FR2826371A1 - Pre-treating natural gas containing acid compounds, involves cooling natural gas to condense water, contacting partially dehydrated natural gas with liquid stream and cooling dehydrated natural gas - Google Patents

Abstract

Natural gas containing acid compounds is pre-treated by performing processes (I-IV). In process (I), the natural gas is cooled. In process (II), the gas phase obtained in process (I) is contacted with liquid phase obtained in process (III), and in process (III), the gas phase obtained in process (II) is contacted with liquid phase obtained in process (IV). The gas phase obtained in process (III) is cooled. Pre-treatment of natural gas containing hydrocarbons, water and acid compounds chosen from hydrogen sulfide and carbon dioxide, involves cooling natural gas to condense portion of water, contacting partially dehydrated natural gas with a liquid stream containing hydrogen in contact zones and cooling dehydrated natural gas to condense and separate acid compounds, in sequential processes (I-IV). The process (I) involves cooling the natural gas to produce a liquid phase and a gas phase. The process (II) involves contacting the gas phase obtained in process (I), in a contact zone (I) (202), with a liquid phase obtained in process (III) to produce a gas phase and a liquid phase. The process (III) involves contacting, in a contact zone (II) (203), the gas phase obtained in process (II) with a liquid phase obtained in process (IV) to produce a gas phase and a liquid phase. The gas phase obtained in process (III) is cooled to produce a liquid phase and a gas phase.

Description

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The invention relates to a process for pretreating a highly acidic natural gas containing a substantial amount of acidic compounds such as hydrogen sulfide (H2S) and carbon dioxide (CO2).

The work carried out by the applicant had made it possible to propose in patent EP 0 665 046 a process making it possible to eliminate a substantial quantity of the acidic compounds present in the natural gas at the outlet of the well, a process whose simplicity allowed easy realization and an investment minimal. According to the method, the initial natural gas is brought into contact in a cyclone chamber with a liquid rich in acidic compounds in order to obtain, on the one hand, at the top of the cyclone chamber, a gaseous fraction depleted in acid compounds and on the other hand, at the bottom of the cyclonic chamber, a liquid phase containing the majority of the acidic compounds and water. The liquid phase recovered at the bottom of the cyclonic chamber is reinjected into a well in the process of exhaustion. The gaseous fraction obtained at the top of the cyclone chamber is cooled at low temperature (up to -300 ° C) and then sent into a separation tank to obtain on the one hand a gas purified in acidic compounds and on the other hand a rich condensate in acid compounds which is recycled to the cyclone enclosure.

However, the method described in patent EP 0 665 046 has drawbacks: 1) The presence of water in the gaseous fraction cooled at low temperature is likely to cause throughout the circuit the formation of solid hydrates may eventually clog pipes, or even damage the constituent elements of the device used. This is why the process described by the patent EP 0 665 046 recommended the use of an anti-hydrate, preferably methanol, to prevent the formation of hydrates during cooling of the gaseous fraction from the cyclone enclosure .

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 2) A significant amount of hydrocarbons is entrained with the liquid phase recovered at the bottom of the cyclone enclosure. The loss of hydrocarbons entrained with the liquid at the bottom of the cyclone enclosure can amount to 10% of the amount of gas treated.

 The present invention is intended to overcome the disadvantages mentioned above.

 It has been discovered by the applicant that it is possible under appropriate thermodynamic conditions to concentrate the initial natural gas into methane while removing the majority of the acid gases and substantially all the water contained therein. By substantially all the water, it is understood that the amount of water present in the final gas is less than 50 ppm molar, preferably less than 10 ppm molar, and even more preferably less than 5 ppm molar. The present invention proposes to replace the contact cyclone chamber by several contacting zones, each contacting zone operating under pressure conditions and determined temperatures.

 The present invention also proposes implementing different cooling means for the gaseous fraction obtained at the top of the cyclone enclosure.

