Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
  • F25J3/0209—Natural gas or substitute natural gas
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D5/00—Condensation of vapours; Recovering volatile solvents by condensation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G5/00—Recovery of liquid hydrocarbon mixtures from gases, e.g. natural gas
  • C10G5/06—Recovery of liquid hydrocarbon mixtures from gases, e.g. natural gas by cooling or compressing
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
  • F25J3/0233—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 1 carbon atom or more
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
  • F25J3/0238—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 2 carbon atoms or more
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
  • F25J3/0242—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 3 carbon atoms or more
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J5/00—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2200/00—Processes or apparatus using separation by rectification
  • F25J2200/02—Processes or apparatus using separation by rectification in a single pressure main column system
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2200/00—Processes or apparatus using separation by rectification
  • F25J2200/70—Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2205/00—Processes or apparatus using other separation and/or other processing means
  • F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
  • F25J2205/04—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum in the feed line, i.e. upstream of the fractionation step
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2210/00—Processes characterised by the type or other details of the feed stream
  • F25J2210/06—Splitting of the feed stream, e.g. for treating or cooling in different ways
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
  • F25J2240/02—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2270/00—Refrigeration techniques used
  • F25J2270/12—External refrigeration with liquid vaporising loop
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2270/00—Refrigeration techniques used
  • F25J2270/60—Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
  • F25J2290/40—Vertical layout or arrangement of cold equipments within in the cold box, e.g. columns, condensers, heat exchangers etc.
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
  • F25J2290/42—Modularity, pre-fabrication of modules, assembling and erection, horizontal layout, i.e. plot plan, and vertical arrangement of parts of the cryogenic unit, e.g. of the cold box

Definitions

• This invention relates to a process and 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 Application Number 61/186,361 which was filed on June 11, 2009.
• the applicants also claim the benefits under Title 35, United States Code, Section 120 as a continuation-in-part of U.S. Patent Application No. 12/689,616 which was filed on January 19, 2010.
• Assignees S.M.E. Products LP and Ortloff Engineers, Ltd. were parties to a joint research agreement that was in effect before the invention of this application was made.
• 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, 90.3% methane, 4.0% ethane and other C 2 components, 1.7% propane and other C 3 components, 0.3% iso-butane, 0.5% normal butane, and 0.8% pentanes plus, with the balance made up of nitrogen and carbon dioxide. Sulfur containing gases are also sometimes present.
• Patent No. 33,408; and co-pending application nos. 11/430,412; 11/839,693; 11/971,491; and 12/206,230 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).
• 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.
• liquids may be condensed and collected in one or more separators as high-pressure liquids containing some of the desired C 2 + components.
• 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.
• the expansion cooled stream(s) is (are) distilled to separate residual methane, nitrogen, and other volatile gases as overhead vapor from the desired C 2 components, C 3 components, and heavier hydrocarbon components as bottom liquid product, or to separate residual methane, C 2 components, nitrogen, and other volatile gases as overhead vapor from the desired C 3 components and heavier hydrocarbon components as bottom liquid product.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the cooled and expanded stream may be supplied to a separator to provide vapor and liquid streams, so that thereafter the vapor is combined with the tower overhead and the liquid is supplied to the column as a top column feed.
• Typical process schemes of this type are disclosed in U.S. Patent Nos. 4,889,545; 5,568,737; and 5,881,569, co-pending application nos. 11/430,412 and 11/971,491, and in Mowrey, E. Ross, "Efficient, High Recovery of Liquids from Natural Gas Utilizing a High Pressure Absorber", Proceedings of the Eighty-First Annual Convention of the Gas Processors Association, Dallas, Texas, March 11-13, 2002.
• the present invention employs a novel means of performing the various steps described above more efficiently and using fewer pieces of equipment. This is accomplished by combining what heretofore have been individual equipment items into a common housing, thereby reducing the plot space required for the processing plant and reducing the capital cost of the facility. Surprisingly, applicants have found that the more compact arrangement also significantly reduces the power consumption required to achieve a given recovery level, thereby increasing the process efficiency and reducing the operating cost of the facility. In addition, the more compact arrangement also eliminates much of the piping used to interconnect the individual equipment items in traditional plant designs, further reducing capital cost and also eliminating the associated flanged piping connections.
