US2770584A - Method of operating a pneumatic lift used to transport granular solids in a hydrocarbon conversion process - Google Patents

Description

NOTE. R3, '1956 F. E. RAY ETAL 2,77%584 METHOD OE OPERATING A PNEUMATTO ETET usEO To TRANSPORT GRANULAR SOLIDS IN A HYDROCARBON CONVERSION PROCESS l1, 1951 3 Sheets-Sheet l Filed Dec.

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METHOD oF OPERATING 0 INVENTUM en/'eral EN? United States Patent O METHOD OF OPERATING A PNEUMATIC LIFT USED TO TRANSPORT GRANULAR SOLIDS IN A HYDROCARBON CONVERSON PROCESS Frederick E. Ray, Woodbury, and Robert D. Drew,

Wenonah, N. J., assignors to Socony Mobil Oil Company, Inc., a corporation of New York Application December 11, 1951, Serial No. 261,062

3 Claims. (Cl. 196-52) This invention deals with the operation of a pneumatic It is particularly ular contact material is moved through conversion and :reconditioning zones in a closed cyclic path.

The invention may be applied to such processes as catalytic cracking, isomerization, hydrogenation, dehydro- ;genation, reforming, hydroforming, aromatization, alkyla ation, ciclicization treating or desulfurization of petroleum fractions. Also, the invention may be applied to coking -of hydrocarbons in the presence of granular coke or re- .fractory solids, viscosity reducing of petroleum residuums at elevated temperatures, pyrolytic conversion processes such as the conversion of propane and ethane to un- .saturated hydrocarbons and of methane to acetylene.

The contact material involved may vary widely in its properties depending upon its use. For catalytic hydrocarbon systems the catalyst may take the form of natural or treated clays, bauxites, inert or active carriers impregnated with certain catalytically act-ive metals or com- ;pounds thereof, or synthetic associations of silica, alumina, magnesia, chromia, molybdenum oxide, etc., or combinations thereof to which may be added small amounts of other compounds, usually metallic compounds for spe- 'ciic purposes. When the contact material is employed principally for heat carrying purposes as in pyrolytic conversion processes, it may take the form of any of a number of refractory materials such as fused alumina, mullite, Carborundum, zirconium oxide, charcoal, etc.; for coking processes the solid material may comprise of a low activity clay catalyst, petroleum coke, pumice or similar materials. The contact material may be -in the form of pellets, spheres, tablets, pills or irregular shaped material of palpable particulate form as distinguished from powdered material. It should be understood that the term granular as employed herein in describing and claiming this invention is intended to broadly cover any of the above forms of Contact material. The contact material involved in this invention may range in size from about 0.005 to 0.5 inch and preferably from about 4-20 mesh by Tyler Standard Screen Analysis. The density of the material as poured into a measuring container may be within the range about 20-130 pounds per cubic foot. In continuous catalytic cracking systems the contact material is passed cyclically through a conversion zone wherein it contacts a hydrocarbon feed at pressures usually above atmospheric and temperatures of the order of 700-1l00 F. whereby the feed is converted and then through a regeneration zone wherein a carbonaceous contaminant deposited on the catalyst in the conversion zone is removed by burning. When the granular catalysts are employed it has been found to be highly desirable to maintain the catalyst as a substantially compact bed or column of gravitating particles in the conversion and regeneration zones. Until recently, continuous bucket elevators were employed exclusively to effect transfer of 2,770,584 Patented Nov. 13, 1956 the catalyst between zones in commercial units. Mechanical elevators have been found to impose certain practical limitations on the overalltunit height and on the amount of catalyst circulated. As a result, heretofore all commercial continuous catalytic cracking units of the cornpact moving bed type have involved side by side arrangement of reactor and kiln, thereby requiring two elevators and have involved relatively low catalyst circulation rates. It has been found desirable to increase catalyst circulation rates in order to permit simplification of other parts of the system, particularly the kiln, and to arrange the reactor and kiln in vertical series so as to require only a single catalyst transfer step per cycle. This could not be done practically with existing mechanical transfer devices. It had been proposed from time to time to effect the catalyst transfer by pneumatic transfer lifts but the use of pneumatic transfer in these cyclic conversion systems was prevented because of the very high catalyst attrition and breakage encountered in the pneumatic transfer step, and further because of excessive power requirements. Pneumatic lifts have been developed recently which provide practical pnuematic transfer of the granular contact material in these cyclic conversion systems, in part by delicate control of the gas velocities at various points along the lift. rl`he lifts are disclosed in application for United States Patent Serial Number 210,942, filed February 14, 1951. These lifts involve essentially the use of a continuous vertical lift passage, open at both ends, and with the ends projected into feeding and receiving zones, terminated intermediate the top and bottom of each zone. Contact material is gravitated into the feeding zone at the bottom of the lift as a substantially compact mass and travels downwardly about the lower end of the lift passage. ln a preferred form of gas lift, a pneumatic transfer gas is introduced into the zone in two streams, a primary and secondary stream. The primary stream is introduced from a point near the bottom of the lift so as to enter the lift without passing through the mass of compacted material, usually directly beneath the lift. The secondary stream is introduced at one or more locations laterally displaced from the centerline of the lift so that it passes through a substantial thickness of the contact material in the feeding zone. The function of the pri mary gas stream is to drive the granular solids up the lift pipe into the receiving zone. The function of the secondary stream of lift gas is to regulate the flow rate of solids in the system by forcing solids into the primary gas stream in the lift passage.

