WO2011034710A1

WO2011034710A1 - Hydrocarbon gas processing

Info

Publication number: WO2011034710A1
Application number: PCT/US2010/046966
Authority: WO
Inventors: Tony L. Martinez; John D. Wilkinson; Joe T. Lynch; Hank M. Hudson; Kyle T. Cuellar
Original assignee: Ortloff Engineers, Ltd.
Priority date: 2009-09-21
Filing date: 2010-08-27
Publication date: 2011-03-24
Also published as: BR112012006219A2; CN102575898B; BR112012006277A2; EP2480845A1; AU2010308519A1; EA021947B1; EA201200520A1; EG27017A; EA024075B1; SA110310707B1; US9476639B2; JP5850838B2; CN102498360B; JP5793145B2; CO6531455A2; EP2480847A4; AR078401A1; WO2011034709A1; MY163645A; US20110067443A1

Abstract

A process and an apparatus are disclosed for the recovery of ethane, ethylene, propane, propylene, and heavier hydrocarbon components from a hydrocarbon gas stream The stream is cooled and divided into first and second streams The first stream is further cooled to condense substantially all of it and is thereafter expanded to the fractionation tower pressure and supplied to the fractionation tower at an upper mid-column feed position The second stream is expanded to the tower pressure and supplied to the column at a mid-column feed position A distillation vapor stream is withdrawn from the column above the feed point of the first stream, combined with a portion of the tower overhead vapor stream, compressed to higher pressure, and directed into heat exchange relation with the remaining tower overhead vapor stream to cool the compressed combined vapor stream and condense at least a part of it, forming a condensed stream

Description

HYDROCARBON GAS PROCESSING

SPECIFICATION

BACKGROUND OF THE INVENTION

901] This invention relates to a process and an apparatus for the separation a gas containing hydrocarbons. [0002] Ethylene, ethane, propylene, propane, and/or heavier hydrocarbons can be recovered from a variety of gases, such as natural gas, refinery gas, and synthetic gas streams obtained from other hydrocarbon materials such as coal, crude oil, naphtha, oil shale, tar sands, and lignite. Natural gas usually has a major proportion of methane and ethane, i.e., methane and ethane together comprise at least 50 mole percent of the gas. The gas also contains relatively lesser amounts of heavier hydrocarbons such as propane, butanes, pentanes, and the like, as well as hydrogen, nitrogen, carbon dioxide, and other gases.

[0003] The present invention is generally concerned with the recovery of ethylene, ethane, propylene, propane, and heavier hydrocarbons from such gas streams. A typical analysis of a gas stream to be processed in accordance with this invention would be, in approximate mole percent, 88.1% methane, 6.0% ethane and other C₂ components, 2.5% propane and other C3 components, 0.2% iso-butane, 0.2% normal butane, and 0.5% pentanes plus, with the balance made up of nitrogen and carbon dioxide. Sulfur containing gases are also sometimes present.

[0004] The historically cyclic fluctuations in the prices of both natural gas and its natural gas liquid (NGL) constituents have at times reduced the incremental value of ethane, ethylene, propane, propylene, and heavier components as liquid products. This has resulted in a demand for processes that can provide more efficient recoveries of these products, for processes that can provide efficient recoveries with lower capital investment, and for processes that can be easily adapted or adjusted to vary the recovery of a specific component over a broad range. Available processes for separating these materials include those based upon cooling and refrigeration of gas, oil absorption, and refrigerated oil absorption. Additionally, cryogenic processes have become popular because of the availability of economical equipment that produces power while simultaneously expanding and extracting heat from the gas being processed. Depending upon the pressure of the gas source, the richness (ethane, ethylene, and heavier hydrocarbons content) of the gas, and the desired end products, each of these processes or a combination thereof may be employed.

[0005] The cryogenic expansion process is now generally preferred for natural gas liquids recovery because it provides maximum simplicity with ease of startup, operating flexibility, good efficiency, safety, and good reliability. U.S. Patent Nos. 3,292,380; 4,061,481; 4,140,504; 4,157,904; 4,171,964; 4,185,978; 4,251,249;

4,278,457; 4,519,824; 4,617,039; 4,687,499; 4,689,063; 4,690,702; 4,854,955;

4,869,740; 4,889,545; 5,275,005; 5,555,748; 5,566,554; 5,568,737; 5,771,712;

5,799,507; 5,881,569; 5,890,378; 5,983,664; 6,182,469; 6,578,379; 6,712,880;

6,915,662; 7,191,617; 7,219,513; reissue U.S. Patent No. 33,408; and co-pending application nos. 11/430,412; 11/839,693; 11/971,491; 12/206,230; 12/689,616;

12/717,394; 12/750,862; 12/772,472; and 12/781,259 describe relevant processes (although the description of the present invention in some cases is based on different processing conditions than those described in the cited U.S. Patents).

[0006] In a typical cryogenic expansion recovery process, a feed gas stream under pressure is cooled by heat exchange with other streams of the process and/or external sources of refrigeration such as a propane compression-refrigeration system. As the gas is cooled, liquids may be condensed and collected in one or more separators as high-pressure liquids containing some of the desired C₂+ components. Depending on the richness of the gas and the amount of liquids formed, the high-pressure liquids may be expanded to a lower pressure and fractionated. The vaporization occurring during expansion of the liquids results in further cooling of the stream. Under some conditions, pre-cooling the high pressure liquids prior to the expansion may be desirable in order to further lower the temperature resulting from the expansion. The expanded stream, comprising a mixture of liquid and vapor, is fractionated in a distillation (demethanizer or deethanizer) column. In the column, the expansion cooled stream(s) is (are) distilled to separate residual methane, nitrogen, and other volatile gases as overhead vapor from the desired C₂ components, C3 components, and heavier hydrocarbon components as bottom liquid product, or to separate residual methane, C₂ components, nitrogen, and other volatile gases as overhead vapor from the desired C3 components and heavier hydrocarbon components as bottom liquid product.

[0007] If the feed gas is not totally condensed (typically it is not), the vapor remaining from the partial condensation can be split into two streams. One portion of the vapor is passed through a work expansion machine or engine, or an expansion valve, to a lower pressure at which additional liquids are condensed as a result of further cooling of the stream. The pressure after expansion is essentially the same as the pressure at which the distillation column is operated. The combined vapor-liquid phases resulting from the expansion are supplied as feed to the column.

[0008] The remaining portion of the vapor is cooled to substantial condensation by heat exchange with other process streams, e.g., the cold fractionation tower overhead. Some or all of the high-pressure liquid may be combined with this vapor portion prior to cooling. The resulting cooled stream is then expanded through an appropriate expansion device, such as an expansion valve, to the pressure at which the demethanizer is operated. During expansion, a portion of the liquid will vaporize, resulting in cooling of the total stream. The flash expanded stream is then supplied as top feed to the demethanizer. Typically, the vapor portion of the flash expanded stream and the demethanizer overhead vapor combine in an upper separator section in the fractionation tower as residual methane product gas. Alternatively, the cooled and expanded stream may be supplied to a separator to provide vapor and liquid streams. The vapor is combined with the tower overhead and the liquid is supplied to the column as a top column feed.

[0009] In the ideal operation of such a separation process, the residue gas leaving the process will contain substantially all of the methane in the feed gas with essentially none of the heavier hydrocarbon components, and the bottoms fraction leaving the demethanizer will contain substantially all of the heavier hydrocarbon components with essentially no methane or more volatile components. In practice, however, this ideal situation is not obtained because the conventional demethanizer is operated largely as a stripping column. The methane product of the process, therefore, typically comprises vapors leaving the top fractionation stage of the column, together with vapors not subjected to any rectification step. Considerable losses of C₂, C₃, and C₄+ components occur because the top liquid feed contains substantial quantities of these components and heavier hydrocarbon components, resulting in corresponding equilibrium quantities of C₂ components, C₃ components, C₄ components, and heavier hydrocarbon components in the vapors leaving the top fractionation stage of the demethanizer. The loss of these desirable components could be significantly reduced if the rising vapors could be brought into contact with a significant quantity of liquid (reflux) capable of absorbing the C₂ components, C₃ components, C₄ components, and heavier hydrocarbon components from the vapors.

