US3206393A - Fluid catalytic cracking of hydrocarbons - Google Patents

Description

Sept. 14, 1965 .1. B. PoHLENz FLUID CATALYTIC CRACKING OF HYDROCARBGNS Filed Nov. 24, 1964 A TTR/VEYS wm mm GNL H Z n R M mm m p. Nk /V Ill am .M l J n .f L y@ NN QN v.1. Inj. B bum Nm. k \m,

United States Patent O M 3,206,393 FLUID CATALYTIC CRACKING F HYDROCARBONS Jack B. Pohlenz, Arlington Heights, Ill., assgnor to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware File'd Nov. 24, 1964, Ser. No. 413,567 The portion of the term of the patent subsequent to Dec. 15, 1981, has been disclaimed r 5 Claims. (Cl. 208-164) This application is a continuation-impart of my presently led application Serial No. 206,271, led June 29, 1962, now Patent 3,161,583, December l5, 1964.

The present invention is directed to an improved manner of operating a fluid catalytic cracking unit and more specifically to obtaining improved product yields from a hydrocarbon charge stream by operating to increase the heavy oil content in the recycle portion thereof, as an independent step or in combination with fresh feed preheat, whereby to provide an increased dilerential temperature between the reaction and regeneration zones and high temperature levels within the regeneration zone.

In the past, as well as with some present day operations, it has been conventional for engineers to design and to operate fluid catalytic cracking units as heat balanced units. In other words, with prior data and experience as a basis for the design of the unit, it was customary to estimate a gasoline yield and coke producing rate and then calculate to obtain a heat balance with a particular combined feed ratio (which may be defined as the ratio of the combined volume of fresh feed and recycle oil relative to the volume of fresh feed) and/or the combined feed temperature which would appear to provide a steadystate operation.

However, the error in such a design was the assumption that coke-make or coke yield, i.e., the weight percent of coke produced based upon lfresh hydrocarbon feed, was a product of the cracking reaction and hence a function of the degree of conversion rather than catalyst circulation rate and the coke to catalyst ratio reaching the regeneration zone. Those units whichwere designed to operate at low conversion levels and hence low coke rates were frequently short on heat so that feed heaters were provided to furnish the thermal requirements. High conversion units, on the other hand, had the problem of too much coke-make for heat balance requirements, so that recycle was provided as a cooling stream to transfer the excess heat into the main column where such heat could be used to regenerate steam. In other cases, Water was sprayed directly into the regeneration zone or, alternatively, a separate stream -of catalyst was withdrawn from the regenerator and passed through special catalyst coolers to preclude what was thought to be excessive regenerator temperatures. In fact, it was customary to operate regenerators below 1l50 F, on the presumption that a higher temperature would reduce catalyst activity and provide a short catalyst life.

As is well known in the petroleum industry and as will be more fully pointed out hereinafter in connection with the accompanying diagrammatic drawing, a conventional fluid catalytic cracking unit makes use of a reactor, stripper, spent catalyst slide valve, regenerator, regenerator standpipe, regenerated catalyst slide valve and a riser line leading back into the reactor, with the catalyst owing through the various sections of the unit, in the order named. A large fractionator or main column is also utilized to receive the overhead cracked vaporous product stream from the reactor. Such fractionator provides gasoline and other desired side-cut product streams therefrom, as well as recycle oil streams which are charged back to the reaction zone. The mixture of fresh hydro- 3,206,393 Patented Sept. 14, k1965 lCe carbon feed stream and recycle, referred to as combined feed, is vaporized upon contacting heated regenerated catalyst particles at the base of the riser line and there is a lluidized lcontacting and lifting of the catalyst to within the reactor. The resulting reactor product vapors, along with a minute quantity of entrained catalyst, are introduced into the main column where, of course, the products are fractionated into the various overhead and sidecut streams in accordance with their volatility. The reactor temperature controls the regenerator slide valve to provide, in turn, variations in catalyst flow from the regenerator to the reactor. At the same time, the spent catalyst valve, regulating catalyst flow from the reactor to regenerator, is operated by catalyst level control means A in the reactor.

As pointed out in my prior application Serial No. 206,271, there are various independent control variables that have a direct bearing on the conversion of the hydrocarbon charge which is introduced into the reaction zone. Also, as used herein, the term conversion may be defined as the volume percent of the charge which is converted to materials lighter than the light cycle oil as separated from the main column, but corrected to take into account the amount of gasoline in the charge stream. One important independent variable in controlling conversion is `the reactor temperature level. Other important control variables are the combined feed ratio (which is the ratio of the total of the fresh and recycle feeds to the fresh feed) and the temperature of the combined feed. The latter is conventionally varied by the amount of preheat given the fresh feed to the reactor. Other independent operational variables include: weight hourly space velocity (defined as the hydrocarbon feed rate divided by the catalyst inventory in the reactor), reactor pressure and catalyst type and quality. The reactor pressure range is generally limited and, in addition, has little effect upon conversion or product distribution for the range, so that it is not a true operational variable. Catalyst activity is important to the process, and should be maintained at a high level in the unit; however, for the purposes of carrying out the present invention, catalyst types will not be considered herein and activity will be presumed to be maintained consistent and at a high level. Thus, a change in the catalyst type or activity will not be considered in connection with the present improved operations as being an operational variable.

The important dependent control variables in a unit may be considered to be: catalyst cir-culation rate and hence catalyst to oil ratio and regenerator temperature. The catalyst to oil ratio, which is the relation of the rate of catalyst to the reactor to the rate of oil entering the reactor, is tied to catalyst circulation rate and does affect the severity of the cracking. However, the severity is also affected by space velocity since, for example, a decrease in space velocity means a lesser quantity of oil is contacting a given quantity of catalyst, per hour, such that there is an increase in conversion following the longer con tact time with the catalyst. Thus, there is an interrelation between catalyst circulation rate, catalyst to oil ratio and space velocity.

