Hydrocarbon gas processing

Abstract

A process and an apparatus are disclosed for a compact processing assembly to improve the recovery of C.sub.2 (or C.sub.3) and heavier hydrocarbon components from a hydrocarbon gas stream. The preferred method of separating a hydrocarbon gas stream generally includes producing at least a substantially condensed first stream and a cooled second stream, expanding both streams to lower pressure, and supplying the streams to a fractionation tower. In the process and apparatus disclosed, the tower overhead vapor is directed to an absorbing means and a heat and mass transfer means inside a processing assembly. The outlet vapor from the processing assembly is compressed to higher pressure and cooled, then a portion is substantially condensed in a heat exchange means inside the processing assembly, expanded to lower pressure, and supplied to the heat and mass transfer means to provide cooling. Condensed liquid from the absorbing means is fed to the tower.

Claims

1. An apparatus for the separation of a gas stream containing methane, C.sub.2 components, C.sub.3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C.sub.2 components, C.sub.3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in said apparatus there being (a) one or more inlet gas heat exchangers and one or more inlet dividers to cool said gas stream under pressure, thereby producing a substantially condensed first stream, and a cooled second stream; (b) a first expansion device connected to receive said substantially cooled first stream under pressure and expand said substantially condensed first stream to a lower pressure, whereby said first stream is further cooled, thereby forming an expanded further cooled first stream; (c) a distillation column connected to said first expansion device to receive said expanded further cooled first stream at a top feed position, with said distillation column producing at least an overhead vapor stream and a bottom liquid stream; (d) a second expansion device connected to receive said cooled second stream under pressure and expand said cooled second stream to said lower pressure, thereby forming an expanded second stream; (e) said distillation column further connected to said second expansion device to receive said expanded second stream at a mid-column feed position; (f) a heater connected to said distillation column to receive and heat said overhead vapor stream, thereby forming a heated gas stream; (g) a compressor connected to said heater to receive and compress said heated gas stream to a higher pressure, thereby forming a compressed gas stream; (h) a cooler connected to said compressor to receive and cool said compressed gas stream, thereby forming a cooled compressed gas stream that is thereafter discharged as said volatile residue gas fraction; and (i) said distillation column adapted to fractionate at least said expanded further cooled first stream and said expanded second stream at said lower pressure whereby the components of said relatively less volatile fraction are recovered in said bottom liquid stream; wherein said apparatus further includes (1) an absorbing section comprising one or more packed beds and trays, wherein said absorbing section is housed in a single equipment item processing assembly and connected to said distillation column to receive and contact said overhead vapor stream with a condensed stream, thereby condensing less volatile components in said overhead vapor stream and forming a partially rectified vapor stream; a rectifying section providing simultaneous heat transfer selected from one or more of a fin and tube type exchanger, a plate type exchanger, a brazed aluminum type exchanger and other type of heat transfer device with said rectifying section housed in said single equipment item processing assembly and connected to said absorbing section to receive said partially rectified vapor stream from an upper region of said absorbing section, whereby said partially rectified vapor stream is cooled while simultaneously condensing the less volatile components in said partially rectified vapor stream, thereby forming a further rectified vapor stream and said condensed stream, said rectifying section being further connected to said absorbing section to direct said condensed stream to said absorbing section (3) a first combiner connected to said rectifying section to receive said further rectified vapor stream and a heated flash expanded stream and form a combined stream; (4) an additional heat exchanger selected from one or more of a fin and tube type exchanger, a plate type exchanger, a brazed aluminum type exchanger, and other type of heat transfer device connected to said first combiner to receive and heat said combined stream forming a heated combined stream; (5) said heater being adapted to be connected to said additional heater to receive and further heat said heated combined stream, thereby forming said heated gas stream; (6) an additional divider connected to said cooler to receive and divide said cooled compressed gas stream into a recycle stream and said volatile residue gas fraction; (7) said additional heat exchanger further connected to said additional divider means to receive and cool said recycle stream to substantial condensation, thereby to supply at least a portion of the heating of step (4) and forming a substantially condensed stream; (8) a third expansion device connected to said additional heat exchanger to receive and expand said substantially condensed stream to said lower pressure, thereby forming a flash expanded stream; (9) said rectifying section further connected to said third expansion device to receive and heat said flash expanded stream, thereby to supply the cooling of step (2) and forming said heated flash expanded stream; (10) said additional heat exchanger further connected to said one or more inlet gas heat exchangers and said at least one or more inlet dividers to receive and further cool under pressure said substantially condensed first stream, thereby to supply at least a portion of the heating of step (4) and forming a further cooled substantially condensed first stream; (11) said first expansion device being adapted to connect to said additional exchanger to receive and expand said further cooled substantially condensed first stream to said lower pressure, thereby forming said expanded further cooled first stream; (12) a second combiner connected to said absorbing section and to said first expansion device to receive a distillation liquid stream from a lower region of said absorbing means and said expanded further cooled first stream and form a combined feed stream, said second combiner being further connected to said distillation column to supply said combined feed stream at said top feed position of said distillation column; and said distillation column being adapted to fractionate at least said combined feed stream and said expanded second stream at said lower pressure whereby the components of said relatively less volatile fraction are recovered in said bottom liquid stream.

2. The apparatus according to claim 1 wherein (1) said one or more inlet gas heat exchangers is adapted to cool said gas stream under pressure sufficiently to be partially condensed, thereby forming a partially condensed gas stream; (2) a separator is connected to said one or more inlet gas heat exchangers to receive and separate said partially condensed gas stream into a vapor stream and at least one liquid stream; (3) said at least one inlet dividers is connected to said feed separating means and adapted to receive and divide said vapor stream into at least said first stream and said cooled second stream; (4) said one or more inlet gas heat exchangers is connected to said at least one inlet dividers and adapted to receive and cool said first stream sufficiently to substantially condense said first stream, thereby forming said substantially condensed first stream; (5) said second expansion device is connected to said at least one inlet dividers and adapted to receive and expand said cooled second stream to said lower pressure, thereby forming said expanded second stream; and (6) said distillation column is adapted to fractionate at least said combined feed stream, said expanded second stream, and said expanded liquid stream at said lower pressure whereby the components of said relatively less volatile fraction are recovered in said bottom liquid stream.

3. The apparatus according to claim 2 wherein (1) said at least one inlet dividers is adapted to divide said vapor stream into at least a further vapor stream and said second cooled stream; (2) a vapor-liquid combiner is connected to said at least one inlet dividers and to said separator to receive said further vapor stream and at least a portion of said at least one liquid stream and form said first stream; (3) said one or more inlet gas heat exchangers is connected to said vapor-liquid combiner and adapted to receive and cool said first stream sufficiently to be substantially condensed, thereby forming said substantially condensed first stream; and (4) said fourth expansion means is adapted to receive and expand any remaining portion of said at least one liquid stream to said lower pressure, whereupon said expanded liquid stream is supplied to said distillation column at said lower mid-column feed position.