• piping flanges are a potential leak source for hydrocarbons (which are volatile organic compounds, VOCs, that contribute to greenhouse gases and may also be precursors to atmospheric ozone formation), eliminating these flanges reduces the potential for atmospheric emissions that can damage the environment.
• FIG. 1 is a flow diagram of a prior art natural gas processing plant in accordance with United States Patent No. 5,568,737;
• FIG. 2 is a flow diagram of a natural gas processing plant in accordance with the present invention.
• FIGS. 3 through 9 are flow diagrams illustrating alternative means of application of the present invention to a natural gas stream.
• 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.
• FIG. 1 is a process flow diagram showing the design of a processing plant to recover C 2 + components from natural gas using prior art according to U.S. Pat. No. 5,568,737.
• inlet gas enters the plant at 110 0 F [43°C] and 915 psia [6,307 kPa(a)] as stream 31.
• the sulfur compounds are removed by appropriate pretreatment of the feed gas (not illustrated).
• 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 divided into two portions, streams 32 and 33.
• Stream 32 is cooled to -26°F [-32 0 C] in heat exchanger 10 by heat exchange with cool distillation vapor stream 41a, while stream 33 is cooled to -32°F [-35 0 C] in heat exchanger 11 by heat exchange with demethanizer reboiler liquids at 41 0 F [5 0 C] (stream 43) and side reboiler liquids at -49°F [-45 0 C] (stream 42).
• Streams 32a and 33a recombine to form stream 31a, which enters separator 12 at -28°F [-33 0 C] and 893 psia [6,155 kPa(a)] where the vapor (stream 34) is separated from the condensed liquid (stream 35).
• Stream 36 containing about 27% of the total vapor, is combined with the separator liquid (stream 35), and the combined stream 38 passes through heat exchanger 13 in heat exchange relation with cold distillation vapor stream 41 where it is cooled to substantial condensation.
• the resulting substantially condensed stream 38a at -139°F [-95 0 C] is then flash expanded through expansion valve 14 to the operating pressure (approximately 396 psia [2,730 kPa(a)]) of fractionation tower 18. During expansion a portion of the stream is vaporized, resulting in cooling of the total stream.
• the expanded stream 38b leaving expansion valve 14 reaches a temperature of -140 0 F [-95 0 C] and is supplied to fractionation tower 18 at a first mid-column feed point.
• the remaining 73% of the vapor from separator 12 enters a work expansion machine 15 in which mechanical energy is extracted from this portion of the high pressure feed.
• the machine 15 expands the vapor substantially isentropically to the tower operating pressure, with the work expansion cooling the expanded stream 39a to a temperature of approximately -95 0 F [-71 0 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 16) that can be used to re-compress the heated distillation vapor stream (stream 41b), for example.
• the partially condensed expanded stream 39a is thereafter supplied as feed to fractionation tower 18 at a second mid-column feed point.
• the recompressed and cooled distillation vapor stream 41e is divided into two streams. One portion, stream 46, is the volatile residue gas product.
• the other portion, recycle stream 45 flows to heat exchanger 10 where it is cooled to -26°F [-32 0 C] by heat exchange with cool distillation vapor stream 41a.
• the cooled recycle stream 45a then flows to exchanger 13 where it is cooled to -139°F [-95 0 C] and substantially condensed by heat exchange with cold distillation vapor stream 41.
• the substantially condensed stream 45b is then expanded through an appropriate expansion device, such as expansion valve 22, to the demethanizer operating pressure, resulting in cooling of the total stream to -147°F [-99 0 C].
• the expanded stream 45c is then supplied to fractionation tower 18 as the top column feed.
• the vapor portion (if any) of stream 45c combines with the vapors rising from the top fractionation stage of the column to form distillation vapor stream 41, which is withdrawn from an upper region of the tower.
• the demethanizer in tower 18 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 fractionation tower may consist of two sections.
• the upper section 18a is a separator wherein the partially vaporized top feed is divided into its respective vapor and liquid portions, and wherein the vapor rising from the lower distillation or demethanizing section 18b is combined with the vapor portion of the top feed to form the cold demethanizer overhead vapor (stream 41) which exits the top of the tower at -144°F [-98 0 C].