 The present invention provides a process for pretreating a pressurized natural gas containing hydrocarbons, at least one of the acidic H2S and CO2 compounds and water, the process comprises the steps of: a) cooling the natural gas to produce a liquid phase and a gaseous phase,

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b) on met en contact dans une première zone de contact la phase gazeuse obtenue à l'étape a) avec une phase liquide obtenue à l'étape c) pour produire une phase gazeuse et une phase liquide, c) on met en contact dans une deuxième zone de contact la phase gazeuse obtenue à l'étape b) avec une phase liquide obtenue à l'étape d) pour produire une phase gazeuse et une phase liquide, d) on refroidit la phase gazeuse obtenue à l'étape c) pour produire une phase liquide et une phase gazeuse.

b) contacting in a first contact zone the gas phase obtained in step a) with a liquid phase obtained in step c) to produce a gaseous phase and a liquid phase, c) contact is made in a second contact zone the gas phase obtained in step b) with a liquid phase obtained in step d) to produce a gaseous phase and a liquid phase, d) the gas phase obtained in step c) is cooled to produce a liquid phase and a gas phase.

In step d) of the process according to the invention, it is possible to cool the gaseous phase obtained in step c) by means of a heat exchanger and / or by means of an expansion turbine.

The process according to the invention may comprise the step: e) the gas phase obtained in step d) is cooled by means of an expansion turbine to produce a gaseous phase and a liquid phase which is recycled at the stage c).

If the process according to the invention uses an expansion turbine, it may comprise the step: f) compressing at least one of the gaseous phases obtained in step d) and in step e) using the energy recovered on the expansion turbine.

In step d) of the process according to the invention, the gas phase obtained in step c) can be cooled by means of a Venturi neck, said liquid phase being drawn off at the level of the Venturi neck and said gaseous phase being recovered at the exit of the divergent tube of the Venturi pass. The liquid phase withdrawn at the Venturi neck can be cooled to produce the recycled liquid in step c) and a gas phase.

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 The gaseous phases obtained in step d) and in step e) can be used for cooling the gaseous phase obtained in step c) and / or for cooling the natural gas in step a).

 In the first contact zone, the liquid obtained in step b) can be heated.

 In step a) of the process according to the invention, the natural gas can be at a pressure of 8 MPa and at a temperature above 15 C.

 The liquids obtained in step a) and in step b) can be introduced into a well.

 According to the present invention, after treatment of the natural gas leaving the production well, a final gas containing the majority of the hydrocarbons contained in the gas is recovered before treatment. By the majority of the hydrocarbons is meant at least 90% hydrocarbons, preferably at least 95% hydrocarbons and very preferably at least 97% hydrocarbons relative to the hydrocarbons contained in the gas before treatment.

 The present invention advantageously avoids the use of an anti-hydrate, such as methanol, the transport, use and regeneration of which are generally expensive, complex and dangerous handling.

 The invention will be better understood on reading the description given below as exemplary embodiments, in the context of non-limiting applications with reference to the appended drawings in which:

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- la figure 3 représente une variante du procédé selon l'invention utilisant un séparateur de type col de Venturi, - la figure 4 représente un séparateur de type col de Venturi. FIG. 1 shows a schematic diagram of the method according to the invention, FIG. 2 represents a variant of the method according to the invention using an expansion turbine,

FIG. 3 represents a variant of the process according to the invention using a Venturi-type separator, FIG. 4 represents a Venturi-type separator.