4. The apparatus according to claim 1 wherein said additional heat exchanger is housed in said processing assembly.

5. The apparatus according to claim 2 wherein said additional heat exchanger is housed in said processing assembly.

6. The apparatus according to claim 3 wherein said additional heat exchanger is housed in said processing assembly.

7. The apparatus according to claim 1, 2, or 3 wherein (1) a pump is connected to said absorbing section to receive and pump said distillation liquid stream from said lower region of said absorbing section to an intermediate pressure, thereby forming a pumped distillation liquid stream; and (2) said second combiner is adapted to be connected to said pump and to said first expansion device to receive said pumped distillation liquid stream and said expanded further cooled first stream and form said combined feed stream.

8. The apparatus according to claim 7 wherein said pump is housed in said processing assembly.

Description

(1) For a better understanding of the present invention, reference is made to the following examples and drawings. Referring to the drawings:

(2) FIGS. 1 and 2 are flow diagrams of prior art natural gas processing plants in accordance with U.S. Pat. No. 4,157,904 or 4,278,457;

(3) FIGS. 3 and 4 are flow diagrams of natural gas processing plants adapted to use the process of co-pending application Ser. No. 15/332,723;

(4) FIG. 5 is a flow diagram of a natural gas processing plant adapted to use the present invention; and

(5) FIGS. 6 through 11 are flow diagrams illustrating alternative means of application of the present invention to a natural gas processing plant.

(6) In the following explanation of the above figures, tables are provided summarizing flow rates calculated for representative process conditions. In the tables appearing herein, the values for flow rates (in moles per hour) have been rounded to the nearest whole number for convenience. The total stream rates shown in the tables include all non-hydrocarbon components and hence are generally larger than the sum of the stream flow rates for the hydrocarbon components. Temperatures indicated are approximate values rounded to the nearest degree. It should also be noted that the process design calculations performed for the purpose of comparing the processes depicted in the figures are based on the assumption of no heat leak from (or to) the surroundings to (or from) the process. The quality of commercially available insulating materials makes this a very reasonable assumption and one that is typically made by those skilled in the art.

(7) For convenience, process parameters are reported in both the traditional British units and in the units of the Système International d'Unités (SI). The molar flow rates given in the tables may be interpreted as either pound moles per hour or kilogram moles per hour. The energy consumptions reported as horsepower (HP) and/or thousand British Thermal Units per hour (MBTU/Hr) correspond to the stated molar flow rates in pound moles per hour. The energy consumptions reported as kilowatts (kW) correspond to the stated molar flow rates in kilogram moles per hour.

DESCRIPTION OF THE PRIOR ART

(8) FIG. 1 is a process flow diagram showing the design of a processing plant to recover C.sub.2+ components from natural gas using prior art according to U.S. Pat. No. 4,157,904 or U.S. Pat. No. 4,278,457. In this simulation of the process, inlet gas enters the plant at 120° F. [49° C.] and 815 psia [5,617 kPa(a)] as stream 31. If the inlet gas contains a concentration of sulfur compounds which would prevent the product streams from meeting specifications, the sulfur compounds are removed by appropriate pretreatment of the feed gas (not illustrated). In addition, the feed stream is usually dehydrated to prevent hydrate (ice) formation under cryogenic conditions. Solid desiccant has typically been used for this purpose.

(9) The feed stream 31 is cooled in heat exchanger 10 by heat exchange with cool residue gas (stream 39a), pumped liquid product at 20° F. [−7° C.] (stream 42a), demethanizer reboiler liquids at 0° F. [−18° C.] (stream 41), demethanizer side reboiler liquids at −45° F. [−43° C.] (stream 40), and propane refrigerant. Stream 31a then enters separator 11 at −29° F. [−34° C.] and 795 psia [5,479 kPa(a)] where the vapor (stream 32) is separated from the condensed liquid (stream 33).

(10) The vapor (stream 32) from separator 11 is divided into two streams, 34 and 37. The liquid (stream 33) from separator 11 is optionally divided into two streams, 35 and 38. (Stream 35 may contain from 0% to 100% of the separator liquid in stream 33. If stream 35 contains any portion of the separator liquid, then the process of FIG. 1 is according to U.S. Pat. No. 4,157,904. Otherwise, the process of FIG. 1 is according to U.S. Pat. No. 4,278,457.) For the process illustrated in FIG. 1, stream 35 contains about 15% of the total separator liquid. Stream 34, containing about 30% of the total separator vapor, is combined with stream 35 and the combined stream 36 passes through heat exchanger 12 in heat exchange relation with the cold residue gas (stream 39) where it is cooled to substantial condensation. (In this context, “combining” is simply mixing together two or more streams by joining the piping or conduits containing the separate streams into a single pipe or conduit, most commonly with a piping toe, as shown in FIG. 3) The resulting substantially condensed stream 36a at −158° F. [−106° C.] is then flash expanded through expansion valve 13 to the operating pressure (approximately 168 psia) of fractionation tower 17. During expansion a portion of the stream is vaporized, resulting in cooling of the total stream. In the process illustrated in FIG. 1, the expanded stream 36b leaving expansion valve 13 reaches a temperature of −176° F. [−115° C.] and is supplied to separator section 17a in the upper region of fractionation tower 17. The liquids separated therein become the top feed to demethanizing section 17b.

(11) The remaining 70% of the vapor from separator 11 (stream 37) enters a work expansion machine 14 in which mechanical energy is extracted from this portion of the high pressure feed. The machine 14 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expanded stream 37a to a temperature of approximately −126° F. [−88° C.]. The typical commercially available expanders are capable of recovering on the order of 80-85% of the work theoretically available in an ideal isentropic expansion. The work recovered is often used to drive a centrifugal compressor (such as item 15) that can be used to re-compress the residue gas (stream 39b), for example. The partially condensed expanded stream 37a is thereafter supplied as feed to fractionation tower 17 at an upper mid-column feed point. The remaining separator liquid in stream 38 (if any) is expanded to the operating pressure of fractionation tower 17 by expansion valve 16, cooling stream 38a to −85° F. [−65° C.] before it is supplied to fractionation tower 17 at a lower mid-column feed point.

