APPARATUS AND METHOD FOR TRANSFERRING A FLUID FROM A SUBCRITICAL GASEOUS STATE INTO A SUPERCRITICAL STATE

Abstract

The present invention relates to an apparatus for transferring a fluid, particularly CO.sub.2, from a subcritical gaseous state into a supercritical state, the apparatus comprising a compressor unit, a pump unit, a drive unit and a liquefaction unit, wherein the compressor unit and the pump unit are commonly driven by the drive unit, and wherein the liquefaction unit is provided downstream of the compressor unit and upstream of the pump unit, wherein the compressor unit is configured to compress the fluid from a first subcritical gaseous state to a first predetermined pressure level of a second subcritical gaseous state, wherein the liquefaction unit is configured to reduce the temperature of the compressed fluid in the second subcritical state downstream of the compressor unit to a predetermined temperature level such that the fluid is transferred from the second subcritical gaseous state to a liquid state.

Claims

1. An apparatus for transferring a fluid, particularly CO.sub.2, from a subcritical gaseous state into a supercritical state, the apparatus comprising a compressor unit (110), a pump unit, a drive unit and a liquefaction unit, wherein the compressor unit and the pump unit are commonly driven by the drive unit, and wherein the liquefaction unit is provided downstream of the compressor unit and upstream of the pump unit, wherein the compressor unit is configured to compress the fluid from a first subcritical gaseous state to a first predetermined pressure level (P1) of a second subcritical gaseous state, wherein the liquefaction unit is configured to reduce the temperature of the compressed fluid in the second subcritical gaseous state downstream of the compressor unit to a predetermined temperature level (T2) such that the fluid is transferred from the second subcritical gaseous state to a liquid state, and wherein the pump unit is configured to compress the fluid in the liquid state downstream of the liquefaction unit to a second predetermined pressure level (P2) such that the fluid is transferred from the liquid state to the supercritical state.

2. The apparatus according to claim 1, wherein the liquefaction unit comprises a cooling unit configured to perform liquefaction of the fluid by means of air and/or cooling water and/or refrigerated water and/or an external refrigeration medium.

3. The apparatus according to claim 1, wherein the liquefaction unit is further configured to perform a process cooling of an external process unit.

4. The apparatus according to claim 1, wherein the liquefaction unit is provided as an open loop refrigerant system comprising a heat exchanging unit and a precooling unit wherein the open loop refrigerant system is configured to extract a portion of the fluid from the compressor unit, to provide this extracted portion of the fluid to the precooling unit in order to precool the extracted portion of the fluid, to provide this precooled extracted portion of the fluid as a refrigerant to the heat exchanging unit, to further provide the compressed fluid in the second subcritical gaseous state downstream of the compressor unit to the heat exchanging unit, to reduce the temperature of the compressed fluid in the second subcritical gaseous state to the predetermined temperature level (T 2) by means of the heat exchanging unit, and to return the extracted portion of the fluid downstream of the heat exchanging unit to the compressor unit.

5. The apparatus according to claim 1, wherein the liquefaction unit comprises a hydrocarbon refrigerant unit configured to perform liquefaction of the fluid by means of a hydrocarbon refrigerant, particularly a C3 refrigerant and/or a C4 refrigerant.

6. The apparatus according to claim 1, wherein the liquefaction unit comprises a coldbox.

7. The apparatus according to claim 1, wherein the drive unit is coupled to the compressor unit and the pump unit via a gearbox and/or wherein the drive unit comprises two output shafts (141, 142), wherein a first output shaft of the drive unit is coupled with the compressor unit and wherein a second output shaft of the drive unit is coupled with the pump unit.

8. The apparatus according to claim 1, wherein the drive unit is provided as an electric motor, a steam turbine, an expansion turbine, a hydraulic power recovery turbine, a gas turbine or a combination thereof.

9. The apparatus according to claim 1, wherein the compressor unit is configured to perform centrifugal compression of the fluid in multiple stages with interstage cooling and/or wherein the pump unit is provided as a centrifugal pump.

10. The apparatus according to claim 1, wherein the apparatus is provided as a heat recovery unit and configured to use waste heat to heat up the fluid in the supercritical state and expand it to a liquefaction pressure level.

