oxygen. In this example, the gas flow is rich in nitrogen. Preferably, the gas flow 1 contains less than 1 mol % of methane.

[0047] The gas flow cooled in the two coolers R4, R5 downstream of the last stage is cooled down to a temperature of less than 50 C. in a first heat exchanger E by heat exchange with at least one fluid resulting from the cold separation. This exchanger E can be of plate and fin type made of brazed aluminum.

[0048] The gas flow 1 is partially condensed in the first heat exchanger E and the two-phase flow formed is separated in a phase separator S, forming a gas 3 enriched in the at least one lighter component, in this instance at least nitrogen. This gas is heated in the first exchanger E up to a temperature greater than ambient temperature, for example greater than 30 C., and is subsequently heated in the first cooler R4 directly following the last stage C4 of the compressor from a temperature of 30 C. up to a temperature of 100 C., being the only cooling fluid sent to this first cooler R4. Subsequently, the gas cooled in the first cooler R4 is cooled in a second cooler R5 against cooling water CW to an ambient temperature of less than 40 C., indeed even of less than 30 C.

[0049] Alternatively, the gas flow 3 enriched in the at least one light component can cool the compressed gas in the second cooler R5, the first being cooled by water.

[0050] Alternatively or in addition, the flow enriched in the at least one light component can cool the compressed gas in a cooler R1, R2, R3 between two stages of the compressor.

[0051] Thus, the gas 3 to be expanded in a turbine T is preheated against the gas compressed in the compressor C1 to C4, so that the heat of compression makes it possible to produce more energy in the turbine.

[0052] The gas flow 3 enriched in light component heated in the first cooler R4 is at 8 bar and is expanded in the turbine T from this pressure down to approximately atmospheric pressure. The gas flow enriched in light component 3 can subsequently be used to regenerate adsorbents for drying the gas feeding the PSA to produce the flow 1. In addition or alternatively, the expanded flow 3 can feed the PSA unit to recover the CO.sub.2 which it contains.

[0053] The liquid 5 from the phase separator S is expanded and subsequently sent to the top of a distillation column C from which a liquid 9 enriched in CO.sub.2 and depleted in the at least one light component is withdrawn at the bottom. At least a part of the liquid is pressurized by a pump P and can be sent to be vaporized in the first heat exchanger E, a part 11 of the vaporized liquid optionally being sent to the bottom of the column C as reboiling and the other part 19 being sent to feed the column N at the bottom. The top gas 7 from the column C is heated in the first exchanger E.

[0054] The column N is a column for the removal of NOx compounds which are heavier than CO.sub.2, NOx being a designation covering the following compounds: nitric oxide (NO), nitrogen dioxide (NO.sub.2), nitrous oxide (N.sub.2O), dinitrogen tetroxide (N.sub.2O.sub.4) and dinitrogen trioxide (N.sub.2O.sub.3). As NO is lighter than CO.sub.2, the column N is used to remove nitrogen dioxide (NO.sub.2), nitrous oxide (N.sub.2O), dinitrogen tetroxide (N.sub.2O.sub.4) and dinitrogen trioxide (N.sub.2O.sub.3), if present in the liquid.

[0055] In this column fed by the flow 19, at least one impurity heavier than CO.sub.2 is scrubbed out by an intermediate reflux of CO.sub.2 15 and a top reflux 23 of pure CO.sub.2 to produce at the bottom a liquid enriched in the at least one heavier impurity 25, such as NOx compounds, for example NO.sub.2.

[0056] The liquid enriched in the at least one heavier impurity 25 is vaporized in the first exchanger E.

[0057] The top gas 21 from the column N constitutes the product purified in the at least one heavier impurity and is heated in the first exchanger E before being compressed in a first compression stage C5 driven by the turbine T. After cooling in R6, the flow is divided, a part 23 being condensed in the first exchanger E and the remainder 27 being compressed in the compression stages C6, C7 to form a pressurized gaseous product. The gas compressed in C7 constitutes the CO.sub.2-rich gaseous product in this example.

[0058] The part 23 is returned at the top of the column N as reflux.

[0059] The exchanger E, the phase separator S and the column C are inside a thermally insulated chamber CB.

[0060] Two means of cold production are used: [0061] A closed cycle in which CO.sub.2 is compressed in a cycle compressor CC and returned to the first heat exchanger, where it is cooled, liquefied, separated and expanded in two different valves to form two flows at 5.5 and 9.5 bar abs. These two flows are heated in the first heat exchanger E to provide cold and are then returned to the cycle compressor CC. [0062] Vaporization of the liquid 9 in the exchanger E.

[0063] Obviously, the system may comprise several phase separators, in series and/or in parallel and upstream of the distillation, and also at least one distillation column.

[0064] If the system does not comprise a column separator, the gas expanded in the turbine will be taken at the top of the distillation column.

[0065] Preferably, at least one of the cycle compressors CC and at least one product compressor C6, C7 are incorporated in a single compression machine.

[0066] The turbine can drive at least one refrigeration cycle compressor, for example CC, and/or at least one other product compressor C6, C7, in addition to or in place of the compressor C5.

[0067] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0068] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0069] Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of comprising). Comprising as used herein may be replaced by the more limited transitional terms consisting essentially of and consisting of unless otherwise indicated herein.

[0070] Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0071] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0072] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

[0073] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.