(12) The demethanizer in tower 17 is a conventional distillation column containing a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing. As is often the case in natural gas processing plants, the fractionation tower may consist of two sections. The upper section 17a is a separator wherein the partially vaporized top feed is divided into its respective vapor and liquid portions, and wherein the vapor rising from the lower distillation or demethanizing section 17b is combined with the vapor portion of the top feed to form the cold demethanizer overhead vapor (stream 39) which exits the top of the tower. The lower, demethanizing section 17b contains the trays and/or packing and provides the necessary contact between the liquids falling downward and the vapors rising upward. The demethanizing section 17b also includes reboilers (such as the reboiler and the side reboiler described previously and supplemental reboiler 18) which heat and vaporize a portion of the liquids flowing down the column to provide the stripping vapors which flow up the column to strip the liquid product, stream 42, of methane and lighter components.

(13) The liquid product stream 42 exits the bottom of the tower at 7° F. [−14° C.], based on a typical specification of a methane concentration of 0.5% on a volume basis in the bottom product. It is pumped to higher pressure by pump 21 (stream 42a) and then heated to 95° F. [35° C.] (stream 42b) as it provides cooling of the feed gas in heat exchanger 10 as described earlier. The residue gas (demethanizer overhead vapor stream 39) passes countercurrently to the incoming feed gas in heat exchanger 12 where it is heated from −176° F. [−115° C.] to −47° F. [−44° C.] (stream 39a) and in heat exchanger 10 where it is heated to 113° F. [45° C.] (stream 39b). The residue gas is then re-compressed in two stages. The first stage is compressor 15 driven by expansion machine 14. The second stage is compressor 19 driven by a supplemental power source which compresses the residue gas (stream 39d) to sales line pressure. After cooling to 120° F. [49° C.] in discharge cooler 20, the residue gas product (stream 39e) flows to the sales gas pipeline at 765 psia [5,272 kPa(a)], sufficient to meet line requirements (usually on the order of the inlet pressure).

(14) A summary of stream flow rates and energy consumption for the process illustrated in FIG. 1 is set forth in the following table:

(15) TABLE-US-00001 TABLE I (FIG. 1) Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31 17,272 2,734 1,070 657 21,961 32 15,282 1,678 360 76 17,613 33 1,990 1,056 710 581 4,348 34 4,541 499 107 23 5,233 35 298 158 107 87 652 36 4,839 657 214 110 5,885 37 10,741 1,179 253 53 12,380 38 1,692 898 603 494 3,696 39 17,236 90 2 0 17,556 42 36 2,644 1,068 657 4,405 Recoveries* Ethane 96.69% Propane 99.84% Butanes+ 99.99% Power Residue Gas Compression 15,204 HP [24,995 kW] Refrigerant Compression  3,548 HP  [5,833 kW] Total Compression 18,752 HP [30,828 kW] *(Based on un-rounded flow rates)

(16) FIG. 2 is a process flow diagram showing one manner in which the design of the processing plant in FIG. 1 can be adjusted to operate at a lower C.sub.2 component recovery level. This is a common requirement when the relative values of natural gas and liquid hydrocarbons are variable, causing recovery of the C.sub.2 components to be unprofitable at times. The process of FIG. 2 has been applied to the same feed gas composition and conditions as described previously for FIG. 1. However, in the simulation of the process of FIG. 2, the process operating conditions have been adjusted to reject nearly all of C.sub.2 components to the residue gas rather than recovering them in the bottom liquid product from the fractionation tower.

(17) In this simulation of the process, inlet gas enters the plant at 120° F. [49° C.] and 815 psia [5,617 kPa(a)] as stream 31 and is cooled in heat exchanger 10 by heat exchange with cool residue gas stream 39a and flashed separator liquids (stream 38a). (One consequence of operating the FIG. 2 process to reject nearly all of the C.sub.2 components to the residue gas is that the temperatures of the liquids flowing down fractionation tower 17 are much warmer, to the point that side reboiler stream 40 and reboiler stream 41 are too warm to be used to cool the inlet gas, so that all of the column reboil heat must be supplied by supplemental reboiler 18. The pumped bottom product (stream 42a) is also too warm to be used to cool the inlet gas. In the FIG. 2 process, the flashed separator liquids are used in heat exchanger 10 in lieu of the side reboiler liquids in order to provide some cooling of the inlet gas while simultaneously reducing the duty required from supplemental reboiler 18.) Cooled stream 31a enters separator 11 at −14° F. [−26° C.] and 795 psia [5,479 kPa(a)] where the vapor (stream 32) is separated from the condensed liquid (stream 33).

(18) The vapor (stream 32) from separator 11 is divided into two streams, 34 and 37, and the liquid (stream 33) is optionally divided into two streams, 35 and 38. For the process illustrated in FIG. 2, stream 35 contains about 36% of the total separator liquid. Stream 34, containing about 33% of the total separator vapor, is combined with stream 35 and the combined stream 36 passes through heat exchanger 12 in heat exchange relation with the cold residue gas (stream 39) where it is cooled to partial condensation. The resulting partially condensed stream 36a at −72° F. [−58° C.] is then flash expanded through expansion valve 13 to the operating pressure (approximately 200 psia [1,380 kPa(a)]) of fractionation tower 17. During expansion some of the liquid in the stream is vaporized, resulting in cooling of the total stream. In the process illustrated in FIG. 2, the expanded stream 36b leaving expansion valve 13 reaches a temperature of −138° F. [−94° C.] and is supplied to fractionation tower 17 at the top feed point.

(19) The remaining 67% of the vapor from separator 11 (stream 37) enters a work expansion machine 14 in which mechanical energy is extracted from this portion of the high pressure feed. The machine 14 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expanded stream 37a to a temperature of approximately −103° F. [−75° C.] before it is supplied as feed to fractionation tower 17 at an upper mid-column feed point. The remaining separator liquid in stream 38 (if any) is expanded to slightly above the operating pressure of fractionation tower 17 by expansion valve 16, cooling stream 38a to −61° F. [−51° C.] before it is heated to 103° F. [39° C.] in heat exchanger 10 as described previously, with heated stream 40a then supplied to fractionation tower 17 at a lower mid-column feed point.

(20) Note that when fractionation tower 17 is operated to reject the C.sub.2 components to the residue gas product as shown in FIG. 2, the column is typically referred to as a deethanizer and its lower section 17b is called a deethanizing section. The liquid product stream 42 exits the bottom of deethanizer 17 at 137° F. [58° C.], based on a typical specification of an ethane to propane ratio of 0.020:1 on a volume basis in the bottom product. The residue gas (deethanizer overhead vapor stream 39) passes countercurrently to the incoming feed gas in heat exchanger 12 where it is heated from −91° F. [−68° C.] to −29° F. [−34° C.] (stream 39a) and in heat exchanger 10 where it is heated to 103° F. [39° C.] (stream 39b) as it provides cooling as described previously. The residue gas is then re-compressed in two stages, compressor 15 driven by expansion machine 14 and compressor 19 driven by a supplemental power source. After stream 39d is cooled to 120° F. [49° C.] in discharge cooler 20, the residue gas product (stream 39e) flows to the sales gas pipeline at 765 psia [5,272 kPa(a)].

