MXPA00008332A - Method and apparatus for removing aromatic hydrocarbons from a gas stream prior to an amine-based gas sweetening process - Google Patents

Abstract

A method is provided for the extraction of aromatic hydrocarbons, including benzene, toluene, ethylbenzene, and xylene, collectively known as"BTEX,"in a continuous process utilizing a glycol contactor to cause absorption of the BTEX upstream of an amine-based gas sweetening process. The preferred glycol for BTEX absorption is triethylene glycol. The glycol used in the glycol contactor for BTEX extraction may either be fully regenerated (dry), or wet glycol from a downstream gas dehydration system. The method may be achieved with the use of a number of separate absorber/contactor vessels, or the method may be achieved within one combination vessel

Description

METHOD AND APPARATUS FOR REMOVING AN AROMATIC HYDROCARBONS STEAM CURRENT BEFORE A GAS SWEATING PROCESS AMINA BASED TECHNICAL FIELD This invention relates to a method and apparatus for removing contaminants from a gas stream and, more particularly, to a method and apparatus for removing aromatic hydrocarbons from a natural gas stream prior to an amine-based gas sweetening or desulfurization process. .

ANTECEDENTS OF THE TECHNIQUE Natural gas often contains excessive amounts of carbon dioxide or hydrogen sulfide, or both, collectively known as acid gases. These pollutants return to natural gas unsuitable for consumption. Water-based amine processors are often used to remove these contaminants from natural gas in a process called "gas sweetening." In the gas sweetening process, after the natural gas stream passes through an aqueous amine solution, chemical reactions are carried out where the natural gas is saturated with water. Consequently, the water must be removed. The water removal is carried out using a dehydration system. The most common system used is a dehydration process that uses triethylene glycol (TEG) as a liquid desiccant. In addition to the carbon dioxide and hydrogen sulfide contaminants, a stream of natural gas often contains one or more aromatic hydrocarbons, including benzene, toluene, ethylbenzene and xylene. These are collectively referred to as BTEX or BTX. When a natural gas is processed in an amine-based gas sweetening process, significant amounts of BTEX are absorbed by the amine. In the gas sweetening process, the amine compounds are generated in a recycling process resulting from the release of BTEX from the amines compounds. BTEX compounds are regulated pollutants that must be avoided at each site of the plant below certain emission levels. In recent years, the amine-based gas sweetening process has been recognized as an important contributor to BTEX emissions. Several methods have been developed to control BTEX emissions. The control of BTEX emissions from an amine-based gas sweetening process is difficult to carry out. Some processes attempt to remove BTEX from the amine stream before the regeneration of the amine. Others try to treat the exhaust gases of the regeneration system to remove BTEX emissions. A process currently accepted for the control of BTEX is to incinerate the exhaust or tail gases of the amine regeneration system. The amine regeneration system essentially purifies the amine compounds by depleting the absorbed contaminants. Therefore, the exhaust gases of the amine regeneration system contain not only the acid gases, but also BTEX which can be absorbed by the amine in the amine contactor and then exhausted by the regeneration process. This incineration of the exhaust gases consumes very large amounts of fuel which makes it an expensive process, and actually increases other pollutants emitted such as carbon dioxide, which is a by-product of combustion. Other processes for BTEX emission control include the use of activated carbon filter systems to absorb the BTEX from the amine stream or from the tail gases in the amine regeneration system. The problem with these filter systems is that saturated carbon filters must still be disposed of as they become saturated with BTEX contaminants. In addition, this process does not eliminate BTEX from byproducts or emissions from the processing plant, unless the carbon is used as fuel or processed in some other way in another additional system of contaminant removal. In all these processes, control of BTEX in an amine-based gas sweetening process is not obtained until after the BTEX has been absorbed into the amine stream. These processes used to remove BTEX require large amounts of fuel, have increased waste and handling requirements, or divert some of the resources from the processing plants for the purpose of depleting BTEX from a rich amine. An example of a prior art system for removing hydrocarbons from a natural gas stream is shown in U.S. Patent No. 4,414,004 to Wagner et al. The invention describes a process for removing condensable aliphatic hydrocarbons and acid gases from a natural gas stream, where the stream is initially treated with polyethylene glycol as a solvent in a first stage of absorption. The desired portion of the gas stream is extracted from this first absorption stage and the stream is then treated with additional polyethylene glycol in a superatmospheric pressure