It is a particular feature of my copending application and of this application to provide improved product yields by providing operations with a high temperature level in the regeneration zone that are above 1150 F., and substantially higher where the construction characteristics of the regenerator permit, and, in most cases, operations with greater temperature differentials between the reaction and regeneration Zones. The term improved product yields, as used herein, means greater economic yield from the charge stream by reason of increasing the yield of gasoline and lighter materials which have more marketability. Although my copending application sets forth improvements obtained from various of the operational ycontrol meansand from the high temperature levels in the vregenerating zone, the present application is directed in rone specic aspect to improving yields at the expense of heavy product by increasing the heavy cycle'oil content inthe combined feed to increase coke-make and the regeneration zone temperature. While such step may be an independent one, it may also be carried out concomitantly with the step of providing increased feed preheat to Vthe fresh feed portion of the hydrocarbon charge going to the unit.

Thus, in one embodiment, the present invention provides in connection with a continuous process for cracking a hydrocarbon charge stream comprising fresh feed and recycle oil in the presence of subdivided catalyst particles, wherein the hydrocarbon stream is subjected to a fluidized contacting of the particles in a reaction zone, conversion yproducts are separated from the contacted particles, separated catalyst particles containing a coke deposit are subject to'a uidized contacting of an oxygen containing stream in a separate regeneration zone, combustion gas products are separated from regenerated catalyst particles and such regenerated catalyst particles with a reduced coke content are returned to the reaction zone for contact gwith the hydrocarbon charge stream, the improved method of effecting improved product yields from the hydrocarbon charge stream by operating to provide high temperature levels in the regeneration zone, which comprises,

vincreasing the combined feed ratio with an increase in heavy recycle oil content of the hydrocarbon stream being introduced to the reaction zone, effecting both a greater conversion in said reaction zone with a higher ltemperature level therein and an increased coke deposition level on the catalyst particles sufficient to provide Va temperature above 1150D F. in the regeneration zone 'when oxidizing the coke on the catalyst particles in the presence of a controlled oxygen containing stream introduced to `such regeneration zone, and regulating the introduction of the oxygen containing stream to the re* generation zone directly responsive to a predetermined i temperature differential between the gas outlet section and the catalyst contacting section of the regeneration zone to minimize excess oxygen therein and to control after burning in the upper portion of the regenerating zone.

In another embodiment,- the invention provides in a continuous process for cracking a hydrocarbon charge stream comprising fresh feed and recycle oil in the presence of subdivided catalyst particles, wherein the hydrocarbon stream is subjected to a fiuidized contacting of the particlesvin a reaction zone, conversion products areseparated from the contacted particles, separated catalyst particles containing a coke deposit are subjected to iluidized contacting of an oxygen containing stream in a 'separate regeneration zone, combustion gas products are separated from regenerated catalyst particles and such regenerated catalyst particles with a reduced coke content are returned to the reaction zone for contact with hydrocarbon charge stream, the improved method of effecting improved product yields from the hydrocarbon charge strearnby operating to provide a high temperature level in the regeneration zone, which comprises, preheating the fresh feed portion of the hydrocarbon stream, concomitantly therewith increasing the combined feed ratio with an increase in the heavy recycle oil content in said charge stream, varying the catalyst circulation rate to effect a coke deposition level on the catalyst particles sufficient to provide a greater temperature spread ben tween the reaction and regenerating zones with temperatures above 1150" F. in the regeneration zone when oxidizing the coke on the catalyst particles in the presence of a controlled voxygen containing stream introduced to n such regeneration zone, and regulating the introduction of the oxygen containing stream to the regeneration zone directly responsive to a predetermined temperature differential between the gas outlet section and the catalyst contacting section of the regeneration zone to minimize excess oxygen therein and to control yor preclude afterburning in the upper portion of the regenerating zone.

With an increase in the heavy oil content of the combined feed to the unit, there is an improvement in gasoline yield at the expense of the heavy recycle -oil make, although in this instance more coke is made in the operation which results in the desired high regeneration zone temperature above 1150 F. and an increased temperature spread between the reactor and regenerator zones. The reactor temperature may be held constant or varied to provide a slightly different conversion; however, preferably the reactor temperature is changed upwardly and greater conversion obtained. On the other hand, increased feed preheat may be utilized at the same time that heavy recycle oil content is increased in the combined feed and an operation used, maintaining substantially constant conversion, which provides a high temperature level in the regeneration zone above 11509 F. and an increasing temperature spread between the reactor and regeneration zones, although there is a resulting slightly higher temperature level in the reactor. Since the effect of the fresh feed preheat step is to reduce coke make and provide greater gasoline yield at the expense of coke, then the combination of such step with the increase in heavy recycle oil content of the combined feed may result in (l) a slight overall reduction in coke yield, (2) no net change, or (3) a slight increase in coke make. In any event, there is a substantial economic advantage to either or both of these operational variations in going to the greater regenerator temperature levels and the greater gasoline yields.

Space velocity is not usually considered an effective means for making minor adjustments in conversion; however, with particular reference to improving product yields by changing space velocity as an operational variable, it may be pointed out that while space velocity has been generally varied as necessary to suit catalyst activity so as to thus provide a desired conversion, there may be a direct operational change in using a space velocity variation along with an increased temperature level in the regenerator to increase conversion. More specifically, there can be a decrease in space velocity to have a greater quantity of catalyst present in the reaction zone relative to the quantity of hydrocarbon charge and at the same time the provision of a coke deposition on the catalyst which provides a higher regenerator temperature level above 1l50 F.

