US20110067441A1

US20110067441A1 - Hydrocarbon Gas Processing

Info

Publication number: US20110067441A1
Application number: US12/868,993
Authority: US
Inventors: Tony L. Martinez; John D. Wilkinson; Joe T. Lynch; Hank M. Hudson; Kyle T. Cuellar
Original assignee: Ortloff Engineers Ltd
Current assignee: Honeywell UOP LLC
Priority date: 2009-09-21
Filing date: 2010-08-26
Publication date: 2011-03-24
Also published as: AR078402A1; EA021947B1; CL2012000687A1; JP2013505422A; WO2011049672A1; JP5850838B2; EP2480847A4; WO2011034709A1; CO6531456A2; ZA201202696B; PE20121421A1; MX348674B; EA024075B1; BR112012006277A2; AU2010308519A1; SG178989A1; TW201127945A; JP2013505421A; PE20121422A1; CA2773211A1

Abstract

A process for the recovery of ethane, ethylene, propane, propylene, and heavier hydrocarbon components from a hydrocarbon gas stream is disclosed. 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, heated, and supplied to the fractionation tower at an upper mid-column feed position. The second stream is expanded to the tower pressure and is then 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 A distillation vapor stream is withdrawn from the column above the feed point of the second stream and is then directed into heat exchange relation with the expanded cooled first stream and the tower overhead vapor stream to cool the distillation vapor stream and condense at least a part of it, forming a condensed stream. At least a portion of the condensed stream is directed to the fractionation tower as its top feed. The quantities and temperatures of the feeds to the fractionation tower are effective to maintain the overhead temperature of the fractionation tower at a temperature whereby the major portion of the desired components is recovered.

Description

This invention relates to a process and an apparatus for the separation of a gas containing hydrocarbons. The applicants claim the benefits under Title 35, United States Code, Section 119(e) of prior U.S. Provisional Applications No. 61/244,181 which was filed on Sep. 21, 2009, No. 61/346,150 which was filed on May 19, 2010, and No. 61/351,045 which was filed on Jun. 3, 2010.

BACKGROUND OF THE INVENTION

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.
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, 80.8% methane, 9.4% ethane and other C₂components, 4.7% propane and other C₃components, 1.2% iso-butane, 2.1% normal butane, and 1.1% pentanes plus, with the balance made up of nitrogen and carbon dioxide. Sulfur containing gases are also sometimes present.
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.
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. Pat. 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. Pat. No. 33,408; and co-pending application Ser. 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).
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 C₂components, C₃components, and heavier hydrocarbon components as bottom liquid product, or to separate residual methane, C₂components, nitrogen, and other volatile gases as overhead vapor from the desired C₃components and heavier hydrocarbon components as bottom liquid product.
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.
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.
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 C₂components, C₃components, C₄components, 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 C₂components, C₃components, C₄components, and heavier hydrocarbon components from the vapors.
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. Pat. Nos. 4,889,545; 5,568,737; and 5,881,569, assignee's co-pending application Ser. 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, Tex., Mar. 11-13, 2002. Unfortunately, these processes require the use of 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.
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. Because of the relatively high concentration of C₂components in the vapors lower in the tower, a significant quantity of liquid can be condensed in this side draw stream without elevating its pressure, often using only the refrigeration available in the cold vapor leaving the upper rectification section and the flash expanded substantially condensed stream. This condensed liquid, which is predominantly liquid methane, can then be used to absorb C₂components, C₃components, C₄components, 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.
Heretofore, such a side draw feature has been employed in C₃+ recovery systems, as illustrated in the assignee's U.S. Pat. No. 5,799,507, as well as in C₂+ recovery systems, as illustrated in the assignee's U.S. Pat. No. 7,191,617 and co-pending application Ser. Nos. 12/206,230 and 12/781,259. Surprisingly, applicants have found that using the flash expanded substantially condensed stream to provide a portion of the cooling of the side draw feature disclosed in assignee's co-pending application Ser. Nos. 12/206,230 and 12/781,259 processes improves the C₂+ recoveries and the system efficiency with no increase in operating cost.
In accordance with the present invention, it has been found that C₂recovery in excess of 87% and C₃and C₄+ recoveries in excess of 99% can be obtained without the need for compression of the reflux stream for the demethanizer. The present invention provides the further advantage of being able to maintain in excess of 99% recovery of the C₃and C₄+ components as the recovery of C₂components is adjusted from high to low values. In addition, the present invention makes possible essentially 100% separation of methane and lighter components from the C₂components and heavier components at the same energy requirements compared to the prior art while increasing 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.

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

FIG. 1 is a flow diagram of a prior art natural gas processing plant in accordance with U.S. Pat. No. 5,890,378;

FIG. 2 is a flow diagram of a prior art natural gas processing plant in accordance with U.S. Pat. No. 7,191,617;

FIG. 3 is a flow diagram of a prior art natural gas processing plant in accordance with assignee's co-pending application Ser. No. 12/206,230;

FIG. 4 is a flow diagram of a natural gas processing plant in accordance with the present invention; and

FIGS. 5 through 8 are flow diagrams illustrating alternative means of application of the present invention to a natural gas stream.

