US3219208A - Rotary feeder and control - Google Patents

Description

Nov. 23, 1965 B. M. HADLEY ETAL 3,219,208

ROTARY FEEDER AND CONTROL Filed July 24, 1961 2 Sheets-Sheet 1 O INVENTORS B.M. HADLEY R.G. ROHLFING W LT A TTORNEVS Nov. 23, 1965 B. M. HADLEY ETAL 3,219,208

ROTARY FEEDER AND CONTROL Filed July 24. 1961 2 Sheets-Sheet 2 -L REACTOR CONTROLLER r HEAT BALANCE -122 C.R.

FIG?

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INVENTORS B.M. HADLEY RG. ROHLFING BY R0. WELTY A RNEKS United States Patent 3,219,208 ROTARY FEEDER AND CONTROL Billy M. Hadley, Raymond G. Rohlfing, and Richard O.

Welty, Bartlesville, Okla, assignors to Phillips Petroleum Company, a corporation of Delaware Filed July 24, 1961, Ser. No. 126,282 16 Claims. (Cl. 21417) This invention relates to an improved feeder for feeding particulate solids at a controlled rate and to an arrangement of apparatus for controlling the rate of feeding of solids. A specific aspect of the invention is concerned with the feeding of particulate catalyst to a catalytic react-or system.

The feeder of the invention is an improvement over that described in De Haven, US. Patent 2,885,246. Particulate catalyst, such as chromium oxide deposited on silica or silica-alumina, is relatively abrasive and it was found that the rotor constructed in accordance with said patent and fabricated of metal suffered excessive attrition. This was partially due to the fact that as the cylindrical rotor became worn and slightly smaller than originally, particulate catalyst entered the space between the rotor and the adjacent housing so as to increase the rate of wear drastically. In order to overcome this excessive wear, the rotor was fabricated of Teflon (polytetrafiuoroethylene) and was constructed with an axial bore which fit the power shaft. The rotor was drilled and tapped for Allen screws which were threaded into the rotor and seated on the shaft. This method of attaching the rotor to the shaft caused improper centering of the rotor and stripping of the threads when excessive friction occurred between the rotor and its housing due to the poor centering. Poor catalyst feed-rate-uniformity and excessive wash-by resulted, which could not be tolerated in controlling an olefin polymerization process in a loop reactor.

Accordingly, it is an object of the invention to provide an improved feeder for particulate solids, such as catalytic material. Another object is to reduce the Wear and Wash-by in a rotary catalyst feeder similar to that in the aforesaid patent. A further object is to provide a rotor construction which maintains the tolerance between the rotor and the surrounding housing substantially uniform during use. Another object is to provide better centering of a rotor on a power shaft in a rotary type feeder and to reduce the wear in such a feeder. It is also an object of the invention to provide an arrangement of apparatus for controlling the rate of rotation of a feeder for particulate solids. An additional object is to provide an improved method of controlling a catalytic reaction. Other objects will become apparent to one skilled in the art upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises providing a tapered rotor for a rotary feeder and providing a construction which applies pressure to the rotor during operation so as to maintain a close tolerance between the rotor surface and the surrounding housing. In another embodiment the rotor of the invention is fabricated of a solid resin which reduces the abrasion thereof by the powdered solids and the adjacent housing in which the rotor is rotated. In a further embodiment of the invention the tapered rotor is centered on the power shaft by means of keys fixed in the shaft and extending or projecting into cooperative slots in the bore wall of the rotor extending the length of the rotor so that the rotor is slidable on the keys along the shaft.

In accordance with another embodiment of the invention, the rotor shaft is operated by an air motor supplied by air thru a conduit or line containing a motor valve for controlling the rate of air flow to the motor. The motor valve is controlled by a speed-recorder-controller 3,219,208 Patented Nov. 23, 1965 having a set-point set by a controller which receives a signal from a computer. The computer computes a value representing a variable function of the catalytic reactor with which it is connected. A speed transmitter is connected with the air motor to operate at the same speed as the motor and this speed transmitter emits a signal to the speed-recorder-controller which indicates that the proper speed of the air motor has been attained and prevents over-correction in the speed of the air motor. The rotary catalyst feeder operated by the air motor delivers catalyst to the reactor system with which the computer is connected.

