SYSTEM AND METHOD FOR IMPROVING PROPANE RECOVERY AND ETHANE REJECTION IN A GSP/ EXPANDER SYSTEM

A system and method for enhancing propane recovery in a GSP system operated in an ethane rejection mode using an add-on system comprising a heat exchanger and a condenser and optionally a reflux column having 0-5 theoretical stages. An overhead stream from a GSP fractionation column and a subcooled expanded GSP stream are diverted from the typical GSP process for processing in the add-on system to provide an additional reflux stream that increases the amount of ethane and propane that feeds into a top level of the GSP fractionation column. In ethane rejection mode, the add-on system results in an NGL product stream preferably comprising less than 6% of the ethane and at least 97% of the propane from the GSP feed stream.

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Description
BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to a system and method for separation of natural gas liquid (NGL) components from natural gas streams processed through NGL extraction methods, such as a modified gas subcooled/expander process (GSP/expander process or simply GSP), in an ethane rejection mode with enhanced propane recovery.

2. Description of Related Art

Various NGL extraction techniques, including the GPS process, are known in the prior art with differing equipment and/or operational requirements depending on whether the operator wants to recover or reject ethane in the NGL product stream. The economics associated with ethane in NGL product streams have varied over time and by geographic location. Many facilities in operation today operate in ethane rejection mode (reducing the amount of ethane in the NGL product stream and increasing the amount of ethane in the residue gas stream) because an operator could lose up to $0.10 for each gallon of ethane in the NGL product stream. This adds up to significant revenue loss, making it desirable to improve upon rejection methods to reduce the amount of ethane in the NGL product stream and increase the amount of ethane in the residue stream. Additionally, propane is significantly more profitable in the NGL product stream than in the residue gas stream, so it is advantageous to increase propane recovery.

A prior art GSP process is disclosed in U.S. Pat. No. 4,157,904. As shown in FIG. 4 of the '904 patent, a cooled feed stream is separated into a vapor stream and a liquid stream in a separator. For a lean feed stream (comprising around 5.5% ethane in the example in the '904 patent), a first portion of the vapor stream is mixed with the entirety of the liquid stream and the mixed stream is subcooled through heat exchange with an overhead stream from a fractionation column (a demethanizer or deethanizer column) and then expanded. The subcooled, expanded stream (or GSP stream) then feeds into an upper level of the GSP fractionation column as a reflux stream. A second portion of the vapor stream is expanded through a turboexpander before feeding into a mid-level of the fractionation column. The fractionation column separates these streams into the overhead stream (which becomes the residue gas stream) and a bottoms stream (which is the NGL stream). For richer feed streams, the '904 patent discloses splitting the liquid stream as shown in FIG. 5 of the '904 patent. A first portion of the liquid stream is combined with the first portion of the vapor stream prior to subcooling, with the combined stream being subcooled and expanded to form the GSP stream that feeds into an upper level of the fractionation column. A second portion of the liquid stream is expanded and then feeds into a mid to lower level of the GSP fractionation column. The feed stream in a GSP process is cooled prior to the feed stream entering the separator, typically through heat exchange with the fractionation column overhead stream and a side stream withdrawn from a lower level of the fractionation column.

Prior art GSP processes may be used in either an ethane recovery or ethane rejection mode; however, its fundamental thermodynamic limitations during ethane rejection cause it to lose significant volumes of valuable propane. When operated in full rejection mode, GSP processes can lose between 5% to 15% of the propane. It is most desirable to recover that propane in the NGL stream. The GSP stream that feeds into an upper level of the fractionation column in prior art GSP systems (at around tray 5, as the highest feeding stream for incoming vapor) typically comprises around 27% of the total ethane and around 33% of the total propane that feeds into fractionation column 17 from the primary fractionation column feeds in an ethane rejection mode for a lean feed stream comprising around 5% ethane. The GSP system shown in FIG. 1 has been modified from the original '904 patent to show modifications made by industry from the time of introduction of the technology. The purpose of FIG. 1 is to provide a typical and modern GSP system where the new technology according to preferred embodiments of the invention is to be applied.

It is known in the prior art to integrate enhanced propane recovery with ethane rejection into a GSP system. For example, U.S. Pat. Nos. 9,637,428 and 10,551,118 teach an add-on column that can be integrated into a GSP system. In the '428 patent, the add-on column comprises a rectifying section and a separation section to achieve internal heat and mass transfer within a single piece of equipment. As shown in FIG. 4 and Table IV of the '428 patent, the prior art GSP system is modified by adding column (117), by combining all of the separator bottoms stream with a part of the separator overhead stream to form the sub-cooled, expanded GSP stream (36b) which is diverted to feed into column 117 (rather than fractionation column 17 as it would normally in operation of the prior art GSP system), and by not feeding a portion of the separator bottoms stream (38a) into a lower tray location of the fractionation column 17. The overhead stream (39) from the fractionation column (17, operated as a deethanizer at a pressure of around 402 psi) is also fed into the add-on column (117) to allow for heat and mass transfer between streams (36b and 39) through direct contact in the add-on column (117). The overhead stream (151) from the add-on column (17) is then processed as the fractionation column overhead stream would normally be processed in a GSP system to become the residue gas stream. The bottoms stream (152) from the add-on column (17), which contains around 40-45% of the total propane the primary fractionation column feed streams (152a and 37a), is then fed into an upper level of the fractionation column (17) as the highest fractionation column feed stream. The bottom stream from the fractionation column is the NGL product stream. According to the example of FIG. 4 of the '428 patent operated in ethane rejection mode, the addition of the add-on column results in ethane recovery in the NGL stream of around 0.92% and propane recovery of around 99.65% (around 3% higher than the prior art process of FIG. 2 in the '428 patent) for a lean feed stream comprising around 4% ethane. The operating pressure of the fractionation column in this example was 402 psi and the residue gas compression requirement for this example is 5,565 HP.

The '118 patent also discloses more complex embodiments of the add-on column (117) compared to the column in the '428 patent. In the '118 patent, the add-on column (as shown in FIG. 8 for example) has a heat exchange section, a heat and mass transfer section, and absorbing section, and a separation section all in a single piece of equipment. Unlike the '428 patent, the '118 patent does not involve heat and mass transfer of the sub-cooled, expanded GSP stream (36b) and fractionation column overhead stream (39) fed in the add-on column (117). The sub-cooled, expanded GSP stream (36b) passes through a heat exchanger housed inside add-on column 117 to exchange heat with stream 151a, which is either a portion of the overhead stream (153) from the add-on column (117, as in FIG. 7) or a portion of the overhead stream (39) from the fractionation column (17, as in FIG. 9). Exiting stream 36c is combined with the bottoms stream (154) from the add-on column to form a feed stream (155) that feeds into a top of the fractionation column (17). The overhead stream (39) from the fractionation column (17) feeds into the add-on column (117). The overhead stream (153) from the add-on column (117), or a portion of that overhead stream, is processed as the fractionation column overhead stream would normally be processed in a GSP system to become the residue gas stream.

In another embodiment in the '118 patent that is more similar to the '428 patent, the subcooled GSP stream (36a) passes through a heat exchanger housed inside add-on column 117 to exchange heat with rising vapors inside add-on column 117, exiting as cooled and substantially condensed stream 151a (as shown in FIG. 8). Stream 115a is then expanded through expansion valve 23 to become stream 151b (at a temperature of around −140 F), which feeds into add-on column 117 for heat and mass transfer with the fractionation column overhead stream (39). Stream 151b is similar to the sub-cooled, expanded stream 36b in a normal GSP operation except that it has undergone an additional heat exchange inside add-on column 117 prior to being expanded and it contains all of the separator (11) bottoms stream (33), rather than only a portion. In this embodiment, the bottoms stream (154) from the add-on column feeds into a top of the fractionation column (17), which is operated at a pressure of around 344 psia. The overhead stream (39) from the fractionation column (17) feeds into the add-on column (117). The overhead stream (153) from the add-on column (117) is processed as the fractionation column overhead stream would normally be processed in a GSP system to become the residue gas stream. According to the example of FIG. 8 of the '118 patent operated in ethane rejection mode, the addition of the add-on column results in ethane recovery in the NGL stream of around 0.6% and propane recovery of around 99.91% for a lean feed stream comprising around 8.5% ethane. A rich feed stream generally contains more than 10% ethane and a corresponding increase in propane and heavier components. The operating pressure of the fractionation column in this example was 344 psia and the residue gas compression requirement for this example is 11,656 HP.

One of the issues with prior art GSP systems is that the subcooled expanded GSP stream that feeds to the top of the fractionation column as a reflux stream frequently has essentially the same composition as the feed gas. The add-on column in the systems of the '428 and '118 patents improve upon prior art GSP systems by creating a reflux stream to the top of the fractionation column that is compositionally different from the feed stream and the turbo-expanded stream. Additionally, of the total amount of ethane fed into a GSP system fractionation column in ethane rejection mode, more ethane (around 70% of the column feed) feeds into the mid-column location as part of the turbo-expanded stream 37a than feeds into the upper part of the column as part of the subcooled expanded GSP stream (as shown in '118 patent, Table II and '428 patent, Table II). With the add-on column in the '428 and '118 patents, that amount is split approximately equally between the turbo-expanded stream that feeds into the mid-fractionation column location and the bottoms stream from the add-on column that feeds into the top of the fractionation column (as shown in '118 patent, Tables III and VI and '428 patent, Table IV). For feed streams that are lean, comprising 3.98-8.44% ethane, the '428 and '118 patents can achieve very low ethane recoveries of <1% and high propane recoveries of 98.46-99.91%. These results are around 5.5-10% more propane recovery than in the GSP systems. While the '428 and '118 patents can achieve high propane recovery in ethane rejection mode, the add-on columns in these patents are relatively expensive and complex pieces of equipment.