Thus, in still another embodiment, the present invention provides in connection with a continuous process for cracking a hydrocarbon charge stream in the presence of subdivided catalyst particles, wherein the hydrocarbon stream is subjected to a fluidized contacting of the particles in a reaction zone, conversion products are separated from the contacted particles, separated catalyst particles containing a coke deposit are subjected yto uidized contacting of an oxygen containing stream in a separate regeneration zone, combustion gas products are separated from regenerated catalyst particles and such regenerated catalyst particles with a reduced coke content are returned to vthe reaction zone for contact with the hydrocarbon charge stream, the improved method of effecting improved product yields from the hydrocarbon stream by operating to provide a high temperature level in the regeneration zone,l which, comprises, decreasing the weight hourly space velocity in the reaction zone -and increasing the reaction Zone temperature to effect ya greater conversion of said hydrocarbon charge stream and providing a coke deposition on the catalyst particles sufiicient to provide a temperature above 1150 F. in the regeneration zone when oxidizing such coke deposition on the catalyst particles in the presence of a controlled oxygen containing stream introduced to such regeneration zone, and regulating the introduction of the oxygen containing stream to the regeneration zone directly responsive to a predetermined temperature differential between the gas outlet section and the catalyst contacting section of the regeneration zone to minimize excess oxygen therein and to control afterburning in the upper portion of the regeneration zone.

In considering more specically the utilization of changing reaction zone temperature as an operational variable, it should be noted that improved product yields will be obtained by increasing the reactor temperature to give an increased conversion of the hydrocarbon charge stream. In other words, there is a definite economic advantage in concomitantly permitting a slightly higher coke deposition on the catalyst and providing higher temperature levels in both the reaction zone and the regeneration zone with the latter being above 1150 F.

In order to more easily refer to the operation of a fluid catalytic cracking unit and certain operating variables in connection therewith, reference is made to the accompanying diagrammatic drawing and the following description thereof.

Fresh hydrocarbon feed passes through line 1 and control valve 2 to a pump 3 that in turn discharges into line 4 connecting with a feed preheater 5. The latter provides a predetermined or controlled variable preheating to the feed stream and passes it to the lower end of riser line 6 where heated catalyst particles combine therewith from standpipe 7, having control valve 8, such that a resulting vapor-catalyst mixture rises in an ascending. fluidized stream to the lower end of reactor 9. In the reactor 9 there may be further uidized contacting between the vaporous feed stream and the catalyst particles within a relatively dense fluidized bed 10 within the lower portion of the chamber, although generally a major portion of the necessary cracking and contact with the catalyst particles takes place in the riser line 6. Catalyst in an oil slurry may be combined with the fresh feed stream in the riser line 6 from line 11 having control valve 12, while in addition, light and heavy recycle oils may be combined therewith by way of line 13 having control valve 14. As hereinbefore noted, the combined feed ratio will vary in accordance with the amount of recycle oils combined with the fresh feed stream to be introduced into the reaction zone.

At the upper end of the reactor 9, the catalyst particles are separated from the vaporous cracked reaction products by centrifugal separating means 15 and then transferred overhead by line 16 to the lower end of the fractionator or main column 17. Separated catalyst particles from the light phase zone in the top of the reactor 9 are returned to the dense phase bed 10 by a suitable dip-leg 13 and resulting catalyst particles with a coke deposition and occluded hydrocarbons settle from the lower portion of reactor 9 into a stripping section 19 such that they may pass concurrently to a stripping gas stream introduced through line 20 having valve 21. Steam, nitrogen or other substantially inert gaseous stripping medium may be utilized in the stripping section to effect the removal of absorbed and occluded hydrocarbon vaporous components. Resulting stripped and coked catalyst particles move from the lower portion of stripping section 19 into the standpipe 22, having control valve 23, such that they may be transferred at a controlled rate to the regenerator 24.

In the regenerating chamber 24, the carbonized catalyst particles are subjected to oxidation and carbon removal in the presence of air being introduced by way of distribution grid 25. The oxidizing air stream enters the regenerator by way of line 26, valve 27 and blower 2S, which in turn connects by way of line 29 to air heater 30. In the present embodiment, the latter is indicated as connecting directly with the lower end of the regenerator 24 and the pipe grid distributor 25. The air heater 30 is utilized in a manner only to heat the air during the initial start-up procedure. A bypass line 31, having control Valve 32, connects with the air line 29 in order to vent a portion of the air stream being introduced to the system from blower 28 and thus regulate the quantity of air actually being introduced into the lower end of the regenerator 24, as will be more fully described hereinafter.

In the lower portion of the regenerator 24, a fluidized dense phase bed 33 provides for hindered settling contact between the coked catalyst particles and the oxidizing air stream while, in the upper portion of the charnber, a light phase zone permits the separation of catalyst particles from the flue gas stream being discharged by way of line 34 and valve 35. Suitable centrifugal separating means 36 provides for removing entrained catalyst particles from the combustion product stream and returns thern by way of dip-leg 37 to the lower dense phase bed 33. A suitable silencing means 38, connecting with the line 35, serves to reduce the noise level of the combustion gas stream passing to the outlet stack 39.