[0010] In recent years, the preferred processes for hydrocarbon separation use an upper absorber section to provide additional rectification of the rising vapors. The source of the reflux stream for the upper rectification section is typically a recycled stream of residue gas supplied under pressure. The recycled residue gas stream is usually cooled to substantial condensation by heat exchange with other process streams, e.g., the cold fractionation tower overhead. The resulting substantially condensed stream is then expanded through an appropriate expansion device, such as an expansion valve, to the pressure at which the demethanizer is operated. During expansion, a portion of the liquid will usually vaporize, resulting in cooling of the total stream. The flash expanded stream is then supplied as top feed to the demethanizer. Typically, the vapor portion of the expanded stream and the demethanizer overhead vapor combine in an upper separator section in the fractionation tower as residual methane product gas. Alternatively, the cooled and expanded stream may be supplied to a separator to provide vapor and liquid streams, so that thereafter the vapor is combined with the tower overhead and the liquid is supplied to the column as a top column feed. Typical process schemes of this type are disclosed in U.S. Patent Nos. 4,889,545; 5,568,737; and 5,881,569; assignee's co-pending application no. 12/717,394; and in Mowrey, E. Ross, "Efficient, High Recovery of Liquids from Natural Gas Utilizing a High Pressure Absorber",

Proceedings of the Eighty-First Annual Convention of the Gas Processors

Association, Dallas, Texas, March 11-13, 2002. These processes use a compressor to provide the motive force for recycling the reflux stream to the demethanizer, adding to both the capital cost and the operating cost of facilities using these processes.

[0011] The present invention also employs an upper rectification section (or a separate rectification column if plant size or other factors favor using separate rectification and stripping columns). However, the reflux stream for this rectification section is provided by using a side draw of the vapors rising in a lower portion of the tower combined with a portion of the column overhead vapor. Because of the relatively high concentration of C₂ components in the vapors lower in the tower, a significant quantity of liquid can be condensed from this combined vapor stream with only a modest elevation in pressure, often using only the refrigeration available in the remaining portion of the cold overhead vapor leaving the upper rectification section of the column. This condensed liquid, which is predominantly liquid methane, can then be used to absorb C₂ components, C3 components, C₄ components, and heavier hydrocarbon components from the vapors rising through the upper rectification section and thereby capture these valuable components in the bottom liquid product from the demethanizer.

[0012] Heretofore, compressing either a portion of the cold overhead vapor stream or compressing a side draw vapor stream to provide reflux for the upper rectification section of the column has been employed in C₂+ recovery systems, as illustrated in assignee's U.S. Patent No. 4,889,545 and assignee's co-pending application no. 11/839,693, respectively. Surprisingly, applicants have found that combining a portion of the cold overhead vapor with the side draw vapor stream and then compressing the combined stream improves the system efficiency while reducing operating cost.

[0013] In accordance with the present invention, it has been found that C₂ recovery in excess of 95% and C3 and C₄+ recoveries in excess of 99% can be obtained. In addition, the present invention makes possible essentially 100% separation of methane and lighter components from the C₂ components and heavier components at lower energy requirements compared to the prior art while maintaining the recovery levels. The present invention, although applicable at lower pressures and warmer temperatures, is particularly advantageous when processing feed gases in the range of 400 to 1500 psia [2,758 to 10,342 kPa(a)] or higher under conditions requiring NGL recovery column overhead temperatures of -50°F [-46°C] or colder. [0014] For a better understanding of the present invention, reference is made to the following examples and drawings. Referring to the drawings:

[0015] FIG. 1 is a flow diagram of a prior art natural gas processing plant in accordance with United States Patent No. 4,889,545;

[0016] FIG. 2 is a flow diagram of a natural gas processing plant in accordance with the present invention; and

[0017] FIGS. 3 through 6 are flow diagrams illustrating alternative means of application of the present invention to a natural gas stream.

[0018] 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.

[0019] For convenience, process parameters are reported in both the traditional British units and in the units of the Systeme International d'Unites (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

[0020] FIG. 1 is a process flow diagram showing the design of a processing plant to recover C₂+ components from natural gas using prior art according to U.S. Pat. No. 4,889,545. In this simulation of the process, inlet gas enters the plant at 120°F [49°C] and 1040 psia [7,171 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.

[0021] The feed stream 31 is cooled in heat exchanger 10 by heat exchange with cool residue gas (stream 43a), liquid product at 72°F [22°C] (stream 42a), demethanizer reboiler liquids at 52°F [11°C] (stream 41), and demethanizer side reboiler liquids at -20°F [-29°C] (stream 40). Note that in all cases exchanger 10 is representative of either a multitude of individual heat exchangers or a single multi-pass heat exchanger, or any combination thereof. (The decision as to whether to use more than one heat exchanger for the indicated cooling services will depend on a number of factors including, but not limited to, inlet gas flow rate, heat exchanger size, stream temperatures, etc.) The cooled stream 31a enters separator 11 at -18°F [-28°C] and 1025 psia [7,067 kPa(a)] where the vapor (stream 32) is separated from the condensed liquid (stream 33). The separator liquid (stream 33) is expanded to the operating pressure (approximately 392 psia [2,701 kPa(a)]) of fractionation tower 17 by expansion valve 16, cooling stream 33a to -53°F [-47°C] before it is supplied to fractionation tower 17 at a lower mid-column feed point.

[0022] The vapor (stream 32) from separator 11 is divided into two streams,

36 and 37. Stream 36, containing about 38% of the total vapor, passes through heat exchanger 12 in heat exchange relation with the cold residue gas (stream 43) where it is cooled to substantial condensation. The resulting substantially condensed stream 36a at -142°F [-96°C] is then flash expanded through expansion valve 13 to slightly above the operating pressure 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 -144°F [-98°C]. The expanded stream 36b is warmed to -139°F

[-95 °C] and further vaporized in heat exchanger 22 as it provides cooling and condensation of compressed recycle stream 44a (described later in paragraph [0026]). The warmed stream 36c is then supplied at an upper mid-column feed point, in absorbing section 17a of fractionation tower 17.

[0023] The remaining 62% 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 -94°F [-70°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 43b), for example. The partially condensed expanded stream 37a is thereafter supplied as feed to fractionation tower 17 at a mid-column feed point.

[0024] 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. The demethanizer tower consists of two sections: an upper absorbing (rectification) section 17a that contains the trays and/or packing to provide the necessary contact between the vapor portions of the expanded streams 36c and 37a rising upward and cold liquid falling downward to condense and absorb the C₂ components, C3 components, and heavier components; and a lower, stripping section 17b that contains the trays and/or packing to provide the necessary contact between the liquids falling downward and the vapors rising upward. The

demethanizing section 17b also includes one or more reboilers (such as the reboiler and side reboiler described previously) 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. Stream 37a enters demethanizer 17 at an intermediate feed position located in the lower region of absorbing section 17a of demethanizer 17. The liquid portion of the expanded stream 37a commingles with liquids falling downward from absorbing section 17a and the combined liquid continues downward into stripping section 17b of demethanizer 17. The vapor portion of the expanded stream 37a rises upward through absorbing section 17a and is contacted with cold liquid falling downward to condense and absorb the C₂ components, C3 components, and heavier components.

[0025] In stripping section 17b of demethanizer 17, the feed streams are stripped of their methane and lighter components. The resulting liquid product (stream 42) exits the bottom of tower 17 at 67 °F [19°C] (based on a typical specification of a methane to ethane ratio of 0.015: 1 on a volume basis in the bottom product) and is pumped to heat exchanger 10 by pump 20 to be heated to 116°F

[47°C] as it provides cooling to the feed gas as described earlier.

[0026] Cold demethanizer overhead stream 39 exits the top of demethanizer

17 at -146°F [-99°C] and is divided into cold residue gas stream 43 and recycle stream 44. Recycle stream 44 is compressed to 492 psia [3,390 kPa(a)] by compressor 21 before entering heat exchanger 22. The compressed recycle stream 44a is cooled from -121°F [-85°C] to -140°F [-96°C] and substantially condensed by heat exchange with expanded substantially condensed stream 36b as described previously. The substantially condensed stream 44b is then expanded through an appropriate expansion device, such as expansion valve 23, to the demethanizer operating pressure, resulting in cooling of the total stream to -150°F [-101°C]. The expanded stream 44c is then supplied to fractionation tower 17 as the top column feed. The vapor portion of stream 44c combines with the vapors rising from the top fractionation stage of the column to form demethanizer overhead stream 39.