environment in a second absorption step, the acid gases being completely or partially absorbed. The solvent which is saturated with the condensable aliphatic hydrocarbons obtained in the first absorption step is then treated with water in an extraction step, to form a hydrocarbon phase containing the condensable aliphatic hydrocarbons and an aqueous ethereal phase, and then the The hydrocarbon phase is separated from the aqueous ethereal phase. The solvent charged with acid gases obtained from the second absorption stage is regenerated by expansion or exhaustion or both, in a regeneration step, and the regenerated solvent is recycled for absorption. U.S. Patent No. 5,453,114 to Ebeling discloses a method for drying natural gas to reduce emissions of aromatic hydrocarbon substances (BTEX) by finally removing such contaminants and discarding them in a burner or an evaporator. The primary stages of this method include passing the natural gas stream through an absorber that has a liquid desiccant, the desiccant absorbs water and hydrocarbon impurities from the gas and forms an exhausted desiccant, passing a portion of the treated gas from an absorber through a desiccant depletion vessel, the rest of the treated gas is passed through for distribution, heating of the spent desiccant and passing through the desiccant-draining vessel to purge the spent desiccant of aromatic hydrocarbons, transporting the spent desiccant from the Exhaustion vessel inside an evaporator to again heat the spent desiccant, and finally transport the treated gas from the exhaustion vessel through a burner in an evaporator, where the treated gas is burned with air. U.S. Patent No. 5,490,873 to Behrens et al., Discloses a process for reducing hydrocarbon emission which includes the steps of contacting a natural gas stream in a glycol contact zone to produce a stream of glycol rich in water and a dry gaseous product. The rich glycol is heated in a glycol regeneration zone at a temperature below the glycol decomposition temperature to produce: (i) a lean glycol in water for use in contact with additional natural gas in the contact zone, and (ii) a gaseous mixture containing water, and also containing hydrocarbons. The partial condensation of this gaseous mixture provides liquid hydrocarbons, aqueous wastes and a gaseous portion that is reintroduced into the contact contact zone, together with an additional natural gas feed, with glycol. Finally, the hydrocarbon liquids are sent to storage for sale or for additional separation. United States Patent No. 5,766,313 for Heath describes a hydrocarbon recovery system to treat emissions from a glycol evaporator. Briefly, the evaporator emissions are condensed, pressurized and separated so that vapors contaminated with hydrocarbons (such as BTEX) can be directed to a burner used to supply heat to an evaporator. U.S. Patent No. 5,084,074 to Beer et al., Discloses a method and apparatus for separating and recovering water and light aromatic hydrocarbons from a gas stream. As with the patent mentioned directly above, the recovered hydrocarbons are used to ignite a regenerator used in the regeneration of glycol. More specifically, the natural gas stream is contacted with an absorbent (such as glycol) to absorb water and light aromatic hydrocarbons (BTEX) to produce a stream charged with water and light hydrocarbons, and a dry gaseous stream . The water and light aromatic hydrocarbon stream is heated in a regenerator to produce water vapor and a light aromatic hydrocarbon stream, and a lean sorbent for contactor recycling. The water in the form of vapor and the stream of light aromatic hydrocarbons are condensed so that the liquefied light aromatic hydrocarbons are recovered and a separate light gas stream is also recovered, for use as fuel gas for the regenerator. Although the references of the prior art may be suitable for the purposes that were designed, none of them describes the method of this invention, which is explained below in detail.

BRIEF DESCRIPTION OF THE INVENTION The method of this invention is a continuous process for the extraction of aromatic hydrocarbons from a gas stream using glycol to reduce the absorption of the aromatic hydrocarbons in a subsequent amine absorber used in a gas sweetening process. The glycol can be ethylene glycol, diethylene glycol, triethylene glycol (TEG), tetraethylene glycol or any mixture of these glycols. The preferred glycol is TEG for the absorption of the aromatic hydrocarbons, since it has the highest solubility for the aromatic hydrocarbons that are part of the BTEX group. The glycol can be completely regenerated (dry) or saturated with water before coming into contact with the stream of natural gas containing the aromatic hydrocarbons. It is known that TEG has a very high affinity for aromatic compounds, especially BTEX. TEG is mainly used in the gas industry to remove water vapor from gas streams. It is also known that TEG absorbs significant amounts of BTEX from the gas stream during the drying process. In relation to a constant natural gas rate, the rate of absorption of BTEX in glycol increases as the rate of glycol circulation increases, or when the contact time between the gas stream and the glycol increases, or both .

