FR2547810A1 - CONTINUOUS PROCESS FOR EXTRACTING FROM NATURAL GAS CURRENT, USING A PHYSICAL SOLVENT, WATER AND HEAVIER HYDROCARBONS THAN METHANE - Google Patents

Abstract

THE INVENTION RELATES TO A CONTINUOUS PROCESS FOR EXTRACTING WATER AND HYDROCARBONS HEAVIER THAN METHANE FROM AN INPUT NATURAL GAS STREAM. THIS PROCESS CONSISTS OF PERFORMING A FIRST EXTRACTION IN A UNIT 10 TO EXTRACT NATURAL GAS CURRENT FROM WATER AND HYDROCARBONS HEAVIER THAN METHANE, USING A SOLVENT, THEN CARRYING OUT SUCCESSIVE INSTANT VAPORIZATIONS INTO UNITS 20, 30, 40 AND 70, IN ORDER TO OBTAIN A LIQUID HYDROCARBON PRODUCT AT C THE COMPOSITION OF WHICH CAN BE SET SELECTIVELY ACCORDING TO MARKET CONDITIONS, AND A CURRENT OF DRY AND SOFT RESIDUAL NATURAL GAS THAT CAN BE CHANNEL. FIELD OF APPLICATION: FLEXIBLE PRODUCTION OF HYDROCARBON PRODUCTS FOLLOWING FLUCTUATING MARKET CONDITIONS.

Description

The invention relates to the treatment of hydrocarbons, and more

  particularly the separation and recovery of ethane and higher boiling hydrocarbons from methane in a stream of natural gas which may or may not contain acidic constituents such as CO 2 and H 25. A stream of gas Typical natural gas contains a mixture of individual gaseous constituents, some of which can be liquefied at atmospheric temperatures and pressures when isolated. The amounts of each constituent vary from one gas to another, with methane being a predominant constituent. Other hydrocarbon constituents include ethane, propane, isobutane, normal butane, isopentane, normal pentane, hexane, heptane, octane, and the like.

  and nonane, in the order of increasing molecular weight and increasing normal boiling temperature.

  Usually, the natural gases contain certain gaseous impurities such as nitrogen, carbon dioxide, carbonyl sulphide, hydrogen sulphide, mercaptans, disulfides and water. However, all these impurities, except water and nitrogen, are eliminated

by softening.

  Many methods have been used to extract liquids from natural gas streams. These processes include oil absorption, refrigerated oil absorption, simple refrigeration, cascade refrigeration, Joule-Thompson expansion. and cryogenic turbodetrate Typical recoveries for these methods are given in Table I.

15 20 25 30 35

TABLE I

  Comparison of typical liquid recoveries I Extraction process Ethanel Propane Butanes Gasoline

(%), (%) (%) (%)

: O M

  Absorption 4 24 75 87 Refrigerated absorption 15 65 90 95 Single refrigeration 35 80 93 97 Cascading cooling 70 96 99 100 Relaxing JouleThompson 75 96 99 100 Turbo regulator 85 97 100 100

  In summary, oil absorption, refrigerated oil absorption, simple refrigeration and cascading refrigeration are processes operating at pipeline pressures, without the loss of gas pressure, but the recovery of desirable liquids (ethane and heavier constituents) is very low, except in the case of the cascade refrigeration process which requires very high investments and operating costs, but which achieves a good recovery of ethane and propane Joule processes -Thompson and cryogenic expansion achieve high recovery of ethane by lowering the pressure of the entire feed gas, which is mainly methane (usually 80-85%), but the recompression of most of the inlet gas is very expensive.

  In all the processes indicated above,

  the ethane and the heavier constituents are recovered in a specific configuration determined by their composition in the crude natural gas stream and the equilibrium at the key working conditions of pressure and temperature in the process.

  In particular, the refrigeration process, which generally recovers 80% of the propane, also generally requires the recovery of 35% of the ethane to bring the recovery of propane to the level of 95% or more, the cascade refrigeration, the Joule-Thompson process or the cryogenic turbo-debit process must be used at the same time as the recovery of ethane is increased to 70% or more, at the cost of a significant capital investment

higher.

  In poor economic conditions, when the price of ethane as a petrochemical feedstock is lower than its equivalent price as fuel 10 and when the price of propane, for use as a feedstock, is attractive, the person responsible for natural gas liquid extraction facility is limited in the choice of operation D because it is unable to minimize the recovery of ethane and maximize the

  propane recovery in response to market conditions.

  In particular, when the price of ethane as a petrochemical load is greater than its value as fuel while the price of propane as

  Propane feed is not attractive, none of the above mentioned processes allows an operator to selectively recover ethane while discarding propane.

  There are extraction processes that use liquids other than hydrocarbon oils to remove acidic constituents, including H 2 S and C O 2, and water. These liquids include most physical solvents such as propylene carbonate, N-methylpyrrolidone, glycerol triacetate, dimethyl ether

  polyethylene glycol, triethylolamine, tributyl phosphate and gammabutyrolactone.

  U.S. Patent Nos. 3,362,133, 3,770,622, 3,837,143, 4,052,176, and 4,070,165 describe various prior art processes for extracting acidic components, hydrocarbons, and the like. heavy or

  water from natural gas streams.

  As reported at the 50th Annual Gas Processors Association Convention, 1719 March 1980, Houston, Texas, USA, in a book entitled "High C 02High H 2 S Removal with SELEXOL Solvent" by John W Sweny, the relative solubility of CO 2 in dimethyl ethylene glycol ether (DMPEG) relative to the methane is 15.0, while that of the propane is 15.3 The relative solubility in D> SEG of H 25 because r: i; -cprt The relative solubilities of isobutane and normal butane and of isopentane and normal pentane in the DMPEG are between those of CO 2 and H 2 S These data indicate that if C 02 and H 2 S are present in a stream of natural gas that contains heavier hydrocarbons as desirable feedstock for the petrochemical industry, substantial amounts of hydrocarbons are required. in C 2 + are lost with the vent currents of

  C 02 and H 2 S in the case of DMPEG treatment.

  A stream of natural gas is usually saturated with water at its ambient temperature which can vary between 24 and 49 ° C., so that its water content can vary from 0.34 kg to more than 0.85 kg per thousand meters. However, difficulties are often encountered in pumping such natural gas, unless the water content is reduced to less than 0.2 kg, and preferably less than 0.12 kg. water per thousand cubic meters of natural gas under normal conditions With respect to the dew point, a natural gas having a dew point of -10 C, and preferably -7 C or less, is generally considered to be It can be safely transported in a pipeline. Dewatering can be carried out in a wide range of pressures from 100 to 35,000 kPa, but is usually carried out at pressures of 3500-10,000 kPa, and generally close to

7000 kPa.

  There is, however, a need for a process in which C 2 + hydrocarbons and water could be withdrawn simultaneously, at any selected degree, without simultaneous extraction of lower molecular weight hydrocarbons.

such as methane.

  There is also a need for a process in which any natural gas, of a very corrosive quality to a quite soft quality, could be handled by the same equipment at the same time as it is dehydrated and

  heavier hydrocarbons are recovered.

  However, daily changes in market conditions may also lower the price of a single liquid hydrocarbon heavier than ethane below its price as a fuel, so that this hydrocarbon must be capable of being selectively discharged; but there is currently no way to do this without also rejecting all the lower molecular weight components. For example, if the price of ethane is less than its value as a fuel, it can be rejected with methane. , but if the price of propane is less than its fuel value while the price of ethane is greater than its value as a fuel, there is no method for recovering ethane and butane. and heavier hydrocarbons (C 4 +) from the natural gas stream. Therefore, for all components heavier than ethane, there is a need for a means for selectively rejecting any one or two selected hydrocarbons of consecutive molecular weight, which are heavier than another recoverable hydrocarbon and In practice, these hydrocarbons which can be selectively rejected are propane, butanes, and propane plus butanes. The invention relates to an extraction process 30 for selectively removing from a stream of natural gas, by contact with a physical solvent, hydrocarbon components C 2 +, C 3 +, C 4 + or C 5 + in accordance with an extremely broad and flexible range of hydrocarbon recoveries, but preferably attaining extremely high hydrocarbon recoveries, in order to selectively reject the C1 + C 2, Cl-C 31 C 1- C 4 or C 2 -C 4 of consecutive molecular weight, and selectively recovering the C 2 components therefrom,

C 3 or C 2 + C 3.

