US3376213A - Catalytic cracking reactor and method of preventing the formation of coke on the conduits - Google Patents

Description

Aprii 2, 1968 K. A. HARPER 3,375,213

CATALYTIC CRACKING REACTOR AND METHOD OF PREVENTING THE FORMATION OF COKE ON THE CONDUITS Filed April 9, 1965 CATALYST EFFLUENT E STEAM S R .V m M NW R HA m H f, 7 IA. A K 3 m Y F B G I F v 2 8 United States Patent Ofilice 3,375,213 Fatented Apr. 2., 1968 3,376,213 CATALYTIC CRACKING REACTUR AND METHOD OF PREVENTING THE FDRMATEON F COKE ON THE CUNDUITS Kenneth A. Harper, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Apr. 9, 1965, Ser. No. 447,020 11 Claims. (Cl. 208-48) AESTRAQT OF THE DISCLOSURE conduits.

This invention relates to an improved catalytic cracki g reactor structure and method of injecting separate liquid oil and vaporous hydrocarbon feed thereto.

A conventional method of converting hydrocarbons to more valuable products involves their high temperature conversion by passing the feed hydrocarbons downwardly through a gravitating bed of particulate solid particles which act as heat carriers and catalyst. Methods and apparatus for efiecting such a process are disclosed in the Van Pool patents, US. 3,131,031 and 2,949,347. In these patents it is disclosed that the feed in both liquid and vapor form is injected into the reactor in admixture in a single conduit. It has been found that this type of apparatus and method of injecting the mixed feeds results in substantial coke deposition within the feed injection conduit, particularly at the bend or elbow therein. It has been found that part of this coking within the feed injection conduit is caused by too long a contact time between the liquid portion of the feed that the vapor portion which is initially at higher temperature than the liquid portion, whereby the liquid oil, being more amenable to coking, deposits coke before reaching the gravitatiug bed of catalyst.

This invention is concerned with an arrangement of apparatus and a method for more efiiciently introducing separate vapor and liquid hydrocarbon streams into a high temperature conversion or cracking zone which minimizes coke deposition in the apparatus upstream of actual contact with the catalyst.

Accordingly, it is an object of the invention to provide an improved arrangement of apparatus for the high temperature conversion of separate feeds of liquid and vaporous hydrocarbons. A further object is to provide an improved means of injecting a hot stream of oil at a term perature near the incipient cracking thereof and a hydrocarbon vapor stream at a higher temperature than the liquid oil stream with mixing thereof prior to contacting the mixed feeds with the catalyst in a catalytic conversion zone. Another object is to provide an improved method of introducing the aforesaid liquid oil-vaporous hydrocarbon stream in admixture to a catalytic reaction zone. Other objects of the invention will become apparent to one skilled in the art upon consideration of the accompanying disclosure.

A broad aspect of the invention as it relates to the injection means comprises a relatively large diameter conduit for the introduction of a hot vapor stream of lighter hydrocarbon material having a first section extending laterally from an inlet in the upright wall of a reactor to an axial locus within the reactor above a mixing and distribution means for the hydrocarbons and a second section extending vertically from the innerv axial end of the first section into the mixing and distribution means; and a relatively small diameter conduit for the liquid oil stream extending from an inlet in the reactor at a level above the upper end of the second section of the large diameter conduit having an axial delivery end section leading into the upper end of the second section of the large diameter conduit for injecting liquid oil axially into the vapor stream in said second section, thereby decreasing contact of the liquid oil with the wall of said second section and minimizing contact time of the liquid and vapor streams. In operating in accordance with the invention, the liquid oil stream is introduced to the reactor at a temperature near the incipient cracking temperature at which only a slight increase in temperature initiates cracking and coke deposition. The vapor stream is preheated to a temperature substantially above the temperature of the liquid oilstream and has a higher cracking temperature. Hence the vapor stream imparts heat to the liquid oil stream during mixing and initiates cracking of the oil so that contact of the oil with the apparatus, particularly the injection conduit, should be avoided as much as possible during this heating and mixing period.