(21) A summary of stream flow rates and energy consumption for the process illustrated in FIG. 2 is set forth in the following table:

(22) TABLE-US-00002 TABLE II (FIG. 2) Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31 17,272 2,734 1,070 657 21,961 32 16,003 1,991 498 120 18,835 33 1,269 743 572 537 3,126 34 5,225 650 163 39 6,149 35 457 268 206 193 1,125 36 5,682 918 369 232 7,274 37 10,778 1,341 335 81 12,686 38/40 812 475 366 344 2,001 39 17,272 2,715 116 8 20,338 42 0 19 954 649 1,623 Recoveries* Propane 89.20% Butanes+ 98.81% Power Residue Gas Compression 15,115 HP [24,849 kW] Refrigerant Compression  3,625 HP  [5,959 kW] Total Compression 18,740 HP [30,808 kW] *(Based on un-rounded flow rates)

DESCRIPTION OF CO-PENDING APPLICATION

(23) Co-pending application Ser. No. 15/332,723 describes one means of improving the performance of the FIG. 1 process to recover more of the C.sub.2 components in the bottom liquid product. FIG. 1 can be adapted to use this process as shown in FIG. 3. The operating conditions of the FIG. 3 process have been adjusted as shown to reduce the methane content of the liquid product to the same level as that of the FIG. 1 process. The feed gas composition and conditions considered in the process presented in FIG. 3 are the same as those in FIG. 1. Accordingly, the FIG. 3 process can be compared with that of the FIG. 1 process.

(24) Most of the process conditions shown for the FIG. 3 process are much the same as the corresponding process conditions for the FIG. 1 process. The main difference is the disposition of substantially condensed stream 36a and column overhead vapor stream 39. In the FIG. 3 process, column overhead vapor stream 39 is divided into two streams, stream 151 and stream 152, whereupon stream 151 is compressed from the operating pressure (approximately 174 psia [1,202 kPa(a)]) of fractionation tower 17 to approximately 379 psia [2,616 kPa(a)] by reflux compressor 22. Compressed stream 151a at −81° F. [−63° C.] and substantially condensed stream 36a at −81° F. [−63° C.] are then directed into a heat exchange means in cooling section 117a of processing assembly 117. This heat exchange means may be comprised of a fin and tube type heat exchanger, a plate type heat exchanger, a brazed aluminum type heat exchanger, or other type of heat transfer device, including multi-pass and/or multi-service heat exchangers. The heat exchange means is configured to provide heat exchange between stream 151a flowing through one pass of the heat exchange means, substantially condensed stream 36a flowing through another pass of the heat exchange means, and a further rectified vapor stream arising from rectifying section 117b of processing assembly 117, so that stream 151a is cooled to substantial condensation (stream 151b) and stream 36a is further cooled (stream 36b) while heating the further rectified vapor stream.

(25) Substantially condensed stream 151b at −171° F. [−113° C.] is then flash expanded through expansion valve 23 to slightly above the operating pressure of fractionation tower 17. During expansion a portion of the stream may be vaporized, resulting in cooling of the total stream. In the process illustrated in FIG. 3, the expanded stream 151c leaving expansion valve 23 reaches a temperature of −185° F. [−121° C.] before it is directed into a heat and mass transfer means in rectifying section 117b of processing assembly 117. This heat and mass transfer means may also be comprised of a fin and tube type heat exchanger, a plate type heat exchanger, a brazed aluminum type heat exchanger, or other type of heat transfer device, including multi-pass and/or multi-service heat exchangers. The heat and mass transfer means is configured to provide heat exchange between a partially rectified vapor stream arising from absorbing section 117c of processing assembly 117 that is flowing upward through one pass of the heat and mass transfer means, and the flash expanded substantially condensed stream 151c flowing downward, so that the partially rectified vapor stream is cooled while heating the expanded stream. As the partially rectified vapor stream is cooled, a portion of it is condensed and falls downward while the remaining vapor continues flowing upward through the heat and mass transfer means. The heat and mass transfer means provides continuous contact between the condensed liquid and the partially rectified vapor stream so that it also functions to provide mass transfer between the vapor and liquid phases, thereby providing further rectification of the partially rectified vapor stream to form the further rectified vapor stream. This further rectified vapor stream arising from the heat and mass transfer means is then directed to the heat exchange means in cooling section 117a of processing assembly 117 to be heated as described previously. The condensed liquid from the bottom of the heat and mass transfer means is directed to absorbing section 117c of processing assembly 117.

(26) The flash expanded stream 151c is further vaporized as it provides cooling and partial condensation of the partially rectified vapor stream, and exits the heat and mass transfer means in rectifying section 117b at −178° F. [−117° C.]. The heated flash expanded stream discharges into separator section 117d of processing assembly 117 and is separated into its respective vapor and liquid phases. The vapor phase combines with the remaining portion (stream 152) of overhead vapor stream 39 to form a combined vapor stream that enters a mass transfer means in absorbing section 117c of processing assembly 117. The mass transfer means may consist of a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing, but could also be comprised of a non-heat transfer zone in a fin and tube type heat exchanger, a plate type heat exchanger, a brazed aluminum type heat exchanger, or other type of heat transfer device, including multi-pass and/or multi-service heat exchangers. The mass transfer means is configured to provide contact between the cold condensed liquid leaving the bottom of the heat and mass transfer means in rectifying section 117b and the combined vapor stream arising from separator section 117d. As the combined vapor stream rises upward through absorbing section 117c, it is contacted with the cold liquid falling downward to condense and absorb C.sub.2 components, C.sub.3 components, and heavier components from the combined vapor stream. The resulting partially rectified vapor stream is then directed to the heat and mass transfer means in rectifying section 117b of processing assembly 117 for further rectification as described previously.