[0027] The cold residue gas stream 43 passes countercurrently to the incoming feed gas in heat exchanger 12 where it is heated to -26°F [-32°C] (stream 43a) and in heat exchanger 10 where it is heated to 98°F [37°C] (stream 43b). 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 24 driven by a supplemental power source which compresses the residue gas (stream 43d) to sales line pressure. After cooling to 120°F [49°C] in discharge cooler 25, the residue gas product (stream 43e) flows to the sales gas pipeline at 1040 psia [7,171 kPa(a)], sufficient to meet line requirements (usually on the order of the inlet pressure). A summary of stream flow rates and energy consumption for the illustrated in FIG. 1 is set forth in the following table:

Table I

(FIG. 1)

Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr]

Stream Methane Ethane Propane Butanes+ Total

31 24,193 1,650 687 234 27,451

32 24,042 1,608 641 168 27,142

33 151 42 46 66 309

36 9,184 614 245 64 10,368

37 14,858 994 396 104 16,774 39 28,419 82 0 0 29,216 44 4,263 12 0 0 4,382 43 24,156 70 0 0 24,834 42 37 1,580 687 234 2,617

Recoveries*

Ethane 95.79%

Propane 100.00%

Butanes+ 100.00%

Power

Residue Gas Compression 13,294

Recycle Compression 224

Total Compression 13,518 HP [ 22,223 kW]

(Based on un-rounded flow rates)

DESCRIPTION OF THE INVENTION

[0029] FIG. 2 illustrates a flow diagram of a process in accordance with the present invention. The feed gas composition and conditions considered in the process presented in FIG. 2 are the same as those in FIG. 1. Accordingly, the FIG. 2 process can be compared with that of the FIG. 1 process to illustrate the advantages of the present invention.

[0030] In the simulation of the FIG. 2 process, inlet gas enters the plant at

120°F [49°C] and 1040 psia [7,171 kPa(a)] as stream 31 and is cooled in heat exchanger 10 by heat exchange with cool residue gas (stream 43a), liquid product at 74°F [24°C] (stream 42a), demethanizer reboiler liquids at 54°F [12°C] (stream 41), and demethanizer side reboiler liquids at -19°F [-28°C] (stream 40). The cooled stream 31a enters separator 11 at -24°F [-31°C] and 1025 psia [7,067 kPa(a)] where the vapor (stream 32) is separated from the condensed liquid (stream 33). The separator liquid (stream 33/38) is expanded to the operating pressure (approximately 401 psia [2,766 kPa(a)]) of fractionation tower 17 by expansion valve 16, cooling stream 38a to -59°F [-51°C] before it is supplied to fractionation tower 17 at a lower mid-column feed point (located below the feed point of stream 37a described later in paragraph [0032]).

[0031] The vapor (stream 32) from separator 11 is divided into two streams,

34 and 37. Stream 34, containing about 28% of the total vapor, passes through heat exchanger 12 in heat exchange relation with the cold residue gas (stream 43) where it is cooled to substantial condensation. The resulting substantially condensed stream 36a at -140°F [-96°C] is then flash expanded through expansion valve 13 to the operating pressure 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. 2, the expanded stream 36b leaving expansion valve 13 reaches a temperature of -144°F [-98°C] before it is supplied at an upper mid-column feed point, in absorbing section 17a of fractionation tower 17.

[0032] The remaining 72% 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 -97°F [-72°C]. The partially condensed expanded stream 37a is thereafter supplied as feed to fractionation tower 17 at a mid-column feed point (located below the feed point of stream 36b).

[0033] 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. The demethanizer tower consists of two sections: an upper absorbing (rectification) section 17a that contains the trays and/or packing to provide the necessary contact between the vapor portion of the expanded streams 36b and 37a rising upward and cold liquid falling downward to condense and absorb the C₂ components, C3 components, and heavier components from the vapors rising upward; and a lower, stripping section 17b that contains the trays and/or packing to provide the necessary contact between the liquids falling downward and the vapors rising upward. The demethanizing section 17b also includes one or more reboilers (such as the reboiler and side reboiler described previously) 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. Stream 37a enters demethanizer 17 at an intermediate feed position located in the lower region of absorbing section 17a of demethanizer 17. The liquid portion of the expanded stream 37a commingles with liquids falling downward from absorbing section 17a and the combined liquid continues downward into stripping section 17b of demethanizer 17. The vapor portion of the expanded stream 37a rises upward through absorbing section 17a and is contacted with cold liquid falling downward to condense and absorb the C₂ components, C3 components, and heavier components.

[0034] A portion of the distillation vapor (stream 45) is withdrawn from the upper region of absorbing section 17a in fractionation column 17, above the feed position of expanded stream 36b in the middle region of absorbing section 17a. The distillation vapor stream 45 at -142°F [-96°C] is combined with a first portion (stream 44) of overhead vapor stream 39 at -144°F [-98°C] to form combined vapor stream 46 at -144°F [-98°C]. The combined vapor stream 46 is compressed to 686 psia

[4,728 kPa(a)] by reflux compressor 21, then cooled from -84°F [-65°C] to -140°F [-96°C] and substantially condensed (stream 46b) in heat exchanger 12 by heat exchange with cold residue gas stream 43, the remaining second portion of demethanizer overhead stream 39 exiting the top of demethanizer 17.

[0035] The substantially condensed stream 46b is flash expanded to the operating pressure of demethanizer 17 by expansion valve 23. A portion of the stream is vaporized, further cooling stream 46c to -149°F [-101°C] before it is supplied as cold top column feed (reflux) to demethanizer 17. This cold liquid reflux absorbs and condenses the C₂ components, C3 components, and heavier components rising in the upper rectification region of absorbing section 17a of demethanizer 17.

[0036] In stripping section 17b of demethanizer 17, the feed streams are stripped of their methane and lighter components. The resulting liquid product (stream 42) exits the bottom of tower 17 at 69 °F [21°C] (based on a typical specification of a methane to ethane ratio of 0.015: 1 on a volume basis in the bottom product) and is pumped to heat exchanger 10 by pump 20 to be heated to 116°F

[47°C] as it provides cooling to the feed gas as described earlier. The cold residue gas stream 43 passes countercurrently to the incoming feed gas and compressed combined vapor stream in heat exchanger 12 where it is heated to -37°F [-39°C] (stream 43a), and countercurrently to the incoming feed gas in heat exchanger 10 where it is heated to 97°F [36°C] (stream 43b) as it provides cooling as previously described. The residue gas is then re-compressed in two stages, compressor 15 driven by expansion machine 14 and compressor 24 driven by a supplemental power source. After stream 43d is cooled to 120°F [49°C] in discharge cooler 25, the residue gas product (stream 43e) flows to the sales gas pipeline at 1040 psia [7,171 kPa(a)] , sufficient to meet line requirements (usually on the order of the inlet pressure). [0037] A summary of stream flow rates and energy consumption for the process illustrated in FIG. 2 is set forth in the following table:

Table II

(FIG. 2)

Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr]

Stream Methane Ethane Propane Butanes+ Total

31 24,193 1,650 687 234 27,451

32 23,983 1,593 626 157 27,042

33 210 57 61 77 409

34 6,607 439 172 43 7,450

35 0 0 0 0 0

36 6,607 439 172 43 7,450

37 17,376 1,154 454 114 19,592

38 210 57 61 77 409

39 27,081 78 0 0 27,845

44 2,925 8 0 0 3,007

45 194 1 0 0 200

46 3,119 9 0 0 3,207 43 24,156 70 0 0 24,838 42 37 1,580 687 234 2,613 Recoveries*

Ethane 95.77%

Propane 99.99%

Butanes+ 100.00%

Power

Residue Gas Compression 12,573

Reflux Compression 401

Total Compression 12,974 HP [ 21,329 kW]

(Based on un-rounded flow rates)

[0038] A comparison of Tables I and II shows that the present invention maintains essentially the same recoveries as the prior art. However, further comparison of Tables I and II shows that the product yields were achieved using significantly less power than the prior art. In terms of the recovery efficiency (defined by the quantity of ethane recovered per unit of power), the present invention represents more than a 4% improvement over the prior art of the FIG. 1 process.