  The invention also relates to a process for producing, at any chosen degree, a residual natural gas of suitable quality for the pipelines, comprising only undesirable hydrocarbon constituents of a stream of natural gas, and for producing, at any chosen degree. ,

  a liquid hydrocarbon comprising only desirable hydrocarbon components.

  The invention also relates to a process for selectively removing from a stream of corrosive natural gas, by contact with a hydrocarbon extraction solvent, constituents of C 2 +, C 3 +, C 4 + or C 5 +, water and acid constituents, and to separate all

  these constituents of the solvent and, in the same equipment, to then separate the acid constituents of the constituents C 2 +, C 3 +, C 4 + or C 5 + in liquid phases.

  It is a particular object of the invention to use a physical solvent as a preferred hydrocarbon extraction solvent and to use a dialkyl ether of polyethylene or polypropylene glycol, or mixtures thereof.

  of these materials, as the preferred physical solvent.

  The subject of the invention is also a process for producing a residual natural gas for use with

  For combustion purposes, this gas has an enthalpy within a specified range.

  Another object of the invention relates to a process for producing a residual natural gas for use as a petrochemical feedstock, of a specified composition, for example consisting of two or three components in defined proportions, composition in which

  the metal constitutes the inert diluent.

  In accordance with these objects and with the principles of the invention, there is provided a useful method when variations in the price of marketing individual hydrocarbons in liquid form cause the marketing price of a particular liquid hydrocarbon to fall below its market price. These prices vary daily It is therefore advantageous to be able to extract all the hydrocarbon liquids while rejecting and returning to the residual gas pipe one or more hydrocarbons whose prices are below

  their value as fuel The extraction plant can thus be exploited constantly at optimal profit levels.

  Another condition of the market may be customer preference, based on the need to supply loads to a chemical facility, for example. In particular, such an installation may require ethane, butanes and all heavier hydrocarbons,

but not propane.

  The invention provides an improvement to a continuous process for separating an inlet natural gas stream from water and heavier hydrocarbons than methane, which process comprises: 1) extracting water and hydrocarbons; heavier than methane from the natural gas stream using a physical solvent, at pipe pressures and at a soil flow rate sufficient to produce a rich solvent containing the water, a hydrocarbon mixture. in Cl +, and a residual natural gas, of suitable quality for the pipes, which is returned to a pipe, 2) to evaporate instantly and successively the rich solvent in several stages of vaporization, at gradually decreasing pressures, to produce several gaseous fractions successive stages of C 1 +, with decreasing methane contents, and liquid mixtures of water, solvent and hydrocarbon mixtures with and 3) to regenerate the liquid mixture from the last of the instantaneous vaporization stages to produce the physical solvent for extraction. This improvement provides a residual natural gas stream and a liquid hydrocarbon product having a composition which can be selectively adjusted to practically any degree chosen in accordance with market conditions. This adjustment of the composition of the liquid hydrocarbon product allows the product: (1) to consist essentially of C 2 +, C 3 + hydrocarbon constituents, C 4 + or C 5 +; or (2) to contain in its entirety C 2 + or C 3 + components, except at least one intermediate component, selected from the group consisting of C 3 and C 4 components, which is combined with the residual gas stream; or (3) to contain other selected components of the input natural gas stream, at any chosen degree. The process has the ability to follow at least one of the following procedures, which consists of: A selectively varying the flow rate of solvent relative to the flow rate of the input natural gas stream during the first extraction to control the composition of the rich solvent relative to selected components of the group consisting of ethane, propane isobutane and normal butane while producing the residual natural gas stream; Bo selectively varying the instantaneous vaporization pressures of the successive stages of instantaneous vaporization to adjust the composition of the successive gas fractions and the successive liquid mixture with respect to the selected constituents; C to recycle at least the first of the successive C 1 + gas fractions obtained by instantaneous vaxorization, to the extraction to extract maximum amounts of ethane and heavier hydrocarbons; D to rectify at least the last of the successive C 1 + gas fractions in order to produce the liquid hydrocarbon comprising the selected constituents and a recycle gas stream comprising C 1, C 1 + C 2, C 1 + C 2 + C 3 or C 1 + C 2 + C 3 + C 4, for recycling to extraction, by: 1) selective variation of the rectification pressure and / or 2) selective variation of the temperature of the rectification residues; E in the second extraction step, extracting an extraction charge stream selected from the group comprising the recycle gas stream, a gas stream from at least one of the various instantaneous vaporization stages, and mixtures of these streams, with the physical solvent at a selected flow rate that determines the selected degree of recovery of the selected C 2 + components in a rich solvent stream, the unextracted portion of the extraction feed stream being recycled to extraction of the input natural gas stream; F to instantaneously vaporize the rich solvent stream and to produce a single gas stream obtained by flash vaporization, containing the selected components of C 2 +, and a bottom solvent stream; G to regenerate the liquid mixture from at least the last of the instant vaporization stages of step B and the bottom solvent stream of step F to produce the physical solvent for the first extraction and the second extraction ; and H to divide the gas stream obtained by simple instantaneous vaporization and to produce a top product stream selected from the group consisting of C 2, C 3 and C 2 + C 3, and a residue stream selected from the group consisting of C 3, C 4 and C 3 + C 40 the residue stream being combined with the residual natural gas stream of step A and the overhead product stream being combined with the liquid hydrocarbon product of the Do step if the natural gas stream is corrosive, it is preferable that it is softened by contact with a non-hydrocarbon-absorbing chemical solvent, such as an amine, before the absorption process of the invention is implemented. if a pretreatment step with an amine is not economical in the gas phase, the corrosive natural gas stream may be treated by the process described. The acidic constituents are then maintained in solution in the liquid phase or in the vapor phase, or well in touch, res respectively, with the heavier hydrocarbon components until the solution or mixture, such as a liquid, can be contacted with a chemical solvent. Since this postabsorption softening is carried out in the liquid phase, the capital invested for the treatment equipment is

relatively low.

  When an operator changes the processing conditions to produce a new liquid mixture of successive molecular weight constituents, in accordance with the needs of the market, he must consider all the processing steps AH He must consider each of the steps in the indicated order However, it does not necessarily have to be modified for some natural gas streams, a variation in solvent flow rate and recycling, in addition to rectification, is suitable, for example, for most gas streams. Naturally, optimum efficiency is obtained when the eight preceding conditions and steps are all used. It is extremely easy, for example, to recover at least 99% of propane with 100% heavier hydrocarbons and less than 2% ethane without additional investment, or to recover more than 98% ethane and more than 99% butanes with all hydrocarbons

  heavier, and less than 2% propane, without additional investment.

  The flexibility of this process is illustrated in Table II which follows. The first four boxes or situations summarize the possibilities of selective extraction of C 2 + hydrocarbons and in particular the choice of extracting or not extracting and then rejecting hydrocarbons. successive lower molecular weights, i.e. C 1 + C 2 C 1 + C 2 + C 3 or C 1 + C 2 + C 3 + C 4 However, it should be noted that C 4 refers to both with isobutane and normal butane, that C 5 refers to both isopentane and normal pentane, as well as all

heavy as C 5.

  It should also be noted that small amounts of other desirable or undesirable constituents, not shown in Table II, may be present. The constituents indicated in the various streams are those

which predominate.

  The last four boxes or situations in the table summarize the possibilities of additional treatment of hydrocarbons discharged from the rectification unit, in addition to any gas resulting from an instantaneous vaporization, which are not recycled to the first extraction unit. This combined charge is extracted into the second extraction unit, with a portion of the same physical solvent as that used in the first extraction unit. Non-extracted hydrocarbons, which are methane or methane plus ethane containing small amounts of desirable hydrocarbons such as ethane or propane, are directed to the first extraction unit, and the rich solvent from the second extraction unit is directed to the single instantaneous vaporization unit The hydrocarbons extracted and obtained by flashing are compressed, cooled and condensed and are then directed to the separation unit which comprises a reboiler. The top stream from the separation unit is combined with the selected liquid hydrocarbon produced from the rectification unit and the residues. of the separation unit 25 constitute the chosen rejection having a value in liquid hydrocarbons lower than its value as fuel and they are combined with quality residual gas

suitable for pipes.

