MXPA97007250A - Process of dehydration and separation of the gasolinas of a gas, that comprises two complementary stages of regeneration of the solve - Google Patents

Abstract

The present invention relates to: The present invention describes a process for treating a gas containing methane, at least one higher hydrocarbon and water, to remove the water and extract the higher hydrocarbon (s), wherein: - a) the gas to be treated is separated into two streams (1) and (2): - b) at least the stream (2) is contacted with a recycled liquid phase containing water and a solvent or solvent, in order to obtain an aqueous liquid phase depleted in solvent or solvent and a gaseous phase loaded with solvent, - c) separates the solvent-depleted aqueous phase and the solvent-charged gas phase; aqueous phase depleted in solvents with one of the solvent-free gas flows defined in a), the solvent is extracted from the aqueous phase depleted by the gas, and a solvent-rich gas phase and a regenerated aqueous liquid phase are obtained; - e) the gaseous phase is mixed either to the gas phase that comes from stage (b), either to the flow (2) above the contact stage (b); - f) the gas phase coming from the mixture is cooled, in order to partially condense it into an aqueous phase that contains solvent, and a phase of hydrocarbons, and to produce the treated gas, released at least a part of the water and the higher hydrocarbons contained; - g) separates by decanting the aqueous phases and the hydrocarbon phase that come from the stage (f), and - h) the aqueous phase containing solvent is recycled to the stage (

