SIDE DRAW REFLUX HEAVY HYDROCARBON REMOVAL SYSTEM AND METHOD

Description

CLAIM OF PRIORITY

This application is a continuation-in-part of U.S. patent application Ser. No. 17/743,811, filed May 13, 2022, which claims the benefit of U.S. Provisional Application No. 63/188,846, filed May 14, 2021, the contents of each of which are hereby incorporated by reference.

FIELD OF THE DISCLOSURE

The present invention relates generally to systems and methods for processing gases and, more particularly, to a system and method for removing heavy hydrocarbon components from a feed gas.

BACKGROUND

Natural gas streams, or other methane-rich gas streams, are often liquefied for ease of transport and use. It is often desirable to process such feed gas streams to remove heavier hydrocarbons (hydrocarbons that are heavier than propane)so as to provide a higher methane purity in the resulting liquid natural gas product and a co-product liquid (natural gas liquids) that contains the heavy hydrocarbons. Such purified liquid natural gas products bum cleaner in LNG-powered vehicles so that less air pollution results. In addition, purifying the feed stream prior to liquefaction prevents freeze-up of the liquefying heat exchanger that would otherwise occur due to presence of heavy hydrocarbon components. The co-product liquid stream, rich in heavy hydrocarbons such as ethane, propane, butane and heavier hydrocarbons, have several valuable industrial uses. It is further desirable that such processing minimizes energy consumption given the volume of gas that must be purified.

SUMMARY OF THE DISCLOSURE

There are several aspects of the present subject matter which may be embodied separately or together in the methods devices and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as set forth in the claims appended hereto.

In one aspect, a system for removing heavy hydrocarbon components from a feed gas stream includes a heavies removal heat exchanger that has a main feed stream cooling passage, a reflux stream cooling passage and a return vapor stream warming passage. The main feed stream cooling passage of the heavies removal heat exchanger is configured to receive and cool at least a portion of the feed gas stream so as to produce a cooled mam feed stream. A scrubbing section includes a main feed inlet, a liquid outlet, a return vapor outlet and a reflux inlet where the main feed inlet is configured to receive the cooled main feed stream. A stripping section has a first fluid inlet, a second fluid inlet, a liquid outlet and a vapor outlet, where the first fluid inlet configured to receive a fluid stream from the liquid outlet of the scrubbing section. A stripping gas feed expansion device has an inlet configured to receive a portion of the expanded feed gas stream with the stripping gas feed expansion device having an outlet in fluid communication with the second fluid inlet of the stripping section. A side draw vapor line is configured to receive a vapor stream from the vapor outlet of the stripping section, where the side draw vapor line in fluid communication with the reflux stream cooling passage of the heavies removal heat exchanger. A reflux separation device is configured to receive fluid from the reflux cooling stream passage of the heavies removal heat exchanger, where the reflux separation device includes a liquid outlet and a vapor outlet and wherein the liquid outlet of the reflux separation device is in fluid communication with the reflux inlet of the scrubbing section. A return vapor expansion device has an inlet configured to receive a vapor stream from the return vapor outlet of the scrubbing section and an outlet configured to direct a cooled vapor stream to the return vapor stream warming passage of the heavies removal heat exchanger. A feed gas compressor has an inlet configured to receive a fluid from the return vapor stream warming passage of the heavies removal heat exchanger and an outlet. The reflux separation device vapor outlet is also in fluid communication with the inlet of the feed gas compressor

In another aspect, a process for removing heavy hydrocarbon components from a feed gas stream includes the steps of expanding the feed gas stream; splitting the expanded feed gas stream into a main feed stream that includes a majority portion of the expanded feed gas stream and a stripping gas feed stream; cooling the mam feed stream in a heavies removal heat exchanger; directing the cooled main feed stream to a scrubbing section; separating the cooled main feed stream into a main stream vapor portion and a main stream liquid portion in the scrubbing section; expanding the stripping gas feed stream, directing the expanded stripping gas feed stream to a stripping section; separating the stripping gas feed stream into a stripping vapor portion and a stripping liquid portion in the stripping section; expanding the main stream liquid portion to create a mam mixed phase stream; directing the main mixed phase stream to the shipping section; cooling the stripping vapor portion to create a reflux mixed phase stream; separating the reflux mixed phase stream into a reflux vapor portion and a reflux liquid portion; directing the reflux liquid portion to the scrubbing section; expanding the main stream vapor portion; waning the expanded main stream vapor portion in the heavies removal heat exchanger to cool the main feed stream; expanding the reflux vapor portion; warming the expanded reflux vapor portion in the heavies removal heat exchanger to cool the main feed stream; compressing the warmed expanded main stream vapor portion and the warmed expanded reflux vapor portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram and schematic illustrating a first embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 2 is a process flow diagram and schematic illustrating a second embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 3 is a process flow diagram and schematic illustrating a third embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 4 is a process flow diagram and schematic illustrating a fourth embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 5 is a process flow diagram and schematic illustrating a fifth embodiment of the heavy hydrocarbon removal system and method of the disclosure,

FIG. 6 is a process flow diagram and schematic illustrating a sixth embodiment of the heavy hydrocarbon removal system and method of the disclosure:

FIG. 7 is a process flow diagram and schematic illustrating a seventh embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 8 is a process flow diagram and schematic illustrating an eighth embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 9 is a process flow diagram and schematic illustrating a nineth embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 10 is a process flow diagram and schematic illustrating a tenth embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 11 is a process flow diagram and schematic illustrating an eleventh embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 12 is a process flow diagram and schematic illustrating a twelfth embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 13 is a process flow diagram and schematic illustrating a thirteen embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 14 is a process flow diagram and schematic illustrating a fourteenth embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 15 is a process flow diagram and schematic illustrating a fifteenth embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 16 is a process flow diagram and schematic illustrating a sixteenth embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 17 is a process flow diagram and schematic illustrating a seventeenth embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 18 is a process flow diagram and schematic illustrating a eighteenth embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 19 is a process flow diagram and schematic illustrating a nineteenth embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 20 is a process flow diagram and schematic illustrating a twentieth embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 21 is a process flow diagram and schematic illustrating a twenty-first embodiment of the heavy hydrocarbon removal system and method of the disclosure;

FIG. 22 is a process flow diagram and schematic illustrating a twenty-second embodiment of the heavy hydrocarbon removal system and method of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of a heavy hydrocarbon removal system in accordance with the disclosure are illustrated in FIGS. 1-19. It should be noted that while the embodiments are illustrated and described below in terms of removing heavy hydrocarbons components from a natural gas feed stream prior to being liquefied, the technology of the disclosure may be used to remove other components from alterative gas feed streams prior to alterative types of downstream processing.

It should also be noted that in the descriptions presented below, the lines or passages and streams are sometimes both referred to by the same reference numbers set out in the figures.

With reference to FIG. 1, a first embodiment of the system of the disclosure is indicated in general at 20. A hydrocarbon feed gas stream 22 (such as a natural gas stream) enters a feed gas expander turbine 23 and the resulting expanded gas stream is split into a main feed stream 24 and a stripping gas feed stream 26.

The main feed stream 24, which contains the bulk of the feed gas stream 22, passes through a heavies removal heat exchanger 28 and is cooled and partially condensed The resulting mixed phase stream 32 is then routed to a scrubbing section 34 of a heavies removal column, indicated in general at 36, where liquids are separated from the main feed vapor The resulting liquid stream 38, which contains a large portion of the feed gas heavy hydrocarbon freezing components is directed to an optional expansion device 42 (such as a Joule-Thomson or JT valve) with the resulting mixed phase stream 44 traveling to the upper portion of the column stripping section 46. As used herein, the term “expansion device” includes, but is not limited to, a JT valve, rotating expander, turbine, orifice plate and any other expansion device known in the art Stream 44 is separated into a vapor portion and a liquid portion upon entering the column stripping section 46.

The stripping gas feed stream 26 travels to an expansion device 48 (such as a Joule-Thomson or JT valve) with the resulting mixed phase stream 52 traveling to the lower portion of the column stripping section 46. The vapor portion of stream 52 is separated from the liquid portion upon entering the stripping column section 46 and rises to provide heating action to the liquids from stream 44 coming down through the stripping section internals thereby revaporizing a portion of the lighter components in said liquids. The liquid portion of stream 52 exits the stripping section 46 as a portion of natural gas liquids (NGL) condensate stream 54 as does the remaining liquid portion of the stream 44. Condensate stream 54 contains a majority of the heavy hydrocarbon freezing components that were present in the feed gas stream 22.

A vapor side draw stream 56 exits the stripping section 46 of the heavies removal column and is cooled and partially condensed in the heavies removal exchanger 28. A resulting mixed phase stream 58 travels to a separation device, such as a heavies removal reflux drum 62, and is separated into vapor and liquid portions. The liquid stream 64 from the separation device 62 is routed via pump 66 (optional) to the top of the heavies removal column scrubbing section 34 as reflux stream 70 after passing through optional control valve 71.

The vapor stream 68 from the separation device 62 is routed across an expansion device 72 (such as a JT valve) where it is cooled to form cooled stream 74, a portion (or all) of which passes through the heavies removal exchanger 28 and is warmed and thereby provides cooling to other streams in the exchanger. Vapor stream 76 is provided as a result.

The vapor portion of the main feed stream 32 in the heavies removal column scrubbing section undergoes mass transfer with the reflux provided by reflux stream 70 within the column scrubbing section internals, which may be trays, random packing, or structured packing. This removes freezing components heavy hydrocarbons from the vapor portion of the main feed stream 32. The scrubbed return vapor stream 82 exits the top of the column 36 and is then routed across an expansion device 84 (such as a JT valve) to produce cooling. The cooled return vapor stream 86 is then routed to the heavies removal exchanger 28 where it is warmed in one or more passages and thereby, along with stream 74, provides cooling to other streams in the exchanger After warming and combination with stream 76, the return vapor stream 88 is compressed by feed gas compressor 92 and sent to a liquefaction process so that a liquefied stream (such a liquid natural gas LNG) is produced.