There is still a need for systems and methods that can more efficiently reject ethane with enhanced propane recovery in the NGL product stream that can be easily added onto existing NGL extraction systems, such as an existing GSP system, and that are effective for rich feed streams, preferably while reducing the amount of propane (total MMSCFD or total lbmol/hr) fed into a top or an upper level of the fractionation column in the NGL extraction system and preferably without involving direct heat exchange and/or mass transfer between the subcooled expanded stream (or GSP stream in a GSP system) that feeds into the fractionation column and the fractionation column overhead stream.

SUMMARY OF THE INVENTION

Systems and methods disclosed herein facilitate the economically efficient rejection of ethane in NGL product streams with enhanced propane recovery by modifying a prior art NGL extraction systems with an add-on system that acts as a reflux system for a fractionation column in the NGL extraction system and changes in certain process flows from the NGL extraction system to incorporate the add-on system. Preferred embodiments of an add-on system may be integrated into an existing NGL extraction system or may be incorporated into a newly built NGL extraction system, as will be understood by those of ordinary skill in the art. The add-on systems and methods are particularly useful with a GSP system and the parameters discussed herein are primarily directed to use with such a system; however, those of ordinary skill in the art will understand that the add-on system and method can also be used with other NGL extraction systems and methods. References herein to the GSP system, fractionation column in the GSP system, specific streams in the GSP system, and the GSP stream (or similar wording) may be substituted with references to other NGL extraction systems, a fractionation column in such other NGL extraction systems, corresponding or similar specific streams in the NGL extraction systems, and a subcooled expanded stream that feeds into the fractionation column in such other NGL extraction systems as will be understood by those of ordinary skill in the art.

According to one preferred embodiment of the invention, an add-on system comprises a heat exchanger and a condenser as separate pieces of equipment from each other and external to a fractionation column used in the GSP system. At least a first portion of a separator overhead stream and a fractionation column overhead stream are preferably diverted from the GSP system to the add-on system to pass through the add-on system heat exchanger. The first portion of the separator overhead stream is warmed through heat exchange with the overhead stream from the fractionation column, which is cooled. The warmed stream then feeds into the fractionation column, preferably at an upper level of the column below the top feed location. The cooled stream then feeds into the add-on system condenser, where it is separated into a condenser overhead stream and a condenser bottoms stream. The condenser overhead stream is then returned to the GSP system for heat exchange with other process streams (in the same manner as the fractionation column overhead stream would normally be processed in the GSP system) and for compression to become the residue gas stream. The condenser bottoms stream is also returned to the GSP system to feed into the fractionation column as a top feed reflux stream. The fractionation column bottoms stream is the NGL product stream. According to another preferred embodiment, the add-on system further comprises a first pump to pump the condenser bottoms stream to the top of the fractionation column.

According to another preferred embodiment, the first portion of the separator overhead stream is a subcooled expanded GSP stream (or “GSP stream”). The GSP stream passes through a heat exchanger in the GSP system (for heat exchange with the add-on condenser overhead stream) and then an expansion valve in the GSP system prior to passing through the add-on heat exchanger.

According to another preferred embodiment, an add-on system comprises a heat exchanger, a condenser, and a reflux column. Most preferably, each of these are separate pieces of equipment from each other and external to the fractionation column used in the GSP system. At least a first portion of a separator overhead stream and a fractionation column overhead stream are preferably diverted from the GSP system to the add-on system. The first portion of the separator overhead stream passes through the add-on system heat exchanger, where it is warmed through heat exchange with an overhead stream from the reflux column, which is cooled. The warmed stream then feeds into the fractionation column, preferably at an upper level of the column. The cooled stream then feeds into the add-on system condenser, where it is separated into a condenser overhead stream and a condenser bottoms stream. The condenser overhead stream is then returned to the GSP system for heat exchange with other process streams (in the same manner as the fractionation column overhead stream would normally be processed in the GSP system) and compression to become the residue gas stream. The condenser bottoms stream feeds into a top level of the reflux column and the fractionation column overhead stream feeds into a bottom level of the reflux column. The fractionation column bottoms stream is the NGL product stream. According to another preferred embodiment, the add-on system further comprises a first pump to pump the condenser bottoms stream to the top of the reflux column and a second pump to pump the reflux column bottoms stream to the top of the fractionation column. According to another preferred embodiment, the reflux column comprises 0 to 5 theoretical stages.

According to another preferred embodiment, a first portion of a separator bottoms stream in the GSP system is not mixed with the first portion of the separator overhead stream prior to heat exchange in the GSP system or prior to feeding into the fractionation column. The first portion of the bottoms stream and first portion of the overhead stream both pass through a heat exchanger in the GSP system as separate streams for heat exchange with the add-on condenser overhead stream to cool the separator streams. The cooled first portion of the bottoms stream then feeds into a top level of the fractionation column. According to another preferred embodiment, an add-on system also further comprises an expansion valve for expanding the cooled first portion of the bottoms stream prior to feeding into the fractionation column.

According to another preferred embodiment, a second portion of the separator overhead stream is expanded in a turboexpander prior to feeding into the fractionation column, preferably at an upper-mid level of the column. According to another preferred embodiment, the turbo-expanded stream feeds into the fractionation column at the same level as the warmed first portion of the separator overhead stream returning from the add-on system.

According to another preferred embodiment, a second portion of the separator bottoms stream is expanded through a valve before feeding into the fractionation column, preferably at a mid to upper-mid level of the column lower than the turboexpanded second portion of the separator overhead stream and lower than the warmed first portion of the separator overhead stream.

According to still other preferred embodiments, the add-on systems further comprise various components necessary to connect the equipment in the add-on systems to components of a typical GSP system to allow for flow of process streams between the two systems.

According to another preferred embodiment, there is no direct contact heat and/or mass transfer between the first portion of the separator overhead stream (or the subcooled expanded GSP stream) and the GSP fractionation column overhead stream in any components of an add-on systems used with a GSP system. According to another preferred embodiment, the first portion of the separator overhead stream (or the subcooled expanded GSP stream) does not feed into the reflux column. In still other preferred embodiments, the first portion of the separator overhead stream (or the subcooled expanded GSP stream) only enters an add-on system for indirect heat exchange with either the fractionation column overhead stream or the reflux column overhead stream and there is no mass transfer between the first portion of the separator overhead stream and any other process streams in the add-on system or GSP system prior to that stream feeding into the fractionation column. According to another preferred embodiment, the first portion of the separator overhead stream (or the subcooled expanded GSP stream) only undergoes mass transfer inside the fractionation column.

Add-on systems and methods according to preferred embodiments operated in ethane rejection mode have the advantage of limiting the total amount of propane (in MMSCFD or lbmol/hr) that feeds into a top or an upper level of the GSP fractionation column. Most preferably, with an add-on system according to a preferred embodiment, the amount of propane feeding into a top level of fractionation column 17 is preferably around 1-20% of the amount of propane in the feed stream, more preferably around 2-10%, and most preferably around 3-6%. This is an improvement over prior art systems that feed around 30% or more of the propane from the feed stream into a top or upper level of the GSP fractionation column.

Add-on systems and methods according to preferred embodiments operated in ethane rejection mode also have the advantage of increasing the percentage of total ethane and propane in the primary fractionation column feed streams that feed into the top/upper level of the GSP fractionation column. Most preferably, with an add-on system according to a preferred embodiment, the amount of propane feeding into a top level of fractionation column 17 is preferably around 3-7% of total amount of propane in the primary fractionation column feed streams and the amount of ethane feeding into a top level of fractionation column 17 is preferably around 25-35% of total amount of ethane in the primary fractionation column feed streams. This is an improvement over prior art systems that feed around 45-50% of the total propane and around 50-60% of the total ethane in the primary fractionation column feed streams to the top/upper level of the column.

Add-on systems and methods according to preferred embodiments operated in an ethane rejection mode are capable of minimizing the amount of ethane in the NGL product stream, with ethane recoveries of around 8% or less, more preferably 6% or less, while increasing propane recoveries to at least 97%, more preferably at least 98%, and most preferably at least 99% of the propane from the feed stream. Even lower ethane recoveries of around 1 to 2% are achievable with add-on systems and methods according to preferred embodiments, while still achieving a propane recovery of 95% or more. For leaner feed streams, even better results are achievable with add-on systems according to preferred embodiments. When compared to a GSP system operated under the same parameters and conditions, the amount of ethane recovery (when operated in rejection mode) is maintained at around 5-7% and the amount of propane recovered is increased by around 7 to 9% when an add-on system according to a preferred embodiment is used.