At the main column 17, the cracked product vapor stream is fractionated to provide a desired overhead gasoline vapor stream passing by way of line 40 and valve 41 to suitable gas concentration equipment, not shown in the lpresent drawing. In addition various side-cut and recycle streams may be taken from the side of the fractionator 17 in accordance with desired molecular weight products. A light recycle oil stream is indicated as being taken from column 16 by way of line 42 and side-cut accumulator 43. An overhead vapor return line 44 returns uncondensed vapors from accumulator 43 to the main column 17 while a condensed light oil fraction is taken from the lower end of the accumulator 43 by Way of line 45, pump 46 and line 47 having valve 48. Similarly, a heavier recycle oil stream may be taken from the main column by way of line 49 and side-cut accumulator 50. An uncondensed vapor stream may be returned to the main column by way of line 51 while a condensed heavy oil fraction passes from the lower end of accumulator 56 by line 52, pump 53 and line 54 having valve 55. For purposes of simplification, all cooling circuits and cooling lines to the column are not shown. Also, suitable lines, not indicated in the present drawing, may be utilized to transfer the light and heavy recycle oil streams from lines 47 and 54 to the recycle inlet line 13 which in turn connects with catalyst riser line 6, such that recycle oil may be combined with fresh hydrocarbon feed stream from line 1 to provide a desired combined feed ratio to the reactor 9. Light reflux to the top of the main column 17 is shown as being introduced by way of line 82 and control valve 83.

A bottoms slurry oil, containing catalyst particles which were entrained with the vapor product stream in line 16, is carried by way of the lower outlet line 56, pump 57 and line 58 to a suitable catalyst settling chamber 59. The settler 59 serves to provide a substantially particle free clarified oil stream overhead by way of line 60 and valve 61, while at the same time effecting the return of the catalyst containing slurry stream through control valve 12 to transfer line 11 such that catalyst particles may be returned to the uidized bed by way of riser line 6. A line 62, with control valve 63 is utilized to pass a portion of the bottoms stream from the main column 17 through a heat exchanger 64 such that heated oil may be returned by way of line 65 to the lower end of the main column 17 and provide a heat supply to such column.

In order to maintain control of the liuidized unit, control instrumentation means are associated with the reaction and regeneration zones to maintain appropriate dense phase bed levels in such zones and a catalyst circulation rate between such zones. At the reactor 9, a level controller LC, with level indicating taps 66 and 67, is connected with the side wall of the reactor. A control line 68 from controller LC connects with the slide valve 23 in the contacted catalyst standpipe 2 and provides means for maintaining a desired dense phase bed 10 level and quantity of catalyst in the lower portion of the reactor 9.

'27 Generally, the slide valve control means, such as used in connection with the slide valve 23, are pneumatic in opera- `tion such that the level control means LC may be of any conventional type suitable to regulate the pneumatic mo- 'tor control means of the valve, although electrical control and motor means may be used.

Within the upper portion of reactor 9, a temperature indicating means 69 connects through control line 70 to a temperature controller TC and control line 71 which in turn connects with an air piston or other motor means .providing for the regulation of the slide valve 8 in the regenerated catalyst standpipe 7. Thus, a variable quantity of hot regenerated catalyst may be withdrawn from standpipe 7 to pass into riser line 6 and enter the reactor chamber 9 in accordance with variations in temperature ,in the latter zone, as provided for by the temperature sensitive means 69 and controller TC. A pressure sensitive means 72 is also positioned in the upper portion of the reactor 9 while a separate pressure indicating means 73 is positioned in the upper portion of the regenerator 24.

iSuch indicating means are connective, through the respective lines 74 and 75, to a differential pressure regulator lDPR in order to provide means for maintaining a deisired differential pressure between the two separate contacting zones. The differential pressure regulator DPR connects through control line 76 with the control valve 35V so as to regulate the ilue gas flow through line 34 and 'in turn vary the internal pressure within the upper portion of the regenerator 24, whereby a predetermined pressure difference .may be maintained between the reactor and the regenerator. Generally, the pressure differential between the two Zones is of the order of about 6 p.s.i. and is necessary to permit the maintenance of suitable pressure differentials across the slide valves in the two standf pipe linesand a continuous circulation of catalyst particles between two separate zones. Pressures in a fluidized unit are, of course, relatively low, being generally below about 25 to 30 p.s.i. The pressure variation in the reactor may be an operating control variable, but because of gas compressor limitations or certain structural and mechanical aspects, it is preferable to utilize low pressures which are merely suiicient to insure adequate differentials and proper flow between various portions of the unit.

An improved control means integrated in connection with high Vtemperature operations and indicated in the present diagrammatic embodiment, is the use of differential temperature control means between the dense phase and light phase zones of regenerator 24 so as to regulate the quantity of air being introduced into the regeneration zone. Temperature indicating means 77 and 78, within the upper and lower portions of the regenerator 24, connect through the respective transmission lines 79 and Si) to a differential temperature controller DTC, which in turn connects through control line 81 with the valve 32 lin the air vent line 31. Thus, where the temperature differential between the upper and lower portion of the regenerator exceeds a predetermined difference, as set within the temperature controller DTC, then valve 52 is adjusted to bypass a greater portion of the air passing through line 29 and effect the reduction of air being introduced by way of distributing grid 25 into the lower portion of the regenerator. Persons familiar with the operation of uidized cracking units realize that uncontrolled after-burning can be a major problem, inasmuch as the high temperature resulting from the oxidation of carbon monoxide to carbon dioxide in a dilute phase in the cyclone separators at the outlet of the regenerator may cause severe mechanical damage. In the prior operation of most present-day units, it has been customary to provide for spray water and/ or heat exchangers as cooling means, or to utilize flue gas analysis and accompanying control apparatus to severely reduce the oxygen introduction into the regenerator zone an as means for controlling the regenerator temperature to below about 1l25 F.