It has been discovered that when solids or catalyst velocity in the lift pipe is too low, refluxing occurs and the performance of the lift is unsatisfactory. When the cata- 4 lyst velocity in the lift is too high, on the other hand, the

fountain of solids at the top of the lift in the receiving zone is too high and `the performance of the lift is again unsatisfactory. With the catalyst circulation fixed by a definite secondary gas flow rate, the total gas flow controls the catalyst velocity in `the lift passage and, consequently, the height of the fountain of particles in the receiving zone at the upper end of the passage. A gas velocity which is too low results in a condition of surge. As the gas velocity is increased, by increasing the primary gas flow rate, the surging stops and the catalyst velocity and the height of the fountain increase.

It has been found that the gas lift will perform best when a condition of mild reiluxing, described as incipient refining, obtains in the lift passage. It has been dis* covered that a pressure reading taken at an intermediate level in the lift passage, and preferably the upper two thirds of the passage, can he used to yield a sensitive indication that mild reiluxing or incipient surging is occurring, `and can be used for operating the lift at peak performance.

The object of this invention is to provide an improved method for operating a gas lift designed to lift granular solids in an upwardly flowing stream of lift gas.

A further .object of this invention is to provide an improved method for automatically operating a gas lift which is de-signed to lift granular solids in an upwardly flowing stream of lift gas at peak performance.

It is a further object of this invention to provide an improved method for pneum-.atically lifting granular contact material in a cyclic hydrocarbon conversion system with minimum attrition or breakage of 'the particles.

These and other objects of the invention will become apparent from the following description of the invention, to be read in conjunction with the referenced sketches.

Figure 1 is an elevational view lof a preferred arrangement and application lof this invention in a cyclic conversion system.

Figure 2 is an elevational View, partly in section, showing a pneumatic lift with gas feeding apparatus and automatic devices for maintaining the lift in operation .at yoptimum performance.

Figure 3 is an elevational View of a gas lift with an alternate arrangement of gas vfeeding apparatus and automatic devices -for maintaining the lift in operation at optimum performance.

Figure 4 .is an elevational view of Ia gas lift showing an `alternate embodiment sof the invention.

Figure 5 is a typical circular pressure-time diagram obtained by recording the static pressure at an intermediate lift pipe :level in an operating moving bed hydrocarbon cracking system for a 24-hour period.