Add-on systems and methods according to preferred embodiments operated in an ethane rejection mode are also capable of reducing power requirements compared to a typical GSP system operated without an add-on system. The primary power use for the base GSP system (such as in FIG. 1) is in the amount of recompression required to compress the residue gas stream up the desired pressure level to be injected into a gas pipeline. The use of the add-on system reduces the amount of vapor, by nature of the recovered propane and so the amount of compression HP is reduced accordingly.

These improvements are achieved by using the add-on system as a “reflux system” to provide a reflux stream to the top of the fractionation column (demethanizer) without the cost of an external refrigeration source. When operating in ethane rejection mode, the desire is to minimize the methane, while maximizing the propane, in the lower sections of the fractionation column. In order to achieve a preferred maximum ethane recovery of around 5.5% with use of an add-on system, additional heat must be added to the bottom of the fractionation column (demethanizer) in the GSP section in order to reject ethane from the NGL product stream. However, heat that is added to the bottom of the fractionation column results in propane boiling off (becoming vapor that rises to the upper sections of the tower) and also increases the temperature in the upper sections of the tower, which contributes to lower propane recoveries in conventional GSP designs operated in ethane rejection mode without an add-on system according to the invention, as more propane is exiting as vapor with the column overhead stream. To off-set the effects of the added heat on the upper sections of the tower and increase propane recovery, the column overhead stream is diverted to feed into an add-on system, which then supplies a reflux stream to the top of the fractionation column. The boil-off of the propane is effectively the target of recondensation using the add-on system. The propane is reliquefied in the add-on system condenser or reflux column and fed back into the upper section of the tower (preferably at tray or stage 1, which is the same feed location as the liquid streams from the GSP section separator that is upstream of the fractionation column) as the reflux stream. Additionally, with an add-on system, heavier components (C3+) are extracted from the fractionation column feed streams in the GSP section resulting in a leaner overhead vapor stream (lower C3+) from the fractionation column compared to the composition of the fractionation overhead stream in the same GSP system operated without an add-on system. That leaner overhead stream serves as a feed stream to the add-on system condenser or reflux column, resulting in the reflux stream that gets recycled back to feed the top of the fractionation column. By providing cooling to the upper section of the fractionation column, which changes the composition of vapor and liquid, the add-on system provides a more efficient separation of ethane and propane components, allowing for more propane to exit the fractionation column as liquid and hence, increasing the overall propane recovery.

BRIEF DESCRIPTION OF THE DRAWINGS

The system and method of the invention are further described and explained in relation to the following drawings wherein:

FIG. 1 is a process flow diagram illustrating principal processing stages of a GSP system without an add-on system according to an embodiment of the invention;

FIG. 2 is a process flow diagram illustrating principal processing stages of a preferred embodiment of an add-on system and method according to the invention incorporated into the embodiment of a GSP system of FIG. 1;

FIG. 3 is a process flow diagram illustrating principal processing stages of another preferred embodiment of an add-on system and method according to the invention incorporated into the embodiment of a GSP system of FIG. 1.

 DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, the basic processing stages of a GSP system 110 is shown. GSP system 110 is similar to FIG. 5 of the '904 patent except for differences in feed stream cooling upstream of the separator and that the first portion of the liquid bottoms stream from the separator is not combined with the first portion of the overhead vapor stream; rather, those streams separately pass through the subcooler heat exchanger 12. The separate cooled streams also separately pass through expansion valves 21, 25 prior to feeding into the fractionation column 17.

The parameters discussed herein are with respect to typical operation of a GSP system 110 in ethane rejection mode for a rich feed stream 31, comprising 10% or more ethane and 5% or more propane, although leaner feed streams may also be used with system 110 and with add-on systems 120 and 220 discussed below. In use of GSP system 110, the feed stream 31 is preferably split into a first portion 31a and a second portion 31b for different heat exchange treatment prior to being separated in separator 11. Preferably, around 30-40% and more preferably around 35% of the flow from stream 31 is sent to stream 31a, with the balance to stream 31b.

Stream 31a passes through heat exchanger 13, where it is cooled through heat exchange with an overhead stream 39a from a fractionation column 17, exiting as stream 31d. Stream 31b passes through heat exchanger 22T, which is a tube side of a shell and tube type heat exchanger disposed internally to fractionation column 17 in a mid-lower section of the column, with the column 17 acting as the shell side of the heat exchanger (although 22T is shown in FIG. 1 as external to column 17). In this way, stream 31b is cooled through heat exchange with cold fluid internal to the fractionation column 17. This aids in cooling this portion of the feed stream and in adding heat to a lower section of column 17. Stream 31b exits heat exchanger 22T as stream 31c. Alternatively, a side stream may be withdrawn from fractionation column 17 to pass through a heat exchanger comprising 22T and a shell side that is external to column 17, with the side stream returning to column 17 after exchanging heat with stream 31b. Streams 31c and 31d are preferably mixed in mixer 24 to form stream 31e, which is then further cooled in heat exchanger 26T through heat exchange with an external refrigerant, preferably propane, exiting as stream 31f. Stream 31f is then separated in separator 11 into overhead stream 32 and bottoms stream 38. Splitters 46 and 19 split those streams into streams 36 and 37 and streams 38a and 38c, respectively.

Preferably in system 110, separator overhead stream 32 is split into a first portion stream 36 and a second portion stream 37, with at least 60% of the flow from stream 32 being sent to stream 37, more preferably at least 65% of the flow from stream 32 being sent to stream 37. Additionally, bottoms stream 38 is preferably split into a first portion stream 38c and a second portion stream 38a, with at least 95% of the flow from stream 38 being sent to stream 38a, more preferably at least 98% of the flow from stream 38 being sent to stream 38a.

The first portion 38c of bottoms stream 38 is diverted to pass through heat exchanger or subcooler 12, along with the first portion of the separator overhead stream 36. These streams are cooled, exiting as streams 38d and 36a, respectively. An overhead stream 39 from fractionation column 17 also passes through heat exchanger 12, exiting as stream 39a, which then passes through heat exchanger 10. In some prior art GSP systems, the first portion of the separator overhead stream and first portion of the separator bottoms streams would be mixed together prior to passing through the subcooler, with the combined subcooled stream then being expanded in a single expansion valve before feeding into an upper level of fractionation column 17. In system 110, they are preferably kept separate, both streams 38c and 36 passing separately through subcooler 12. Stream 38d is expanded in expansion valve 25 before feeding into a top level of fractionation column 17 as stream 38e. Stream 38e in system 110 feeds into a top level or stage of fractionation column 17 and is the only stream feeding into the column at that location.

Stream 36a is expanded in valve 21 before feeding into an upper level of fractionation column 17 as stream 36b. Stream 36b in system 110 feeds in lower than stream 38e, at around stage or tray 5 as shown in FIG. 1 (although this location may be varied as will be understood by those of ordinary skill in the art). A second portion 37 of overhead stream 32 is expanded through a turboexpander 14 with expanded stream 37a feeding into a mid-upper level of the GSP fractionation column 17, at around stage or tray 7 (although this location may be varied as will be understood by those of ordinary skill in the art). Stream 37a in system 110 feeds fractionation column 17 at a location lower than stream 36b. A second portion 38a of bottoms stream 38 is expanded in valve 16 with exiting expanded stream 38b feeding into a mid-level or slightly higher stage or tray of GSP fractionation column 17, such as around stage or tray 10 as shown in FIG. 1 (although this location may be varied as will be understood by those of ordinary skill in the art). Stream 38b in system 110 feeds fractionation column 17 at a location lower than stream 37a. Streams 38e, 36b, 37a, and 38b are the primary feed streams into fractionation column 17 in system 110. Vapor stream 41 from reboiler 18 also feeds into column 17 as a returning stream but is not considered a primary feed stream.

Very little of the total amount of ethane and propane that feed into fractionation column 17 from primary fractionation column feed streams (streams 38e, 36b, 37a, and 38b) feeds into this top location. Stream 36b, or the combined subcooled, expanded stream in some GSP systems, are referred to as a subcooled expanded GSP stream or “GSP stream”. The GSP stream 36b in system 110 typically comprises substantially more of the total amount of ethane and propane that feed into fractionation column 17 from primary fractionation column feed streams as compared to the top feed stream 38e, but the majority of the ethane and propane that are in the primary fractionation column feed streams are contained in streams 37a and 38b that feed lower than the GSP stream but still in the upper half of the fractionation column 17 in system 110.

GSP fractionation column 17 separates streams 38e, 36b, 37a, and 38a (and returning reboiler stream 41) into an overhead stream 39 and a bottoms stream 42 (NGL product stream). Overhead stream 39 is warmed in subcooler 12, with stream 39a then being further warmed in heat exchanger 13. Stream 39b is then compressed in compressor 15 to become stream 39c, which is further cooled in another heat exchanger (preferably an air cooler) 74 to form the residue gas stream 39d. Stream 39d may be further compressed to meet pipeline specifications. GSP system 110 may have an additional or different separator and additional heat exchange components as will be understood by those of ordinary skill in the art.