à une pression de 8 MPa et une température de 50 C, saturé en eau (3600 ppm molaire), contenant 32 % molaires d'H2S, Il % molaires de CO2 et 57 % molaires de méthane (moins de 1 % molaire de C2+) est introduit dans un échangeur de chaleur (101) où il est refroidi à 30 C. La température de refroidissement est choisie de manière à être légèrement supérieure à la température de formation d'hydrates à la pression du gaz naturel arrivant par le conduit 1. Le fluide en sortie de l'échangeur (101) est introduit par un conduit (2) dans un séparateur (201), et on soutire par un conduit (3) un effluent liquide contenant essentiellement de l'eau et très peu de composés acides dissous. Cet effluent liquide peut être éventuellement réchauffé dans l'échangeur de chaleur (102). On soutire également du séparateur (201) par un conduit (4) un gaz saturé en eau contenant 1550 ppm molaires d'eau. Le refroidissement dans l'échangeur (101) permet ainsi d'obtenir un gaz présentant une teneur en eau beaucoup plus faible. In the exemplary embodiment of the method of the invention according to FIG. 1, a very acidic natural gas coming from a production well via a pipe (1)

at a pressure of 8 MPa and a temperature of 50 C, saturated with water (3600 molar ppm), containing 32 mol% of H2S, II mol% of CO2 and 57 mol% of methane (less than 1 mol% of C2 +) is introduced into a heat exchanger (101) where it is cooled to 30 C. The cooling temperature is chosen to be slightly higher than the hydrate formation temperature at the pressure of the natural gas arriving via the pipe 1. The fluid leaving the exchanger (101) is introduced via a pipe (2) into a separator (201), and a liquid effluent containing essentially water and very few acid compounds is withdrawn via a pipe (3). dissolved. This liquid effluent may be optionally heated in the heat exchanger (102). A gas saturated with water containing 1550 ppm molar of water is also withdrawn from the separator (201) via a line (4). The cooling in the exchanger (101) thus makes it possible to obtain a gas with a much lower water content.

première zone de mise en contact (202). Cette zone de mise en contact (202) fonctionne à une pression de 7, 97 MPa et une température de 17 C environ. The gas from the separator (201) via the conduit (4) is introduced into a

first contacting area (202). This contacting zone (202) operates at a pressure of 7.97 MPa and a temperature of about 17 C.

It may consist of a balloon provided with packings known to those skilled in the art. It receives, by a conduit (5), a liquid flow composed of a majority

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pourcentage molaire du mélange en ILS dépasse 40 % ; et - d'obtenir un gaz partiellement déshydraté quittant la zone (202) par le conduit (8). En effet, l'eau contenue dans le gaz arrivant par le conduit (4) est absorbée par le liquide arrivant par le conduit (5) car l'eau a une affinité plus forte pour l'H2S que pour les hydrocarbures. of H2S (about 70 mol%) which is at a temperature of about 5 C. Thus a mixture is formed by contacting the gas arriving via the conduit (4) and the liquid arriving via the conduit (5) in the zone (202). This contacting simultaneously makes it possible: to raise the mole fraction of H 2 S in the mixture contained in the zone (202); dissolving any solid particles (mainly sulfur-based) of the mixture contained in the zone (202). Work conducted by Alberta Sulfur Research Ltd. and presented in the publication "Recent Developments in the Mitigation of Sulfur Deposition in Sour Gas Facilities" (PD Clark, P. Davis, J. Simion, E. Fitzpatrick and CSC LauLaurance Reid Gas Conditioning Conference 1995 Norman Oklahoma) show indeed that the solubility of sulfur is substantially increased when the

molar percentage of ILS mixture exceeds 40%; and - obtaining a partially dehydrated gas leaving the zone (202) through the conduit (8). In fact, the water contained in the gas arriving via the pipe (4) is absorbed by the liquid arriving via the pipe (5) because the water has a stronger affinity for the H2S than for the hydrocarbons.

molaires par de l'H2S, le reste étant de l'eau, du CO2 et un peu de méthane entraîné. On peut éventuellement récupérer les hydrates sous forme de dépôt à ce niveau. Ce liquide est évacué par le conduit (6), éventuellement réchauffé dans l'échangeur (103), mélangé à l'effluent liquide récupéré en fond de séparateur (201) et évacué par le conduit (7) grâce à une pompe (301) à une pression de 38 MPa pour être réinjecté dans un puits de pétrole épuisé. At the bottom of the zone (202), a liquid formed at more than 75% is obtained

molars with H2S, the rest being water, CO2 and some entrained methane. The hydrates can optionally be recovered in the form of a deposit at this level. This liquid is discharged through the pipe (6), optionally heated in the exchanger (103), mixed with the liquid effluent recovered at the bottom of the separator (201) and discharged through the pipe (7) by means of a pump (301) at a pressure of 38 MPa to be reinjected into an exhausted oil well.