(27) The liquid phase (if any) from the heated flash expanded stream leaving rectifying section 117b of processing assembly 117 that is separated in separator section 117d combines with the distillation liquid leaving the bottom of the mass transfer means in absorbing section 117c of processing assembly 117 to form combined liquid stream 154. Combined liquid stream 154 leaves the bottom of processing assembly 117 and is pumped to higher pressure by pump 24 (stream 154a at −170° F. [−112° C.]). Further cooled stream 36b at −169° F. [−112° C.] is flash expanded through expansion valve 13 to the operating pressure of fractionation tower 17. During expansion a portion of the stream may be vaporized, resulting in cooling of the total stream to −177° F. [−116° C.]. Flash expanded stream 36c then joins with pumped stream 154a to form combined feed stream 155, which then enters fractionation column 17 at the top feed point at −176° F. [−116° C.].

(28) The further rectified vapor stream leaves the heat and mass transfer means in rectifying section 117b of processing assembly 117 at −182° F. [−119° C.] and enters the heat exchange means in cooling section 117a of processing assembly 117. The vapor is heated to −96° F. [−71° C.] as it provides cooling to streams 36a and 151a as described previously. The heated vapor is then discharged from processing assembly 117 as cool residue gas stream 153, which is heated and compressed as described previously for stream 39 in the FIG. 1 process.

(29) A summary of stream flow rates and energy consumption for the process illustrated in FIG. 3 is set forth in the following table:

(30) TABLE-US-00003 TABLE III (FIG. 3) Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31 17,272 2,734 1,070 657 21,961 32 15,276 1,676 359 76 17,604 33 1,996 1,058 711 581 4,357 34 3,247 356 76 16 3,742 35 499 264 178 145 1,089 36 3,746 620 254 161 4,831 37 12,029 1,320 283 60 13,862 38 1,497 794 533 436 3,268 39 17,608 179 3 0 18,020 151 1,610 16 0 0 1,647 152 15,998 163 3 0 16,373 154 373 144 3 0 521 155 4,119 764 254 161 5,352 153 17,235 35 0 0 17,499 42 37 2,699 1,070 657 4,462 Recoveries* Ethane 98.70% Propane 100.00% Butanes+ 100.00% Power Residue Gas Compression 14,660 HP [24,101 kW] Refrigerant Compression  3,733 HP  [6,137 kW] Reflux Compression   354 HP   [582 kW] Total Compression 18,747 HP [30,820 kW] *(Based on un-rounded flow rates)

(31) A comparison of Tables I and III shows that, compared to the FIG. 1 process, the FIG. 3 process improves ethane recovery from 96.69% to 98.70%, propane recovery from 99.84% to 100.00%, and butane+ recovery from 99.99% to 100.00%. Comparison of Tables I and III further shows that these increased product yields were achieved without using additional power.

(32) The process of co-pending application Ser. No. 15/332,723 can also be operated to reject nearly all of the C.sub.2 components to the residue gas rather than recovering them in the liquid product. The operating conditions of the FIG. 3 process can be altered as illustrated in FIG. 4 (including the idling of the heat exchange means in cooling section 117a of processing assembly 117) to reduce the ethane content of the liquid product to the essentially the same level as that of the FIG. 2 process. The feed gas composition and conditions considered in the process presented in FIG. 4 are the same as those in FIG. 2. Accordingly, the FIG. 4 process can be compared with that of the FIG. 2 process.

(33) Most of the process conditions shown for the FIG. 4 process are much the same as the corresponding process conditions for the FIG. 2 process. The main differences are again the disposition of substantially condensed stream 36a and column overhead vapor stream 39. In the FIG. 4 process, substantially condensed stream 36a is flash expanded through expansion valve 23 to slightly above the operating pressure (approximately 200 psia [1,381 kPa(a)]) of fractionation tower 17. During expansion a portion of the stream is vaporized, resulting in cooling of the total stream. In the process illustrated in FIG. 4, the expanded stream 36b leaving expansion valve 23 reaches a temperature of −156° F. [−104° C.] before it is directed into the heat and mass transfer means in rectifying section 117b of processing assembly 117.

(34) The flash expanded stream 36b is further vaporized as it provides cooling and partial condensation of the combined vapor stream, and exits the heat and mass transfer means in rectifying section 117b at −83° F. [−64° C.]. The heated flash expanded stream discharges into separator section 117d of processing assembly 117 and is separated into its respective vapor and liquid phases. The vapor phase combines with overhead vapor stream 39 to form the combined vapor stream that enters the mass transfer means in absorbing section 117c as described previously, and the liquid phase combines with the condensed liquid from the bottom of the mass transfer means in absorbing section 117c to form combined liquid stream 154. Combined liquid stream 154 leaves the bottom of processing assembly 117 and is pumped to higher pressure by pump 24 so that stream 154a at −73° F. [−58° C.] can enter fractionation column 17 at the top feed point. The further rectified vapor stream leaves the heat and mass transfer means in rectifying section 117b and discharges from processing assembly 117 at −104° F. [−76° C.] as cold residue gas stream 153, which is then heated and compressed as described previously for stream 39 in the FIG. 2 process.

(35) A summary of stream flow rates and energy consumption for the process illustrated in FIG. 4 is set forth in the following table:

(36) TABLE-US-00004 TABLE IV (FIG. 4) Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31 17,272 2,734 1,070 657 21,961 32 15,902 1,943 474 112 18,652 33 1,370 791 596 545 3,309 34 3,263 399 97 23 3,827 35 507 293 221 202 1,224 36 3,770 692 318 225 5,051 37 12,639 1,544 377 89 14,825 38/40 863 498 375 343 2,085 39 13,802 2,765 294 16 17,061 154  300 744 575 241 1,861 153  17,272 2,713 37 0 20,251 42 0 21 1,033 657 1,710 Recoveries* Propane 96.50% Butanes+ 100.00% Power Residue Gas Compression 15,114 HP [24,847 kW] Refrigerant Compression  3,621 HP  [5,953 kW] Reflux Compression    0 HP    [0 kW] Total Compression 18,735 HP [30,800 kW] *(Based on un-rounded flow rates)

(37) A comparison of Tables II and IV shows that, compared to the FIG. 2 process, the FIG. 4 process improves propane recovery from 89.20% to 96.50% and butane+ recovery from 98.81% to 100.00%. Comparison of Tables II and IV further shows that these increased product yields were achieved without using additional power.

DESCRIPTION OF THE INVENTION

Example 1

(38) In those cases where it is desirable to maximize the recovery of C.sub.2 components in the liquid product (as in the FIG. 1 prior art process described previously, for instance), the present invention offers significant efficiency advantages over the prior art process depicted in FIG. 1 and the process of co-pending application Ser. No. 15/332,723 depicted in FIG. 3. FIG. 5 illustrates a flow diagram of the FIG. 1 prior art process that has been adapted to use the present invention. The operating conditions of the FIG. 5 process have been adjusted as shown to increase the ethane content of the liquid product above the level that is possible with the FIGS. 1 and 3 processes. The feed gas composition and conditions considered in the process presented in FIG. 5 are the same as those in FIGS. 1 and 3. Accordingly, the FIG. 5 process can be compared with that of the FIGS. 1 and 3 processes to illustrate the advantages of the present invention.

