PROCESS AND APPARATUS FOR CATALYTICALLY CRACKING HYDROCARBONS WITH RECYCLED SLURRY FILTER BACKFLUSH

Abstract

A process for catalytically cracking hydrocarbons is disclosed. The process comprises contacting a hydrocarbon feed stream with a catalyst to catalytically crack the hydrocarbon feed stream to provide a cracked stream and spent catalyst. The spent catalyst is disengaged from the cracked stream in a reactor vessel. Hydrocarbons are stripped from the spent catalyst. The cracked stream is fractionated in a main fractionation column into products comprising a slurry oil stream from a bottom of the main fractionation column. The slurry oil stream is filtered in a filter vessel through a filter to provide a filtered slurry oil stream. Thereafter, the filter is backflushed with a hydrocarbon stream to produce a backflushed hydrocarbon stream comprising catalyst fines. The backflushed hydrocarbon stream is recycled to the reactor vessel. An apparatus for catalytically cracking hydrocarbons is also disclosed.

Claims

1. A process for catalytically cracking hydrocarbons, comprising: contacting a hydrocarbon feed stream with a catalyst to catalytically crack said hydrocarbon feed stream to provide a cracked stream and spent catalyst; disengaging said spent catalyst from said cracked stream in a reactor vessel; stripping hydrocarbons from said spent catalyst; fractionating said cracked stream in a main fractionation column into products comprising a slurry oil stream; filtering said slurry oil stream through a filter to provide a filtered oil stream; backflushing the filter with a hydrocarbon stream to produce a backflushed hydrocarbon stream comprising catalyst fines; and recycling said backflushed hydrocarbon stream to the reactor vessel.

2. The process of claim 1, wherein said hydrocarbon stream is a naphtha stream.

3. The process of claim 1, wherein the step of backflushing the filter comprises: passing a washing fluid to the filter vessel to wash the filter; and passing said hydrocarbon stream through the filter vessel to backflush the filter.

4. The process of claim 3, wherein the washing fluid comprises light cycle oil, heavy cycle oil or a mixture thereof.

5. The process of claim 1, wherein the step of recycling said backflushed hydrocarbon stream comprises passing said backflushed hydrocarbon stream to the reactor vessel at a location above or in a catalyst bed in the reactor vessel.

6. The process of claim 1, wherein the reactor vessel communicates with a riser reactor and further comprises a disengaging chamber in fluid communication with the riser reactor, and a stripping section in fluid communication with the disengaging chamber.

7. The process of claim 6 further comprising passing said backflushed hydrocarbon stream to the stripping section through a distributor.

8. The process of claim 7, wherein the distributor has an outlet located inside the disengaging chamber.

9. The process of claim 2, wherein said naphtha stream is taken from the main fractionation column.

10. The process of claim 6 further comprising recycling said filtered slurry oil stream to the riser reactor.

11. A process for catalytically cracking hydrocarbons, comprising: contacting a hydrocarbon feed stream with a catalyst to catalytically crack said hydrocarbon feed stream to provide a cracked stream and spent catalyst; disengaging said spent catalyst from said cracked stream into a catalyst bed in a reactor vessel; stripping hydrocarbons from said spent catalyst; fractionating said cracked stream in a main fractionation column into products comprising a slurry oil stream; filtering said slurry oil stream in a filter vessel through a filter to provide a filtered slurry oil stream; backflushing the filter with a naphtha stream to produce a backflushed naphtha stream comprising catalyst fines; and recycling said backflushed naphtha stream to a location above or in the catalyst bed in the reactor vessel.

12. The process of claim 11, wherein the naphtha stream is a heavy naphtha stream.

13. The process of claim 11, wherein the naphtha stream is taken from the main fractionation column.

14. The process of claim 1, wherein the step of backflushing the filter comprises: passing a washing fluid to the filter vessel to wash the filter; and passing said naphtha stream through the filter vessel to backflush the filter.

15. An apparatus for catalytically cracking hydrocarbons, comprising: a riser reactor, a disengaging chamber in fluid communication with the riser reactor, a stripping section in fluid communication with the disengaging chamber; a filter; and a distributor in fluid communication with the filter and the stripping section in fluid communication with the filter.