Turning now to Figure l, there is shown a typical application of this invention in a cyclic continuous moving bed catalytic cracking process.k 1n the drawing there is shown a reactor which is adapted to conne a moving compact 'bed tof catalyst and which internally may incorporate those features Yby now well known to the a-rt for accomplishing uniform flow, contacting, engaging, and disengaging of the catalyst and reactant. Catalyst enters the 'reactor through a gravity feed leg 11, which may be ofthe type disclosed and claimed in United States-Patent Number 2,410,309, and catalyst is withdrawn from the reactor via two or more conduits 12 Aand 13 from which it flows through branch conduits 14 to the upper end of a catalyst regenerator 15. The withdrawal system may be similar to that now disclosed and claim-ed 'in United States Patent No. 2,546,625 which issued March 27, 1951. Vaporized hydrocarbon feed, for example, a '50G-'900 F. gas loil cut, may enter the upper section ofthe reactor via pipe 17. The feed may be preheated `in `a heater, not shown, to a temperature ofthe order of 700-900 F. A suitable high boiling liquid `hydrocarbon yfeed may be supplied into the reactor via pipe 18, either cold or in preheated condition.

The internal liquid feed arrangement may be lsimilar to that ,disclosed in application Serial Number 719,724, led inthe United States Patent Oice on January 2, 1947, now Patent No. 2,574,850. The cracked vlower boiling gaseous 'hydrocarbon .products may .be withdrawn from the 'lower'.section ofthe reactor via pipe 20. The internal arrangement associated with pipe 20 may be similar -to that 'disclosed and claimed in United States Patents 2,458,498 and 2,459,096. A suitable inert seal gas such as .steam or ilue gas may he supplied to an upper seal zone in the reactor via pipe 21. The irate -of seal gas supply is .maintained by differential pressure ,controller sufficient to control the pressure in the seal zone slightly above that in the reaction Zone proper. Similarly, a seal and purge Agas is `admitted into the lower section of the reactor via pipe 22 to purge ga-seous hydrocarbons from the eluent catalyst. It should be understood that the word gaseous as employed herein i-s intended in a broad sense as covering materials in the gaseous phase under the particular operating conditions involved regardless of what may be the phase of such material under ordinary atmospheric conditions. The reactor may be operated at a pressure near or stomewhat above or below that in the kiln. When the reactor pressure is substantially above that in the kiln it may be desirable to provide a depressurizing zone in the legs 12 and 13.

While the invention is not limited thereto the kiln shown vis of 'annular shape so as to provide a central shaft through which a lift conduit 25 extends, The kiln 15 is provided with a central air inlet 26 and ue' gas outlets 16 and 19 adjacent either end. A bank ,of cool: ing tubes is provided in the lower section of the kiln supplied with a suitable cooling liquid or gas via pipe 27. Oooling uid leaves these tubes via pipe 28. Suitable internal arrangements for the kiln here shown are disclosed and claimed in application Serial Number 186,953, led in the United States Patent Oice September 27, 1950, now U. S. Patent No. 2,695,220, and Serial Number 186,954, filed in the United States Patent Oice September 27, 1950.

The catalyst passes from kiln 15 via two or more pipes 30 and 31 as compact streams delivering onto compact gravity feed legs in pipes 32 and 33, respectively. These legs are vented to the atmosphere on their upper ends, and suitable flow measuring devices may be provided in association therewith.

A lift gas is drawn through the downcomer 5.0 by means of the 'blower 51 and delivered under pressure to the heater 52. The blower is driven by the motor 57, the motor speed being controlled automatically by the pressure regulating controller 56 to maintain the blower discharge pressure substantially constant. The lift gas may suitably be lair, steam or other inert gas, air being preferred. Fuel is introduced into the heater 52l and burned -to heat the `air to a temperature nea-r the temperature of the catalyst. The heated air is delivered through the conduit 53 to the primary gas conduit 38 and secondary gas conduit 54.l In the preferred form of lift, the primary conduit is projected into the brot-tom of the lift tank 34 and terminated beneath the lift pipe. The secondary 4conduit 54 may be split into several conduits 4 3 distributed about the wall of the tank 34, so that ythe gas passes through the catalyst bed in tank 34 before entering the lift pipe 25, thereby driving catalyst into the primary gas stream. The combined gas` streams lift the particles up the pipe `25 to the separator 36. rfhe gas is withdrawn from the separator 36 through the conduit 6,3 and the solids are withdrawn through the feed leg 11 to the seal pot 21 and then conveyed into the reactor -10. The dual pressure controller 15 is used to control valve 21 in the inert gas line 55 attached to the seal pot 21, so as to maintain `a pressure in the seal pot slightly higher than the pressure in the reactor, thereby preventing the escape of reaction products up the feed les.