(39) Most of the process conditions shown for the FIG. 5 process are much the same as the corresponding process conditions for the FIG. 1 process. The main difference is the disposition of substantially condensed stream 36a and column overhead vapor stream 39. In the FIG. 5 process, column overhead vapor stream 39 at −141° F. [−96° C.] and 236 psia [1,625 kPa(a)] (the operating pressure of fractionation tower 17) is directed to separator section 117d inside single equipment item processing assembly 117. Substantially condensed stream 36a at −105° F. [−76° C.] and partially cooled recycle stream 151a at −95° F. [−71° C.] are directed into a heat exchange means in cooling section 117a inside processing assembly 117. This heat exchange means may be comprised of a fin and tube type heat exchanger, a plate type heat exchanger, a brazed aluminum type heat exchanger, or other type of heat transfer device, including multi-pass and/or multi-service heat exchangers. The heat exchange means is configured to provide heat exchange between substantially condensed stream 36a flowing through one pass of the heat exchange means, partially cooled recycle stream 151a flowing through another pass of the heat exchange means, and a combined stream arising from rectifying section 117b inside processing assembly 117, so that stream 36a is further cooled (stream 36b) and stream 151a is cooled to substantial condensation (stream 151b) while heating the combined stream.

(40) Absorbing section 117c inside processing assembly 117 contains a mass transfer means. This mass transfer means may consist of a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing, but could also be comprised of a non-heat transfer zone in a fin and tube type heat exchanger, a plate type heat exchanger, a brazed aluminum type heat exchanger, or other type of heat transfer device, including multi-pass and/or multi-service heat exchangers. The mass transfer means is configured to provide contact between cold condensed liquid leaving the bottom of a heat and mass transfer means in rectifying section 117b inside processing assembly 117 and column overhead vapor stream 39 arising from separator section 117d inside processing assembly 117. As the column overhead vapor stream rises upward through absorbing section 117c, it is contacted with the cold liquid falling downward to condense and absorb C.sub.2 components, C.sub.3 components, and heavier components from the vapor stream. The resulting partially rectified vapor stream is then directed to the heat and mass transfer means in rectifying section 117b inside processing assembly 117 for further rectification.

(41) Substantially condensed stream 151b at −168° F. [−111° C.] is flash expanded through expansion valve 23 to slightly above the operating pressure of fractionation tower 17. During expansion a portion of the stream may be vaporized, resulting in cooling of the total stream. In the process illustrated in FIG. 5, the expanded stream 151c leaving expansion valve 23 reaches a temperature of −174° F. [−114° C.] before it is directed into the heat and mass transfer means in rectifying section 117b inside processing assembly 117. This heat and mass transfer means may also be comprised of a fin and tube type heat exchanger, a plate type heat exchanger, a brazed aluminum type heat exchanger, or other type of heat transfer device, including multi-pass and/or multi-service heat exchangers. The heat and mass transfer means is configured to provide heat exchange between the partially rectified vapor stream arising from absorbing section 117c inside processing assembly 117 that is flowing upward through one pass of the heat and mass transfer means, and the flash expanded substantially condensed stream 151c flowing downward, so that the partially rectified vapor stream is cooled while heating the expanded stream. As the partially rectified vapor stream is cooled, a portion of it is condensed and falls downward while the remaining vapor continues flowing upward through the heat and mass transfer means. The heat and mass transfer means provides continuous contact between the condensed liquid and the partially rectified vapor stream so that it also functions to provide mass transfer between the vapor and liquid phases, thereby providing further rectification of the partially rectified vapor stream to form a further rectified vapor stream. The condensed liquid from the bottom of the heat and mass transfer means is directed to absorbing section 117c inside processing assembly 117.

(42) The flash expanded stream 151c is further vaporized as it provides cooling and partial condensation of the partially rectified vapor stream, and exits the heat and mass transfer means in rectifying section 117b inside processing assembly 117 at −172° F. [−113° C.]. The heated flash expanded stream then mixes with the further rectified vapor stream to form a combined stream at −172° F. [−113° C.] that is directed to the heat exchange means in cooling section 117a inside processing assembly 117. The combined stream is heated as it provides cooling to streams 36a and 151a as described previously.

(43) The distillation liquid leaving the bottom of the mass transfer means in absorbing section 117c discharges from the bottom of processing assembly 117 (stream 154) and is pumped to higher pressure by pump 24 (stream 154a at −146° F. [−99° C.]). Further cooled substantially condensed stream 36b at −157° F. [−105° C.] is flash expanded through expansion valve 13 to the operating pressure of fractionation tower 17. During expansion a portion of the stream may be vaporized and thereby cool the total stream, but in this instance there is no significant vaporization and the stream instead warms slightly to −156° F. [−104° C.]. Flash expanded stream 36c then joins with pumped stream 154a to form combined feed stream 155, which enters fractionation column 17 at the top feed point at −154° F. [−103° C.].

(44) The heated combined stream 152 is discharged from the heat exchange means in cooling section 117a inside processing assembly 117 at −109° F. [−79° C.] and is divided into two portions, stream 156 and stream 157. Stream 157 is heated in heat exchangers 12 and 10 as described previously for stream 39 in the FIG. 1 process. Stream 156 is directed to heat exchanger 22 where it is heated to 91° F. [33° C.] (stream 156a) as it provides cooling to recycle stream 151. Heated stream 156a rejoins heated stream 157b to form stream 152a at 102° F. [39° C.], which is then compressed as described previously for stream 39 in the FIG. 1 process. After cooling to 120° F. [49° C.] in discharge cooler 20, stream 152d is divided into the residue gas product (stream 153) and the recycle stream (stream 151). Stream 153 flows to the sales gas pipeline at 765 psia [5,272 kPa(a)], while recycle stream 151 is directed to heat exchanger 22 to be cooled as described previously.

