JP5351934B2 - Method and apparatus for converting sulfur compounds in a hydrocarbon stream - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the capital invested to an apparatus by combining a caustic-prewashing section, an extractor, a sedimentation separation tank and a sand filter constituting the apparatus, in the apparatus and a method for extracting sulfur compounds from a hydrocarbon stream. <P>SOLUTION: The prewashing section 30 to convert hydrogen sulfide to a sulfide salt by a reaction using an alkali such as a caustic is communicated with an extraction section 32 located right above the prewashing section 30 and to convert mercaptan to mercaptide by a reaction using an alkali. A hydrocarbon product goes out the extraction section 32 through a coalescer 58 to prevent the alkali from flowing out along with the hydrocarbon product stream. The prewashing section 30 to convert hydrogen sulfide to sodium sulfide by the reaction using an alkali such as a caustic prepares the hydrocarbon stream for extraction. The used alkali is continuously recovered, and the reproduced alkali is continuously added to the prewashing section 30. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention generally relates to a method and apparatus for removing organic sulfur compounds from a stream containing hydrocarbons. Specifically, the present invention relates to the use of an aqueous caustic solution to remove mercaptans from hydrocarbon streams.

  At present, it is customary to treat sour hydrocarbons and gas streams for mercaptan removal. Typically, an extraction process is used when processing light hydrocarbons and gas streams for mercaptan removal. Traditionally, mercaptans have been removed from hydrocarbon streams due to their malodour.

  US Pat. No. 5,244,643 describes a process in which a hydrocarbon gas stream containing mercaptan sulfur, air, and an alkaline aqueous solution containing a mercaptan oxidation catalyst are mixed in a mixer where the mercaptan is converted to disulfide. It is disclosed. The effluent recovered from the top of the mixer is allowed to settle into a vessel to produce separate streams of alkaline aqueous solution containing air, a liquid hydrocarbon product containing disulfide, and a mercaptan oxidation catalyst.

  US Pat. No. 4,562,300 discloses a method in which a hydrocarbon stream containing an organic mercaptan is contacted with sodium hydroxide to obtain the hydrocarbon without the organic mercaptan. The caustic solution rich in mercaptans is oxidized using a catalyst and the organic mercaptans are converted to organic disulfides. A mixture of the regenerated caustic solution free of organic mercaptan and the organic disulfide is passed into a settling separator where the organic disulfide and caustic solution are separated. The hydrocarbon stream from which mercaptan is extracted in the upstream direction is mixed with a regenerated caustic solution containing a small amount of organic disulfide, and the organic disulfide is extracted from the regenerated caustic solution. These processes leave disulfides in the liquid hydrocarbon stream. Current and anticipated government regulations tend to be more restrictive, as the inclusion of organic disulfides in the liquid hydrocarbon product stream is undesirable.

In the liquid-liquid extraction process, disulfide is removed from the hydrocarbon stream and does not circulate again. For liquid-liquid extraction processes, see J.A. R. Salaza, Handbook of Petroleum Refining Processes 9-4-9-5 (Robert A. Meyers ed. 1986). In a typical extraction process, a liquid hydrocarbon stream is fed to an amine absorption column and contacted with an amine such as diethylamine, and acidic gases such as hydrogen sulfide and carbon dioxide are absorbed from the hydrocarbon stream. A hydrocarbon stream slightly containing hydrogen sulfide and other acidic gases is prewashed with a prewasher containing 6.5 to 7.0% by weight of a liquid caustic agent, and the residual hydrogen sulfide is dissolved in the caustic agent. Convert to sodium sulfide. Subsequently, the hydrocarbon stream depleted in hydrogen sulfide is contacted with a counter-current of about 14% by weight liquid caustic in the extractor. A jet deck in the extractor facilitates contact with the countercurrent. Mercaptans in the hydrocarbon stream react with the caustic agent to produce mercaptides. The mercaptide in the hydrocarbon stream is soluble in caustic. The product hydrocarbon stream containing a slight amount of mercaptans exits the extraction column through the settling tank and passes to the top of the sand filter, and the mercaptide-rich caustic is from the bottom of the column. leak.
The settling tank acts as a buffer to settling the stream and buffer the rapid rise of caustic to the sand filter. The sand filter fuses caustic and sinks to the bottom of the vessel, while the product hydrocarbon stream exits the vessel through an outlet that shields the top and prevents the caustic droplets from descending. leak. The caustic rich in mercaptides is injected with air and catalyst as it leaves the extraction column and is fed to an oxidizer for regeneration. The caustic solution is regenerated by oxidizing mercaptides to disulfides using a phthalocyanine catalyst. Caustic rich in disulfide is fed from the oxidizer to the disulfide separator. The disulfide separator releases excess air and removes disulfide from the caustic before the regenerated caustic is discharged and circulated to the extractor. The disulfide passes through the sand filter and is removed from the process.