However, the use of spray water has proved to be undesirable because of (1) damage to the catalyst by sintering or breakage by thermal shock of the particles, and (2) its nullifying effect on feed preheat. Prior attempts to reduce the iiow of the air stream and the introduction of oxygen into the regeneration zone has required sensitive means for detecting small oxygen concentrations and adjustment of the air introduction rate, all of which has been difficult from the practicable aspects. In connection with the present improved operations, where it is desired to have cracking operations which maintain a high temperature level in the regenerator, in other words, above about 1l50 F., it is, of course, desirableto have means for precluding or controlling the problems of afterburning. It has been found that a temperature rise above `a predetermined temperature differential between the dense and dilute phases or between the dense phase and the flue gas outlet line is a very sensitive indicating means toshow variations in the oxygen content of the gas leaving the dense phase itself. With the adoption of this procedure, afterburning may be controlled such that the regenerator temperatures can be maintained at a steady-state level. ln practice, it has been found that fromy 1% to 2% of the air blower output may be vented and that a temperature rise, over and above the predetermined differential set in the DTC may be utilized to control valve 32 and the vent rate through line 31. At the present time, it is generally necessary to determine bytrial and error on any particular unit that temperature differential or rise which, when maintained constant, will regenerate the catalyst to lower the colte deposit level on the catalyst to a desired lower level, generally 0.3 to 0.4 weight percent, and maintain the oxygen concentration in the flue gask below 0.2%. Also, temperature differentials will vary depending upon the locations of the temperature sensitive meansl in the regenerator or in the regenerator outlet line. Desired temperature differences between thermocouples in the lower and outlet zones of the regenerator may vary by 20 to 30 F. On the other hand, a thermocouple or other temperature sensitive means could be placed at a point sufficiently downstream in the fiue gas line as to provide a desired temperature differential with the downstream temperature being 5 to 10 F. less than the dense phase temperature.

To better illustratethe advantages of higher regenerator temperature levels in combination with adjustments in certain of the operational variables as noted hereinf before, reference is made to the following series of illus,- trative operations.

In each of the examples the hydrocarbon charge is a typical feed for a fluidized unit, being a blend of atmospheric, vacuum and coking unit gas oilswith a API gravity of about 31.0; a sulfur content of about 0.4%; a molecular weight of 320; a UOP characterization factor, or K factor, of about 12.0; and a boiling range of from about 475 F. to about 1000 F. The catalyst .circulation rates shown are based on a raw oil or fresh feed charge of 20,000 barrels per day. In each case, except for Example VII, there is 5 volume percent, based on fresh feed, of slurry in the feed, with the balance of the recycle being heavy cycle oil. The catalyst activity in all cases is 32, based upon the UOP determination of weight activity such as described in Industrial Engineering Chemistry (1952), volume 44, pages 2857 to 2863 and/or Petroleum Rener, volume 31, No. 9 (September 1952), pages 274-276.

EXAMPLE I In this typical fluid catalyticv cracking operation, the fresh feed or raw oil temperature to the unit is at 400 F.; the combined feed ratio is 1.5; the weight hourly space velocity (WHSV) is set at 6; the temperature ranges for the reactor are 900 F. in the dense phase and 885 F. in the light phase, while the regenerator dense phase is 1120 F. and the light phase 1135 F. The coke-make is 7.5 weight percent and catalyst circulation rate of 3.45

pounds per hour. The resulting conversion is 65 volume percent, with the debutanized gasoline being 47.5 volume percent. Other product yields are in accordance with the quantities set forth in the accompanying Table A under the column headed for Example I.

EXAMPLE II In another operation, the processing conditions provided are similar to those of Example I, except that there is feed preheat providing an increased raw oil temperature of the order of 600 F. The increase in the feed temperature will reduce catalyst circulation rate which in turn will reduce conversion. Thus, in order to maintain or increase conversion there is provided an increased dense phase reactor temperature. In this case, the reactor temperature level is raised to 945 F. and the resulting conversion is 72 volume percent, with debutanized gasoline production being 52.5 volume percent. The dense phase regenerator temperature is 1175 F. and the coke-make is 6.8 Weight percent. The catalyst circulation rate is 3.0)(106 pounds per hour. Other product yield quantities are shown in Table A.

A comparison of conversion products with the results of Example I shows that this feed preheating operation, with a resulting regenerator temperature above l150 F. and an increased temperature differential between the reactor and regenerator increasing to 230 F., as compared to 220 F., provides the greater gasoline yield at the expense of coke-make.

EXAMPLE III In another operation, the processing conditions are modified from those of the rst example to provide for an increase in the quantity of heavy recycle oil such that the combined feed ratio to the reactor is 2.0 In this instance thel reactor temperature level is increased to 913 F. to in turn provide for a higher conversion of 75 volume percent. The regenerator temperature increases to 1165 F. with a resulting temperature differential between the reactor and regenerator zones of 252 F. The increased heavy oil content in the combined feed, in the absence of other changes will, of course, result in a greater coke deposition on the catalyst particles and an overall increase in coke-make in the operation, with such coke production being 9.5 Weight percent. The catalyst cir- 'culation rate increases to 3.82 106 pounds per hour. The

resulting overall conversion is 75 volume percent, providing some 54.0 volume percent of debutanized gasoline. Other yield data are shown in the Table A.

In comparing the yield data of Examples I and III, it should be particularly noted that a definite economic advantage is attained by producing a greater gasoline yield at the expense of generally less valuable heavy cycle oil, even though slightly more coke is made in the operation.