[0039] Like the prior art of the FIG. 1 process, the present invention uses the expanded substantially condensed feed stream 36b supplied to absorbing section 17a of demethanizer 17 to provide bulk recovery of the C₂ components, C₃ components, and heavier hydrocarbon components contained in expanded feed 37a and the vapors rising from stripping section 17b, and the supplemental rectification provided by reflux stream 46c to reduce the amount of C₂ components, C₃ components, and C₄+ components contained in the inlet feed gas that is lost to the residue gas. However, the present invention reduces the rectification required in absorbing section 17a over that of the prior art FIG. 1 process by condensing reflux stream 46c without warming any of the feeds (stream 36b and 37a) to absorbing section 17a. If the substantially condensed stream 36b is warmed to provide condensing as is taught in the prior art FIG. 1 process, not only is there less cold liquid from stream 36b available for rectification of the vapors rising in absorbing section 17a, there is much more vapor in the upper region of absorbing section 17a that must be rectified by the reflux stream. As can be seen by comparing reflux stream 44 in Table I with reflux stream 46 in Table II, the net result is that more reflux is required by the prior art FIG. 1 process to prevent the C₂ components from escaping to the residue gas stream than the present invention requires, reducing its recovery efficiency compared to the present invention. The key improvement of the present invention over the prior art process is that only the cold residue gas stream 43 is needed to provide the cooling in heat exchanger 12, thereby condensing sufficient methane from compressed combined vapor stream 46a for use as reflux while avoiding adding significant rectification load in absorbing section 17a due to the excessive vaporization of stream 36b that is inherent in the prior art FIG. 1 process.

Other Embodiments

[0040] In accordance with this invention, it is generally advantageous to design the absorbing (rectification) section of the demethanizer to contain multiple theoretical separation stages. However, the benefits of the present invention can be achieved with as few as two theoretical stages. For instance, all or a part of the expanded reflux stream (stream 46c) leaving expansion valve 23 and all or a part of the expanded substantially condensed stream 36b from expansion valve 13 can be combined (such as in the piping joining the expansion valves to the demethanizer) and if thoroughly intermingled, the vapors and liquids will mix together and separate in accordance with the relative volatilities of the various components of the total combined streams. Such commingling of the two streams, combined with contacting at least a portion of expanded stream 37a, shall be considered for the purposes of this invention as constituting an absorbing section.

[0041] FIGS. 3 through 6 display other embodiments of the present invention.

FIGS. 2 through 4 depict fractionation towers constructed in a single vessel. FIGS. 5 and 6 depict fractionation towers constructed in two vessels, absorber (rectifier) column 17 (a contacting and separating device) and stripper (distillation) column 19. In such cases, the overhead vapor stream 48 from stripper column 19 flows to the lower section of absorber column 17 (via stream 49) to be contacted by reflux stream 46c and expanded substantially condensed stream 36b. Pump 18 is used to route the liquids (stream 47) from the bottom of absorber column 17 to the top of stripper column 19 so that the two towers effectively function as one distillation system. The decision whether to construct the fractionation tower as a single vessel (such as demethanizer 17 in FIGS. 2 through 4) or multiple vessels will depend on a number of factors such as plant size, the distance to fabrication facilities, etc.

[0042] Some circumstances may favor withdrawing the distillation vapor stream 45 in FIGS. 3 and 4 from the lower region of absorbing section 17a above the feed point of expanded stream 37a (stream 51), rather than from the upper region of absorbing section 17a above the feed point of expanded substantially condensed stream 36b (stream 50). Likewise in FIGS. 5 and 6, the vapor distillation stream 45 may be withdrawn from absorber column 17 above the feed point of expanded substantially condensed stream 36b (stream 50) or above the feed point of expanded stream 37a (stream 51). In other cases, it may be advantageous to withdraw the distillation vapor stream 45 from the upper region of stripping section 17b in demethanizer 17 (stream 52) in FIGS. 3 and 4. Similarly in FIGS. 5 and 6, a portion (stream 52) of overhead vapor stream 48 from stripper column 19 may be combined with stream 44, with any remaining portion (stream 49) flowing to the lower section of absorber column 17.

[0043] As described earlier, the compressed combined vapor stream 46a is substantially condensed and the resulting condensate used to absorb valuable C₂ components, C3 components, and heavier components from the vapors rising through absorbing section 17a of demethanizer 17 or through absorber column 17. However, the present invention is not limited to this embodiment. It may be advantageous, for instance, to treat only a portion of these vapors in this manner, or to use only a portion of the condensate as an absorbent, in cases where other design considerations indicate portions of the vapors or the condensate should bypass absorbing section 17a of demethanizer 17 or absorber column 17. Some circumstances may favor partial condensation, rather than substantial condensation, of compressed combined vapor stream 46a in heat exchanger 12. Other circumstances may favor that distillation vapor stream 45 be a total vapor side draw from fractionation column 17 or absorber column 17 rather than a partial vapor side draw. It should also be noted that, depending on the composition of the feed gas stream, it may be advantageous to use external refrigeration to provide partial cooling of compressed combined vapor stream 46a in heat exchanger 12.

[0044] Feed gas conditions, plant size, available equipment, or other factors may indicate that elimination of work expansion machine 14, or replacement with an alternate expansion device (such as an expansion valve), is feasible. Although individual stream expansion is depicted in particular expansion devices, alternative expansion means may be employed where appropriate. For example, conditions may warrant work expansion of the substantially condensed portion of the feed stream (stream 36a) or the substantially condensed reflux stream (stream 46b) leaving heat exchanger 12.

[0045] Depending on the quantity of heavier hydrocarbons in the feed gas and the feed gas pressure, the cooled feed stream 31a leaving heat exchanger 10 in FIGS. 2 through 6 may not contain any liquid (because it is above its dewpoint, or because it is above its cricondenbar). In such cases, separator 11 shown in FIGS. 2 through 6 is not required.

[0046] The high pressure liquid (stream 33 in FIGS. 2 through 6) need not be expanded and fed to a mid-column feed point on the distillation column. Instead, all or a portion of it may be combined with the portion of the separator vapor (stream 34) flowing to heat exchanger 12. (This is shown by the dashed stream 35 in FIGS. 2 through 6.) Any remaining portion of the liquid may be expanded through an appropriate expansion device, such as an expansion valve or expansion machine, and fed to a mid-column feed point on the distillation column (stream 38a in FIGS. 2 through 6). Stream 38 may also be used for inlet gas cooling or other heat exchange service before or after the expansion step prior to flowing to the demethanizer.

[0047] In accordance with the present invention, the use of external refrigeration to supplement the cooling available to the inlet gas from other process streams may be employed, particularly in the case of a rich inlet gas. The use and distribution of separator liquids and demethanizer side draw liquids for process heat exchange, and the particular arrangement of heat exchangers for inlet gas cooling must be evaluated for each particular application, as well as the choice of process streams for specific heat exchange services. [0048] In accordance with the present invention, the splitting of the vapor feed may be accomplished in several ways. In the processes of FIGS. 2, 3, and 5, the splitting of vapor occurs following cooling and separation of any liquids which may have been formed. The high pressure gas may be split, however, prior to any cooling of the inlet gas as shown in FIGS. 4 and 6. In some embodiments, vapor splitting may be effected in a separator.

[0049] It will also be recognized that the relative amount of feed found in each branch of the split vapor feed will depend on several factors, including gas pressure, feed gas composition, the amount of heat which can economically be extracted from the feed, and the quantity of horsepower available. More feed to the top of the column may increase recovery while decreasing power recovered from the expander thereby increasing the recompression horsepower requirements. Increasing feed lower in the column reduces the horsepower consumption but may also reduce product recovery. The relative locations of the mid-column feeds may vary depending on inlet composition or other factors such as desired recovery levels and amount of liquid formed during inlet gas cooling. Moreover, two or more of the feed streams, or portions thereof, may be combined depending on the relative temperatures and quantities of individual streams, and the combined stream then fed to a mid- column feed position.

[0050] The present invention provides improved recovery of C₂ components,

C3 components, and heavier hydrocarbon components or of C3 components and heavier hydrocarbon components per amount of utility consumption required to operate the process. An improvement in utility consumption required for operating the demethanizer or deethanizer 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 tower reboilers, or a combination thereof.

[0051] 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.