  Hydrogen sulfide must be removed in a prewasher prior to extraction. Alternatively, it is desirable for the caustic agent to react with the hydrogen sulfide in the extractor, leaving the mercaptan in the hydrocarbon stream. Eventually, the caustic in the precleaner becomes sulfide excess and must be replaced for proper hydrogen sulfide conversion. In the mercaptan extraction system, the caustic agent in the pre-cleaner must be replaced batchwise. As a result, the hydrogen sulfide conversion rate at the end of the exchange cycle is low. The prewasher must also be large in size to ensure proper mixing of caustic and hydrocarbon. Furthermore, in the conventional mercaptan extraction system, four containers, that is, a caustic prewasher, an extractor, a sedimentation separator, and a sand filter are used. Each container requires its own support and substrate structure, and a large amount of capital is required to build this system.

  The object of the present invention is therefore to combine the extractor, sedimentation tank and sand filter in one container, thereby reducing the capital required for the construction of the extraction system. In addition, a further object of the present invention is to combine the caustic prewasher, extractor, sedimentation tank and sand filter in one container, thereby reducing the capital required to build the extraction system. It is.

  We have developed a method and apparatus for combining the functions of the extractor and sand filter into one common extractor. The coalescer is placed at the top of the extraction part of the container and performs the function previously performed by the sand filter. The coalescer is placed at a sufficient distance from the jet deck at the top of the extraction section so as to buffer the rapid rise of caustic agent, and functions as a sedimentation separation tank.

  We have also developed a method and apparatus for combining the prewasher, extractor, sedimentation tank and sand filter functions into one common extractor. The extraction part is arranged directly on the caustic pre-cleaning part.

  We have further developed a configuration that allows for continuous recovery of spent caustic from the caustic precleaning section and continuous replacement of regenerated caustic to the precleaning section of the mercaptan extraction system.

  Further objects, embodiments and details of the invention will be understood by reference to the following detailed description.

  With reference to the drawings, a general interpretation of the method and apparatus of the present invention will be understood. Referring to FIG. 1, a hydrocarbon liquid stream such as LPG or naphtha containing mercaptan sulfur and hydrogen sulfide is fed through line 10 to amine absorber 12. An amine such as diethylamine or monoethylamine is fed to the amine absorber 12 through line 14. The amine absorber 12 includes a series of trays. The line 10 supplying the hydrocarbon stream has a distributor below the midpoint of the amine absorber 12. A nozzle on line 14 for supplying amine is placed toward the top of the vessel to contact the counter flow of amine descending the vessel and hydrocarbon rising through the amine absorber 12. The amine in the amine absorber 12 reacts with hydrogen sulfide to produce thiolamide. Typically, a hydrocarbon stream containing approximately 1000 to 2000 wppm hydrogen sulfide will have a concentration of hydrogen sulfide reduced to 15 wppm within the amine absorber 12. The thiolamide-rich amine effluent stream exits from the bottom of the amine absorber 12 through line 16 while the hydrocarbon effluent stream has a substantial hydrogen sulfide concentration from the top of the amine absorber 12 through line 18. Spills in a degraded state. In addition, carbon dioxide or other acidic gases that may be present in the feed stream of line 10 also react with the amine and are absorbed by the amine effluent stream exiting amine absorber 12 through line 16.