16. The apparatus of claim 15, wherein the filter is in a filter vessel and the distributor is in fluid communication with the filter vessel and the stripping section is in fluid communication with the filter vessel.

17. The apparatus of claim 15 further comprising a main fractionation column in fluid communication with said riser reactor and said filter vessel in fluid communication with said main column.

18. The apparatus of claim 15, wherein the distributor is located inside the disengaging chamber.

19. The apparatus of claim 15, wherein the distributor is located above or in a catalyst bed in the disengaging chamber.

20. The apparatus of claim 15 further comprising a second distributor in fluid communication with the filter and the riser reactor in fluid communication with the second distributor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a schematic drawing of an FCC unit with a filter vessel.

[0011] FIG. 2 is a schematic drawing of a filter vessel in accordance with an exemplary embodiment of the present disclosure.

DEFINITIONS

[0012] The term communication means that material flow is operatively permitted between enumerated components.

[0013] The term downstream communication means that at least a portion of material flowing to the subject in downstream communication may operatively flow from the object with which it communicates.

[0014] The term upstream communication means that at least a portion of the material flowing from the subject in upstream communication may operatively flow to the object with which it communicates.

[0015] The term direct communication means that flow from the upstream component enters the downstream component without undergoing a compositional change due to physical fractionation or chemical conversion.

[0016] The term bypass means that the object is out of downstream communication with a bypassing subject at least to the extent of bypassing.

[0017] The term column means a distillation column or columns for separating one or more components of different volatilities. Unless otherwise indicated, each column includes a condenser on an overhead of the column to condense and reflux a portion of an overhead stream back to the top of the column and a reboiler at a bottom of the column to vaporize and send a portion of a bottoms stream back to the bottom of the column. Feeds to the columns may be preheated. The top pressure is the pressure of the overhead vapor at the vapor outlet of the column. The bottom temperature is the liquid bottom outlet temperature. Overhead lines and bottoms lines refer to the net lines from the column downstream of any reflux or reboil to the column. Stripping columns omit a reboiler at a bottom of the column and instead provide heating requirements and separation impetus from a fluidized inert media such as steam or nitrogen.

[0018] As used herein, the term True Boiling Point (TBP) or TBP method means a test method for determining the boiling point of a material which corresponds to ASTM D-2892 for the production of a liquefied gas, distillate fractions, and residuum of standardized quality on which analytical data can be obtained, and the determination of yields of the above fractions by both mass and volume from which a graph of temperature versus mass % distilled is produced using fifteen theoretical plates in a column with a 5:1 reflux ratio.

[0019] As used herein, the term T5 or T95 means the temperature at which 5 volume percent or 95 volume percent, as the case may be, respectively, of the sample boils using ASTM D-86 .

[0020] As used herein, the term initial boiling point (IBP) means the temperature at which the sample begins to boil using ASTM D-86.

[0021] As used herein, the term end point (EP) means the temperature at which the sample has all boiled off using ASTM D-86.

[0022] As used herein, the term separator means a vessel which has an inlet and at least an overhead vapor outlet and a bottoms liquid outlet and may also have an aqueous stream outlet from a boot. A flash drum is a type of separator which may be in downstream communication with a separator that may be operated at higher pressure.

[0023] As used herein, the term predominant or predominate means greater than 50%, suitably greater than 75% and preferably greater than 90%.

DETAILED DESCRIPTION

[0024] FIG. 1 illustrates a process and apparatus 101 for catalytically cracking hydrocarbons. The process and apparatus 101 comprise an FCC unit 10 and an FCC recovery section 90 that includes a filter vessel 80.

[0025] The FCC unit 10 includes an FCC reactor 12 comprising a riser reactor 20 and a catalyst regenerator 14. A hydrocarbon feed stream comprising an FCC feedstock in a feed line 60 is fed to the FCC reactor 12 through feed distributors 16. The riser reactor 20 is in fluid downstream communication with the feed distributor 16 for feeding the hydrocarbon feed stream into the riser reactor.