A ilow meter 60 is located in the downeomer 50 Where it measures the total lift gas low. A ow regulating controller A61 is operably connected to the flow meter 60 and valve 62 in the primary gas conduit 3,78, so as to maintain the total gas'ow through. the lift constant. In this type of gas lift, the ow of catalyst through the lift is determined by the flow rate of secondary Vgas through the conduit 54. i It has 'been found that the ow of solids is substantially proportional to lthe pressure at the bottom of the lift. Therefore, a pressure regulating controller 58 is operably connected to a pressure tap 5 at the bottom of the lift arid valve 5,9 in conduit 54, so as to maintain the catalyst vcirculation substantially constant,

A pressure ,tap 7. 0 is located in the upper two thirds of the lift pipe and connected to `the indicator 79. It has been discovered that this pressure reading can be used to set the gas ow rate for minimum attrition. The gas flow isset above the refluxing rate, i. e., the rate at which violent surging or refluxing in the pipe .occurs with sudden changes 1in pressure and a Arapid increase in catalyst break.-

age. The gas flow is then reduced gradually by resetting the flow regulating controller 61 until the pressure as indicated on the pressure indicator 79 shows a magnitude of iiuctuation of about 100 percent. This is known as the threshold relluxing rate. Any slight further decrease in total gas flow rate would cause the pressure in the pipe as indicated by the indicator to rise 3 or 4 times its normal value and reluxing would be present in the pipe. The flow regulating controller is then set for a flowrate about 1% above the threshold reiluxing rate, and the catalyst attrition Will be at a minimum value. Broadly, for best performance, the total gas ow rate should Ibe about 0.5-2.0 percent above the threshold refluxing rate and for preferred operation, the total gas flow rate through the lift pipe should be about 0.7 5-l.25 percent above the threshold refluxing rate.

Referring now more particularly to Figure 2, the caltalyst delivers from legs 32 and 33 onto a bed 29 thereof in a lift feed tank 34. A substantially vertical tapered lift pipe 25 extends upwardly from a location within and intermediate the ends of a combination settling--surge vessel 36 which is positioned a substantial distance above the reactor lil. The lower end of the lift pipe may be ilared outwardly to form a mouthpiece 35. This mouthpiece is preferably dared outwardly along a curve, approximately a hyperbolic spiral. A detailed view of t-he mouthpiece is shown on Figure 2. The mouthpiece may be a separate member which is attached to a vertical member to form the assembled lift pipe or may be merely the lower end of a continuous pipe. When the expression lift passage is used herein it is meant to` include the entire passage from top to bottom including generally a vertical portion and also in preferable designs the curved inlet portion in addition to the vertical portion. The primary gas is introduced through the pipe 38 which terminates directly under the lift pipe above the surface of the mass of solids. The secondary gas is introduced through the pipes 43 into the annular space behind the baffle 47. The secondary gas moves inwardly through the mass of solids about the bottom ofthe lift pipe into the lower end of the pipe. Preferably the contact material is suspended upwardly from a level below or at least not above the level of primary gas entry.

All the lift gas is passed downwardly through the downcomer 5'@ to the blower 5i. The gas is transferred through the conduit 4tlto the heater 52. In order to malte the operation more stable a pressure controller 56 is connected to pressure tap 64 in line 44 and used to control the speed of the blower. This is` particularly necessary when the blower has a steep performance curve, C. F. M. v. R. P. M. In Figure 2 the controller is used to operate an automatic valve in the steam line supplying steam to a steam turbine used to drive the blower 5l. The lift gas, heated in the heater 52, is discharged through the conduit 53 and split into primary and secondary gas streams.