A broad aspect of the method comprises injecting into a catalytic reaction zone a stream of hot liquid oil at a temperature near incipient cracking temperature having a tendency to coke when heated to a higher temperature and a hotter hydrocarbon vapor stream wherein the hot liquid oil stream is injected directly into the hot vapor stream axially into a relatively short, straight cylindrical conduit leading into a catalytic zone; the hot oil being injected along the line of flow of the hot vapor in a small stream so that the injected oil is surrounded by vapor to substantially prevent contacting of liquid oil with the wall of the conduit. The liquid is particularly applicable to the injection of a heavy gas oil at a temperature in the range of about 650 to 725 F. into a light gas oil vapor stream at a temperature in the range of about 800- 0 F. In such a method or process, the usual cracking catalysts may be utilized, particularly silica-alumina catalysts having high cracking activity.

A more complete understanding of the invention may be had by reference to the accompanying schematic drawing of which FIGURE 1 is a vertical view in partial cross section showing a preferred arrangement of apparatus in accordance with the invention; FIGURE 2 is a plan view in section taken on the line 22 of FIGURE 1; FIGURE 3 is a fragmentary view in cross section of the feed distributing means in the reactor of FIGURE 1; and FIG- URE 4 is a fragmentary view in cross section of the injection conduits of FIGURE 1 at their juncture.

Referring to FIGURE 1 of the drawing, a catalytic reactor 10 comprises an upright shell 12 provided with partitions 14, 16, 18, and 20 which divide the reactor into an upper reaction zone 22, a product withdrawal zone 24, and a stripping zone 26. The upright section of the reactor is provided with catalyst feeding and distribution means comprising catalyst inlet conduits 28 which lead into a surge box 30 from which several downlegs 32 (three in the reactor shown) extend to an upright frusto-conical member 34 which is capped by cylindrical section 36 into which the catalyst particles feed directly. Obviously the number of downlegs 32 may be varied without departing from the structure of the invention.

The vapor inlet or injection conduit comprises an inlet connector 38 which connects with a feed line 40 and with a laterally extending conduit 42 which leads to an axial locus within the reactor directly above the feed distribution means identified hereinafter. The inner end of conduit 42 joins axial delivery conduit 44 which is a relatively short conduit for the purpose of minimizing the contact time between the hot vaporous feed and the oil feed injected thereto.

The liquid oil injection conduit comprises an axial conduit 46 having a connector 48 thereon which joins feed line 50. The delivery end of feed conduit 46 leads axially into the upper end of vapor conduit 44 and is of considerably smaller diameter than conduit 44. This assures injecting the liquid oil axially along the direction of flow of the injected vapor stream at this point so as to minimize contacting of the wall of conduit 44 with liquid oil while the two streams are flowing toward the reaction zone.

The means of mixing and distributing the two feed streams into the catalyst comprises a pair of laterally extending, vertically spaced-apart discs 52 and 54 which provide a passageway 56 therebetween for radially outward flow of the mixed streams of feed. Upper disc 52 has an axial opening into which the delivery end of conduit 44 extends in sealed relation therewith. Discs 52 and 54 are concentric with respect to the frusto-conical member 34 and the reactor shell as well as with delivery conduit 44. The structure shown and described provides an annular passageway 58 for gravitation of catalyst particles in a compact mass adjacent the periphery of the distribution discs so that the mixed feed is injected into the gravitating compact curtain of catalyst particles in intimate contact therewith for elfecting the desired catalytic cracking and/ or other high temperature reaction desired.

The structure of the generally conical discs 52 and 54 is shown more clearly in FIGURE 3 and comprises spacer elements 60 which may be transverse sections of pipe or rod welded at the ends to the upper and lower discs 52 and 54, respectively. These spacer elements 60 are distributed uniformly around the periphery of the discs. They may also be formed of metal plates placed edgewise in radial arrangement in the structure to minimize resistance to flow and provide a larger percent of the space between the plates for outward flow of feed near the periphery thereof. Stiltening structure for the arrangement of discs further comprises an inverted frusto-conical member 62 attached by welding to the bottom side of disc 54 and a ring 64 similarly attached to the bottom surface of disc 54. Between ring 64 and member 62 are positioned a series of 6 radial gussets 66 at several equal intervals such as 60 apart around the ring 64.

While discs 52 and 54 are shown as frusto-conical terminating in a generally horizontal lip section at the periphery, it is not essential that these discs be in this form since horizontal flat plates properly spaced apart will suffice for the intended function of this structurehlt is also feasible to fabricate the upper disc in iirusto-conical form without the horizontal lip section and utilize a fiat circular disc for member 54. The frusto conical form of the upper disc has some advantage in facilitating flow of catalyst thereover. Inverted frusto-conical member 62 may also be in the form of a complete cone so as to enclose the bottom side of the disc 54.