 The temperature of the zone (202) is adjusted to be high enough to guard against hydrate formation. However, in cases where

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hydrates would be formed, the contacting zone (202) can be made as a cyclone-type enclosure so as to avoid clogging or clogging by the solid particles. A heating means (107) may also be used to raise the temperature of the mixture in the zone (202) above the hydrate formation temperature. This heating means may consist of a reboiler (107) heating the liquid at the bottom of the zone (202). The heat input by the reboiler (107) also makes it possible to vaporize the hydrocarbons present in the liquid at the bottom of the zone (202) and thus to limit the losses of hydrocarbons entrained with the liquid discharged through the conduit (6) in the bottom of the area (202).

At the head of the contact zone (202), a gas formed essentially of H28 (33 mol%), CO2 (12 mol%) and methane (54 mol%) and strongly depleted in water (200 ppm molar) is removed. through the conduit (8).

5 C environ. Elle reçoit un flux liquide composé d'environ 50 % molaires d'ILS par un conduit (9) qui est à une température de-30 C environ. Cet appoint d'lus liquide, ne contenant pratiquement plus d'eau (40 ppm molaires) permet de retirer la majorité de l'eau présente dans le gaz contenu dans la zone (203) en raison de l'affinité de l'his liquide déshydraté pour l'eau plus forte que l'affinité des hydrocarbures pour l'eau. The gas from the first contact zone (202) through the conduit (8) is introduced into a second contacting zone (203). This contacting zone (203) operates at a pressure of 7.94 MPa and a temperature of

About 5 C. It receives a liquid stream composed of about 50 mol% of ILS through a conduit (9) which is at a temperature of -30 C. This addition of fluid, containing practically no water (40 ppm molar) makes it possible to remove the majority of the water present in the gas contained in the zone (203) because of the affinity of the liquid he dehydrated for water stronger than the affinity of hydrocarbons for water.

 At the head of the contact zone (203) is evacuated through the conduit (10) a gas formed substantially dols, CO2 and methane and substantially no longer containing water (about 16 ppm molar).

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 The gas transported through the conduit (10) passes through different cooling systems to liquefy the acidic compounds. First a gas-gas heat exchanger (104). The exchanger (104) is evacuated via the conduit (11) to a fluid at approximately -5 ° C. This fluid is introduced into a heat exchanger (105), using, for example, a propane refrigerant, and exits through the conduit. (12) at the temperature of -30 C.

 The fluid flowing in the line (12) is introduced into the separator tank (204). The flask (204) is at a temperature of -30 ° C. and at a pressure of 7.88 MPa. A partially acid-purified gas (204) is discharged from the flask (204) through line (13) and a condensate rich in HS and CO through line (14). The condensate circulating in the conduit (14) is recycled through the pump (302) into the contact zone (203) via the conduit (9).

The methane contained in the condensate circulating in the conduit (14) is largely recovered in the contact zone (203).

 The gas flowing in the duct (13) can be used as a coolant in the exchanger (104) and in the exchanger (101).

 Finally, a methane loss of 823 kmol / h is observed, ie less than 7 mol% of the amount present in the feedstock arriving via the pipe (1). The feed gas was purified of 4750 kmol / hr of tLS, ie 72 mol% of the amount present in the feedstock. The main advantage of the process according to the invention is always to use streams having molar fractions of water and associated temperatures which are such that the formation of hydrates is impossible. This is in particular due to the use of the balloon (201) making it possible to reduce the quantity of water present in the gas and the use of the two contact zones (202) and (203) making it possible to obtain a very high gas. poor in water which can then be cooled without the risk of hydrate formation. So

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 the method according to the invention does not require mixing the natural gas with an anti-hydrate compound.