In addition to using TEG as a compound to dehydrate a gas stream or to absorb BTEX in a gas stream, TEG is also used in the refinery industry to remove BTEX compounds from various liquid products, whether by BTEX concentrate for use. in other products or simply for refining liquid products. However, these other uses of TEG are found in liquid / liquid extraction processes that are very different from a natural gas sweetening process. A typical amine-based gas treatment system for gas sweetening includes a contactor to expose the natural gas stream to amine-based compounds, followed by a gas dehydration system. Typically, a TEG gas dehydration system is used since it is the most efficient large scale gas dehydration system available. In addition to the amine contactor the gas dehydration system, a process for regeneration of the saturated glycol, and for regeneration of the saturated amine compounds must also be provided. The method of this invention uses an exhausted process stream (rich or wetted in glycol) to perform the BTEX absorption work upstream of the amine absorber. Lean or dry glycol, of course, can be used in the absorption of BTEX upstream of the amine absorber, if this excess capacity is available or needed. The rich or wet glycol is recovered from the gas dehydration system. The vessel used for upstream BTEX uptake may be a contactor of the same type as the amine contactor or the downstream glycol contactor for dehydration. By using wet glycol for the absorption of BTEX, no additional fuel costs are involved in the overall gas sweetening process. The transfer of the rich or wet glycol from the gas dehydration system can be obtained by a booster pump, or depending on the arrangement of the plant, gravity flow can be used to transfer the wet glycol. The solubility of BTEX in the glycol does not change significantly after it has been used in a dehydration system, since the concentration of glycol is reduced only slightly by the absorption of water. This means that rich or moist glycol has approximately the same capacity to absorb BTEX as compared to lean or dry glycol. This further improves the desirability of using rich glycol from the dehydration system, since a separate system of complete glycol regeneration is not required for the absorption of BTEX. Only one contactor and additional pumps are required, if the rich glycol is used for the absorption of BTEX. In addition, it is depleted of glycol rich in the glycol regeneration system is not adversely affected by the presence of BTEX. In fact, glycol depletion is enhanced by the presence of aromatic compounds, such as benzene, which act as an azeotropic forming agent, reducing the energy requirements for glycol regeneration. The main structural components that can be used to obtain the method of this invention include a first upstream glycol contactor for extracting BTEX from a stream of natural gas passing through. As discussed in the foregoing, the particular glycol used may be ethylene, diethylene, TEG, tetraethylene glycol or any mixture of these glycols. The natural gas stream then passes through an amine contactor for gas sweetening. The next major component of the system is a second downstream glycol contactor for dehydration. The rich or wet glycol leaving the second downstream glycol contactor can be used as the glycol circulating in the first upstream glycol contactor. A pump can be used to transfer this rich glycol. The terms "upstream" and "downstream" used throughout this document refer to the flow of gas, and not to the displacement flow of glycol or amine. The specific construction of the first glycol contactor can be any conventional contactor that uses trays, packaging or any other method to cause intimate contact between the liquid glycol, which flows down through the absorber or contactor, and the gas flowing upward . To maximize BTEX absorption in the circulating glycol, the particular BTEX absorption rate of the glycol used will determine the optimal glycol circulation rates and the specific design of the absorber. For example, a low BTEX absorption rate in the glycol used may require higher rates of glycol circulation through the contactor or an increased contact time between the glycol and the gas stream. A conventional glycol regeneration system can be used to remove the absorbed BTEX from the glycol stream. In the preferred mode, a unique glycol regeneration system can be used which receives rich glycol from the first glycol contactor, and returns regenerated glycol to the second downstream contactor used for dehydration. Alternatively, an additional glycol regeneration system can be used to service the glycol regeneration from the first upstream glycol contactor while the original glycol regeneration system can service the second downstream contactor. The first upstream glycol contactor for BTEX extraction may be contained within the same vessel as the amine absorber for gas sweetening, using existing absorber design techniques. Alternatively, the first upstream glycol contactor for BTEX extraction, the amine contactor for gas sweetening and the second downstream glycol contactor for dehydration may be contained within the same vessel, since only the separation of liquid between each is required. one of the absorption processes. Whenever a first separate upstream glycol contactor is used, or whenever this first upstream glycol contactor is used in the same vessel as the other contactors, emphasis should be placed on a maximization of glycol contact time with the current of natural gas to maximize the absorption of BTEX before entering the amine contactor. The same glycol stream can be used both in the upstream glycol contactor and in the second downstream glycol contactor, since the upstream BTEX uptake does not adversely affect the dehydration capacity of the glycol stream in the second. downstream glycol contactor. As discussed above, the glycerol rich with BTEX extracted from the upstream glycol contactor can be transferred to the glycol regeneration system. The apparatus of this invention can be a single container incorporating the main steps in the method, or it can be an apparatus constituted by a pair of containers, as further described below.

