Coil wound heat exchanger
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-02-03
- Publication Date
- 2026-08-13
Smart Images
Figure US2026013696_13082026_PF_FP_ABST
Abstract
Description
ATTORNEY REF: HON-08457 USTITLE: COIL WOUND HEAT EXCHANGER
[0001] BACKGROUND
[0002] Coil-wound heat exchangers (“CWHE”) are often a preferred type of heat exchanger used in natural gas liquefaction systems. In a CWHE, the fluids to be cooled are circulated through many layers of tubes that are wrapped around a central mandrel, separated by axial spacers, and contained within a shell space. The assembly of tubes, mandrel and spacers forms a tube bundle, or bundle. Refrigeration is provided by a flow of an expanded refrigerant (often a mixed refrigerant) through the shell space. A common problem with CWHEs is temperature maldistribution of the refrigerant between concentric zones in the shell space, meaning that there is a radial temperature gradient between zones in a particular location between the warm and cold ends of the bundle.
[0003] Attempts have been made to correct such radial temperature maldistribution by “zoning” the tube sheets— meaning routing tubes that are connected to each of the cold end and warm end tube sheets through a single zone. Valves are provided upstream of each of the warm end tube sheets to enable flow through each zone to be independently controlled, thereby providing a means for reducing temperature gradients by changing the proportion of tube side flow in each zone to more closely match the proportion of shell side refrigerant in that zone. One drawback to such configurations is increased costs when building the CWHE, because the number of tube sheets required at both the cold and warm ends is a function of the number of zones, which often results in a greater number of tube sheets than required to accommodate the number of tubes in the bundle.
[0004] Improved CWHE configurations that enable flow adjustments to correct radial temperature maldistribution with less of the incremental cost and complexity associated with other prior art solutions to radial maldistribution are disclosed in U.S. Patent No. 11 ,561 ,049, which is incorporated by reference in its entirety. These configurations are described in greater detail herein in connection with FIGS. 2, 2A, and 2B. In such configurations, temperature sensors are provided in each of the zones in the shell space of a warm bundle. In the event that a temperature difference is detected between zones, flow to the appropriate zone can be adjusted using a control valve to reduce the temperature differential.
[0005] One drawback to such configurations is the increased complexity and cost of the heat exchanger due to the inclusion of temperature sensors within the shell space. Due to the cold temperatures within the shell space, it is possible for the temperature sensors to malfunction or give inaccurate readings. Further, the temperature sensors cannot be inspected or replaced once they are sealed within the shell space.ATTORNEY REF: HON-08457 US
[0006] In view of the drawbacks noted above, it is desirable to provide a CHWHE that enables flow adjustments to correct radial temperature maldistribution, but with reduced system complexity and manufacturing cost.
[0007] SUMMARY
[0008] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0009] Several aspects of the systems and methods are outlined below.
[0010] Aspect 1 : A coil-wound heat exchanger comprising:
[0011] a shell;
[0012] a first bundle comprising a warm bundle end and a cold bundle end located distal to the warm bundle end;
[0013] a mandrel centrally located within the first bundle, a first bundle shell space extending from the warm bundle end to the cold bundle end and extending from the first bundle mandrel to the shell;
[0014] a plurality of tubes located in the first bundle shell space, each of the plurality of tubes having a first tube end located at the warm bundle end and a second tube end located at the cold bundle end, the plurality of tubes being wound around the mandrel forming a plurality of wound layers, the plurality of wound layers being divided into a plurality of zones that are concentrically arranged in the first bundle shell space, the plurality of tubes comprising a plurality of tube sets, each of the plurality of tube sets being located in a different one of the plurality of zones;
[0015] a plurality of cold end conduits, each of the plurality of cold end conduits being in downstream fluid flow communication with one of the plurality of tube sets;
[0016] a plurality of cold end valves, each of the plurality of cold end valves being located on one of the plurality of cold end conduits and outside the shell;
[0017] a consolidated cold end conduit in downstream fluid flow communication with the plurality of cold end conduits and the plurality of cold end valves;
[0018] a first temperature sensor located on one of the plurality of cold end conduits and outside the shell;
[0019] a second temperature sensor located on the consolidated cold end conduit and outside of the shell; and
[0020] a controller electrically connected to the first temperature sensor, theATTORNEY REF: HON-08457 USsecond temperature sensor, and the plurality of cold end valves;
[0021] wherein the controller is adapted to adjust a position of at least one of the plurality of cold end valves based on a temperature difference between the first temperature sensor and the second temperature sensor; and
[0022] wherein each of the plurality of tubes is fed by a first fluid source.
[0023] Aspect 2: The coil-wound heat exchanger of Aspect 1 , wherein the first fluid source is a mixed refrigerant.
[0024] Aspect 3: The coil-wound heat exchanger of Aspect 1 , further comprising an expansion valve in downstream fluid flow communication with the consolidated cold end conduit and in upstream fluid flow communication with the first bundle shell space at the cold bundle end of the first bundle.