(45) A summary of stream flow rates and energy consumption for the process illustrated in FIG. 5 is set forth in the following table:

(46) TABLE-US-00005 TABLE V (FIG. 5) Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31 17,272 2,734 1,070 657 21,961 32 15,258 1,669 356 75 17,576 33 2,014 1,065 714 582 4,385 34 1,910 209 45 9 2,200 35 1,208 639 428 349 2,631 36 3,118 848 473 358 4,831 37 13,348 1,460 311 66 15,376 38 806 426 286 233 1,754 39 17,964 407 12 1 18,515 151 3,790 3 0 0 3,843 152 21,025 16 0 0 21,320 156 5,306 4 0 0 5,380 157 15,719 12 0 0 15,940 154 629 394 12 1 1,038 155 3,747 1,242 485 359 5,869 153 17,235 13 0 0 17,477 42 37 2,721 1,070 657 4,484 Recoveries* Ethane 99.51% Propane 100.00% Butanes+ 100.00% Power Residue Gas Compression 14,118 HP [23,210 kW] Refrigerant Compression  3,988 HP  [6,556 kW] Total Compression 18,106 HP [29,766 kW] *(Based on un-rounded flow rates)

(47) A comparison of Tables I and V shows that, compared to the prior art of FIG. 1, the present invention improves ethane recovery from 96.69% to 99.51%, propane recovery from 99.84% to 100.00%, and butane+ recovery from 99.99% to 100.00%. The economic impact of these improved recoveries is significant. Using an average incremental value $0.10/gallon [€ 21.9/m.sup.3] for hydrocarbon liquids compared to the corresponding hydrocarbon gases, the improved recoveries represent more than US$690,000 [€ 580,000] of additional annual revenue for the plant operator. Comparison of Tables III and V shows that the present invention is also an improvement over co-pending application Ser. No. 15/332,723, increasing the ethane recovery from 98.70% to 99.51%. Comparison of Tables I, III, and V further shows that these increased product yields were achieved using less power than the FIGS. 1 and 3 processes. In terms of the recovery efficiency (defined by the quantity of C.sub.2 components and heavier components recovered per unit of power), the present invention represents more than a 5% improvement over the prior art of the FIG. 1.

(48) The improvement in recovery efficiency provided by the present invention over that of the prior art of the FIG. 1 process is primarily due to the supplemental indirect cooling of the column overhead vapor provided by flash expanded stream 151c in rectifying section 117b inside processing assembly 117, in addition to the direct-contact cooling provided by stream 36b in the prior art process of FIG. 1. Although stream 36b is quite cold, it is not an ideal reflux stream because it contains significant concentrations of the C.sub.2 components, C.sub.3 components, and C.sub.4+ components that demethanizer 17 is supposed to capture, resulting in losses of these desirable components due to equilibrium effects at the top of column 17 for the prior art process of FIG. 1. For the present invention shown in FIG. 5, however, the supplemental cooling provided by flash expanded stream 151c has no equilibrium effects to overcome because there is no direct contact between flash expanded stream 151c and the column overhead vapor stream to be rectified.

(49) The present invention has the further advantage of using the heat and mass transfer means in rectifying section 117b to simultaneously cool the column overhead vapor stream and condense the heavier hydrocarbon components from it, providing more efficient rectification than using reflux in a conventional distillation column. As a result, more of the C.sub.2 components, C.sub.3 components, and heavier hydrocarbon components can be removed from the column overhead vapor stream using the refrigeration available in flash expanded stream 151c than is possible using conventional mass transfer equipment and conventional heat transfer equipment.

(50) The present invention offers two other advantages over the prior art in addition to the increase in processing efficiency. First, the compact arrangement of processing assembly 117 of the present invention incorporates what would normally be three separate equipment items (the heat exchange means in cooling section 117a, the heat and mass transfer means in rectifying section 117b, and the mass transfer means in absorbing section 117c) into a single equipment item (processing assembly 117 in FIG. 5 of the present invention). This reduces the plot space requirements and eliminates the interconnecting piping, reducing the capital cost of modifying a processing plant to use the present invention. Second, elimination of the interconnecting piping means that a processing plant modified to use the present invention has far fewer flanged connections, reducing the number of potential leak sources in the plant. Hydrocarbons are volatile organic compounds (VOCs), some of which are classified as greenhouse gases and some of which may be precursors to atmospheric ozone formation, which means the present invention reduces the potential for atmospheric releases that may damage the environment.

(51) One additional advantage of the present invention is how easily it can be incorporated into an existing gas processing plant to effect the superior performance described above. As shown in FIG. 5, only six connections (commonly referred to as “tie-ins”) to the existing plant are needed: for substantially condensed stream 36a (represented by the dashed line between stream 36a and stream 36b that is removed from service), for column feed line 155 (represented by the connection with stream 154a), for column overhead vapor stream 39 (represented by the dashed line between stream 39 and stream 152 that is removed from service, the connection with stream 156, and the connection with stream 157b), and for residue gas line 153 (represented by the connection with stream 151). The existing plant can continue to operate while the new processing assembly 117 is installed near fractionation tower 17, with just a short plant shutdown when installation is complete to make the new tie-ins to these six existing lines. The plant can then be restarted, with all of the existing equipment remaining in service and operating exactly as before, except that the product recovery is now higher with no increase in compression power.

(52) The main reason the present invention is more efficient than our co-pending application Ser. No. 15/332,723 depicted in FIG. 3 is that it removes nearly all of the heat of compression added by reflux compressor 22 in the FIG. 3 process by withdrawing recycle stream 151 in the FIG. 5 process downstream of discharge cooler 20 after the residue gas has been compressed. In the FIG. 3 process, compressor discharge stream 151a is much hotter than compressor suction stream 151 (−81° F. [−63° C.] for stream 151a versus −167° F. [−110° C.] for stream 151). This additional heat in the compressed stream must be removed in cooling section 117a inside processing assembly 117 in the FIG. 3 process, meaning less cooling is available for streams 36a and 151a. Contrast this with the FIG. 5 embodiment of the present invention, where the cooled compressed recycle stream 151 is nearly the same temperature as compressor suction stream 152a (120° F. [49° C.] for stream 151 versus 102° F. [39° C.] for stream 152a). This allows streams 151 and 36 to be cooled to significantly lower temperatures by cool residue gas stream 152 in heat exchangers 22 and 12 before entering processing assembly 117. This means more cooling is available in cooling section 117a inside processing assembly 117 of the present invention, allowing more flow for flash expanded stream 151c (more than twice the flow compared to stream 151c in FIG. 3), which in turn allows more reflux flow to the top of demethanizer 17 (10% higher flow for stream 155 in FIG. 5 compared to stream 155 in FIG. 3).

Example 2

(53) The present invention also offers advantages when product economics favor rejecting the C.sub.2 components to the residue gas product. The present invention can be easily reconfigured to operate in a manner similar to that of our U.S. Pat. Nos. 9,637,428 and 9,927,171 as shown in FIG. 6. The operating conditions of the FIG. 5 embodiment of the present invention can be altered as illustrated in FIG. 6 to reduce the ethane content of the liquid product to the same level as that of the FIG. 2 prior art process and of co-pending application Ser. No. 15/332,723 depicted in FIG. 4. The feed gas composition and conditions considered in the process presented in FIG. 6 are the same as those in FIGS. 2 and 4. Accordingly, the FIG. 6 process can be compared with that of the FIGS. 2 and 4 processes to further illustrate the advantages of the present invention.