[0026] A conventional FCC feedstock and higher boiling hydrocarbon feedstock are suitable fresh hydrocarbon feed streams. The most common of such conventional fresh hydrocarbon feedstocks is a vacuum gas oil (VGO), which is typically a hydrocarbon material having a boiling range with an IBP of at least about 232 C. (450 F.), a T5 of about 288 C. (550 F.) to about 343 C. (650 F.), a T95 between about 510 C. (950 F.) and about 570 C. (1058 F.) and/or an EP of no more than about 626 C. (1158 F.) prepared by vacuum fractionation of atmospheric residue. Such a fraction is generally low in coke precursors and heavy metal contamination which can serve to contaminate catalyst. Atmospheric residue is another suitable feedstock boiling with an IBP of at least about 315 C. (600 F.), a T5 between about 340 C. (644 F.) and about 360 C. (680 F.) and/or a T95 of between about 700 C. (1292 F.) and about 900 C. (1652 F.) obtained from the bottoms of an atmospheric crude distillation column. Atmospheric residue is generally high in coke precursors and metal contamination. Other heavy hydrocarbon feedstocks which may serve as fresh hydrocarbon feed include heavy bottoms from crude oil, heavy bitumen crude oil, shale oil, tar sand extract, deasphalted residue, products from coal liquefaction, and vacuum reduced crudes. Fresh hydrocarbon feedstocks also include mixtures of the above hydrocarbon streams and the foregoing list is not exhaustive.

[0027] In the FCC unit 10, the FCC feed stream in the feed line 60 is fed to the FCC reactor 12 to be contacted with a regenerated cracking catalyst. Specifically, in an embodiment, regenerated cracking catalyst entering from a regenerator conduit 18 is contacted with the FCC feed stream in a riser reactor 20 of the FCC reactor 12. The regenerator conduit 18 is in downstream communication with the regenerator 14. The riser reactor 20 has an inlet 18i in downstream communication with said regenerator conduit 18. The regenerator conduit 18 is connected to the FCC riser reactor 20 at a lower end.

[0028] In the riser 20 of the FCC reactor 12, the FCC feed stream is contacted with catalyst to catalytically crack the FCC feed stream to provide a cracked stream.

[0029] The contacting of the hydrocarbon feed stream with cracking catalyst may occur in the riser reactor 20 of the FCC reactor 12, extending upwardly to the bottom of a reactor vessel 22. The reactor vessel 22 has an outer wall 23. The contacting of feed and catalyst is fluidized by gas from a fluidizing line 24. Heat from the catalyst vaporizes the hydrocarbon feed stream which is thereafter cracked to lighter molecular weight hydrocarbons in the presence of the cracking catalyst as it is transferred up the riser reactor 20 into the reactor vessel 22. In the FCC reactor 12, the FCC feed stream cracks to conventional cracked products such as gasoline and diesel. The cracked stream of hydrocarbon products and spent catalyst in the riser reactor 20 are thereafter discharged from the riser outlet 200 into a disengaging chamber 27 which contains the riser outlet. The disengaging chamber 27 is in downstream fluid communication with the riser reactor 20. The disengaging chamber 27 has an outer wall 43. The cracked stream of hydrocarbon products is disengaged from the spent catalyst in the disengaging chamber 27 using a rough-cut separator 26. Cyclonic separators which may include one or two stages of cyclones 28 in the reactor vessel 22 further separate catalyst from hydrocarbon products. A cracked stream of product gases exits the reactor vessel 22 through a product outlet 31 to a cracked line 32 for transport to a downstream FCC recovery section 90. In an embodiment, the regenerator conduit 18 is in downstream communication with the disengaging chamber 27. The outlet temperature of the cracked products leaving the riser reactor 20 may be between about 472 C. (850 F.) and about 555 C. (1031 F.).

[0030] Inevitable side reactions occur in the riser reactor 20 leaving coke deposits on the catalyst that lower catalyst activity. The spent or coked catalyst requires regeneration for further use. Coked catalyst, after separation from the gaseous cracked product hydrocarbons, falls into a spent catalyst bed 21 in the stripping section 34 where steam from line 33 is injected through a distributor 35 to purge any residual hydrocarbon vapor. The stripping section 34 is in downstream fluid communication with the disengaging chamber 27. After the stripping operation, the spent catalyst is fed to the catalyst regenerator 14 through a spent catalyst conduit 36. The catalyst regenerator 14 may be in downstream communication with the riser reactor 20, specifically, the riser outlet 200.