[0025] Aspect 4: A system for liquefying a feed gas, the system comprising:
[0026] a coil-wound heat exchanger comprising a first bundle, a shell, and a shell space contained within the shell, the first bundle comprising:
[0027] a warm end and a cold end;
[0028] a mandrel centrally located within the first bundle,
[0029] a warm bundle shell space extending from the warm end to the cold end and extending from the mandrel to the shell;
[0030] a plurality of tubes located in the first bundle shell space, each of the plurality of tubes having a first tube end located at the warm end of the warm bundle and a second tube end located at the cold end of the warm bundle, the plurality of tubes being wound around the mandrel forming a plurality of wound layers, the plurality of wound layers being divided into a plurality of zones that are concentrically arranged in the first bundle shell space, the plurality of tubes comprising a plurality of tube sets, each of the plurality of tube sets being located in a different one of the plurality of zones;
[0031] a feed circuit having a feed stream conduit, at least one warm end feed tube sheet located at the warm end, at least one cold end feed tube sheet located at the cold end, and a product conduit, the at least one warm end feed tube sheet and the at least one cold end feed tube sheet being in fluid flow communication with a plurality of feed tubes, the feed stream conduit, the at least one warm end feed tube sheet, the at least one cold end feed tube sheet, and the product conduit all being in fluid flow communication;
[0032] a refrigerant circuit comprising a closed loop, the refrigerant circuit comprising:
[0033] a compression circuit comprising at least one compression stage and at least one selected from the group of an intercooler and an aftercooler;ATTORNEY REF: HON-08457 US
[0034] a refrigerant stream conduit;
[0035] a plurality of warm end refrigerant tube sheets in downstream fluid flow communication with the refrigerant stream conduit;
[0036] a plurality of cold end refrigerant tube sheets located at the cold end in downstream fluid flow communication with the plurality of warm end refrigerant tube sheets; and
[0037] a plurality of cold end conduits, each of the plurality of cold end conduits being in downstream fluid flow communication with a different one of the plurality of tube sets;
[0038] a plurality of cold end valves, each of the plurality of cold end valves being located on one of the plurality of cold end conduits and outside the shell space;
[0039] a consolidated cold end refrigerant conduit in downstream fluid flow communication with the plurality of cold end conduits and the plurality of cold end valves;
[0040] an expansion valve in downstream fluid flow communication with the consolidated cold end refrigerant conduit;
[0041] an expanded refrigerant conduit in downstream fluid flow communication with the expansion valve and in upstream fluid flow communication with the shell space at the cold end; and
[0042] a vaporized refrigerant conduit located at the warm end, the vaporized refrigerant conduit being in downstream fluid flow communication with the shell space and in upstream fluid flow communication with the compression circuit;
[0043] a first temperature sensor located on one of the plurality of cold end conduits and outside the shell;
[0044] a second temperature sensor located on the consolidated cold end refrigerant conduit and outside of the shell; and
[0045] a controller electrically connected to the first temperature sensor, the second temperature sensor, and the plurality of cold end valves;
[0046] wherein the controller is adapted to adjust a position of at least one of the plurality of cold end valves based on a temperature difference between the first temperature sensor and the second temperature sensor.
[0047] Aspect 5: The system of Aspect 4, wherein the refrigerant is a mixed refrigerant.
[0048] Aspect 6: The system of Aspect 4, wherein the refrigerant circuit further comprises a separator in upstream fluid flow communication with the refrigerant stream conduit, the separator having an inlet, a vapor outlet and a liquid outlet, the inlet being in downstream fluid flow communication with the compression circuit, the liquid outlet beingATTORNEY REF: HON-08457 USin upstream fluid flow communication with the refrigerant stream conduit.
[0049] Aspect 7: A coil-wound heat exchanger comprising:
[0050] a shell;
[0051] a first bundle comprising a warm bundle end and a cold bundle end located distal to the warm bundle end;
[0052] a mandrel centrally located within the first bundle, a first bundle shell space extending from the warm bundle end to the cold bundle end and extending from the first bundle mandrel to the shell;
[0053] a plurality of tubes located in the first bundle shell space, each of the plurality of tubes having a first tube end located at the warm bundle end and a second tube end located at the cold bundle end, the plurality of tubes being wound around the mandrel forming a plurality of wound layers, the plurality of wound layers being divided into a plurality of zones that are concentrically arranged in the first bundle shell space, the plurality of tubes comprising a plurality of tube sets, each of the plurality of tube sets being located in a different one of the plurality of zones;
[0054] a plurality of cold end conduits, each of the plurality of cold end conduits being in downstream fluid flow communication with one of the plurality of tube sets;
[0055] a plurality of cold end valves, each of the plurality of cold end valves being located on one of the plurality of cold end conduits and outside the shell;
[0056] a consolidated cold end conduit in downstream fluid flow communication with the plurality of cold end conduits and the plurality of cold end valves;
[0057] a first temperature sensor located on the consolidated cold end conduit and outside of the shell; and
[0058] a controller electrically connected to the first temperature sensor and the plurality of cold end valves;
[0059] wherein the controller is adapted to adjust a position of at least one of the plurality of cold end valves based on a temperature difference between the first temperature sensor and a modeled temperature;
[0060] wherein the modeled temperature is determined using a mathematical model that comprises mass, heat and momentum inside the coil wound heat exchanger; and wherein each of the plurality of tubes is fed by a first fluid source.
[0061] Aspect 8: The coil-wound heat exchanger of Aspect 7, wherein the first fluid source is a mixed refrigerant.
