Process and Apparatus for Catalytically Cracking Hydrocarbons with Recycled Slurry Filter Backflush

The field is related to catalytically cracking of hydrocarbons. The field particularly relates to catalytically cracking hydrocarbons and recycling a filter backflush stream.

FCC technology, now more than 50 years old, has undergone continuous improvement and remains the predominant source of gasoline production in many refineries. This gasoline, as well as lighter products, is formed from cracking heavier, less valuable hydrocarbon feed stocks such as gas oil and residues.

In its most general form, the FCC process and apparatus comprises a reactor that is closely coupled with a regenerator, followed by downstream hydrocarbon product separation. Hydrocarbon feed contacts catalyst in the reactor to crack the hydrocarbons down to smaller molecular weight products. During this process, coke tends to accumulate on the catalyst which is burned off in the regenerator.

Although the FCC process upgrades heavy oil into lighter, more valuable products, it also creates a heavier, hydrogen deficient product known as slurry oil or main column bottoms. Slurry oil is obtained from the bottom of the main fractionation column and has a nominal boiling point starting at least at about 250° C. (482° F.). The slurry oil is typically blended into fuel oil, bunker fuel, or another similarly low value product pool. The slurry oil typically contains a fraction of light cycle oil (LCO) that is, if recovered, ideally used in distillate (diesel) blending. The fraction of LCO present in the slurry oil is adjusted to control the bottom temperature in the main fractionation column for process reliability reasons, and typically ranges from 1 to 15 wt-% of the total slurry oil. Too hot of a temperature in the main column bottoms promotes coking and fouling in the slurry oil recycle circuit. However, leaving LCO in the slurry oil reduces the total value of products recovered from the FCC process. In ideal operation, the refiner would like to maximize LCO recovery from the slurry oil to maximize product value upgrade.

In addition to LCO, the slurry oil also contains small catalyst particles, or catalyst fines, carried over in the hydrocarbon vapors from the FCC reactor. These fines are typically sized in the range of about 0 to about 40 microns and concentrated in the range of about 1000 to about 5000 wppm. Refiners often want to remove these fines to increase the value of the product, typically referred to as clarified oil when fines are removed.

Currently most FCC units do not have slurry filter installed and hence the basic sediment and water (BS&W) in the slurry oil recycle circuit may range from about 1000 to about 3000 wppm. Most of this BS&W is contributed by the ash content, which is from the FCC catalyst that escapes the reactor cyclones. If a slurry filter is installed, all of this catalyst is returned back to the riser along with heavy cycle oil (HCO) or raw oil. This sets up a recycle loop and leads to an increase in BS&W by about 2.5 to about 3 times the original value. In some instances, BS&W may be present as high as 7000-10000 ppm in the slurry oil filter inlet. The only way out for these fines to escape out of the current reactor-regenerator system is for coke to build up on catalyst particles to increase its size sufficiently to be separated from the product gases by the reactor cyclones, which then gets passed onto the regenerator. Coke is burned off in the regenerator to make the catalyst fines again which fines will not be captured by the regenerator cyclones but will pass out with the flue gas. The high solids content in slurry oil recycle circuit leads to increased erosion of the piping and equipment. Reducing the solids in this circuit will improve reliability and on-stream availability.

A process and apparatus of improved efficiency in removing catalyst fines from slurry oil is sought that would increase the recovery of catalyst fines, reduce the erosion of piping and loss of containment, and improve the performance and reliability of the unit.

A process and apparatus 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 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. The process and apparatus recycle the backflushed hydrocarbon stream to the stripping section in the reactor vessel and over the top of a catalyst bed. This way the stripper mitigates hydrocarbon carried along with spent catalyst into the regenerator and also cracks and recovers the hydrocarbons of the backflushed hydrocarbon stream downstream.

Additional features and advantages of the present disclosure will be apparent from the description, figure and claims provided herein.

The term “communication” means that material flow is operatively permitted between enumerated components.

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.

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.

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.

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

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.

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.

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 .

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

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

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.

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

illustrates a process and apparatusfor catalytically cracking hydrocarbons. The process and apparatuscomprise an FCC unitand an FCC recovery sectionthat includes a filter vessel.

The FCC unitincludes an FCC reactorcomprising a riser reactorand a catalyst regenerator. A hydrocarbon feed stream comprising an FCC feedstock in a feed lineis fed to the FCC reactorthrough feed distributors. The riser reactoris in fluid downstream communication with the feed distributorfor feeding the hydrocarbon feed stream into the riser reactor.