 Without departing from the scope of the invention, it is possible to implement more than two contact zones. One or more contact zones operating under thermodynamic conditions intermediate between those of the zones (202) and (203) can be arranged between the contact zone (202) and (203).

Table 1 shows, in the exemplary embodiment described with reference to FIG. 1, the material balance obtained with the method:

<Tb>
<tb> Driving <SEP> 1 <SEP> 3 <SEP> 4 <SEP> 6 <SEP> 13 <SEP> 14
<tb> Temperature <SEP> (C) "50, <SEP> 0 <SEP> 30, <SEP>0" 30, <SEP> 0 <SEP> 17, <SEP> 0-30, <SEP> 0- 30, <SEP> 0
<tb> Pressure <SEP> (MPa) <SEP> 8.00 <SEP> 7, <SEP> 97 <SEP> 7, <SEP> 97 <SEP> 7.97 <SEP> 7, <SEP> 88 <SEP> 7, <SEP> 88
<tb> Flow <SEP> molar
<tb> (kmol / h)
<tb> H20 <SEP> 75, <SEP> 3 <SEP> 42.9 <SEP> 32.3 <SEP> 32.3 <SEP> 0.0 * <SEP> 0.4
<tb> N2 <SEP> 8, <SEP> 1 <SEP> 0.0 * <SEP> 8.1 <SEP> 0.2 <SE> 7.9 <SEP> 1, <SEP> 0
<tb> C02 <SEP> 2219, <SEP> 4 <SEP> 0.1 <SEP> 2219.3 <SEP> 614.9 <SEP> 1604.3 <SEQ> 1715.2
<tb> H2S <SEP> 6570, <SEP> 7 <SEP> 0.9 <SEP> 6569, <SEP> 9 <SEP> 4749.6 <SEP> 1820.4 <SEQ> 4355.9
<tb> Methane <SEP> 11839, <SEP> 8 <SEP> 0.0 * <SEP> 11839.8 <SEP> 823.8 <SEP> 11015.6 <SEP> 3235, <SEP> 5
<tb> Ethane <SEP> 96, <SEP> 2 <SEP> 0.0 * <SEP> 96.2 <SEP> 24.3 <SEP> 71.9 <SEP> 65.4
<tb> Propane <SEP> 37, <SEP> 2 <SEP> 0.0 * <SEP> 37.2 <SEP> 22.8 <SEP> 14.4 <SEP> 29.4
<tb> Butane <SEP> 5, <SEP> 0 <SEP> 0, <SEP> 0 * <SEP> 5.0 <SEP> 4.6 <SEP> 0.4 <SEP> 1.8
<tb> Pentane <SEP> 2, <SEP> 3 <SEP> 0.0 * <SEP> 2,3 <SEP> 2,3 <SEP> 0,0 * <SEP> 0,2
<tb> Total <SEP> (kmol / h) <SEP> 20854, <SEP> 0 <SEP> 44, <SEP> 0 <SEP> 20810, <SEP> 1 <SEP> 6274, <SEP> 9 <SEP > 14534, <SEP> 9 <SEP> 9405.0
<Tb>
* less than 0.05
Table 1
Another possible configuration of the device described in FIG. 1 allowing the application of the present method is presented in FIG.

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 modification compared to Figure 1 relates to the cooling means for cooling the fluid flowing in the conduit (11).