EXAMPLE IV In still another fluidized operation, the processing conditions are modified to include an increase in feed preheat such that the raw oil temperature is 600 F. (as in Example II) and, in addition, the combined feed ratio is increased to 2.0, by providing a greater quantity of heavy cycle oil to the reactor, in a manner similar to the operation of Example III. In this instance the reactor temperature level is increased to 936 F. while the regenerator temperature increases to 1200 F., with a resulting differential of some 264 F. An overall conversion of 75 volume percent is attained, while debutanized gasoline production increases to 54.5 volume percent. Coke yield is slightly greater, at 8.6 weight percent, than that of Example I, and catalyst circulation rate is slightly lower at 3.30 106 pounds per hour. Additional yield data are again set forth in the accompanying Table A.

It should be noted that this operation is of particular merit in improving product yields. The gasoline yield 4is greater than in any of the prior examples, being some 54.5 Volume percent, while the generally less valuable heavy cycle oil is decreased to 2.1 weight percent as compared with 10.6 weight percent in Example I. As noted, the coke-make is somewhat higher than the lower temperature operation of Example I but is substantially lower than that of Example III. With still greater feed preheat or with a slight reduction in the quantity of heavy oil recycle there can be a lessening of the coke yield; however, in general, the economics will prefer the reduction in heavy cycle oil production at the expense of making slightly more coke.

EXAMPLE V In this modified fluidized catalytic cracking operation, there is embodied a change in the reactor temperature level to increase conversion while, of course, at the same time increasing the regenerator temperature to a substantially higher level. In other words, with a charge stream, as set forth under the conditions of Example I, being introduced to the unit at CFR of 400, a WHSV of 6.0 and a raw oil temperature of 400 F., there may be set an increased level of temperature in the reactor to 950 F., and a resulting higher regenerator temperature to 1180 F. The resulting conversion is 78 volume percent with the debutanized gasoline yield being 54.5 volume percent. The coke make is 8.2 weight percent and the catalyst circulation rate will be slightly higher at 3.61)( 106 pounds per hour following the reactor temperature adjustment to the higher level. Other product yield data are shown in the Table A.

In connection with this present high temperature operation, it may be noted that the gasoline yield is substantially higher than the operation of Example I, and the heavy cycle oil is cracked to extinction.

EXAMPLE VI In this modified operation, the space velocity is reduced, as compared with the conditions of Example I, to show how this operational variable causes an increase in the temperature spread between the reaction and regeneration zones and an increase in conversion with little or no increase in coke-make. Raw oil temperature is held to 400 F. and the combined feed ratio maintained at 1.5.

With a decrease in WHSV from 6 to 2.5 to provide a greater quantity of catalyst in contact with the feed; a reduced catalyst circulation rate of 2.75X 106 pounds per hour; a retained reactor temperature of 900 F. and an increased regenerator temperature, there is a resulting increase in conversion to 72 volume percent. Coke-make remains substantially unchanged at 7.6 weight percent. Other yield results are set forth in Table A.

It may be particularly noted in connection with this improved operation that the debutanized gasoline yield increases from 47.5 to 51.0 volume percent and that heavy cycle oil production decreases substantially by dropping from 10.0 to 5.0 volume percent.

EXAMPLE VII In still another operation, there may be provided an increase in the heavy oil content of the raw oil charge to in turn illustrate the use of the higher regenerator temperature operation in effecting the conversion of heavy stocks to gasoline. Specifically, in this case, there is provided an 8 volume percent quantity of slurry as compared to the 5 volume percent slurry in Example I. The conibined feed ratio remains at 1.5, raw oil temperature at 400 F., and WHSV at 6.0. Reactor temperature is raised to 910 F. to increase conversion slightly and the regenerator temperature raises to l F. with cokemake being 7.6 weight percent and catalyst circulation rate going to a decreased rate of 2.75 X106 pounds per hour.

In comparing this operation with Example I, it will be noted that there is a definite increase in differential temperature between the contact zones, i.e., from 220 F. to 280 F., and that conversion increases from 65 to .67,

` charge stocks and operating conditions. n use `of changes in an operation making use of higher regenerator temperature levels, above the 1l50 F. range rvolume percent. Debutanized gasoline production in- .creases from 47.5 to 48.5 volume percent, while claried lslurry decreases by 2.2 weight percent.

Other product yield data are shown in Table A. In this instance,

:there was but a small increase in the heavy oil content of .the charge; however, Where the regenerator can accommodate` higher temperature ranges, there may be increased 'quantities of heavy oil content in the charge stream and `the reactor temperature level raised to provide greater economic yields from `the uidized unit.

The foregoing examples are representative of test data which have been obtained. Actually in studying diiferenttest operations in connection with fluid catalytic cracking systems, it has been determined that the quantitative yeffects of varying certain of the `aforedescribed independent operational variables on conversion can be predicted.

As a'result, one can estimate the effect of a change in these variables on product yield. Por example, it has been found that with changes in reactor temperature, a

variation of 3 to 4 F. will change conversion about j 1%. A change in combined feed ratio of 0.1 will in turn :change conversion by about 2%. A change in feed preheat, such that the combined feed temperature changes about 100 F., will eifect an approximate 2% decrease in conversion. Thus, if conversion is to be held constant or increased,v then the reactor temperature will have to be adjusted upwardly. Of course, the interrelations of adjusting the Various independent as well as dependent operational variables is a complex one and the above noted resulting changes are not necessarily fixed for all types of However, the

will result in greater economic yields to the reliner.

stream, the improved method of effecting improved product yields from the hydrocarbon charge stream by operating to provide a high temperature level in the regeneration zone which comprises, increasing the combined feed ratio with an increase in the heavy recycle 15 oil content of the charge stream being introduced to the reaction zone, effecting both a greater conversion in said reaction zone and an increased coke deposition level on the catalyst particles sufficient to provide a temperature above 1150 F. in the regeneration zone when oxidizing the coke on the catalyst particles in the presence of a controlled oxygen containing stream introduced to such regeneration zone, and regulating the' introduction of the oxygen containing stream to the regeneration zone directly responsive to a predetermined temperature dierential between the gas outlet section and the catalyst contacting section of the regeneration zone to minimize excess oxygen therein and to `control afterburning in the upper portion of the regenerating zone.