When the velocity of the particles travelling upwardly through the pipe 25 is too low, a reliuxing condition occurs in the pipe which may become so violent that ilow of solids through the pipe is seriously curtailed or completely stopped. Attrition or breakage of the particles is found to be excessive when reliuxing occurs in the pipe. When the velocity or" the particles is too high, on the other hand, the particles shoot out of the top of the pipe at excessive velocity and high attrition rates are again encountered. The total gas flow controls the catalyst velocity whereas the secondary gas ow controls the catalyst circulation rate. in starting the lift, therefore, the valve 66 is opened wide enough to provide a total gas flow, as measured by the tlow meter 60 in the downcomer 5i) which is calculated or known to provide a catalyst velocity above the refluxing rate. The catalyst flow rate is then adjusted by opening the valve 67 in the secondary gas line. Et has been found that the catalyst ilow rate is related to the pressure drop across the lift. Therefore, when the top of the lift is vented to the atmosphere or the pressure there is maintained constant, the catalyst flow rate can be maintained constant by means of a pressure controller 68 whichv is attach-sd to a pressure tap 69 and used to operate the valve 67 automatically'. In order that the catalyst attrition be somewhere near the minimum obtainable, the valve 67 is maintained in a iixed position and the total gas flow is reduced by gradually closing the valve 66. The pressure at the bottom of the lift, as indicated by a pressure gauge attached to the pressure tap 69, falls to a minimum valve and then with further reduction in total gas flow commences to rise.. The lift will give fairly satisfactory performance and reasonably low attrition if operated at the flow rate which yielded the minimum pressure at the bottom of the lift or just slightly above that flow rate. The valve 67 can then be placed on automatic operation to hold the catalyst circulation constant.

It has been discovered that when the gas flow rate is adjusted so that the pressure drop across the lift is at a minimum Valve, as indicated hereinabove, the attrition of the catalyst in the lift may vary app-reciably. I-t is believed that this lack of uniformity of attrition is caused by variation in gas velocity which are too slight to effect measurable changes in the overall pressure drop and consequently cannot be detected., Experimental operation of a lift pipe designed for commercial operation at a catalyst circulation rate of 360 tons per hour of `granular catalyst particles has shown that control of the gas velocity is extremely critical with a three percent increase in velocity causing a twenty-five percent increase in catalyst attrition. A similar decrease in velocity below optimum may even cause more serious diiculty because of the violent retluxing condition which occurs at too low a gas velocity. It has been found that the gas .dow rate which provides optimum ygas velocity can be determined much more accurately by measuring the static pressure at intermediate points `along the lift pipe, preferably at elevations above the Ibottom third of the pi-pe. When the gas velocity is too low and retlluxing occurs in the pipe, the static pressure rises to about four times its normal value. Excessive velocities cause the static pressure to be depressed. Furthermore, at optimum velocity, iluctuations in static pressure are larger than at excessive gas velocity although they are more uniform and not as violent as those which occur when reiluxing is presen-t. Optimum gas velocity is found to occur when the intermediate pressure fluctuations are at their maximum value `and yet still of a uniform character. This may be: described as a condition `of incipient surging or refluxing. If the total gas flow `rate is continuously or periodically adjusted to maintain optimum -gas velocity in the pipe, as indicated by the intermediate static pressure, the best all round lift performance is obtained and catalyst attrition is at the minimum v-alue.

The gas veloci-ty may be controlled by using the intermediate static pressure as a guide and adjusting the total gas flow rate in accordance with the pressure reading obtained. The gas flow rate is kept low enough to get a maximum Width of the pressure band at as high a pressure as possible with out having the pressure increase sharply to several times its normal value. The threshold reliuxing velocity is determined periodically by lowering the gas flow rate 'until the static pressure rises rapidly.` The -gas flow rate is then raised to increase the gas velocity to an incipient re-iluxing condition. An increase of about one percent over the threshold reuxing rate is found to shift conditions in the lift pipe from refluxing to incipient retluxing. The total gas flow rate can then be adjusted to maintain the intermediate static pressure and/or the Width of the pressure band constant. l

The gas lift may also be automatically operated at optimum gas velocity continuously. Figure 2 shows a static pressure tap 70 attached to a dampener 7l, designed to remove pressure fluctuations. The steady pressure is then applied to `a pressure controller 72. Since the optimum gas velocity is very critical, in a preferred form of a'z'zoassa the invention :the ,controller is .not used to `operatedhe valve 66 butis used to operate; the valve -73 fin fa :small :bypass conduit yparallelingthe main'valvev. .Becauserthe gas lilowthrough 'the thy-pass valve 73 is =a `minorrfracti'on ofthe-.flow through the main valve, the valve7'has. suffcientsensitivity-to provide close accurate adjustment of fthe optimum gasvelocity. The main lvalve 66=is setby hand at altlow ratesknown to be slightly'below optimum. The auxiliary valve is then automatically controlled to maintain the velocity atv optimum `and yattrition'innthelift at a minimum.