Description

PROCESS OF DEHYDRATION AND SEPARATION OF GASOLINES OF A GAS COMPRISING TWO COMPLEMENTARY STAGES OF REGENERATION OF THE SOLVENT DESCRIPTION OF THE INVENTION The present invention relates to a process for treating a gas containing methane, at least one higher hydrocarbon and water, in order to remove the water and / or extract the hydrocarbon (s) superior (is) The process accog to the invention advantageously allows operations to treat a natural gas: dehydration and separation of at least a part of the condensable hydrocarbons included in natural gas, within an integrated and optimized process. Petroleum products, and particularly natural gas, as well as other gases comprising hydrocarbons, such as refinery gases, contain undesirable products for transport and / or handling. Among these products, one of the main constituents to be eliminated is water, which turns out to be a promoter of hydrates, and which favors corrosion, particularly when the petroleum product contains acidic compounds such as H2S and / or C02. Hydrates can cause clogging of transport ducts, and action REF: 25665 corrosive of the acid gases contained in a natural gas causes the deterioration of the conduits and of the natural gas treatment and distribution facilities, located below. These two phenomena have extremely penalizing consequences, which can lead to the interruption of hydrocarbon production. The gas treatment may also comprise a step of extracting the higher hydrocarbons, for example a liquid fraction of natural gas (NGL) defined as that comprising the LPG fraction and the gasoline fraction (C5 +). This stage has the function either to adjust the hydrocarbon dew point, to avoid the condensation of a hydrocarbon fraction during gas transport, or to recover an LGN fraction; more valuable than the gas treated. To ensure the treatment of natural gas, different treatments are described in the prior art. In the French patent FR-B-2 605 241, a treatment process that uses a refrigerated physical solvent, and that allows performing all the operations of natural gas treatment: dehydration, alone or associated with extraction, is already described. of the higher hydrocarbons, and / or the deacidification of this gas, if it contains acidic compounds. In the French patent FR-B-2 636 857, it is shown that when the process comprises a step of separation of the higher hydrocarbons (NGL), the recovery of the solvent can be improved by the application of a washing step of the liquid hydrocarbons with water that comes from the dehydration of the gas. The applications of such a process are discussed, for example, in the publication "IFPEXOL for Environmentally Sound Gas Processing "by J. Larue, A. Minkkinen and S. Patel, presented at the 17th" GPA "Convention, in March 1992, in Anaheim, California (USA). The publication "Integrated Natural Gas Treatment: Gained Industrial Experience with IFPEXOL Process" by S. Patel, A. Mikkinen, J. Larue and JF Levier, presented at GCR 95 in Cannes (France) in November 1995, describes in particular the form of washing the liquid hydrocarbon phase with water, in order to recover at least part of the solvent it contains. Figure 1 illustrates the process as described in the prior art, when the gas to be treated contains methane, water, at least one condensable hydrocarbon, and possibly acidic compounds. The process is then described as follows. The natural gas to be treated arrives through the conduit 1. A fraction or all of this gas is brought into contact, in the contact zone Gl, formed for example by a filling, with a mixture of solvent and water coming from the conduit 2. The solvent used can be selected from methanol, 1 ethanol, propanol, methyl propyl ether, ethyl propyl ether, dipropyl ether, methyl tert-butyl ether, dimethoxymethane, dimethoxyethane, and ethoxyethanol. The solvent used is preferably methanol. A gaseous phase charged with solvent is evacuated through the upper part through the conduit 3. In the lower part, an aqueous phase substantially liberated from solvent is transferred through the conduit 4. Mention that the treatment process can be optimized, adapting the fraction of gas that must pass within the contact zone Gl and the fraction of gas that passes outside this contact zone, depending on the composition of the gas to be treated and of the required efficiency. This option, represented in dotted lines on Figure 1, allows a part of the gas to be treated, which passes through conduit 18, to be mixed directly with the gas leaving the contact zone through conduit 3. The gas fraction that does not pass within the contact zone may be, for example, between 0 and 50% of the amount of gas to be treated. The gaseous phase of the upper part, which contains water and solvent, is most often close to saturation. This phase is cooled in the exchanger El by a cooling generating fluid, to cause the condensation of an aqueous phase containing solvent and a liquid hydrocarbon phase. It has been shown that the solvent entrained in the gas phase at the outlet of the contact zone Gl can be sufficient to avoid the problems of formation of hydrates bound to the cooling stage El. A maximum can be contributed to the process through line 5, to compensate for solvent losses in the treated gas, in the liquid hydrocarbon fraction (NGL), and eventually in the water returned by the conduit 19. Through this conduit 19, a purge current can be established, to keep the amounts constant. of solvent and water present in the whole circuit. The gaseous and liquid phase mixture thus obtained leaves the exchanger El through line 6. The two liquid phases and the gas phase are separated in a Bl flask. The dehydrated treated gas is discharged from this balloon flask through line 7. The two liquid phases coming from the condensation are separated by decantation in the lower part of Bl. The aqueous phase consisting essentially of water and solvent leaves the flask Bl through line 8. A pump Pl allows the aqueous phase to be injected again via line 9 into line 2, and then into the contact zone Gl. The hydrocarbon phase, consisting essentially of the condensable hydrocarbons of natural gas (C3 +) (possibly containing dissolved ethane and methane) and solvent, can be evacuated to a stabilization and washing circuit through conduit 10. In this process step, it can be considered an exchange of heat between the gas coming from the contact zone Gl and the hydrocarbon phase evacuated by the conduit 10. This has not been represented in Figure 1. A pump P2 allows to send the phase hydrocarbon liquid through line 11 to a stabilization column Sl. The objective of this operation is to separate from the hydrocarbon liquid phase the most volatile compounds (C- and Cr), which are evacuated out of the process through line 12. The hydrocarbon phase containing the constituents of molar mass greater than C2 is sends, through line 13, to a washing zone with water G2, in order to remove the solvent it contains. The aqueous phase, evacuated from the contact zone Gl by line 4 is released, at least in part, from the solvent, and is recovered with a pump P3. A fraction of this aqueous phase, whose flow rate is controlled, is sent to the contact zone G2 through the conduit 14. The other fraction is evacuated through the conduit 19. In this contact zone G2, the fraction of the aqueous phase that arrives through the pipe 14 it is possible to ensure the washing of the hydrocarbon phase. The solvent that has more affinity for water than for the hydrocarbon phase is recovered, at least in part, in the aqueous phase at the end of this stage. The hydrocarbon liquid phase, liberated from most of the solvent that it contained at the beginning of the contact zone G2, is evacuated through line 15. The solvent-containing aqueous phase is evacuated from the contact zone G2 by line 16. This phase is recovered with pump P4, and injected into the contact zone Gl. Depending on its concentration in solvent, this phase is injected into the contact zone Gl via line 17, or is injected into line 2, in order to be mixed with the aqueous phase coming from the flask Bl through line 9. This process presents important advantages in relation to the previous techniques. It allows a significant gain in acquisition costs, as well as in the dimensions and weight of the facilities, which can be particularly advantageous in a context of production and hydrocarbons at sea. In addition, the separation of water and solvent by contact with the gas to be treated makes it possible to avoid a separation by distillation. However, it is evident that it is possible to reach additional gains in acquisition costs, dimensions and weight, and operating expenses linked to the gas treatment, operating according to the process of the invention. The process and the installation according to the invention are advantageously used to dehydrate a gas such as natural gas, comprising water and at least one higher hydrocarbon, as well as to obtain at least partial separation of the condensable hydrocarbons. In a general manner, the process of the invention can be defined as one comprising the following steps: a) the gas to be treated is separated into two streams (1) and (2). The fraction of gas present in the flow (2) can represent from 25 to 95% of the gas to be treated; it will preferably represent 30 to 50% of the total gas; - b) at least the flow (2) is contacted with a recycled liquid phase containing both water and a solvent, which generally consists of an organic compound that is not hydrocarbon, usually liquid, different from water, less partially miscible with water and distillable at a temperature lower than the water distillation temperature. During this step, the solvent passes preferably to the gas. Upon leaving this contact zone, an aqueous solvent-depleted liquid phase is obtained, by comparison with the recycled liquid phase, and a gaseous phase charged with solvent; - c) the aqueous phase depleted in solvent and the gas phase charged in solvent are separated; d) the solvent-depleted aqueous phase is brought into contact with the flow (1) of gas to be treated solvent-free in a contact zone, the residual solvent is extracted from the aqueous phase depleted by the gas, and are obtained from this stage a gaseous phase rich in solvent, and a regenerated aqueous liquid phase; e) the solvent-rich gas phase obtained from step (d) is mixed either to the gas phase charged in solvent coming from step (b), or to the flow of solvent-free gas (2) above from stage (b); - f) the gas phase coming from the mixture, to partially condense an aqueous phase and a hydrocarbon phase containing both solvent is cooled, and to produce the treated gas, released at least partly water and Higher hydrocarbons it contained; g) the aqueous phases and the hydrocarbon phase that come from step (f) are separated by decantation; and - h) the solvent-rich aqueous phase is recycled to step (b) of the process. If this is necessary, the liquid hydrocarbon phase can be stabilized and / or released from the solvent it contains. To do this, the liquid hydrocarbon phase is sent to a stabilization column. During the stabilization stage, the most volatile compounds of the hydrocarbon liquid phase (Ci and C2) are evacuated out of the process. The hydrocarbon phase containing the compounds higher than C2 is subsequently contacted with a solvent-free aqueous phase, which may be all or part of the water coming from step (d). At the end of this contact, which can be carried out for example in a static mixer, the solvent-free hydrocarbon phase and the solvent-laden aqueous phase are separated. The hydrocarbon phase is transferred. The aqueous phase laden with solvent is recycled to stage (b) and / or to stage (d). The advantages and characteristics of the invention will appear better on reading the descriptions given by way of example of embodiment, in the context of the applications, in no way limiting, to the treatment of natural gas, referring to the attached drawings. Figures 2 and 3 schematize the process according to the invention, namely, an improvement of the process such as that described in the prior art, which allows the section and / or the height of the contact zone Gl to be reduced by the introduction into the installation of a mixer and a separator, located above the contact zone Gl, and which allow a first exchange between the aqueous solution loaded with solvent and all or part of the gas to be treated. Figure 2 shows an application of the process according to the invention.