[0062] BRIEF DESCRIPTION OF THE FIGURES
[0063] The present invention will hereinafter be described in conjunction with theATTORNEY REF: HON-08457 USappended drawing figures wherein like numerals denote like elements.
[0064] FIG. 1 is a schematic view of a first exemplary embodiment of a natural gas liquefaction system in accordance with the prior art;
[0065] FIG. 2 is a schematic view of a prior art method of managing temperature differences for liquid mixed refrigerant (MRL) streams in different zones of the coil wound heat exchanger of FIG. 1 ;
[0066] FIG. 3 is a schematic view of an exemplary implementation a natural gas liquefaction system implementing inventive concepts of the present invention;
[0067] FIG. 4 is a schematic view of the liquid mixed refrigerant (MRL) streams of the coil wound heat exchanger of the system of FIG. 3;
[0068] FIG. 5 is a flow diagram illustrating a first method of managing temperature differences for MRL streams in different zones of a coil wound heat exchanger implementing concepts of the present invention.; and
[0069] FIG. 6 is a flow diagram illustrating a second method of managing temperature differences for MRL streams in different zones of a coil wound heat exchanger implementing concepts of the present invention.
[0070] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0071] The ensuing detailed description provides preferred exemplary embodiments only, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the ensuing detailed description of the preferred exemplary embodiments will provide those skilled in the art with an enabling description for implementing the preferred exemplary embodiments of the invention. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention.
[0072] In order to aid in describing the invention, directional terms may be used in the specification and claims to describe portions of the present invention (e.g., upper, lower, left, right, etc.). These directional terms are merely intended to assist in describing and claiming the invention and are not intended to limit the invention in any way. In addition, reference numerals that are introduced in the specification in association with a drawing figure may be repeated in one or more subsequent figures without additional description in the specification in order to provide context for other features.
[0073] In the claims, letters are used to identify claimed steps (e.g. (a), (b), and (c)). These letters are used to aid in referring to the method steps and are not intendedATTORNEY REF: HON-08457 USto indicate the order in which claimed steps are performed, unless and only to the extent that such order is specifically recited in the claims.
[0074] Unless otherwise indicated, the articles “a” and “an” as used herein mean one or more when applied to any feature in embodiments of the present invention described in the specification and claims. The use of “a” and “an” does not limit the meaning to a single feature unless such a limit is specifically stated. The article “the” preceding singular or plural nouns or noun phrases denotes a particular specified feature or particular specified features and may have a singular or plural connotation depending upon the context in which it is used.
[0075] Directional terms may be used in the specification and claims to describe portions of the present invention (e.g., upper, lower, left, right, etc.). These directional terms are merely intended to assist in describing exemplary embodiments and are not intended to limit the scope of the claimed invention. As used herein, the term “upstream” is intended to mean in a direction that is opposite the direction of flow of a fluid in a conduit from a point of reference. Similarly, the term “downstream” is intended to mean in a direction that is the same as the direction of flow of a fluid in a conduit from a point of reference.
[0076] The term “fluid flow communication,” as used in the specification and claims, refers to the nature of connectivity between two or more components that enables liquids, vapors, and / or two-phase mixtures to be transported between the components in a controlled fashion (i.e. , without leakage) either directly or indirectly. Coupling two or more components such that they are in fluid flow communication with each other can involve any suitable method known in the art, such as with the use of welds, flanged conduits, gaskets, and bolts. Two or more components may also be coupled together via other components of the system that may separate them, for example, valves, gates, or other devices that may selectively restrict or direct fluid flow.
[0077] The term “downstream fluid flow communication”, as used in the specification and claims, refers to a component that is in fluid flow communication with, and is downstream from, another component when fluid is flowing in the direction of steady state operation for the system being described.
[0078] The term “upstream fluid flow communication”, as used in the specification and claims, refers to a component that is in fluid flow communication with, and is upstream from, another component when fluid is flowing in the direction of steady state operation for the system being described.
[0079] The term “conduit,” as used in the specification and claims, refers to one or more structures through which fluids can be transported between two or moreATTORNEY REF: HON-08457 UScomponents of a system. For example, conduits can include pipes, ducts, passageways, and combinations thereof that transport liquids, vapors, and / or gases.
[0080] The term “circuit”, as used in the specification and claims, is intended to refer to a group of conduits and other equipment through which a particular fluid flows. In an open circuit, all of the fluid that enters the circuit at an upstream end will also exit the circuit at a downstream end, allowing for losses due to leakage. In closed circuit, all of the fluid in the circuit (again allowing for losses due to leakage) circulates a closed loop, through a group of conduits and other equipment.
[0081] Unless otherwise stated herein, any and all percentages identified in the specification, drawings, and claims should be understood to be on a mole percentage basis. Unless otherwise stated herein, any and all pressures identified in the specification, drawings, and claims should be understood to mean gauge pressure.
[0082] Unless otherwise stated herein, introducing a stream at a location is intended to mean introducing substantially all of the said stream at the location. All streams discussed in the specification and shown in the drawings (typically represented by a line with an arrow showing the overall direction of fluid flow during normal operation) should be understood to be contained within a corresponding conduit. Each conduit should be understood to have at least one inlet and at least one outlet. Further, each piece of equipment should be understood to have at least one inlet and at least one outlet.