  First and second non-extracted hydrocarbons + -, u separation residues + u S u - uu ủ residual natural gas Rectifying residues + + + + mf separa + + + + U The selected products of the separation head stream IIIJN 1 are formed from the separation residues III, the gas obtained by evaporation, and the instantaneous mixture is obtained. 'o from the second I', I o-, o, extraction G & az obtained instantaneous vaporization + rejects of II e _______ to rectification,, ii uj o Rejects consisting of I 4 P current of head of recu U o> ci _tification UU -Products consisting of the rectifying residues; Wn p Non-extracted hydrocarbons from the first extraction O Targeted discharges * UH Uw Uw U Ql 4; This process can be carried out to remove the C 2 + liquid hydrocarbons from the input natural gas stream and to reject the methane contained in it, to the degree chosen, so that the liquid product of the rectification, used for demethanization purposes, includes up to 98% ethane, all the heavier hydrocarbons contained in the incoming natural gas stream, and less than 2% of the methane contained therein, chosen degree (case I

of Table II).

  Moreover, this process can be implemented to remove C 3 + liquid hydrocarbons from the natural gas stream and to reject the methane and ethane they contain at the chosen degree, the rectification of step D being carried out As de-ethanization (case II of Table II) The liquid product of the de-ethanisation thus comprises up to 99% of propane, all the heavier hydrocarbons present in the natural gas stream and less

  2% ethane of this gas, at the chosen degree.

  This process can also be used to recover C 4 + liquid hydrocarbons and to reject methane, ethane and propane which they contain, at the chosen degree, the rectification of step D constituting depropanisation. which gives a liquid product comprising about 100% butanes, all the heavier hydrocarbons present in the natural gas stream, and less than 2% ethane and propane of this gas, at the chosen degree (case III).

of Table II).

  In addition, the process can be carried out to recover C 5 + liquid hydrocarbons from the natural gas stream and to reject the ethane, propane and butane they contain at the chosen degree, the rectification constituting a step debutanizer which gives a liquid product comprising about 100% pentanes, all the heavier hydrocarbons present in the natural gas stream, and less than 2% ethane, propane and butanes,

  at the chosen degree (case IV of Table II).

  Ethane and propane can be rejected almost completely during the first extraction and in the multiple stages of flash vaporization Alternatively, they can be partially rejected during the first extraction, more rejected in multiple stages of flash, and practically rejected in their entirety after being subjected to the rectification operation; the first or the first two streams of residual gas are generally recycled to the first extraction and the last one or two last residual gas streams are directed to the rectification. In the second variant, they may be rejected only slightly or not rejected. at all, in the first extraction, moderately discharged into the flash vapor stages, and rejected mainly during rectification, or all of the residual gas from the multiple stages of instantaneous vaporization can then be directed to demethanization. either of these variants can be used for the selective release of propane, in accordance with the invention, since a relatively small portion of methane and 98% of ethane and propane are available as a stream extraction charge for the second extraction unit. The selective release of propane, in accordance with case V of Table II, is obtained by carrying out the rectification as depropanisation and by countercurrent extrac- tion of the extraction feed stream, containing C 1, C 2 and C 3, with the physical solvent in the second extraction, so that C 1 is removed and returned to the first extraction The rich solvent is then subjected to a single flash, compressed, condensed and treated in the separation unit which is used as a de-ethanizing unit, thereby producing C 2 as a top product which is combined with C 4 + from the rectification unit, and C 3 as a residual product,

  which is combined with the residual natural gas from the first extraction.

  According to case VI of Table II, the extraction feed stream essentially comprises C 1, C 2, C 3 and C 4 hydrocarbons, since the rectification unit is used for a debutanization function. After the second extraction, C 1 is mainly the non-extracted hydrocarbon which is recycled to the first extraction, and C 2, C 3 and C 4 form the vaporized residual gas stream which is depropanized in the separator to give C 4 as the residual stream discharged to the reactor. residual gas line and C 2 + C 3 as the overhead product stream which is combined with the residue stream from the rectification unit used at a debutanization function. In accordance with case VII of Table II, in which C 5 + liquid hydrocarbons form the residue of the rectification unit used as the debutanization unit, the first extraction and the multiple stages of flash are carried out in such a way that With a recycle of the first two streams of residual gas to the first extractions substantially all of the C 1 hydrocarbons and most of the C 2 hydrocarbons are not extracted and are present in the residual natural gas stream. remaining C 2, C 3 and C 4 form the extraction feed stream for the second extraction The C 2 hydrocarbon forms the overhead stream which is recycled to the first extractions and the C 3 and C hydrocarbons 4 are extracted during the second extraction and depropanized in the separator to conduct C 3 hydrocarbons as overhead stream which is combined with hydrocarbons

  C 5 + fluids to form the liquid hydrocarbon product.

  The residual current from the depropanizer in the separator is C 4 which is combined with the residual natural gas stream from the first extraction. In accordance with case VIII of Table II, in which C 5 + liquid hydrocarbons also form the residue of the rectification unit used for an end of debutanization, the first extraction and the multiple stages of instantaneous vaporization are carried out and the residual or exhaust gas recirculation is carried out so that substantially all the C 2 constituents

  are extracted in addition to certain constituents in C 1.

  The second extraction feed stream comprises C 1, C 2, C 3 and C 4 hydrocarbons. The top stream of the second extraction is C 1, the single flash gas consists of C 2, C 3 and C 4, the deethanizer head stream from the separator is C 2, and the deethanizer residues are C 3 and C 4. The combined residual natural gas stream therefore contains C 1 hydrocarbons. , C 3 and C 4 and the combined liquid hydrocarbon product stream contains C 2 hydrocarbons

and C 5 +.

  Since the gaseous feed stream of the second extraction unit contains substantially lower amounts of methane than the input natural gas stream arriving at the first extraction unit, the relative partial pressures of the heavier hydrocarbons in the load of the second extractor are much higher This situation significantly lowers the solvent demands of the second extraction unit (in the range of 0.14 to 28 m 3 per thousand cubic meters of load of the second extractor, under normal conditions) in relation to the solvent demands of the first extraction unit (0.71 to 71 m 3 per thousand cubic meters of input natural gas constituting the charge of the first extractor, under normal conditions), provided that the first and second

  Extraction units work at the same pressure.

  However, no external factor requires that the pressure prevailing in the second extractor is equal to that prevailing in the first extractor, since the first extractor generally works at the pressures of the residual gas pipes. A minimum pressure of 2700 kPa is essential for the Second Extraction Unit Since gas compression is very expensive, it may be preferable to have the

  extraction unit at a pressure as close as possible to 2700 kPa and, therefore, to lose the advantage

  In other words, it may be preferable to use solvent feed rates of the second unit of the second extractor, which results in higher partial pressures. higher extraction, similar to that required for the first extraction unit, ie from 0.71 to 71 m 3 per thousand cubic meters of extraction load, under normal conditions In general and following the pressures prevailing in extractors, the flow rates of solvent to the first and second extractors can therefore vary from 0.14 to

  0.71 m 3 / km 3 load under normal conditions.

  The preferred physical solvent in the invention should be ethane-selective and the heavier hydro-carbon components of the input natural gas stream, relative to methane, so that the relative volatility of methane over ethane or at least 0, and that the hydrocarbon loading capacity, defined by the solubility of the ethane in the solvent, is at least 1.77 m 3 of ethane per m 3 of solvent, in normal conditions. The physical solvent is selected from the group consisting of dialkyl ethers of polyalkylene glycol, N-methylpyrrolidone, dimethylformamide, propylene carbonate, tetramethylsulfone, glycerol triacetate, triethanolamine, tributylphosphate, and the like. The solvent is preferably selected from the group consisting of polyethylene glycol dimethyl ether, polypropylene glycol dimethyl ether, tetramethylene glycol dimethyl ether, and mixtures of these materials, and the solvent is , even more preferably, polyethylene glycol dimethyl ether containing 3-10 ethylene units and having

  a molecular weight of 146 to 476.

  Regeneration of the solvent is effected by applying heat to a reboiler to produce a head vapor stream which is cooled, condensed, stabilized, pumped and returned to the generator as

  reflux, after elimination of excess residual water.

  In general, the chosen flow rate of the solvent is between 0.14 and 71 m 3 per thousand cubic meters of natural gas stream under normal conditions.