A more complete understanding of the invention may be obtained by reference to the accompanying schematic drawing of which FIGURE 1 is a vertical longitudinal partial section of a rotary feeder for particulate solids constructed in accordance with the invention; FIGURE 2 is a vertical cross section of the feeder of FIGURE 1 taken on the line 2-2; FIGURE 3 is a vertical cross section of the feeder of FIGURE 1 taken on the line 3-3; and FIGURE 4 is a pictorial view of an arrangement of apparatus for controlling the feed rate of solid, particu late, catalytic material to a catalytic reactor.

Referring to FIGURES l, 2, and 3, the feeder shown comprises a shaft 10 having an outer end 12 containing a key slot for a power drive hookup. A tapered rotor 14 in the form of a frustum of a cone is fabricated with an axial bore 16 so that the rotor is slidable onto shaft 10. Shaft 10 is provided with 3 keyways 18 positioned apart and each is fitted with a key 20 which is snugged into the keyway. Keyways or grooves 22 are cut in rotor 14 the full length of the bore 16 so that the keys are in sliding engagement with the keyway in the rotor. This construction permits the rotor to he slid onto the end of the shaft while the keys are in position therein and movement of the rotor farther onto the shaft as the rotor becomes worn or the surrounding bearing surface becomes worn.

A housing 24 surrounds rotor 14 and the major portion of the shaft 10. A pair of bearings 26 and 28 are positioned either side of a collar 30 which is set on shaft 10 in fixed relation thereto by a socket screw 32 projecting.

into a recess in the shaft. Collar 30 is set against a shoulder 34 on the shaft and, in cooperation with a retainer ring 36 and a fiat washer 38, prevents axial move ment of the shaft away from the rotor end thereof. A second flat washer 40 is positioned against a shoulder 42 in the housing adjacent bearing 26 and a chevron type packing-ring-assembly and retainer 44 surrounds the shaft and is forced against washer 42 by spring 46 to seal the shaft against leakage of abrasive material from the feeder rotor into bearings 26 and 28. A flat ring 48 in the rotor housing seats on shoulder 50 of the housing to hold spring 46 in tension against the packing ring assembly.

The interior of the rotor housing is provided with a replacable sleeve 52 which is tapered to fit the surface of rotor 14 to provide a bearing surface therefor. This sleeve is machined to be slidably engageable with the inside of the housing so as to be removable therefrom. A plate 54 is countersunk into the end of the rotor housing and into sleeve 52 so as to lock the sleeve in fixed position to prevent rotation thereof with the rotor and to prevent axial movement thereof due to the force of spring 46. Plate 54 is held in position by means of screw 56 which extends and threads into the end of the rotor housing. More than one of these plates 54 may be utilized.

The end of the housing comprises a cap or cover 60 which is attached to the end of the rotor housing by socket cap type screws 62. A gasket 64 forms a seal between cap 60 and the end of the housing. In order to apply tension on the end of rotor 14, a cover plate 66 is attached to the outer end of rotor 14 by means of screws 68 and an axial spring plunger 70 is threaded into cap 60 and locked therein by lock nut 72. In this manner plunger element 74 is forced against cover plate 66 and this force is transmitted to rotor 14 so that it maintains a close engagement with sleeve 52.

It should be noted that rotor 14 and sleeve 52 should be fabricated so that rotor 14 extends beyond the end of shaft to provide a take-up space 76 in bore 16 and a space 78 between the rotor 14 and flat ring 48 for takeup.

Rotor 14 is provided with pockets or dimples or other suitable receptacle 80 spaced in circumferential align ment around the outer surface of the rotor so that these pockets rotate in a common plane. A threaded inlet 82 and a threaded outlet 84 provide for attachment of inlet and outlet conduits for feeding powdered material to and delivering same from the rotor, respectively.

With cap 60 removed from the end of the rotor housing, the rotor-shaft assembly may be removed thru the end of the housing by removing socket screw 32. It is also feasible to remove rotor 14, leaving the shaft in place, by unscrewing machine screws 68 far enough to place a pulling device on the heads of the screws. Another method of pulling rotor 14 comprises drilling plate 66 near the center, tapping the hole and inserting a bolt so that the head of the bolt can be pulled, thereby pulling the rotor which is slidably attached to the shaft by keys 20.