11. The apparatus according to claim 1, wherein the first predetermined pressure level (P1) is in a range between 50 bar and 70 bar, preferably between 55 bar and 65 bar, and/or wherein the predetermined temperature level (T2) is in a range between 10 C. and 30 C., preferably between 15 C. and 25 C., and/or wherein the second predetermined pressure level (P2) lies above 100 bar, preferably above 125 bar, preferably above 150 bar.

12. The apparatus according to claim 1, wherein the fluid is CO.sub.2 or a fluid mixture comprising CO.sub.2, especially an azeotropic mixture of CO.sub.2 and ethane.

13. A method for transferring a fluid, particularly CO.sub.2, from a subcritical gaseous state into a supercritical state using an apparatus according to claim 1, comprising: compressing the fluid from a first subcritical gaseous state by means of the compressor unit to a first predetermined pressure level (P1) of a second subcritical gaseous state; reducing the temperature of the compressed fluid in the second subcritical gaseous state by means of the liquefaction unit downstream of the compressor unit to a predetermined temperature level (T2) such that the fluid is transferred from the second subcritical gaseous state to a liquid state; and compressing the fluid in the liquid state by means of the pump unit downstream of the liquefaction unit to a second predetermined pressure level (P2) such that the fluid is transferred from the liquid state to the supercritical state.

14. The method according to claim 13, wherein the fluid in the first subcritical gaseous state is provided by a separation unit separating a specific component from a fluid mixture of various components.

15. The method according to claim 13, wherein the fluid in the supercritical state is used for long distance transportation, pipeline transportation, storage, Enhanced Oil Recovery, sequestration, or a combination thereof.

Description

[0031] The present invention will now be described further, by way of example, with reference to the accompanying drawings, in which

[0032] FIG. 1 schematically shows preferred embodiments of an apparatus according to the present invention.

[0033] FIG. 2 schematically shows a pressure-temperature-diagram representing a transfer of CO.sub.2 from a subcritical, gaseous state into a supercritical state according to a preferred embodiment of the present invention.

[0034] FIG. 3 schematically shows a pressure-temperature-diagram representing a transfer of CO.sub.2 from a subcritical, gaseous state into a supercritical state according to a preferred embodiment of the present invention.

[0035] FIG. 4 schematically shows another preferred embodiment of an apparatus according to the present invention.

DETAILED DESCRIPTION

[0036] FIG. 1a schematically shows a preferred embodiment of an apparatus 100 according to the present invention for transferring, transforming or converting a fluid in a subcritical gaseous state into a supercritical state.

[0037] The subcritical gaseous fluid, particularly dry CO.sub.2 of high purity, can be provided by a separation unit 101 for separating a specific component from a fluid mixture of various components.

[0038] Supercritical CO.sub.2 can be further processed in a CO.sub.2 utilising unit 102, e.g. for long distance transportation, pipeline transportation, storage, Enhanced Oil Recovery, sequestration, or a combination thereof.

[0039] For example, the CO.sub.2 can be provided by the separation unit 101 in an initial or first subcritical gaseous state with a pressure p.sub.0 of ca. 5 bar and a temperature T.sub.0 of ca. 35 C. The critical pressure p.sub.c of CO.sub.2 is 73.3 bar and the critical temperature T.sub.c is 304.1 K or 31 C.

[0040] In order to compress the CO.sub.2 from this first subcritical gaseous state to its supercritical state, the apparatus 100 comprises a compressor unit or compressor stage 110, e.g. a centrifugal compressor. This compressor unit 110 is configured to compress the fluid from its first subcritical gaseous state and from its initial pressure level p.sub.0 to a first predetermined pressure level p.sub.1 of a second subcritical gaseous state, i.e. such that fluid remains in a subcritical gaseous state. For example, this first predetermined pressure level p.sub.1 can be in the range between 55 bar and 65 bar. After this compression, the fluid can have a temperature level T.sub.1 above its critical temperature.

[0041] A liquefaction unit or liquefaction stage 120 is provided downstream of the compression unit 110 and is configured to reduce the temperature of the compressed fluid in the second subcritical gaseous state to a predetermined temperature level T.sub.2 such that the fluid is transferred from the second subcritical gaseous state to a liquid state. For example, this predetermined temperature level T.sub.2 can be in a range between 15 C. and 25 C. The pressure of the fluid during and after liquefaction can remain at least essentially at the first predetermined pressure level p.sub.1.

[0042] The liquefaction unit 120 can for comprise a cooling unit configured for cooling and liquefying the fluid by means of air and/or cooling water and/or refrigerated water and/or an external refrigeration medium.