  The selected instantaneous vaporization pressures performed in the successive stages vary between 8960 k Pa and 14 k Pa. The temperature of the residues of the rectification and separation units varies between -18 ° C. and C. The invention will be described in greater detail with regard to attached drawings by way of non-limiting example and in which: Figure 1 is a simplified diagram showing the connections between the basic operations performed according to the invention; and Fig. 2 is a detailed block diagram schematically illustrating various combinations of preferred embodiments for treating both

  mild and corrosive natural gases whose water content can reach saturation.

  The simplified scheme of FIG. 1 associates the processes, as indicated in cases I to IV of Table II, which produce a recycle stream of successively descending molecular weight hydrocarbons, which hydrocarbons are selected from C-hydrocarbons. 1 to C 4, and the methods as indicated in cases V to VIII of Table II, which extract from this recycling stream

  all C 1 and C 2 hydrocarbons to recycle them to the first extraction, and then remove the C 2, C 3 or C 2 + C 3 hydrocarbons to combine them with the liquid hydrocarbon products from the rectification.

  As indicated generally in FIG. 1, a soft or corrosive natural gas inlet 13 arrives at the first extraction unit 10 which also receives a solvent 55 via a line 55 and recycled materials via lines 22, 92 and 152. non-extracted gas exits through a line 12 and rich solvent exits through a line 15

  to arrive at multiple stages of instant vaporization

  The vaporized materials are directed to a grinding unit 90 through line 42, to a second extraction unit 150 via line 137, and to the first line of extraction via a line 22. The solvent flows from the multiple stages 20, 30, 40 and 70 of vaporization to a solvent regeneration unit 50 through line 45, and additional solvent arrives via line 165. This regenerated solvent returns to the first unit 10 of extraction. by a con10 duite 55 and the second unit 150 of extraction by a

driving 141.

  The overhead or reject hydrocarbons, of progressively lower molecular weight, are recycled from the rectification unit 90 through line 92 to the first extraction unit 10 and are directed by

  the pipe 131 to the second extraction unit 150.

  The residual currents of C 2 +, C 3 +, C 4 + or C 5 + hydrocarbons leave the rectification unit 90 via a line 95. The non-extracted hydrocarbons are recycled from the second extraction unit 150 to The rich solvent stream flows to a single flash stage 160 via a line 155. The rectified solvent is directed to the solvent regeneration unit 50 through a flow path.

driving 165.

  Hydrocarbons having undergone a single instantaneous vaporization are directed by a line 162 of the single instantaneous vaporization stage 160 to a separation unit 170. The overhead stream consisting of C 2, C 3 or C 2 + C 3 hydrocarbons passes through a line 172 to join the residual liquid hydrocarbon stream of line 95 to form a stream 97 which exits the plant through line 84 and which constitutes the product liquid However, if the input natural gas present in line 13 is corrosive, the combined liquid hydrocarbons are directed by a line 181 to a liquid softening unit 80 and that unit, in the form of softened liquid hydrocarbons, through line 82 to line 84 to form the liquid product of the process The residues of the separation unit 170 are discharged via a pipe 175 to be associated with the non-extracted hydrocarbons passing in line 12 and proving from the first extraction unit 10 to form a soft residual gas passing through a

conduct 19.

  FIG. 2 represents in a more detailed form the diagram of an installation implementing the improved process for separating hydrocarbons according to the invention, this diagram being similar to that of FIG. 1 with regard to the main elements. the various gas flow paths resulting from instantaneous vaporization and from multiple stages

  , 30, 40 and 70 instantaneous vaporization, and the gas flow circuits from the rectification unit 90 are illustrated in much more detail.

  The process shown diagrammatically in FIG. 2 comprises a first extraction unit (absorption), a medium pressure flashing unit 20, a low pressure flashing unit 30, a pressure flashing unit 40 atmospheric, an instantaneous vaporization unit 70, a regenerator 50, a unit 90

  grinding unit, a liquid softening unit 80, a second extraction unit 150, a simple flash unit 160, and a separation unit 170.

  A large number of pipes, compressors, coolers and valves can be used to direct each of these evaporated and liquid streams to these units, according to any desired sequence, to extract any hydrocarbon and / or to reject any particular hydrocarbon

  or C 1 -C 4 hydrocarbon group.

  When the inlet stream 13 is made of a soft natural gas, with a pressure of 2200 to 9100 kPa, this gas has generally been softened by countercurrenting in an aqueous solution of amine which has eliminated the corrosive materials, including H 2 S and C 02, while saturating with water

natural gas.

  Extractor 11 is maintained at a temperature

  from about -10 to 50 ° C, and preferably from about 21 ° C to 27 ° C.

  Solvent is provided using line 55 at a rate sufficient to reduce the water content of the soft natural gas leaving line 12 to less than 0.2 kg per thousand cubic meters, and preferably less than 0.12 kg / km 3, under normal conditions Under these conditions, ethane 10 and other hydrocarbon components of higher molecular weight passing through line 12 are reduced to a very low value. As the solvent arrives via line 55, the proportion of ethane relative to the predominant methane can be varied at will, but the proportion of solvent is usually 0.71 to 71 m 3 of solvent per thousand cubic meters of natural gas. of entry, whether mild or corrosive, in

normal conditions.

  The rich solvent passing through the pipe 15 arrives at the tank 21 of instantaneous vaporization under average pressure from which are mainly discharged methane and certain heavier hydrocarbons, through a pipe 22 A mixture of solvent, hydrocarbon constituents and water is discharged by a line 25 and a valve 26 and arrives at the tank 31 of low-pressure instantaneous vaporization of which a mixture of additional methane and some heavier hydrocarbons is discharged through a pipe 32. A mixture of solvent, methane remaining, Ethane, heavier hydrocarbons and water is discharged through line 35 and valve 36 Alternatively, the mixture may be channeled through line 37 and valve 39 to a line 44, rather than the

  line 45, in order to be directed towards the vat 71 of vacuum vaporization.

  It should be noted that the lower the flow rate of the solvent, the lower the amount of C 1 + hydrocarbons withdrawn from the input natural gas. It should be noted that the higher the input natural gas contains In addition, the smaller the amount of metal extracted at a given solvent flow rate, the lower the instantaneous vaporization pressure, the greater the amount of methane removed in each stage. However, the number of instantaneous vaporization stages used is generally a function of the inlet natural gas pressure, because the higher the inlet pressure, the greater the number of stages that can be used. and the more the pressure drop between two

  floors is low, which increases the overall efficiency.

  If the input natural gas is, for example, at a pressure of 8300 kPa, four stages of instantaneous vaporization may be desirable. But if the input natural gas is at a low to moderate pressure, for example 4100 k In general, the lower the pressure drop between the instantaneous vaporization stages, the lower the amount of desirable hydrocarbons removed by instantaneous vaporization of the solvent, and therefore the lower is the recycling of the desirable constituents. to the first

extraction unit 11.

  However, if economic considerations of capital investment are considered in terms of energy savings and plant sizing, a single instantaneous vaporization stage can be used effectively to separate C 1 + hydrocarbons. A liquid stream containing water and a physical solvent If the economic conditions indicate that two stages of instantaneous vaporization are optimal, the two gas streams resulting from the instantaneous sprays can be directed to the rectification unit 90 or else alternatively, the second vaporized stream may be directed to the rectification unit 90, while the first vaporized stream may be directed to the first

  extraction unit 10 or to the second extraction unit 150.

  The solvent regeneration unit 50 comprises the solvent regenerator 51, a reboiler 59 having a circulation line 54, a head discharge line 52 and a condenser 53, a decanter 61, a residual water discharge line 68. a water return pipe 65, a pump 66, a hydrocarbon vapor return line 62 from the settling tank 61 to the vacuum evaporation tank 71 or to the tank 41 for instantaneous vaporization at atmospheric pressure through Via a pipe 63 and a valve 69. The charge supplied to the solvent generator 50 may come from the tank 41 of instantaneous vaporization.

  at atmospheric pressure or tank 71 of vacuum vaporization by a pipe 45 and a pump 46, or by a pipe 75 and a pump 76, respectively The solvent without water is discharged from the regenerator 51 by a pipe 55 and a pump 56, cooled in a cooler 57 and directed by a valve 58 to the first extractor 11 or to the second extractor 151 via a pipe 141 and a valve 143.