[0031] FIG. 1 depicts a regenerator 14 known as a combustor. However, other types of regenerators may be equally used. In the catalyst regenerator 14, a stream of oxygen-containing gas, such as air, is introduced from line 37 through an air distributor 38 to contact the coked catalyst, burn coke deposited thereon, and provide regenerated catalyst and flue gas. Catalyst and air flow upwardly together along a combustor riser 40 located within the catalyst regenerator 14 and, after regeneration, are initially separated by discharge through a disengager 42. Finer separation of the regenerated catalyst and flue gas exiting the disengager 42 is achieved using first stage separator cyclone 44, and second stage separator cyclone 46, respectively, within the catalyst regenerator 14. Catalyst separated from flue gas dispenses through diplegs from cyclones 44, 46 while flue gas significantly lighter in catalyst sequentially exits cyclones 44, 46 and exits the regenerator vessel 14 through a flue gas outlet 47 in a flue line 48. The regenerated catalyst is recycled back to the riser reactor 20 through the regenerated catalyst conduit 18.

[0032] As a result of the coke burning, the flue gas vapors exiting at the top of the catalyst regenerator 14 in the flue line 48 contain CO, CO.sub.2 and H.sub.2O, along with smaller amounts of other species. Catalyst regeneration temperature is between about 500 C. (932 F.) and about 900 C. (1652 F.). Both the cracking and regeneration occur at an absolute pressure below about 5 atmospheres.

[0033] In the FCC recovery section 90, the cracked stream in the cracked line 32 is separated into product streams. The gaseous cracked stream in the cracked line 32 is fed to a lower section of a FCC main fractionation column 92. The main fractionation column 92 is in downstream fluid communication with the riser reactor 20 and the FCC reactor 12. In the main fractionation column 92, the cracked stream is fractionated into products. Several fractions may be separated and taken from the main fractionation column 92 including a heavy slurry oil stream from a main column bottom outlet 930 in a bottoms line 93, a HCO stream in a heavy line 94, a LCO stream in a light line 95 and a heavy naphtha stream in a naphtha line 98. Gasoline and gaseous light hydrocarbons are removed in an overhead line 97 from the main fractionation column 92 and condensed before entering a main column receiver 99. In the main column receiver 99, vapor is separated from the liquid component. A condensed unstabilized, light naphtha stream is removed in a liquid overhead line 103 while a light hydrocarbon stream is removed in vapor overhead line 102 from the main column receiver 99. An aqueous stream is removed from a boot in the receiver 99 in line 107. A portion of the light naphtha stream in the liquid overhead line 103 may be refluxed to the main fractionation column 92 in a reflux line 111. A light naphtha product stream may be taken in a concentration line 105. Both streams in lines 102 and 105 may enter a vapor recovery section (not shown) downstream of the main fractionation column 92.

[0034] The light unstabilized naphtha fraction may have an initial boiling point (IBP) in the C.sub.5 range, i.e., between about 0 C. (32 F.) and about 35 C. (95 F.), and an end point (EP) at a temperature greater than or equal to about 127 C. (260 F.). The heavy naphtha fraction may have an IBP just above about 127 C. (260 F.) and an EP at a temperature above about 204 C. (400 F.), preferably between about 200 C. (392 F.) and about 221 C. (430 F.). The LCO stream may have an IBP just above about the EP temperature of the heavy naphtha and an EP in a range of about 360 C. (680 F.) to about 382 C. (720 F.). The LCO stream may have a T5 in the range of about 213 C. (416 F.) to about 244 C. (471 F.) and a T95 in the range of about 354 C. (669 F.) to about 377 C. (710 F.). The HCO stream may have an IBP just above the EP temperature of the LCO stream and an EP in a range of about 385 C. (725 F.) to about 427 C. (800 F.). The HCO stream may have a T5 in the range of about 332 C. (630 F.) to about 349 C. (660 F.) and a T95 in the range of about 382 C. (720 F.) to about 404 C. (760 F.). The heavy slurry oil stream may have an IBP just above the EP temperature of the HCO stream and includes everything boiling at a higher temperature.