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

DESCRIPTION OF THE PRIOR ART

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. 5,890,378. In this simulation of the process, inlet gas enters the plant at 85° F. [29° C.] and 970 psia [6,688 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.
The feed stream 31 is cooled in heat exchanger 10 by heat exchange with cool residue gas (stream 45 b), demethanizer lower side reboiler liquids at 32° F. [0° C.] (stream 40), and propane refrigerant. 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 31 a enters separator 11 at 0° F. [−18° C.] and 955 psia [6,584 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 444 psia [3,061 kPa(a)]) of fractionation tower 20 by expansion valve 12, cooling stream 33 a to −27° F. [−33° C.] before it is supplied to fractionation tower 20 at a first lower mid-column feed point.
The vapor (stream 32) from separator 11 is further cooled in heat exchanger 13 by heat exchange with cool residue gas (stream 45 a) and demethanizer upper side reboiler liquids at −39° F. [−39° C.] (stream 39). The cooled stream 32 a enters separator 14 at −31° F. [−35° C.] and 950 psia [6,550 kPa(a)] where the vapor (stream 34) is separated from the condensed liquid (stream 37). The separator liquid (stream 37) is expanded to the tower operating pressure by expansion valve 19, cooling stream 37 a to −66° F. [−54° C.] before it is supplied to fractionation tower 20 at a second lower mid-column feed point.
The vapor (stream 34) from separator 14 is divided into two streams, 35 and 36. Stream 35, containing about 39% of the total vapor, passes through heat exchanger 15 in heat exchange relation with the cold residue gas (stream 45) where it is cooled to substantial condensation. The resulting substantially condensed stream 35 a at −123° F. [−86° C.] is then flash expanded through expansion valve 16 to slightly above the operating pressure of fractionation tower 20. 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 35 b leaving expansion valve 16 reaches a temperature of −130° F. [−90° C.]. The expanded stream 35 b is warmed to −126° F. [−88° C.] and further vaporized in heat exchanger 22 as it provides cooling and partial condensation of distillation vapor stream 42 withdrawn from stripping section 20 b of fractionation tower 20. The warmed stream 35 c is then supplied at an upper mid-column feed point, in absorbing section 20 a of fractionation tower 20.
The remaining 61% of the vapor from separator 14 (stream 36) enters a work expansion machine 17 in which mechanical energy is extracted from this portion of the high pressure feed. The machine 17 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expanded stream 36 a to a temperature of approximately −86° F. [−66° 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 18) that can be used to re-compress the residue gas (stream 45 c), for example. The partially condensed expanded stream 36 a is thereafter supplied as feed to fractionation tower 20 at a mid-column feed point.
The demethanizer in tower 20 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 20 a that contains the trays and/or packing to provide the necessary contact between the vapor portions of the expanded streams 35 c and 36 a rising upward and cold liquid falling downward to condense and absorb the C₂components, C₃components, and heavier components; and a lower, stripping section 20 b 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 20 b also includes one or more reboilers (such as reboiler 21 and the side reboilers 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 41, of methane and lighter components. Stream 36 a enters demethanizer 20 at an intermediate feed position located in the lower region of absorbing section 20 a of demethanizer 20. The liquid portion of the expanded stream 36 a comingles with liquids falling downward from absorbing section 20 a and the combined liquid continues downward into stripping section 20 b of demethanizer 20. The vapor portion of the expanded stream 36 a rises upward through absorbing section 20 a and is contacted with cold liquid falling downward to condense and absorb the C₂components, C₃components, and heavier components.
A portion of the distillation vapor (stream 42) is withdrawn from the upper region of stripping section 20 b. This stream is then cooled and partially condensed (stream 42 a) in exchanger 22 by heat exchange with expanded substantially condensed stream 35 b as described previously, cooling stream 42 from −96° F. [−71° C.] to about −128° F. [−89° C.] (stream 42 a). The operating pressure (441 psia [3,038 kPa(a)]) in reflux separator 23 is maintained slightly below the operating pressure of demethanizer 20. This provides the driving force which causes distillation vapor stream 42 to flow through heat exchanger 22 and thence into the reflux separator 23 where the condensed liquid (stream 44) is separated from any uncondensed vapor (stream 43).
The liquid stream 44 from reflux separator 23 is pumped by pump 24 to a pressure slightly above the operating pressure of demethanizer 20, and stream 44 a is then supplied as cold top column feed (reflux) to demethanizer 20 at −128° F. [−89° C.]. This cold liquid reflux absorbs and condenses the C₃components and heavier components rising in the upper rectification region of absorbing section 20 a of demethanizer 20.
The liquid product stream 41 exits the bottom of the tower at 112° F. [44° C.], based on a typical specification of a methane to ethane ratio of 0.025:1 on a molar basis in the bottom product. Cold demethanizer overhead stream 38 exits the top of demethanizer 20 at −128° F. [−89° C.] and combines with vapor stream 43 to form cold residue gas stream 45 at −128° F. [−89° C.]. The cold residue gas stream 45 passes countercurrently to the incoming feed gas in heat exchanger 15 where it is heated to −37° F. [−38° C.] (stream 45 a), in heat exchanger 13 where it is heated to −5° F. [−21° C.] (stream 45 b), and in heat exchanger 10 where it is heated to 80° F. [27° C.] (stream 45 c). The residue gas is then re-compressed in two stages. The first stage is compressor 18 driven by expansion machine 17. The second stage is compressor 25 driven by a supplemental power source which compresses the residue gas (stream 45 d) to sales line pressure. After cooling to 120° F. [49° C.] in discharge cooler 26, the residue gas product (stream 451) flows to the sales gas pipeline at 1015 psia [6,998 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 process 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	53,228	6,192	3,070	2,912	65,876
32	49,244	4,670	1,650	815	56,795
33	3,984	1,522	1,420	2,097	9,081
34	47,282	4,037	1,178	405	53,293
37	1,962	633	472	410	3,502
35	18,582	1,587	463	159	20,944
36	28,700	2,450	715	246	32,349
38	44,854	790	11	0	45,920
42	12,398	720	42	3	13,270
43	8,242	135	2	0	8,421
44	4,156	585	40	3	4,849
45	53,096	925	13	0	54,341
41	132	5,267	3,057	2,912	11,535
Recoveries*
Ethane	85.05%
Propane	99.57%
Butanes+	99.99%
Power

\begin{matrix} Residue Gas Compression & 24, 134 HP & [39, 676 kW] \\ Refrigerant Compression & \underline{7, 743 HP} & \underline{[12, 729 kW]} \\ Total Compression & 31, 877 HP & [52, 405 kW] \end{matrix}

*(Based on un-rounded flow rates)

FIG. 2 represents an alternative prior art process according to U.S. Pat. No. 7,191,617. The process of FIG. 2 has been applied to the same feed gas composition and conditions as described above for FIG. 1. In the simulation of this process, as in the simulation for the process of FIG. 1, operating conditions were selected to minimize energy consumption for a given recovery level.
In the simulation of the FIG. 2 process, inlet gas enters the plant as stream 31 and is cooled in heat exchanger 10 by heat exchange with cool residue gas (stream 45 b), demethanizer lower side reboiler liquids at 33° F. [0° C.] (stream 40), and propane refrigerant. The cooled stream 31 a enters separator 11 at 0° F. [−18° C.] and 955 psia [6,584 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 450 psia [3,103 kPa(a)]) of fractionation tower 20 by expansion valve 12, cooling stream 33 a to −27° F. [−33° C.] before it is supplied to fractionation tower 20 at a first lower mid-column feed point.
The vapor (stream 32) from separator 11 is further cooled in heat exchanger 13 by heat exchange with cool residue gas (stream 45 a) and demethanizer upper side reboiler liquids at −38° F. [−39° C.] (stream 39). The cooled stream 32 a enters separator 14 at −29° F. [−34° C.] and 950 psia [6,550 kPa(a)] where the vapor (stream 34) is separated from the condensed liquid (stream 37). The separator liquid (stream 37) is expanded to the tower operating pressure by expansion valve 19, cooling stream 37 a to −64° F. [−53° C.] before it is supplied to fractionation tower 20 at a second lower mid-column feed point.
The vapor (stream 34) from separator 14 is divided into two streams, 35 and 36. Stream 35, containing about 37% of the total vapor, passes through heat exchanger 15 in heat exchange relation with the cold residue gas (stream 45) where it is cooled to substantial condensation. The resulting substantially condensed stream 35 a at −115° F. [−82° C.] is then flash expanded through expansion valve 16 to the operating pressure of fractionation tower 20. During expansion a portion of the stream is vaporized, resulting in cooling of stream 35 b to −129° F. [−89° C.] before it is supplied to fractionation tower 20 at an upper mid-column feed point.
The remaining 63% of the vapor from separator 14 (stream 36) enters a work expansion machine 17 in which mechanical energy is extracted from this portion of the high pressure feed. The machine 17 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expanded stream 36 a to a temperature of approximately −84° F. [−65° C.]. The partially condensed expanded stream 36 a is thereafter supplied as feed to fractionation tower 20 at a mid-column feed point.
A portion of the distillation vapor (stream 42) is withdrawn from the upper region of the stripping section in fractionation tower 20. This stream is then cooled from −91° F. [−68° C.] to −122° F. [−86° C.] and partially condensed (stream 42 a) in heat exchanger 22 by heat exchange with the cold demethanizer overhead stream 38 exiting the top of demethanizer 20 at −127° F. [−88° C.]. The cold demethanizer overhead stream is warmed slightly to −120° F. [−84° C.] (stream 38 a) as it cools and condenses at least a portion of stream 42.
The operating pressure (447 psia [3,079 kPa(a)]) in reflux separator 23 is maintained slightly below the operating pressure of demethanizer 20. This provides the driving force which causes distillation vapor stream 42 to flow through heat exchanger 22 and thence into the reflux separator 23 where the condensed liquid (stream 44) is separated from any uncondensed vapor (stream 43). Stream 43 then combines with the warmed demethanizer overhead stream 38 a from heat exchanger 22 to form cold residue gas stream 45 at −120° F. [−84° C.].
The liquid stream 44 from reflux separator 23 is pumped by pump 24 to a pressure slightly above the operating pressure of demethanizer 20, and stream 44 a is then supplied as cold top column feed (reflux) to demethanizer 20 at −121° F. [−85° C.]. This cold liquid reflux absorbs and condenses the C₃components and heavier components rising in the upper rectification region of the absorbing section of demethanizer 20.
The liquid product stream 41 exits the bottom of tower 20 at 114° F. [45° C.]. The cold residue gas stream 45 passes countercurrently to the incoming feed gas in heat exchanger 15 where it is heated to −36° F. [−38° C.] (stream 45 a), in heat exchanger 13 where it is heated to −5° F. [−20° C.] (stream 45 b), and in heat exchanger 10 where it is heated to 80° F. [27° C.] (stream 45 c) as it provides cooling as previously described. The residue gas is then re-compressed in two stages, compressor 18 driven by expansion machine 17 and compressor 25 driven by a supplemental power source. After stream 45 e is cooled to 120° F. [49° C.] in discharge cooler 26, the residue gas product (stream 45 f) flows to the sales gas pipeline at 1015 psia [6,998 kPa(a)].
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	53,228	6,192	3,070	2,912	65,876
32	49,244	4,670	1,650	815	56,795
33	3,984	1,522	1,420	2,097	9,081
34	47,440	4,081	1,204	420	53,536
37	1,804	589	446	395	3,259
35	17,553	1,510	445	155	19,808
36	29,887	2,571	759	265	33,728
38	48,675	811	23	1	49,805
42	5,555	373	22	2	6,000
43	4,421	113	2	0	4,562
44	1,134	260	20	2	1,438
45	53,096	924	25	1	54,367
41	132	5,268	3,045	2,911	11,509
Recoveries*
Ethane	85.08%
Propane	99.20%
Butanes+	99.98%
Power