The feed gas compressor 92 is preferably powered by the feed gas expander turbine 23, while a booster compressor 94 (which may or may not be powered by the gas expander turbine 23) may optionally also be provided. By expanding the feed gas stream 22 prior to cooling. greater power is developed by the turbine 23, which results in greater power being available to run the compressor 92 (and any booster compressors). This decreases net power usage of the system and thus increases system efficiency in some applications. Furthermore, expanding the feed gas stream 22 prior to cooling lowers equipment cost as, in some applications, carbon steel may be used to construct the feed gas turbine 23 (as opposed to stainless steel, which is required for expanding at colder fluid temperatures).

As examples only, the systems described herein may provide purified gas to the liquefaction processes and systems described in commonly owned U.S. Pat. No. 9,411,877 to Gushanas et al., U.S. Pat. No. 10,480,851 to Ducote et al. or U.S. Pat. No. 10,663,221 to Ducote et al., the contents of each of which are hereby incorporated by reference.

It should be noted that, in alternative embodiments, streams 74 and 86 may be combined prior to introduction into the heat exchanger 28, as illustrated in FIG. 2. Furthermore, the vessel head 95 (FIG. 1) separating the scrubbing and stripping sections of column 36 may optionally be removed so that the functions are combined into a single column with trap-out trays or other devices used to capture liquid. In other alterative embodiments, the scrubbing and stripping sections may be provided as entirely separate individual columns.

Advantages of the embodiment of FIG. 1 include the expander 23 both extracting power and providing cooling to the feed gas stream. In addition, the side draw reflux stream provides high recovery of heavy hydrocarbons, including captures of Benzene, Toluene, Ethylbenzene, Xylenes (BTEX).

In a second embodiment of the system of the disclosure, indicated in general at 100 in FIG. 2, a reboiler service has been added to the system of FIG. 1 whereby the liquid stream 102 from the scrubbing section 104, after being expanded and cooled in optional reboiler expansion device 115, such as a JT valve, is warmed in the heavies removal exchanger 107 to provide cooling therein. In an alternative embodiment, a portion of stream 102 may go directly to the stripping section either before or after passing through expansion device 115. An expansion device 117 has also been added to vapor side draw stream 119 to cool the vapor from the stripping section prior to travel to the heavies removal exchanger 107. In addition, optional streams 108 and 112 from the exchanger may be used to optimize the temperatures of the stripping gas stream 114 and reboiler return stream 116, respectively Furthermore, line 118 may optionally be provided (either with or without control valve 122) to provide injection of side draw reflux to the stripping section 124. In an alterative embodiment, a branch 83 may direct a portion of the scrubbed return vapor stream 82 to the separation device (reflux drum) 62. The remaining components of the system of FIG. 2 may generally be the same and provide the same functionality as those illustrated in FIG. 1.

In a third embodiment of the system of the disclosure, indicated in general at 150, in FIG. 3, an expansion device 152, such as a JT valve, is substituted for the feed gas expander turbine 24 of the systems of FIGS. 1 and 2. System 150 of FIG. 3 also substitutes a return vapor expander turbine 154 for the JT valve 84 of systems 20 and 100 of FIGS. 1 and 2 that receives the return vapor stream 156 from the heavies removal column 158. This return vapor expander turbine 154 preferably powers the feed gas compressor 162. The remaining components of the system of FIG. 2 may generally be the same and provide the same functionality as those illustrated in FIG. 1. In an alterative version of the system of the disclosure, as illustrated in FIG. 3, a portion 163 of the scrubber liquid stream goes through the scrubber liquid reheat passage of the heavies removal heat exchanger 167 and a remaining portion 165 of the scrubber liquid stream goes directly to the stripping section.

In a fourth embodiment of the system of the disclosure, indicated in general at 180 in FIG. 4, a cascade side draw reflux arrangement has been added to the system of FIG. 2. More specifically, a vapor side draw stream 182 exits the stripping section 182 of the heavies removal column and is cooled and partially condensed in the heavies removal exchanger 184. A resulting mixed phase stream 186 travels to a first reflux separation device, such as a warm reflux drum 188, and is separated into vapor and liquid portions. The liquid stream 192 from the warm reflux drum 188 is routed via pump 194 (optional) to the top of the stripping section 182 of the heavies removal column as reflux stream 196 after passing through optional expansion device 198.

With continued reference to FIG. 4, the vapor stream 202 from the warm reflux drum 188 travels to heavies removal exchanger 184 and is cooled and partially condensed. A resulting mixed phase stream 204 travels to a second reflux separation device, such as cold reflux drum 206, and is separated into vapor and liquid portions. The liquid stream 208 from the separation device 206 is routed via pump 212 (optional) to the top of the heavies removal column scrubbing section 214 as reflux stream 216 after passing through optional control valve 218. Vapor stream 222 exits the top of cold reflux drum 206 and joins return vapor stream 224 after passing through expansion device 226. While a single packing section for the scrubbing section 214 is illustrated in FIG. 4, the scrubbing section may optionally be provided with two (or more) packing sections based on design considerations.

The remaining components of the system of FIG. 4 may generally be the same and provide the same functionality as those illustrated in FIGS. 1 and 2.

The cascade reflux arrangement of FIG. 4 lowers the level of heavy hydrocarbon components present in the reflux streams (as compared to the systems of FIGS. 1-3) in some applications.