[0035] The main fractionation column 92 has the main column bottoms outlet 930 in a bottom 104 of the main fractionation column 92 from which a slurry oil stream is taken. The main column bottoms outlet 930 is taken from the bottom 104 of the main fractionation column 92 meaning below a lowest tray in the column. The feed distributors 16 in the FCC reactor 12 may be in downstream communication with the main column bottoms outlet 930. A portion of the slurry oil stream in the bottoms line 93 may be cooled and recycled in line 91 back to the main fractionation column 92. A process slurry oil stream is taken from the slurry oil stream in a process line 64.

[0036] A lowest auxiliary outlet 940 and a penultimate lowest outlet 950 may be in the side 106 of the main fractionation column 92. The HCO stream may be taken from the lowest auxiliary outlet 940 of the main fractionation column 92. An HCO stream is taken in line 94 from the lowest auxiliary outlet 940 in the side 106 of the main fractionation column 92. An HCO product stream is taken in line 115 from line 94 regulated by a control valve 15 on line 115. A recycle HCO stream may be taken in line 114 from line 94, cooled and returned to the main column 92.

[0037] A diesel stream may be recovered in an LCO product line 117 at a flow rate regulated by a control valve 17 thereon. An LCO stream is taken in line 95 from the penultimate lowest auxiliary outlet 950 in the side 106 of the main fractionation column 92. An LCO product stream is taken in line 117 from line 95 regulated by a control valve 17 on line 117. A recycle LCO stream is taken in line 116 from line 95, cooled and returned to the main column 92. Any or all of the product streams in lines 94, 95, and 96 may be cooled and pumped back to the main column 92 typically at a higher location. Specifically, a side stream may be taken from the side outlet 940, 950, or 960 in the side 106 of the main fractionation column 92. The side stream may be cooled and returned to the main fractionation column 92 to cool the main fractionation column 92. A heat exchanger may be in downstream communication with the side outlet 940, 950, or 960.

[0038] A recycle heavy naphtha stream may be taken in line 118 and returned to the main fractionation column 92 after cooling. A heavy naphtha product stream may be taken in line 98. Gasoline may be recovered from the light naphtha concentration stream in the concentration line 105.

[0039] The process slurry oil stream in process line 64 may comprise catalyst fines and remaining bottoms oil from which catalyst fines can be removed. The process slurry oil stream may have between about 500 wppm and about 6000 wppm, preferably between about 1000 and about 5000 wppm of catalyst fines. These products are more valuable if separated from each other and if the catalyst fines are removed from it.

[0040] The present disclosure provides passing the slurry oil stream in process line 64 to a filter vessel 80 to filter the catalyst fine. A hydrocarbon stream is passed to the filter vessel 80 to backflush the filter in the filter vessel 80 to produce a backflushed hydrocarbon stream comprising catalyst fines. The backflushed hydrocarbon stream is recycled to the reactor vessel 22. Applicants found that the heavy naphtha stream can be used to backflush the filter. Typically, the hydrocarbon stream used to backflush the filter vessel is heavy cycle oil (HCO), light cycle oil (LCO) or fresh feed which are typically a heavier hydrocarbon stream. The heavier hydrocarbon streams are used due to the temperature of the filter and properties of the slurry oil being filtered. Suitably, the heavier hydrocarbons may only be returned to the reactor riser. Thus, the backflushed hydrocarbon stream and catalyst re-enter the reactor system and get recycled back to the main column and main column bottoms section. This may cause issues such as increased erosion of the piping and equipment and lowering the value of the product, as previously described. We have found a suitable new backflush hydrocarbon stream and a backflush sequence to address these issues. The process discloses a lighter hydrocarbon, such as heavy naphtha for backflushing the filter vessel, which can then be returned to a location that bypasses the reactor riser and subsequently the main column. This eliminates the catalyst fines recycle to main column system and also brings an added benefit to the reactor performance.