.Figure 3 shows an kalternate embodiment. The flow meter't) may be an orifice plate,`venturi or-other suitable device'for measuring gas'ow. TherrheaterSZmay `be pla-ced in theprimary gas l-ine'38, .as shown, since't-he primary :gas pipe carries 85-95 percent of the'total gas tlow, generally. The pressure tap 70 is connected toa limitcontroll'erfdesi-gncd to control thewidtho'f'the pressure libandbetween maximum fand minimum ranges. The'limitcontroller'is connectedtoa valve '8-1 ina small bleed linefS-Z. The bleed line can be arranged -to withdraw gas from lthe primary gas piper-3.8 when the valve 81 ,is-.opened or alternatively may admit lgas'from a pressure source,notshown. By this expedient if the static pressure variation decreases, theiigas rate is descreased and'vice versa. The optimum variation for any lift pipe is readily .determined Iby a reuxing te-st and the controller limits set accordingly.

EReferring now to Fig-ure 4, .ain-arrangement is lshown in fwhichathe main valve- 66 is operated-automatically by a fllow controller S3 to maintain a constant flow through t-he lift pipe 25. A limit controller 84 is connected to the pressure tap 70 and used tovoperate the valve 73'n line y85, which -bypasses the main valve 66. :The flow controller l83 has pressure lines S6, 87 oneach -side of the meter v260 vand ahy-pass 'line -88 connecting these lines. Normally, thevalve 89 in l=ine`88 is closed. Howeven the limit controller 84 is designed to yautomatically operate valve -89-when the valve 73 is operated, such that the pressuredrop across the ow meter is -not'changed It is "also possible to have the limit controller 84 operate directly upon `the flow controller -83 to reset the'ilow meter to'a new control point whenever the owthroughithe by-pass line'85 is increased or decreased. The controller 83-must be changed so that the controlled ilowrate is increased or decreased an yamount `equal to the increase `or decrease in the lay-pass conduit `85.

Asa further embodiment, instead of using a limit controller in the apparatus shown on Figure 3, an automatic sampling instrument can be used to continuously run reiluxing tests. The instrument is connected to the pressure tap /70 in place of llimit controller 80 and operates valve `81.as`shown on Figure 3. The instrument 80 reduces the total gas ow until the lift static pressure rises about 100 percent and then the instrument increases the total gas rate about 1 percent. This series of operations is continuous, keeping the lift gas velocitywithin 4an optimum range.

Example A commercial catalytic cracking system which has reactor superposed the' kiln and incorporates a 237-foot pneumatic lift pipe, was operated at a catalyst circulation'rate of 340 tons per hour, using a standard cracking catalyst. The lift pipe has a mouthpiece at the bottom which flares outwardly along a hyperbolic spiral curve. The lower frusto-conical section of the pipe extends upwardly about 65 percent ofthe total length and the upperportion of the pipe is flared outwardly along a smooth curve to a maximum internal diameter of 3953". The internal diameter of the pipe is 25.65F', 27, V29" and 3117" 'at the lower endof the frusto-conical section, 50 feet above, 100 feet above and 150 feet above that level. Pressure taps were located at elevations of 166 feet and 214 feet above the bottom of the pipe and readingsftaken continuously for a 24-hour period. 'The pressurel-timexdiagrams :aren shownf on .v-Figure 5. .During normal :operation these spressures were Ifoun'd yto fluctuate overlacertainband-Wi'dth around a-zquite constant 4average value. Ther time of fluctuation from oneedgeof'thezband tothe= omen-averaged; about one a minute. fW-hentheiprimarywairgowwas vdecreased the band was'enlarged and the :average 4Value shifted in the kdirection of `highenpressures. yOn further decrease in primary'air flow, reuxing occurred, fas .evidenced-bythe momentary `pressure increasesitovalues extending outside, and'on the high side of, the bands of normal operation,` such as shownfa't points A, B,'CDfandfE on'the pressure .diagram lof Figure :5. -During theiperiodzfrom 1:00p. m. to :7:0.0 p.\m. lthe/air ow was varied,iasin`dicatcd on FigureS, toishow thefdifferencein.pressure-time diagram at1dfferent gas rates. When operated continuously .atincipient refluxing conditions, such as indicated on .the Figure-'Sibetween 7:00 p. m. and 9:00 a.fm., the attrition rate `was less thanone and one-half tonsper day lfor Ia circulation rate of 340 tons 'per hour. The gasl flow for minimum attrition, 'at `the operating conditions` obtaining, wasrabout 212,600s. c. f. In. The Athreshold reuxing ra-tewas -found to be about 12,475 s.l c. f. m.