In a fifth embodiment of the system of the disclosure, indicated in general at 250 in FIG. 5, a split feed reflux arrangement has been added to the system 100 of FIG. 2. More specifically, the system 250 includes a branch off of the hydrocarbon feed gas stream 254 before the feed gas expander 256. A small portion of the feed gas stream splits off at the branch and flows through line 252 as a split feed reflux gas stream that is cooled in the heavies removal exchanger 258 and at least partially condensed to form mixed phase stream 262. This stream is then expanded via a split feed reflux expansion device 264, such as a JT valve, with the resulting cooled stream 266 directed to the scrubbing section 268 of the heavies removal column as reflux to aid in the removal of heavy hydrocarbons from the column main feed Such a system provides improved efficiency for some high pressure feed gas applications. The scrub section can be single or double packed and the stream 266 may enter the scrub section above the packing or at a mid-point between the two packing sections.

In an alternative embodiment, the expansion device 264 of FIG. 5 may be omitted. In a further alterative embodiment, line 272 may optionally be provided (either with or without control valve 274) to provide injection of side draw reflux to the stripping section 276.

The remaining components of the system of FIG. 5 may generally be the same and provide the same functionality as those illustrated in FIGS. 1 and 2.

In a sixth embodiment of the system of the disclosure, indicated in general at 300 in FIG. 6, a reflux heat exchanger 302 has been added to the system of FIG. 5 to provide additional cooling to the vapor side draw 304 from the stripping section 306 of the column prior to the reflux drum 308. The cooling in supplemental reflux heat exchanger 302 is provided by the cooled (via heavies removal heat exchanger 312) and expanded (via expansion device 314) split feed reflux stream 316. The remaining components of the system of FIG. 6 may generally be the same and provide the same functionality as those illustrated in FIGS. 1-5.

The additional heat exchanger 302 allows for cooler reflux and provide more efficient removal of heavy hydrocarbons in some applications. It should be noted that the heat exchangers 312 and 302 may be combined into a single heat exchanger in alternative embodiments.

In a seventh embodiment of the system of the disclosure, indicated in general at 318 in FIG. 7, the cascade side draw reflux arrangement of FIG. 4 may be added to the system of FIG. 5. As a result, the system 318 of FIG. 7 includes a first reflux separation device, such as a warm reflux drum 317, which receives and separates a mixed phase stream 315 (resulting from cooling of side draw vapor stream 313) into liquid and vapor portions. The vapor portion 311 is cooled and the resulting mixed phase stream 309 is provided to a second reflux separation device, such as cold reflux drum 319, and is separated into vapor and liquid portions, which are further processed as explained with reference to FIG. 4.

In an eighth embodiment of the system of the disclosure, indicated in general at 320 in FIG. 8, a feed separation device 322 has been added to the system of FIG. 2. As in previous embodiments, the feed gas stream 324 is expanded by feed gas expander 326 and then cooled by the heavies removal heat exchanger 328. The resulting mixed phase stream 332 is directed to the feed separation device 322 where it is separated into a vapor portion and a liquid portion The liquid portion exits the feed separation device 322 as liquid stream 334 and, after expansion via separated feed liquid expansion device 336 (such as a JT valve) is warmed in the heavies removal heat exchanger to provide refrigeration therein. The resulting mixed phase stream 338, which may pass through optional cooled separated feed liquid expansion device 340, such as a JT valve, is directed to the stripping section 342 of the heavies removal column where it is separated into vapor and liquid portions.

The vapor stream 344 from the feed separation device 322 is directed through (optional) separated feed vapor expansion device 346, such as a JT valve, where it is cooled and partially condensed so that mixed phase stream 348 is formed. Mixed phase stream 348 is then directed to the scrubbing section 352 of the heavies removal column where it is separated into vapor and liquid portions. Such a system provides improved efficiency at moderate pressure for some applications and may also be beneficial for richer feed gas applications.

The remaining components of the system of FIG. 7 may generally be the same and provide the same functionality as those illustrated in FIGS. 1 and 2.

The system 320 of FIG. 8 may include an optional branch 354 to the stripping section 342 from the mixed phase stream 338. Branch 354 may optionally include an expansion device 356. such as a JT valve. Such an arrangement may be desirable when additional flow is required at the top of the stripping section to meet wetting criteria. In such an embodiment, the stripping section 342 has two layers of internal trays or the like to allow for the additional injection location higher in the stripping section.

The embodiment of FIG. 8 provides improved efficiency at moderate feed pressures and/or when the feed gas stream 324 is rich in some applications.

In a nineth embodiment of the system of the disclosure, indicated in general at 380 in FIG. 9, a split feed reflux arrangement has been added to the system 320 of FIG. 8. More specifically, the system 380 includes a branch off of the hydrocarbon feed gas stream 382 before the feed gas expander 384. A small portion of the feed gas stream splits off at the branch and flows through line 386 as a split feed reflux gas stream that is cooled in the heavies removal exchanger 388 and at least partially condensed to form mixed phase stream 392. This stream is then expanded via an expansion device 394, such as a JT valve, with the resulting cooled stream 396 directed to the scrubbing section 398 of the heavies removal column as reflux to aid in the removal of heavy hydrocarbons from the column main feed. In an alternative embodiment, expansion device 394 may be omitted. In a further embodiment, a branch 395 may be added to the line 397 leading from the heavies removal heat exchanger 388 so that a portion of the mixed phase stream in line 397 may be transferred to line 399, which also enters the stripping section 393 of the heavies removal column.