The aqueous phase charged with solvent, which comes from the ball separator flask Bl through line 8 is sent by the pump Pl to the conduit 9, to a mixer M21, also connected to the gas bypass line 18. drawn During the mixing step , the gas is charged with solvent. The two aqueous and gaseous phases are separated in a separating flask B21. The solvent-laden gas from the flask ball B21 through line 21 is mixed to the gas exiting the contact area Gl, and then sent via line 3 to the exchanger El. The aqueous phase, which comes from the flask ball B21 is released from a part of the solvent that it contained when leaving the flask. It is injected through line 22 at the top of the Gl contact zone. The solvent concentration of the aqueous phase flowing through the conduit 22 is much lower than that of the solution circulating in the conduit 9. Due to this reduced concentration, the section and / or the height of the contact zone Gl will be reduced sensibly in relation to those that are necessary in the process such as that described in the prior art. If the process includes a step of washing the higher hydrocarbons, the aqueous phase coming from the washing conduit 17 may optionally be injected into the contact region Gl, or mixed to the aqueous phase in the duct 22. The point selection of injection of the aqueous phase will be carried out according to its solvent content. With a minor amount of solvent passing from the aqueous phase to the gas phase during the contact stage in the Gl zone, the size of the equipment used for this contact is significantly reduced. Another embodiment of the process of the invention is described below, in relation to Figure 3. According to this embodiment, the set of gas produced, which comes from ducts 3 and 18, is sent to mixer M22. The whole of the produced gas is mixed, in the mixer M22, with the aqueous solution loaded in solvent coming from the flask Bl, and circulating in the conduit 9. The gas leaving the separating balloon flask B22 through the conduit 23 sends directly to the exchanger El, while the aqueous phase coming from the B22 flask via line 24 is injected into the contact zone Gl. As described above, if the process contains a washing step of the higher hydrocarbons, the aqueous phase coming from the washing by the duct 17, can possibly be injected in the contact zone Gl, or mixed with the aqueous phase in the duct 24 The solvent used in the process of the invention can be selected from methanol, ethanol, propanol, methyl propyl ether, ethyl propyl ether, dipropyl ether, methyl tert-butyl ether, dimethoxymethane, dimethoxyethane, and methoxyethanol. Methanol is used most of the time. The following Example 1 illustrates a process according to the prior art, and Examples 2 and 3 illustrate the two particular embodiments of the process of the invention. EXAMPLE 1 In this example, one proceeds according to the prior art, represented by Figure 1. A natural gas is produced on the site, at a pressure of 6 MPa and a temperature of 50 ° C; its composition is given in Table 1, and it is saturated in water (water content at the beginning of the process: around 6000 ppm mol). Its flow was -of 108 tons / hour, which corresponds to a production of 3.0 MNmVdia.