[0043] The liquefaction unit 120 can also be used for cooling purposes in an external process unit, e.g. for cooling process streams in a nearby LNG facility.

[0044] The liquefaction unit 120 can further comprise a hydrocarbon refrigerant unit configured to perform liquefaction of the fluid by means of a hydrocarbon refrigerant, e.g. a C3 refrigerant like propane C.sub.3H.sub.8 and/or a C4 refrigerant like butane C.sub.4H.sub.10. For example, a C3 or C4 refrigeration of that kind can also be used for nearby LNG facilities.

[0045] It is also possible, that the liquefaction unit 120 comprises a coldbox, e.g. an assembly of various cryogenic components in a steel containment, which can further be used for the treatment of cryogenic fluids and gases in external process units.

[0046] A pump unit 130, e.g. a centrifugal pump, is provided downstream of the liquefaction unit 120 and is configured to compress the fluid in the liquid state to a second predetermined pressure level p.sub.2 such that the fluid is transferred from the liquid state to the supercritical state. This second predetermined pressure level p.sub.2 can e.g. be above 150 bar.

[0047] A common drive unit 140 is provided for commonly driving both the compressor unit 110 and the pump unit 130, e.g. indirectly via a common gearbox 150. For this purpose, an output shaft or driven shaft 141 of the drive unit 140 is directly connected or coupled with the gearbox 150 and the gearbox 150 is directly connected or coupled with both the compressor unit 110 and the pump unit 130. The drive unit 140 can e.g. be provided as an electric motor, a steam turbine, an expansion turbine, a hydraulic power recovery turbine (HPRT), a gas turbine or a combination thereof.

[0048] It is also possible that the drive unit is directly coupled with both the compressor unit 110 and the pump unit 130 as shall now be explained with reference to FIG. 1b.

[0049] In FIG. 1b, a preferred embodiment of an apparatus according to the present invention is schematically shown and referred to as 100. In FIGS. 1a and 1b, identical reference signs refer to identical elements or to elements of at least the same function.

[0050] As shown in FIG. 1b, a corresponding drive unit 140 is provided as a double-end drive unit with two driven shafts or output shafts 141, 142. A first output shaft or driven shaft 141 of this drive unit 140 is coupled with the compressor unit 110 and a second output shaft or driven shaft 142 of the drive unit 140 is coupled with the pump unit 130.

[0051] FIG. 2 schematically shows a pressure-temperature-diagram 200 representing the transfer of CO.sub.2 from the subcritical, gaseous state into the supercritical state by means of the apparatus 100 of FIG. 1a or the apparatus 100 of FIG. 1b

[0052] Depending on its pressure and temperature, CO.sub.2 can exist in its solid state in a solid phase range 201, in the liquid state in a liquid phase range 202, and in the gaseous phase in a gaseous state range 203. A pressure p.sub.t of 5.2 bar and a temperature T.sub.t of 216.6K or 56.6 C. represents the triple point of CO.sub.2, at which the gaseous state, the liquid state, and the solid state exist in thermodynamic equilibrium. In a supercritical range 204, with pressures above the critical pressure p.sub.c of CO.sub.2 of 73.3 bar and with temperatures above the critical temperature T.sub.c of 304.1 K or 31 C., distinct liquid and gaseous phases do not exist anymore.

[0053] Point 210 represents the CO.sub.2 in its first subcritical gaseous state as provided by the separation unit 101 with the initial pressure p.sub.0 of ca. 5 bar and the initial temperature T.sub.0 of ca. 35 C.

[0054] Arrow 215 represents the step of compressing the CO.sub.2 in its first subcritical gaseous state 210 by means of the compressor unit 110 from its initial pressure p.sub.0 to the first predetermined pressure level p.sub.1 of e.g. 65 bar.

[0055] Point 220 represents the CO.sub.2 in the second subcritical gaseous state after compression step 215, still in its subcritical gaseous state, with the first predetermined pressure level p.sub.1 of e.g. 65 bar. For example, after the compression, the CO.sub.2 can have a temperature level T.sub.1 of e.g. 40 C.

[0056] Arrow 225 represents the step of reducing the temperature of the CO.sub.2 in the second subcritical gaseous state 220 from the temperature level T.sub.1 to the predetermined temperature level T.sub.2 of e.g. 25 C., such that the fluid is transferred from the second subcritical gaseous state to a liquid state.