2. .In a continuous process for cracking a hydrocarbon charge stream comprising fresh feed and recycle oil in the presence of subdivided catalyst particles, wherein the hydrocarbon stream is subjected to a tluidized contacting of the particles in a reaction zone, conversion products are separated from the contacted particles, separated I claim as my invention:

1. In a continuous process for cracking a hydrocarbon charge stream comprising fresh feed and recycle oil in the presence of subdivided catalyst particles, wherein the hydrocarbon stream is subjected to a fluidized con- Table A EXAMPLE I II III IV V VI VII Processing Conditions: l

Reactor temp. dense, "F 900 945 913 936 950 900 910 Reactor temp. dilute, F 885 930 898 921 935 885 885 Regenerator temp., dense F.-- 1, 120 1, 175 1, 165 1, 20() 1,180 1,180 1,190 Regenerator temp., dilute F 1, 135 1, 190 1, 180 1, 215 1, 195 1, 195 1, 205 AT (diierential temp., between reactor and regenerator, F.) 220 230 252 264 230 280 280 Combined feed ratio 1 50 1. 50 2 00 2 00 1. 50 1 50 1 50 Raw oil temperature, F 400 600 400 600 400 400 400 Weight hourly space velocity (WHSV) 6 6 6 2. 5 Catalyst activity (UOP) 32 32 32 32 32 32 32 Catalyst cir. rate, lb./hr. 10fi 3. 45 3.00 3 82 3 30 3. 61 2 75 2 75 Conversion, volume percent 65 72 75 75 78 72 67 Wt. Vol. Wt. Vol. Wt. Vol. Wt. Vol. Wt. Vol. Wt. Vol. Wt. Vol. Per- Per- Per- Per- Per- Per- Per- Per- Per- Per- Per- Per- Per- Percent cent cent cent cent cent cent cent cent cent cent cent cent cent Products: f Has 0.2 0. 2 0. 0.2 0.2 6.7 8.7 8.0 8.2 7.2 Total C4 fraction 7.9 9. 4 14. 0 9. 2 13. 7 9. 3 8. 5 12. 6 Debutanized gasoline (380 at 90%). 41. 0 45. 5 52. 5 l16. 7 54 47. 3 42. O 48. 5 Light cycle oil 20. 5 18.5 18 18. 6 18 18.6 20. 5 20 Heavy cycle oil- 10. 6 5.3 5 2.1 2 2. 1 10.6 10 Clarified slurry 5. 6 5. 6 5 5. 7 5 5. 7 3.4 3 Coke--- '7.5 6.8 9.5 8.6 7.6

C3 and Lighter, Mole percent:

catalyst particles containing a coke deposit are subjected' to iiuidized contacting of an oxygen containing stream in a separate regeneration zone, combustion gas products are separatedfrom regenerated catalyst particles and such regenerated catalyst particles with a reduced'coke content are returned to the reaction zone for contact With the hydrocarbon charge stream, the improved method of effecting improved product yields from the hydrocarbon charge stream by operating to provide a high temperature level in the regeneration zone, which comprises, preheating the fresh feed portion of the hydrocarbon stream, concom-it'antly therewith increasing the combined feed ratio with an increase in heavy recycle oil, varying the catalyst circulation rate to effect a coke deposition level on the catalyst particles :sufficient to provide a greater temperature spread between the reaction and regeneration zones with a temperature above 1150 F, in the regeneration zone when oxidizing the coke deposit on the catalyst particles in the presence of a controlled oxygen containing stream introduced to such regeneration zone, and regulating the introduction of the oxygen containing stream to the regeneration zone directly responsive to a predetermined temperature differential between the gas outlet section and the catalyst contacting section of the regeneration zone to minimize excess oxygen therein and to preclude afterburning in the upper portion of the regeneration zone.

3. In a continuous process for cracking a hydrocarbon charge stream in the presence of subdivided catalyst particles, wherein the hydrocarbon stream is subjected to a uidized contacting of the particles in a reaction zone, conversion products are separated from the contacted particles, separated catalyst particles containing a coke deposit are subjected to fluidized contacting of an oxygen containing stream in a separate regeneration zone, combustion gas products are separated from regenerated catalyst particles 'and such regenerated catalyst particles with a reduced cok-e content are returned to the reaction zone for contact with the hydrocarbon charge stream, the improved method of effecting improved product yields from the hydrocarbon stream by operating to provide a high temperature level in the regeneration zone, which comprises, decreasing the weight hourly space velocity in the reaction zone and increasing the reaction zone temperature to effect a greater conversion of said hydrocarbon charge stream and providing a coke deposition on the catalyst particles sufficient to provide a temperature above 1l50 F. in the regeneration zone when oxidizing such coke deposition on the catalyst particles in the presence of a controlled oxygen containing stream introduced to such regeneration zone, and regulating the introduction of the oxygen containing stream to the regeneration zone directly responsive to a predetermined temperature differential between the gas outlet section and the catalyst contacting section of the regeneration zone to minimize excess oxygen therein and to control afterburning in the upper portion of the regeneration zone.