\begin{matrix} Residue Gas Compression & 23, 636 HP & [38, 857 kW] \\ Refrigerant Compression & \underline{7, 561 HP} & \underline{[12, 430 kW]} \\ Total Compression & 31, 197 HP & [51, 287 kW] \end{matrix}

*(Based on un-rounded flow rates)

A comparison of Tables I and II shows that, compared to the FIG. 1 process, the FIG. 2 process maintains essentially the same ethane recovery (85.08% versus 85.05%) and butanes+recovery (99.98% versus 99.99%), but the propane recovery drops from 99.57% to 99.20%. However, comparison of Tables I and II further shows that the power requirement for the FIG. 2 process is about 2% lower than that of the FIG. 1 process.
FIG. 3 represents an alternative prior art process according to co-pending application Ser. No. 12/206,230. The process of FIG. 3 has been applied to the same feed gas composition and conditions as described above for FIGS. 1 and 2. In the simulation of this process, as in the simulation for the process of FIGS. 1 and 2, operating conditions were selected to minimize energy consumption for a given recovery level.
In the simulation of the FIG. 3 process, inlet gas enters the plant as stream 31 and is cooled in heat exchanger 10 by heat exchange with cool residue gas (stream 45 b), demethanizer lower side reboiler liquids at 36° F. [2° C.] (stream 40), and propane refrigerant. The cooled stream 31 a enters separator 11 at 1° F. [−17° C.] and 955 psia [6,584 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 452 psia [3,116 kPa(a)]) of fractionation tower 20 by expansion valve 12, cooling stream 33 a to −25° F. [−32° C.] before it is supplied to fractionation tower 20 at a first lower mid-column feed point.
The vapor (stream 32) from separator 11 is further cooled in heat exchanger 13 by heat exchange with cool residue gas (stream 45 a) and demethanizer upper side reboiler liquids at −37° F. [−38° C.] (stream 39). The cooled stream 32 a enters separator 14 at −31° F. [−35° C.] and 950 psia [6,550 kPa(a)] where the vapor (stream 34) is separated from the condensed liquid (stream 37). The separator liquid (stream 37) is expanded to the tower operating pressure by expansion valve 19, cooling stream 37 a to −65° F. [−54° C.] before it is supplied to fractionation tower 20 at a second lower mid-column feed point.
The vapor (stream 34) from separator 14 is divided into two streams, 35 and 36. Stream 35, containing about 38% of the total vapor, passes through heat exchanger 15 in heat exchange relation with the cold residue gas (stream 45) where it is cooled to substantial condensation. The resulting substantially condensed stream 35 a at −119° F. [−84° C.] is then flash expanded through expansion valve 16 to the operating pressure of fractionation tower 20. During expansion a portion of the stream is vaporized, resulting in cooling of stream 35 b to −129° F. [−90° C.] before it is supplied to fractionation tower 20 at an upper mid-column feed point.
The remaining 62% of the vapor from separator 14 (stream 36) enters a work expansion machine 17 in which mechanical energy is extracted from this portion of the high pressure feed. The machine 17 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expanded stream 36 a to a temperature of approximately −85° F. [−65° C.]. The partially condensed expanded stream 36 a is thereafter supplied as feed to fractionation tower 20 at a mid-column feed point.
A portion of the distillation vapor (stream 42) is withdrawn from an intermediate region of the absorbing section in fractionation column 20, above the feed position of expanded stream 36 a in the lower region of the absorbing section. This distillation vapor stream 42 is then cooled from −101° F. [−74° C.] to −124° F. [−86° C.] and partially condensed (stream 42 a) in heat exchanger 22 by heat exchange with the cold demethanizer overhead stream 38 exiting the top of demethanizer 20 at −128° F. [−89° C.]. The cold demethanizer overhead stream is warmed slightly to −124° F. [−86° C.] (stream 38 a) as it cools and condenses at least a portion of stream 42.
The operating pressure (448 psia [3,090 kPa(a)]) in reflux separator 23 is maintained slightly below the operating pressure of demethanizer 20. This provides the driving force which causes distillation vapor stream 42 to flow through heat exchanger 22 and thence into the reflux separator 23 where the condensed liquid (stream 44) is separated from any uncondensed vapor (stream 43). Stream 43 then combines with the warmed demethanizer overhead stream 38 a from heat exchanger 22 to form cold residue gas stream 45 at −124° F. [−86° C.].
The liquid stream 44 from reflux separator 23 is pumped by pump 24 to a pressure slightly above the operating pressure of demethanizer 20, and stream 44 a is then supplied as cold top column feed (reflux) to demethanizer 20 at −123° F. [−86° C.]. This cold liquid reflux absorbs and condenses the C₂components, C₃components, and heavier components rising in the upper rectification region of the absorbing section of demethanizer 20.
The liquid product stream 41 exits the bottom of tower 20 at 113° F. [45° C.]. The cold residue gas stream 45 passes countercurrently to the incoming feed gas in heat exchanger 15 where it is heated to −38° F. [−39° C.] (stream 45 a), in heat exchanger 13 where it is heated to −4° F. [−20° C.] (stream 45 b), and in heat exchanger 10 where it is heated to 80° F. [27° C.] (stream 45 c) as it provides cooling as previously described. The residue gas is then re-compressed in two stages, compressor 18 driven by expansion machine 17 and compressor 25 driven by a supplemental power source. After stream 45 e is cooled to 120° F. [49° C.] in discharge cooler 26, the residue gas product (stream 45 f) flows to the sales gas pipeline at 1015 psia [6,998 kPa(a)].
A summary of stream flow rates and energy consumption for the process illustrated in FIG. 3 is set forth in the following table:

TABLE III

(FIG. 3)
Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr]

Stream	Methane	Ethane	Propane	Butanes+	Total

31	53,228	6,192	3,070	2,912	65,876
32	49,340	4,702	1,672	831	56,962
33	3,888	1,490	1,398	2,081	8,914
34	47,289	4,040	1,179	404	53,301
37	2,051	662	493	427	3,661
35	17,828	1,523	444	152	20,094
36	29,461	2,517	735	252	33,207
38	49,103	691	19	0	50,103
42	4,946	285	8	0	5,300
43	3,990	93	1	0	4,119
44	956	192	7	0	1,181
45	53,093	784	20	0	54,222
41	135	5,408	3,050	2,912	11,654
Recoveries*
Ethane	87.33%
Propane	99.36%
Butanes+	99.99%
Power

\begin{matrix} Residue Gas Compression & 23, 518 HP & [38, 663 kW] \\ Refrigerant Compression & \underline{7, 554 HP} & \underline{[12, 419 kW]} \\ Total Compression & 31, 072 HP & [51, 082 kW] \end{matrix}

*(Based on un-rounded flow rates)

A comparison of Tables I, II, and III shows that the FIG. 3 process improves the ethane recovery from 85.05% (for FIG. 1) and 85.08% (for FIG. 2) to 87.33%. The propane recovery for the FIG. 3 process (99.36%) is lower than that of the FIG. 1 process (99.57%) but higher than that of the FIG. 2 process (99.20%). The butanes+recovery is essentially the same for all three of these prior art processes. Comparison of Tables I, II, and III further shows that the FIG. 3 process using slightly less power than both prior art processes (more than 2% less than the FIG. 1 process and 0.4% less than the FIG. 2 process).