  If the natural input stream arriving at the circuit through the line 13 does not contain water, the solvent can bypass the regenerator 50 through a line 48 and a valve 47, when the valve 49 is closed, in order to join the line The return of the solvent to the first extractor 11 and the second extractor 151 o As is apparent from Figure 2, the head streams flowing in the lines 22 and 32 can bypass, respectively, the rectification unit 90 to be recycled. directly to the extraction 11 via a pipe 112 and a valve 114 and a pipe 111 and a valve 113, via a pipe 92 Alternatively, these currents flowing in the pipes 22 and 32 can join the line 42 to pass through the cooler 74 and a valve 103 to arrive at the rectification unit 91. However, before receiving the currents flowing in the lines 22 and 32, the line 42 has previously received the current instantaneous vaporization at atmospheric pressure and, in some installations, the instantaneous vaporization head stream under

vacuum flowing in the pipe 72.

  The grinding unit 90 comprises a grinding column 91, a reboiler 99, a circulation line 98, a head discharge line 92, a waste discharge line 95 and a pump 96. The temperature at the bottom of the column 91 is controlled by the application of heat through the reboiler 99 and return of the bottom liquid heated by line 98 to the rectification column 91. The bottom liquid meets the specifications required for the product with respect to the undesirable constituents. (such as methane, ethane, propane, butanes, C 02, H 25 and other 15) and it comes out of the plant through line 95 and pump 96 to be conveyed through pipelines via However, if acidic components have not been previously removed, the unit 80 for softening the liquid is required. unites Figure 80 includes a main contact bowl 81 and a desorption unit 85. If the method does not require a rectification unit 90, a liquid reservoir 77 is used. The cooled stream passing through the line 42 is led through a line 158. and a valve 159 to the reservoir 77, then via a pipe 78, a pump 79 and a valve 187 to the main contact curve 81. If the rectification unit 90 is used in the process, the corrosive liquids are directed from the column The amine contact tank 81 produces a mild product passing through a valve 104 and its conduit 82, which consists of mainly ethane and heavier liquid hydrocarbons, suitable for pipeline transport. The identity of these heavier hydrocarbons depends on the previous treatment of demethanization, de-ethanization, depropanization or debutanization, carried out in the rectification column. The corrosive amine stream passing through line 83 is desorbed in unit 85, giving a flow of CO 2 and H 2 S leaving via a line 86, with a negligible hydrocarbon content The flow of mild amines returns to the tank 81 of contact by a pipe 87 If the liquid product meets the criteria requested without that it is necessary to use the grinding unit 90 and if the liquids are also soft, the liquid product can bypass both the grinding unit 90 and the liquid softening unit 80

  via line 84 and valve 88.

  The first extraction unit 10, the medium pressure flash unit 20, the low pressure flash unit 15, the atmospheric pressure flash unit, the instant spray unit 70 under vacuum and the rectification unit, as well as the recycle lines of the methane-rich streams passing through the pipe 92, and the liquid softening unit 80 and the solvent regenerator 50, are sufficient, with their accessories consisting of compressors, coolers, valves and pipes, to produce (a) a dry, mild residual gas directed to a pipeline through line 12 and (b) C 2 + liquids, C 3+ liquids, C 2 liquids 4 + or C 5 + fluids transmitted via a line 95, the C 2, C 31 C 4 hydrocarbons of successive molecular masses being selectively rejected and discharged as part of

  dry and soft residual gas passing in line 12.

  However, when market prices for liquid hydrocarbons vary, so that the market price of an individual liquid hydrocarbon falls below its price as fuels it becomes advantageous to be able to extract only the hydrocarbons 35 liquids whose prices are higher than their value in

as fuel.

  To carry out a selective extraction, it is necessary to add a second extraction unit 150, a simple flashing unit 160 and a separation or division unit 170. The extraction unit 150 receives a gaseous hydrocarbon stream via a line 137 and a Solvent stream from line 55 through line 141 and valve 143 Methane or ethane exits via line 152 as overhead stream, is compressed by a compressor 153 and is cooled by a heat exchanger. heat 154 before passing through a valve 156 and joining a pipe 92 to be recycled to the first extractor 11 via the pipe 28

and the valve 24.

  The selective supply circuit of the second extractor 101 in gas resulting from the instantaneous evaporation and overhead products of the rectification column com15 takes a collecting pipe 137 which receives the contents of the lines 138, 131, 101 and 121. and 131 are connected by valves 139 and 133, respectively, to line 92, which is the outlet line of the products

  at the top of the rectification column 91, upstream and downstream of the compressor 93, respectively.

  The vaporized gases from the medium pressure flash tank 21 can follow three paths to the following main processing units, namely: (1) the first extractor 11 to which they arrive via lines 22, 112, 92 and 28, (2) the second extractor 151 to which they arrive through the lines 22, 121, 131 and 137, and (3) the column 91 of rectification to which they arrive by the lines 22 and 42 The vaporization gases from the low-pressure flash vat 31 can also arrive at the same processing units by three paths, namely: (1) at the first extractor 11 through lines 32, 111, 92 and 28, (2) at the second extractor 151

  by the lines 32, 101, 121, 131 and 137, and (3) to the rectification column 91 through the lines 32 and 42.

  The vaporized gases from atmospheric pressure flash tank 41 and vacuum evaporation vessel 71 may arrive at the following main two-path processing unit, namely: at column 91 for rectification by the pipe 42 (and via line 72 in the case of tank 71) and to unit 81 for softening liquid through lines 42 and 158, reservoir 77 and line 78. Line 32, which is the head discharge line of the low-pressure flash tank 31, is connected to line 101 via valve 102, upstream of compressor 33, and to valve 107, downstream of The pipe 32 has its own valve 34 and is connected to the pipes 22 and 42

  to feed the rectification column 91.

  Depending on the working pressure of the second extraction unit 150, the gases coming from the pipe 92 can feed the second extractor 151 through the pipe 131. The latter comprises a valve 133 and a cooler 135 and it opens into the According to the working pressures of the tank 31 and the second extractor 151, the pipe 101 can be used to directly transmit the gases of the stream 32 to the pipe 127 via the

  conduit 108 which comprises a valve 109.

  The pipe 22, which is the head discharge pipe 25 of the medium pressure flash tank 21, is connected to a compressor 23 and to a pipe 115, comprising a valve 117, upstream of the compressor 23, and to the pipe 121 which comprises a valve 123 downstream of this compressor The pipe 22 is also connected to the pipe 112 which comprises a valve 114 and which opens into the pipe 92, upstream of the cooler 94.

91 column rectification.

  The pipe 121 has an additional valve 125 and opens into the pipe 131, upstream of the cooler 135. The bypass pipe 127, which comprises a valve 129, is connected to the pipe 121.

  upstream of the valve 125 and it opens into the pipe 137.

  The bypass line 108, which includes a valve 129, is connected to the pipe 101 upstream of the valve 106 and

  it opens into the line 127.

  The bottom stream passing through the pipe 155, according to the flow rate of the solvent, comprises C 2 + C 3 liquid hydrocarbons or C 2 + C 3 + C 4 liquid hydrocarbons which are directed towards the spray tank 161 simple instant of which a head stream exits through a line 162, passes into a compressor 163 10 and into a heat exchanger 164 to enter the separator or divider 171 The bottom current passing in the conduit 165 is then pumped by a pump 166 in

  a line 45 connected to the regenerator 50 of solvent.

  The hydrocarbon stream flowing in line 162 enters the separator 171 which is equipped with a reboiler 179 and a recirculation line 178 for heating the contents. The overhead stream is ethane if the unit is used. as de-ethanizer or ethane plus propane if the unit is used as a depropanizer. The overhead products passing through line 172 are combined with the products from line 95 to exit the circuit via line 84. Accordingly, the bottom stream passing through line 175 and pumped by pump 176 comprises propane or methane. propane plus butanes if the unit is used as de-ethanizer, or butane if the unit is used as a depropanizer. The hydrocarbon stream flowing in the pipe passes through a valve 177 to arrive at line 12 containing natural gas. residual line 173 and valve 174 may alternatively be used to recycle the contents of line 175 to the first extractor

  11 via line 152.

  According to the recovery objectives, the recycling gases of the circuit passing through the pipe 92 can bypass the first extractor 11, via the pipe 29 and the valve 149, and arrive directly at the residual gas pipe 12. residual gas, of quality for pipelines, leaves the circuit only by the pipe 19 If the main objective is to produce a chosen liquid, the residual gas enters the circuit only through the pipe 13 and its constituents come out only by the pipe 84 in the form of this liquid product, the other constituents leaving only through the pipe 19 in the form of residual natural gas On the other hand, if the main objective is to produce a natural gas chosen, the selected constituents come out under form of this gas only

  by line 19 and the other components exit as a residual liquid only through line 84.