Fractionation column 17 in GSP system 110 does not have a condenser, but does have a reboiler 18 to provide an ascending vapor stream 41, with GSP stream 36a and stream 38e providing reflux. For a rich feed stream having 10% or more ethane, a GSP system 110 operated in ethane rejection mode will result in a propane recovery in the NGL stream of less than 92% and an ethane recovery of less than 6%.

Referring to FIG. 2, a preferred embodiment for an add-on system 120 for use with a GSP system, such as system 110, is shown. The primary components of system 120 are shown in the dashed line box and may be added onto any existing GSP system (such as 110) with a few modifications to the process flows for the existing GSP system or included as part of a newly built GSP system to operate the GSP system in an ethane rejection with enhanced propane recovery mode. System 120 preferably comprises an expansion valve 125, heat exchanger 130, a condenser 155, and a pump 199. System 120 also preferably comprises a reboiler 18 for fractionation column 17 and mixers, valves, piping, and other connectors as further described and needed to connect system 120 to GSP system 110. Heat exchanger 130 is preferably a shell and tube type heat exchanger, but other types of heat exchangers such as a plate-fin heat exchanger may also be used. Heat exchanger 130 is preferably external to fractionation column Condenser 155 is preferably external to fractionation column.

In addition to the heat exchanger 130, condenser 155, and pump 199, system 120 involves a few modifications to the stream flows in the typical GSP system 110. First, the GSP stream 36b is diverted to system 120. In GSP system 110, stream 36b would normally feed into an upper level of GSP fractionation column 17 as a reflux stream, but is instead diverted to pass through heat exchanger 130. Stream 36b passes through heat exchanger 130, exiting as warmed stream 36c. Stream 36c feeds into an upper level of fractionation column 17. Most preferably, stream 36c will feed into column 17 at the same stage or tray location as stream 36b would normally feed into column 17 in GSP system 110 (such as around stage or tray 5).

Second, fractionation column overhead stream 39 is also diverted to system 120. In GSP system 110, overhead stream 39 would normally pass through the GSP subcooler 12 and then be further processed as the residue gas stream in GSP system 110, but is instead diverted to pass through heat exchanger 130. In system 120, overhead stream 39 is cooled in heat exchanger 130 through heat exchange with stream 36b, exiting as stream 39a. Stream 39a feeds into condenser 155, where it is separated into a condenser overhead stream 152 and a condenser bottoms stream 154. Overhead stream 152 is then returned to GSP system 110 and processed as fractionation column overhead stream 39 would normally be processed in GSP system 110 (such as shown in FIG. 1). Overhead stream 152 passes through GSP subcooler 12, exiting as stream 152a. Stream 152a then passes through heat exchanger 13, exiting as stream 152b. Stream 152b is then compressed in compressor 15 (preferably part of a turboexpander unit combining expander 14 and compressor 15) to form stream 152c, cooled in cooler 74 to form stream 152d, which is the residue gas stream. Stream 152d may be further compressed as needed to meet pipeline specifications.

Third, turboexpanded stream 37a (a second portion of separator 11 overhead stream 32) preferably feeds into fractionation column 17 at a location slightly higher than it would in system 110. In system 110, the turboexpanded stream 37a feeds below the feed location of subcooled expanded GSP stream 36b. With add-on system 120, stream 37a preferably feeds higher in the fractionation column, most preferably at the same stage as stream 36c.

With use of system 120 according to a preferred embodiment, fractionation column 17 utilizes condenser 155 to provide an additional reflux stream 154a. The primary fractionation column feed streams with use of system 120 comprise streams 38e, 154a, 36c, 37a, and 38b. Vapor stream 41 from reboiler 18 also feeds into column 17 as a returning stream but is not considered a primary fractionation column feed stream. Streams 38e and 154a preferably feed into a top level of fractionation column 17. Most preferably, this is around stage or tray 1 as shown in FIG. 2 (although this location may be varied as will be understood by those of ordinary skill in the art). Streams 38e and 154a preferably feed into fractionation column 17 at the same stage or tray level. Streams 37a and 36c preferably feed into an upper level of fractionation column 17, but lower than the feed location of streams 38e and/or 154a. Most preferably, this is around stage or tray 5 as shown in FIG. 2 (although this location may be varied as will be understood by those of ordinary skill in the art). Streams 37a and 36c preferably feed into fractionation column 17 at the same stage or tray level. Stream 38b preferably feeds into fractionation column 17 at a mid-level or slightly higher stage or tray, but lower than the feed level of streams 37a and/or 36c. Most preferably, this is around stage or tray 10 as shown in FIG. 2 (although this location may be varied as will be understood by those of ordinary skill in the art).

For a rich feed stream having 10% or more ethane, a GSP system with system 120 operated in ethane rejection mode will result in a propane recovery in the NGL stream of at least 97%, more preferably between 99-99%, and an ethane recovery of less than 6%. This is substantially more propane recovery and around the same ethane recovery compared to system 110 operated without system 120.

Referring to FIG. 3, another preferred embodiment for an add-on system 220 for use with a GSP system, such as system 110, is shown. The primary components of system 120 are shown in the dashed line box and may be added onto any existing GSP system (such as 110) with a few modifications to the process flows for the existing GSP system or included as part of a newly built GSP system to operate the GSP system in an ethane rejection mode with enhanced propane recovery mode. System 220 is similar to system 120 with the addition of a couple of pieces of equipment and some process flow changes. System 220 preferably comprises a reflux column 250 and a second pump 258. Reflux column 250 is preferably a distillation column that comprises 2 to 5 theoretical stages.

Like system 120, GSP stream 36b from separator 11 is diverted to system 220 to pass through heat exchanger 130 but is warmed through heat exchange with an overhead stream 251 from reflux column 250. Warmed stream 36c then feeds into an upper level of fractionation column 17, preferably around stage or tray 5 and preferably at the same location as stream 37a. Cooled overhead stream 251a exits heat exchanger 130 to feed into condenser 155. Condenser overhead stream 152 returns to GSP system 110 to be processed into the residue gas stream, like in system 120.

Like system 120, overhead stream 39 from fraction column 17 is also diverted to system 220, but feeds into a bottom level of reflux column 250 as an ascending vapor stream in system 220. Condenser bottoms stream 154 is pumped in pump 199, with stream 154a feeding into a top of column 250 as a reflux stream. Column 250 separates streams 39 and 154a into overhead stream 251 and bottoms stream 256. Bottoms stream 256 is then pumped in pump 258, with stream 256a feeding into a top of fractionation column 17, preferably in the same location as previously described for stream 154a in system 120.

With use of system 220 according to a preferred embodiment, fractionation column 17 utilizes reflux column 250 to provide an additional reflux stream 256a. The primary fractionation column feed streams with use of system 220 comprise streams 38e, 256a, 36c, 37a, and 38b. Vapor stream 41 from reboiler 18 also feeds into column 17 as a returning stream but is not considered a primary fractionation column feed stream. Streams 38e and 256a preferably feed into a top level of fractionation column 17. Most preferably, this is around stage or tray 1 as shown in FIG. 3 (although this location may be varied as will be understood by those of ordinary skill in the art). Streams 38e and 256a preferably feed into fractionation column 17 at the same stage or tray level. Streams 37a and 36c preferably feed into an upper level of fractionation column 17, but lower than the feed location of streams 38e and/or 256a. Most preferably, this is around stage or tray 5 as shown in FIG. 3 (although this location may be varied as will be understood by those of ordinary skill in the art). Streams 37a and 36c preferably feed into fractionation column 17 at the same stage or tray level. Stream 38b preferably feeds into fractionation column 17 at a mid-level or slightly higher stage or tray, but lower than the feed level of streams 37a and/or 36c. Most preferably, this is around stage or tray 10 as shown in FIG. 3 (although this location may be varied as will be understood by those of ordinary skill in the art).

For a rich feed stream having 10% or more ethane, a GSP system with system 220 operated in ethane rejection mode will result in a propane recovery in the NGL stream of at least 98%, more preferably at least 99%, and an ethane recovery of less than 6%. This is substantially more propane recovery and around the same ethane recovery compared to system 110 operated without system 220 and is an improvement of at least around 0.5% propane recovery compared to system 120.

Preferred parameters for the various streams in a GSP system 110 (without systems 120 or 220), with add-on system 120, or with add-system 220 with add-on system 220 operated in ethane rejection mode in various examples based on a computer simulation are shown in the table below. The flow rates, temperatures and pressures of various flow streams referred to in connection with the discussion of systems 110 (as shown in FIG. 1, for example), 110 with add-on system 120 (as shown in FIG. 2, for example), or 110 with add-on system 220 (as shown in FIG. 3, for example) and their methods according to preferred embodiments of the invention are for a feed stream 31 having the parameters indicated below when operated in ethane rejection mode. Many of the streams have the same composition, temperature, pressure, and flow rate in systems 110, 120, and 220. For example, feed stream 31 and remixed feed stream 31f are identical in each of the systems 110, 120, and 220. In the Tables below, such identical streams are identified only by their stream number (e.g., 31 and 31f). For streams with differences in composition or physical parameters, the streams will be identified by a stream number followed by a dash and the system number (for example, stream 31d-110 refers to stream 31d in system 110, as shown in FIG. 1 for example; 31d-120 refers to stream 31d in system 120, as shown in FIG. 2 for example).