DESCRIPTION OF THE INVENTION

FIG. 4 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. 4 are the same as those in FIGS. 1, 2, and 3. Accordingly, the FIG. 4 process can be compared with that of the FIGS. 1, 2, and 3 processes to illustrate the advantages of the present invention.
In the simulation of the FIG. 4 process, inlet gas enters the plant at 85° F. [29° C.] and 970 psia [6,688 kPa(a)] as stream 31 and is cooled in heat exchanger 10 by heat exchange with cool residue gas (stream 45 b), demethanizer lower side reboiler liquids at 32° F. [0° C.] (stream 40), and propane refrigerant. The cooled stream 31 a enters separator 11 at 1° F. [−17° C.] and 955 psia [6,584 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 452 psia [3,116 kPa(a)]) of fractionation tower 20 by expansion valve 12, cooling stream 33 a to −25° F. [−32° C.] before it is supplied to fractionation tower 20 at a first lower mid-column feed point (located below the feed point of stream 36 a described later in paragraph [0058]).
The vapor (stream 32) from separator 11 is further cooled in heat exchanger 13 by heat exchange with cool residue gas (stream 45 a) and demethanizer upper side reboiler liquids at −38° F. [−39° C.] (stream 39). The cooled stream 32 a enters separator 14 at −31° F. [−35° C.] and 950 psia [6,550 kPa(a)] where the vapor (stream 34) is separated from the condensed liquid (stream 37). The separator liquid (stream 37) is expanded to the tower operating pressure by expansion valve 19, cooling stream 37 a to −66° F. [−54° C.] before it is supplied to fractionation tower 20 at a second lower mid-column feed point (also located below the feed point of stream 36 a).
The vapor (stream 34) from separator 14 is divided into two streams, 35 and 36. Stream 35, containing about 38% of the total vapor, passes through heat exchanger 15 in heat exchange relation with the cold residue gas (stream 45) where it is cooled to substantial condensation. The resulting substantially condensed stream 35 a at −122° F. [−86° C.] is then flash expanded through expansion valve 16 to slightly above the operating pressure of fractionation tower 20. During expansion a portion of the stream is vaporized, resulting in cooling of the total stream. In the process illustrated in FIG. 4, the expanded stream 35 b leaving expansion valve 16 reaches a temperature of −130° F. [−90° C.]. The expanded stream 35 b is warmed slightly to −129° F. [−89° C.] and further vaporized in heat exchanger 22 as it provides a portion of the cooling of distillation vapor stream 42. The warmed stream 35 c is then supplied at an upper mid-column feed point, in absorbing section 20 a of fractionation tower 20.
The remaining 62% of the vapor from separator 14 (stream 36) enters a work expansion machine 17 in which mechanical energy is extracted from this portion of the high pressure feed. The machine 17 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expanded stream 36 a to a temperature of approximately −86° F. [−65° C.]. The partially condensed expanded stream 36 a is thereafter supplied as feed to fractionation tower 20 at a mid-column feed point (located below the feed point of stream 35 c).
The demethanizer in tower 20 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 20 a that contains the trays and/or packing to provide the necessary contact between the vapor portions of the expanded streams 35 c and 36 a rising upward and cold liquid falling downward to condense and absorb the C₂components, C₃components, and heavier components from the vapors rising upward; and a lower, stripping section 20 b 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 20 b also includes one or more reboilers (such as reboiler 21 and the side reboilers 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 41, of methane and lighter components. Stream 36 a enters demethanizer 20 at an intermediate feed position located in the lower region of absorbing section 20 a of demethanizer 20. The liquid portion of the expanded stream 36 a comingles with liquids falling downward from absorbing section 20 a and the combined liquid continues downward into stripping section 20 b of demethanizer 20. The vapor portion of the expanded stream 36 a rises upward through absorbing section 20 a and is contacted with cold liquid falling downward to condense and absorb the C₂components, C₃components, and heavier components.
A portion of the distillation vapor (stream 42) is withdrawn from an intermediate region of absorbing section 20 a in fractionation column 20, above the feed position of expanded stream 36 a in the lower region of absorbing section 20 a. This distillation vapor stream 42 is then cooled from −103° F. [−75° C.] to −128° F. [−89° C.] and partially condensed (stream 42 a) in heat exchanger 22 by heat exchange with the cold demethanizer overhead stream 38 exiting the top of demethanizer 20 at −129° F. [−89° C.] and with the expanded substantially condensed stream 35 b as described previously. The cold demethanizer overhead stream is warmed slightly to −127° F. [−88° C.] (stream 38 a) as it provides a portion of the cooling of distillation vapor stream 42.
The operating pressure (448 psia [3,090 kPa(a)]) in reflux separator 23 is maintained slightly below the operating pressure of demethanizer 20. This provides the driving force which causes distillation vapor stream 42 to flow through heat exchanger 22 and thence into the reflux separator 23 where the condensed liquid (stream 44) is separated from any uncondensed vapor (stream 43). Stream 43 then combines with the warmed demethanizer overhead stream 38 a from heat exchanger 22 to form cold residue gas stream 45 at −127° F. [−88° C.].
The liquid stream 44 from reflux separator 23 is pumped by pump 24 to a pressure slightly above the operating pressure of demethanizer 20, and stream 44 a is then supplied as cold top column feed (reflux) to demethanizer 20 at −127° F. [−88° C.]. This cold liquid reflux absorbs and condenses the C₂components, C₃components, and heavier components rising in the upper rectification region of absorbing section 20 a of demethanizer 20.
In stripping section 20 b of demethanizer 20, the feed streams are stripped of their methane and lighter components. The resulting liquid product (stream 41) exits the bottom of tower 20 at 113° F. [45° C.] (based on a typical specification of a methane to ethane ratio of 0.025:1 on a molar basis in the bottom product). The cold residue gas stream 45 passes countercurrently to the incoming feed gas in heat exchanger 15 where it is heated to −40° F. [−40° C.] (stream 45 a), in heat exchanger 13 where it is heated to −4° F. [−20° C.] (stream 45 b), and in heat exchanger 10 where it is heated to 80° F. [27° C.] (stream 45 c) as it provides cooling as previously described. The residue gas is then re-compressed in two stages, compressor 18 driven by expansion machine 17 and compressor 25 driven by a supplemental power source. After stream 45 e is cooled to 120° F. [49° C.] in discharge cooler 26, the residue gas product (stream 45 f) flows to the sales gas pipeline at 1015 psia [6,998 kPa(a)].
A summary of stream flow rates and energy consumption for the process illustrated in FIG. 4 is set forth in the following table:

TABLE IV

(FIG. 4)
Stream Flow Summary - Lb. Moles/Hr [kg moles/Hr]