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.

In the FCC unit, the FCC feed stream in the feed lineis fed to the FCC reactorto be contacted with a regenerated cracking catalyst. Specifically, in an embodiment, regenerated cracking catalyst entering from a regenerator conduitis contacted with the FCC feed stream in a riser reactorof the FCC reactor. The regenerator conduitis in downstream communication with the regenerator. The riser reactorhas an inletin downstream communication with said regenerator conduit. The regenerator conduitis connected to the FCC riser reactorat a lower end.

In the riserof the FCC reactor, the FCC feed stream is contacted with catalyst to catalytically crack the FCC feed stream to provide a cracked stream.

The contacting of the hydrocarbon feed stream with cracking catalyst may occur in the riser reactorof the FCC reactor, extending upwardly to the bottom of a reactor vessel. The reactor vesselhas an outer wall. The contacting of feed and catalyst is fluidized by gas from a fluidizing line. 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 reactorinto the reactor vessel. In the FCC reactor, 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 reactorare thereafter discharged from the riser outletinto a disengaging chamberwhich contains the riser outlet. The disengaging chamberis in downstream fluid communication with the riser reactor. The disengaging chamberhas an outer wall. The cracked stream of hydrocarbon products is disengaged from the spent catalyst in the disengaging chamberusing a rough-cut separator. Cyclonic separators which may include one or two stages of cyclonesin the reactor vesselfurther separate catalyst from hydrocarbon products. A cracked stream of product gases exits the reactor vesselthrough a product outletto a cracked linefor transport to a downstream FCC recovery section. In an embodiment, the regenerator conduitis in downstream communication with the disengaging chamber. The outlet temperature of the cracked products leaving the riser reactormay be between about 472° C. (850° F.) and about 555° C. (1031° F.).

Inevitable side reactions occur in the riser reactorleaving 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 bedin the stripping sectionwhere steam from lineis injected through a distributorto purge any residual hydrocarbon vapor. The stripping sectionis in downstream fluid communication with the disengaging chamber. After the stripping operation, the spent catalyst is fed to the catalyst regeneratorthrough a spent catalyst conduit. The catalyst regeneratormay be in downstream communication with the riser reactor, specifically, the riser outlet.

depicts a regeneratorknown as a combustor. However, other types of regenerators may be equally used. In the catalyst regenerator, a stream of oxygen-containing gas, such as air, is introduced from linethrough an air distributorto contact the coked catalyst, burn coke deposited thereon, and provide regenerated catalyst and flue gas. Catalyst and air flow upwardly together along a combustor riserlocated within the catalyst regeneratorand, after regeneration, are initially separated by discharge through a disengager. Finer separation of the regenerated catalyst and flue gas exiting the disengageris achieved using first stage separator cyclone, and second stage separator cyclone, respectively, within the catalyst regenerator. Catalyst separated from flue gas dispenses through diplegs from cyclones,while flue gas significantly lighter in catalyst sequentially exits cyclones,and exits the regenerator vesselthrough a flue gas outletin a flue line. The regenerated catalyst is recycled back to the riser reactorthrough the regenerated catalyst conduit.

As a result of the coke burning, the flue gas vapors exiting at the top of the catalyst regeneratorin the flue linecontain CO, COand HO, 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.

In the FCC recovery section, the cracked stream in the cracked lineis separated into product streams. The gaseous cracked stream in the cracked lineis fed to a lower section of a FCC main fractionation column. The main fractionation columnis in downstream fluid communication with the riser reactorand the FCC reactor. In the main fractionation column, the cracked stream is fractionated into products. Several fractions may be separated and taken from the main fractionation columnincluding a heavy slurry oil stream from a main column bottom outletin a bottoms line, a HCO stream in a heavy line, a LCO stream in a light lineand a heavy naphtha stream in a naphtha line. Gasoline and gaseous light hydrocarbons are removed in an overhead linefrom the main fractionation columnand condensed before entering a main column receiver. In the main column receiver, vapor is separated from the liquid component. A condensed unstabilized, light naphtha stream is removed in a liquid overhead linewhile a light hydrocarbon stream is removed in vapor overhead linefrom the main column receiver. An aqueous stream is removed from a boot in the receiverin line. A portion of the light naphtha stream in the liquid overhead linemay be refluxed to the main fractionation columnin a reflux line. A light naphtha product stream may be taken in a concentration line. Both streams in linesandmay enter a vapor recovery section (not shown) downstream of the main fractionation column.