In a tenth embodiment of the system of the disclosure, indicated in general at 400 in FIG. 10, a cold reflux stream is provided to the stripping section 402 of the heavies removal column. More specifically, as described previously for the systems of FIGS. 2 and 5, split reflux line 404 may be provided (either with control valve 406) after reflux pump 408 to provide injection of side draw reflux to the stripping section 402. Such a split of the side draw reflux provides additional efficiency in the removal of heavy hydrocarbons in some applications. The split reflux also lowers BTEX and enhances control of reflux BTEX concentration in the reflux stream and thus lowers BTEX in the clean gas exiting the top of the heavies removal column in some applications. As a result, the system 400 is suitable for applications having high BTEX levels in the feed gas stream.

In addition, as illustrated in FIG. 10, the system 400 may include an optional branch 412 to the stripping section 402 from the reboiler line 414 that leads from the heavies removal heat exchanger 416. Such an arrangement may be desirable when additional flow is required at the top of the stripping section to meet wetting criteria. In such an embodiment, the stripping section 402 has two layers of internal trays or the like to allow for the additional injection location higher in the stripping section.

As illustrated by system 430 of FIG. 11 at 432, the feed separation device of FIG. 7 (322 in FIG. 7) may be added to the system of FIG. 9. The system of FIG. 11 also illustrates that the system of 400 of FIG. 10 may be modified to omit the expansion device 418 present in the liquid line 420 leading from the scrubbing section 422 of the heavies removal column to the heavies removal heat exchanger 416. In the system 430 of FIG. 11, expansion devices, such as JT valves 434, 436, 438 and 442, have been added to the lines 444, 446, 448 and 452, respectively, leading to the scrubbing section 454 of the heavies removal column, with the scrubbing section including multiple layers of internal trays of the like to accommodate the multiple injection locations.

As illustrated by system 500 of FIG. 12, the system of FIG. 10 may be modified to add a side draw expansion device, such as JT valve 502, to the side draw vapor line 504 exiting stripping section 506. Furthermore, as described previously with respect to FIG. 2, a branch 507 may direct a portion of the scrubbed return vapor stream 508 from the heavies removal column 509 to the separation device (reflux drum) 512 prior to expansion device 514. In an alterative embodiment, the expansion device 514 and corresponding line portion 516 may be omitted so that all of the scrubbed return vapor stream 508 is directed to reflux drum 512. The vapor stream 518 from the reflux drum is then directed to through, and warmed within, the heavies removal heat exchanger 522 after passing through and being cooled in an expansion device, such as JT valve 524.

In the embodiments of FIGS. 13-15, optimization of the stripping gas temperature is obtained in some applications to provide improved control for tighter natural gas liquids (NGL) specifications.

In the system indicated in general at 550 in FIG. 13, a feed gas heat exchanger 552. receives the feed gas stream 554. A cooled feed gas stream 556 exits the feed gas heat exchanger and is expanded and cooled within feed gas expander turbine 558. The stream exiting the turbine is split to form main stream 562, which contains the majority of the feed gas stream. and stripping gas stream 064. Stripping gas stream 564 travels through the feed gas heat changer 552 and is warmed so that refrigeration is provided to cool feed gas stream 554. The warned stripping gas stream 566 exits the feed gas heat exchanger 552 and is expanded in an optional expansion device, such as JT valve 568, and directed to the stripping section 572. Such an arrangement optimizes the temperature of the stripping gas in some applications to meet some specifications for NGL condensate stream 574. For example, the warmer stripping gas lowers the levels of methane present in the NGL condensate stream 574. Alternative options for Warming the stripping gas stream include using heating mediums other than fluids and different types of heat exchangers, including braised aluminum heat exchangers, plate-frame heat exchangers and shell & tube heat exchangers.

As illustrated by system 600 in FIG. 14, the split feed reflux arrangement of FIG. 5 may added to the system 550 of FIG. 13. More specifically, the system 600 includes a branch off of the cooled hydrocarbon feed gas stream 602 downstream of the feed gas heat exchanger 604 before the feed gas expander 606. As in the embodiment of FIG. 5, a small portion of the feed gas stream splits off at the branch and flows through line 608 as a split feed reflux gas stream that is cooled in the heavies removal exchanger 612 and at least partially condensed to form mixed phase stream 614. This stream is then expanded via optional expansion device 616, such as a JT valve, with the resulting cooled stream directed to the scrubbing section 618 of the heavies removal column as reflux.

In addition, the cold reflux stream 622 of the systems of FIGS. 2, 5 and 10 may optionally be added to the system 600 of FIG. 14.

As illustrated by the system 650 of FIG. 15, the split feed reflux and side draw reflux heat exchange arrangement of FIG. 6, including reflux heat exchanger 652, may be combined with the feed gas heat exchanger 654, which is also employed in the systems of FIGS. 13 and 14.