Stream	Methane	Ethane	Propane	Butanes+	Total

31	53,228	6,192	3,070	2,912	65,876
32	49,407	4,712	1,676	832	57,046
33	3,821	1,480	1,394	2,080	8,830
34	47,346	4,041	1,176	401	53,354
37	2,061	671	500	431	3,692
35	17,991	1,536	447	152	20,274
36	29,355	2,505	729	249	33,080
38	49,756	713	14	0	50,779
42	4,688	249	7	0	5,000
43	3,336	57	0	0	3,420
44	1,352	192	7	0	1,580
45	53,092	770	14	0	54,199
41	136	5,422	3,056	2,912	11,677
Recoveries*
Ethane	87.56%
Propane	99.55%
Butanes+	99.99%
Power

\begin{matrix} Residue Gas Compression & 23, 552 HP & [38, 719 kW] \\ Refrigerant Compression & \underline{7, 520 HP} & \underline{[12, 363 kW]} \\ Total Compression & 31, 072 HP & [51, 082 kW] \end{matrix}

* (Based on un-rounded flow rates)

A comparison of Tables I, II, III, and IV shows that, compared to the prior art, the present invention matches or exceeds the propane and butanes+recoveries of all the prior art processes while significantly improving the ethane recovery. The ethane recovery for the present invention (87.56%) is higher than the FIG. 1 process (85.05%), the FIG. 2 process (85.08%), and the FIG. 3 process (87.33%). Comparison of Tables I, II, III, and IV further shows that the improvement in yields was achieved without using more power than the prior art, and in some cases using significantly less power. In terms of the recovery efficiency (defined by the quantity of ethane recovered per unit of power), the present invention represents an improvement of 5%, 3%, and 0.3%, respectively, over the prior art of the FIG. 1, FIG. 2, and FIG. 3 processes. Although the power required for the present invention is essentially the same as that for the prior art FIG. 3 process, the present invention improves both the ethane recovery and the propane recovery by 0.2% compared to the FIG. 3 process without using more power.
Like the FIGS. 1, 2, and 3 prior art processes, the present invention uses the expanded substantially condensed feed stream 35 c supplied to absorbing section 20 a of demethanizer 20 to provide bulk recovery of the C₂components, C₃components, and heavier hydrocarbon components contained in expanded feed 36 a and the vapors rising from stripping section 20 b, and the supplemental rectification provided by reflux stream 44 a to reduce the amount of C₂components, C₃components, and C₄+ components contained in the inlet feed gas that is lost to the residue gas. However, the present invention improves the rectification in absorbing section 20 a over that of the prior art processes by making more effective use of the refrigeration available in process streams 38 and 35 b to improve the recoveries and the recovery efficiency.
Comparing reflux stream 44 in Table I for the FIG. 1 prior art process with that in Table IV for the present invention, it can be seen that although the compositions of the streams are similar, the FIG. 1 process has over 3 times as much supplemental reflux as the present invention. Surprisingly, however, the FIG. 1 process achieves much lower ethane recovery than the present invention despite the much greater quantity of reflux. The better recovery achieved by the present invention can be understood by comparing the condition of the warmed expanded substantially condensed stream 35 c in the FIG. 1 prior art process with that of the corresponding stream in the FIG. 4 embodiment of the present invention. Although the temperature of this stream is only slightly warmer in the FIG. 1 process, the proportion of this stream that has been vaporized before entering demethanizer 20 is vastly higher than that of the present invention (42% versus 12%). This means that not only is there less cold liquid in stream 35 c of the FIG. 1 process available for rectification of the vapors rising in absorbing section 20 a, there is much more vapor in the upper region of absorbing section 20 a that must be rectified by reflux stream 44 a. The net result is that reflux stream 44 a of the FIG. 1 process allows more of the C₂components to escape to demethanizer overhead stream 38 than the present invention does, reducing both the recovery and the recovery efficiency of the FIG. 1 process compared to the present invention. The key improvement of the present invention over the FIG. 1 prior art process is that the cold demethanizer overhead vapor stream 38 is used to provide a portion of the cooling of distillation vapor stream 42 in heat exchanger 22 so that sufficient methane can be condensed for use as reflux, without adding significant rectification load in absorbing section 20 a due to the excessive vaporization of stream 35 c that is inherent in the FIG. 1 prior art process.
Comparing reflux stream 44 in Tables II and III for the FIGS. 2 and 3 prior art processes with that in Table IV for the present invention, it can be seen that the present invention produces both more reflux and a better reflux stream than these prior art processes. Not only is the quantity of reflux higher (10% higher than the FIG. 2 process and 34% higher than the FIG. 3 process), the concentration of C₂+ components is significantly lower (12.6% for the present invention, versus 19.6% for the FIG. 2 process and 16.9% for the FIG. 3 process). This makes reflux stream 44 a of the present invention more effective for rectification in absorbing section 20 a of demethanizer 20, improving both the recovery and the recovery efficiency of the present invention compared to the FIGS. 2 and 3 prior art processes. The key improvement of the present invention over the FIGS. 2 and 3 prior art processes is that the expanded substantially condensed stream 35 b (which is predominantly liquid methane) is a better refrigerant medium than demethanizer overhead vapor stream 38 (which is primarily methane vapor), so using stream 35 b to provide a portion of the cooling of distillation vapor stream 42 in heat exchanger 22 allows more methane to be condensed and used as reflux in the present invention.