The light unstabilized naphtha fraction may have an initial boiling point (IBP) in the Crange, 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.

The main fractionation columnhas the main column bottoms outletin a bottomof the main fractionation columnfrom which a slurry oil stream is taken. The main column bottoms outletis taken from the bottomof the main fractionation columnmeaning below a lowest tray in the column. The feed distributorsin the FCC reactormay be in downstream communication with the main column bottoms outlet. A portion of the slurry oil stream in the bottoms linemay be cooled and recycled in lineback to the main fractionation column. A process slurry oil stream is taken from the slurry oil stream in a process line.

A lowest auxiliary outletand a penultimate lowest outletmay be in the sideof the main fractionation column. The HCO stream may be taken from the lowest auxiliary outletof the main fractionation column. An HCO stream is taken in linefrom the lowest auxiliary outletin the sideof the main fractionation column. An HCO product stream is taken in linefrom lineregulated by a control valveon line. A recycle HCO stream may be taken in linefrom line, cooled and returned to the main column.

A diesel stream may be recovered in an LCO product lineat a flow rate regulated by a control valvethereon. An LCO stream is taken in linefrom the penultimate lowest auxiliary outletin the sideof the main fractionation column. An LCO product stream is taken in linefrom lineregulated by a control valveon line. A recycle LCO stream is taken in linefrom line, cooled and returned to the main column. Any or all of the product streams in lines,, andmay be cooled and pumped back to the main columntypically at a higher location. Specifically, a side stream may be taken from the side outlet,, orin the sideof the main fractionation column. The side stream may be cooled and returned to the main fractionation columnto cool the main fractionation column. A heat exchanger may be in downstream communication with the side outlet,, or.

A recycle heavy naphtha stream may be taken in lineand returned to the main fractionation columnafter cooling. A heavy naphtha product stream may be taken in line. Gasoline may be recovered from the light naphtha concentration stream in the concentration line.

The process slurry oil stream in process linemay 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.

The present disclosure provides passing the slurry oil stream in process lineto a filter vesselto filter the catalyst fine. A hydrocarbon stream is passed to the filter vesselto backflush the filter in the filter vesselto produce a backflushed hydrocarbon stream comprising catalyst fines. The backflushed hydrocarbon stream is recycled to the reactor vessel. 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.

Referring back to, a heavy naphtha stream in linefor the backflushing step may be taken through a valve from the heavy naphtha product stream in line. 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 linefrom the filter vesseland recycled to the reactor vessel. Applicants found that recycling the backflushed naphtha stream to the stripping sectionand over the top of the spent catalyst bedis beneficial for the process for addressing the aforesaid issues. Recycling the backflushed naphtha stream to the top of the spent catalyst bedmitigates 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 linemoves downwardly and collects in the spent catalyst bed. 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 lineand separated in the main fractionation column.

Referring back to, the slurry oil stream in process lineis passed to the filter vesselwhere the slurry oil stream is passed through a filter. The filter vesselis in downstream fluid communication with the main fractionation column. A filtered slurry oil stream is taken in linefrom the filter vessel. When the filter requires backflushing, a backflush heavy naphtha stream is taken in linefrom the heavy naphtha product lineand passed to the filter vesselto 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 linefrom the filter vessel.

The backflushed naphtha stream in lineis recycled back to the reactor vessel. In an embodiment, backflushed naphtha in lineis passed through a distributorinto the stripping section. The outlet of the distributoris located at or above the top of the spent catalyst bedin the stripping section. In an embodiment, the outlet of the distributormay be located in the spent catalyst bedin the stripping section. The outlet of the distributormay be located inside the disengaging chamber. Particularly, the outlet of the distributoris located above or in the spent catalyst bedin the disengaging chamber. The distributoris in fluid downstream communication with the filter vessel. The distributorfeeds the backflushed hydrocarbon stream in lineto the top or in the spent catalyst bedthrough the outlet of the distributor. In an embodiment, the lineto the distributorpasses through the wallof the reactor vesseland the wallof the disengaging chamberinto the stripping sectionto feed the distributorwhich distributes the backflushed naphtha stream in lineover the top or in the spent catalyst bed. The catalyst fines present in the backflushed naphtha stream in linemove downwardly and collect in the spent catalyst bed. The backflushed naphtha stream is stripped from the catalyst fines by the stripping gas from lineand moves upwardly along with the gaseous cracked stream in the cracked line. 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 lineand separated in the main fractionation column.

