Patent Application
20150368568
The technical field generally relates to methods and apparatuses for processing hydrocarbons, and more particularly relates to methods and apparatuses for removing contaminants from a hydrocarbon stream with alkaline and amine and for removing the alkaline and amine from the hydrocarbon stream.
Sour hydrocarbon streams are typically treated to remove mercaptans, such as by extraction processes. Mercaptans have traditionally been removed from hydrocarbon streams because of their malodorous scent. Sour hydrocarbon streams may also include acid gases such as carbon dioxide. Attempts have been made to remove acid gases from hydrocarbon streams through the absorption of acid gases with amines.
In a typical liquid-liquid extraction process, caustic is used to convert mercaptans to mercaptides. Hydrogen sulfide must be removed in a prewash vessel before extraction or the caustic will preferably react with the hydrogen sulfide in the extractor vessel and leave mercaptans in the hydrocarbon stream. Often, a liquid hydrocarbon stream is fed to an amine absorber column to be contacted with an amine, such as diethanolamine, to absorb acid gases such as hydrogen sulfide and carbon dioxide from the hydrocarbon stream. The hydrocarbon stream lean of hydrogen sulfide and other acid gases is then prewashed in a prewash vessel containing liquid caustic to convert the remaining hydrogen sulfide to sodium sulfide which is soluble in caustic. The hydrocarbon stream, depleted of hydrogen sulfide, flows through the extraction vessel and is subjected to counter-current flow of liquid caustic. Mercaptans in the hydrocarbon stream react with the caustic to yield mercaptides. The mercaptides in the hydrocarbon stream are soluble in the caustic. A product hydrocarbon stream lean in mercaptans may pass overhead from the extraction column. The mercaptide rich caustic exits the bottom of the extraction column.
The amine used to absorb acid gases may be soluble in the hydrocarbon stream. However, the product formed from the extraction process may be required to be amine-free. Therefore, an amine removal process must be performed. However, addition of a water wash to remove amine from the hydrocarbon product stream can add 10% or more to the installation cost of an extraction process unit.
Accordingly, it is desirable to provide methods and apparatuses for removing amines from extracted hydrocarbon streams. In addition, it is desirable to provide methods and apparatuses that economically extract contaminants from hydrocarbon streams. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
Methods and apparatuses for processing hydrocarbons are provided. In an exemplary embodiment, a method for processing a hydrocarbon stream includes feeding a hydrocarbon stream including amine and mercaptan to an extraction zone. The method includes contacting the hydrocarbon stream with an alkaline stream in the extraction zone to convert the mercaptan to a mercaptide. Further, the method includes contacting the hydrocarbon stream with water in the extraction zone to remove the amine from the hydrocarbon stream.
In another embodiment, a method for processing hydrocarbons including feeding a hydrocarbon stream containing sulfur compounds and acid gases to a prewash zone containing amine to remove the acid gases. The method includes withdrawing a prewashed hydrocarbon stream from the prewash zone and feeding the prewashed hydrocarbon stream to an extraction zone. The method contacts the prewashed hydrocarbon stream with an alkaline stream in the extraction zone to convert mercaptans to mercaptides. Further, the method contacts the hydrocarbon stream with water in the extraction zone, wherein the water removes amine entrained in the hydrocarbon stream. The method includes withdrawing an extracted hydrocarbon stream from the extraction zone.
In accordance with another exemplary embodiment, an apparatus for processing a hydrocarbon stream is provided. The apparatus comprises an extraction vessel including an extraction section positioned below a wash section. The apparatus also includes a hydrocarbon conduit connected to the extraction vessel for delivering a hydrocarbon stream including a mercaptan and an amine for upward flow through the extraction section and through the wash section. An alkaline conduit is connected to the extraction vessel for delivering an alkaline stream for downward flow through the extraction section. A water conduit is connected to the extraction vessel for delivering water for downward flow through the wash section and through the extraction section. The apparatus further includes an effluent outlet for removing the alkaline stream and the water from the extraction vessel.