Other Embodiments

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 pumped condensed liquid (stream 44 a) from reflux separator 23 and all or a part of the warmed expanded substantially condensed stream 35 c from heat exchanger 22 can be combined (such as in the piping joining the pump and heat exchanger 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 comingling of the two streams, combined with contacting at least a portion of expanded stream 36 a, shall be considered for the purposes of this invention as constituting an absorbing section.
FIGS. 5 through 8 display other embodiments of the present invention. FIGS. 4 through 6 depict fractionation towers constructed in a single vessel. FIGS. 7 and 8 depict fractionation towers constructed in two vessels, absorber (rectifier) column 27 (a contacting and separating device) and stripper (distillation) column 20. In such cases, a portion of the distillation vapor (stream 54) is withdrawn from the lower section of absorber column 27 and routed to reflux condenser 22 to generate reflux for absorber column 27. The overhead vapor stream 50 from stripper column 20 flows to the lower section of absorber column 27 (via stream 51) to be contacted by reflux stream 52 and warmed expanded substantially condensed stream 35 c. Pump 28 is used to route the liquids (stream 47) from the bottom of absorber column 27 to the top of stripper column 20 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 20 in FIGS. 4 through 6) or multiple vessels will depend on a number of factors such as plant size, the distance to fabrication facilities, etc.
Some circumstances may favor withdrawing the distillation vapor stream 42 in FIGS. 5 and 6 from the upper region of stripping section 20 b in demethanizer 20 (stream 55). In other cases, it may be advantageous to withdraw a distillation vapor stream 54 from the lower region of absorbing section 20 a (above the feed point of expanded stream 36 a), withdraw a distillation vapor stream 55 from the upper region of stripping section 20 b (below the feed point of expanded stream 36 a), combine streams 54 and 55 to form combined distillation vapor stream 42, and direct combined distillation vapor stream 42 to heat exchanger 22 to be cooled and partially condensed. Similarly, in FIGS. 7 and 8 a portion (stream 55) of overhead vapor stream 50 from stripper column 20 may be directed to heat exchanger 22 (optionally combined with distillation vapor stream 54 withdrawn from the lower section of absorber column 27), with the remaining portion (stream 51) flowing to the lower section of absorber column 27.
Some circumstances may favor mixing the remaining vapor portion (stream 43) of cooled distillation vapor stream 42 a with the fractionation column overhead (stream 38), then supplying the mixed stream to heat exchanger 22 to provide a portion of the cooling of distillation vapor stream 42 or combined distillation vapor stream 42. This is shown in FIGS. 6 and 8, where the mixed stream 45 resulting from combining the reflux separator vapor (stream 43) with the column overhead (stream 38) is routed to heat exchanger 22.
As described earlier, the distillation vapor stream 42 or the combined distillation vapor stream 42 is partially condensed and the resulting condensate used to absorb valuable C₂components, C₃components, and heavier components from the vapors rising through absorbing section 20 a of demethanizer 20 or through absorber column 27. 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 20 a of demethanizer 20 or absorber column 27. Some circumstances may favor total condensation, rather than partial condensation, of distillation vapor stream 42 or combined distillation vapor stream 42 in heat exchanger 22. Other circumstances may favor that distillation vapor stream 42 be a total vapor side draw from fractionation column 20 or absorber column 27 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 distillation vapor stream 42 or combined distillation vapor stream 42 in heat exchanger 22.
Feed gas conditions, plant size, available equipment, or other factors may indicate that elimination of work expansion machine 17, 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 35 a).
When the inlet gas is leaner, separator 11 in FIG. 4 may not be justified. In such cases, the feed gas cooling accomplished in heat exchangers 10 and 13 in FIG. 4 may be accomplished without an intervening separator as shown in FIGS. 5 through 8. The decision of whether or not to cool and separate the feed gas in multiple steps will depend on the richness of the feed gas, plant size, available equipment, etc. Depending on the quantity of heavier hydrocarbons in the feed gas and the feed gas pressure, the cooled feed stream 31 a leaving heat exchanger 10 in FIGS. 4 through 8 and/or the cooled stream 32 a leaving heat exchanger 13 in FIG. 4 may not contain any liquid (because it is above its dewpoint, or because it is above its cricondenbar), so that separator 11 shown in FIGS. 4 through 8 and/or separator 14 shown in FIG. 4 are not required.
The high pressure liquid (stream 37 in FIG. 4 and stream 33 in FIGS. 5 through 8) need not be expanded and fed to a lower 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 35 in FIG. 4 and stream 34 in FIGS. 5 through 8) flowing to heat exchanger 15. (This is shown by the dashed stream 46 in FIGS. 5 through 8.) 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 lower mid-column feed point on the distillation column (stream 37 a in FIGS. 5 through 8). Stream 33 in FIG. 4 and stream 37 in FIGS. 4 through 8 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.
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.
Some circumstances may favor using a portion of the cold distillation liquid leaving absorbing section 20 a or absorber column 27 for heat exchange, such as dashed stream 49 in FIGS. 5 through 8. Although only a portion of the liquid from absorbing section 20 a or absorber column 27 can be used for process heat exchange without reducing the ethane recovery in demethanizer 20 or stripper column 20, more duty can sometimes be obtained from these liquids than with liquids from stripping section 20 b or stripper column 20. This is because the liquids in absorbing section 20 a of demethanizer 20 (or absorber column 27) are available at a colder temperature level than those in stripping section 20 b (or stripper column 20).
As shown by dashed stream 53 in FIGS. 5 through 8, in some cases it may be advantageous to split the liquid stream from reflux pump 24 (stream 44 a) into at least two streams. A portion (stream 53) can then be supplied to the stripping section of fractionation tower 20 (FIGS. 5 and 6) or the top of stripper column 20 (FIGS. 7 and 8) to increase the liquid flow in that part of the distillation system and improve the rectification, thereby reducing the concentration of C₂+ components in stream 42. In such cases, the remaining portion (stream 52) is supplied to the top of absorbing section 20 a (FIGS. 5 and 6) or absorber column 27 (FIGS. 7 and 8).
In accordance with the present invention, the splitting of the vapor feed may be accomplished in several ways. In the processes of FIGS. 4 through 8, 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 or after the cooling of the gas and prior to any separation stages. In some embodiments, vapor splitting may be effected in a separator.
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.
The present invention provides improved recovery of C₂components, C₃components, and heavier hydrocarbon components or of C₃components 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.
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

1. In a process for the separation of a gas stream containing methane, C₂components, C₃components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂components, C₃components, and heavier hydrocarbon components or said C₃components 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 heated and 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 heated, thereafter discharging at least a portion of said heated overhead vapor stream as said volatile residue gas fraction;

(5) a 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 and is directed into heat exchange relation with said expanded cooled first stream and said overhead vapor stream, whereby said distillation vapor stream is cooled sufficiently to condense at least a part of it and thereby form a residual vapor stream and a condensed stream, thereby supplying at least a portion of the heating of steps (2) and (4);

(6) at least a portion of said condensed stream is supplied to said distillation column at a top feed position; and

(7) 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, C₂components, C₃components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂components, C₃components, and heavier hydrocarbon components or said C₃components 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 heated and 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 heated, thereafter discharging at least a portion of said heated overhead vapor stream as said volatile residue gas fraction;

(8) a 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 and is directed into heat exchange relation with said expanded cooled first stream and said overhead vapor stream, whereby said distillation vapor stream is cooled sufficiently to condense at least a part of it and thereby form a residual vapor stream and a condensed stream, thereby supplying at least a portion of the heating of steps (4) and (7);

(9) at least a portion of said condensed stream is supplied to said distillation column at a top feed position; and

(10) 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.

3. In a process for the separation of a gas stream containing methane, C₂components, C₃components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂components, C₃components, and heavier hydrocarbon components or said C₃components and heavier hydrocarbon components, in which process

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

(8) a 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 and is directed into heat exchange relation with said expanded cooled combined stream and said overhead vapor stream, whereby said distillation vapor stream is cooled sufficiently to condense at least a part of it and thereby form a residual vapor stream and a condensed stream, thereby supplying at least a portion of the heating of steps (4) and (7);

4. In a process for the separation of a gas stream containing methane, C₂components, C₃components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂components, C₃components, and heavier hydrocarbon components or said C₃components and heavier hydrocarbon components, in which process

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

(2) said expanded cooled first stream is heated and 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 heated, thereafter discharging at least a portion of said heated first overhead vapor stream as said volatile residue gas fraction;

(6) a 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 and is directed into heat exchange relation with said expanded cooled first stream and said first overhead vapor stream, whereby said distillation vapor stream is cooled sufficiently to condense at least a part of it and thereby form a residual vapor stream and a condensed stream, thereby supplying at least a portion of the heating of steps (2) and (5);

(7) at least a portion of said condensed stream is supplied to said contacting and separating device at a top feed position; and

(8) 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.

5. In a process for the separation of a gas stream containing methane, C₂components, C₃components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂components, C₃components, and heavier hydrocarbon components or said C₃components and heavier hydrocarbon components, in which process

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

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

(4) said expanded cooled first stream is heated and 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 heated, thereafter discharging at least a portion of said heated first overhead vapor stream as said volatile residue gas fraction;

(9) a 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 and is directed into heat exchange relation with said expanded cooled first stream and said first overhead vapor stream, whereby said distillation vapor stream is cooled sufficiently to condense at least a part of it and thereby form a residual vapor stream and a condensed stream, thereby supplying at least a portion of the heating of steps (4) and (8);

(10) at least a portion of said condensed stream is supplied to said contacting and separating device at a top feed position; and

(11) 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.

6. In a process for the separation of a gas stream containing methane, C₂components, C₃components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂components, C₃components, and heavier hydrocarbon components or said C₃components and heavier hydrocarbon components, in which process

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

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

(4) said expanded cooled combined stream is heated and 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;

(9) a 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 and is directed into heat exchange relation with said expanded cooled combined stream and said first overhead vapor stream, whereby said distillation vapor stream is cooled sufficiently to condense at least a part of it and thereby form a residual vapor stream and a condensed stream, thereby supplying at least a portion of the heating of steps (4) and (8);

7. The improvement according to claim 1 wherein

(1) said overhead vapor stream is combined with said residual vapor stream to form a combined vapor stream; and

(2) said combined vapor stream is directed into heat exchange relation with said distillation vapor stream and heated, thereby to supply at least a portion of said cooling of said distillation vapor stream, and thereafter discharging at least a portion of said heated combined vapor stream as said volatile residue gas fraction.

8. The improvement according to claim 2 wherein

9. The improvement according to claim 3 wherein

10. The improvement according to claim 4 wherein

(1) said first overhead vapor stream is combined with said residual vapor stream to form a combined vapor stream; and

11. The improvement according to claim 5 wherein

12. The improvement according to claim 6 wherein

13. The improvement according to claim 1, 2, 3, 7, 8, or 9 wherein said distillation vapor stream is withdrawn from a region of said distillation column below said mid-column feed position.