TABLE 1A Feed & Separator Stream Compositions App Stream No. SEPARATOR SEPARATOR FEED OVERHEAD BOTTOMS 31; 31a; 31b; 31c*; 32; 36; 36a; 36b; 38; 38a; 38b′ 38c; 31d; 31e; 31f 36c*; 37; 37a 38d; 38e Mole Fraction % % % CO2 0.119067 0.116655 0.129949 C1 75.2598 82.00142 44.84021 C2 16.9075 14.15 29.34989 C3 4.34356 2.43354 12.96197 N2 0.46198 0.537606 0.120739 *Stream 36c is only in systems 120 and 220, but the composition of stream 36c is the same in both systems 120 and 220. There is no stream 36c in system 110.

TABLE 1B Feed Stream Properties App Stream No. 31 31f 31a- 110 31a-120 31a-220 Temperature F. 110 −10 110 110 110 Pressure psia 914.2 904.2 914.2 914.2 914.2 Std Vapor Volumetric Flow 220 220 77.02331 77.71973 77.02331 MMSCFD Std Liquid Volumetric Flow 2977.22 2977.22 1042.343 1051.767 1042.343 sgpm Volume Fraction Vapor % 100 93.27717 100 100 100 App Stream No. 31d-110 31d-120 31d-220 31b-110 31b-120 31b-220 Temperature F. −16.3385 −15.714 −15.7546 110 110 110 Pressure psia 909.2 909.2 909.2 914.2 914.2 914.2 Std Vapor Volumetric Flow 77.02331 77.71973 77.02331 142.9767 142.2803 142.9767 MMSCFD Std Liquid Volumetric Flow 1042.343 1051.767 1042.343 1934.878 1925.453 1934.878 sgpm Volume Fraction Vapor % 91.54799 91.7235 91.7122 100 100 100 App Stream No. 31c-110 31c-120 31c-220 31e-110 31e-120 31e-220 Temperature F. 46.93017 46.68355 46.93017 22.07025 21.99856 22.32402 Pressure psia 909.2 909.2 909.2 909.2 909.2 909.2 Std Vapor Volumetric Flow 142.9767 142.2803 142.9767 220 220 220 MMSCFD Std Liquid Volumetric Flow 1934.878 1925.453 1934.878 2977.22 2977.22 2977.22 sgpm Volume Fraction Vapor % 99.42364 99.41375 99.42364 97.87529 97.8689 97.89782

TABLE 1C Separator Stream Properties App Stream No. 32 36 Separator 1st Pt 36a-110 36a-120 36a-220 Overhead Sep. OH 1st Pt Sep. OH after Ht. Ex. 12 Temperature F. −10.1901 −10.1901 −66.5611 −71.8719 −72.4734 Pressure psia 901.2 901.2 896.2 896.2 896.2 Std Vapor Volumetric Flow 180.0886 63.03101 63.03101 63.03101 63.03101 MMSCFD Std Liquid Volumetric Flow 2330.782 815.7736 815.7736 815.7736 815.7736 sgpm Volume Fraction Vapor % 100 100 52.56092 0 0 App Stream No. 36b-110 36b-120 36b-220 36c-120* 36c-220* Temperature F. −134.228 −141.243 −141.618 −79.3574 −80.869 Pressure psia 259.2 259.2 259.2 256.7 256.7 Std Vapor Volumetric Flow 63.03101 63.03101 63.03101 63.03101 63.03101 MMSCFD Std Liquid Volumetric Flow 815.7736 815.7736 815.7736 815.7736 815.7736 sgpm Volume Fraction Vapor % 96.32393 94.82031 94.70466 99.44199 99.40683 App Stream No. 37 37a 2nd Pt Expanded 38 38c Sep. 2nd Pt Separator 1st Pt 38d-110 38d-120 38d-220 OH Sep. OH Bottoms Sep. Bt. 1st Pt Sep. Bt. After Ht. Ex. 12 Temperature F. −10.1901 −91.929 10.1901 −10.1901 −66.5611 71.8719 −72.4734 Pressure psia 901.2 264.2 901.2 901.2 896.2 896.2 896.2 Std Vapor Volumetric 117.0576 117.0576 39.91141 0.399114 0.399114 0.399114 0.399114 Flow MMSCFD Std Liquid Volumetric 1515.008 1515.008 646.4387 6.464387 6.464387 6.464387 6.464387 Flow sgpm Volume Fraction Vapor % 100 99.03151 0 0 0 0 0 App Stream No. 38b 38a 2nd Pt Sep. 38e-110 38e-120 38e-220 2nd Pt Sep. Bt. after 1st Pt Sep. Bt. After Valve 25 Bt. Valve 16 Temperature F. −96.0354 −99.0844 −99.4229 −10.1901 −55.5395 Pressure psia 270 270 270 901.2 295 Std Vapor Volumetric Flow 0.399114 0.399114 0.399114 39.5123 39.5123 MMSCFD Std Liquid Volumetric Flow 6.464387 6.464387 6.464387 639.9743 639.9743 sgpm Volume Fraction Vapor % 78.5395 76.72294 76.50051 0 87.69074

TABLE 2 Residue Gas Stream Compositions & Properties App Stream No. 39-110 152-120 152-220 39a-110 152a-120 152a-220 Mole % % % % % % Fraction CO2 0.129108 0.129612 0.129955 0.129108 0.129612 0.129955 C1 81.60633 81.92502 81.93647 81.60633 81.92502 81.93647 C2 17.31578 17.38407 17.41033 17.31578 17.38407 17.41033 C3 0.419447 0.058258 0.020435 0.419447 0.058258 0.020435 N2 0.500937 0.502894 0.502812 0.500937 0.502894 0.502812 Temperature −77.6444 −86.7591 −87.4655 −22.1124 −21.0842 −21.1409 F. Pressure 259.2 256.7 255.7 254.2 251.7 250.7 psia Std Vapor 202.8906 202.1014 202.1395 202.8906 202.1014 202.1395 Volumetric Flow MMSCFD Std Liquid 2623.475 2608.216 2608.505 2623.475 2608.216 2608.505 Volumetric Flow sgpm Volume 100 100 100 100 100 100 Fraction Vapor % App Stream No. 39b-110 152b-120 152b-220 39c-110 152c-120 152c-220 Mole % % % % % % Fraction CO2 0.129108 0.129612 0.129955 0.129108 0.129612 0.129955 C1 81.60633 81.92502 81.93647 81.60633 81.92502 81.93647 C2 17.31578 17.38407 17.41033 17.31578 17.38407 17.41033 C3 0.419447 0.058258 0.020435 0.419447 0.058258 0.020435 N2 0.500937 0.502894 0.502812 0.500937 0.502894 0.502812 Temperature 70.75666 72.77007 71.96429 107.5476 109.6963 108.9145 F. Pressure 249.2 246.7 245.7 314.8249 311.537 310.3687 psia Std Vapor 202.8906 202.1014 202.1395 202.8906 202.1014 202.1395 Volumetric Flow MMSCFD Std Liquid 2623.475 2608.216 2608.505 2623.475 2608.216 2608.505 Volumetric Flow sgpm Volume 100 100 100 100 100 100 Fraction Vapor % App Stream No. 39d-110 152d-120 152d-220 Mole Fraction % % % CO2 0.129108 0.129612 0.129955 C1 81.60633 81.92502 81.93647 C2 17.31578 17.38407 17.41033 C3 0.419447 0.058258 0.020435 N2 0.500937 0.502894 0.502812 Temperature F. 120 120 120 Pressure psia 309.8249 306.537 305.3687 Std Vapor 202.8906 202.1014 202.1395 Volumetric Flow MMSCFD Std Liquid 2623.475 2608.216 2608.505 Volumetric Flow sgpm Volume Fraction 100 100 100 Vapor %

TABLE 3 NGL Stream Compositions & Properties App Stream No. 42-110 42-120 42-220 42a-110 42a-120 42a-220 Mole Fraction % % % % % % CO2 3.48E−08 3.54E−08 3.55E−08 3.48E−08 3.54E−08 3.55E−08 C1 1.47E−11 1.67E−11 1.67E−11 1.47E−11 1.67E−11 1.67E−11 C2 12.06591 11.52629 11.52502 12.06591 11.52629 11.52502 C3 50.8774 52.73076 52.82937 50.8774 52.73076 52.82937 N2 0 0 0 0 0 0 Temperature F. 133.9615 133.8675 133.7856 138.242 138.1809 138.1 Pressure psia 263.2 263.2 263.2 485.8282 485.8282 485.8282 Std Vapor 17.1094 17.89865 17.94827 17.1094 17.89865 17.94827 Volumetric Flow MMSCFD Std Liquid 353.7453 369.0044 369.9491 353.7453 369.0044 369.9491 Volumetric Flow sgpm Volume 0 0 0 0 0 0 Fraction Vapor %