[0041] Referring back to FIG. 1, a heavy naphtha stream in line 82 for the backflushing step may be taken through a valve from the heavy naphtha product stream in line 98. While backflushing the filter, the naphtha stream will dislodge the solids including the catalyst fines deposited in and on the filter. A backflushed naphtha stream may be taken in line 86 from the filter vessel 80 and recycled to the reactor vessel 22. Applicants found that recycling the backflushed naphtha stream to the stripping section 34 and over the top of the spent catalyst bed 21 is beneficial for the process for addressing the aforesaid issues. Recycling the backflushed naphtha stream to the top of the spent catalyst bed 21 mitigates the hydrocarbon carried along with spent catalyst into the regenerator, so the hydrocarbon stream can be recovered. The catalyst fines present in the backflushed naphtha stream in line 86 moves downwardly and collects in the spent catalyst bed 34. The naphtha stream moves upwardly in the reactor vessel. While moving upwardly, the naphtha stream may further crack into C8 aromatics, which is a valuable downstream petrochemicals feedstock. The naphtha and the C8 aromatics are removed with the gaseous cracked stream in the cracked line 32 and separated in the main fractionation column 92.

[0042] Referring back to FIG. 1, the slurry oil stream in process line 64 is passed to the filter vessel 80 where the slurry oil stream is passed through a filter. The filter vessel 80 is in downstream fluid communication with the main fractionation column 92. A filtered slurry oil stream is taken in line 84 from the filter vessel. When the filter requires backflushing, a backflush heavy naphtha stream is taken in line 82 from the heavy naphtha product line 98 and passed to the filter vessel 80 to backflush and remove the solids and sediments deposited on the filter. After backflushing the filter, the solids including the catalyst fines are taken in a backflushed naphtha stream. The backflushed naphtha stream is taken in line 86 from the filter vessel.

[0043] The backflushed naphtha stream in line 86 is recycled back to the reactor vessel 22. In an embodiment, backflushed naphtha in line 86 is passed through a distributor 87 into the stripping section 34. The outlet of the distributor 87 is located at or above the top of the spent catalyst bed 21 in the stripping section 34. In an embodiment, the outlet of the distributor 87 may be located in the spent catalyst bed 21 in the stripping section 34. The outlet of the distributor 87 may be located inside the disengaging chamber 27. Particularly, the outlet of the distributor 87 is located above or in the spent catalyst bed 21 in the disengaging chamber 27. The distributor 87 is in fluid downstream communication with the filter vessel 80. The distributor 87 feeds the backflushed hydrocarbon stream in line 86 to the top or in the spent catalyst bed 34 through the outlet of the distributor 87. In an embodiment, the line 86 to the distributor 87 passes through the wall 23 of the reactor vessel 22 and the wall 43 of the disengaging chamber 27 into the stripping section 34 to feed the distributor 87 which distributes the backflushed naphtha stream in line 86 over the top or in the spent catalyst bed 34. The catalyst fines present in the backflushed naphtha stream in line 86 move downwardly and collect in the spent catalyst bed 21. The backflushed naphtha stream is stripped from the catalyst fines by the stripping gas from line 33 and moves upwardly along with the gaseous cracked stream in the cracked line 32. While moving upwards, the naphtha stream may further crack into C8 aromatics, which is valuable for downstream petrochemicals feedstock. The naphtha and the C8 aromatics are removed with the gaseous cracked stream in the cracked line 32 and separated in the main fractionation column 92.

[0044] In an embodiment, a portion of the filtered slurry oil stream 84 may be taken in a recycle slurry oil stream in recycle line 57. The recycle slurry oil stream in line 57 may be recycled to the riser reactor 20. In an aspect, the recycle slurry oil stream in line 57 is recycled to the riser reactor 20 through the feed distributor 16. The feed distributor 16 is in fluid downstream communication with the filter vessel 80.

[0045] FIG. 2 shows an exemplary embodiment of the filter vessel 80 comprising a filter 88. A plurality of filters 88 may be employed in the filter vessel 80. A tube sheet 90 is provided in the filter vessel 80 which divides the filter vessel 80 into a filter chamber 89 below the tube sheet 90 and a filtrate chamber 92 above the tube sheet 90. The tube sheet 90 may comprise holes or some arrangements to permit the filter 88 on the tube sheet to communicate with the filtrate chamber 92 perhaps through an end of the filter. As shown, the filter chamber 89 comprises the filter 88. The slurry oil stream in line 64 is passed to the filter vessel 80 in filter chamber 89 of the filter vessel 80. A valve 39 is provided in the line 64 to control the flow of the slurry oil stream in line 64 to the filter vessel. In the filtering step, the slurry oil stream is passed through the filter 88 in the filter chamber 89 to allow liquid to pass while solids are retained to separate solids from the slurry oil. For solid-liquid separation, the filtering aperture size of the filter 88 can be selected to achieve the desired filtering precision for separation, wherein the filter 88 can be sintered metal powder plate, sintered wire web or made by any suitable method. In order to enhance filtering efficiency, the filtering temperature may be about 100 C. to about 350 C., or about 200 C. to about 320 C.