  Caustic recirculation conduit 20 is coupled to line 18 to mix an aqueous alkaline solution, such as aqueous caustic, and the hydrocarbon effluent from amine absorber 12 in line 22 before entering the extractor 24. A pressure differential indicating controller (PDIC) 26 controls the pressure drop through a control valve 28, such as in the range of 7 to 103 kPa (1 to 15 psig), preferably 28 to 55 kPa (4 to 8 psig), etc. Allows proper mixing of liquid caustic with liquid hydrocarbons.

  The premixed hydrocarbon and aqueous caustic stream flows into line 24 through extractor 24. The extractor 24 is constituted by a lower preliminary cleaning unit 30 and an upper extraction unit 32 that are non-porous and separated by a downwardly convex baffle 34. It is desirable that the extraction unit 32 is located immediately above the preliminary cleaning unit 30 and that both units share at least one common wall 33. The preliminary cleaning unit 30 has a coalescer 36 adjacent to the top of the preliminary cleaning unit 30. The line 22 is supplied to the preliminary cleaning unit 30 in the vicinity of the bottom of the preliminary cleaning unit 30.

In the pre-cleaning section 30, a caustic agent of 3 to 20 baume (2 to 12 wt%), preferably 5 to 17 baume (3 to 12 wt%), desirably 8 to 12 baume (5 to 8 wt%), etc. Is reacted with residual hydrogen sulfide to produce a sulfide such as sodium sulfide.
Usually, the alkaline aqueous solution is 10 baume (7% by weight). The high-concentration aqueous caustic and the sulfide dissolved therein sink to the bottom of the precleaning section 30, while the hydrocarbons with reduced hydrogen sulfide rise toward the top of the precleaning section 30. The coalescer 36 collects the fine droplets of caustic agent that rises in the pre-cleaning section 30 and weighs enough to begin to settle through the pre-cleaning section 30 with the remaining caustic. Fulfills the function of giving.

  The transfer conduit 38 communicates with the pre-cleaning unit 30, and is connected to the inlet near the top of the pre-cleaning unit 30 above the coalescer 36 and the discharge port close to the bottom of the extraction unit 32. have. The high concentration caustic pushes the low concentration hydrocarbons through the transfer conduit 38 without the need for a pump. The pump 42 pumps up the used caustic agent through the recirculation conduit 20 from the bottom of the preliminary cleaning unit 30. Spent caustic is recovered from the recirculation conduit 20 through a line 44 that is regulated by a control valve 46. The caustic flow rate through the control valve 46 is automatically controlled by a liquid level indicating controller (LIC) 48 that monitors the caustic level at the hydrocarbon-caustic interface in the preclean section 30. The The LIC 48 that senses the level of caustic agent in the precleaning unit 30 transmits a signal for setting the control valve 46 to the fully opened state, and sets the caustic agent level in the precleaning unit 30 to a desired set value. Set to. Further, the used caustic is continuously recovered from the precleaning section 30 through the line 44 via the recirculation conduit 20. The spent caustic recovered through line 44 evaporates volatile hydrocarbons from the top of the tank before the spent caustic descends from the spent caustic degassing tank (not shown) and is processed. For the above tank. The regenerated caustic in line 50 is continuously fed to the caustic recirculation conduit 20 and subsequently to the prewash section 30 at a flow rate adjusted by a control valve 52 controlled by a flow rate controller (FRC) 98. In addition, water is added to the caustic recirculation conduit 20 via line 54.

  The alkaline aqueous solution such as an aqueous caustic agent in the extraction section 32 has a concentration of 17-25 baume (12-19 wt%), preferably 18-22 baume (13-16 wt%), and usually 20 baume (14 wt%). have. A hydrocarbon stream substantially free of hydrogen sulfide exits the outlet of the transfer conduit 38 and flows into the extraction section 32. The mercaptan in the extraction unit 32 reacts with the caustic agent to produce sodium mercaptide and water. The low-concentration hydrocarbon rises to the top of the extraction section 32, while the aqueous caustic and the mercaptide dissolved in the aqueous caustic settle to the bottom of the extraction section 32, and are nonporous and convex downward. The baffles 34 gather together. The hydrocarbons rise to a coalescer 58 consisting of 61 cm (2 feet) of mesh blanket, and the coalescer removes the fine caustic agent droplets and hydrocarbons carried to the top of the extractor 32. Use these fineness to fuse. The coalescer 58 fuses fine droplets of caustic agent to form large droplets, which tend to settle again to the bottom of the extraction unit 32. Treated hydrocarbons substantially free of mercaptans and mercaptides exit the extractor 32 via product conduit 60.

