US2775548A - Hydrocarbon conversion system - Google Patents

Description

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ATTORNEY Dec. 25, 1956 R. KOLLGAARD HYDROCARBON CONVERSION SYSTEM Filed April 30, 1952 United States Patent O HYDROCARBON CONVERSION SYSTElv/I Application April 30, 1952, Serial No. 285,279 5 Claims. (Cl. 196-52) This invention relates to a method and apparatus for carrying out hydrocarbon conversions, particularly as applied to systems involving the continuous circulation of granular contact material. The invention is especially applicable to thosecyclic systems wherein the granular contact material is passed by gravity flow downwardly through a plurality of superimposed contact zones combined into a single unitary structure and, upon discharge lfrom the lower end of the unitary structure, is elevated by a pneumatic lift, comprising one or more confined lift paths, to a raised level substantially higher than the conversion unit, where the contact material is then disengaged from the lift gas and is returned by gravity flow into the upper end of the conversion unit. A typical example of such conversion unit is disclosed in an article entitled Houdriflow: New design in catalytic cracking, appearing at page 78 of the January 13, 1949, issue of the fOil and Gas Journal.`

In such systems, it is common practice to locate the reactor or hydrocarbon conversion zone directly over the kiln o`r`regeneration zone, with su'icient Vertical `space therebetween to accommodate the usual seal leg. `The granular contact material is introduced into the upper end of the conversion zone and passes downwardly therethrough in the form of a compact moving mass. The hydrocarbons to be converted are introduced in known manner into the conversion zone, and are passed through the moving mass of contact material. The gaseous products of conversion are subsequently separated from the Contact material, removed from the conversion zone, andconveyed to other portions of the systems for further processing. The contact materia-l, after suitable purging with steam or other inert gas, is passed downwardly through an elongated seal leg and introduced into the upper end of the kiln or regeneration zone. Within the kiln, the carbonaceous material which formed on the contact material during the hydrocarbon conversion is removed by combustion in the ypresence of oxygen-containing gas. The aforesaid seal leg connecting the conversion andregeneration zones is of such length as to maintain a continuous ow of contact material therebetween and, in conjunction with the usual sealing gas, to prevent undesirable migration of the incompatible gaseous material between the two zones.

The contact material continues to gravitate as a compact moving mass in passing through the kiln or regeneration zonefwhich zone may comprise one or more stages of regeneration. The gaseous products of combust-ion, or ilue gases are separated from the contact material and withdrawn from the kiln. The Contact material is discharged from the lower end thereof as a compact moving stream, and is introduced into the engager or introduction chamber of the pneumatic lift. The lift engager surrounds the lower end of the lift pipe, and forms therewith anannular space wherein the contact material gravitates about the lower end ofthe lift pipe as a compact moving mass; Within thelift engagerthe contact material is engaged by a stream of lift gas, such as air,

flue gas, etc., and is elevated thereby through the lift pipe to a disengager vessel surrounding the upper end of the Ilift pipe. Within the disengager the contact material is separated from the lift gas `by gravitational deceleration. The disengaged contact material is then passed by gravity ow into 4the upper end of the reactor conversion zone. Provision -is normally made for a surge supply of contact material, eitherby a supply hopper located inthe upper end of the unitary structure, immediately above the conversion zone, or by an accumulated bed of the contact material maintained in thelower region of the disengager vessel.

In the operation of such units, the regenerated contact material is usually withdrawn from the lower end of the kiln at a temperature in the range of about 1050- 1150" F., and is thereafter passed directly, and without substantial loss of heat, into the lift engager for pneumatic elevation through the lift pipe. The temperature loss` while the contact'material is being conveyed from the discharge outlet of the kiln to the lift engager and then from the lift engager through the lift to the liftdisengager is normally in the order of about 20-30" F. At the slightly lower temperature the Contact material is then passed downwardly into the conversion zone. Since in certain operations, such as those employing liquid hydrocarbon.

feed in the conversion zone, a maximum eiciency, from the standpoint of benecial-utilization of available heat,` is obtained when the regenerated contact material is introduced at the maximum practicable temperature into the conversion zone, the `loss in temperature of the contact material during conveyance from the kiln to the reactor must subsequently be compensated for in the .conversion zone. Compensation therefor by increasing the circulation rate of` the contact materialis` undesirable because it imposes a heavier duty on the lift system.