Table 1 Composition% in Weight N2 1.6 C02 3.4 Methane 70.4 Ethane 11.6 Propane 6.9 Butane 3.7 Pentane 1.4 C5 + 1.9 The solvent used for this application is methanol.

Half of the gas produced (50%) was injected into the contact zone Gl via conduit 1, the other half (50%) was directed to the upper part of the contact zone by conduit 18. The contact zone Gl It contains a structured filling. An aqueous solution of recycled methanol was injected into the upper part of the contact zone through conduit 2, at a temperature of -25 ° C. At the end of the contacting step, a solvent-depleted aqueous solution is removed from the zone of contact through conduit 4. This solution contains 160 ppm by mass of methanol. Its flow is 245 kg / hour; this corresponds approximately to the amount of water initially contained in the 108 tons / hour of sas to be treated.

The gas containing the methanol was directed to the exchanger El through the conduit 3. The gas received, through conduit 5, a maximum of 40 kg / hr of methanol. After the exchanger El, its temperature was -25 ° C. The BL flask allows to separate: - a flow of 99500 kg / hour of treated gas, which contains a residual proportion of water of 14 ppm mol, or 10.5 kg / MNm3; - a flow of 616 kg / hour of water charged with methanol, which is recycled to the contact zone Gl; and - a flow of 8400 kg / hour of condensed hydrocarbon phase (NGL), which may optionally be stabilized, and then washed, in order to be released from the solvent it contains, before its evaluation. EXAMPLE 2 In this example, the natural gas, produced on the site, under the conditions of pressure, temperature, flow rate and composition described in Example 1, was treated according to the process of the invention described in Figure 2. In this example another Once, the solvent used is methanol. In this example, the bypass gas coming from the conduit 18 was contacted with the solvent-charged aqueous phase that came from the separating balloon flask Bl through the conduit 8, in the mixer M21. During this mixing step, the gas was charged with solvent. The two phases, aqueous and gaseous, were separated in a B21 separating balloon flask. The solvent charged gas coming from the B21 flask through the duct 21 was mixed with the gas leaving the contact zone Gl, and then it was sent through the duct 3 to the exchanger El. The aqueous phase coming from the balloon flask B21 was freed from a part of the solvent it contained when leaving Bl flask. This phase was injected through the conduit 22 to the upper part of the contact zone Gl. At the first contact between the gas and the solvent-rich solution in the mixer M21, the solvent concentration of the aqueous solution was divided by a factor of 2.5 relative to the solution circulating in the conduit 9. On the other hand, being all the same, identical results were obtained as those described in Example 1 with a reduced Gl contact column. In fact, the contact of the aqueous solution partially impoverished in solvent with 44% of the gas to be treated is sufficient for the exhaustion of the solution.