 In FIG. 2, the flow evacuated from the exchanger (104) via the duct (11) to the temperature of -5 ° C. is sent to a separator tank (205). This balloon (205) separates a liquid effluent rich in acidic compounds, discharged through the conduit (16) and a gas, discharged through the conduit (17). The conduit (17) supplies the gas to an expansion turbine (401) in which it undergoes isentropic expansion. The flow from the expansion turbine (401) is at low temperature (about -30 C) and is sent through the conduit (18) into the separator tank (204). A partially acid purified gas (204) is discharged from the flask (204) through line (19) and a condensate rich in ILS and CO through line (14). The separation of partially purified gas into acidic compounds and condensate rich in ILS and CO is favored by the low pressure value in the flask (204) obtained as a result of the expansion of the gas in the turbine (401). The condensate circulating in the line (14) is raised in pressure by the pump (302) and is mixed with the liquid stream from the balloon (205) through the conduit (16). This mixture is recycled to the contact zone (203) through the pump (303).

 The gas from the flask (204) via the duct (19) can be used as a coolant in the exchanger (104) and then in the exchanger (101). This exit gas exchanger (101) is directed by the conduit (20) to the compressor (402) to be recompressed before being exported through the conduit (21). The compressor (402) can be coupled to the turbine (401) to use the work of the isentropic expansion as a source of energy. A second compressor powered by a source external to the process of the invention can also compress the gas from the balloon (204) to compensate for the energy loss during

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 the expansion and compression performed by the turbine (401) coupled to the compressor (402).

Table 2 shows, in the exemplary embodiment described with reference to FIG. 2), the material balance obtained:

<Tb>
<tb> Driving <SEP> 1 <SEP> 11 <SEP> 17 <SEP> 19 <SEP> 21
<tb> Temperature <SEP> (C) <SEP> 50, <SEP> 0-5, <SEP> 0-5, <SEP> 0-30, <SEP> 0 <SEP> 49, <SEP> 0
<tb> Pressure <SEP> (MPa) <SEP> 10, <SEP> 0 <SEP> 9.95 <SEP> 9.95 <SEP> 5.1 <SEP> 7.7
<tb> Flow <SEP> molar
<tb> (kmol / h)
<tb> H20 <SEP> 75, <SEP> 3 <SEP> 0.4 <SEP> 0.2 <SEP> 0.0 * <SEP> 0.0 *
<tb> N2 <SEP> 8, <SEP> 1 <SEP> 8.9 <SEP> 8.7 <SEP> 8.7 <SEP> 8.8
<tb> C02 <SEP> 2219, <SEP> 4 <SEP> 3320.0 <SEP> 3030.0 <SEP> 2155.8 <SEQ> 2149.5
<tb> H2S <SEP> 6570, <SEP> 7 <SEP> 6176.1 <SEP> 5301.5 <SEP> 1987.3 <SEP> 1961.1
<tb> Methane <SEP> 11839, <SEP> 8 <SEP> 14251.1 <SEP> 13642.7 <SEP> 13379.2 <SE> 13390.5
<tb> Ethane <SEP> 96, <SEP> 2 <SEP> 137.0 <SEP> 125.6 <SE> 99.3 <SE> 99.3
<tb> Propane <SEP> 37, <SEP> 2 <SEP> 44.0 <SEP> 38.3 <SEP> 18.7 <SEP> 18.6
<tb> Butane <SEP> 5, <SEP> 0 <SEP> 2.2 <SEP> 1.8 <SEP> 0.4 <SEP> 0.4
<tb> Pentane <SEP> 2, <SEP> 3 <SEP> 0.3 <SEP> 0.2 <SEP> 0.0 * <SEP> 0.0 *
<tb> Total <SEP> (kmol / h) <SEP> 20854, <SEP> 0 <SEP> 23940, <SEP> 0 <SEP> 22148, <SEP> 9 <SEQ> 17649, <SEP> 4 <SEP > 17628, <SEP> 1
<Tb>
- "outside U, Ub
Table 2
A third possible configuration of the device described in FIG. 1 allowing the application of the present method is presented in FIG. 3. The modification with respect to FIG. 1 relates to the cooling means serving to cool the fluid flowing in the conduit (FIG. ).