An embodiment of the system of the disclosure including a heat pump is indicated in general at 700 is illustrated in FIG. 16. In the system 700, a hydrocarbon feed gas stream 702 (such as a natural gas stream) enters a feed gas expander turbine 704 and the resulting expanded gas stream is split into a main feed stream 706 and a stripping gas feed stream 708.

The main feed stream 706, which contains the bulk of the feed gas stream 702, passes through a heavies removal heat exchanger 712 and is cooled and partially condensed. The resulting mixed phase stream 714 is then routed to a scrubbing section 716 of a heavies removal column, indicated in general at 718, where liquids are separated from the main feed vapor. An NGL condensate stream 720 containing heavy hydrocarbons exits the bottom of the stripping. section 736. The resulting liquid stream 722, which contains a large portion of the feed gas heavy hydrocarbon freezing components is directed to an optional expansion device 724 (such as a Joule-Thomson or JT valve) with the resulting mixed phase stream 726 being warmed in the heavies removal heat exchanger 712 and then to a stripping section heat exchanger 728 where it is further warmed and directed to stripping section 736 of the column 718. The stripping section heat exchanger 728 also receives a stream 732 after it has passed through a stripping gas feed expansion device 734 so that at least a portion of d stripping gas 708 is warmed prior to introduction into the stripping section 736 of column 718. The remaining portion of the stripping gas 708 is expanded via a scrub expansion device, such as JT valve 738, and joined with the mixed phase stream 714 that is routed to the scrubbing section 716.

A side draw vapor stream 742 exits the stripping section 736 of the column 718 and is cooled via a side draw expansion device, such as JT valve 744, with the resulting stream traveling to heat pump compressor 746. The compressed gas leaving the compressor 746 is cooled in reflux compressor aftercooler 748 and then cooled in stripping section heat exchanger 728 so that a mixed phase stream 752 is formed. Mixed phase stream 752 travels to a first reflux separation device, such as a warm reflux drum 754, and is separated into vapor and liquid portions. The liquid stream 756 from the warm reflux drum 754 is routed to the top portion of the stripping section 736 of the heavies removal column as reflux stream 737 after passing through an optional expansion device, such as JT valve 758.

With continued reference to FIG. 16, the vapor stream 762 from the warm reflux drum 754 travels to heavies removal exchanger 712 and is cooled and at least partially condensed. A resulting stream 764 travels through an optional expansion device, such as JT valve 766, to a second reflux separation device, such as cold reflux drum 768, and is separated into vapor and liquid portions. A portion of vapor stream 762 from the warm reflux drum 754 is split off and travels through an expansion device, such as JT valve 772, with the resulting mixed phase stream joining the mixed phase stream from JT valve 766 in traveling to cold reflux drum 768. The liquid stream 774 from the cold reflux drum 768 is routed to the top portion of the heavies removal column scrubbing section 716 as reflux stream 778 after passing through an optional control valve 776. Vapor stream 782 exits the top of cold reflux drum 768 and joins the scrubbed return vapor stream to form stream 783 after passing through an optional expansion device, such as JT valve 784.

The scrubbed return vapor stream exits the top of the column 718 and is then routed across an expansion device, such as JT valve 786, to produce cooling. The cooled return vapor stream is then combined with the stream from JT valve 784 (as noted previously) with the resulting stream 783 being routed to the heavies removal exchanger 712 where it is wanned and thereby provides cooling to other streams in the heat exchanger. After warming, the return vapor stream 788 is compressed by feed gas compressor 792 and sent as stream 794 to liquefaction so that a liquefied stream (such a liquid natural gas or LNG) is produced

The feed gas compressor 792 is preferably powered by the feed gas expander turbine 704. The reflux compressor 746 may also be powered by the feed gas expander turbine 704 or alternatively with a dedicated motor 796.

With reference to FIG. 17, a seventeenth embodiment of the system of the disclosure is indicated in general at 800. A hydrocarbon feed gas stream 802 (such as a natural gas stream) is split to form a stripping gas feed stream 804 and a main feed stream 806. As in previous embodiments, stripping gas feed stream 804 is expanded in expansion device 808 and directed as mixed phase stream 809 to a stripping section 810. The shipping section 810 may include an upper packing section 811, an added middle packing section 813 and lower packing section 815, with the stream 809 entering the stripping section below the lower packing section 815. As an example only, the packing sections may include beds of random packing with a distribution tray between each packing bed to red-distribute the liquid evenly over the beds. The beds could also be trays or even red packing.

Main feed stream 806 is expanded in expansion device 812 with the resulting stream directed to heavies removal heat exchanger 814. The resulting mixed phase stream 820 is directed to a feed separation device 822 where it is separated into a vapor portion and a liquid portion. The liquid portion exits the feed separation device 822 as liquid stream 824 and, after expansion via separated feed liquid expansion device 826 is directed to the stripping section 810 of the heavies removal column as mixed phase stream 828. Mixed phased stream 828 may enter the stripping section below the added middle packing section 813. With the additional mid-weight hydrocarbons from the reflux drum (via a reflux recycle stream described below), the additional middle packing section provides for improved separation of the freezing components. The additional middle packing section 813 is not required.