[0083] FIG. 1 shows an exemplary natural gas liquefaction system 100 using a coil-wound heat exchanger (“CWHE”) 114 having a warm bundle 112, a cold bundle 113, and a shell 115. A feed stream 101 , comprising natural gas, and a mixed refrigerant stream 102 are pre-cooled in a precooling system 104 to form a pre-cooled feed stream 106 and a pre-cooled mixed refrigerant stream 105. The pre-cooled mixed refrigerant stream 105 is then separated into a vapor (“MRV”) stream 108 and a liquid (“MRL”) stream 110 using a phase separator 107. The pre-cooled feed stream 106 and the MRV stream 108 each enter the warm bundle 112 at a warm end 174 and exit at a cold end 176, where each is cooled to about -110 degrees C. and condensed by refrigeration provided to the shell side of the CWHE 114 from vaporization of an expanded MRL stream 118 to form a cooled feed stream 116 and a cooled MRV stream 119. The MRL stream 110 also enters the warm bundle 112 at the warm end 174 and exits at the cold end 176, where it is cooled to about -110 degrees C. to form a subcooled MRL stream 117.
[0084] The subcooled MRL stream 117 is reduced in pressure to form the expanded MRL stream 118, while the cooled feed stream 116 and cooled MRV streamATTORNEY REF: HON-08457 US119 are further cooled to around -150° C. in the cold bundle 113 of the CWHE 114 and exit at a cold bundle cold end 180 to form a product stream 120, comprising liquid natural gas (“LNG”), and a subcooled liquid MRV stream 122 which is reduced in pressure and sent to the shell side of the cold bundle 113 where it is vaporized to provide refrigeration. A vaporized mixed refrigerant stream 124 exits the shell side of the CWHE 114 at the warm end 174, is compressed to 40-70 bar, then cooled to form the mixed refrigerant stream 102, thereby completing the refrigeration loop.
[0085] It should be understood that the natural gas liquefaction system 100 shown in FIG. 1 is intended to be exemplary and provide context for the invention. The inventive concepts described herein could be implemented in other applications in which a coil wound heat exchanger is used.
[0086] In each of the subsequent embodiments disclosed herein, elements shared with the first embodiment (system 100) are represented by reference numerals increased by factors of 100. For example, the warm bundle 112 shown in FIG. 1 corresponds to the warm bundle 212 of FIG. 2 and the warm bundle 312 of FIG. 3 . In the interest of balancing clarity and brevity, some features of subsequent embodiments that are shared with the first embodiment are numbered in the figures but are not separately called out in the specification.
[0087] FIG. 2 is a diagram that schematically represents a prior art method of managing temperature differentials MRL streams in different zones in a CWHE 214. The diagram is a schematic representation of a typical bundle winding for liquid mixed refrigerant (MRL) streams where the tubesheets at both warm and cold ends of the warm bundle all correspond to different zones of the coil wound heat exchanger of FIG. 1. The CWHE 214 includes two process tube zones, an inner zone and an outer zone. The MRL stream 210 enters the warm bundle 212 and is routed to tube sheets 226 and 228. The MRL stream 210 is then routed through inner zone process tubes 293a, 293b and outer zone process tubes 295a, 295b. At the cold end 276 of the warm bundle 212, the process tubes 293a-b, 295a-b are routed from the warm bundle 212 to the cold end tube sheets 232, 234. The tube sheets 232, 234 combine the flows from the inner and outer zone process tubes 293a-b, 295a-b prior to exiting the cold end 276 of the warm bundle 212, forming a combined subcooled MRL stream 291. The combined subcooled MRL stream 291 is reduced in pressure to form the expanded MRL stream 218, which reenters the shell at the cold end 276 of the warm bundle 212. An inner zone temperature sensor 251 is provided in the shell space of the warm bundle 212 in the inner process tube zone. An outer zone temperature sensor 252 is provided in the shell space of the warm bundle 212 in the outer process tube zone. The intrabundle temperature sensorsATTORNEY REF: HON-08457 USmay be located at different zones at the same elevation and are used to detect temperature maldistribution by measuring the radial temperature differential from within the warm bundle 212.
[0088] FIG. 3 shows an exemplary embodiment of a natural gas liquefaction system 300 implementing inventive concepts of the present invention. A coil-wound heat exchanger (“CWHE”) 314 is shown having a warm bundle 312, a cold bundle 313, and a shell 315. A feed stream 301 , comprising natural gas, and a mixed refrigerant stream 302 are pre-cooled in a precooling system 304 to form a pre-cooled feed stream 306 and a pre-cooled mixed refrigerant stream 305. The pre-cooled mixed refrigerant stream 305 enters a phase separator 307 via an inlet (not shown) and is then separated into a vapor (“MRV”) stream 308 which exits the phase separator 307 through a vapor outlet (not shown) and a liquid (“MRL”) stream 310 which exits the phase separator 307 through a liquid outlet (not shown). The MRV stream 308 enters the warm end 374 of the warm bundle 312 via a vaporized refrigerant conduit 346. The pre-cooled feed stream 306 and the MRV stream 308 each enter the warm bundle 312 at a warm end 374 and exit at a cold end 376, where each is cooled to about -110 degrees C. and condensed by refrigeration provided to the shell side of the CWHE 314 from vaporization of an expanded MRL stream 318 to form a cooled feed stream 316 and a cooled MRV stream 319.