(54) When operating the present invention in this manner, many of the process conditions shown for the FIG. 6 process are much the same as the corresponding process conditions for the FIG. 2 process, although most of the process configuration is like the FIG. 5 embodiment of the present invention. The main difference relative to the FIG. 5 embodiment is that the flash expanded stream 36b directed to the heat and mass transfer means in rectifying section 117b inside processing assembly 117 for FIG. 6 originates from substantially condensed stream 36a, rather than from the compressed residue gas stream 152d as in FIG. 5. As such, there is no recycle, and heat exchanger 22 can be taken out of service (as indicated by the dashed lines) when operating in this manner.

(55) For the operating conditions shown in FIG. 6, combined stream 36 is cooled to −92° F. [−69° C.] in heat exchanger 12 by heat exchange with cool residue gas stream 152. The substantially condensed stream 36a is flash expanded through expansion valve 23 to slightly above the operating pressure (approximately 200 psia [1,381 kPa(a)]) of fractionation tower 17. During expansion a portion of the stream may be vaporized, resulting in cooling of the total stream. In the process illustrated in FIG. 6, the expanded stream 36b leaving expansion valve 23 reaches a temperature of −156° F. [−104° C.] before it is directed into the heat and mass transfer means in rectifying section 117b inside processing assembly 117.

(56) The flash expanded stream 36b is further vaporized as it provides cooling and partial condensation of the partially rectified vapor stream, and exits the heat and mass transfer means in rectifying section 117b inside processing assembly 117 at −83° F. [−64° C.]. The heated flash expanded stream 36c is then mixed with pumped liquid stream 154a to form combined feed stream 155, which enters fractionation column 17 at the top feed point at −82° F. [−64° C.].

(57) The further rectified vapor stream leaves the heat and mass transfer means in rectifying section 117b inside processing assembly 117 at −104° F. [−76° C.]. Since the heat exchange means in cooling section 117a inside processing assembly 117 has been idled, the vapor simply discharges from processing assembly 117 as cool residue gas stream 152, which is heated and compressed as described previously for stream 39 in the FIG. 2 process.

(58) A summary of stream flow rates and energy consumption for the process illustrated in FIG. 6 is set forth in the following table:

(59) TABLE-US-00006 TABLE VI (FIG. 6) Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr] Stream Methane Ethane Propane Butanes+ Total 31 17,272 2,734 1,070 657 21,961 32 15,902 1,943 474 112 18,652 33 1,370 791 596 545 3,309 34 3,263 399 97 23 3,827 35 507 293 221 202 1,224 36 3,770 692 318 225 5,051 37 12,639 1,544 377 89 14,825 38/40 863 498 375 343 2,085 39 13,802 2,765 294 16 17,061 154  300 744 575 241 1,861 155  4,070 1,436 893 466 6,912 153  17,272 2,713 37 0 20,251 42 0 21 1,033 657 1,710 Recoveries* Propane 96.50% Butanes+ 100.00% Power Residue Gas Compression 15,114 HP [24,847 kW] Refrigerant Compression  3,621 HP  [5,953 kW] Reflux Compression    0 HP    [0 kW] Total Compression 18,735 HP [30,800 kW] *(Based on un-rounded flow rates)

(60) A comparison of Tables II and VI shows that, compared to the prior art, the FIG. 6 process improves propane recovery from 89.20% to 96.50% and butane+ recovery from 98.81% to 100.00%. Comparison of Tables II and VI further shows that these increased product yields were achieved without using additional power. The economic impact of these improved recoveries is substantial. Using an average incremental value $0.58/gallon [€ 129/m.sup.3] for hydrocarbon liquids compared to the corresponding hydrocarbon gases, the improved recoveries represent more than US$4,720,000 [€ 3,930,000] of additional annual revenue for the plant operator. A comparison of Tables IV and VI shows that the FIG. 6 process has essentially the same performance as co-pending application Ser. No. 15/332,723 when rejecting C.sub.2 components to the residue gas product.

OTHER EMBODIMENTS

(61) Some circumstances may favor mounting the liquid pump inside the processing assembly to further reduce the number of equipment items and the plot space requirements. Such embodiments are shown in FIGS. 7 and 10, with pump 124 mounted inside processing assembly 117 as shown to send the distillation liquid stream from separator section 117d via conduit 154 to combine with stream 36c and form combined feed stream 155 that is supplied as the top feed to column 17. The pump and its driver may both be mounted inside the processing assembly if a submerged pump or canned motor pump is used, or just the pump itself may be mounted inside the processing assembly (using a magnetically-coupled drive for the pump, for instance). For either option, the potential for atmospheric releases of hydrocarbons that may damage the environment is reduced still further.

(62) Some circumstances may favor locating the processing assembly at a higher elevation than the top feed point on fractionation column 17. In such cases, it may be possible for distillation liquid stream 154 to flow by gravity head and combine with stream 36c so that the resulting combined feed stream 155 then flows to the top feed point on fractionation column 17 as shown in FIGS. 8 and 11, eliminating the need for pump 24/124 shown in the FIGS. 5 through 7, 9, and 10 embodiments.

(63) Some circumstances may favor eliminating cooling section 117a from processing assembly 117, and using a heat exchange means external to the processing assembly for feed cooling, such as heat exchanger 25 shown in FIGS. 9 through 11. Such an arrangement allows processing assembly 117 to be smaller, which may reduce the overall plant cost and/or shorten the fabrication schedule in some cases. Note that in all cases exchanger 25 is representative of either a multitude of individual heat exchangers or a single multi-pass heat exchanger, or any combination thereof. Each such heat exchanger may be comprised of a fin and tube type heat exchanger, a plate type heat exchanger, a brazed aluminum type heat exchanger, or other type of heat transfer device, including multi-pass and/or multi-service heat exchangers.

(64) The present invention provides improved recovery of C.sub.2 components, C.sub.3 components, and heavier hydrocarbon components per amount of utility consumption required to operate the process. An improvement in utility consumption required for operating the process may appear in the form of reduced power requirements for compression or re-compression, reduced power requirements for external refrigeration, reduced energy requirements for supplemental heating, or a combination thereof.

(65) While there have been described what are believed to be preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto, e.g. to adapt the invention to various conditions, types of feed, or other requirements without departing from the spirit of the present invention as defined by the following claims.