• the lower, demethanizing section 18b contains the trays and/or packing and provides the necessary contact between the liquids falling downward and the vapors rising upward.
• the demethanizing section 18b also includes reboilers (such as the reboiler and the side reboiler described previously) which heat and vaporize a portion of the liquids flowing down the column to provide the stripping vapors which flow up the column to strip the liquid product, stream 44, of methane and lighter components.
• the liquid product stream 44 exits the bottom of the tower at 64°F [18°C], based on a typical specification of a methane to ethane ratio of 0.010:1 on a mass basis in the bottom product.
• the demethanizer overhead vapor stream 41 passes countercurrently to the incoming feed gas and recycle stream in heat exchanger 13 where it is heated to -40 0 F [-40 0 C] (stream 41a) and in heat exchanger 10 where it is heated to 104 0 F [40 0 C] (stream 41b).
• the distillation vapor stream is then re-compressed in two stages.
• the first stage is compressor 16 driven by expansion machine 15.
• the second stage is compressor 20 driven by a supplemental power source which compresses the residue gas (stream 4Id) to sales line pressure.
• stream 41e is split into the residue gas product (stream 46) and the recycle stream 45 as described earlier.
• Residue gas stream 46 flows to the sales gas pipeline at 915 psia [6,307 kPa(a)], sufficient to meet line requirements (usually on the order of the inlet pressure).
• FIG. 2 illustrates a flow diagram of a process in accordance with the present invention.
• the feed gas composition and conditions considered in the process presented in FIG. 2 are the same as those in FIG. 1. Accordingly, the FIG. 2 process can be compared with that of the FIG. 1 process to illustrate the advantages of the present invention.
• inlet gas enters the plant as stream 31 and is divided into two portions, streams 32 and 33. The first portion, stream 32, enters a heat exchange means in the upper region of feed cooling section 118a inside processing assembly 118.
• This heat exchange means may be comprised of a fin and tube type heat exchanger, a plate type heat exchanger, a brazed aluminum type heat exchanger, or other type of heat transfer device, including multi-pass and/or multi-service heat exchangers.
• the heat exchange means is configured to provide heat exchange between stream 32 flowing through one pass of the heat exchange means and a distillation vapor stream arising from separator section 118b inside processing assembly 118 that has been heated in a heat exchange means in the lower region of feed cooling section 118a.
• Stream 32 is cooled while further heating the distillation vapor stream, with stream 32a leaving the heat exchange means at -25 0 F [-32 0 C].
• the second portion, stream 33 enters a heat and mass transfer means in demethanizing section 118e inside processing assembly 118.
• This heat and mass transfer means may also be comprised of a fin and tube type heat exchanger, a plate type heat exchanger, a brazed aluminum type heat exchanger, or other type of heat transfer device, including multi-pass and/or multi-service heat exchangers.
• the heat and mass transfer means is configured to provide heat exchange between stream 33 flowing through one pass of the heat and mass transfer means and a distillation liquid stream flowing downward from absorbing section 118d inside processing assembly 118, so that stream 33 is cooled while heating the distillation liquid stream, cooling stream 33a to -47°F [-44 0 C] before it leaves the heat and mass transfer means.
• the heat and mass transfer means provides continuous contact between the stripping vapors and the distillation liquid stream so that it also functions to provide mass transfer between the vapor and liquid phases, stripping the liquid product stream 44 of methane and lighter components.
• Streams 32a and 33a recombine to form stream 31a, which enters separator section 118f inside processing assembly 118 at -32°F [-36 0 C] and 900 psia [6,203 kPa(a)], whereupon the vapor (stream 34) is separated from the condensed liquid (stream 35).
• Separator section 118f has an internal head or other means to divide it from demethanizing section 118e, so that the two sections inside processing assembly 118 can operate at different pressures.
• Stream 36 containing about 27% of the total vapor, is combined with the separated liquid (stream 35, via stream 37), and the combined stream 38 enters a heat exchange means in the lower region of feed cooling section 118a inside processing assembly 118.
• This heat exchange means may likewise be comprised of a fin and tube type heat exchanger, a plate type heat exchanger, a brazed aluminum type heat exchanger, or other type of heat transfer device, including multi-pass and/or multi-service heat exchangers.