4. In a continuous process for cracking a hydrocarbon charge stream in the presence of subdivided catalyst particles, wherein the hydrocarbon stream is subjected to a uidized contacting of the particles in a reaction zone, conversion products are separated from the contacted particles, separated catalyst particles containing a coke deposit are subjected to fluidized contacting of an oxygen containing stream in a separate regeneration zone, combustion gas products are separated from regenerated catalyst particles and such regenerated catalyst particles with a reduced coke content are returned to the reaction zone for contact with the hydrocarbon charge stream, the

improved method of effecting improved product yields from the hydrocarbon charge stream by operating to provide a high temperature level in the regeneration zone, which comprises, increasing the reaction zone temperature and effecting a greater conversion of said ch-arge stream in said reaction zone, varying the catalyst circulation rate to effect a coke deposition on the catalyst sufficient to provide a temperature above 1150 F. in the regeneration zone when oxidizing the coke deposition on the catalyst particles in the presence of a controlled oxygen containing stream introduced to such regeneration zone, and regulating the introduction of the oxygen containing stream to the regeneration zone directly responsive to a predetermined temperature differential between the gas outlet section and the catalyst contacting section of the regeneration zone to minimize excess oxygen therein and to control afterburning in the upper portion of the regeneration zone.

5. In a continuous process for cracking a hydrocarbon charge stream comprising fresh feed and recycle oil in the presence of subdivided cat-alyst particles, wherein the hydrocarbon stream is subjected to a fluidized contacting of the particles in a reaction zone, conversion products are separated from the contacted particles, separated catalyst particles containing a coke deposit are subjected to fluidized contacting of an oxygen containing stream in a separated regeneration zone, combustion gas products are separated from regenerated catalyst particles and such regenerated catalyst particles with a reduced coke content are returned to the reaction zone for contact With the hydrocarbon charge stream, the improved method of effecting improved product yields from a hydrocarbon charge stream when the latter is varied to have an increased amount of heavy oil in the fresh feed portion thereof by operating in a manner providing a high temperature level in the regeneration zone in a manner which comprises, increasing the reaction zone temperature, varying the catalyst circulation rate, effecting a coke deposition level on the catalyst particles sufficient to provide a greater temperature spread between the reacti-on and regeneration zones with a temperature above 1l50 F. in the regeneration zone when oxidizing the coke deposition on the catalyst particles in the presence of a controlled oxygen containing stream introduced to such regeneration zone, and regulating the introduction of the oxygen containing stream to the regeneration zone directly responsive to a predetermined temperature differential between the gas outlet section and the catalyst contacting section of the regeneration zone to minimize excess oxygen therein and to control afterburning in the upper portion of the regeneration zone.

References Cited bythe Examiner UNITED STATES PATENTS 3,161,583 12/64 Pohlenz 208-164 OTHER REFERENCES Modern Fluid Catalytic Cracking by E. Van Dornick, The Petroleum Engineer, April 1947, pages 149, 150, 152 and 154.

DELBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner.

Claims (1)

1. IN A CONTINUOUS PROCESS FOR CRACKING A HYDROCARBON CHARGE STREAM COMPRISING FRESH FEED AND RECYCLE OIL IN THE PRESENCE OF SUBDIVIDED CATALYST PARTICLES, WHEREIN THE HYDROCARBON STREAM IS SUBJECTED TO A FLUIDIZED CONVERSION OF THE PARTICLES IN A CONFINED REACTION ZONE, CONVERSION PRODUCTS ARE SEPARATED FROM THE CONTACTED PARTICLES, SEPARATED CATALYST PARTICLES CONTAINING A COKE DEPOSIT ARE SUBJECTED TO A FLUIDIZED CONTACTING OF AN OXYGENCONTAINING STREAM IN A SEPARATE CONFINED REGENERATION ZONE, COMBUSTION GAS PRODUCTS ARE SEPARTED FROM REGENERATED CATALYST PARTICLES AND SUCH REGENERATED CATALYST PARTICLES WITH A REDUCED COKE CONTENT ARE RETURNED TO THE REACTION ZONE FOR CONTACT WITH THE HYDROCARBON CHARGE STREAM, THE IMPROVED METHOD OF EFFECTING IMPROVED PRODUCT YIELDS FROM THE HYDROCARBON CHARGE STREAM BY OPERATING TO PROVIDE A HIGH TEMPERATURE LEVEL IN THE REGENERATION ZONE WHICH COMPRISES, INCREASING THE COMBINED FEED RATIO WITH AN INCREASE IN THE HEAVY RECYCLE OIL CONTENT OF THE CHARGE STREAM BEING INTRODUCED TO THE REACTION ZONE, EFFECTING BOTH A GREATER CONVERSION IN SAID REACTION ZONE AND AN INCREASED COKE DEPOSITION LEVEL ON THE CATALYST PARTICLES SUFFICIENT TO PROVIDE A TEMPERATURE ABOVE 1150*F. IN THE REGENERATION ZONE WHEN OXIDIZING THE COKE ON THE CATALYST PARTICLES IN THE PRESENCE OF A CONTROLLED OXYGEN CONTAINING STREAM INTRODUCED TO SUCH REGENERATION ZONE, AND REGULATING THE INTRODUCTION OF THE OXYGEN CONTAINING STREAM TO THE REGENERATION ZONE DIRECTLY RESPONSIVE TO A PREDETERMINED TEMPERATURE DIFFERENTIAL BETWEEN THE GAS OUTLET SECTION AND THE CATLYST CONTACTING SECTION OF THE REGENERATION ZONE TO MINIMIZE EXCESS OXYGEN THEREIN AND TO CONTROL AFTERBURNING IN THE UPPER PORTION OF THE REGENERATING ZONE.

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