The vapor stream 823 exiting the top of the feed separation device 822, after expansion via expansion device 830, is cooled in the heavies removal heat exchanger 814. The resulting mixed phase stream 832 is directed to the scrubbing section 834 of the heavies removal column. By decreasing the pressure of the vapor stream 823 before the stream enters the heat exchanger 814, the temperature profiles of passages B and A2 of the heat exchanger 814 better match, providing better efficiency. This also allows the feed heat exchanger and reflux heat exchanger to be combined into a single unit. It also helps to reduce probability of formation of solids in the A2 heat exchanger passage.

As in the embodiment of FIG. 3, the system 800 of FIG. 17 uses a return vapor expander turbine 836 that receives the return vapor stream 838 from the heavies removal column 814. This return vapor expander turbine 836 preferably powers the feed gas compressor 842. In addition, as in the system of FIG. 10, the system 800 may include an optional branch 839 to the shipping section from the reboiler line 841 that leads from the heavies removal heat exchanger 814. Such an arrangement may be desirable when additional flow is required at the top of the stripping section to meet wetting criteria.

A reflux recycle line 844 includes a control valve 846 and receives a portion of the liquid reflux stream exiting the reflux pump 848. The reflux recycle stream in line 844 travels to a reflux recycle warming passage E in the heavies removal heat exchanger 814, where it is warmed and vaporized. The resulting stream 852 joins the main feed stream 806. In addition, an optional second reflux recycle line 853 may direct a portion of the liquid reflux stream exiting reflux pump 848 to the top of the stripping section The remaining aspects of the reflux handling system of FIG. 17 are the same as FIGS. 2 and 3.

The streams 844 and 852 provide mid-weight hydrocarbon components, such as propane, butane, etc. to the front of the process. These mid-weight hydrocarbons need to be provided in sufficient quantities so they will form a liquid phase at a temperature warmer than the desublimation temperature of the heavier weight freezing components, such as benzene and other similar components that enter the process. Returning the stream 844 through the heavies removal heat exchanger helps to balance the heat exchanger heating and cooling curves which improves the efficiency of the process. By vaporizing the stream 852 before mixing with the feed gas stream 806, the mixing process is improved and there is no concern of maldistribution into the feed stream.

In the system of FIG. 17, the inlet feed gas 806 is cooled to a temperature where a two phase flow 825 exiting expansion device 821 will exist at the process conditions of the feed separation vessel 822. The feed separation vessel 822 separates out the liquid phase 824, which contains much of the recycled mid-weight hydrocarbons from the reflux drum as well as most of the heavier freezing components. As noted previously, the liquid stream 824 is sent to the stripping section 814 of the column to separate out the high molecular weight hydrocarbons and freezing components.

In an alternative embodiment, the stream in reflux recycle line 844 may be mixed into the feed gas stream 806 before the heat exchanger 814 without warning the stream, but it may not be optimum. In an alternative embodiment, the recycle stream in line 844 can also be mixed at the exit of the passage A1 of the heavies removal heat exchanger 814 without warning the recycle stream through the heavies heat exchanger. This may also not be optimal since it risks poor mixing and could create poor separation in the feed separation vessel 822 due to poor distribution of the liquid vapor flow regimes.

An additional section of packing is added to the stripping section of the column.

A reboiler 862 can be added as an optional item depending on the amount of mid-weight hydrocarbons that need to be recycled along with the amount of heavier freezing components and desire to produce NGL liquids in liquid stream 864 exiting the stripping section 810.

The system of FIG. 17 is best designed for a lean natural gas stream (low quantities of propanes, butanes, pentanes and heavier components) but with freezing contaminants in the incoming stream, such as benzenes or others. When a stream has very low concentrations of mid-weight hydrocarbons, it can be difficult to remove to an acceptable level the freezing components The freezing components stay in the vapor phase and will tend to desublimate freeze) directly from the vapor phase to solid before they can be drawn into a liquid phase. This takes place since there are limited amounts of mud-weight hydrocarbons which will only form a liquid phase at temperatures lower than the desublimation temperature of the freezing components.

In an alternative embodiment of the system of the disclosure, indicated in general at 900 in FIG. 18, an expansion device 910 has been added to the line 912 leading from the heavies removal heat exchanger 914 to the scrubbing section 916 of a heavies removal column. As an example only, the expansion device 910 may be a valve (such as a JT valve) or a turbine. If the expansion device 910 is a turbine, it may be used to power a compressor. In some applications, expansion device 910 allows for the heavies removal column to operate at optimal pressure for improved separation. In addition, a stream of a refrigerant 918, such as a mixed refrigerant from a liquefier, travels to passage 922 of the heavies removal heat exchanger 914 where it is cooled. The cooled stream is expanded via an expansion device 924 which may be, as an example only, a JT valve. The resulting stream flows through a supplemental refrigeration passage 926 to provide additional cooling in the heavies removal heat exchanger 914. The remaining components of the system of FIG. 18 may generally be the same and provide the same functionality as those illustrated in FIG. 2.