When 56% of the gas is derived, the methanol concentration of the water coming from the contact zone through line 4 is 160 ppm by mass, as in Example 1. The depletion of the solution is obtained using a column of a diameter reduced by 6% compared to the previous example. The steel weight attached to this decrease in diameter varies in proportion to this reduction. The necessary filling volume is also reduced accordingly, by 12%; instead, the height of the filling is identical to that of example 1. EXAMPLE 3 In this example, natural gas, produced on the site, under the conditions of pressure, temperature, flow rate and composition described in example 1, was treated according to the process of the invention described in Figure 3. In this example again, the solvent used is methanol. According to this example, a part of the gas to be treated was sent to the contact zone Gl by conduit 1. As previously, the gas charged in solvent after contact, left Gl through conduit 3. The gas was mixed with the gas derived solvent-free in the duct 18. The whole gas was mixed with the aqueous solution loaded with recycled solvent, in an M22 mixer. The mixture was sent to the B22 separating balloon flask. Two phases were obtained from separating balloon flask B22: - the gas containing the solvent, which was sent through line 23 to the heat exchanger El; the partially depleted aqueous solvent solution, which was sent via line 24 to the contact zone Gl. At the first contact between the gas and the solvent-rich solution in the M22 mixer, the solvent concentration of the aqueous solution was divided by a factor of 3.5 relative to the solution circulating in the conduit 9. On the other hand, being all the same, identical results were obtained as those described in Example 1 with a reduced Gl contact column. In effect, the contact of the aqueous solution partially impoverished in solvent with 31% of the gas to be treated is sufficient for the exhaustion of the solution. When 69% of the gas is derived, the methanol concentration of the water coming from the contact zone through line 4 is 160 ppm by mass, as in Example 1.

The depletion of the solution is obtained using a column with a diameter reduced by 21% in relation to Example 1. The weight of steel added to this decrease in diameter varies in proportion to this reduction. The necessary filling volume is also reduced accordingly, by 38%; on the other hand, the height of the filling is identical to that of example 1. The comparison of Example 1 according to the prior art, on the one hand, and of Examples 2 and 3 according to the invention, on the other hand, shows that the process according to the invention it allows a significant reduction of the section of the contact area and, therefore, of the dimensions and weight induced by this equipment, as well as of the volume of filling required for a gas treatment operation. The process according to the invention has the advantage of being less expensive in acquisition costs than the processes described in the prior art, by the double reduction of the section of the contact area and the volume of filling required for the operations.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following:

Claims (16)