Calculations have shown that for the method of this invention, approximately one third of BTEX can be extracted from the natural gas stream by using the first upstream glycol contactor. Therefore, the potential emissions of the subsequent amine system can be reduced by a proportional amount, since the absorption of BTEX in amine is directly related to the concentration of BTEX in the gas stream. This reduction of BTEX can be carried out without any modification downstream to the gas sweetening process. These calculations are based on the use of a contactor that is of the same construction as a standard contactor for sweetening or dehydrating gas. Modifications to this standard contactor can be made to increase the contact time between the glycol and the natural gas stream, in turn, which can further improve the degree of BTEX extraction. The BTEX that has been absorbed from the natural gas stream by the glycol is removed in a currently available glycol regeneration system, as discussed further in the following. The advantages of the invention described herein will be further apparent from the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figures IA and IB are schematic diagrams illustrating the method of this invention; and Figure 2 is a schematic diagram of a single container which contains an upstream glycol contacting section for BTEX extraction, an amine contacting section for gas sweetening and a second downstream glycol contacting section for dehydration.

BEST MODE FOR CARRYING OUT THE INVENTION Figures IA and IB are schematic diagrams illustrating the method of this invention. As used in these figures, the thicker continuous transfer lines indicate gas flow, the thicker discontinuous transfer lines indicate gas flow in an alternative method for glycol regeneration, the thinner discontinuous transfer lines indicate glycol flow , and dot transfer lines indicate glycol flow in an alterative method for glycol regeneration, thinner continuous transfer lines indicate amine flow, and discontinuous transfer lines in combination with continuous transfer lines indicate vapor flow of water and hydrocarbon. An acid gas reservoir 10, or some other source of acid gas stream is supplied by the pump 12 through an inlet separator 14 to separate free liquids from the production field, such as salt water. The natural gas stream is then transferred to the first glycol contactor 16 that absorbs BTEX from the natural gas stream. After the gas stream passes through the first glycol contactor 16, it is then passed through the separator 20. The glycol passing through the contactor 16 is then transferred directly to the glycol regeneration system 40. The separator 20 captures any glycol that is transported by the contactor 16. The glycol that is collected in the separator 20 can be discarded, or the retained glycol can be returned to the glycol regeneration system 40. Subsequently, the gas stream is transferred to the amine contactor 22 for gas sweetening, to remove acid gases such as hydrogen sulfide and carbon dioxide. The volume of the saturated amine stream returns to the amine regeneration system. However, some amine and water compounds, along with other pollutants, will remain in the natural gas stream. Accordingly, a separator 23 is provided to further remove the remaining amine compounds and other contaminants. The gas stream is then transferred to the second downstream glycol contactor 24. Since the amine used for sweetening in contactor 22 is actually a solution diluted with water, the gas leaving the amine contactor 22 will be saturated with water vapor. The gas stream is then transferred to the second glycol contactor 24. The dehydration is obtained in this second contactor 24 by contacting the gas stream a second time with the glycol. The gas stream is then transferred to another heat exchanger 26 to an outlet separator 28. Since the glycol leaving the glycol regeneration system 40 is hot, the heat exchanger 26 provides the final step of cooling the lean glycol before the glycol is introduced into the second glycol contactor 24. The gas stream passing through the heat exchanger 26 acts as a cooling source for the glycol. The volume of the glycol used in the second glycol contactor 24 passes through the contactor 24 and is pumped upstream by the pump 32 for introduction into the first glycol contactor 16. However, as with the first glycol contactor 16, part of the glycol will remain suspended in the gas stream of the output contactor 24. Accordingly, the outlet separator 28 is used for removal of the suspended glycol. After passing through separator 28, the natural gas stream is ready for consumption as dry and sweet gas. The amine regeneration system 30 is used to provide amine