[0046] Filtered liquid oil passes from the filters 88 through the tube sheet 90 into the filtrate chamber 92. The tube sheet 90 separates the filter chamber 89 from the filtrate chamber 92. A filtered slurry oil stream is taken in a filtered oil line 84 from the filtrate chamber 92 of the filter vessel 80 perhaps near a top of the vessel 80. A valve 49 may be provided on the filtered slurry oil line 84. After a period of filtration, the filters 88 may become clogged with solids and sediments thereby diminishing the filtration flow rate. After the filtration period, to remove the clogged solids from the filters 88, a backflushing operation is initiated to backflush the filter 88 and remove the solids and sediments deposited thereon.

[0047] For backflushing, the backflushing naphtha stream is taken in line 82 and passed to the filter vessel 80 to backflush the filter 88. In backflushing step, the flow of the slurry oil stream in line 64 is stopped by closing the valve 39 on the line 64. In an aspect, a backflush gas in line 72 may be passed to the filter vessel 80 as part of the backflush operation. In an embodiment, the backflush gas in line 72 may be comprise nitrogen and/or fuel gas. The backflush gas is taken from a reservoir 70 and passed to the filter vessel 80 in line 72. A valve 19 may be provided on the backflush gas line 72 to regulate the flow of the backflush gas to the filter vessel 80. In an exemplary embodiment, the backflush gas in line 72 may be combined with the backflush naphtha stream in line 82 to provide a combined backflush stream in line 74. The combined backflush stream in line 74 is passed to the filter vessel 80. A valve 81 may be provided on the combined backflush line 74 to regulate the flow of the combined backflush stream to the filter vessel 80. In the filter vessel 80, the backflushing naphtha stream in line 82 and the backflush gas in line 72 are passed into the filtrate chamber 92 of the filter vessel 80 through the tube sheet 90 and through the filter 88 into the filter chamber 89. The backflush hydrocarbon stream and gas stream flow through the filter 88, dislodges the solids including the catalyst fines deposited on the filter 88 in a backflushed hydrocarbon stream. A backflushed gas stream may be removed from the filter chamber 89 of the filter vessel 80 in line 85. A valve 69 may be provided on the backflushed gas line 85. The backflushed hydrocarbon stream is taken in line 86 from a bottom of the filter chamber 89 of the filter vessel 80. The backflushed hydrocarbon stream in bottoms line 86 may be recycled to the reactor vessel 22 as described for FIG. 1. A valve 59 may be provided on the line 86 to regulate the flow of the backflushed hydrocarbon stream 86 to the reactor vessel 22.

[0048] The filter 88 may require an optional pre-backflush step before the backflushing step to remove any residual matter already deposited on the filter. The pre-backflush will ensure that mainly naphtha is sent to the stripping section 34. For pre-backflush step, a washing fluid from line 75 may be passed to the filter vessel 80 to pre-wash the filter 88. In pre-backflush step, the flow of the backflush naphtha stream is stopped by closing the valve 29 on the line 82. The washing fluid from line 75 is passed to the filter vessel 80 through line 74 by opening the valve 81 of the line 74. The washing fluid from line 75 passes through the filter 88 and removes some of the deposited residual matter on the filter. The washing fluid along with the residual matter is taken from the bottoms of the filter vessel 80 in line 86 by opening the valve 59 on the bottoms line 86. In an embodiment, the washing fluid may comprise a light cycle oil stream, a heavy cycle oil stream, or a mixture thereof. In an exemplary embodiment, the light cycle oil stream for prewashing may be taken from the LCO product stream in line 117 of the main fractionation column 92. In an exemplary embodiment, the heavy cycle oil stream for prewashing may be taken from the HCO product stream in line 115 of the main fractionation column 92.