[0089] The MRL stream 310 is split after entering the CWHE 314 and before entering the warm end 374 of the warm bundle 312. The split MRL streams 310a, 310b enter inner zone process tubes 478 and outer zone process tubes 479, respectively. The split MRL streams 310a-b exit the warm bundle 312 at the cold end 376 to form an inner subcooled MRL stream 317a in an inner cold end conduit 319 and an outer subcooled MRL stream 317b in an outer cold end conduit 321 , corresponding to the inner and outer zone process tubes 378, 379. An inner cold end valve 388 is in fluid flow communication with the inner subcooled MRL stream 317a, and an outer cold end valve 390 is in fluid flow communication with the outer subcooled MRL stream 317b. The inner and outer subcooled MRL streams 317a, 317b are recombined after the valves 388, 390 in a consolidated cold end conduit 392 to form a combined subcooled MRL stream 391. The combined subcooled MLR stream 391 is reduced in pressure via an expansion valve 332 to form the expanded MRL stream 318, which re-enters the shell space via an expanded refrigerant conduit 338 at the cold end 376 of the warm bundle 312. The cooled feed stream 316 and cooled MRV stream 322 are further cooled to around -150° C. in the cold bundle 313 of the CWHE 314 to form a product stream 320, comprising liquid natural gas (“LNG”), and a subcooled liquid MRV stream 322 which is reduced inATTORNEY REF: HON-08457 USpressure and sent to the shell side of the cold bundle 313 where it is vaporized to provide refrigeration.
[0090] A vaporized mixed refrigerant stream 324 exits the shell side of the CWHE 314 at the warm end 374, is compressed in a compression stage via a compressor 342, then cooled via a cooler 344, which may be an intercooler or an aftercooler, to form the mixed refrigerant stream 302, thereby completing the closed loop of the refrigerant circuit 330.
[0091] A first temperature sensor 382 is located on the inner subcooled MRL stream 317a, and a second temperature sensor 386 is located on the combined subcooled MRL stream 391. The MRL cold end valves 388, 390 are adjusted via a controller 398 depending on the temperature difference between the first and second temperature sensors 382, 386. Ideally, both cold end valves 388, 390 are fully open to allow for maximum flow and refrigeration duty of the MRL streams.
[0092] FIG. 5 is a flow diagram illustrating a first method of managing temperature differences for MRL streams in the natural gas liquefaction system 300 shown in FIG 3. At step 550, both inner and outer MRL cold end valves 388, 390 are fully open to allow for maximum flow and refrigeration duty of the MRL streams. At step 551 , a temperature measurement of the inner subcooled MRL stream 317a in the inner cold end conduit (“Ti”) is compared to a temperature measurement of the combined subcooled MRL stream 391 in the consolidated cold end conduit (“Tc”). A temperature measurement is taken from the inner zone MRL stream here for the sake of example, but the same process shown in FIG. 5 may be undertaken using a temperature of the outer zone MRL stream (“To”). If Ti is equal to Tc, no temperature maldistribution is detected, and the process ends at step 552. If Tc is less than Ti, then the inner MRL cold end valve 388 is throttled or closed at step 553 in an effort to equalize Ti and Tc. Tc is compared to Ti again at step 555, and if Tc is not equal to Ti, then at step 553 the inner MRL cold end valve 388 is throttled further. Once Tc is equal to Ti (or the difference between Tc and Ti is less than a predetermined amount), no temperature maldistribution is detected, and the process ends at step 557.
[0093] If at step 551 Tc is measured to be greater than Ti, then at step 554 the outer MRL cold end valve 390 is throttled or closed at step 554 in an effort to equalize Ti and Tc. Tc is compared to Ti again at step 556, and if Tc is not equal to Ti, then at step 554 the outer MRL cold end valve 390 is throttled further. Once Tc is equal to Ti, no temperature maldistribution is detected, and the process ends at step 558.
[0094] Alternatively, as shown in FIG. 3, the temperature of the combined subcooled MRL stream 391 can be equalized by comparing the temperature of theATTORNEY REF: HON-08457 UScombined subcooled MRL stream 391 to a temperature estimate 384 derived from a model CWHE for a given plant condition. The modeled temperature 384 is determined using heat exchanger temperature profiles, also called cooling curves, which can be calculated via a mathematical model based on the balances of mass, heat and momentum inside of a CWHE. This mathematical model can be a one-dimensional, two-dimensional, or three-dimensional representation of a CWHE. In the illustrated embodiment, a one-dimensional model is used to derive the modeled temperature 384, which is an estimate of the tube-side circuit temperature at the cold end of each bundle of a CWHE with the necessary data for the inputs for the model. These inputs include composition, temperature, pressure, and flow rate of each circuit inside the CWHE. This data can be obtained bytaking field measurements while the CWHE is in operation. Given that the one-dimensional model assumes no radial temperature maldistribution, it gives the estimate of the “best heat transfer’’ inside CWHE. It is desirable for the temperature Tc of the combined subcooled MRL stream 391 to be less than or equal to modeled temperature 384. If the temperature Tc of the combined MRL stream 391 is found to be warmer than the modeled temperature 384, it implies that temperature maldistribution still exists inside the warm bundle 312, even after achieving the equalization of Ti 382 and Tc 386. Under this condition, further adjustment of the cold end valves 388 and 390 is needed to reduce the temperature of the combined MRL stream 391 , in order to minimize the difference between temperatures Tc and Te.