regenerated again to the amine contactor 22. Figure IA shows that the wet glycol leaving the glycol contactor 24 can be transferred to the first glycol contactor 26 by means of a pump 32. Alternatively, gravity flow can be used, depending on the specific arrangement of the plant. Figures IA and IB further illustrate a glycol regeneration system with vapor recovery capacity. As shown, the rich or wet glycol enters the glycol regeneration system 40 from the first glycol contactor 16. The gas stream traveling through the contactor 16 cools the glycol leaving the contactor 16. Part of the cooled glycol stream is first directed through the reflux condenser 43 at the top of the column 44 and then to the tank 46 glycol separator. The remaining part of the cooled glycol stream is transferred directly to the glycol separator tank 46 through the bypass valve 45. Most of the hydrocarbons and other volatile compounds that are entrained in the rich and wet glycol are separated in the glycol separator tank 46. The separation gas leaving the glycol separator tank 46 is burned as fuel in the glycol evaporator 42 or directed to other processes. The liquid hydrocarbons that are separated in the glycol separator tank are directed to a hydrocarbon storage tank (not shown). From the glycol separator tank 46, the rich glycol passes through the heat exchanger 52 where it is heated by hot lean glycol from the glycol evaporator 42. From the heat exchanger 52, the rich glycol enters the column 44 where the liquid glycol descends into the glycol evaporator 42 and the water vapor and hydrocarbon vapors, which include the BTEX vapors, flow upward to exit of the column as an outflow gas stream. At least a certain portion of the glycol remains in the vaporized state in the middle part of the column 44. The circulation of the rich glycol cooled through the reflux condenser 43 is regulated so that the temperatures at the top of the column 44 cause the glycol condenses as a liquid and falls out of the vapor stream leaving the column 34, without condensing the water and the hydrocarbon vapors. The output gas stream is then transferred to the condenser 48 to condescend the water, BTEX or other hydrocarbons, of the exhaust gases. At least a portion of BTEX and hydrocarbons will not condense in the condenser 48, which leaves part of the BTEX and hydrocarbons in a state of steam. A compressor 49 is used to compress the vapors and liquids of the condenser 48 in a three-phase separator 50, which allows water, BTEX and other hydrocarbons to be collected and separated within the three-phase separator 50. The three-phase separator 50 will separate water, liquid hydrocarbons and non-condensed hydrocarbon vapors in three separate streams. The water from the three-phase separator 50 is sent to storage of waste water (not shown). The condensed hydrocarbon liquids include BTEX and condensates are sent to hydrocarbon liquid storage (not shown). The remaining compressed hydrocarbon vapors are used as fuel for the glycol evaporator 46 or can be used in other processes. In any case, the totality of BTEX and the hydrocarbons that are collected by the glycol stream are burned as fuel or are directed to other processes, so they are eliminated as a source of emission into the atmosphere. The dry (lean) glycol of the glycol evaporator 42 is then transferred by the pump 54 for reintroduction back to the second glycol contactor 24. As also shown, the same heat exchanger 52 used to heat the wet glycol of the separator tank 46 is also used to cool the dry glycol returning to the second glycol contactor 24. A glycol refrigerant 53, which removes excess heat from the atmosphere, is usually needed in addition to the heat exchangers 52 and 26, before the pump 54 to further cool the lean glycol to the desired temperatures before it is introduced. to the contactor 24. Several commercial glycol regeneration systems are available which can condense or otherwise process the BTEX and hydrocarbon vapors, preventing BTEX from leaving the atmosphere as a volatile emission. Many existing gas sweetening plants have vapor recovery units in place as part of the plant dehydration system.The same steam recovery units are also suitable for use in the glycol regeneration system 40. 