In the system of FIG. 19, indicated in general at 950, a separation device 952 has been added to the system of FIG. 18 to receive a stream 954 from the heavies removal heat exchanger 956. Stream 954 is produced after feed stream 962 passes partially through a passage of the heavies removal heat exchanger 956. The vapor stream 964 from the separation device 952 travels back to another passage of the heat exchanger 956 for further cooling before traveling to expansion device 966 and then to the scrubbing section 968 of the heavies removal column. The liquid stream 972 from the separation device 952 is directed through expansion device 974 and then to the scrubbing section 976 of the heavies removal column. Expansion device 974 may be, as an example only, a JT valve.

New Stuff Below

In the system of FIG. 20, indicated in general at 1000, a natural gas stream 1010 enters the system 1000 and is expanded by expansion turbine 1012. The resulting expanded stream 1013 enters a heavy hydrocarbon removal (HHC) unit or system 1014.

Stream 1013 enters heavy hydrocarbon removal system (HHC) heat exchanger 1016, where it is cooled and partially condensed into stream 1018. Stream 1018 enters separation device 1022 which results in a liquid stream 1024 that is directed to heavy hydrocarbon removal (HHC) column 1026. A vapor stream 1028 exits separation device 1022 and is cooled in heat exchanger 1016, with the resulting cooled stream 1032 also entering HHC column 1026. A liquid stream 1034 exits the HHC column 1026 and is warmed and at least partially vaporized in heat exchanger 1016 with the resulting stream 1036 directed back to the HHC column. Side draw stream 1038 exits the HHC column and is cooled in heat exchanger 1016 with the resulting two-phase stream 1042 directed back to separation device 1044. A resulting liquid stream is pumped via pump 1046 back to column 1026 for use as reflux. Vapor stream 1048 exits separation device 1048 and joins vapor stream 1052 exiting the top of column 1026. The resulting combined vapor stream 1054 is warned in the heat exchanger 1016, and the resulting warmed vapor stream 1056 exits heat exchanger 1016 and the Heavy Hydrocarbon Removal Unit 1014.

Vapor stream 1056 is compressed in first compressor 1058 which may be powered by expansion turbine 1012. The resulting compressed vapor stream 1062 is further compressed in second compressor 1064 with the resulting stream 1066 being directed to liquefaction system 1070. The resulting liquid stream 1072 is expanded via expansion device 1074 (such as a turbine) and directed to end flash and separation vessel 1076. Liquid natural gas product stream 78 exits the bottom of vessel 1076 and is pumped via pump 1082 to storage tank 1084 which dispenses to a tanker ship 1086 (or truck).

Boil-off gas stream 1092 is joined by boil-off gas streams from the storage tank 1084 and the tanker ship 1086 via line 1094. The combined boil-off gas stream 1096 is directed to boil-off gas suction separation device 1098. The liquid stream 1102 from the boil-off gas suction separation device 1098 is pumped back to the recycle separation device 1076 via pump 1104. The vapor stream 1106 from the boil-off gas suction separation device 1098 is directed to a BOG compressor system where it is compressed by first boil-off gas compressor 1108 and then cooled by first after-cooler 1110. The resulting stream is then compressed by second boil-off gas compressor 1112 and then cooled by second after-cooler 1114. A first portion 1116 of the stream exiting the second after-cooler 1114 is directed to a liquid petroleum (LP) fuel gas skid 1117 (that includes a scrubber and heating), while a second portion is directed to boil-off gas (BOG) recycle line 1118. Bypass line 1119, as determined by the setting of valve 1121, directs BOG from line 1096 around the BOG compressor system so that it may rejoin the stream exiting second after-cooler 1114.

BOG recycle line/stream 1118 is directed back to the HHC unit 1014 and is split into streams 1122 and 1124. Stream 1122 is directed to the HHC column 1026 as a stripping gas. Stream 1124 joins the expanded natural gas feed stream 1013 prior to entry into the HHC heat exchanger 1016.

A heavy hydrocarbon liquid stream 1126 exits the bottom of HHC column 1026 (and thus the HHC unit 1014), and is directed to a condensate stabilization system 1128, which directs a liquid petroleum gas stream 1132 back to compressed natural gas stream 1066 and a natural gas light component stream 1134 and stabilized condensate stream 1136 to LP fuel gas skid 1117. A liquid petroleum/LP stream 1136 exits the LP fuel zas skid 1138 for further use, processing or storage.

Please note that the BOG recycle stream 1118 may enter streams of the heavy hydrocarbon removal unit other than feed stream 1013 and as a stripping gas stream 1122. Such alternative system configurations are illustrated in FIGS. 21 and 22, described below.

In the system of FIG. 21, indicated in general at 2000, the BOG recycle line/stream 2118 is directed back to the HHC unit 2014 and joins the expanded natural gas feed stream 2013 prior to entry into the HHC heat exchanger 2016. A stream 2222 also branches off of line/steam 2013 prior to the HHC heat exchanger 2016 and is directed to the HHC column 2026 as a stripping gas.

In the system of FIG. 22, indicated in general at 3000, the BOG recycle line/stream 3118 is directed through the liquefier 3070 where it is cooled and then expanded via Joule-Thomson expansion valve 3224. The resulting expanded stream 3226 is directed so as to join the liquid stream exiting pump 3104, where the resulting combined stream joins the expanded natural gas stream exiting expansion turbine 3074 prior to entry into end flash and separation vessel 3076.

While the preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the appended clams.