In an embodiment, a portion of the filtered slurry oil streammay be taken in a recycle slurry oil stream in recycle line. The recycle slurry oil stream in linemay be recycled to the riser reactor. In an aspect, the recycle slurry oil stream in lineis recycled to the riser reactorthrough the feed distributor. The feed distributoris in fluid downstream communication with the filter vessel.

shows an exemplary embodiment of the filter vesselcomprising a filter. A plurality of filtersmay be employed in the filter vessel. A tube sheetis provided in the filter vesselwhich divides the filter vesselinto a filter chamberbelow the tube sheetand a filtrate chamberabove the tube sheet. The tube sheetmay comprise holes or some arrangements to permit the filteron the tube sheet to communicate with the filtrate chamberperhaps through an end of the filter. As shown, the filter chambercomprises the filter. The slurry oil stream in lineis passed to the filter vesselin filter chamberof the filter vessel. A valveis provided in the lineto control the flow of the slurry oil stream in lineto the filter vessel. In the filtering step, the slurry oil stream is passed through the filterin the filter chamberto 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 filtercan be selected to achieve the desired filtering precision for separation, wherein the filtercan 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.

Filtered liquid oil passes from the filtersthrough the tube sheetinto the filtrate chamber. The tube sheetseparates the filter chamberfrom the filtrate chamber. A filtered slurry oil stream is taken in a filtered oil linefrom the filtrate chamberof the filter vesselperhaps near a top of the vessel. A valvemay be provided on the filtered slurry oil line. After a period of filtration, the filtersmay become clogged with solids and sediments thereby diminishing the filtration flow rate. After the filtration period, to remove the clogged solids from the filters, a backflushing operation is initiated to backflush the filterand remove the solids and sediments deposited thereon.

For backflushing, the backflushing naphtha stream is taken in lineand passed to the filter vesselto backflush the filter. In backflushing step, the flow of the slurry oil stream in lineis stopped by closing the valveon the line. In an aspect, a backflush gas in linemay be passed to the filter vesselas part of the backflush operation. In an embodiment, the backflush gas in linemay be comprise nitrogen and/or fuel gas. The backflush gas is taken from a reservoirand passed to the filter vesselin line. A valvemay be provided on the backflush gas lineto regulate the flow of the backflush gas to the filter vessel. In an exemplary embodiment, the backflush gas in linemay be combined with the backflush naphtha stream in lineto provide a combined backflush stream in line. The combined backflush stream in lineis passed to the filter vessel. A valvemay be provided on the combined backflush lineto regulate the flow of the combined backflush stream to the filter vessel. In the filter vessel, the backflushing naphtha stream in lineand the backflush gas in lineare passed into the filtrate chamberof the filter vesselthrough the tube sheetand through the filterinto the filter chamber. The backflush hydrocarbon stream and gas stream flow through the filter, dislodges the solids including the catalyst fines deposited on the filterin a backflushed hydrocarbon stream. A backflushed gas stream may be removed from the filter chamberof the filter vesselin line. A valvemay be provided on the backflushed gas line. The backflushed hydrocarbon stream is taken in linefrom a bottom of the filter chamberof the filter vessel. The backflushed hydrocarbon stream in bottoms linemay be recycled to the reactor vesselas described for. A valvemay be provided on the lineto regulate the flow of the backflushed hydrocarbon streamto the reactor vessel.

The filtermay 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. For pre-backflush step, a washing fluid from linemay be passed to the filter vesselto pre-wash the filter. In pre-backflush step, the flow of the backflush naphtha stream is stopped by closing the valveon the line. The washing fluid from lineis passed to the filter vesselthrough lineby opening the valveof the line. The washing fluid from linepasses through the filterand 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 vesselin lineby opening the valveon the bottoms line. 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 lineof the main fractionation column. In an exemplary embodiment, the heavy cycle oil stream for prewashing may be taken from the HCO product stream in lineof the main fractionation column.

In an embodiment, the backflush naphtha stream in linemay comprise a cracked naphtha stream. In an aspect, the backflushing naphtha stream in linemay comprise a cracked heavy naphtha stream. Passing the naphtha stream in lineto backflush the filter and routing the backflushed naphtha stream in lineto the stripping section, minimizes the hydrocarbon carried along with spent catalyst into the regeneratorwhere it is lost to combustion. Most of the naphtha in the backflushed streamis recovered as product.

It is contemplated that the filter vesselmay 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 vesselmay be used.

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.

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.