Claims

WE CLAIM:

1. In a process for the separation of a gas stream containing methane, C₂ components, C₃ components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C₃ components, and heavier hydrocarbon components or said C₃ components and heavier hydrocarbon components, in which process

(a) said gas stream is cooled under pressure to provide a cooled stream;

(b) said cooled stream is expanded to a lower pressure whereby it is further cooled; and

(c) said further cooled stream is directed into a distillation column and fractionated at said lower pressure whereby the components of said relatively less volatile fraction are recovered;

the improvement wherein following cooling, said cooled stream is divided into first and second streams; and

(1) said first stream is cooled to condense substantially all of it and is thereafter expanded to said lower pressure whereby it is further cooled;

(2) said expanded cooled first stream is thereafter supplied to said distillation column at an upper mid-column feed position;

(3) said second stream is expanded to said lower pressure and is supplied to said distillation column at a mid-column feed position below said upper mid-column feed position; (4) an overhead vapor stream is withdrawn from an upper region of said distillation column and divided into at least a first portion and a second portion;

(5) a distillation vapor stream is withdrawn from a region of said distillation column above said upper mid-column feed position and is combined with said first portion to form a combined vapor stream;

(6) said combined vapor stream is compressed to higher pressure;

(7) said compressed combined vapor stream is directed into heat exchange relation with said second portion, whereby said second portion is heated and said compressed combined vapor stream is cooled sufficiently to condense at least a part of it and thereby form a condensed stream, and thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction;

(8) at least a portion of said condensed stream is expanded to said lower pressure and is thereafter supplied to said distillation column at a top feed position; and

(9) the quantities and temperatures of said feed streams to said distillation column are effective to maintain the overhead temperature of said distillation column at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

2. In a process for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in which process (a) said gas stream is cooled under pressure to provide a cooled stream;

the improvement wherein prior to cooling, said gas stream is divided into first and second streams; and

(3) said second stream is cooled and thereafter expanded to said lower pressure and supplied to said distillation column at a mid-column feed position below said upper mid-column feed position;

(4) an overhead vapor stream is withdrawn from an upper region of said distillation column and divided into at least a first portion and a second portion;

(6) said combined vapor stream is compressed to higher pressure; (7) said compressed combined vapor stream is directed into heat exchange relation with said second portion, whereby said second portion is heated and said compressed combined vapor stream is cooled sufficiently to condense at least a part of it and thereby form a condensed stream, and thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction;

3. In a process for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in which process

(a) said gas stream is cooled under pressure to provide a cooled stream;

the improvement wherein said gas stream is cooled sufficiently to partially condense it; and

(1) said partially condensed gas stream is separated thereby to provide a vapor stream and at least one liquid stream;

(2) said vapor stream is thereafter divided into first and second streams;

(3) said first stream is cooled to condense substantially all of it and is thereafter expanded to said lower pressure whereby it is further cooled;

(4) said expanded cooled first stream is thereafter supplied to said distillation column at an upper mid-column feed position;

(5) said second stream is expanded to said lower pressure and is supplied to said distillation column at a mid-column feed position below said upper mid-column feed position;

(6) at least a portion of said at least one liquid stream is expanded to said lower pressure and is supplied to said distillation column at a lower mid-column feed position below said mid-column feed position;

(7) an overhead vapor stream is withdrawn from an upper region of said distillation column and divided into at least a first portion and a second portion;

(8) a distillation vapor stream is withdrawn from a region of said distillation column above said upper mid-column feed position and is combined with said first portion to form a combined vapor stream;

(9) said combined vapor stream is compressed to higher pressure;

(10) said compressed combined vapor stream is directed into heat exchange relation with said second portion, whereby said second portion is heated and said compressed combined vapor stream is cooled sufficiently to condense at least a part of it and thereby form a condensed stream, and thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction;

(11) at least a portion of said condensed stream is expanded to said lower pressure and is thereafter supplied to said distillation column at a top feed position; and

(12) the quantities and temperatures of said feed streams to said distillation column are effective to maintain the overhead temperature of said distillation column at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

4. In a process for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in which process

(a) said gas stream is cooled under pressure to provide a cooled stream;

the improvement wherein prior to cooling, said gas stream is divided into first and second streams; and (1) said first stream is cooled to condense substantially all of it and is thereafter expanded to said lower pressure whereby it is further cooled;

(3) said second stream is cooled under pressure sufficiently to partially condense it;

(4) said partially condensed second stream is separated thereby to provide a vapor stream and at least one liquid stream;

(5) said vapor stream is expanded to said lower pressure and is supplied to said distillation column at a mid-column feed position below said upper mid-column feed position;

(9) said combined vapor stream is compressed to higher pressure;

5. In a process for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in which process

(a) said gas stream is cooled under pressure to provide a cooled stream;

(1) said partially condensed gas stream is separated thereby to provide a vapor stream and at least one liquid stream; (2) said vapor stream is thereafter divided into first and second streams;

(3) said first stream is combined with at least a portion of said at least one liquid stream to form a combined stream, whereupon said combined stream is cooled to condense substantially all of it and is thereafter expanded to said lower pressure whereby it is further cooled;

(4) said expanded cooled combined stream is thereafter supplied to said distillation column at an upper mid-column feed position;

(6) any remaining portion of said at least one liquid stream is expanded to said lower pressure and is supplied to said distillation column at a lower mid-column feed position below said mid-column feed position;

(9) said combined vapor stream is compressed to higher pressure;

6. In a process for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in which process

(a) said gas stream is cooled under pressure to provide a cooled stream;

(1) said first stream is cooled to condense substantially all of it and is thereafter expanded to said lower pressure whereby it is further cooled; (2) said expanded cooled first stream is thereafter supplied at a mid-column feed position to a contacting and separating device that produces a first overhead vapor stream and a bottom liquid stream, whereupon said bottom liquid stream is supplied to said distillation column;

(3) said second stream is expanded to said lower pressure and is supplied to said contacting and separating device at a first lower column feed position below said mid-column feed position;

(4) a second overhead vapor stream is withdrawn from an upper region of said distillation column and is supplied to said contacting and separating device at a second lower column feed position below said mid-column feed position;

(5) said first overhead vapor stream is divided into at least a first portion and a second portion;

(6) a distillation vapor stream is withdrawn from a region of said contacting and separating device above said mid-column feed position and is combined with said first portion to form a combined vapor stream;

(7) said combined vapor stream is compressed to higher pressure;

(8) said compressed combined vapor stream is directed into heat exchange relation with said second portion, whereby said second portion is heated and said compressed combined vapor stream is cooled sufficiently to condense at least a part of it and thereby form a condensed stream, and thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction; (9) at least a portion of said condensed stream is expanded to said lower pressure and is thereafter supplied to said contacting and separating device at a top feed position; and

(10) the quantities and temperatures of said feed streams to said contacting and separating device are effective to maintain the overhead temperature of said contacting and separating device at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

7. In a process for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in which process

(a) said gas stream is cooled under pressure to provide a cooled stream;

(3) said second stream is cooled and thereafter expanded to said lower pressure and supplied to said contacting and separating device at a first lower column feed position below said mid-column feed position;

(7) said combined vapor stream is compressed to higher pressure;

8. In a process for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in which process

(a) said gas stream is cooled under pressure to provide a cooled stream;

(4) said expanded cooled first stream is thereafter supplied at a mid-column feed position to a contacting and separating device that produces a first overhead vapor stream and a bottom liquid stream, whereupon said bottom liquid stream is supplied to said distillation column;

(5) said second stream is expanded to said lower pressure and is supplied to said contacting and separating device at a first lower column feed position below said mid-column feed position;

(6) at least a portion of said at least one liquid stream is expanded to said lower pressure and is supplied to said distillation column at a mid-column feed position;

(7) a second overhead vapor stream is withdrawn from an upper region of said distillation column and is supplied to said contacting and separating device at a second lower column feed position below said mid-column feed position;

(8) said first overhead vapor stream is divided into at least a first portion and a second portion;

(9) a distillation vapor stream is withdrawn from a region of said contacting and separating device above said mid-column feed position and is combined with said first portion to form a combined vapor stream;

(10) said combined vapor stream is compressed to higher pressure; (11) said compressed combined vapor stream is directed into heat exchange relation with said second portion, whereby said second portion is heated and said compressed combined vapor stream is cooled sufficiently to condense at least a part of it and thereby form a condensed stream, and thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction;

(12) at least a portion of said condensed stream is expanded to said lower pressure and is thereafter supplied to said contacting and separating device at a top feed position; and

(13) the quantities and temperatures of said feed streams to said contacting and separating device are effective to maintain the overhead temperature of said contacting and separating device at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

9. In a process for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in which process

(a) said gas stream is cooled under pressure to provide a cooled stream;