  Spent caustic rich in mercaptides is collected through line 62 through the bottom drain of downwardly convex baffle 34. The line 62 actually extends through the interior of the pre-cleaning section 30 onto the coalescer 36 and through its common wall 33.

  Line 64 adds an oxidation catalyst to line 62. In the present invention, it is not necessary to use a specific mercaptan oxidation catalyst. Many suitable catalysts are known in the art. A preferred group of catalysts includes sulfonated metal phthalocyanines. A particularly suitable sulfonated metal phthalocyanine is a highly monosulfonated cobalt phthalocyanine prepared by the method described in US Pat. No. 4,049,572, the teaching of which is hereby incorporated by reference. Other phthalocyanine catalysts are described in US Pat. No. 4,897,180. Further, dipolar catalysts suitable for use in alkaline contact solutions are disclosed in US Pat. No. 4,956,324, US Pat. No. 3,923,645, US Pat. No. 3,980,582 and US Pat. No. 090,954. Usually, the oxidation catalyst in the alkaline aqueous solution has a concentration of 10 to 500 wppm, preferably 200 wppm. The spent caustic stream with added catalyst is preferably heated in a heater 66 by indirect heat exchange with a low pressure stream as the heat exchange fluid. The heater 66 preferably heats the used aqueous caustic agent in the range of 38 ° C. (100 ° F.) to 43 ° C. (110 ° F.). Sufficient air to oxidize the mercaptide is added through line 68 to the spent caustic stream in line 62 to form oxidant supply line 70. The spent aqueous caustic and air mixture is distributed to the oxidizer 72. Within the oxidizer 72, sodium mercaptide reacts catalytically with oxygen and water to produce caustic and organic disulfide. The rashig rings in the oxidizer 72 increase their surface area and improve contact with the catalyst. Outlet conduit 74 collects effluent from the top of oxidizer 72. The effluent from the oxidizer 72 is composed of three phases including an air phase, a liquid disulfide phase, and a liquid aqueous caustic phase.

The outlet conduit 74 supplies the effluent from the oxidizer 72 to a disulfide separator 76 composed of a vertical portion 78 and a horizontal portion 80. Once stored in the separator, the air phase exits the top of the vertical section 78 through line 82. The two liquid phases sink into the horizontal part 80 of the disulfide separator 76. The light disulfide phase exits the top of horizontal section 80 through line 84. The disulfide effluent leaving disulfide separator 76 is conveyed by line 84 to sand filter 86 where the remaining caustic is fused and separated and removed from the process through line 88. .
Heavy regenerated caustic exits from the bottom of the horizontal portion 80 through line 90. The vertical section 78 of the disulfide separator 76 has a carbon Raschig ring to enlarge its surface area so that liquid attached to the air is separated from the air and does not flow out through the line 82. .
A portion of the horizontal portion 80 of the disulfide separator 76 includes anthracite that functions as a coalescer. The caustic droplets contained in the disulfide phase coalesce into large, heavy droplets that settle into the heavy aqueous caustic phase, not the inlet to line 84 but the line. It flows out from the inlet to 90.

The line 90 for transporting the regenerated caustic is separated into two lines, a line 92 and a line 50.
Line 92 conveys the regenerated caustic to extractor 32 at a flow rate adjusted by control valve 94 controlled by flow rate controller (FRC) 96. Line 50 carries regenerated caustic to caustic recirculation conduit 20 at a flow rate adjusted by control valve 52 controlled by FRC 98. The FRCs 96 and 98 measure the caustic flow rates in lines 92 and 50, respectively, and send signals to control valves 52 and 94 to adjust their fully open state to obtain the desired input flow rate. By determining the desired input flow rate, the desired caustic concentration value in each part of the extractor 24 is obtained.