[0057] Point 230 represents the CO.sub.2 in its liquid state after this liquefaction step 225. In the course of this liquefaction, the temperature of the CO.sub.2 is reduced from the temperature level T.sub.1 to the predetermined temperature level T.sub.2 of e.g. 25 C.

[0058] Arrow 235 represents the step of compressing the CO.sub.2 in the liquid state 230 by means of the pump unit 130 to the second predetermined pressure level p.sub.2 such that the fluid is transferred to the supercritical state.

[0059] Point 240 represents the CO.sub.2 after this compression step 235 in its supercritical state with the second predetermined pressure level p.sub.2 of e.g. 150 bar.

[0060] The compression of the initially provided CO.sub.2 in its first subcritical gaseous state by means of the compressor unit 110 can also be performed by means of a centrifugal compression in multiple stages with interstage cooling, as shall now be explained with reference to FIG. 3.

[0061] FIG. 3 also schematically shows a pressure-temperature-diagram 300 representing the transfer of CO.sub.2 from the subcritical, gaseous state into the supercritical state by means of the apparatus 100 of FIG. 1a or the apparatus 100 of FIG. 1b.

[0062] FIG. 3 shows the liquid phase range 302, the gaseous phase range 303 and the supercritical range 304 of CO.sub.2. Point 310 represents the CO.sub.2 in the first subcritical gaseous state provided by the separation unit 101, in this example with an initial pressure of 5 bar and an initial temperature of 40 C.

[0063] The arrows 315 represent the step of compressing the CO.sub.2 in the first subcritical gaseous state 310 by means of a centrifugal compression in multiple stages with interstage cooling from the initial pressure to the first predetermined pressure level p.sub.1 of e.g. 65 bar. As can be seen, the CO.sub.2 is compressed in a multitude of compressing steps, wherein after each compressing step a cooling step is performed in which the temperature of the compressed fluid is reduced, since each compression step particularly increases the temperature of the fluid.

[0064] Point 320 represents the CO.sub.2 in its second subcritical gaseous state after this compression step 315 with the first predetermined pressure level p.sub.1 and with a temperature level than can e.g. correspond to the critical temperature T.sub.c.

[0065] Arrow 325 represents the step of reducing the temperature of the CO.sub.2 in the second subcritical gaseous state 320 to the predetermined temperature level T.sub.2 of e.g. 15 C., such that the fluid is transferred from the second subcritical gaseous state to a liquid state.

[0066] Point 330 represents the CO.sub.2 in its liquid state after this liquefaction step 325 with the predetermined temperature level T.sub.2 of 15 C. and with the first predetermined pressure level p.sub.1 of 65 bar.

[0067] Arrow 335 represents the step of compressing the CO.sub.2 in the liquid state 330 to the second predetermined pressure level p.sub.2 such that the fluid is transferred to the supercritical state. In this example, the second predetermined pressure level p.sub.2 corresponds to 200 bar.

[0068] Point 340 represents the CO.sub.2 after this compression step 335 in the supercritical state.

[0069] FIG. 4 schematically shows another preferred embodiment of an apparatus 400 according to the present invention.

[0070] In accordance with the apparatus 100 and 100 as shown in FIG. 1a and FIG. 1b, the apparatus 400 of FIG. 4 is configured to transfer a fluid, e.g. CO.sub.2, from a subcritical gaseous state provided by a separation unit 401 into a supercritical state for a CO.sub.2 utilising unit 402. For this purpose, the apparatus 400 comprises a compressor unit 410, a liquefaction unit 420, a pump unit 430 and a common drive unit 440.

[0071] The compressor unit 410 comprises several individual compressors 411, 413, 416 and heat exchangers 414, 417 for performing the centrifugal compression in multiple stages with interstage cooling and for compressing the fluid from its first subcritical gaseous state to its second subcritical gaseous state. The compressors 411, 413, 416 and the pump unit 430 are commonly driven by the drive unit 440. Further, a control element 418 can be provided.

[0072] The liquefaction unit 420 is provided as an open loop refrigerant system with a heat exchanging unit 422 and a precooling unit 421, wherein this precooling unit 421 is provided as a valve unit, particularly for a cascade Joule-Thomson expansion.