(c) said further cooled stream is directed into a distillation column and fractionated at said lower pressure whereby the components of said relatively less volatile fraction are recovered; the improvement wherein prior to cooling, said gas stream is divided into first and second streams; and

(2) said expanded cooled first stream is thereafter supplied at a mid-column feed position to a contacting and separating device that produces an overhead vapor stream and a bottom liquid stream, whereupon said bottom liquid stream is supplied to said distillation column;

(5) said vapor stream is expanded to said lower pressure and is supplied to said contacting and separating device at a first lower column feed position below said mid-column feed position;

(8) said first overhead vapor stream is divided into at least a first portion and a second portion; (9) a distillation vapor stream is withdrawn from a region of said contacting and separating device above said mid-column feed position and is combined with said first portion to form a combined vapor stream;

(10) said combined vapor stream is compressed to higher pressure;

(11) said compressed combined vapor stream is directed into heat exchange relation with said second portion, whereby said second portion is heated and said compressed combined vapor stream is cooled sufficiently to condense at least a part of it and thereby form a condensed stream, and thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction;

10. In a process for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in which process

(a) said gas stream is cooled under pressure to provide a cooled stream; (b) said cooled stream is expanded to a lower pressure whereby it is further cooled; and

(2) said vapor stream is thereafter divided into first and second streams;

(4) said expanded cooled combined stream is thereafter supplied at a mid-column feed position to a contacting and separating device that produces a first overhead vapor stream and a bottom liquid stream, whereupon said bottom liquid stream is supplied to said distillation column;

(6) any remaining portion of said at least one liquid stream is expanded to said lower pressure and is supplied to said distillation column at a mid-column feed position; (7) a second overhead vapor stream is withdrawn from an upper region of said distillation column and is supplied to said contacting and separating device at a second lower column feed position below said mid-column feed position;

(10) said combined vapor stream is compressed to higher pressure;

11. The improvement according to claim 1, 2, 3, 4, or 5 wherein said distillation vapor stream is withdrawn from a region of said distillation column below said upper mid-column feed position and above said mid-column feed position.

12. The improvement according to claim 1, 2, 3, 4, or 5 wherein said distillation vapor stream is withdrawn from a region of said distillation column below said mid-column feed position.

13. The improvement according to claim 6, 7, 8, 9, or 10 wherein said distillation vapor stream is withdrawn from a region of said contacting and separating device below said mid-column feed position and above said first and second lower column feed positions.

14. The improvement according to claim 6, 7, 8, 9, or 10 wherein said second overhead vapor stream is divided into said distillation vapor stream and a second distillation vapor stream, whereupon said second distillation vapor stream is supplied to said contacting and separating device at said second lower column feed position.

15. In an apparatus for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in said apparatus there being

(a) a first cooling means to cool said gas stream under pressure connected to provide a cooled stream under pressure; (b) a first expansion means connected to receive at least a portion of said cooled stream under pressure and expand it to a lower pressure, whereby said stream is further cooled; and

(c) a distillation column connected to receive said further cooled stream, said distillation column being adapted to separate said further cooled stream into an overhead vapor stream and said relatively less volatile fraction;

the improvement wherein said apparatus includes

(1) first dividing means connected to said first cooling means to receive said cooled stream and divide it into first and second streams;

(2) second cooling means connected to said first dividing means to receive said first stream and cool it sufficiently to substantially condense it;

(3) second expansion means connected to said second cooling means to receive said substantially condensed first stream and expand it to said lower pressure, said second expansion means being further connected to said distillation column to supply said expanded cooled first stream to said distillation column at an upper mid-column feed position;

(4) said first expansion means being connected to said first dividing means to receive said second stream and expand it to said lower pressure, said first expansion means being further connected to said distillation column to supply said expanded second stream to said distillation column at a mid-column feed position below said upper mid-column feed position;

(5) second dividing means connected to said distillation column to receive said overhead vapor stream separated therein and divide it into at least a first portion and a second portion; (6) heat exchange means connected to said second dividing means to receive at least a portion of said second portion and heat it, thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction;

(7) vapor withdrawing means connected to said distillation column to receive a distillation vapor stream from a region of said distillation column above said upper mid-column feed position;

(8) combining means connected to said second dividing means and said vapor withdrawing means to receive said first portion and said distillation vapor stream and form a combined vapor stream;

(9) compressing means connected to said combining means to receive said combined vapor stream and compress it to higher pressure;

(10) said heat exchange means being further connected to said compressing means to receive said compressed combined vapor stream and cool it sufficiently to condense at least a part of it, thereby forming a condensed stream while supplying at least a portion of the heating of step (6);

(11) third expansion means connected to said heat exchange means to receive said condensed stream and expand it to said lower pressure, said third expansion means being further connected to said distillation column to supply at least a portion of said expanded condensed stream to said distillation column at a top feed position; and

(12) control means adapted to regulate the quantities and temperatures of said feed streams to said distillation column to maintain the overhead temperature of said distillation column at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

16. In an apparatus for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in said apparatus there being

(a) a first cooling means to cool said gas stream under pressure connected to provide a cooled stream under pressure;

(b) a first expansion means connected to receive at least a portion of said cooled stream under pressure and expand it to a lower pressure, whereby said stream is further cooled; and

the improvement wherein said apparatus includes

(1) first dividing means prior to said first cooling means to divide said gas stream into first and second streams;

(3) second expansion means connected to said second cooling means to receive said substantially condensed first stream and expand it to said lower pressure, said second expansion means being further connected to said distillation column to supply said expanded cooled first stream to said distillation column at an upper mid-column feed position; (4) said first cooling means being connected to said first dividing means to receive said second stream and cool it;

(5) said first expansion means being connected to said first cooling means to receive said cooled second stream and expand it to said lower pressure, said first expansion means being further connected to said distillation column to supply said expanded cooled second stream to said distillation column at a mid-column feed position below said upper mid-column feed position;

(6) second dividing means connected to said distillation column to receive said overhead vapor stream separated therein and divide it into at least a first portion and a second portion;

(7) heat exchange means connected to said second dividing means to receive at least a portion of said second portion and heat it, thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction;

(8) vapor withdrawing means connected to said distillation column to receive a distillation vapor stream from a region of said distillation column above said upper mid-column feed position;

(9) combining means connected to said second dividing means and said vapor withdrawing means to receive said first portion and said distillation vapor stream and form a combined vapor stream;

(10) compressing means connected to said combining means to receive said combined vapor stream and compress it to higher pressure;

(11) said heat exchange means being further connected to said compressing means to receive said compressed combined vapor stream and cool it sufficiently to condense at least a part of it, thereby forming a condensed stream while supplying at least a portion of the heating of step (7);

(12) third expansion means connected to said heat exchange means to receive said condensed stream and expand it to said lower pressure, said third expansion means being further connected to said distillation column to supply at least a portion of said expanded condensed stream to said distillation column at a top feed position; and

(13) control means adapted to regulate the quantities and temperatures of said feed streams to said distillation column to maintain the overhead temperature of said distillation column at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

17. In an apparatus for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in said apparatus there being

(c) a distillation column connected to receive said further cooled stream, said distillation column being adapted to separate said further cooled stream into an overhead vapor stream and said relatively less volatile fraction; the improvement wherein said apparatus includes

(1) said first cooling means being adapted to cool said gas stream under pressure sufficiently to partially condense it;

(2) separating means connected to said first cooling means to receive said partially condensed gas stream and separate it into a vapor stream and at least one liquid stream;

(3) first dividing means connected to said separating means to receive said vapor stream and divide it into first and second streams;

(4) second cooling means connected to said first dividing means to receive said first stream and cool it sufficiently to substantially condense it;

(5) second expansion means connected to said second cooling means to receive said substantially condensed first stream and expand it to said lower pressure, said second expansion means being further connected to said distillation column to supply said expanded cooled first stream to said distillation column at an upper mid-column feed position;

(6) said first expansion means being connected to said first dividing means to receive said second stream and expand it to said lower pressure, said first expansion means being further connected to said distillation column to supply said expanded second stream to said distillation column at a mid-column feed position below said upper mid-column feed position;

(7) third expansion means connected to said separating means to receive at least a portion of said at least one liquid stream and expand it to said lower pressure, said third expansion means being further connected to said distillation column to supply said expanded liquid stream to said distillation column at a lower mid-column feed position below said mid-column feed position; (8) second dividing means connected to said distillation column to receive said overhead vapor stream separated therein and divide it into at least a first portion and a second portion;