[0049] In an embodiment, the backflush naphtha stream in line 82 may comprise a cracked naphtha stream. In an aspect, the backflushing naphtha stream in line 82 may comprise a cracked heavy naphtha stream. Passing the naphtha stream in line 82 to backflush the filter and routing the backflushed naphtha stream in line 86 to the stripping section 34, minimizes the hydrocarbon carried along with spent catalyst into the regenerator 90 where it is lost to combustion. Most of the naphtha in the backflushed stream 86 is recovered as product.

[0050] It is contemplated that the filter vessel 80 may be used in different configurations to provide necessary capacity and achieve desired quality for sufficient slurry oil filtration and separation. It is further contemplated that more than one filter vessel 80 may be used.

SPECIFIC EMBODIMENTS

[0051] While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims.

[0052] A first embodiment of the present disclosure is a process for catalytically cracking hydrocarbons comprising contacting a hydrocarbon feed stream with a catalyst to catalytically crack the hydrocarbon feed stream to provide a cracked stream and spent catalyst; disengaging the spent catalyst from the cracked stream in a reactor vessel; stripping hydrocarbons from the spent catalyst; fractionating the cracked stream in a main fractionation column into products comprising a slurry oil stream from a bottom of the main fractionation column; filtering the slurry oil stream in a filter vessel through a filter to provide a filtered slurry oil stream; backflushing the filter with a hydrocarbon stream to produce a backflushed hydrocarbon stream comprising catalyst fines; and recycling the backflushed hydrocarbon stream to the reactor vessel. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the hydrocarbon stream is a naphtha stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the step of backflushing the filter comprises passing a washing fluid to the filter vessel to wash the filter; and passing the hydrocarbon stream through the filter vessel to backflush the filter. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the washing fluid comprises light cycle oil, heavy cycle oil or a mixture thereof. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the step of recycling the backflushed hydrocarbon stream comprises passing the backflushed hydrocarbon stream to the reactor vessel at a location above or in a catalyst bed in the reactor vessel. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the reactor vessel communicates with a riser reactor and further comprises a disengaging chamber in fluid communication with the riser reactor, and a stripping section in fluid communication with the disengaging chamber. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising passing the backflushed hydrocarbon stream to the stripping section through a distributor. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the distributor has an outlet located inside the disengaging chamber. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the naphtha stream is taken from the main fractionation column. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising recycling the filtered slurry oil stream to the riser reactor.

[0053] A second embodiment of the present disclosure is a process for catalytically cracking hydrocarbons comprising contacting a hydrocarbon feed stream with a catalyst to catalytically crack the hydrocarbon feed stream to provide a cracked stream and spent catalyst; disengaging the spent catalyst from the cracked stream into a catalyst bed in a reactor vessel; stripping hydrocarbons from the spent catalyst; fractionating the cracked stream in a main fractionation column into products comprising a slurry oil stream from a bottom of the main fractionation column; filtering the slurry oil stream in a filter vessel through a filter to provide a filtered slurry oil stream; backflushing the filter with a naphtha stream to produce a backflushed naphtha stream comprising catalyst fines; and recycling the backflushed naphtha stream to a location above or in the catalyst bed in the reactor vessel. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the naphtha stream is a heavy naphtha stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the naphtha stream is taken from the main fractionation column. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the step of backflushing the filter comprises passing a washing fluid to the filter vessel to wash the filter; and passing the naphtha stream through the filter vessel to backflush the filter.

[0054] A third embodiment of the invention is an apparatus for catalytically cracking hydrocarbons, comprising a riser reactor, a disengaging chamber in fluid communication with the riser reactor, a stripping section in fluid communication with the disengaging chamber; a filter; and a distributor in fluid communication with the filter and the stripping section in fluid communication with the filter. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph, wherein the filter is in a filter vessel and the distributor is in fluid communication with the filter vessel and the stripping section is in fluid communication with the filter vessel. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising a main fractionation column in fluid communication with the riser reactor and the filter vessel in fluid communication with the main column. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph, wherein the distributor is located inside the disengaging chamber. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph, wherein the distributor is located above or in a catalyst bed in the disengaging chamber. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising a second distributor in fluid communication with the filter and the riser reactor in fluid communication with the second distributor.

[0055] Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of this invention, without departing from the spirit and scope thereof, to make various changes and modifications of the invention and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0056] In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.