The gas-solids separating means in the lower portion of reactor section 22 comprises upright withdrawal pipes 68 for product gases which are capped by umbrella-like members 70 in unsealed relation with the pipes so as to provide for entry of gases withhout entry of catalyst particles thereto. These pipes 68 extend through partition 14 into efiluent collecting space 24 for discharge or recovery through outlet 72.

The catalyst recovery means comprises pipes or tubes 74 extending from the catalyst bed above plate 14 thru partition 16 to distributors 76 which connect with another series of pipes or conduits 78 for delivery of the catalyst to a series of separate compartments in annular arrangement around the lower section of the reactor between partitions 18 and 20. These separate compartments are supplied with steam thru a like number of lines 80 for the stripping step. The steam and stripped hydrocarbons from the catalyst are discharged thru outlet 72 along with the recovered hydrocarbons for passage to fractionating and recovery means not shown. The effluent line 82 con meets with the lower section of the catalyst space between partitions 18 and 20 for withdrawal of catalyst and passage thereof to regeneration equipment, not shown.

In FIGURE 2 is shown the plan view of the catalyst feeding apparatus as well as the feed injection arrangement and is self-explanatory when viewed in conjunction with the distributor of FIGURE 1. Corresponding parts in FIGURE 2 are correspondingly numbered.

Referring to FIGURE 4 conduit 42 connects with con duit 44 by means of elbow 45. Elbow 45 may be a L or any larger angle substantially less than 180. Conduit 46 is jointed at connector 47 and is provided with nozzle 49 which has a flange 51 extending between the two halves or connector 47. Conduit 46 and nozzle 49' are co-axial with conduit 44 and directed along the line of flow of vapors in conduit 44.

The catalyst used in the process is usually in the form of small beads or pellets to A in diameter. Steam is injected thru vapor feed line 40 in admixture with the vapor feed and thru line 37 into the upper section of reactor 10 to prevent carbon deposition on the apparatus above the catalyst bed. The steam injected thru line 37 passes thru the catalyst bed and is recovered thru efiluent outlet 72 along with steam from lines 40 and 80.

Specific conditions and ranges of operation are presented in the table below to illustrate but not unnecessarily limit the invention.

TABLE Specific Range Liquid Feed (Gas Oil):

API at 60 F 21. 8 1526 IBP, F 550 500-600 B arrels/Hour 50 Temperature, F- 700 650-725 Vapor Feed (Light Gas 0 API at 60 F. (liq) 26. 6 20-82 IBP, 400 375-600 Barrels/Hour (vapor measured as qu' 400 Temperature, F 830 800-850 Steam Feed (with Vapor Feed):

Pounds/Hour 4, 000 Steam to Reactor Vessel: Pounds/Hour. 50-200 Vapor/Liquid Vol. Ratio 8:1 411-2021 Catalyst (Silica-Alumina):

Sire, inch (avg) 0.125 /s-%a Temperature, F. 1,025 000-1, 100 Reactor Conditions:

Avg. ten1p., F 890 850 925 Pressure,.p.s.l.g 12 8-l5 Oat/Oil Wt. ratio.

In one embodiment of the invention in a cracking reactor having an 11 5' ID, conduit 42 had a 14" dimeter and section 44 had a length of about 3, while conduit 46 had a diameter of 3" and nozzle 49 had a diameter of 1%.".

The invention described reduces coke deposition in the apparatus described by decreasing the time of contact of the liquid and vapor feeds before contacting the same with the catalyst and by providing a vapor barrier around the liquid feed as it enters the core of the vapor feed-and passes therewith into the distribution means for radial injection into the catalyst curtain and bed. The vapor barrier is enhanced by vaporization of liquid oil adjacent the periphery of the injected liquid oil stream where it contacts the hotter vapor stream.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. A method of catalytically cracking a hot liquid bydrocarbon oil stream and a hotter hydrocarbon vapor stream, said oil tending to coke when mixed with said hot vapor stream, which comprises the steps of:

(a) injecting said vapor stream thru a short relatively large diameter conduit downwardly and axially into a cracking zone;

(b) injecting a relatively small diameter stream of said hot liquid oil axially of and directly into said vapor stream so that the injected oil is surrounded by and in contact with said vapor stream to substantially avoid contact of said oil with the walls .of said conduit; and

(c) deflecting the resulting mixed streams from steps (a) and (b) radially outwardly into a descending annular curtain of hot particulate cracking catalyst so as to effect contact thereof with said catalyst under cracking conditions to crack hydrocarbons of both streams.