Embodiments of methods and apparatuses for removing amines from extracted hydrocarbon streams will hereinafter be described in conjunction with the following drawing figure wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the methods and apparatuses for processing hydrocarbon streams claimed herein. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.
As described herein, methods and apparatuses are provided for removing amine and other aqueous soluble impurities, such as caustic, from extracted hydrocarbon streams. In an exemplary embodiment, amine and alkaline are contacted with the hydrocarbon stream in an extraction zone to facilitate removal of mercaptans and acid gases from the hydrocarbon stream. Then, the hydrocarbon stream passes through a wash section of the extraction zone where the hydrocarbon stream is contacted with water. The water removes amine other aqueous soluble impurities in the hydrocarbon stream. The hydrocarbon stream also passes through a coalescer that removes any entrained alkaline in the hydrocarbon stream. Thereafter, the hydrocarbon stream exits the extraction zone, substantially free of amine and alkaline.
A general understanding of the method and apparatus claimed herein can be obtained by reference to
Referring then to
A caustic recirculation conduit 20 joins the hydrocarbon effluent stream 18 to allow an aqueous alkaline solution such as aqueous caustic and the hydrocarbon effluent stream 18 from the amine absorber vessel 12 to mix in combined stream 22 before entering an extraction vessel 24. A pressure differential indicator controller (PDIC) 26 maintains a pressure drop across a control valve 28 such as 7 to 103 kilopascals (kPa) and preferably 28 to 55 kPa to ensure adequate mixing between the liquid caustic and the liquid hydrocarbon in the combined stream 22. Alternatively, a static mixer can be used for adequate mixing.
As shown, the premixed hydrocarbon and aqueous caustic combined stream 22 enters the extraction vessel 24. The extraction vessel 24 comprises a lower prewash zone 30 and an upper extraction zone 32 separated by an imperforate, downwardly convexed baffle 34. As used herein, the term “zone” can refer to an area including one or more equipment items and/or one or more sub-zones. Equipment items can include one or more reactors or reactor vessels, heaters, exchangers, pipes, pumps, compressors, and controllers. Additionally, an equipment item, such as a reactor, dryer, or vessel, can further include one or more zones or sub-zones. The extraction zone 32 is directly above the prewash zone 30 and both zones 30 and 32 preferably share at least one common wall 33. The prewash zone 30 includes a coalescer 36 proximate a top of the prewash zone 30. The combined stream 22 is fed into the prewash zone 30 proximate a bottom of the prewash zone 30.
In the prewash zone 30, an aqueous alkaline solution such as caustic of from about 2 to about 15 weight percent (wt %), such as from about 3 to about 12 wt %, for example from about 6 to about 12 wt %, reacts with any remaining hydrogen sulfide to yield a sulfide salt such as sodium sulfide. The higher density aqueous caustic and sulfides dissolved therein gravitate to the bottom of the prewash zone 30 while the hydrocarbon depleted of hydrogen sulfide rises to the top of the prewash zone 30. A coalescer 36 serves to gather together smaller droplets of caustic that rise in the prewash zone 30 to give them sufficient weight to begin descending through the prewash zone 30 with the rest of the caustic. The prewash zone 30 can also be used to remove COS from the hydrocarbon by reacting it with a solvent composed of a mixture of amine and alkaline. In an exemplary embodiment, the amine is from about 5 to about 20 wt % of the solution and the caustic is from about 6 to about 12 wt %.