• the heat exchange means is configured to provide heat exchange between stream 38 flowing through one pass of the heat exchange means and the distillation vapor stream arising from separator section 118b, so that stream 38 is cooled to substantial condensation while heating the distillation vapor stream.
• the resulting substantially condensed stream 38a at -138°F [-95 0 C] is then flash expanded through expansion valve 14 to the operating pressure (approximately 400 psia [2,758 kPa(a)]) of rectifying section 118c (an absorbing means) and absorbing section 118d (another absorbing means) inside processing assembly 118. During expansion a portion of the stream may be vaporized, resulting in cooling of the total stream.
• the expanded stream 38b leaving expansion valve 14 reaches a temperature of -139°F [-95 0 C] and is supplied to processing assembly 118 between rectifying section 118c and absorbing section 118d.
• the liquids in stream 38b combine with the liquids falling from rectifying section 118c and are directed to absorbing section 118d, while any vapors combine with the vapors rising from absorbing section 118d and are directed to rectifying section 118c.
• the recompressed and cooled distillation vapor stream 41c is divided into two streams.
• One portion, stream 46, is the volatile residue gas product.
• the other portion, recycle stream 45, enters a heat exchange means in the feed cooling section 118a inside processing assembly 118.
• This heat exchange means may also be comprised of a fin and tube type heat exchanger, a plate type heat exchanger, a brazed aluminum type heat exchanger, or other type of heat transfer device, including multi-pass and/or multi-service heat exchangers.
• the heat exchange means is configured to provide heat exchange between stream 45 flowing through one pass of the heat exchange means and the distillation vapor stream arising from separator section 118b, so that stream 45 is cooled to substantial condensation while heating the distillation vapor stream.
• the substantially condensed recycle stream 45a leaves the heat exchange means in feed cooling section 118a at -138°F [-95 0 C] and is flash expanded through expansion valve 22 to the operating pressure of rectifying section 118c inside processing assembly 118. During expansion a portion of the stream is vaporized, resulting in cooling of the total stream. In the process illustrated in FIG. 2, the expanded stream 45b leaving expansion valve 22 reaches a temperature of -146°F [-99 0 C] and is supplied to separator section 118b inside processing assembly 118. The liquids separated therein are directed to rectifying section 118c, while the remaining vapors combine with the vapors rising from rectifying section 118c to form the distillation vapor stream that is heated in cooling section 118a.
• Rectifying section 118c and absorbing section 118d each contain an absorbing means consisting of a plurality of vertically spaced trays, one or more packed beds, or some combination of trays and packing.
• the trays and/or packing in rectifying section 118c and absorbing section 118d provide the necessary contact between the vapors rising upward and cold liquid falling downward.
• the liquid portion of the expanded stream 39a commingles with liquids falling downward from absorbing section 118d and the combined liquid continues downward into demethanizing section 118e.
• the stripping vapors arising from demethanizing section 118e combine with the vapor portion of the expanded stream 39a and rise upward through absorbing section 118d, to be contacted with the cold liquid falling downward to condense and absorb most of the C 2 components, C 3 components, and heavier components from these vapors.
• the vapors arising from absorbing section 118d combine with any vapor portion of the expanded stream 38b and rise upward through rectifying section 118c, to be contacted with the cold liquid portion of expanded stream 45b falling downward to condense and absorb most of the C 2 components, C 3 components, and heavier components remaining in these vapors.
• the liquid portion of the expanded stream 38b commingles with liquids falling downward from rectifying section 118c and the combined liquid continues downward into absorbing section 118d.
• distillation liquid flowing downward from the heat and mass transfer means in demethanizing section 118e inside processing assembly 118 has been stripped of methane and lighter components.
• the resulting liquid product (stream 44) exits the lower region of demethanizing section 118e and leaves processing assembly 118 at 65 0 F [18 0 C].
• the distillation vapor stream arising from separator section 118b is warmed in feed cooling section 118a as it provides cooling to streams 32, 38, and 45 as described previously, and the resulting distillation vapor stream 41 leaves processing assembly 118 at 105 0 F [40 0 C].