[0073] The open loop refrigerant system 420 is configured to extract a portion of the fluid from the compressor unit 410, particularly downstream of the compressor unit 410 by means of a manifold 419. This extracted portion of the fluid is provided to the precooling unit 421 in order to precool the extracted portion of the fluid by means of a cascade Joule-Thomson expansion. This precooled extracted portion of the fluid is provided as a refrigerant to the heat exchanging unit 422. Further, the compressed fluid in the second subcritical gaseous state downstream of the compressor unit 410 is provided to the heat exchanging unit 422. The temperature of the compressed fluid in the second subcritical gaseous state is reduced to the predetermined temperature level by means of the heat exchanging unit 422, thereby transferring the fluid from the second subcritical gaseous state to its liquid state.

[0074] In the course of the corresponding heat exchange, the temperature of the extracted portion of the fluid is increased again. Downstream of the heat exchanging unit 422, the extracted portion of the fluid is returned to the compressor unit 410, for example to a manifold 412 between the compressors 411, 413. A control unit 423 can be provided, e.g. for measuring a temperature and flowrate of the returning portion of the fluid and for controlling the amount of fluid extracted downstream of the compressor unit 410 by means of the manifold 419.

[0075] The fluid in its liquid state downstream of the heat exchanger unit 422 is provided to the pump unit 430 via a scrubber or absorber 424 for absorbing gas components in the stream of liquid fluid. The pump unit 430 compresses the fluid in the liquid state to the second predetermined pressure level such that the fluid is transferred to the supercritical state.

REFERENCE LIST

[0076] 100 apparatus for transferring a subcritical gaseous fluid into a supercritical state [0077] 100 apparatus for transferring a subcritical gaseous fluid into a supercritical state [0078] 101 separation unit [0079] 102 CO.sub.2 utilising unit [0080] 110 compressor unit [0081] 120 liquefaction unit [0082] 130 pump unit [0083] 140 drive unit [0084] 141 output shaft of the drive unit 140 [0085] 140 drive unit, double-end drive unit [0086] 141 first output shaft of the double-end drive unit 140 [0087] 142 second output shaft of the double-end drive unit 140 [0088] 150 gearbox [0089] 200 pressure-temperature-diagram of CO.sub.2 [0090] 201 solid phase range [0091] 202 liquid phase range [0092] 203 gaseous phase range [0093] 204 supercritical range [0094] 210 CO.sub.2 in a first subcritical gaseous state with an initial pressure p.sub.0 and an initial temperature T.sub.0 [0095] 215 compressing the CO.sub.2 to a first predetermined pressure level p.sub.1 [0096] 220 CO.sub.2 in a second subcritical gaseous state with the first predetermined pressure level p.sub.1 [0097] 225 reducing the temperature of the CO.sub.2 to a predetermined temperature level T.sub.2 [0098] 230 CO.sub.2 in a liquid state with the predetermined temperature level T.sub.2 [0099] 235 compressing the CO.sub.2 to a second predetermined pressure level p.sub.2 [0100] 240 CO.sub.2 in a supercritical state with a second predetermined pressure level p.sub.2 [0101] 300 pressure-temperature-diagram of CO.sub.2 [0102] 302 liquid phase range [0103] 303 gaseous phase range [0104] 304 supercritical range [0105] 310 CO.sub.2 in a first subcritical gaseous state with an initial pressure and an initial temperature [0106] 315 compressing the CO.sub.2 in multiple stages with interstage cooling [0107] 320 CO.sub.2 in a second subcritical gaseous state with a first predetermined pressure level p.sub.1 [0108] 325 reducing the temperature of the CO.sub.2 to a predetermined temperature level T.sub.2 [0109] 330 CO.sub.2 in a liquid state with the predetermined temperature level T.sub.2 [0110] 335 compressing the CO.sub.2 to a second predetermined pressure level p.sub.2 [0111] 340 CO.sub.2 in a supercritical state with a second predetermined pressure level p.sub.2 [0112] 400 apparatus for transferring a subcritical gaseous fluid into a supercritical state [0113] 401 separation unit [0114] 402 CO.sub.2 utilising unit [0115] 410 compressor unit [0116] 411 compressor [0117] 412 manifold [0118] 413 compressor [0119] 414 heat exchanger [0120] 415 manifold [0121] 416 compressor [0122] 417 heat exchanger [0123] 418 control element [0124] 419 manifold [0125] 420 liquefaction unit [0126] 421 precooling unit, valve unit [0127] 422 heat exchanger unit [0128] 423 control element [0129] 424 scrubber [0130] 430 pump unit [0131] 440 drive unit