  The pressure in the amine absorber 12 and the extractor 24 is carbonized in the product conduit 60 leaving the extractor 32 by a control valve 61 controlled by a pressure indicating controller (PIC) 63 that monitors the pressure in the product conduit 60. It is maintained by adjusting the hydrogen flow rate. The pressure is desirably maintained at a level at which the hydrocarbon is maintained in a liquefied state. This pressure is usually in the range of 517 to 2758 kPa (75 to 400 psig). The temperature of the hydrocarbon stream is desirably maintained around 38 ° C. (100 ° F.). The heater 66 preferably sets the caustic temperature within the range of 38 ° C. (100 ° F.) to 43 ° C. (110 ° F.) before the spent caustic flows through line 70 into the oxidizer 72. Raise. The oxidation reaction is exothermic, which raises the temperature of the effluent of the outlet conduit 74, preferably to the extent that it does not exceed 57 ° C (135 ° F). Accordingly, the temperature of the disulfide separator 76 is preferably less than 57 ° C. (135 ° F.). The pressure in the oxidizer 72 and disulfide separator 76 is preferably adjusted by adjusting the pressure in line 82 by a control valve 85 controlled by a pressure indicating controller (PIC) 87 that monitors the pressure in line 82. It is maintained within the range of 345 to 448 kPa (50 to 65 psig).

  FIG. 2 shows the interior of the extractor 24 in more detail. The preclean section 30 is substantially hollow with a few exceptions. The outlet of the line 22 extends to a distributor 26 that distributes the feed upward. The distributor 26 has a cylindrical pipe which is perpendicular to the line 22 and whose opening faces upwards at an angle of 45 ° to the horizontal. Caustic-hydrocarbon interface 57 is typically located between distributor 26 and coalescer 36. The coalescer 36 is formed of a mesh blanket having a thickness of 30 cm (1 foot) extending near the upper end of the preliminary cleaning unit 30 and extending over the entire cross section. An inlet 38a to a transfer conduit 38 disposed above the coalescer 36 supplies fluid to the distributor 56 of the extractor 32 through the outlet 38b. The inlet to the line 62 extends through a portion of the preliminary cleaning unit 30 above the coalescer 36.

The inside of the extraction unit 32 is shown in FIG. 3 together with the contents of FIG. The distributor 56 has a cylindrical pipe that extends perpendicular to the discharge port 38 b of the transfer conduit 38 that communicates with the distributor 56. Supply to the extraction unit 32 is performed by an opening disposed at 45 ° downward in the horizontal direction.
The distributor 56 is disposed on a supply deck 102 constituted by a horizontal plate 104 and two upstanding weirs 106 and 108 that extend partially across the cross section of the extraction section 32. The distributor 56 is disposed in a supply pan 109 defined by weirs 106, 108, the plate 104 and the inner surface of the common wall 33 of the extraction section 32 of the extractor 24. The downcomer 110 has a discharge port 112 disposed in the inlet pan 107 defined by the inner surface of the common wall 33 of the plate 104, weir 106 and extractor 24.

  FIG. 2 shows six jet decks 120 on the supply deck 102. For the extraction unit 32 of the present invention, a jet deck 120 is used more or less. In the extraction unit, it is desirable to use 2 to 15 decks, and 6 to 8 decks are standard. In addition, other types of structures for smooth liquid-liquid contact are contemplated, such as packed beds or trays.

  2 and 4 are referenced for the description of the jet deck 120. Each jet deck 120 has an outlet pan 122 defined by the inner surface of the common wall 33 of the extractor 24, a horizontal pan plate 124 communicating with the inlet 126 of the downcomer 110, and a vertical weir 128. The jet deck 120 also includes a plate 129 constituted by the porous sieve portion 130 and the non-porous portion 131. The non-hole portion 131 is separated from the sieve portion 130 by a vertical weir 134. The introduction pan 132 is defined by the non-hole portion 131, the inner surface of the common wall 33 and the weir 134. Regenerated caustic from line 92 is fed to the top pan of the jet deck 120.