TABLE 4 Fractionation Column Overhead Stream Compositions & Properties App Stream No. 39-110 39-120 39-220 39a-110 39a-120 From To: From Frac. From Ht. Ex. From Frac. From Frac. Col. 17 to From Ht. Ex. 130 to Col. 17 to Ht. Col. 17 to Ht. Reflux Col. 12 to Ht. Condenser Ex. 12 Ex. 130 150 Ex. 13 155 Mole Fraction % % % % % CO2 0.129108 0.132626 0.130547 0.129108 0.132626 C1 81.60633 76.91818 76.72986 81.60633 76.91818 C2 17.31578 22.29479 22.42056 17.31578 22.29479 C3 0.419447 0.191522 0.255104 0.419447 0.191522 N2 0.500937 0.46078 0.461667 0.500937 0.46078 Temperature F. −77.6444 −74.3206 −73.3153 −22.1124 −86.7591 Pressure psia 259.2 259.2 259.2 254.2 256.7 Std Vapor Volumetric 202.8906 222.0842 221.4263 202.8906 222.0842 Flow MMSCFD Std Liquid Volumetric 2623.475 2942.67 2936.869 2623.475 2942.67 Flow sgpm Volume Fraction Vapor 100 100 100 100 99.31145 %

TABLE 5 Condenser Stream Compositions & Properties App Stream No. 152-120 152-220 154-120 154-220 154a-120 154a-220 Condenser Overhead Condenser Bottoms Pumped Condenser to Ht. Ex. 12 to Pump 154 Bottoms Mole Fraction % % % % % % CO2 0.129612 0.129955 0.163112 0.164625 0.163112 0.164625 C1 81.92502 81.93647 26.2804 26.43721 26.2804 26.43721 C2 17.38407 17.41033 71.96045 72.81567 71.96045 72.81567 C3 0.058258 0.020435 1.539314 0.547151 1.539314 0.547151 N2 0.502894 0.502812 0.034856 0.035051 0.034856 0.035051 Temperature F. −86.7591 −87.4655 −86.7591 −87.4655 −86.3084 −87.4655 Pressure psia 256.7 255.7 256.7 255.7 300 300 Std Vapor Volumetric 202.1014 202.1395 19.98289 20.27466 19.98289 20.27466 Flow MMSCFD Std Liquid Volumetric 2608.216 2608.505 334.4544 338.9904 334.4544 338.9904 Flow sgpm Volume Fraction Vapor 100 100 0 0 0 0 %

TABLE 6 Reflux Column Stream Compositions & Properties App Stream No. 251a-220 251-220 Cooled Reflux 256-220 256a-220 Reflux Col. Col. Overhead Reflux Col. Pumped Reflux Overhead to Ht. from Ht. Ex. 130 Bottoms to Col. Bottoms to Ex. 130 to Condenser 155 Pump 258 Frac. Col. 17 Mole Fraction % % % % CO2 0.133116 0.133116 0.136753 0.13997 C1 76.87731 76.87731 22.1607 22.3411 C2 22.46093 22.46093 74.9285 74.92857 C3 0.068449 0.068449 2.717671 2.534219 N2 0.460173 0.460173 0.030434 0.030439 Temperature F. −75.86343 −87.4655 −74.4297 −74.9655 Pressure psia 258.2 255.7 259.2 285 Std Vapor Volumetric 222.4142 222.4142 19.28551 19.37453 Flow MMSCFD Std Liquid Volumetric 2947.495 2947.495 328.3438 329.5982 Flow sgpm Volume Fraction Vapor 100 99.30527 0 0 %

TABLE 7A Primary Fractionation Column Feeds - Top of Column App Stream No. 38e-110 38e-120 38e-220 154a-120 256a-220 1st pt 1st pt 1st pt Condenser Reflux Col. of Sep BT. of Sep BT. of Sep BT. BT. BT. Mole Fraction % % % % % CO2 0.129949 0.129949 0.129949 0.163112 0.13997 C1 44.84021 44.84021 44.84021 26.2804 22.3411 C2 29.34989 29.34989 29.34989 71.96045 74.92857 C3 12.96197 12.96197 12.96197 1.539314 2.534219 N2 0.120739 0.120739 0.120739 0.034856 0.030439 Temperature F. −96.0354 −99.0844 −99.4229 −86.3084 −74.9655 Pressure psia 270 270 270 300 285 Std Vapor 0.399114 0.399114 0.399114 19.98289 19.37453 Volumetric Flow MMSCFD Std Liquid 6.464387 6.464387 6.464387 334.4544 329.5982 Volumetric Flow sgpm Volume Fraction 78.5395 76.72294 76.50051 0 0 Vapor %

TABLE 7B Primary Fractionation Column Feeds - Upper Feed App Stream No. 36b-110 1st pt of 36c-120 36c-220 Sep OH 1st pt of Sep 1st pt of Sep 37a-110* 37a-120* 37a-220* (GSP OH after Ht OH after Ht 2nd pt Sep 2nd pt Sep 2nd pt Sep stream) Ex 130 Ex 130 OH OH OH Mole Fraction % % % % % % CO2 0.116655 0.116655 0.116655 0.116655 0.116655 0.116655 C1 82.00142 82.00142 82.00142 82.00142 82.00142 82.00142 C2 14.15 14.15 14.15 14.15 14.15 14.15 C3 2.43354 2.43354 2.43354 2.43354 2.43354 2.43354 N2 0.537606 0.537606 0.537606 0.537606 0.537606 0.537606 Temperature −134.228 −79.3574 −80.869 −91.929 −91.929 −91.929 F. Pressure psia 259.2 256.7 256.7 264.2 264.2 264.2 Std Vapor 63.03101 63.03101 63.03101 117.0576 117.0576 117.0576 Volumetric Flow MMSCFD Std Liquid 815.7736 815.7736 815.7736 1515.008 1515.008 1515.008 Volumetric Flow sgpm Volume 96.32393 99.44199 99.40683 99.03151 99.03151 99.03151 Fraction Vapor % *Stream 37a in system 110 preferably feeds into fractionation column 17 at a lower stage or tray location than GSP stream 36b; however, with use of systems 120 or 220, stream 37a preferably feeds into column 17 at the same location or level as stream 36c, which is higher than 37a would normally feed into column 17 in system 110.

TABLE 7C Percentage Total C1, C2, and C3 in Primary Fractionation Column Feeds System 110 System 120 System 220 Total C1 fed in Primary Fractionation Col. Feed 330.785 170.823 169.900 Streams (MMSCFD) % of Total C1 Feed to Top Tray/Stage 50.000 3.179 2.653 % of Total C1 Feed to Upper Tray/Stage (5-7) 44.644 86.449 86.919 % of Total C1 Feed to Upper Tray/Stage (10) 5.356 10.372 10.428 Total C2 fed in Primary Fractionation Col. Feed 37.196 51.576 51.714 Streams (MMSCFD) % of Total C2 Feed to Top Tray/Stage 0.315 28.108 28.299 % of Total C2 Feed to Upper Tray/Stage (5-7) 68.508 49.407 49.276 % of Total C2 Feed to Upper Tray/Stage (10) 31.177 22.485 22.425 Total C3 fed in Primary Fractionation Col. Feed 9.556 9.863 10.047 Streams (MMSCFD) % of Total C3 Feed to Top Tray/Stage 0.541 3.643 5.402 % of Total C3 Feed to Upper Tray/Stage (5-7) 45.862 44.432 43.621 % of Total C3 Feed to Upper Tray/Stage (10) 53.596 51.925 50.977

TABLE 8 Percentage C2 & C3 Recovered in NGL Streams System 110 System 120 System 220 % C2 Recovered 5.550 5.5464 5.561 % C3 Recovered 91.094 98.768 99.227

TABLE 9 Energy Streams Energy Stream From Block To Block System 110 System 120 System 220 Energy Rate Btu/Hr Q-1 — Reboiler 18 1.94654E+07 1.94896E+07 1.95303E+07 Q-2 Ht. Ex. 22T Fractionation 1.48000E+07 1.48000E+07 1.48000E+07 Col. 17 Q-3 Ht. Ex. 26T — 1.83141E+07 1.82762E+07 1.84478E+07 Q-5 Ht. Ex./Air — −2.88552E+06  −2.37964E+06  −2.55342E+06  Cooler 74 Power Hp Q-4 — NGL Pump 43 84.11 87.88 88.10 Q-Exp Expander 14 Compressor 15 2796.25 2796.25 2796.25 Q-7 — Condenser N/A 7.86 8.13 Pump 199 Q-8 — Reflux Col. N/A N/A 5.32 Pump 258

It will be appreciated by those of ordinary skill in the art that the values in the Tables above are based on the particular parameters and composition of the feed stream 31 in the computer simulation Examples of operating systems 110, 120, and 220. The values will differ depending on the parameters and composition of the feed stream 31, the particular type of GSP system used upstream of systems 120 or 220 (if different from system 110), and the operational parameters for systems 110, 120, and 220 as will be understood by those of ordinary skill in the art.