1A and IB also show an alternative method for providing regenerated glycol for both the first glycol contactor 16 and the second glycol contactor 24. In this alternative arrangement, the first glycol contactor 16 may have its own glycol regeneration system 60. This system 60 can be identical in construction to the glycol regeneration system 40 described above As shown by the dot transfer lines in Figure 1A, the wet glycol leaving the glycol contactor 16 can be directly transferred. to the system 60 of regeneration of dedicated glycol, and the dry or lean glycol can then be returned directly to the contact or 16 glycol. As also shown, a heat exchanger 62 can be used to provide the final necessary cooling for the hot regenerated glycol. The heat exchanger 62 is not required if only the glycol regeneration system 40 is used because the wet glycol leaving the second glycol contactor 24 is already cooled. The cooling of the glycol through a heat exchanger 62 is obtained by using a stream of refrigerant gas as the cooling element through the heat exchanger 62. The thicker discontinuous transfer lines illustrate the flow of gas stream through the heat exchanger 62. The existing glycol regeneration system 40 can be used only for glycol regeneration used in the second glycol contactor 24. Thus, the dot transfer lines also indicate that the rich glycol leaving the second glycol contactor 24 can be directly introduced into the glycol regeneration system 40., and the dry or lean glycol is then returned directly to the second glycol contactor 24. Although Figures IA and IB describe specific gas sweetening processes enhanced by the first glycol contactor 16, it will be understood that the first glycol contactor 16 can be used in an amine-based gas sweetening process which includes a gas contactor. amine for sweetening gas, and a glycol contactor for dehydration. Accordingly, the various heat exchangers, separators and regeneration systems are illustrated only to show an example of the manner in which the generic gas sweetening process occurs. Figure 2 is a schematic diagram of a single container which contains a first glycol contactor section upstream for BTEX extraction, an amine contactor section for gas sweetening, and a second downstream glycol contactor section for dehydration. The method of this invention incorporates the use of a single container which can be advantageous for treating smaller volumes of gas, and for the treatment of a gas stream where there is limited land space. For example, a platform 5 offshore has limited space available and incorporates the use of a single vessel to treat gas vapor which is highly advantageous. Weight limitations, such as on an offshore platform, also make the use of a single vessel more advantageous. In addition, it is unnecessary to use an intermediate pump to move the glycol from the downstream glycol contactor to the upstream glycol contactor, since gravity flow is used. The structure of a single container can be a combination of an absorber / contactor vessel 70 which includes three main sections for gas treatment, specifically, a glycol contact section 72 upstream for BTEX extraction, an amine contact section 74 for acid gas removal, which is current below the glycol contactor 72, and a downstream glycol contact section 76 for dehydration, which is downstream of the amine contactor 74. As in Figures IA and IB, the thicker continuous transfer lines indicate the gas flow, the transfer lines discontinuous indicate the glycol flux, and the thinnest solid lines indicate the amine flux. The 72, 74 and 76 contact sections can be constructed from typical countercurrent mixing equipment, such as trays or packaging, designed to cause countercurrent currents to mix effectively. The lean glycol of a regeneration system (such as the regeneration system 40 of Figure IB) enters the upper end of the combination vessel 70. Acid gas under pressure enters the lower end of the combination vessel 70. The force of gravity causes the glycol to pass through the combination vessel 70 in a downward direction and the gas under pressure passes through the combination vessel 70 in an upward direction. Beginning first with an explanation of the glycol flow and gas flow at the lower end of the combination vessel 70, the acid gas passes through the first contact section 72 in a countercurrent relationship with the downwardly flowing glycol. BTEX extraction is obtained in this section and the rich glycol flows away from the combination vessel 70, at outlet 73. The rich glycol is then transferred to the glycol regeneration system. In order to trap the rich glycol for removal from the combination vessel 70, and to allow the acid gas to continue to move upwardly through the vessel, a device known in the art is used as a "roll tray" 78. Essentially , a stirring tray allows the gas to move upwards and simultaneously traps the rich glycol fluid in a tray communicating with the outlet 73. The gas continues to move upwards, through the mixing vessel 70, through an 80 humidity extractor. The moisture extractors are used between the contacting sections to filter or separate any glycol or amine, which have been entrained in the gas flow through each contacting section. The gas