 In FIG. 3, the flow evacuated from the exchanger (104) through the duct (11) to the temperature of -5 ° C is passed through a Venturi-neck separator (501).

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 Figure 4 shows in detail the venturi-type separator (501). It comprises an intake duct (40) of the gas to be treated. This duct (40) is extended by a convergent tube (41), then by tube (42) of small diameter relative to the duct (40). This tube (42) constitutes the Venturi neck. Thus the gas introduced into the duct (40) undergoes a speed increase that can reach a supersonic speed in the Venturi neck (42). This increase in velocity allows isentropic expansion, i.e., a reduction in pressure and temperature, of the gas in the Venturi neck (42). If the treated gas contains acidic compounds, the latter condense in the form of fine droplets. Arranged in the Venturi neck (42), delta wings (43) provide vortex movement to the gas so as to press the condensate droplets onto the inner wall of the Venturi neck (42) as a thin layer. film of liquid. A circumferential slot (44), disposed downstream of the delta wings (43) in the Venturi neck (42), retrieves the thin film of liquid in the enclosure (45) and discharges it through the conduit ( 46). Downstream of the slot (44), the gas separated from the condensed droplets undergoes a decrease in velocity through the diverging tube (47).

This decrease in speed is accompanied by an increase in the pressure and the temperature of the gas at the outlet of the diverging tube (47). This type of separator may for example be of the TWISTER Supersonic Separator type marketed by TWISTER BV.

 Referring to Figure 3, the gas introduced into the separator (501) is expanded isentropically at the Venturi neck and cooled (30bar and-46 C). Thus, at the level of the Venturi pass, an effluent rich in H2S is condensed. This effluent is collected at the level of the Venturi pass and then discharged through the conduit (22). At the outlet of the Venturi pass, the gas is channeled in a diverging tube which allows it to rise in pressure (75 bar) and temperature

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 (19 C). The gas exits the separator (501) through the conduit (23). The Venturi neck separator is a means of cooling the gas that does not require energy input.

 Due to the fact that the flow flowing in the duct (10) contains only a low water content (about 16 molar ppm), no hydrates are formed at the separator (501) or at the level of the effluent liquid recovered by the conduit (22). Thus the method according to the invention does not require the use of an anti-hydrate continuously. The effluent circulating in the conduit (22) is cooled to -30 C through the heat exchanger (106) can use a propane refrigerant. The cooled effluent is directed to the flask (204) through the conduit (24). The flask (204) produces an ILS-rich liquid effluent discharged through the conduit (14) and a gas discharged through the conduit (25). This gas flowing in the conduit (25) is remixed to the gas flowing in the conduit (23) to produce a mixture of gas flowing in the conduit (26). This gas mixture is used as a coolant in the exchanger (104) and in the exchanger (101) before being exported. The liquid effluent circulating in the conduit (14) is redirected through the pump (302) and the conduit (9) to the contact zone (203).

 Table 3 shows, in the exemplary embodiment described with reference to FIG. 3, the material balance obtained:

<Desc / Clms Page number 14>

<Tb>
<tb> Conduit <SEP> 1 <SEP> 11 <SEP> 23 <SEP> 25 <SEP> 26
<tb> Temperature <SEP> (C) <SEP> 50.0 <SEP> -5.0 <SEP> 19.0 <SEP> -30.0 <SEP> 15.4
<tb> Pressure <SEP> (Mpa) <SEP> 10.0 <SEP> 9. <SEP> 95 <SEP> 7. <SEP> 5 <SEP> 7. <SEP> 5 <SEP> 7. <SEP> 5
<tb> Flow <SEP> Molar
<tb> (kmol / h)
<tb> H20 <SEP> 75. <SEP> 3 <SEP> 0.4 <SEP> 0.0 * <SEP> 0.0 * <SEP> 0.0 *
<tb> N2 <SEP> 8. <SEP> 1 <SEP> 8.9 <SEP> 7.1 <SEP> 0.7 <SEP> 7.8
<tb> C02 <SEP> 2219. <SEP> 4 <SEP> 3320.0 <SEP> 1584.5 <SE> 83.9 <SEP> 1668.4
<tb> H2S <SEP> 6570. <SEP> 7 <SEP> 6176.1 <SEP> 1085.6 <SEP> 96.5 <SEP> 1182.1
<tb> Methane <SEP> 11839. <SEP> 8 <SEP> 14251.1 <SEP> 10953.5 <SEP> 619.4 <SEP> 11572.9
<tb> Ethane <SEP> 96. <SEP> 2 <SEP> 137.0 <SEP> 79.9 <SEP> 3.4 <SEP> 83.3
<tb> Propane <SEP> 37. <SEP> 2 <SEP> 44.0 <SEP> 12.4 <SEP> 0.8 <SEP> 13.2
<tb> Butane <SEP> 5. <SEP> 0 <SEP> 2.2 <SEP> 0.2 <SEP> 0.0 * <SEP> 0.2
<tb> Pentane <SEP> 2. <SEP> 3 <SEP> 0.3 <SEP> 0.0 * <SEP> 0.0 * <SEP> 0.0 *
<tb> Total <SEP> (kmol / h) <SEP> 20854.0 <SEP> 23940. <SEP> 0 <SEP> 13723. <SEP> 2 <SEP> 804. <SEP> 7 <SEP> 14527. <SEP > 9
<tb> * <SEP> lower <SEP> than <SEP> 0.05
<Tb>
Table 3

Claims (12)

A process for pretreating a pressurized natural gas containing hydrocarbons, at least one of hydrogen sulphide and carbon dioxide acid compounds, and water, wherein: a) the natural gas is cooled to produce a liquid phase; and a gaseous phase, b) contacting in a first contact zone the gaseous phase obtained in step a) with a liquid phase obtained in step c) to produce a gaseous phase and a liquid phase, c) the gas phase obtained in step b) is brought into contact with a liquid phase obtained in step d) in a second contact zone to produce a gaseous phase and a liquid phase; d) the gaseous phase obtained is cooled to step c) to produce a liquid phase and a gas phase.  2) The method of claim 1 wherein in step d), the gas phase obtained in step c) is cooled by means of a heat exchanger.  3) Method according to one of claims 1 and 2 wherein in step d), the gas phase obtained in step c) is cooled by means of an expansion turbine.  4) Process according to claim 2 wherein: e) the gas phase obtained in step d) is cooled by means of an expansion turbine to produce a gaseous phase and a liquid phase which is recycled in step c) . <Desc / Clms Page number 16>  5) Method according to one of claims 3 and 4 wherein: f) compressing at least one of the gaseous phases obtained in step d) and step e) using the energy recovered on the expansion turbine .  6) Method according to one of claims 1 and 2 wherein in step d), the gas phase obtained in step c) is cooled by means of a Venturi neck, said liquid phase being withdrawn at the level of Venturi neck and said gas phase being recovered at the outlet of the divergent tube of the Venturi neck.  7) The method of claim 6 wherein in step d), said liquid phase withdrawn at the Venturi neck is cooled to produce the liquid recycled in step c) and a gas phase.  8) Method according to one of the preceding claims wherein: g) is used at least one of the gaseous phase obtained in step d) and step e) for cooling the gas phase obtained in step c).  9) Method according to one of the preceding claims wherein: h) is used at least one of the gaseous phases obtained in step d) and step e) for cooling the natural gas in step a).  10) Method according to one of the preceding claims wherein in said first contact zone, the liquid obtained in step b) is heated.  11) Method according to one of the preceding claims wherein in step a) the natural gas is at a pressure of 8 MPa and at a temperature above 15 C. <Desc / Clms Page number 17>  12) Method according to one of the preceding claims wherein: i) is introduced the liquids obtained in step a) and step b) in a well.