In conversion systems wherein the kiln is operated at maximum permissible temperatures,\from the standpoint of avoiding deactivation of the particular contact material, and wherein the contact .material is introduced at maximum practicable temperatures into the conversion zone, a common practice is to convey the contact ma terial between the two zones as nearly as possible at the temperature at which it is withdrawn from the kiln. Such temperature is usually above the allowable maximum for carbon steel, thus requiring more expensive alloy steel y fabrication for those elements, such as the regenerated contact material withdrawal conduits, the lower seal leg, the lift engager, the lift pipe, the disengager, and the return conduit, which are subjected to the high temperaures. Fabrication of such aifected elements with temperatureresistant alloys represents a susbtantial increase `in cost.

In accordance with the present invention, separate kilns or regeneration zones are provided at opposite ends of the unit, that is, both above and below thefreactor or conversion zone. A partial regeneration of `the contact material, in one or more stages,` is effected `within the lower regeneration zone, and the partially regenerated contact material is withdrawntherefrom at a temperature substantially lower than the vtemperature which would normally be attained if regeneration were complete. The partially regenerated contact material is then introduced into and conveyed through the lift system at temperatures substantially below the acceptable maximum for carbon steel equipment. After disengagement from the lift gas, the partially regenerated contact material is introduced into the upper end of the upper regeneration zone, wherein the regeneration of the contact material is resumed to the desired degree of completion. The fully regenerated catalyst is then passed by gravity flow, and

with negligible heat loss, through a seal leg directly into` Patented Dec. 25, eV

to be converted at the highest practicable temperature. The countercurrent flow of gas through the compact moving bed of contact material within the upper regeneration zone provides an additive pressure drop which reduces the lengthof seal leg required 'between theupper regeneration zone and the conversion zone to Vbalance the pressurexdifferential between the two zones.

For a fuller Yunderstanding of the invention reference may be had to the following speciicationand claims taken inconnection with the accompanying drawing forming a part of thisl application, Ain which:

Figure 1 is a fragmentary elevational view showing the upper end portion' of amultiple lift hydrocarbon conversion unit embodying the present invention, and comprising the upper'kiln lor regeneration zone; and

Figure l-A is a fragmentary elevational view showing the lower portion of' the multiple lift hydrocarbon conversion unitof Figurev 1, and comprising the reactor or conversion zone and the lower kiln or regeneration zone. Figure Vl may bey superimposed over Figure l-A to show the complete hydrocarbon conversion unit.

yReferring to the drawing, the conversion unit as a whole comprises an elongated upright cylindrical vessel orhousing, generally indicatedby the numeral 10. Vessel is divided into an' upper portion 11, shown in Fig. 1 and in the upper halr of Fig. l-A, and a lower portion 12 of substantially greater diameter than upper portion 11, the two portions being joined by a frusto-conical section 13.

Upper cylindrical portion 11 of the vessel 10 is partitioned internally, as shown diagrammatically by broken lines, to form a confined regeneration zone 14 at its upper end and a confined conversion zone 15 at its lower end, the two zones being connected by a contact material transfer conduit or seal leg 16 of suiiicient length to preclude the migration of incompatible: gaseous material between the two zones.

Lower cylindrical portion 12 is likewise internally partitioned to. form a confined regeneration zone 17. The vessel 10 extends below the regeneration zone 17 to form a supportingskirt. Although, in the speciiic form illustrated, the vessel or housing 10 is of increased diameter in its lower portion, it is to be understood that the vessel may, if desired, be of uniform diameter throughout or be of increased diameter in its intermediate or its upper portions. Structural support considerations are a primary factor in -inuencing the selection of the base of the vessel for enlargement.

The bottom of regeneration zone 17 is. located a suiicient distance above grade to permit the contact material to ilow by force of gravity from the bottom of the kiln downwardly and outwardly through a plurality of sloping conduits 18 to a `corresponding plurality of lift engagers 19, each associated with a lift pipe 20. The invention is notlimited with respect to the number of Alift pipes which may be employed` or with respect to whether or not the lift pipes are fedl from a common engager vessel or are discharged into a common disengager or individual disengager vessels. The present embodiment of the invention utilizeswfourlift pipes, uniformly spaced in a circle concentric to the conversion unit. Since the four separate pneumatic lifts are thus located at an angular spacing of 90 about the periphery of the unit, a plan view has not been. considered necessary, and has therefore been omitted.