14. The improvement according to claim 1, 2, 3, 7, 8, or 9 wherein

(1) a first distillation vapor stream is withdrawn from said region of said distillation column below said upper mid-column feed position and above said mid-column feed position;

(2) a second distillation vapor stream is withdrawn from a region of said distillation column below said mid-column feed position; and

(3) said first distillation vapor stream is combined with said second distillation vapor stream to form said distillation vapor stream.

15. The improvement according to claim 4, 5, 6, 10, 11, or 12 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.

16. The improvement according to claim 4, 5, 6, 10, 11, or 12 wherein

(1) a first distillation vapor stream is withdrawn from said region of said contacting and separating device below said mid-column feed position and above said first and second lower column feed positions;

(2) said second overhead vapor stream is divided into a second distillation vapor stream and a third distillation vapor stream, whereupon said second distillation vapor stream is supplied to said contacting and separating device at said second lower column feed position;

(3) said first distillation vapor stream is combined with said third distillation vapor stream to form said distillation vapor stream.

17. The improvement according to claim 1, 2, 3, 7, 8, or 9 wherein

(1) said condensed stream is divided into at least a first portion and a second portion;

(2) said first portion is supplied to said distillation column at said top feed position; and

(3) said second portion is supplied to said distillation column at a second mid-column feed position below said mid-column feed position.

18. The improvement according to claim 13 wherein

19. The improvement according to claim 14 wherein

20. The improvement according to claim 4, 5, 6, 10, 11, or 12 wherein

(2) said first portion is supplied to said contacting and separating device at said top feed position; and

(3) said second portion is supplied to said distillation column at a top feed position.

21. The improvement according to claim 15 wherein

22. The improvement according to claim 16 wherein

23. In an apparatus for the separation of a gas stream containing methane, C₂components, C₃components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂components, C₃components, and heavier hydrocarbon components or said C₃components 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) 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 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;

(4) heat exchange means connected to said second expansion means to receive said expanded cooled first stream and heat it, said heat exchange means being further connected to said distillation column to supply said heated expanded first stream to said distillation column at an upper mid-column feed position;

(5) said first expansion means being connected to said 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;

(6) said heat exchange means being further connected to said distillation column to receive at least a portion of said overhead vapor stream separated therein and heat it, thereafter discharging at least a portion of said heated overhead vapor stream 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 below said upper mid-column feed position and above said mid-column feed position;

(8) said heat exchange means being further connected to said vapor withdrawing means to receive said distillation vapor stream and cool it sufficiently to condense at least a part of it, thereby supplying at least a portion of the heating of steps (4) and (6);

(9) separating means connected to said heat exchange means to receive said partially condensed distillation vapor stream and separate it, thereby forming a residual vapor stream and a condensed stream, said separating means being further connected to said distillation column to supply at least a portion of said condensed stream to said distillation column at a top feed position; and

(10) 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.

24. In an apparatus for the separation of a gas stream containing methane, C₂components, C₃components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂components, C₃components, and heavier hydrocarbon components or said C₃components and heavier hydrocarbon components, in said apparatus there being

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

(4) second cooling means connected to said 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;

(6) heat exchange means connected to said second expansion means to receive said expanded cooled first stream and heat it, said heat exchange means being further connected to said distillation column to supply said heated expanded first stream to said distillation column at an upper mid-column feed position;

(7) said first expansion means being connected to said 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 connected to said first 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;

(9) said heat exchange means being further connected to said distillation column to receive at least a portion of said overhead vapor stream separated therein and heat it, thereafter discharging at least a portion of said heated overhead vapor stream 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 below said upper mid-column feed position and above said mid-column feed position;

(11) said heat exchange means being further connected to said vapor withdrawing means to receive said distillation vapor stream and cool it sufficiently to condense at least a part of it, thereby supplying at least a portion of the heating of steps (6) and (9);

(12) second separating means connected to said heat exchange means to receive said partially condensed distillation vapor stream and separate it, thereby forming a residual vapor stream and a condensed stream, said second separating means being further connected to said distillation column to supply at least a portion of said 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.

25. In an apparatus for the separation of a gas stream containing methane, C₂components, C₃components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂components, C₃components, and heavier hydrocarbon components or said C₃components and heavier hydrocarbon components, in said apparatus there being

the improvement wherein said apparatus includes

(4) combining means connected to said dividing means and said first 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 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;

(7) heat exchange means connected to said second expansion means to receive said expanded cooled combined stream and heat it, said heat exchange means being further connected to said distillation column to supply said heated expanded combined stream to said distillation column at an upper mid-column feed position;

(8) said first expansion means being connected to said 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;

(9) third expansion means being connected to said first 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;

(10) said heat exchange means being further connected to said distillation column to receive at least a portion of said overhead vapor stream separated therein and heat it, thereafter discharging at least a portion of said heated overhead vapor stream 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 below said upper mid-column feed position and above said mid-column feed position;

(12) said heat exchange means being further connected to said vapor withdrawing means to receive said distillation vapor stream and cool it sufficiently to condense at least a part of it, thereby supplying at least a portion of the heating of steps (7) and (10);

(13) second separating means connected to said heat exchange means to receive said partially condensed distillation vapor stream and separate it, thereby forming a residual vapor stream and a condensed stream, said second separating means being further connected to said distillation column to supply at least a portion of said condensed stream to said distillation column at a top feed position; and

(14) 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.

26. In an apparatus for the separation of a gas stream containing methane, C₂components, C₃components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂components, C₃components, and heavier hydrocarbon components or said C₃components 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

(4) heat exchange means connected to said second expansion means to receive said expanded cooled first stream and heat it, said heat exchange means being further connected to a contacting and separating means to supply said heated expanded 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;

(5) said first expansion means being connected to said 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;

(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) said heat exchange means being further connected to said contacting and separating means to receive at least a portion of said second overhead vapor stream separated therein and heat it, thereafter discharging at least a portion of said heated second overhead vapor stream 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 below said mid-column feed position and above said first and second lower column feed positions;

(10) said heat exchange means being further connected to said vapor withdrawing means to receive said distillation vapor stream and cool it sufficiently to condense at least a part of it, thereby supplying at least a portion of the heating of steps (4) and (8);

(11) separating means connected to said heat exchange means to receive said partially condensed distillation vapor stream and separate it, thereby forming a residual vapor stream and a condensed stream, said separating means being further connected to said contacting and separating means to supply at least a portion of said condensed stream to said contacting and separating means at a top feed position; and

(12) 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.

27. In an apparatus for the separation of a gas stream containing methane, C₂components, C₃components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂components, C₃components, and heavier hydrocarbon components or said C₃components and heavier hydrocarbon components, in said apparatus there being

the improvement wherein said apparatus includes

(6) heat exchange means connected to said second expansion means to receive said expanded cooled first stream and heat it, said heat exchange means being further connected to a contacting and separating means to supply said heated expanded 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;

(7) said first expansion means being connected to said 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 first 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;

(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) said heat exchange means being further connected to said contacting and separating means to receive at least a portion of said second overhead vapor stream separated therein and heat it, thereafter discharging at least a portion of said heated second overhead vapor stream 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 below said mid-column feed position and above said first and second lower column feed positions;

(13) said heat exchange means being further connected to said vapor withdrawing means to receive said distillation vapor stream and cool it sufficiently to condense at least a part of it, thereby supplying at least a portion of the heating of steps (6) and (11);

(14) second separating means connected to said heat exchange means to receive said partially condensed distillation vapor stream and separate it, thereby forming a residual vapor stream and a condensed stream, said second separating means being further connected to said contacting and separating means to supply at least a portion of said 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.