As can be seen in these Examples, by adding a heat exchanger 130 and condenser 155 in add-on system 120 or by adding a heat exchanger 130, condenser 155, and reflux column 250 in add-on system 220, significantly more propane is recovered compared to system 110 with a relatively small increase in energy/power requirements. System 120 and 220 achieve these results by altering the feeds into the fractionation column 17 in several key ways: (1) stream 36c in systems 120 and 220 feeds into column 17 at a temperature range of −70 to −90° F., more preferably −75 to −85° F., which is significantly warmer than stream 36b feeds into column 17 at a temperature range of −130 to −140° F.; (2) less than 10% and more preferably less than 5% of the total methane in the primary column feed streams is fed into the top stage/tray location in systems 120 and 220, which is significantly less than the 45%-55% in system 110; and (3) the percentage of the total amount of ethane and total amount of propane in in the primary column feed streams that feeds into the top stage/tray location in systems 120 and 220 is significantly higher than in system 110. The addition of reflux stream 154a in system 120 and reflux stream 256a in system 220 aids in increasing the amounts of these components fed higher in the column as compared to system 110 without an add-on system. In systems 120 and 220, preferably around 25-35%, more preferably around 27-30%, of the total ethane in the primary fractionation column feed streams feeds into the top of the column, whereas less than 1% feeds into the top of the column in system 110. In systems 120 and 220, preferably around 2-7%, more preferably around 3-6%, of the total propane in the primary fractionation column feed streams feeds into the top of the column, whereas less than 1% feeds into the top of the column in system 110. Use of systems 120 or 220 according to preferred embodiments aids in increasing the amounts of both ethane and propane fed into a top level of fractionation column 17, allowing more propane to be recovered than when GSP system 110 is operated without add-on systems 120 or 220 without significant change in the ethane recovery.

Comparing the streams of systems 120 and 220 to a prior art example, the total amount of propane fed into the top of column 17 is actually reduced, even when the amount of propane in feed stream 31 is increased. Referring to Example 4 in the '428 patent, stream 152a in Example 4 feeds the fractionation column at the highest level of all fractionation column feed streams and contains 112 lbmol/hr propane, based on a feed stream (stream 31) flow rate of 13,726 lbmol/hr containing 1.7% propane (and 3.98% ethane). Stream 152a feeds into an upper level of fractionation column 17 in the '428 patent, which appears to be below the top level (around tray 5), but the specific level for the example is not stated. In contrast, the total amount of propane fed into the top level of fractionation column 17 in system 120 is 39.45 lbmol/hr and in system 220 is 59.59 lbmol/hr, both based on an example having a feed stream (stream 31) flow rate of 24,155.6 lbmol/hr containing 4.34% propane (and 16.9% ethane). This is both a higher feed flow rate and higher percentages of propane and ethane compared to the '428 patent, but the resulting amount of propane in lbmol/hr feeding into the top of column 17 is substantially reduced by around 45-65%. This data is shown in Table 10 below.

TABLE 10 Comparison to Example 4 of ′428 Patent Streams Feeding Top/Upper Column System 110 System 120 System 220 428 Ex. 4 Stream 38e lbmol/hr Propane 5.680194 5.680194 5.680194 NA Stream 256a lbmol/hr Propane NA 33.77386 NA NA Stream 154a lbmol/hr Propane NA NA 53.91015 NA Stream 152a lbmol/hr Propane NA NA NA 112 Total lbmol/hr Propane to 5.680194 39.45405 59.59034 112 Top/Upper Column Reduction (%) in lbmol/hr 94.9284 64.77317 46.79434 propane compared to ′428 Patent Feed Stream 31 Total lbmol/hr 24115.6 24115.6 24115.6 13726 Percentage of Feed Total Flow 0.023554 0.163604 0.247103 0.81597 Rate as Propane to Top/Upper Column Feed Stream 31 Propane lbmol/hr 1047.476 1047.476 1047.476 233 Percentage of Feed Propane 0.542275 3.766585 5.688948 48.06867 Flow Rate as Propane to Top/Upper Column

When using an add-on system 120 or 220, the amount of propane (in MMSCFD or lbmol/hr) feeding into a top level of fractionation column 17 is preferably around 1-20% of amount of propane in the feed stream, more preferably around 2-10%, and most preferably around 3-6%, when the feed stream is a rich stream comprising at least 10% ethane and 5% propane. For leaner feeds, these amounts will be further reduced.

A preferred method for processing a feed stream in an ethane rejection mode in a GSP system (preferably system 110) modified with add-on components, preferably an add-on system 120 according to a preferred embodiment of the invention, comprises the following steps: (1) separating the feed stream in a separator into a separator overhead stream and a separator bottoms stream; (2) splitting the separator overhead stream into a first portion and a second portion; (3) splitting the separator bottoms stream into a first portion and a second portion; (4) separating a plurality of fractionation column feed streams into a fractionation column overhead stream and a fractionation column bottoms stream in a fractionation column; (5) separating the fractionation overhead stream into a condenser overhead stream and a condenser bottoms stream in a condenser; (6) cooling at least a first part of the feed stream in a first heat exchanger through heat exchange with the condenser overhead stream prior to feeding the first part of the feed stream into the separator; (7) cooling a first part of the separator overhead stream and a first part of the separator bottoms stream in a second heat exchanger through heat exchange with the condenser overhead stream prior to the condenser overhead stream undergoing heat exchange in the first heat exchanger; (8) expanding the cooled first part of the separator overhead stream (after the second heat exchanger); (9) warming the first part of the separator overhead stream (after expanding in step 8) in a third heat exchanger through heat exchange with a stream that feeds into the condenser after heat exchange in the third heat exchanger; (10) expanding the first part of the separator bottoms stream (after the second heat exchanger); (11) expanding a second portion of the separator overhead stream, preferably in a turboexpander; and (12) expanding a second part of the separator bottoms stream. The fractionation column feed streams preferably comprises the primary fractionation column feed streams and stream recycled from a reboiler. The primary fractionation column feed streams preferably comprise: (a) the condenser bottoms stream; (b) the first part of the separator bottoms stream after expansion in step 10; (c) the first part of the separator overhead stream after the heat exchange in step 9; (d) the second part of the separator overhead stream after expansion in step 11; and (e) the second part of the separator bottoms stream after expansion in step 12. Primary fractionation column feed streams (a) and (b) preferably feed into a top level of the fractionation column; streams (c) and (d) preferably feed into an upper level of the fractionation column, but preferably lower than the top feed level, and stream (e) to a mid-to-upper level of the fractionation column. The stream that feeds into the condenser in step 9 is the fractionation column overhead stream. The fractionation column bottoms stream is the NGL stream and the condenser overhead stream is the residue gas stream.

Another preferred method for processing a feed stream in an ethane rejection mode in a GSP system (preferably system 110) modified with add-on components, preferably an add-on system 220 according to a preferred embodiment of the invention, comprises the following steps: steps 1-12 above with the following modification to step 5: (5-i) separating the fractionation column overhead stream and a condenser bottoms stream into a reflux column overhead stream and a reflux column bottoms stream in a reflux column and (5-ii) separating the reflux column overhead stream into a condenser overhead stream and a condenser bottoms stream in a condenser. The primary fractionation column feed streams preferably comprise: (a) the reflux column bottoms stream; (b) the first part of the separator bottoms stream after expansion in step 10; (c) the first part of the separator overhead stream after the heat exchange in step 9; (d) the second part of the separator overhead stream after expansion in step 11; and (e) the second part of the separator bottoms stream after expansion in step 12. Fractionation column feed streams (a) and (b) preferably feed into a top level of the fractionation column; streams (c) and (d) preferably feed into an upper level of the fractionation column, but preferably lower than the top feed level, and stream (e) to a mid-to-upper level of the fractionation column. The stream that feeds into the condenser in step 9 is the reflux column overhead stream. The fractionation column bottoms stream is the NGL stream and the condenser overhead stream is the residue gas stream.

The method also preferably comprises the following steps: (13) splitting the feed stream into the first part and a second part; (14) cooling the second part of the feed stream through heat exchange with streams preferably internal to a lower portion of the fractionation column (although a withdrawn stream external to the fractionation column may also be used); (15) mixing the first part and the second part of the feed stream after heat exchange in steps 6 and 14; (16) cooling the mixed feed stream from step 15 in a feed stream heat exchanger with external refrigeration and prior to feeding the cooled, mixed stream into the separator for separation in step 1; (17) compressing the condenser overhead stream after heat exchange in step 6; and (18) further cooling the condenser overhead stream after compression in step 17, preferably with an air cooler. After step 18, the condenser overhead stream may be further processed, including additional compression, as needed to meet pipeline or end use specifications.

The source of feed gas stream 31 is not critical to the systems and methods of the invention; however, natural gas drilling and processing sites with flow rates of 20 to 300 MMSCFD and containing up to 25% ethane and 15% propane are particularly suitable. Where present, it is generally preferable for purposes of the present invention to remove as much of the water vapor, carbon dioxide, and other contaminants from feed stream 31 prior to processing with systems GSP system 110 and add-on system 120 or 220 Methods for removing water vapor, carbon dioxide, and other contaminants are generally known to those of ordinary skill in the art and are not described herein. This type of pretreatment would normally be done with any of these GSP systems even without using an add-on system and is not a special requirement of using add-on system 120 or 220.