A transfer conduit 38 has an inlet in communication with the prewash zone 30 proximate a top of the prewash zone 30 above the coalescer 36 and an outlet in communication with the extraction zone 32 proximate a bottom of the extraction zone 32. The higher density caustic pushes the lower density hydrocarbon up through the transfer conduit 38 without the need for a pump. A pump 42 pumps spent caustic out of the bottom of the prewash zone 30 through the recirculation conduit 20. Spent caustic is withdrawn from the recirculation conduit 20 through a line 44 regulated by a control valve 46. The flow rate of caustic through the control valve 46 is automatically controlled by a level indicator controller (LIC) 48 which monitors the level of caustic in the prewash zone 30 at the hydrocarbon-caustic interface. The LIC 48 sensing the level of caustic in the prewash zone 30 signals a setting for the control valve 46 relative to fully open to bring the level of the caustic in the prewash zone 30 to a desired, preset level. Accordingly, spent caustic is continuously withdrawn from the prewash zone 30 through the line 44 via the recirculation conduit 20. The spent caustic withdrawn through the line 44 may be sent to a spent caustic degassing drum (not shown) which allows volatile hydrocarbons to evaporate off of the top of the drum before the spent caustic descends out of the drum to treatment. Regenerated caustic in a line 50 is continuously fed to the caustic recirculation conduit 20 and hence to the prewash zone 30 at a flow rate regulated by a control valve 52 governed by a flow rate controller (FRC) 98. Additionally, water 54 is added to the caustic recirculation conduit 20.
An aqueous alkaline solution such as aqueous caustic in the extraction zone 32 has a concentration of from about 12 to about 19 wt %), such as from about 13 to about 16 wt %. A hydrocarbon stream substantially devoid of hydrogen sulfide exits the outlet of the transfer conduit 38 into the extraction zone 32. Mercaptans in the extraction zone 32 react with the caustic to yield sodium mercaptides and water. The lower density hydrocarbons rise to the top of the extraction zone 32 while the aqueous caustic and mercaptides dissolved in the aqueous caustic sink to the bottom of the extraction zone 32 where it collects at the imperforate, downwardly convexed baffle 34. The hydrocarbon rises to a coalescer 58 comprising a mesh blanket having a thickness of about 61 centimeters (cm) that coalesces smaller caustic droplets carried to the top of the extraction zone 32 with hydrocarbon because of their smaller size. The coalescer 58 coalesces smaller droplets of caustic together to form larger droplets that will tend to sink back to the bottom of the extraction zone 32. Treated hydrocarbon substantially devoid of mercaptans and mercaptides exits the extraction zone 32 via a product conduit 60.
Spent caustic rich in mercaptides is withdrawn through a drain at the lowermost portion of the downwardly convexed baffle 34 through a line 62. The line 62 actually extends through the prewash zone 30 above the coalescer 36 and through the common wall 33 thereof.
A line 64 adds oxidation catalyst to the line 62. A specific mercaptan oxidation catalyst is not required. Many suitable catalysts are known in the art. One preferred class of catalyst comprises sulfonated metal phthalocyanine. A particularly preferred sulfonated metal phthalocyanine is highly monosulfonated cobalt phthalocyanine or other phthalocyanine catalysts. Additional dipolar type catalysts are suitable for use in an alkaline contacting solution. Typically, the oxidation catalyst in the aqueous alkaline solution will have a concentration of from about 10 to about 500 wppm, such as a concentration of about 200 wppm. The spent caustic stream with added catalyst may be heated in an indirect heat exchanger with low pressure stream as a heat exchange fluid in a heater 66. The heater 66 may heat the spent aqueous caustic from about 38° C. to about 43° C. Air sufficient to oxidize the mercaptides is added to the spent caustic stream in the line 62 through a line 68 to form an oxidizer feed line 70. The spent aqueous caustic and air mixture is distributed into an oxidation vessel 72. In the oxidation vessel 72, the sodium mercaptides catalytically react with oxygen and water to yield caustic and organic disulfides. Rashig rings or other particulate packing in the oxidation vessel 72 may increase the surface area therein to improve contact with the catalyst. An exit conduit 74 withdraws effluent from a top of the oxidation vessel 72. The effluent from the oxidation vessel 72 comprises three phases including an air phase, a liquid disulfide phase and a liquid aqueous caustic phase.