28. In an apparatus for the separation of a gas stream containing methane, C₂components, C₃components, and heavier hydrocarbon components into a volatile residue gas fraction and a relatively less volatile fraction containing a major portion of said C₂components, C₃components, and heavier hydrocarbon components or said C₃components and heavier hydrocarbon components, in said apparatus there being

the improvement wherein said apparatus includes

(7) heat exchange means connected to said second expansion means to receive said expanded cooled combined stream and heat it, said heat exchange means being further connected to a contacting and separating means to supply said heated expanded 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;

(8) said first expansion means being connected to said 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;

(9) third expansion means connected to said first 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;

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

(11) 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;

(12) said heat exchange means being further connected to said contacting and separating means to receive at least a portion of said second overhead vapor stream separated therein and heat it, thereafter discharging at least a portion of said heated second overhead vapor stream 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 below said mid-column feed position and above said first and second lower column feed positions;

(14) said heat exchange means being further connected to said vapor withdrawing means to receive said distillation vapor stream and cool it sufficiently to condense at least a part of it, thereby supplying at least a portion of the heating of steps (7) and (12);

(15) second separating means connected to said heat exchange means to receive said partially condensed distillation vapor stream and separate it, thereby forming a residual vapor stream and a condensed stream, said second separating means being further connected to said contacting and separating means to supply at least a portion of said condensed stream to said contacting and separating means at a top feed position; and

(16) 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.

29. The improvement according to claim 23 wherein

(1) a combining means is connected to said distillation column and said separating means to receive said overhead vapor stream and said residual vapor stream and form a combined vapor stream; and

(2) said heat exchange means is adapted to receive said combined vapor stream from said combining means and direct it into heat exchange relation with said distillation vapor stream, thereby heating said combined vapor stream and supplying at least a portion of said cooling of said distillation vapor stream, and thereafter discharging at least a portion of said heated combined vapor stream as said volatile residue gas fraction.

30. The improvement according to claim 24 wherein

(1) a combining means is connected to said distillation column and said second separating means to receive said overhead vapor stream and said residual vapor stream and form a combined vapor stream; and

31. The improvement according to claim 25 wherein

(1) a second combining means is connected to said distillation column and said second separating means to receive said overhead vapor stream and said residual vapor stream and form a combined vapor stream; and

(2) said heat exchange means is adapted to receive said combined vapor stream from said second combining means and direct it into heat exchange relation with said distillation vapor stream, thereby heating said combined vapor stream and supplying at least a portion of said cooling of said distillation vapor stream, and thereafter discharging at least a portion of said heated combined vapor stream as said volatile residue gas fraction.

32. The improvement according to claim 26 wherein

(1) a combining means is connected to said contacting and separating means and said separating means to receive said second overhead vapor stream and said residual vapor stream and form a combined vapor stream; and

33. The improvement according to claim 27 wherein

(1) a combining means is connected to said contacting and separating means and said second separating means to receive said second overhead vapor stream and said residual vapor stream and form a combined vapor stream; and

34. The improvement according to claim 28 wherein

(1) a second combining means is connected to said contacting and separating means and said second separating means to receive said second overhead vapor stream and said residual vapor stream and form a combined vapor stream; and

35. The improvement according to claim 23 or 29 wherein said vapor withdrawing means is adapted to be connected to said distillation column to receive said distillation vapor stream from a region of said distillation column below said mid-column feed position.

36. The improvement according to claim 24, 25, 30, or 31 wherein said vapor withdrawing means is adapted to be connected to said distillation column to receive said distillation vapor stream from a region of said distillation column below said mid-column feed position.

37. The improvement according to claim 23 wherein

(1) said vapor withdrawing means is adapted to be connected to said distillation column to receive a first distillation vapor stream from said region of said distillation column below said upper mid-column feed position and above said mid-column feed position;

(2) a second vapor withdrawing means is connected to said distillation column to receive a second distillation vapor stream from a region of said distillation column below said mid-column feed position;

(3) a combining means is connected to said vapor withdrawing means and said second vapor withdrawing means to receive said first distillation vapor stream and said second distillation vapor stream and form said distillation vapor stream; and

(4) said heat exchange means is adapted to be connected to said combining means to receive said distillation vapor stream.

38. The improvement according to claim 24 wherein

39. The improvement according to claim 25 or 30 wherein

(3) a second combining means is connected to said vapor withdrawing means and said second vapor withdrawing means to receive said first distillation vapor stream and said second distillation vapor stream and form said distillation vapor stream; and

(4) said heat exchange means is adapted to be connected to said second combining means to receive said distillation vapor stream.

40. The improvement according to claim 29 wherein

41. The improvement according to claim 31 wherein

(3) a third combining means is connected to said vapor withdrawing means and said second vapor withdrawing means to receive said first distillation vapor stream and said second distillation vapor stream and form said distillation vapor stream; and

(4) said heat exchange means is adapted to be connected to said third combining means to receive said distillation vapor stream.

42. The improvement according to claim 26 or 32 wherein

(1) a second 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 means is adapted to be connected to said second dividing means to receive said second distillation vapor stream at said second lower column feed position; and

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

43. The improvement according to claim 27, 28, 33, or 34 wherein

44. The improvement according to claim 26 wherein

(1) said vapor withdrawing means is adapted to be connected to said contacting and separating means to receive a first distillation vapor stream from said region of said contacting and separating means below said mid-column feed position and above said first and second lower column feed positions;

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

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

(4) a combining means is connected to said vapor withdrawing means and said second dividing means to receive said first distillation vapor stream and said third distillation vapor stream and form said distillation vapor stream; and

(5) said heat exchange means is adapted to be connected to said combining means to receive said distillation vapor stream.

45. The improvement according to claim 27 wherein

46. The improvement according to claim 28 or 33 wherein

(4) a second combining means is connected to said vapor withdrawing means and said second dividing means to receive said first distillation vapor stream and said third distillation vapor stream and form said distillation vapor stream; and

(5) said heat exchange means is adapted to be connected to said second combining means to receive said distillation vapor stream.

47. The improvement according to claim 32 wherein

48. The improvement according to claim 34 wherein

(4) a third combining means is connected to said vapor withdrawing means and said second dividing means to receive said first distillation vapor stream and said third distillation vapor stream and form said distillation vapor stream; and

(5) said heat exchange means is adapted to be connected to said third combining means to receive said distillation vapor stream.

49. The improvement according to claim 23, 29, 37, or 40 wherein

(1) a second dividing means is connected to said separating means to receive said condensed stream and divide it into at least a first portion and a second portion;

(2) said distillation column is adapted to be connected to said second dividing means to receive said first portion at said top feed position; and

(3) said distillation column is further adapted to be connected to said second dividing means to receive said second portion at a second mid-column feed position below said mid-column feed position.

50. The improvement according to claim 24, 25, 30, 31, 38, or 41 wherein

(1) a second dividing means is connected to said second separating means to receive said condensed stream and divide it into at least a first portion and a second portion;

51. The improvement according to claim 35 wherein

52. The improvement according to claim 36 wherein

53. The improvement according to claim 39 wherein

54. The improvement according to claim 26 or 32 wherein

(2) said contacting and separating means is adapted to be connected to said second dividing means to receive said first portion at said top feed position; and

(3) said distillation column is adapted to be connected to said second dividing means to receive said second portion at a top feed position.

55. The improvement according to claim 27, 28, 33, or 34 wherein

56. The improvement according to claim 42 wherein

(1) a third dividing means is connected to said separating means to receive said condensed stream and divide it into at least a first portion and a second portion;

(2) said contacting and separating means is adapted to be connected to said third dividing means to receive said first portion at said top feed position; and

(3) said distillation column is adapted to be connected to said third dividing means to receive said second portion at a top feed position.

57. The improvement according to claim 43 wherein

(1) a third dividing means is connected to said second separating means to receive said condensed stream and divide it into at least a first portion and a second portion;

58. The improvement according to claim 44 or 47 wherein

59. The improvement according to claim 45 or 48 wherein

60. The improvement according to claim 46 wherein