I-It is to 4fbe understood thatthe specific examples -of apparatus, design 'and arrangement, and of operation and application of i this invention are'intended only as illustrativefof 'the inventionand itis intended to cover all changes andfmodi'cations of the example herein chosen for=purposesf0f disclosure, which do not constitute departurefrom -the spirit and scope of the invention.

We claim:

1. In'afhydrocarbon conversion process-in which la granular*solidisl-gravitated as a substantially compact columnar= mass through reaction andk regeneration Zones andlifted from a location below one of the zones `to 'a locationabove `the vlother VVzone through an upwardly'directed'liftpassage lby means 'of a flowingv stream of lift gas, theimproved method of controllingthe lifting step foroptimum performance withminimum attrition which comprises: gravitating granular solids downwardly from the bottom of one of the Zonesto a feeding vzone located at the bottom-of the'lift passage, introducing a lift gas into the feeding zone, so as to support and transport the granular solids upwardly through the ylift passage, measuring continuously the static pressure in said passage at a loca'tion'in the upper-two thirds of the passage, and controlling-'the flow rate vof thelift gas admitted to said feeding zone in'response to said static pressure, so that the flow is` maintained below that point at which` minimum pressure occurs and slightly'above that point at which the pressure increases very substantially with any further reduction 1n `gas flowrate, whereby the attrition of the vgranular solids during transfer through the lift passage is minimized.

'2. In a hydrocarbon conversion process in which a granular solid material is gravitated -as a substantially compact columnar mass'through reaction and regeneration zones and lifted from a location below one of the zonesto a'location above the other zone through anupwardly directe'd `lift passage by means of a flowing stream of lift gas, the improved method of controlling the lifting step for minimum attrition of the solids which comprises: gravitating .granular solids downwardly from the bottom of one of'the zones to a feeding zone located at the bottom of the lift passage, so as to form a substantially compact vbed of solids-about the lower end of the passage, measuring the flow of a stream of lift gas, splitting the stream of lift gas into primary and secondary gas streams, and controlling the flow rate of the primary gas stream in response to change in the measurement of total lgas liow to maintain the total gas flow substantially constant, introducing at least the major portion of 'thepiimarygas into the feeding zone, so as to enter the'liftspassage-without passing through any substantial thickness of the solids bed in said feeding zone, introducing the secondary gas into the feeding zone, so as to pass `through a substantial thickness of the solids bed before entering the lift passage, continuously measuring the static pressure at the bottom of the lift passage and controlling the flow rate of the secondary gas, in order to maintain said static pressure at the bottom of the lift passage substantially constant, continuously measuring the static pressure in the lift passage at a location in the upper two thirds of the passage, bleeding a minor proportion of the primary gas stream out of said stream at a point intermediate the point at which said stream is controlled in response to total gas ilow indication and the point at which said primary gas stream enters the lift passage, and controlling the low rate of the bleed stream in response to the static pressure indication in the upper two thirds of the lift passage, so as to maintain said static pressure below the threshold refluxing pressure and above the minimum pressure, whereby the breakage of particles during transfer through the lift passage is minimized.