  FIG. 3 shows a composition in which the vertical weirs 106, 108 extend in parallel across the extraction section 32 to define the introduction pan 107 and the supply pan 109. FIG. 4 shows a composition in which the vertical weirs 128, 134 extend in parallel across the extractor 32 and define the inlet pan 132 and the outlet pan 122. Since the height of the weirs 106, 108, 128 and 134 is 30.5 cm (1 foot), if the amount of caustic agent exceeds 30.5 cm (1 foot), the weirs will overflow from each weir. It is also possible to set the height of the weir higher than this. In the supply deck 102, the caustic agent overflowing the introduction pan 107 and the supply pan 109 spills down to the caustic agent-hydrocarbon interface 111 below the supply deck 102. In the case of the jet deck 120, the overflowing caustic agent flows out onto the sieve part 130 and comes into contact with hydrocarbons rising through the holes of the sieve part 130. Caustic that flows into the outlet pan 122 of the jet deck 120 passes through the inlet 126 of the downcomer pipe 110 to the inlet pan 132 of the jet deck 120 below it, and subsequently to the inlet pan 107 of the supply deck 102. , Respectively, flows down through the discharge port 112. This arrangement allows the hydrocarbon and caustic to be in proper contact, while the hydrocarbon rises to the top of the extraction section 32 and exits through the product conduit 60.

  The coalescer 58 is located on the jet deck 120 near the top of the extraction unit 32. The coalescer 58 formed of a mesh blanket is disposed over the entire cross section of the extraction unit 32. The coalescer 58 is the last barrier to prevent caustic from flowing out with the hydrocarbon product, so that the amount of caustic that passes therethrough is 2 ppm or less, preferably 1 ppm or less. It is important to have sufficient properties. A coalescer such as COALEX from Koch-Otto-York is preferred.

  The coalescer 58 is disposed at a distance from the uppermost jet deck 120 and provides an open settling volume 59 that functions as a buffer zone when there is a sudden rise in caustic. The sedimentation capacity 59 occupies a capacity sufficient to accommodate at least another jet deck 120. The coalescer 58 and settling volume 59 of the extractor 24 eliminates the need for a conventional liquid-liquid extraction process sand filter and settling vessel.

FIG. 2 is a process flow schematic diagram for the process of the present invention. It is detail drawing of the extractor shown in FIG. It is a perspective view of the supply deck of the extraction part of this invention. It is a perspective view of the jet deck of the extraction part of this invention.

12 Amine absorber 20 Alkali (caustic) recirculation conduit 22 Hydrocarbon supply conduit (line)
24 container (device, extractor)
30 Pre-cleaning section 32 Extraction sections 36, 58 Coalescer 72 Oxidizer 76 Disulfide separator 78 Vertical section 80 Horizontal section 86 Sand filter

Claims (4)

A method for converting sulfur compounds in a hydrocarbon stream, the method comprising:
Mixing the hydrocarbon stream and the alkali stream;
Supplying the hydrocarbon stream mixed with the alkali stream to a pre-cleaning section (30) containing alkali to convert hydrogen sulfide into a sulfide;
Continuously recovering the spent alkali stream containing sulfide from the pre-cleaning section (30);
Recycling at least a portion of the spent alkali stream and mixing it with the hydrocarbon stream;
Continuously adding a regenerated alkali stream to the prewash section (30);
Recovering the pre-cleaned hydrocarbon stream from the pre-cleaning section (30); and extracting the pre-cleaned hydrocarbon stream separately from the pre-cleaning section (30). Supplying to (32).   The part of the used alkali stream is recycled to the prewash section (30) and the other part of the used alkali stream is removed from the used alkali stream. the method of.   The method of claim 1, wherein the regenerated alkali stream is added to the spent alkali stream. 4. An apparatus (24) for contacting a hydrocarbon stream comprising a sulfur compound in any of claims 1 to 3 with alkali, the apparatus comprising:
A container (24) containing a pre-cleaning section for contacting the hydrocarbon stream with alkali;
A hydrocarbon removal conduit (38) in communication with the vessel (24) having an inlet for recovering a hydrocarbon stream from the vessel;
An alkali recirculation conduit (20) having an inlet in communication with the container (24) for recovering the spent alkali stream from the container and an outlet in communication with the container;
An apparatus comprising: an alkali addition line (50) in communication with said alkali recirculation conduit (20); and an alkali removal line (44) in communication with said alkali recirculation conduit (20).

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