[0095] FIG. 6 is a flow diagram illustrating a second method of managing temperature differences for MRL streams in the natural gas liquefaction system 300 shown in FIG 3. At step 650, both cold end valves 388, 390 are in a fully open position. At step 651 , a temperature measurement of the inner subcooled MRL stream 317a in the inner cold end conduit (“Ti”) is compared to a temperature measurement of the combined subcooled MRL stream 391 in the consolidated cold end conduit (“Tc”). A temperature measurement is taken from the inner zone MRL stream here for the sake of example, but the same process shown in FIG. 6 may be undertaken using a temperature of the outer zone MRL stream (“To”). If Ti is equal to Tc, no temperature maldistribution is detected, and Tc then is compared to the modeled temperature 384 (“Te”) at step 660. If Tc is less than or equal to Te, then the process ends at step 661. If Tc is greater than Te, then at step 662 either the inner or outer MRL cold end valves 388, 390 are throttled, and Tc is compared to Te again. A trial and error procedure can be used to determine which of the cold end valves 388, 390 should be throttled in an effort to reduce the Tc temperature measure to be equal to or less than Te. Once Tc is less than or equal to Te, the process ends at step 661.ATTORNEY REF: HON-08457 US
[0096] If at step 651 Tc is less than Ti, then the inner MRL cold end valve 388 is throttled at step 653 in an effort to equalize Ti and Tc. Tc is compared to Ti again at step 655, and if Tc is not equal to Ti, then at step 653 the inner MRL cold end valve 388 is throttled further. Once Tc is equal to Ti, then Tc is compared to Te at step 663. If Tc is greater than Te, then at step 665 the inner MRL cold end valve 388 is throttled, and Tc is then compared to Te again at step 663. Once Tc is less than or equal to Te, then the process ends at step 667, and the inner MRL cold end valve 388 is opened or no longer throttled.
[0097] If at step 651 Tc is less than Ti, then the outer MRL cold end valve 390 is throttled at step 654 in an effort to equalize Ti and Tc. Tc is compared to Ti again at step 656, and if Tc is not equal to Ti, then at step 656 the outer MRL cold end valve 390 is throttled further. Once Tc is equal to Ti, then Tc is compared to Te at step 664. If Tc is greater than Te, then at step 666 the outer MRL cold end valve 390 is throttled, and Tc is then compared to Te again at step 664. Once Tc is less than or equal to Te, then the process ends at step 668, and the outer MRL cold end valve 390 is opened or no longer throttled.
[0098] FIG. 4 is a diagram that schematically represents an MRL stream circuit in the exemplary CWHE shown in FIG. 3. The MRL stream 310 enters the warm bundle 312 at the warm end 374 and is routed to tube sheets 326 and 328. The MRL stream 310 is then routed through inner zone process tubes 393a, 393b and outer zone process tubes 395a, 395b. At the cold end 376 of the warm bundle 312, the process tubes 393a-b, 395a-b are routed from the warm bundle 312 to the cold end tube sheets 323a-b, 333a-b so that each of the cold end tube sheets 323a-b, 333a-b is in fluid flow communication with process tubes from a single zone. For example, each of inner zone process tubes 393a, 393b terminate at cold end tube sheets 323a, 323b, respectively. Similarly, each of the outer zone process tubes 395a, 395b terminate at cold end tube sheets 333a, 333b, respectively.
[0099] From the inner zone tube sheets 323a, 323b, the MRL stream is combined and cooled, exiting the shell at the cold end 376 of the warm bundle 312 to form an inner subcooled MRL stream 317a in an inner cold end conduit 319. Similarly, from the outer zone tube sheets 333a, 333b, the MRL stream is combined and cooled, exiting the shell at the cold end 376 of the warm bundle 312 to form an outer subcooled MRL stream 317b in an outer cold end conduit 321. An inner cold end valve 388 is in fluid flow communication with the inner subcooled MRL stream 317a, and an outer cold end valve 390 is in fluid flow communication with the outer subcooled MRL stream 317b. The inner and outer subcooled MRL streams 317a, 317b are recombined after the valvesATTORNEY REF: HON-08457 US388, 390 to form a combined subcooled MRL stream 391 in a consolidated cold end conduit 392. The combined subcooled MLR stream 391 is reduced in pressure to form the expanded MRL stream 318, which re-enters the shell space at the cold end 376 of the warm bundle 312.
[0100] A first temperature sensor 382 is located on the inner subcooled MRL stream 317a, and a second temperature sensor 386 is located on the combined subcooled MRL stream 391. In the illustrated embodiment, a third temperature sensor 394 is located on the outer subcooled MRL stream 317b. In the illustrated embodiment, the first temperature sensor 382 is located on the conduit for the inner subcooled MRL stream 317a upstream of the inner MRL cold end valve 388, the second temperature sensor 386 is located on the conduit for the combined MRL stream 391 upstream of expansion valve 332 and downstream from where the inner and outer subcooled MRL streams 317a, 317b are combined to form the combined MRL stream 391 , and the third temperature sensor 394 is located on the conduit for the outer subcooled MRL stream 317b upstream of the outer MRL cold end valve 390. In this way, the temperatures of both the inner and outer zone MRL streams can be monitored, and either can be compared to the temperature of the combined subcooled MRL stream 391 in an effort to reduce radial maldistribution within the CWHE.