3. In a hydrocarbon conversion process in which a granular solid material is gravitated as a substantially compact columnar mass through reaction and regeneration Zones and lifted from a location below one of the zones to a location above the other zone through an upwardly extending lift passage by means of a flowing stream of lift gas, the improved method of controlling the lifting step for minimum attrition of the solids which comprises: gravitating granular solids downwardly from the bottom of one of the zones to a feeding Zone located at the bottom of the lift passage, so as to form a substantially compact bed of solids about the lower end of the passage, measuring the flow of a stream of lift gas, splitting the stream of lift gas into primary and secondary gas streams, and controlling the flow rate of the primary gas stream in response to change in flow rate of the total gas flow to maintain the total gas flow substantially constant at a predetermined ow rate, introducing at least the major portion of the primary gas into the feeding zone, so as to enter lthe lift passage without passing through any substantial thickness of the solids bed in said feeding zone, introducing the secondary gas into the feeding zone, so as to pass through a substantial thickness of the solids bed before entering the lift passage, measuring the static pressure at the bottom of the lift passage and controlling the flow rate of the secondary gas, in order to maintain the static pressure at the bottom of the lift passage substantially constant, whereby the flow rate of solids through the lift is maintained substantially constant, measuring the static pressure in the lift passage at a location in the upper two thirds of the passage, and changing the predetermined low rate at which the total gas tlow is maintained an amount sufficient to maintain said static pressure substantially constant, said constant pressure value being below the threshold reuxing pressure and above the minimum pressure, whereby particle attrition during transfer through the lift passage is minimized.

References Cited in the file of this patent UNITED STATES PATENTS 568,445 Kennedy Sept. 29, 1896 2,561,409 Ardern July 24, 1951 2,561,771 Ardern July 24, 1951 2,606,863 Rehbein Aug. 12, 1952 OTHER REFERENCES Houdriow: New design in catalytic cracking, Oil and Gas Journal, lan. 13, 1.949, vol. 47, pages 78 and 79.

Claims (1)

1. IN A HYDROCARBON CONVERSION PROCESS IN WHICH A GRANULAR SOLID IS GRAVITATED AS A SUBSTANTIALLY COMPACT COLUMAR MASS THROUGH REACTION AND REGENERATION ZONES AND LIFTED FROM A LOCATION BELOW ONE OF THE ZONE TO A LOCATION ABOVE THE OTHER ZONE THROUGH AN UPWARDLY DIRECTED LIFT PASSAGE BY MEANS OF A FLOWING STREAM OF LIFT GAS, THE IMPROVED METHOD OF CONTROLLING THE LIFTING STEP FOR OPTIMUM PERFORMANCE WITH MINIMUM ATTRITION WHICH COMPRISES: GRAVITATING GRANULAR SOLIDS DOWNWARDLY FROM THE BOTTOM OF ONE OF THE ZONES TO A FEEDING ZONE LOCATED AT THE BOTTOM OF THE LIFT PASSAGE, INTRODUCING A LIFT GAS INTO THE FEEDING ZONE, SO AS TO SUPPORT AND TRANSPORT THE GRANULAR SOLIDS UPWARDLY THROUGH THE LIFT PASSAGE, MEASURING CONTINUOUSLY THE STATIC PRESSURE IN SAID PASSAGE AT A LOCATION IN THE UPPER TWO THIRDS OF THE PASSAGE, AND CONTROLLING THE FLOW RATE OF THE LIFT GAS ADMITTED TO SAID FEED ING ZONE IN RESPONSE TO SAID STATIC PRESSURE, SO THAT THE FLOW IS MAINTAINED BELOW THAT POINT AT WHICH MINIMUM PRESSURE OCCURS AND SLIGHTLY ABOVE THAT POINT AT WHICH THE PRESSURE INCREASE VERY SUBSTANTIALLY WITH ANY FURTHER REDUCTION IN GAS FLOW RATE, WHEREBY THE ATTRITION OF THE GRANULAR SOLIDS DURING TRANSFER THROUGH THE LIFT PASSAGE IS MINIMIZED.

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