(9) heat exchange means connected to said second dividing means to receive at least a portion of said second portion and heat it, thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction;

(10) vapor withdrawing means connected to said distillation column to receive a distillation vapor stream from a region of said distillation column above said upper mid-column feed position;

(11) combining means connected to said second dividing means and said vapor withdrawing means to receive said first portion and said distillation vapor stream and form a combined vapor stream;

(12) compressing means connected to said combining means to receive said combined vapor stream and compress it to higher pressure;

(13) said heat exchange means being further connected to said compressing means to receive said compressed combined vapor stream and cool it sufficiently to condense at least a part of it, thereby forming a condensed stream while supplying at least a portion of the heating of step (9);

(14) fourth expansion means connected to said heat exchange means to receive said condensed stream and expand it to said lower pressure, said fourth expansion means being further connected to said distillation column to supply at least a portion of said expanded condensed stream to said distillation column at a top feed position; and (15) control means adapted to regulate the quantities and temperatures of said feed streams to said distillation column to maintain the overhead temperature of said distillation column at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

18. In an apparatus for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in said apparatus there being

the improvement wherein said apparatus includes

(4) said first cooling means being connected to said first dividing means to receive said second stream, said first cooling means being adapted to cool said second stream under pressure sufficiently to partially condense it;

(5) separating means connected to said first cooling means to receive said partially condensed second stream and separate it into a vapor stream and at least one liquid stream;

(6) said first expansion means being connected to said separating means to receive said vapor stream and expand it to said lower pressure, said first expansion means being further connected to said distillation column to supply said expanded vapor stream to said distillation column at a mid-column feed position below said upper mid-column feed position;

(7) third expansion means connected to said separating means to receive at least a portion of said at least one liquid stream and expand it to said lower pressure, said third expansion means being further connected to said distillation column to supply said expanded liquid stream to said distillation column at a lower mid-column feed position below said mid-column feed position;

(8) second dividing means connected to said distillation column to receive said overhead vapor stream separated therein and divide it into at least a first portion and a second portion;

(14) fourth expansion means connected to said heat exchange means to receive said condensed stream and expand it to said lower pressure, said fourth expansion means being further connected to said distillation column to supply at least a portion of said expanded condensed stream to said distillation column at a top feed position; and

(15) control means adapted to regulate the quantities and temperatures of said feed streams to said distillation column to maintain the overhead temperature of said distillation column at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

19. In an apparatus for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in said apparatus there being

the improvement wherein said apparatus includes

(4) first combining means connected to said first dividing means and said separating means to receive said first stream and at least a portion of said at least one liquid stream and form a combined stream; (5) second cooling means connected to said first combining means to receive said combined stream and cool it sufficiently to substantially condense it;

(6) second expansion means connected to said second cooling means to receive said substantially condensed combined stream and expand it to said lower pressure, said second expansion means being further connected to said distillation column to supply said expanded cooled combined stream to said distillation column at an upper mid-column feed position;

(7) said first expansion means being connected to said first dividing means to receive said second stream and expand it to said lower pressure, said first expansion means being further connected to said distillation column to supply said expanded second stream to said distillation column at a mid-column feed position below said upper mid-column feed position;

(8) third expansion means being connected to said separating means to receive any remaining portion of said at least one liquid stream and expand it to said lower pressure, said third expansion means being further connected to said distillation column to supply said expanded liquid stream to said distillation column at a lower mid-column feed position below said mid-column feed position;

(9) second dividing means connected to said distillation column to receive said overhead vapor stream separated therein and divide it into at least a first portion and a second portion;

(10) heat exchange means connected to said second dividing means to receive at least a portion of said second portion and heat it, thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction;

(11) vapor withdrawing means connected to said distillation column to receive a distillation vapor stream from a region of said distillation column above said upper mid-column feed position;

(12) second combining means connected to said second dividing means and said vapor withdrawing means to receive said first portion and said distillation vapor stream and form a combined vapor stream;

(13) compressing means connected to said second combining means to receive said combined vapor stream and compress it to higher pressure;

(14) said heat exchange means being further connected to said compressing means to receive said compressed combined vapor stream and cool it sufficiently to condense at least a part of it, thereby forming a condensed stream while supplying at least a portion of the heating of step (10);

(15) fourth expansion means connected to said heat exchange means to receive said condensed stream and expand it to said lower pressure, said fourth expansion means being further connected to said distillation column to supply at least a portion of said expanded condensed stream to said distillation column at a top feed position; and

(16) control means adapted to regulate the quantities and temperatures of said feed streams to said distillation column to maintain the overhead temperature of said distillation column at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

20. In an apparatus for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in said apparatus there being

(c) a distillation column connected to receive said further cooled stream, said distillation column being adapted to separate said further cooled stream into a first overhead vapor stream and said relatively less volatile fraction;

the improvement wherein said apparatus includes

(3) second expansion means connected to said second cooling means to receive said substantially condensed first stream and expand it to said lower pressure, said second expansion means being further connected to a contacting and separating means to supply said expanded cooled first stream to said contacting and separating means at a mid-column feed position, said contacting and separating means being adapted to produce a second overhead vapor stream and a bottom liquid stream; (4) said first expansion means being connected to said first dividing means to receive said second stream and expand it to said lower pressure, said first expansion means being further connected to said contacting and separating means to supply said expanded second stream to said contacting and separating means at a first lower column feed position below said mid-column feed position;

(5) said distillation column being connected to said contacting and separating means to receive at least a portion of said bottom liquid stream;

(6) said contacting and separating means being further connected to said distillation column to receive at least a portion of said first overhead vapor stream at a second lower column feed position below said mid-column feed position;

(7) second dividing means connected to said contacting and separating means to receive said second overhead vapor stream separated therein and divide it into at least a first portion and a second portion;

(8) heat exchange means connected to said second dividing means to receive at least a portion of said second portion and heat it, thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction;

(9) vapor withdrawing means connected to said contacting and separating means to receive a distillation vapor stream from a region of said contacting and separating device above said mid-column feed position;

(10) combining means connected to said second dividing means and said vapor withdrawing means to receive said first portion and said distillation vapor stream and form a combined vapor stream; (11) compressing means connected to said combining means to receive said combined vapor stream and compress it to higher pressure;

(12) said heat exchange means being further connected to said compressing means to receive said compressed combined vapor stream and cool it sufficiently to condense at least a part of it, thereby forming a condensed stream while supplying at least a portion of the heating of step (8);

(13) third expansion means connected to said heat exchange means to receive said condensed stream and expand it to said lower pressure, said third expansion means being further connected to said contacting and separating means to supply at least a portion of said expanded condensed stream to said contacting and separating means at a top feed position; and

(14) control means adapted to regulate the quantities and temperatures of said feed streams to said contacting and separating means to maintain the overhead temperature of said contacting and separating means at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

21. In an apparatus for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in said apparatus there being

the improvement wherein said apparatus includes

(3) second expansion means connected to said second cooling means to receive said substantially condensed first stream and expand it to said lower pressure, said second expansion means being further connected to a contacting and separating means to supply said expanded cooled first stream to said contacting and separating means at a mid-column feed position, said contacting and separating means being adapted to produce a second overhead vapor stream and a bottom liquid stream;

(4) said first cooling means being connected to said first dividing means to receive said second stream and cool it;

(5) said first expansion means being connected to said first cooling means to receive said cooled second stream and expand it to said lower pressure, said first expansion means being further connected to said contacting and separating means to supply said expanded cooled second stream to said contacting and separating means at a first lower column feed position below said mid-column feed position;

(6) said distillation column being connected to said contacting and separating means to receive at least a portion of said bottom liquid stream;

(7) said contacting and separating means being further connected to said distillation column to receive at least a portion of said first overhead vapor stream at a second lower column feed position below said mid-column feed position;

(8) second dividing means connected to said contacting and separating means to receive said second overhead vapor stream separated therein and divide it into at least a first portion and a second portion;

(10) vapor withdrawing means connected to said contacting and separating means to receive a distillation vapor stream from a region of said contacting and separating device above said mid-column feed position;

(12) compressing means connected to said combining means to receive said combined vapor stream and compress it to higher pressure; (13) said heat exchange means being further connected to said compressing means to receive said compressed combined vapor stream and cool it sufficiently to condense at least a part of it, thereby forming a condensed stream while supplying at least a portion of the heating of step (9);