[0101] The inner and outer MRL cold end valves 388, 390 are adjusted depending on the temperature difference between the first and second temperature sensors 382, 386. Ideally, both cold end valves 388, 390 are fully open to allow for maximum flow and refrigeration duty of the MRL streams. If the temperature of the combined subcooled MRL stream 391 is less than the temperature of the inner subcooled MRL stream 317a, the inner MRL cold end valve 388 is throttled or closed to equalize the temperatures of the combined subcooled MRL stream 391 and the inner subcooled MRL stream 317a. If the temperature of the combined subcooled MRL stream 391 is greater than the temperature of the inner subcooled MRL stream 317a, the outer MRL cold end valve 390 is throttled or closed to equalize the temperatures of the combined subcooled MRL stream 391 and the inner subcooled MRL stream 317a. This process is described in greater detail above with respect to FIG. 5.
[0102] While the illustrated embodiments entail splitting and recombining the MRL stream, the inventive concepts disclosed herein could also be utilized with the feed stream and / or the MRV stream. For example, either the MRV stream or the feed stream could be split into different groups of tubes, brought out of the shell where temperature measurements are conducted, and then fed back into the shell. The present invention could be utilized with any or all of the MRL stream, the feed stream, and the MRVATTORNEY REF: HON-08457 USstream. When all of the tube bundles are within a single shell, as illustrated in FIG. 1 and FIG. 3, the MRL stream is the most convenient embodiment to implement in practice, because the MRL stream typically already exits the shell at the cold end of the warm bundle. In embodiments where each tube bundle is located within its own independent and distinct shell, it will be convenient for the MRL stream, the feed stream, and the MRV stream at each bundle to implement this invention in practice.
[0103] It is also desirable to implement the inventive concepts disclosed herein with the MRL stream because the MRL stream remains in a liquid state when it enters and exits the warm bundle. In contrast, the MRV stream and feed streams will be mixed vapor and liquid phase when exiting the cold end of the warm bundle. Additional parts, different sensors and valves, and different pipes will be required if implementing the concepts of the present invention with MRV streams or feed streams. Because the feed stream and MRV stream undergo partial condensation after entering the shell at the warm bundle, they are more capable of self-adjusting to shell-side radial temperature maldistribution, whereas the liquid MRL stream is less capable of doing so. In other words, the liquid MRL stream is less capable of adapting or responding to maldistribution of refrigeration duty on the shell side, whereas the feed stream and vapor MRV stream can adapt or self-regulate more easily to maldistribution of refrigeration duty on the shell side. This is because the feed stream and MRV stream will undergo partial condensation from vapor phase to mixed vapor and liquid phases in the warm bundle, but the MRL stream remains in liquid phase throughout the warm bundle.
[0104] While the embodiments of the present invention illustrated herein include a two-bundle CHWE with cold and warm bundles, the concepts of the present invention could be implemented in a three-bundle CHWE having cold, middle, and warm bundles. In a three-bundle configuration, the feed stream may be routed out of the shell at the warm bundle and re-enter at the middle bundle. MRL streams may exit the shell at the cold end of the middle bundle.
[0105] As such, an invention has been disclosed in terms of preferred embodiments and alternate embodiments thereof. Of course, various changes, modifications, and alterations from the teachings of the present invention may be contemplated by those skilled in the art without departing from the intended spirit and scope thereof. It is intended that the present invention only be limited by the terms of the appended claims.
Claims
ATTORNEY REF: 08263 USCLAIMS1. A coil-wound heat exchanger comprising:a shell;a first bundle comprising:a warm bundle end and a cold bundle end located distal to the warm bundle end;a mandrel centrally located within the first bundle, a first bundle shell space extending from the warm bundle end to the cold bundle end and extending from the first bundle mandrel to the shell;a plurality of tubes located in the first bundle shell space, each of the plurality of tubes having a first tube end located at the warm bundle end and a second tube end located at the cold bundle end, the plurality of tubes being wound around the mandrel forming a plurality of wound layers, the plurality of wound layers being divided into a plurality of zones that are concentrically arranged in the first bundle shell space, the plurality of tubes comprising a plurality of tube sets, each of the plurality of tube sets being located in a different one of the plurality of zones;a plurality of cold end conduits, each of the plurality of cold end conduits being in downstream fluid flow communication with one of the plurality of tube sets;a plurality of cold end valves, each of the plurality of cold end valves being located on one of the plurality of cold end conduits and outside the shell;a consolidated cold end conduit in downstream fluid flow communication with the plurality of cold end conduits and the plurality of cold end valves;a first temperature sensor located on one of the plurality of cold end conduits and outside the shell;a second temperature sensor located on the consolidated cold end conduit and outside of the shell; anda controller electrically connected to the first temperature sensor, the second temperature sensor, and the plurality of cold end valves;wherein the controller is adapted to adjust a position of at least one of the plurality of cold end valves based on a temperature difference between the first temperature sensor and the second temperature sensor; andwherein each of the plurality of tubes is fed by a first fluid source.