The specific operating parameters described with examples herein are based on the specific computer modeling and feed stream parameters set forth above. These parameters and the various composition, pressure, and temperature values described above will vary depending on the feed stream parameters as will be understood by those of ordinary skill in the art. As used herein, “ethane rejection mode” refers to processing a natural gas stream operated in a specific method to decrease the amount of ethane recovered from the feed stream in the NGL product stream, while still maximizing the amount of propane and heavier hydrocarbons in the NGL product stream. In ethane rejection mode, the systems and methods according to preferred embodiments of the invention are configured to recover less than 10%, preferably less than 8%, and most preferably less than 6% of the ethane from the feed stream in the NGL product stream, while preferably still recovering 96% or more, preferably 98% or more, and most preferably 99% or more of the propane from the feed stream in the NGL product stream.

Heat exchangers as described herein and shown in the figures are preferably a single heat exchanger in which all streams shown in the figures simultaneously pass through so that certain stream(s) are cooled and other stream(s) are warmed through heat exchange between the passing streams. Most preferably, only the streams shown on the figures pass through any particular heat exchanger and no other streams undergo heat exchange with that set of streams in any particular heat exchanger. Although other heat exchange configurations and multiple heat exchangers may be used to achieve the heat exchange described herein, most preferably the heat exchange is specifically limited as shown in the figures, with the heat exchange shown being the only heat exchange between given streams prior to or after various processing equipment. For example, streams 36, 38c, and 152 are preferably the only streams that pass through heat exchanger 12 and all of these streams preferably pass simultaneously through a single heat exchanger 12; with stream 38e not undergoing any other heat exchange with other process streams or external refrigeration or heat sources between separator 11 and fractionation column 17; with stream 36 not undergoing any other heat exchange with other process streams or external refrigeration or heat sources between separator 11 and heat exchanger 130; and with stream 152 not undergoing any other heat exchange with other process streams or external refrigeration or heat sources between condenser 155 and heat exchanger 13. Any change in temperature of a stream while flowing through piping from one piece of equipment to another piece of equipment as a result of a differential between the temperature of the stream and the ambient air temperature surrounding the piping, without more, is not considered heat exchange for purposes of the invention.

All numerical values indicated as a percentage being “at least” X means the range of X % to 100% and value indicates as percentage being “less than” X means the range of 0% to X %. All numerical values herein indicated as a range (including as “at least” or “less than”) include each individual value or ratio within those ranges and any and all subset combinations within ranges, including subsets that overlap from one preferred range to a more preferred range. Any operating parameter, step, process flow, or equipment indicated as preferred or preferable herein may be used alone or in any combination with other preferred/preferable features. Any component or processing step described herein with respect to any one preferred embodiment of an add-on system may be used with any other embodiment of an add-on system, even if not specifically described with such embodiment, unless it is specifically described as excluded for use with such embodiment. Other alterations and modifications of the invention will likewise become apparent to those of ordinary skill in the art upon reading this specification in view of the accompanying drawings, and it is intended that the scope of the invention disclosed herein be limited only by the broadest interpretation of the appended claims to which the inventor is legally entitled.

Claims

1. A propane recovery system for increasing propane recovery in an NGL stream produced from a feed stream comprising methane, ethane, and propane in a GSP system operated in an ethane rejection mode, the GSP system comprising a fractionation column to separate a plurality of fractionation column feed streams comprising (1) a first stream comprising a subcooled expanded first part of a separator overhead stream, (2) a second stream comprising a subcooled expanded first part of a separator bottoms stream, (3) a third stream comprising an expanded second part of the separator overhead stream, and (4) a fourth stream comprising an expanded second part of the separator bottoms stream into a fractionation column overhead stream and a fractionation column bottoms stream;

the propane recovery system comprising:
a first heat exchanger to warm the first stream through heat exchange with a first set of streams prior to the first stream feeding into the fractionation column;
a condenser for separating a condenser feed stream into a condenser overhead stream and a condenser bottoms stream;
wherein the second stream feeds into a top level of the fractionation column;
wherein the third stream and the warmed first stream feed into an upper level of the fractionation column below where the second stream feeds into the fractionation column;
wherein the fourth stream feeds into a mid-to-upper level of the fractionation column;
wherein the NGL stream comprises less than 6% of the ethane in the feed stream and more than 98% of the propane in the feed stream.

2. The propane recovery system of claim 1 wherein the first set of streams comprises the fractionation column overhead stream and wherein the condenser feed stream comprises the fractionation column overhead stream after passing through the first heat exchanger.

3. The propane recovery system of claim 1 wherein the first set of streams consists of the fractionation column overhead stream and wherein the condenser feed stream consists of the fractionation column overhead stream after passing through the first heat exchanger.

4. The propane recovery system of claim 2 wherein the feed stream comprises 10% or more ethane.

5. The propane recovery system of claim 2 wherein the plurality of fractionation column feed streams further comprises the condenser bottoms stream, which feeds into a top level of the fractionation column.

6. The propane recovery system of claim 1 further comprising a reflux column for separating the fractionation column overhead stream and the condenser bottoms stream into a reflux column overhead stream and a reflux column bottoms stream, wherein the reflux column has 0 to 5 theoretical stages.

7. The propane recovery system of claim 6 wherein the first set of streams comprises the reflux column overhead stream and wherein the condenser feed stream comprises the reflux column overhead stream after passing through the first heat exchanger.

8. The propane recovery system of claim 6 wherein the first set of streams consists of the reflux column overhead stream and wherein the condenser feed stream consists of the reflux column overhead stream after passing through the first heat exchanger.

9. The propane recovery system of claim 7 wherein the feed stream comprises 10% or more ethane.

10. The propane recovery system of claim 7 wherein the plurality of fractionation column feed streams further comprises the reflux column bottoms stream, which feeds into a top level of the fractionation column.

11. A method for increasing propane recovery in an NGL stream produced from a feed stream comprising methane, ethane, and propane in a GSP system operated in an ethane rejection mode, the method comprising:

(1) separating the feed stream in a separator into a separator overhead stream and a separator bottoms stream;
(2) splitting the separator overhead stream into a first portion and a second portion;
(3) splitting the separator bottoms stream into a first portion and a second portion;
(4) separating a plurality of fractionation column feed streams into a fractionation column overhead stream and a fractionation column bottoms stream in a fractionation column;
(5) separating a condenser feed stream into a condenser overhead stream and a condenser bottoms stream in a condenser;
(6) cooling at least a first part of the feed stream in a first heat exchanger through heat exchange with the condenser overhead stream prior to separating the first part of the feed stream step 1;
(7) cooling a first part of the separator overhead stream and a first part of the separator bottoms stream in a second heat exchanger through heat exchange with the condenser overhead stream in a second heat exchanger prior to the condenser overhead stream undergoing heat exchange in the first heat exchanger in step 6;
(8) expanding the first part of the separator overhead stream after cooling in the second heat exchanger;
(9) warming the first part of the separator overhead stream after expanding in step 8 in a third heat exchanger through heat exchange with a first set of streams;
(10) expanding the first part of the separator bottoms stream after heat exchange in the second heat exchanger in step 6;
(11) expanding a second portion of the separator overhead stream;
(12) expanding a second part of the separator bottoms stream;
wherein the plurality of fractionation column feed streams comprise: (a) the first part of the separator bottoms stream after expanding in step 10; (b) the first part of the separator overhead stream after the heat exchange in step 9; (c) the second part of the separator overhead stream after expanding in step 11; and (d) the second part of the separator bottoms stream after expanding in step 12.

12. The method for increasing propane recovery of claim 11 wherein the first set of streams in step 9 comprises the fractionation column overhead stream and wherein the condenser feed stream comprises the fractionation column overhead stream after heat exchange in step 9.

13. The method of increasing propane recovery of claim 11 wherein the first set of streams in step 9 consists of the fractionation column overhead stream and wherein the condenser feed stream consists of the fractionation column overhead stream after heat exchange in step 9.

14. The method of increasing propane recovery of claim 12 wherein the feed stream comprises 10% or more ethane.

15. The method of increasing propane recovery of claim 12 wherein the plurality of fractionation column feed streams further comprises the condenser bottoms stream.

16. The method of increasing propane recovery of claim 11 further comprising: (13) separating the fractionation column overhead stream and the condenser bottoms stream into a reflux column overhead stream and a reflux column bottoms stream in a reflux column, wherein the reflux column has 0 to 5 theoretical stages.

17. The method of increasing propane recovery of claim 16 wherein the first set of streams in step 9 comprises the reflux column overhead stream and wherein the condenser feed stream comprises the reflux column overhead stream after heat exchange in step 9.

18. The method of increasing propane recovery of claim 16 wherein the first set of streams in step 9 consists of the reflux column overhead stream and wherein the condenser feed stream consists of the reflux column overhead stream after heat exchange in step 9.

19. The method of increasing propane recovery of claim 17 wherein the feed stream comprises 10% or more ethane.

20. The method of increasing propane recovery of claim 17 wherein the plurality of fractionation column feed streams further comprises the reflux column bottoms stream.

Patent History
Publication number: 20240318910
Type: Application
Filed: Mar 22, 2023
Publication Date: Sep 26, 2024
Inventor: Rayburn C. Butts (Midland, TX)
Application Number: 18/124,795
Classifications
International Classification: F25J 3/02 (20060101);