2. The method of claim 1 wherein said oil is a heavy oil at a temperature in the range of about 650 to 725 F. and said vapor is at a temperature in the range of about 800 to 850 F.

3. The method of claim 2 wherein said heavy oil is a heavy gas oil and said vapor stream is a light gas oil.

4. Apparatus for catalytically cracking a mixed feed of heavy oil and lighter hydrocarbons comprising in combination:

(1) an upright reaction vessel having catalyst inlet means in its upper section communicating with catalyst distribution means for gravitating an annular curtain of catalyst around the axis of said vessel, a catalyst outlet and a steam inlet in its lower section, and a product outlet from its intermediate section;

(2) a vapor feed conduit passing into said vessel laterally thru the upright wall of said vessel and then obliquely to a locus above the catalyst distribution means of (1) and then downwardly and axially of said vessel to a level within said curtain of catalyst;

(3) a liquid feed conduit extending into said vessel from a level above the axial portion of the conduit of (2) and into the vapor conduit of (2) in sealed relation therewith, said liquid feed conduit being of smaller transverse cross section than said vapor conduit and terminating adjacent the juncture with said liquid feed conduit concentric with the axial section thereof so as to deliver the liquid feed stream into direct contact with the central portion of the vapor feed stream;

(4) bafile means axially below the lower end of the vapor conduit of (2) for distributing the resulting mixed feeds radially outwardly from the lower end of the conduit of (2) into the curtain of catalyst .of (1); and

(5) means in said vessel intermediate the product outlet and the catalyst distribution means of 1) for separating reaction product gases from catalyst and passing said gases to said outlet.

5. The apparatus of claim 4 including an internal axial nozzle within and adjacent the lower end of the liquid feed inlet of (3) for concentrating the liquid feed axially of the vapor feed stream and minimizing deposition of liquid feed on the wall of the axial section of the conduit of (2).

6. The apparatus of claim 4 wherein the catalyst distribution means of 1) comprises an upright frusto-conical member communicating thru its upper end with said catalyst inlet means and the means of (4) comprises a pair of vertically spaced-apart discs Within said member forming an annular passage with said member for flow of catalyst and fluids, the upper disc having an axial opening communicating with the lower end of the axial section of the vapor conduit of (2) to provide for radially outward flow of fluids between said discs into gravitating catalyst in said annular passageway.

7. The apparatus of claim 6 including an internal axial nozzle within and adacent the lower end of the liquid teed inlet of (3) for concentrating the liquid feed axially of the vapor feed stream and minimizing deposition of liquid feed on the wall of the axial section of the conduit of (2).

8. Means for injecting a hot hydrocarbon vapor stream and a hot liquid hydrocarbon oil stream having a tendency to coke, to an axial mixing and distribution means within an upright reactor, comprising:

(1) a relatively large diameter conduit for said vapor stream having a first section extending laterally and obliquely from an inlet in the upright wall of said reactor to an axial locus within said reactor above said mixing and distribution means and a second section extending vertically from the inner axialend of said first section into said mixing and distribution means; and

(2) a relatively small diameter conduit for said liquid oil stream extending from an inlet in said reactor at a level above the upper end of the second section of (1) having an axial delivery end section leading into and terminating at the upper end of the second section of the conduit of (1) for injecting liquid oil axially into direct contact with the larger diameter vapor stream in said second section, thereby decreasing contact of said oil in liquid form with the wall of said second section.

9. The means of claim 8 including an internal axial nozzle in said axial delivery end section for concentrating said liquid stream axially of the vapor stream in said second section.

10. The means of claim 8 wherein the conduit of (2) extends axially from an axial inlet in the top of said reactor.

11. The means of claim 9 wherein the conduit of (2) extends axially from an axial inlet in the top of said reactor.

References Cited UNITED STATES PATENTS 2,587,669 3/1952 Weinrich 208-166 2,886,520 5/1959 Cicalese 208167 ABRAHAM RIMENS, Primary Examiner.

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