2. The coil-wound heat exchanger of claim 1 , wherein the first fluid source is a mixed refrigerant.ATTORNEY REF: HON-08457 US3. The coil-wound heat exchanger of claim 1 , further comprising an expansion valve in downstream fluid flow communication with the consolidated cold end conduit and in upstream fluid flow communication with the first bundle shell space at the cold bundle end of the first bundle.
4. A system for liquefying a feed gas, the system comprising:a coil-wound heat exchanger comprising a first bundle, a shell, and a shell space contained within the shell, the first bundle comprising:a warm end and a cold end;a mandrel centrally located within the first bundle,a warm bundle shell space extending from the warm end to the cold end and extending from the mandrel to the shell;a plurality of tubes located in the first bundle shell space, each of the plurality of tubes having a first tube end located at the warm end of the warm bundle and a second tube end located at the cold end of the warm bundle, the plurality of tubes being wound around the mandrel forming a plurality of wound layers, the plurality of wound layers being divided into a plurality of zones that are concentrically arranged in the first bundle shell space, the plurality of tubes comprising a plurality of tube sets, each of the plurality of tube sets being located in a different one of the plurality of zones; a feed circuit having a feed stream conduit, at least one warm end feed tube sheet located at the warm end, at least one cold end feed tube sheet located at the cold end, and a product conduit, the at least one warm end feed tube sheet and the at least one cold end feed tube sheet being in fluid flow communication with a plurality of feed tubes, the feed stream conduit, the at least one warm end feed tube sheet, the at least one cold end feed tube sheet, and the product conduit all being in fluid flow communication;a refrigerant circuit comprising a closed loop, the refrigerant circuit comprising:a compression circuit comprising at least one compression stage and at least one selected from the group of an intercooler and an aftercooler;a refrigerant stream conduit;a plurality of warm end refrigerant tube sheets in downstream fluid flow communication with the refrigerant stream conduit;a plurality of cold end refrigerant tube sheets located at the cold end in downstream fluid flow communication with the plurality of warm end refrigerant tube sheets; andATTORNEY REF: HON-08457 USa plurality of cold end conduits, each of the plurality of cold end conduits being in downstream fluid flow communication with a different one of the plurality of tube sets;a plurality of cold end valves, each of the plurality of cold end valves being located on one of the plurality of cold end conduits and outside the shell space;a consolidated cold end refrigerant conduit in downstream fluid flow communication with the plurality of cold end conduits and the plurality of cold end valves;an expansion valve in downstream fluid flow communication with the consolidated cold end refrigerant conduit;an expanded refrigerant conduit in downstream fluid flow communication with the expansion valve and in upstream fluid flow communication with the shell space at the cold end; anda vaporized refrigerant conduit located at the warm end, the vaporized refrigerant conduit being in downstream fluid flow communication with the shell space and in upstream fluid flow communication with the compression circuit;a first temperature sensor located on one of the plurality of cold end conduits and outside the shell;a second temperature sensor located on the consolidated cold end refrigerant conduit and outside of the shell; anda controller electrically connected to the first temperature sensor, the second temperature sensor, and the plurality of cold end valves;wherein the controller is adapted to adjust a position of at least one of the plurality of cold end valves based on a temperature difference between the first temperature sensor and the second temperature sensor.
5. The system of claim 4, wherein the refrigerant is a mixed refrigerant.
6. The system of claim 4, wherein the refrigerant circuit further comprises a separator in upstream fluid flow communication with the refrigerant stream conduit, the separator having an inlet, a vapor outlet and a liquid outlet, the inlet being in downstream fluid flow communication with the compression circuit, the liquid outlet being in upstream fluid flow communication with the refrigerant stream conduit.
7. A coil-wound heat exchanger comprising:a shell;a first bundle comprisingATTORNEY REF: HON-08457 USa warm bundle end and a cold bundle end located distal to the warm bundle end;a mandrel centrally located within the first bundle, a first bundle shell space extending from the warm bundle end to the cold bundle end and extending from the first bundle mandrel to the shell;a plurality of tubes located in the first bundle shell space, each of the plurality of tubes having a first tube end located at the warm bundle end and a second tube end located at the cold bundle end, the plurality of tubes being wound around the mandrel forming a plurality of wound layers, the plurality of wound layers being divided into a plurality of zones that are concentrically arranged in the first bundle shell space, the plurality of tubes comprising a plurality of tube sets, each of the plurality of tube sets being located in a different one of the plurality of zones;a plurality of cold end conduits, each of the plurality of cold end conduits being in downstream fluid flow communication with one of the plurality of tube sets;a plurality of cold end valves, each of the plurality of cold end valves being located on one of the plurality of cold end conduits and outside the shell;a consolidated cold end conduit in downstream fluid flow communication with the plurality of cold end conduits and the plurality of cold end valves;a first temperature sensor located on the consolidated cold end conduit and outside of the shell; anda controller electrically connected to the first temperature sensor and the plurality of cold end valves;wherein the controller is adapted to adjust a position of at least one of the plurality of cold end valves based on a temperature difference between the first temperature sensor and a modeled temperature;wherein the modeled temperature is determined using a mathematical model that comprises mass, heat and momentum inside the coil wound heat exchanger; and wherein each of the plurality of tubes is fed by a first fluid source.
8. The coil-wound heat exchanger of claim 7, wherein the first fluid source is a mixed refrigerant.