stream continues its displacement through the amine contacting section 74, where the gas stream is in countercurrent contact with the amine supplied through the amine inlet 75. The amine leaves in section 74 through the amine outlet 77 where the rich amine is transferred to an amine regeneration system (such as an amine regeneration system, of Figure IA). In order to trap the rich amine, a second stirring tray 78 can be used within the amine contacting section 74. The gas stream continues its upward movement, through the combination vessel 70, as it is passed through another moisture extractor 80 (for amine filtering) and into the downstream glycol contacting section 76. Within this section, the gas stream comes into countercurrent contact with the lean glycol supplied from the regeneration system at the inlet 71. The water introduced from the amine contacting section 74 is removed in section 76. In section 76 a third stirring tray assembly 78 is used to collect the wet glycol. This wet glycol is transferred by the glycol derivative line 82 into the glycol contacting section 72 which obtains upstream BTEX extraction. Due to the downward flow of the wet glycol in the bypass line 82, there is no need for a separate pump. Finally, the gas stream passes through another moisture extractor 80 (to filter the suspended glycol liquid) and the dry and sweetened gas is the resulting product leaving the vessel 70. Therefore, Figure 2 illustrates a container only one that can be used to obtain the method of this invention. If the amount of sweet dry gas must be increased, a plurality of containers 70 can be used to treat an acid gas stream. Depending on the available land space, weight restrictions and other factors, a plurality of containers 70 may be more advantageous than using the scheme shown in Figures IA and IB. Although Figure 2 illustrates a container having three separate sections, the scope of this invention also contemplates the use of two containers to carry out the method of this invention. More specifically, the upstream glycol contactor can be found in a container and the amine contactor and the downstream glycol contactor can be found together in a second container. In such a case, the upstream glycol contactor may be placed at a lower elevation than the downstream glycol contactor so that the glycol flows from the glycol contactor downstream and back to the glycol contactor upstream and may operate through the glycol contactor. gravity and in this way an intermediate pump for transfer is not required. Alternatively, this arrangement of two vessels can be configured to have the glycol contactor upstream and the amine contactor in one vessel, and to have the glycol contactor downstream in another vessel. In any case, a single line or connection line can be used to connect the gas flow between the two vessels. This invention has been described with respect to a particular embodiment thereof, but it will be understood that other changes or modifications can be made to these preferred embodiments, which do not depart from the proposed scope of the claims herein.

Claims (20)

1. CLAIMS f ^ 1. A method for removing aromatic hydrocarbons from a gas stream treated in an amine-based gas sweetening process to prevent the same aromatic hydrocarbons from entering the amine process and becoming a potential source of emissions, the method it comprises the steps of: providing a gas flow containing aromatic hydrocarbons including BTEX; initially treat the flow of 10 gas per passage through the first glycol contactor when absorbing BTEX; and then treat the gas flow by passage through an amine-based gas sweetening process that includes an amine contactor for gas sweetening, to remove acid gases, and a glycol contactor for 15 dehydration and additional absorption of BTEX.
2. 2. The method, as described in claim 1, further including the step of: recirculating the wet glycol produced by the second glycol contactor through the 20 first glycol contactor.
3. 3. The method, as described in claim 2, wherein: the recirculation step is obtained by pumping the wet glycol from a glycol stream outlet in the second glycol contactor, to a glycol stream inlet in the first glycol contactor.
4. 4. The method, as described in claim 2, wherein: the recirculation step is obtained by gravity flow between the glycol stream output and the second glycol contactor, and a glycol stream inlet in the first glycol contactor. glycol.
5. 5. The method, as described in claim 1, further including the step of: regenerating the glycol used in the first and second glycol contactors by a regeneration system that interconnects a glycol stream outlet in the first glycol contactor and a glycol stream inlet in the second glycol contactor.