The exit conduit 74 carries the effluent from the oxidation vessel 72 to a disulfide separator 76 comprising a vertical section 78 and a horizontal section 80. Once settled in the separator, the air phase exits the top of the vertical section 78 through a line 82. The two liquid phases settle in the horizontal section 80 of the disulfide separator 76. The lighter disulfide phase exits the top of the horizontal section 80 through a line 84. The disulfide effluent from the disulfide separator 76 is carried by the line 84 to a sand filter 86 to coalesce and separate any traces of caustic and is removed from the process through a line 88. Heavier regenerated caustic exits the bottom of the horizontal section 80 through the line 90. The vertical section 78 of the disulfide separator 76 includes carbon Rashig rings or other particulate packing to increase the surface area such that liquid entrained in the air is knocked out of entrainment and prevented from exiting through the line 82. A portion of the horizontal section 80 of the disulfide separator 76 includes anthracite coal or other material to serve as a coalescer. Caustic droplets contained in the disulfide phase will be coalesced into larger, heavier droplets that will fall down to the heavier aqueous caustic phase to exit the inlet to the line 90 instead of the inlet to the line 84.
The line 90 carrying regenerated caustic splits into two lines 92 and 50. The line 92 carries regenerated caustic to the extraction zone 32 at a rate regulated by a control valve 94 governed by a flow rate controller (FRC) 96. The line 50 carries regenerated caustic to the caustic recirculation conduit 20 at a flow rate regulated by the control valve 52 governed by the FRC 98. FRC 96 and FRC 98 measure the flow rate of caustic in their respective lines 92 and 50 and signal the control valves 52 and 94, a setting relative to fully open to obtain a desired input flow rate. The desired input flow rate is determined to obtain a desired caustic concentration in the respective section of the extraction vessel 24.
The pressure in the amine absorber vessel 12 and in the extraction vessel 24 is maintained by regulating the flow of hydrocarbon from the extraction zone 32 in the product conduit 60 by a control valve 61 governed by a pressure indicator controller (PIC) 63 that monitors the pressure in the product conduit 60. The pressure should preferably be kept at a level to ensure that the hydrocarbon remains in a liquefied state. This pressure typically ranges from about 517 to about 2758 kPa. The temperature of the hydrocarbon streams may be maintained at a temperature of about 35° C. to about 40° C. The heater 66 raises the temperature of the spent caustic to from about 40° C. to about 45° C. before it enters the oxidation vessel 72 in the line 70. The oxidation reaction is exothermic which results in an increase in the temperature of the effluent in the exit conduit 74 typically not to exceed 57° C. Hence, the temperature in the disulfide separator 76 may be less than 57° C. The pressure in the oxidation vessel 72 and in the disulfide separator 76 may be maintained from about 345 to about 448 kPa in the line 82 by a control valve 85 regulated by a pressure indicator controller (PIC) 87 monitoring the pressure in the line 82.
In
The hydrocarbon stream 102 moves upward through contact trays 110 in the lower section 104 of the extraction zone 106. An exemplary lower section 104 of the extraction zone 106 includes from about 7 to about 12 trays 110. At each tray 110 in the lower section 104, the hydrocarbon stream 102 contacts an alkaline stream 112 that is introduced to the extraction zone 106 proximate the top of the lower section 104 of the extraction zone 106, such as above the uppermost tray 110 in the lower section 104 of the extraction zone 106. During contact between the alkaline stream 112 and the hydrocarbon stream 102, mercaptans react with the alkaline stream 112 to yield sodium mercaptides and water. The lower density hydrocarbon stream 102 rises to the top of the lower section 104 of the extraction zone 106 while the alkaline stream 112 and mercaptides dissolved in the alkaline stream 112 sink to the bottom of the lower section 104 of the extraction zone 106.