  The flexibility presented by this treatment plant for selectively extracting desired hydrocarbon constituents from a mild or corrosive inlet gas stream and having any saturation water content, using a solvent physical,

  is illustrated in the following examples.

  Example 1 NI Case As shown in FIGS. 1 and 2, an ethane recovery plant is operated to process 100,000 m 3 / day (100 km 3 / d), under normal conditions, of softened natural gas. In order to obtain a 95% ethane recovery, the composition of the natural gas entering the extractor 11 of the extraction unit 10 is as follows: Component Mole percent Nitrogen 2, 02 Methane 80.62 Ethane 9.69 Propane 4.83 Isobutane 0.50 N-butane 1, g 45 Isopentane 0.30 N-pentane 0.37 Hexane plus 0.22, 00 Moisture content 2.9 kg / km 3 / day Inlet pressure: 4410 k Pa Inlet temperature: 50 ° C. In this example, the molar ratio of the solvent to the fresh feed stream passing through line 13 is of the order of 1.36: 1.00 L Ethane and the heavier liquids present in the inlet gas stream are selectively absorbed and removed from the first extractor via line 15. The first extractor 11 through the pipe 12 and is mainly composed of nitrogen, methane and small amounts of ethane following the desirable recoveries of ethane Practically all the propane and heavier constituents

are removed from the stream 13.

  In order to remove the methane from the recovered hydrocarbons while saving energy, the pressure prevailing in the pipe 15 is lowered in several successive stages, for example from 4410 k Pa to 2760 k Pa in the medium-pressure flash tank 21. then at 2070 k Pa in the low-pressure flash vat 31 and finally at 35 k Pa in the vat 71 under vacuum, so that vapor streams 22,

  32, 72 are separated from liquid streams 25, 35, 75.

  The vapor streams flowing in lines 22, 32, 72 contain, respectively, about 88, 86 and 40% methane, mole percent. The vapor stream passing through line 22 contains about 30% less methane and about 94% of the ethane present in the stream The stream of liquid flowing in line 25 contains about 30% less methane and about 94% of the ethane present in the line. The stream passing through line 32 contains about 51% less methane than the amount of methane present in the stream

passing in the pipe 15.

  The stream of liquid passing through the line 75 leaving the vacuum evaporating tank 71 contains about 1.5 mole% of hydrocarbons and water, the remainder being solvent, and is discharged to the generator 51. of solvent where it is brought to about 150 ° C. under a pressure of about 138 kPa to totally eliminate the water, and it is finally cooled to about 50 ° C.

in the cooler 57.

  The process of the process described in this example can be more clearly understood by considering

  the compositions of the various streams in kg / moles per hour.

  Eleven constituents of 15 currents are given in the

Tables III and IV below.

TABLE III

  Material balance sheet for illustrative example 1 N of line 13 55 12 15 28 22 25

_ __ _,

Constituents, kg-moles / hour

_ _ _ _ ,,

  Nitrogen 3.75 3.75 0.19 0.19 0.12 0.07 Methane 149.27 148.90 43.46 43.09 12.97 30.49 Ethane 17.93 0.91 20.40 3 37 1.27 19.13 Propane 8.94 trace 9.45 0.51 0.25 9.19 Isobutane 0.93 0.96 0.03 0.02 0.94 n-butane 2.68 2.75 0 , 07 0.03 2.72 Isopentane 0.56 0.56 0.56 n-Pentane 0.69 0.69 0.69 Hexane plus 0.49 0.49 0.49 Water 0.66 0.66 0, 66 Solvent 253.17 253.17 253.17 TOTAL kgmol / hour 185.90 253.17 153.56 332.88 47.26 14.66 318.11 wt O) ri Ln oeo I

TABLE IV

  Material balance for illustrative example 1 N of line 32 35 72 75 92 93 68 62 Constituents, kg-moles / hour Nitrogen 0.03 0.03 0.03 Methane 9.10 21.40 21.40 0, 15 21.03 0.37 0.15 Ethane 1 '20 17.94 17.94 0, 74 0.91 17.03 0.78 Propane 0.25 8.94 8.94 0.86 trace 8.94 0 , 86 Isobutane 0.02 0.93 0.93 0.15 0.93 0.15 n-butane 0.03 2.68 2.68 0.52 2.68 0.52 Isopentane 0.56 0.56 0 , 17 0.56 0.17 n-pentane 0.69 0.69 0.25 0.89 0.25 Hexane plus 0.49 0.49 0.22 0.49 0.22 Water 0.66 0.66 0.66 trace Solvent 253, 17 253.17 trace TOTAL, kg-moles / hour 10.63 307.49 53.63 256.89 21.97 31, 69 0.66 3.06

_ _

  If <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> </ I> propane entering the circuit through the pipe 13 can leave the circuit via the pipe 12 at the same time as 99% of propane with about 2% of ethane can be easily recovered from the current flowing in the pipe 13, as constituents of the the line containing 100% butanes and heavier hydrocarbons. These desirable recoveries can be obtained by changing the operating conditions, so that the molar ratio of the solvent to the fresh feed is significantly lowered to about 0.95. the pressure prevailing in the medium pressure vessel 15 is about 1725 k Pa, and the low pressure vessel is working at about 1035 k Pa, while the demethanizer

  is used as de-ethanizer at about 1900 k Pa.

  Similarly, by changing the flow rate of the solvent to the first extractor, changing the pressure in the successive stages of instantaneous vaporization and adjusting the pressure and temperature in the demethanizer unit, propane or butanes can be rejected at any chosen degree

  to give liquid products in C 4 ±> or C 5 + for 25 cases III or IV, respectively.

Example 2

  Extraction of C 2 and C 4 + liquids from soft natural gas and propane rejection (Case V) The process as described in Example 1 is carried out in a very similar manner to remove the hydrocarbons in C 2 + of the input natural gas, except that only the vapors from the instantaneous vaporization tank 21 are recycled directly to the first extractor 11 via lines 112, 92 and 28. All other currents flow, either directly to the line 137, or via the rectification column 91, working as a depropanizer, to the

driving 137.

  The pipe 137, which arrives at the second extractor 151, contains C1 + C 2 + C 3 hydrocarbons. The ratio of the flow of the solvent, via the pipe 141 and the valve 143, to the gas flow, through the pipe 137, is sufficient for the overhead stream from the second extractor 51 to contain mainly methane with a certain amount of ethane This ratio varies from 0.14

  to 28 cubic meters per thousand cubic meters under normal conditions.

  The overhead stream from the single flash tank 161 flows to the divider or separator 1712 working as a deethanizer, wherein the pressure and temperature are flow regulated in the recycle line 178 and the reboiler 179 so that the Ethane proceeds as a top product through line 172 to conduit 95, while propane exits through line 175, pump 176, and valve 177 to conduit 12. Combined liquid hydrocarbon product from lines 172 and 95 is therefore at C 2 and C 4 + and leaves the circuit through lines 97 and 84, because the gases are soft and the product responds acux specifications Residual natural gas

  contains C 1 and C 3 hydrocarbons and may be useful for a dehydrogenation process.

Example 3

  Extraction of C 2, C 3 and C 5 + liquids of soft natural inlet gas and rejection of butanes (Case VI) The process is carried out as in Example 2, except that the rectification tower 91 is used as debutanizer, so that the current flowing in line 92 consists of C 1, C 2, C 3 and C 4 hydrocarbons, that the current flowing in line 152 is composed of C 1 hydrocarbons, and that the current flowing in line 165 consists of C 2, C 3 and C 4 hydrocarbons. The separator 171 is used as depropanizer,

  so that the current flowing in line 175 is con-

  C 4 hydrocarbons and that the current flowing in the duct 172 consists of C 2 and C 3 hydrocarbons, thus increasing the C 5 + liquid product. The residual natural gas consists mainly of C 1 hydrocarbons and C 4 and may be useful for dehydrogenation, in addition to its fuel value Similarly, the conditions may be modified to produce other liquid hydrocarbons and / or other natural gases

  residuals of different compositions, as indicated in cases VII and VIII.

  Although a few schematic embodiments have been illustrated and described above, it should be noted that the process steps are important and that they can be arranged in a multitude of combinations in accordance with the work objectives and the given market conditions. according to the invention is extremely flexible and can not be limited to the schematic arrangements described in the examples or represented

on the drawings.