(14) third expansion means connected to said heat exchange means to receive said condensed stream and expand it to said lower pressure, said third expansion means being further connected to said contacting and separating means to supply at least a portion of said expanded condensed stream to said contacting and separating means at a top feed position; and

(15) control means adapted to regulate the quantities and temperatures of said feed streams to said contacting and separating means to maintain the overhead temperature of said contacting and separating means at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

22. In an apparatus for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in said apparatus there being

(b) a first expansion means connected to receive at least a portion of said cooled stream under pressure and expand it to a lower pressure, whereby said stream is further cooled; and (c) a distillation column connected to receive said further cooled stream, said distillation column being adapted to separate said further cooled stream into a first overhead vapor stream and said relatively less volatile fraction;

the improvement wherein said apparatus includes

(5) second expansion means connected to said second cooling means to receive said substantially condensed first stream and expand it to said lower pressure, said second expansion means being further connected to a contacting and separating means to supply said expanded cooled first stream to said contacting and separating means at a mid-column feed position, said contacting and separating means being adapted to produce a second overhead vapor stream and a bottom liquid stream;

(6) said first expansion means being connected to said first dividing means to receive said second stream and expand it to said lower pressure, said first expansion means being further connected to said contacting and separating means to supply said expanded second stream to said contacting and separating means at a first lower column feed position below said mid-column feed position; (7) third expansion means connected to said separating means to receive at least a portion of said at least one liquid stream and expand it to said lower pressure, said third expansion means being further connected to said distillation column to supply said expanded liquid stream to said distillation column at a mid-column feed position;

(8) said distillation column being connected to said contacting and separating means to receive at least a portion of said bottom liquid stream;

(9) said contacting and separating means being further connected to said distillation column to receive at least a portion of said first overhead vapor stream at a second lower column feed position below said mid-column feed position;

(10) second dividing means connected to said contacting and separating means to receive said second overhead vapor stream separated therein and divide it into at least a first portion and a second portion;

(11) heat exchange means connected to said second dividing means to receive at least a portion of said second portion and heat it, thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction;

(12) vapor withdrawing means connected to said contacting and separating means to receive a distillation vapor stream from a region of said contacting and separating device above said mid-column feed position;

(13) combining means connected to said second dividing means and said vapor withdrawing means to receive said first portion and said distillation vapor stream and form a combined vapor stream; (14) compressing means connected to said combining means to receive said combined vapor stream and compress it to higher pressure;

(15) said heat exchange means being further connected to said compressing means to receive said compressed combined vapor stream and cool it sufficiently to condense at least a part of it, thereby forming a condensed stream while supplying at least a portion of the heating of step (11);

(16) fourth expansion means connected to said heat exchange means to receive said condensed stream and expand it to said lower pressure, said fourth expansion means being further connected to said contacting and separating means to supply at least a portion of said expanded condensed stream to said contacting and separating means at a top feed position; and

(17) control means adapted to regulate the quantities and temperatures of said feed streams to said contacting and separating means to maintain the overhead temperature of said contacting and separating means at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

23. In an apparatus for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in said apparatus there being

the improvement wherein said apparatus includes

(5) separating means connected to said first cooling means to receive said partially condensed second stream and separate it into a vapor stream and at least one liquid stream; (6) said first expansion means being connected to said separating means to receive said vapor stream and expand it to said lower pressure, said first expansion means being further connected to said contacting and separating means to supply said expanded vapor stream to said contacting and separating means at a first lower column feed position below said mid-column feed position;

(7) third expansion means connected to said separating means to receive at least a portion of said at least one liquid stream and expand it to said lower pressure, said third expansion means being further connected to said distillation column to supply said expanded liquid stream to said distillation column at a mid-column feed position;

(11) heat exchange means connected to said second dividing means to receive at least a portion of said second portion and heat it, thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction; (12) vapor withdrawing means connected to said contacting and separating means to receive a distillation vapor stream from a region of said contacting and separating device above said mid-column feed position;

(13) combining means connected to said second dividing means and said vapor withdrawing means to receive said first portion and said distillation vapor stream and form a combined vapor stream;

(14) compressing means connected to said combining means to receive said combined vapor stream and compress it to higher pressure;

24. In an apparatus for the separation of a gas stream containing methane, C₂ components, C3 components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂ components, C3 components, and heavier hydrocarbon components or said C3 components and heavier hydrocarbon components, in said apparatus there being

the improvement wherein said apparatus includes

(4) first combining means connected to said first dividing means and said separating means to receive said first stream and at least a portion of said at least one liquid stream and form a combined stream;

(5) second cooling means connected to said first combining means to receive said combined stream and cool it sufficiently to substantially condense it; (6) second expansion means connected to said second cooling means to receive said substantially condensed combined stream and expand it to said lower pressure, said second expansion means being further connected to a contacting and separating means to supply said expanded cooled combined stream to said contacting and separating means at a mid-column feed position, said contacting and separating means being adapted to produce a second overhead vapor stream and a bottom liquid stream;

(7) said first expansion means being connected to said first dividing means to receive said second stream and expand it to said lower pressure, said first expansion means being further connected to said contacting and separating means to supply said expanded second stream to said contacting and separating means at a first lower column feed position below said mid-column feed position;

(8) third expansion means connected to said separating means to receive any remaining portion of said at least one liquid stream and expand it to said lower pressure, said third expansion means being further connected to said distillation column to supply said expanded liquid stream to said distillation column at a mid-column feed position;

(9) said distillation column being connected to said contacting and separating means to receive at least a portion of said bottom liquid stream;

(10) said contacting and separating means being further connected to said distillation column to receive at least a portion of said first overhead vapor stream at a second lower column feed position below said mid-column feed position; (11) second dividing means connected to said contacting and separating means to receive said second overhead vapor stream separated therein and divide it into at least a first portion and a second portion;

(12) heat exchange means connected to said second dividing means to receive at least a portion of said second portion and heat it, thereafter discharging at least a portion of said heated second portion as said volatile residue gas fraction;

(13) vapor withdrawing means connected to said contacting and separating means to receive a distillation vapor stream from a region of said contacting and separating device above said mid-column feed position;

(14) second combining means connected to said second dividing means and said vapor withdrawing means to receive said first portion and said distillation vapor stream and form a combined vapor stream;

(15) compressing means connected to said second combining means to receive said combined vapor stream and compress it to higher pressure;

(16) said heat exchange means being further connected to said compressing means to receive said compressed combined vapor stream and cool it sufficiently to condense at least a part of it, thereby forming a condensed stream while supplying at least a portion of the heating of step (12);

(17) fourth expansion means connected to said heat exchange means to receive said condensed stream and expand it to said lower pressure, said fourth expansion means being further connected to said contacting and separating means to supply at least a portion of said expanded condensed stream to said contacting and separating means at a top feed position; and (18) control means adapted to regulate the quantities and temperatures of said feed streams to said contacting and separating means to maintain the overhead temperature of said contacting and separating means at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

25. The improvement according to claim 15, 16, 17, 18, or 19 wherein said vapor withdrawing means is connected to said distillation column to receive said distillation vapor stream from a region of said distillation column below said upper mid-column feed position and above said mid-column feed position.

26. The improvement according to claim 15, 16, 17, 18, or 19 wherein said vapor withdrawing means is connected to said distillation column to receive said distillation vapor stream from a region of said distillation column below said mid-column feed position.

27. The improvement according to claim 20, 21, 22, 23, or 24 wherein said vapor withdrawing means is connected to said contacting and separating means to receive said distillation vapor stream from a region of said contacting and separating means below said mid-column feed position and above said first and second lower column feed positions.

28. The improvement according to claim 20, 21, 22, or 23 wherein

(1) a third dividing means is connected to said distillation column to receive said first overhead vapor stream and divide it into said distillation vapor stream and a second distillation vapor stream;

(2) said contacting and separating device is adapted to be connected to said third dividing means to receive said second distillation vapor stream at said second lower column feed position; and (3) said combining means is adapted to be connected to said third dividing means to receive said distillation vapor stream.

29. The improvement according to claim 24 wherein

(2) said contacting and separating device is adapted to be connected to said third dividing means to receive said second distillation vapor stream at said second lower column feed position; and

(3) said second combining means is adapted to be connected to said third dividing means to receive said distillation vapor stream.