• the distillation vapor stream is then re-compressed in two stages, compressor 16 driven by expansion machine 15 and compressor 20 driven by a supplemental power source.
• stream 41b is cooled to 110 0 F [43 0 C] in discharge cooler 21 to form stream 41c
• recycle stream 45 is withdrawn as described earlier, forming residue gas stream 46 which thereafter flows to the sales gas pipeline at 915 psia [6,307 kPa(a)].
• the improvement in recovery efficiency provided by the present invention over that of the prior art of the FIG. 1 process is primarily due to two factors.
• rectifying section 118c and absorbing section 118d in processing assembly 118 of the present invention can operate at higher pressure than fractionation column 18 of the prior art while maintaining the same recovery level.
• This higher operating pressure plus the reduction in pressure drop for the distillation vapor stream due to eliminating the interconnecting piping, results in a significantly higher pressure for the distillation vapor stream entering compressor 20, thereby reducing the power required by the present invention to restore the residue gas to pipeline pressure.
• the volatile components are stripped out of the liquid continuously, reducing the concentration of the volatile components in the stripping vapors more quickly and thereby improving the stripping efficiency for the present invention.
• the present invention offers two other advantages over the prior art in addition to the increase in processing efficiency.
• Second, elimination of the interconnecting piping means that a processing plant utilizing the present invention has far fewer flanged connections compared to the prior art, reducing the number of potential leak sources in the plant.
• Hydrocarbons are volatile organic compounds (VOCs), some of which are classified as greenhouse gases and some of which may be precursors to atmospheric ozone formation, which means the present invention reduces the potential for atmospheric releases that can damage the environment.
• VOCs volatile organic compounds
• Some circumstances may favor supplying liquid stream 35 directly to the lower region of absorbing section 118d via stream 40 as shown in FIGS. 2, 4, 6, and 8.
• an appropriate expansion device such as expansion valve 17
• the resulting expanded liquid stream 40a is supplied as feed to the lower region of absorbing section 118d (as shown by the dashed lines).
• Some circumstances may favor combining a portion of liquid stream 35 (stream 37) with the vapor in stream 36 (FIGS. 2 and 6) or with cooled second portion 33a (FIGS. 4 and 8) to form combined stream 38 and routing the remaining portion of liquid stream 35 to the lower region of absorbing section 118d via streams 40/4Oa.
• Some circumstances may favor combining the expanded liquid stream 40a with expanded stream 39a (FIGS. 2 and 6) or expanded stream 34a (FIGS. 4 and 8) and thereafter supplying the combined stream to the lower region of absorbing section 118d as a single feed.
• the quantity of liquid separated in stream 35 may be great enough to favor placing an additional mass transfer zone in demethanizing section 118e between expanded stream 39a and expanded liquid stream 40a as shown in FIGS. 3 and 7, or between expanded stream 34a and expanded liquid stream 40a as shown in FIGS. 5 and 9.
• the heat and mass transfer means in demethanizing section 118e may be configured in upper and lower parts so that expanded liquid stream 40a can be introduced between the two parts.
• the cooled second portion 33a is combined with the separated liquid (stream 35, via stream 37), and the combined stream 38 is directed to the heat exchange means in the lower region of feed cooling section 118a inside processing assembly 118 and cooled to substantial condensation.
• the substantially condensed stream 38a is flash expanded through expansion valve 14 to the operating pressure of rectifying section 118c and absorbing section 118d, whereupon expanded stream 38b is supplied to processing assembly 118 between rectifying section 118c and absorbing section 118d.
• separator 12 can be used to separate cooled feed stream 31a into vapor stream 34 and liquid stream 35.
• separator 12 can be used to separate cooled first portion 32a into vapor stream 34 and liquid stream 35.
• the cooled feed stream 31a entering separator section 118f in FIGS. 2 and 3 or separator 12 in FIGS. 6 and 7 may not contain any liquid (because it is above its dewpoint, or because it is above its cricondenbar). In such cases, there is no liquid in streams 35 and 37 (as shown by the dashed lines), so only the vapor from separator section 118f in stream 36 (FIGS. 2 and 3), the vapor from separator 12 in stream 36 (FIGS.