  It is very important to note that the large recoveries of ethane and heavier hydrocarbons are obtained by a proper separation of the constituents in the rectification unit 90 and in the separation or division unit 170 and the closure of the process loop through recycling to the first extractor; therefore, any C 2 + components exiting in the head streams of the medium, low, atmospheric and vacuum vacuum boilers and in the head stream of the rectification tower have

  second-chance to be recovered in all cases I to VIII.

  When a second extraction unit 150 is used for the selective rejection of an intermediate component, the overhead stream of the second extractor, passing through line 152, may contain undesirable hydrocarbons which have a second chance of further recovery in being recycled to the first extractor 11, which closes another loop, as in cases V to VIII This concept of recycling is one of the main factors to achieve unusually high recovery values This second chance of recovery of undesirable hydrocarbons, accompanied by a simultaneous release of intermediate boiling hydrocarbons, provides a further degree of freedom in the process design that does not exist in any of the liquid extraction processes

  natural gas described above.

  Another important feature of the invention is that the rich solvent exiting the second extractor 151 in stream 155 contains no more than the specified amounts of light undesirable hydrocarbons allowed in the stream of the final liquid product. While it is preferable to maximize the recovery of desirable hydrocarbons at the bottom of the second extractor 151 in line 155, it may be more economical to recycle any undesired, unwanted heavier hydrocarbons to the first extraction unit to increase yield, while Ensuring that the lighter components in the rich solvent stream 155 meet the current specifications. This can easily be achieved by selecting the working pressure of the second extraction unit 150 and setting the flow rate of the solvent

in driving 141.

  Another important element, particular to the present invention, is the ability to set and establish a pressure for each of the intermediate instantaneous vaporizations of the medium pressure vessel to the vacuum vessel, on the basis of economic objectives for a pump. The pressures are selected so that any undesired constituents, after controlling the flow rate of the solvent to the first extractor 11 in the line 55, are flashed and recycled directly to the first extractor 11, or subjected to a vacuum. further processing in the second extractor 151 by shortcircuiting the rectification tower 91 so that desirable constituents are recovered at a high efficiency The direct charge currents of the rectification unit 90 are composed mainly of constituents

desirable for the current 95.

  By selecting the pressure inside the rectification tower 91 and the temperature of its residues to obtain a primary separation of hydrocarbons of progressively decreasing molecular weights, plus a secondary separation in the second extraction unit 150, followed by A tertiary separation between desirable and undesirable hydrocarbons, by means of the separation unit 170, by similar selection of its pressure and temperature selectively eliminates particular undesirable constituents, even though the particular Hydrocarbons removed are located between desirable components. These desirable constituents are ethane, propane, butanes or C 5 + hydrocarbons according to the prevailing market conditions. The working pressure of the rectification unit 90 can also be modified at will, in accordance with the functional objectives, which makes it possible to the same equipment as a demethanizer if a C 2 + product is desired, as a de-ethanizer if a C 3 + product is desired, as a depropanizer if it is desired to

  produced in C 4 +, or as debutanizer if a C 5 + product is desired. The working pressure in the rectification unit 90 can vary between 345 and 3100 kPa.

  Similarly, the separation unit 170 is used as deethanizer or depropanizer. The pressure of the unit 170 can also be varied at will. However, if the ethane is to be removed, as in the case VII, It is simpler to carry out this elimination using the grinding tower 91 so that, for most functions, the separation unit 171 must simply separate the C 3 products.

  C 4 products, as shown in Table II.

  Another factor allowing unusually high recoveries of hydrocarbons and an extremely flexible degree of selectivity of the constituents is essentially the recognition of the relative solubility characteristics of the gases and the loading capacity of the various physical solvents such as DMPEG. the relative solubilities of ethane, propane, isobutane, normal butane, isopentane and normal pentane, hexane, heptane, etc. relative to methane, the desired hydrocarbons can be recovered selectively from a stream of natural gas by adjusting the flow rate of solvent to the extraction units 10 and 150, recycling to the extractor 11 of the resulting gas mixtures of instantaneous vaporization, adjustment of the working pressures prevailing in intermediate units 20, 30,, 70 of instantaneous vaporization, and level adjustment

  temperature and pressure in the rectification unit 90 and in the separation unit 170.

  It goes without saying that many modifications can be made to the method described and shown

  without departing from the scope of the invention.

Claims (16)