The hydrocarbon stream 102, substantially devoid of mercaptans and hydrogen sulfides, passes from the lower section 104 of the extraction zone 106 to an upper section 114 of the extraction zone 106. Specifically, the hydrocarbon stream 102 moves above the entry point of the alkaline stream 112. A stream of water 116 is fed into the upper section 114 of the extraction zone 106, proximate the top of the upper section 114 of the extraction zone 106. Specifically, the water 116 is introduced above the uppermost tray 110 in the upper section 114 of the extraction zone 106. In an exemplary embodiment, the upper section 114 of the extraction zone 106 includes from about 2 to about 4 trays 110.
The water 116 move downward through the upper section 114 of the extraction zone 106. As the water 116 contacts the hydrocarbon stream 102 in the upper section 114 of the extraction zone 106, it absorbs amine from the hydrocarbon stream 102. As a result, the hydrocarbon stream 102 exiting the upper section 114 of the extraction zone 106 is substantially devoid of amine. For example, after passing through the upper section 114 of the extraction zone 106, the hydrocarbon stream 102 may include less than about 5 wppm amine, such as less than about 2 wppm amine, for example less than 1 wppm amine or no amine
As shown, the hydrocarbon stream 102 than passes through a coalescer 120. The coalescer 120 may be the same or similar to the coalescer 58 of
The exemplary extraction zone 106 is operated at a temperature of from about 26° C. to about 49° C., such as from about 32° C. to about 43° C. Further, the exemplary extraction zone 106 is operated at a pressure of from about 517 kPa to about 2758 kPa, such as from about 690 kPa to about 2070 kPa.
As shown, an effluent stream 124 of alkaline solution rich in mercaptides exits the bottom of the extraction column 108. Alternatively, the effluent stream 124 may exit through a side outlet above an integral prewash zone as in
At the oxidation unit 130, sodium mercaptides catalytically react with oxygen and water to yield caustic and organic disulfides. The oxidized effluent 132 then passes from the top of the oxidation unit 130 to a disulfide separator 134, similar to or the same as disulfide separator 76 of
After settling in the disulfide separator 134, spent air 136 exist the top of a vertical section of the disulfide separator 134. A lighter liquid phase of disulfide 138 exits the top of a horizontal section of the disulfide separator 134. A heavier liquid phase of alkali forming a recovered alkaline stream 140 exits the bottom of the horizontal section of the disulfide separator 134.
The recovered alkaline stream 140 is pumped by pump 142 to a dehydration unit 144. Alternatively, the dehydration unit 144 may be positioned upstream of pump 142 to allow dehydration at lower pressure. At the dehydration unit 144, the water content of the recovered alkaline stream 140 is reduced. Specifically, the recovered alkaline stream 140 may include water introduced into the extraction zone 106 at water stream 116 and have a reduced alkaline content. In an exemplary embodiment, the dehydration unit 144 includes a water balance column operated at about 60° C. to about 70° C. As a result, the alkaline stream 112 is formed with a selected water content and alkali content. For example, the alkaline stream 112 may have a water content of about 85 wt % to about 89 wt % and an alkaline concentration of about 11 wt % to about 15 wt %.
In cases where amine builds up in the circulating alkaline stream 112 to unacceptable amounts, the circulating alkaline stream may be bled or purged and fresh alkaline solution may be added. For example, the alkaline stream may be bled or purged when the amine concentration reaches about 5 wt %.
The apparatuses and methods described herein provide for the removal of mercaptans and acid gases from hydrocarbon streams. Such removal is performed with alkali and amine. The apparatuses and methods described herein further provide for the removal of the alkaline and amine from the product stream formed by extraction. Further, the apparatuses and methods described herein remove alkaline and amine within an extraction zone, and more specifically, within an extraction vessel without requiring use of additional vessels. As a result, unit costs are reduced.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the claimed subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment or embodiments. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope set forth in the appended claims.