• separator section 118f in processing assembly 118 (FIGS. 2 through 5) or separator 12 (FIGS. 6 through 9) may not be required.
• Feed gas conditions, plant size, available equipment, or other factors may indicate that elimination of work expansion machine 15, or replacement with an alternate expansion device (such as an expansion valve), is feasible.
• an alternate expansion device such as an expansion valve
• individual stream expansion is depicted in particular expansion devices, alternative expansion means may be employed where appropriate.
• conditions may warrant work expansion of the substantially condensed portion of the feed stream (stream 38a) or the substantially condensed recycle stream (stream 45a).
• the use of external refrigeration to supplement the cooling available to the inlet gas from the distillation vapor and liquid streams may be employed, particularly in the case of a rich inlet gas.
• a heat and mass transfer means may be included in separator section 118f (or a collecting means in such cases when the cooled feed stream 31a or the cooled first portion 32a contains no liquid) as shown by the dashed lines in FIGS. 2 through 5, or a heat and mass transfer means may be included in separator 12 as shown by the dashed lines in FIGS. 6 though 9.
• This heat and mass transfer means may be comprised of a fin and tube type heat exchanger, a plate type heat exchanger, a brazed aluminum type heat exchanger, or other type of heat transfer device, including multi-pass and/or multi-service heat exchangers.
• the heat and mass transfer means is configured to provide heat exchange between a refrigerant stream (e.g., propane) flowing through one pass of the heat and mass transfer means and the vapor portion of stream 31a (FIGS. 2, 3, 6, and 7) or stream 32a (FIGS. 4, 5, 8, and 9) flowing upward, so that the refrigerant further cools the vapor and condenses additional liquid, which falls downward to become part of the liquid removed in stream 35.
• a refrigerant stream e.g., propane
• conventional gas chiller(s) could be used to cool stream 32a, stream 33a, and/or stream 31a with refrigerant before stream 31a enters separator section 118f (FIGS. 2 and 3) or separator 12 (FIGS. 6 and 7) or stream 32a enters separator section 118f (FIGS. 4 and 5) or separator 12 (FIGS. 8 and 9).
• separator section 118f FIGGS. 2 and 3
• separator 12 FIGS. 6 and 7
• separator 12 FIGS. 4 and 5
• separator 12 FIGS. 8 and 9
• the heat and mass transfer means in demethanizing section 118e may include provisions for providing supplemental heating with heating medium as shown by the dashed lines in FIGS. 2 through 9.
• another heat and mass transfer means can be included in the lower region of demethanizing section 118e for providing supplemental heating, or stream 33 can be heated with heating medium before it is supplied to the heat and mass transfer means in demethanizing section 118e.
• the multi-pass and/or multi-service heat transfer device will include appropriate means for distributing, segregating, and collecting stream 32, stream 38, stream 45, and the distillation vapor stream in order to accomplish the desired cooling and heating.
• a mass transfer means can be located below where expanded stream 39a (FIGS. 2, 3, 6, and 7) or expanded stream 34a (FIGS.
• FIGS. 2, 3, 6, and 7 embodiments of the present invention is providing a separator vessel for cooled first portion 31a, a separator vessel for cooled second portion 32a, combining the vapor streams separated therein to form vapor stream 34, and combining the liquid streams separated therein to form liquid stream 35.
• Another less preferred option for the present invention is cooling stream 37 in a separate heat exchange means inside feed cooling section 118a (rather than combining stream 37 with stream 36 or stream 33a to form combined stream 38), expanding the cooled stream in a separate expansion device, and supplying the expanded stream to an intermediate region in absorbing section 118d.
• 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 above absorbing section 118d may increase recovery while decreasing power recovered from the expander and thereby increasing the recompression horsepower requirements. Increasing feed below absorbing section 118d reduces the horsepower consumption but may also reduce product recovery. [0055]
• the present invention provides improved recovery of C 2 components, C 3 components, and heavier hydrocarbon components or of C 3 components and heavier hydrocarbon components per amount of utility consumption required to operate the process. An improvement in utility consumption required for operating the process may appear in the form of reduced power requirements for compression or re-compression, reduced power requirements for external refrigeration, reduced energy requirements for supplemental heating, or a combination thereof.

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