  A continuous process for extracting water and hydrocarbons heavier than methane (C 1 +) from an input natural gas stream with the aid of a physical solvent, this process making it possible to produce: (1) a liquid hydrocarbon product having a composition which can be selectively adjusted to practically any degree selected according to market conditions, or alternatively a liquid hydrocarbon by-product containing the remaining components, and (2) a residual natural gas stream comprising the remaining constituents or, alternatively, a natural gas of a selected pipe-grade composition, the process being characterized in that it consists of: A as a first extraction step (10) Extracting water and hydrocarbons heavier than methane from the natural gas stream, using the physical solvent, at pipe pressures, and at a solvent flow rate sufficient to produce at least one part of the pipeline-grade residual natural gas stream, which is returned to a pipeline, a rich solvent stream containing water, the solvent and a C 1 + hydrocarbon mixture, the flow rate wherein the solvent is selectively modified according to the flow rate and composition of the natural gas stream during the first extraction, in order to control the composition of the rich solvent stream as a function of selected components of the group comprising the ethane (C 2), propane (C 3), isobutane and normal butane (C 4), pentanes and heavier hydrocarbons (C 5 +); B to be subjected to successive instantaneous vaporizations the stream of rich solvent in several stages (20, 30, 40, 70) instantaneous vaporization, at gradually decreasing pressures, to produce several successive gas fractions C 1 +, having contents methane, and mixtures of liquid water, solvent and hydrocarbon mixtures with lower and lower methane contents, the instantaneous vaporization pressures of said successive stages of instantaneous vaporization being modified to regulate the compositions of successive gas fractions and of successive liquid mixtures as a function of the constituents chosen; C regenerating (50) the liquid mixture from at least the last flash stage of step B to produce said physical solvent for the first extraction; D recycle at least the first of the successive C 1 + gas fractions obtained by flash vaporization to the first extraction to extract maximum amounts of ethane and heavier hydrocarbon components (C 2 +); and E rectifying (90) at least the last of the successive C 1 + gas fractions to produce at least a portion of said liquid hydrocarbon product comprising C 2 +, C 3 +, C 4 + or C 5 + constituents and the remaining constituents forming an overhead gas stream comprising C 1, C 1 + C 2, C 1 + C 2 + C 3, or C 1 + C 2 + C 3 + C 4, which can be recycled to the extraction by: 1) selective variation of the rectification pressure and / or 2) selective variation of the temperature of the rectification residues.   The process according to claim 1, wherein, in response to market conditions, it is possible, at any chosen degree, to associate at least one intermediate component selected from the group consisting of C 3 and CO 3 components with the current. residual natural gas, the method being further characterized in that it comprises: A extracting, during a second extraction step (150), an extraction feed stream selected from the overhead gas and / or the successive C 1 gas fractions of step B, the physical solvent being at a chosen flow rate which determines the selected degree of recovery of said selected C 2 + components in a second solvent stream rich, the unextracted portion of said extraction feed stream being recycled to the first extraction of the natural feed stream of input made in step A of claim 1; B to instantaneously vaporize the second stream of rich solvent and thereby produce a gaseous stream obtained by a single instantaneous vaporization, containing said selected components of C 2 +, and a bottom solvent stream which is recycled to the stage regeneration C of claim 1; and C separating (170) said single flash gas stream and producing an overhead stream of a product selected from the group consisting of C 2, C 3 and C 2 + C 3 hydrocarbons, and a bottom stream selected from the group consisting of C 3, C 4 and C 3 + C 4 hydrocarbons, the bottom stream being associated with the residual natural gas stream of step A of claim 1 and the head product stream being associated with the liquid hydrocarbon product of step E of claim 1.   The process according to claim 2, characterized in that the input natural gas stream is selected from the group consisting of: A natural gas saturated with water; B a natural gas with a water content below saturation; C corrosive natural gas; A corrosive natural gas which is previously softened in the gaseous phase with the aid of an aqueous solution of amine; and E a soft natural gas.   Process according to claim 3, characterized in that the physical solvent is selective towards ethane and the heavier hydrocarbon components of the input natural gas stream, relative to the methane, so that the relative volatility of the methane relative to ethane is at least 5.0 and the hydrocarbon loading capacity, defined as the solubility of the ethane in the solvent, is at least 1.77 m 3 ethane per m 3 of solvent, in normal conditions.   The process according to claim 4, wherein the physical solvent is selected from the group consisting of dialkyl ethers of polyalkylene glycol, N-methylpyrrolidone, dimethylformamide, propylene carbonate, tetramethylsulfone, glycerol triacetate, triethanolamine, phosphate tributyl and gammabutyrolactone. Process according to Claim 5, characterized   in that the solvent is selected from the group consisting of polyethylene glycol dimethyl ether, polypropylene glycol dimethyl ether, tetramethylene glycol dimethyl ether and mixtures of these materials.   Process according to claim 6, characterized in that the solvent is polyethylene glycol dimethyl ether containing 3-10 ethylene units and having   a molecular weight of 146 to 476.   8 Continuous process for extracting water and hydrocarbons heavier than methane (C 1 +) from an input natural gas stream with the aid of a physical solvent, which process produces: (1) a liquid hydrocarbon product having a composition that can be selectively adjusted to any degree selected in accordance with market conditions or, alternatively, a liquid hydrocarbon by-product, and (2) a residual natural gas stream comprising the remaining components, or, alternatively, a natural product gas product of a selected composition having a quality for pipelines, the process being characterized in that it consists of: A to extract, during a first extraction step (10), water and hydrocarbons heavier than methane from the natural gas stream, using said physical solvent, at sufficient pipe pressures and solvent flow rate to produce at least a portion of the stream of e) residual natural gas, of piping quality, which is returned to a pipeline, a rich solvent stream containing said water, and a mixture of C 1 + hydrocarbons, the flow rate of the solvent being selectively modified with respect to the flow rate of flow and composition of the natural gas stream during the first extraction step to control the composition of the solvent rich stream relative to the selected components of the group consisting of ethane (C 2), propane ( C 3), isobutane and normal butane (C 4), pentanes and heavier hydrocarbons (C 5 +); B to be subjected to successive instantaneous vaporizations (20, 30, 40, 70) said rich solvent stream in several stages of flashing, at gradually decreasing pressures, to produce several successive gas fractions C 1 i, having contents methane which successively decreases and liquid mixtures of water, solvent and hydrocarbon mixtures having methane contents which successively decrease, the instantaneous vaporization pressures in the successive stages of instantaneous vaporization being modified to adjust the compositions of the successive gaseous fractions and successive liquid mixtures with respect to the selected constituents; C to recycle at least the first of the successive C 1 + gas fractions obtained by flash vaporization to the first extraction step in order to extract maximum amounts of ethane and heavier hydrocarbon components (C 2 +) ; D to rectify (90) at least the last of the successive C 1 + gas fractions in order to produce at least a portion of said liquid hydrocarbon product comprising constituents of C 2 +, C 3 +, C 4 + or C 5 + and the Remaining components forming a head gas stream comprising C 1 + C 1 + C 2, C 1 + C 3 + C or C 1 + C 2 + C 3 + C 4, which can be recycled to the first extraction by: 1 ) selective variation of the rectification pressure and / or 2) selective variation of the bottom temperature of the rectification; E to extract, as the second extraction stage (150), an extraction charge stream, chosen between the overhead gas stream and / or the successive C 1 + gas fractions of stage B, the physical solvent being used at a selected flow rate which determines the selected degree of recovery of said selected C 2 + components in a second rich solvent stream, the unextracted portion of said extraction feed stream being recycled to the first extraction of the feed stream. natural gas input from step A; To instantaneously vaporize the second stream of rich solvent and to produce, by a single instantaneous vaporization, a gas stream containing said selected components of C 2 + and a bottom solvent stream; G regenerating (50) the mixture of the type from at least the last of the flash vapor stages of step B and the bottom solvent stream of step F to produce said physical solvent for the first extraction and at the second extraction; and H separating (170) said gaseous stream resulting from a single flash vaporization of step F to produce a top product stream selected from the group consisting of C 2 t C 3 and C 2 + C 3 and a bottom reject stream selected from the group consisting of C 3, C 4 and C 3 + C 4, the bottom stream being associated with said portion of the residual natural gas stream of step A to produce said residual natural gas stream or, alternatively, said natural gas produced, and the overhead product stream being associated with said portion of said liquid hydrocarbon product of step D to yield said liquid hydrocarbon product or alternatively said liquid hydrocarbon product. Process according to claim 8, characterized in that the input natural gas stream is selected from the group consisting of: A natural gas saturated with water; B a natural gas with a water content below saturation; C corrosive natural gas; A corrosive natural gas which is previously softened in the gas phase with an aqueous solution of amine; and E a soft natural gas.   Process according to claim 9, characterized in that the physical solvent is selective towards ethane and the heavier hydrocarbon components of the input natural gas stream relative to methane, so that the relative volatility of the methane relative to the ethane is at least 5.0 and the hydrocarbon charge capacity, defined as the solubility of the ethane in the solvent, is at least 17.7 m 3 of ethane per m 3 of ethane. solvent under normal conditions.   Process according to claim 10, characterized in that the physical solvent is selected from the group consisting of dialkyl ethers of polyalkylene glycol, N-methylpyrrolidone, dimethylformamide, propylene carbonate, tetramethylsulfone, glycerol triacetate. ,   triethanolamine, tributyl phosphate and gamma butyrolactone.   Process according to Claim 11, characterized   in that the solvent is selected from the group consisting of polyethylene glycol dimethyl ether, polypropylene glycol dimethyl ether, tetramethylene glycol dimethyl ether and mixtures of these materials.   Process according to Claim 12, characterized in that the solvent is polyethylene glycol dimethyl ether containing 3-10 ethylene units and having   a molecular weight of 146 to 476.   A process for extracting from an input natural gas stream, with the aid of a physical solvent, selected hydrocarbons at any chosen degree and under pipe pressures, the process being characterized in that it consists of A to contact an inlet natural gas stream with a physical solvent at a selected flow rate as a function of the flow rate of the gas stream to extract a residual natural gas stream as the first current, and a solvent rich stream comprising a solvent, water and a C + hydrocarbon mixture as the second stream; B to subject the second stream to instant vaporization at substantially atmospheric pressure to produce a C 1 + gas fraction as the third stream, and a liquid mixture comprising a solvent and water as the fourth stream ; C compressing, cooling, condensing and demethanizing the third stream to produce a residual gas stream comprising substantially methane, and a liquid product stream comprising the remaining hydrocarbon components of the third stream; and Do to regenerate the fourth solvent-containing stream and recycle the regenerated solvent to the stage A contacting.   Process according to Claim 148, characterized in that the physical solvent is selective towards ethane and heavier hydrocarbon constituents of the input natural gas stream, relative to methane, so that the relative volatility of the methane relative to the ethane is at least 5.0 and the hydrocarbon charge capacity, defined as the solubility of ethane in the solvent, is at least 1.77 m 3 ethane per m 3 of solvent The process according to claim 15, wherein the physical solvent is selected from the group consisting of dialkyl ethers of polyalkylene glycol, N-methylpyrrolidone, dimethylformamide, propylene carbonate, tetramethylsulfone, and the like. , of glycerol triacetate,   of triethanolamine, tributyl phosphate and gammabutyrolactone.   Process according to Claim 16, characterized in that the solvent is chosen from the group consisting of   polyethylene glycol dimethyl ether, polypropylene glycol dimethyl ether, tetramethylene glycol dimethyl ether and mixtures of these materials.   Process according to claim 17, characterized in that the solvent is polyethylene glycol dimethyl ether containing 3-10 ethylene units and having a molecular weight of 146 to 476. The process according to claim 18, characterized in that that the instantaneous vaporization of step B is carried out in at least two stages to produce at least two Ci + gas fractions having a methane content which gradually decreases.   Method according to one of claims 18 and   19, characterized in that the demethanization is carried out as deethanization and in that the residual gas stream consists essentially of methane and ethane.   Method according to one of claims 18 and   19, characterized in that the demethanization is carried out as a depropanizer and in that the residual gas stream consists essentially of methane, ethane and propane.   Method according to one of claims 18 and   19, characterized in that the demethanization is carried out as debutanization and in that the residual gas stream consists essentially of methane, ethane, propane and butane.