1. CLAIMS 1. Process for the treatment of a gas containing methane, water and at least one hydrocarbon higher than methane, the process aims to clean at least part of the gas from water and hydrocarbons higher than methane, the process is characterized in that it comprises the following steps: a) the gas to be treated is separated into two streams (1) and (2); - b) at least the flow (2) of the gas is contacted with a recycled liquid phase containing both water and a solvent or solvent, consisting of an organic compound that is not hydrocarbon, normally liquid, different from water at least partially miscible with water and distillable at a temperature lower than the water distillation temperature, in order to obtain an aqueous liquid phase depleted in solvent or solvent, by comparison with the recycled liquid phase, and a gas phase charged with water. solvent; - c) the aqueous phase depleted in solvent and the gas phase charged in solvent are separated; d) the solvent-depleted aqueous phase is contacted with the flow (1) of gas to be treated solvent-free in a contact zone, the solvent is extracted from the aqueous phase depleted by the gas to be treated, and from this stage a gaseous phase rich in solvent, and a regenerated aqueous liquid phase; e) the solvent-rich gas phase obtained from step (d) is mixed either to the gaseous phase charged in solvent coming from step (b), or to the flow of gas (2) free of solvent from the stage (a); - f) the gaseous phase coming from the mixture is cooled, in order to partially condense it into an aqueous phase and a hydrocarbon phase, containing the two solvents, and to produce the treated gas, released at least in part from the water and from the higher hydrocarbons it contained; g) the aqueous phases and the hydrocarbon phase coming from stage (f) are decanted off; and - h) the solvent-rich aqueous phase is recycled to step (b).
2. 2. Process according to claim 1, characterized in that, in step (a), the fraction of gas present in the flow (2) is greater than that present in the flow (1).
3. Process according to claim 1 or 2, characterized in that the solvent-rich gas phase coming from step (d) is mixed with the solvent-rich gas phase that comes from step (b) of the process.
4. 4. Process according to claim 1, characterized in that at the end of the contact step (c), all of the gas to be treated is contacted during step (b) with the solvent-rich recycled aqueous phase.
5. 5. Process according to any of claims 1 to 4, characterized in that, at the end of contact steps (b) and (d), a maximum of solvent is added to the gas phase, in order to avoid formation problems of hydrates bound to the cooling stage (f) and to compensate for solvent losses in the treated gas.
6. Process according to claims 1 to 5, characterized in that the solvent is selected from methanol, ethanol, propanol, methyl propyl ether, ethyl propyl ether, dipropyl ether, methyl tertiary butyl ether, dimethoxymethane, dimethoxyethane, and methoxyethanol.
7. Process according to claim 6, characterized in that the solvent is methanol.
8. Process according to any of claims 1 to 7, characterized in that the aqueous phase rich in solvent recycled to step (b) contains from 50 to 95% by weight of solvent.
9. 9. Process according to any of claims 1 to 8, characterized in that the temperature of the gas phase at the end of step (f) is between -15 and -80 ° C, the gas obtained at the end of the stage ( f) is released from most of the propane it contained at the beginning of the process.
10. 10. Process according to any of claims 1 to 9, characterized in that the fraction of gas passing through the contact zone of stage (d) represents from 25 to 95% of the gas to be treated.
11. 11. Process according to any of claims 1 to 9, characterized in that the fraction of gas passing through the contact zone of stage (d) represents 30 to 50% of the gas to be treated.
12. 12. Process according to any of claims 1 to 11, characterized in that the liquid phase of hydrocarbons coming from step (g) is subjected to a stabilization step, to eliminate volatile compounds.
13. 13. Process according to any of claims 1 to 12, characterized in that the liquid hydrocarbon phase coming from stage (g) is subjected to a washing step, in order to recover the solvent.
14. Process according to claim 13, characterized in that the washing of the hydrocarbon liquid phase is carried out with the regenerated aqueous phase coming from step (d), on which a purge stream is established, in order to maintain the amounts of solvent and water present in the entire circuit are appreciably constant.
15. 15. Process according to claim 13, characterized in that the step of washing the liquid phase of hydrocarbons is carried out by the application of decanter mixers. Process according to claim 13, characterized in that the step of washing the liquid phase of hydrocarbons is carried out by contact in a column. PROCESS OF DEHYDRATION AND SEPARATION OF GASOLINES OF A GAS COMPRISING TWO COMPLEMENTARY STAGES OF REGENERATION OF THE SOLVENT SUMMARY OF THE INVENTION The present invention describes a process for treating a gas containing methane, at least one higher hydrocarbon and water, to remove the water and extract the higher hydrocarbon (s), in which : a) the gas to be treated is separated into two streams (1) and (2); - b) at least the flow (2) is contacted with a recycled liquid phase containing water and a solvent or solvent, in order to obtain an aqueous solvent-depleted solvent phase and a solvent-laden gas phase; - c) the aqueous phase depleted in solvent and the gas phase charged in solvent are separated; d) the solvent-depleted aqueous phase is contacted with one of the solvent-free gas streams defined in a), the solvent is extracted from the aqueous phase depleted by the gas, and a solvent-rich gas phase is obtained , and a regenerated aqueous liquid phase; e) the gaseous phase is mixed either to the gas phase coming from stage (b), or to the flow (2) above the contact stage (b); - f) the gaseous phase coming from the mixture is cooled, in order to partially condense it in an aqueous phase containing solvent, and a hydrocarbon phase, and to produce the treated gas, released at least in part from the water and from the Higher hydrocarbons it contained; g) the aqueous phases and the hydrocarbon phase coming from stage (f) are decanted off; and - h) the solvent-containing aqueous phase is recycled to step (b). Figure 3 to publish.