Within each lift engager 19 the partially regenerated contact material gravitates asa compact moving column aboutv and below the lower end of the associated lift pipe 20. Lift gas introduced into the lift engager, as by conduits 21 and 22, engages the contact material and transports it upwardly through the lift pipe to ardisengager vessel 23 individual to and surrounding the upper end of the lift pipe. Within the disengager 23` the contact material is separated from the lift gas inknownmanner. Thev disengagedcontact material isthen. passed, in

major part, from the lower end of each disengagcr 23 throughconduit 24 into the upper end of the upper kiln or regeneration zone 4. A minor portion of the disengaged contact material is separately withdrawn from the disengager 23 through conduit 25 and is passed downwardly and inwardly to an elutriator 26 mounted axially on top of the vessel or housing 10`. The lower end of the elutriator is connected to a central flue gasv outlet 27, through which it receives a portion of the ue gases discharged from upper kiln 14;

Separation of the fines from the larger-size particles of Contact material is elected in known manner within the elutriator 26. A detailed descriptionr andillustration of the elutriator are omitted, since they are disclosed in a companion application iledconcurrently herewith.

The flue gases and entrained nes are discharged from the elutriator through outlets 28, and are conveyed through conduits 29 to the side inlets 30 of a cyclone separator 31 mounted on top of the elutriator. The separated larger-size particles flow downwardly from the bottom of the elutriator into the upper kiln.

The cyclone separator 31 separates the fines from the flue gases, the former, being discharged from the elutriator, and from the system, through conduit 32, and the latter being passed upwardly directly into a stack 33 extending axially upward from the cyclone separator.

The upper kiln 14 is provided with a second flue gas outlet 34 through which iue gases are removed and conveyed by conduit 35, under control of a damper or valve 36, directly into the stack 33. By adjustment of the valve 36, any desired proportion of the iiue gas may be made to flow throughvthe elutriator 26.

The lift gas separated from the contact material within the disengager 2'3 is discharged from the latter through overhead conduit 37, and is conveyed directly to the inlet Sil, where it admixes with the gas discharge from the elutriator 26 and passes into the cyclone separator. Thus, a single cyclone separator is used. for removing lines from the gas streams discharging from both the elutriator 26 and the several lift disengagers 23. By reason of the. symmetrical arrangement of the elutriator and the disengagers with respect to the axis of the vessel 10, conduit and support requirements, aswell as equipment for the removal of fines from the system are held to a minimum.

In atypical operationin accordance with the invention and, for` convenience of description, considering the reaction zone 15 as a starting` point, the contact material admitted to the reaction zone through seal leg 16 is contacted with the hydrocarbons tol be converted while the contact material gravitates Vin the form of a compact moving bed. The hydrocarbon charge is introduced into the upper end of the conversion zone through an inlet conduit 41 and in known manner is brought into contact with the gravitatingv bed of contact material. The gaseous products of conversion flow concurrently with the contact .material to the lower end of the conversion zone, where the gaseous products are disengaged and purged from the gravitating contact material and are separately withdrawn from the conversion zone through outlet 42. The separated contact material. continues its gravitation as a compacty mov-ing mass downwardly into the lower regeneration zone 17, wherein a portion of the carbonaceous deposit formed on the contact material within the conversion zonev 15 is removed by combustion in air introduced at the lower end of the zone 17 and passed countercurrently to the contact material. Combustion is continued untilthe residuaryv coke deposit is about 0.4 to 1.0 weight percent, and preferably about 0.6 to 0.7 weight percent. At the upper end of the lower kiln gaseous combustion products are disengaged from the contact material and are separately withdrawn through outlet 43. Controlled 'regeneration in the lower kiln, or cooling at the lower end thereof, is provided so that the contact material discharges therefrom at a temperature substantially below the tem'p'eratur'eA at which the icontact material isV introduced finto the reaction zone.

The partially regenerated contact material, at a relatively low temperature compared to the temperatures heretofore employed at this point, is then introduced to the lift system and is elevated through the one or more lift pipes by means of lift gas comprising at least a por; tion of the flue gas discharged from the lower regeneration zone together with additional gas, such as steam, introduced through lift gas inlets 21 and 22, respectively. At the upper end of the lift system the contact material is disengaged from the lift gas within the disengagers 23 and is then passed downwardly by gravity ow into the upper regeneration zone 14, the temperature of the contact material having been slightly reduced in passing through the lift system. Within the upper regeneration zone 14 the contact material is more completely regenerated by contact with combustion-supporting gas introduced into the lower region of the upper regeneration zone through an inlet, not shown. This iinal stage of regeneration is carried out to the point where the weight percent of carbon has been reduced to the desired minimum. The gaseous products of regeneration are removed through outlets 27 and 34. The contact material, now substantially at its maximum temperature, is then passed downwardly into and through conversion zone 15, thus ending a complete cycle of circulation of the contact material.