6. 6. The method, as described in claim 1, further comprising the step of: regenerating the glycol used in the second glycol contactor by a first regeneration system that interconnects a glycol stream outlet in the second glycol contactor, with a glycol stream inlet in the second glycol contactor; and regenerating the glycol used in the first glycol contactor by a second regeneration system that interconnects a glycol stream outlet in the first glycol contactor with a glycol stream inlet in the first glycol contactor.
7. 7. The method, as described in claim 1, wherein: the first glycol contactor and the amine contactor are placed in a single container for first contact of the gas flow with the glycol for the absorption of BTEX, and then put in contact the flow of gas with the amines for the removal of acid gases.
8. 8. The method, as described in claim 1, wherein: the first glycol contactor and the amine contactor are placed in separate respective containers.
9. 9. The method, as described in claim 1, wherein: the second glycol contactor and the amine contactor are placed in a single container for gas flow contact with amines for acid gas removal, and then put into Contact the gas flow with glycol for dehydration and additional absorption of BTEX.
10. 10. The method, as described in the claim 1, in which: the first glycol contactor, the amine contactor and the second glycol contactor are placed in a single vessel for first contact of the gas flow with glycol for BTEX absorption, then contacting the gas flow for amines for removal of acid gases, and then contacting the gas flow with glycol for dehydration and additional absorption of BTEX.
11. 11. The method, as described in claim 10, further including the step of recirculating the wet glycol produced by the second glycol contactor through the first glycol contactor.
12. 12. The method, as described in claim 1, further including the step of: recirculating the amine used in the amine contactor by an amine regeneration system connected to the amine contactor.
13. 13. An apparatus for gas sweetening and removal of aromatic hydrocarbons from a gas stream passing through the apparatus from an upstream position to a downstream position, the apparatus comprises: a container having an upper end and a lower end; an upstream glycol contacting section for BTEX absorption placed inside the container and placed adjacent to the lower end; a downstream glycol contacting section for dehydration and additional absorption of BTEX, placed inside the container and located adjacent to the upper end; an amine contactor section for gas sweetening placed within the container and located between the upstream glycol contactor and the downstream glycol contactor; a glycol derivation line interconnecting the glycol contacting sections upstream and downstream; and wherein the gas stream makes a countercurrent contact with the glycol flowing through the glycol contacting sections upstream and downstream, and with an amine flowing through the amine contactor, the glycol derivatization line. it allows the glycol to flow from the glycol contacting section downstream to the upstream glycol contacting section.
14. 14. The apparatus as described in claim 13, wherein: the upstream and downstream glycol contacting sections each contain respective roll tray mounts for retaining and separating glycol from the gas stream.
15. 15. The apparatus as described in the claim 13, wherein: the amine contacting section includes a stirring tray assembly thereon for retaining and separating amine from the gas stream.
16. 16. The apparatus as described in claim 13, further including: at least one moisture extractor positioned within the container and placed in contact with the gas flow to filter the glycol or amine from the gas flow.
17. 17. An apparatus for gas sweetening and removal of aromatic hydrocarbons from a gas stream passing through the apparatus from an upstream position to a downstream position, the apparatus comprises: a container for use in the treatment of the gas stream that containing aromatic hydrocarbons including BTEX, the gas stream flows through the container from an upstream position to a downstream position; an amine contactor in the gas sweetening vessel to remove acid gases from the gas stream flowing through the amine contactor; and a first glycol contactor in the container, in an upstream position from the amine contactor to absorb BTEX from the gas stream.
18. 18. The apparatus as described in the claim 17, which further includes: a second glycol contactor in the vessel in a downstream position from the amine contactor for dehydration and additional BTEX absorption of the gas stream.
19. 19. The apparatus as described in claim 18, further including: a glycol line interconnecting the first and second glycol contactors to recirculate glycol from the second glycol contactor to the first glycol contactor.
20. 20. The apparatus as described in claim 18, wherein: the glycol flows in a closed circuit through the first and second glycol contactors and the apparatus further includes a glycol regeneration system which interconnects the first glycol contactor with the glycol contactor. second glycol contactor for regenerating rich glycol leaving the first glycol contactor and re-introducing lean glycol into the second glycol contactor.