The transfer of contact material from the upper regeneration zone 14 into the conversion zone 15 through seal leg conduit 16 is elected with a minimum heat loss, so that the contact material when it initially contacts the hydrocarbons to be converted is at the maximum practicable temperature. The lengthof the seal leg conduit 16 for conveying fresh regenerated contact material into the conversion zone is substantially shorter than that required in a system where the seal leg receives the contact material directly from a supply hopper which is either separate from or incorporated within the lift disengager, since the pressure drop through the moving bed of the upper kiln 14 is additive to the pressure drop through the moving column in conduit 16 for maintaining a pressure balance.

The following data will exemplify a typical application of the split kiln arrangement of the illustrated conversion unit. In a unit adapted to receive an oil charge of about 10,600 barrels per day, and having a nominal cokeburning capacity of about 6,000 lbs. per hour, contact material comprising bead catalyst having an average particle-size of between about l-15, and preferably 2 8 millimeters in diameter, may be circulated through the system at a rate of approximately 250 tons per hour. To maintain such catalyst circulation the lift system may comprise four lift pipes arranged as illustrated in the drawing accompanying this application and `'having an inside diameter of 12". During the operation, the temperatures and pressures within the various portions of the system may vary as indicated below:

It is to be noted that the present arrangement permits -obtained for two principal reasons.v

the elimination' ofthe usual supply or su'r'ge hopper at the top of or above the conversion zone, since the surge capacity may be provided in the upper regenerator bed.

While the total bed depth of contact material in the two regeneration zones of the herein disclosed embodiment of the invention may, -by reason of the smaller diameter of the upper kiln, exceed the bed depth which would be required in a single elongated lower kiln of the same diameter as the present lower kiln 17, there is neverthelessV a substantial saving in total height of the entire conversion unit. This saving -in total height is First, the surge hopper normally required in the path of contact material flow between the point of disengagement from the lift gas and the surface of the bed within the conversion zone is eliminated, and the required surge capacity is provided in the bed of contact material in the upper kiln or regeneration zone. Second, the length of the seal leg or compact moving column of contact material required between the source of supply of fresh regenerated congration.

In -a unit of the type disclosed in the foregoing example, which may be in excess of about 200 feet in overall height, the required length of seal leg between the upper kiln and the reactor or conversion zone may be in the order of about 40 feet. In a comparable unit comprising a single regenerator vessel with an overhead reactor, the required length for the seal leg would be approximately 60v feet. Thus, the net saving in overall height which m-ay be attributed to the split-kiln arrangement is in the order of about 20 feet. Obviously, the amount of saving in overall height will depend upon the design of the particular unit under consideration. In any case, however, the saving would be substantial.

When it is considered that the shortening of the seal leg is reflected in a comparable shortening of the supporting structure, the utility lines, and the lift system, it is readily apparent that considerable savings in costs of material and construction are effected.

Furthermore, by reason of the fact that the temperature of the contact material, as delivered to the lift system, is low enough to permit the use of carbon steel rather than more expensive 4alloys in the fabrication of the catalyst withdrawal system of the lower kiln, and those portions of the lift system which are usually adversely affected by the transportation of material at extremely high temperatures.

An additional substantial advantage in the use of the herein disclosed method and apparatus is that, by reason of the fact that the catalyst may be delivered from the upper kiln into the conversion zone at maximum temperatures, the split kiln arrangement permits the use of substantially lower contact material circulation rates.

The fact that the regeneration of the contact material is carried out in two separate kilns does not preclude the use, where desired, of multi-stage regeneration in one or both of the kilns.

The invention is applicable also to conversion units employing means other than pneumatic means for elevating the contact material, such as a bucket conveyor, and, where a pneumatic lift is employed, the invention is not limited to a multiple lift pipe system or to the particle arrangement of multiple lift pipes herein disclosed as illustrating one embodiment of the invention. It is to be understood also that other elutriator means may be employed for the removal of nes from the system.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, vand verein-eA thereforeV only such limitations should. be, imposed as are; indicated in. thel appended claims.v

What is claimed is:

'1. I'n a hydrocarbon conversion process in which granular contactmaterial gravitates successively through superimposed conversion and regeneratiorrzones, and is thereafter pneumatically elevated through. a lift pipel for return to said conversion zone, and in which the elevated temperature at which regenerated contact material is to 'be kintroduced into said conversionzone is` of such magnitude as` to be detrimental to the materials of construction usually employed in the fabrication of lift pipes, thernethod of transporting contact material from said regeneration zone to said conversion zone so that its temperature while being pneumatically lifted is substantially below, and its temperature or introduction to said conversion zone is` at, said elevated temperature which comprises the steps of: effectingronly partial regeneration of said contact material in the presence of oxygenfcontaining gas within said regeneration zone; introducing, said partially regenerated Contact material into said litt pipe at a relatively low temperature substantially below such detrimental temperature; elevating said low-temperature contact material through said lift pipe` to an elevatedV location substantially above said conversion zone by means of lift gas comprising gaseous combustion products withdrawn from said regeneration zone; separating said partially regenerated contact material from said lift gas at said elevated location; passing said contact material by gravity flow through a second regeneration zone located above said conversion zone to complete the desiredregeneration of said contact material in the presence of additional oxygen-containing gas, thereby raising the temperature of said contact material to said said relatively low temperature before introducing; the

same into said lift. pipe.-

3. A method as' dened in claim 1 in which said'relatively lowy temperature at which partially regeneratedcontact material is introduced into said lift pipe isin the range of about 950-1025 F., and said elevatedtemperature at which regenerated contact material is introduced into said conversion zone 'is in the range of about 1100-1150 F.

4. A method as defined in. claim 1 in which said regenerated contact material is passed from` said second regeneration zone to said conversion zone as -a compact moving stream adaptedV to provide a seal leg: sufficient to prevent undesirable migration of gaseous material between .said zones.

5. A method as defined in clairn 1 in which said partial regeneration of Contact material within the rst regeneration zone is such as to reduce the carbonaceous deposit on said Contact material to approximately 0.4 to

1.0 wt. percent thereof.

References Cited inthe file of this patent UNITED STATES PATENTS 2,486,627 Arnold Nov. 1, 1949 2,506,122 Watson May 2, 1950 2,508,993 Crowley May 23, 1950 2,561,331 Barker Iuly 24, 1951 2,561,771 Ardern July 24, 1951

Claims (1)

1. IN A HYDROCARBON CONVERSION PROCESS IN WHICH GRANULAR CONTACT MATERIAL GRAVITATES SUCCESSIVELY THROUGH SUPERIMPOSED CONVERSION AND REGENERATING ZONES, AND IS THEREAFTER PNEUMATICALLY ELEVATED THROUGH A LIFT PIPE FOR RETURN TO SAID CONVERSION ZONE, AND IN WHICH THE ELEVATED TEMPERATURE AT WHICH REGENERATED CONTACT MATERIAL IS TO BE INTRODUCED INTO SAID CONVERSION ZONE IS OF SUCH MAGNITUDE AS TO BE DETRIMENTAL TO THE MATERIALS OF CONSTRUCTION USUALLY EMPLOYED IN THE FABRICATION OF LIFT PIPES, THE METHOD OF TRANSPORTING CONTACT MATERIAL FROM SAID REGENERATION ZONE TO SAID CONVERSION ZONE SO THAT ITS TEMPERATURE WHILE BEING PNEUMATICALLY LIFTED IS SUBSTANTIALLY BELOW, AND ITS TEMPERATURE OF INTRODUCTION TO SAID CONVERSION ZONE IS AT, SAID ELEVATED TEMPERATURE WHICH COMPRISES THE STEPS OF: EFFECTING ONLY PARTIAL REGENERATION OF SAID CONTACT MATERIAL IN THE PRESENCE OF OXYGEN-CONTAINING GAS WITHIN SAID REGENERATION ZONE; INTRODUCING SAID PARTIALLY REGENERATED CONTACT MATERIAL INTO SAID LIFT PIPE AT A RELATIVELY LOW TEMPERATURE SUBSTANTIALLY BELOW SUCH DETRIMENTAL TEMPERATURE; ELEVATING SAID LOW-TEMPERATURE CONTACT MATERIAL THROUGH SAID LIFT PIPE TO AN ELEVATED LOCATION SUBSTANTIALLY ABOVE SAID CONVERSION ZONE BY MEANS OF LIFT GAS COMPRISING GASEOUS COMBUSTION PRODUCTS WITHDRAWN FROM SAID REGENERATION ZONE; SEPARATING SAID PARTIALLY REGENERATED CONTACT MATERIAL FROM SAID LIFT GAS AT SAID ELEVATED LOCATION; PASSING SAID CONTACT MATERIAL BY GRAVITY FLOW THROUGH A SECOND REGENERATION ZONE LOCATED ABOVE SAID CONVERSION ZONE TO COMPLETE THE DESIRED REGENERATION OF SAID CONTACT MATERIAL IN THE PRESENCE OF ADDITIONAL OXYGEN-CONTAINING GAS, THEREBY RAISING THE TEMPERATURE OF SAID CONTACT MATERIAL SO THAT ELEVATED TEMPERATURE; AND PASSING SAID REGENERATED CONTACT MATERIAL BY GRAVITY FLOW AND WITHOUT SUBSTANTIAL REDUCTION IN TEMPERATURE DIRECTLY TO SAID CONVERSION ZONE.

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