Before the feeder was constructed in accordance with the invention, the rotor was attached by Allen screws to the shaft and these screws forced the rotor out of round thereby causing excessive wear on the rotor and housing. Frequent take-up on the screws caused thread failure and the life of the feeder rotor assembly was limited to a range of several days to several weeks, at most. The structure of the rotor was changed so that it was slidably attached by three keys fitted into the shaft tightly and slidably engaging grooves or keyways in the rotor. The rotor was tapered at an angle of 3 with the axis substantially as shown in the drawing. With this new improved arrangement, keyed feeder rotors lasted about 6 months.

The rotor is advantageously fabricated out of Teflon which is a trademarked composition consisting essentially of polytetrafluoroethylene. Other solid resins may be utilized, including Marlex (a trademark of Phillips Petroleum Company identifying high density polyethylene and other polyolefins), polychlorotrifiuoroet hylene, nylon, etc. Teflon has been found to be the most suitable in service in feeding particulate chromium oxide-silicaalumina catalyst to a reactor in use in polymerizing ethylene.

In FIGURE 4, a catalyst feeder 90 constructed in accordance with the invention is operated by an air motor 92 connected with the shaft 94 of the feeder thru coupler 96 and gear reductor 98. The inlet of feeder 90 is connected with a catalyst supply 100 and its outlet is connected with reactor 102 which may be a loop reactor or a stirred reactor or any other type of catalytic reactor.

Air motor 92 is connected to an air supply 104 by means of conduit 106 containing motor valve 108. In the embodiment illustrated in the drawing m-otor valve 108 is air operated and controlled. Instrument air line 110 connects with a speed-recorder-controller 112 which is under the control of controller 114 to which it is connected by instrument air line 116. Control 114 is con nected thru instrument air line 118 with a heat-balance computer-recorder 120 which is connected by a series of lines illustrated by line 122 with reactor system 102. The arrangement of computer 120 with the reactor system is fully described in the copending application of D. E. Berger et al. S.N. 683,662, filed September 12, 1957, now U.S. Patent 3,078,265.

The heat-balance computer-recorder may be replaced by any other computer-recorder that computes a value representing a variable function of the catalytic reaction being effected in the reactor system. While the heat balance is a reliable indicator for control of the rate of feeding catalyst to a reactor engaged in olefin polymerization, it is also feasible to utilize a computer which determines a value representing rate of conversion of feed, pressure in the reactor, temperature in the reactor, volume of off-gas from the process, etc.

The computer-recorder emits a signal thru line 118 to controller 114 which changes the set point of speedrecorder-controller 112 to reestablish the desired production rate in the reactor system by changing the speed of air motor 92 and therefore, the rate of rotation of feeder 90 which feeds more or less catalyst into the reactor to change the rate of production of polymer or other product being made. The set point of instrument 112 determines the amount of opening of motor valve 108 which controls the rate of flow of air to air motor 92. In order to avoid over correction in the change in rate of motor 92, a pneumatic speed transmitter 124 is operated olf pulley 126 of air motor 92 by means of belt 128 which also passes over pulley 130 of instrument 124. The direct drive of instrument 124 with pulleys of the same size, operates speed transmitter 124 at the same speed as motor 92. This pneumatic speed transmitter emits a signal via line 132 to speed-recorder-controller 112 which is proportional to the speed of instrument 124 and also motor 92. The signal emitted by controller 114 is fed continuously to instrument 112 which controls valve 108 to maintain the correct speed of motor 92. Instrument 124 senses the speed of motor 92 and continuously feeds a signal to SRC 112 which regulates valve 108 so as to provide a differential of zero between the signals in lines 116 and 132. This is a cascading arrangement of controls.

An arrangement of apparatus which effects the control disclosed herein comprises a Gast Rotary Air Motor Model 4AM-FCW-1OC, a Starrett Micro-Control Valve- 0.312 Port. /2 NPT Air to Close (Modern Mfg. Co., Bartlesville, Oklahoma) as valve 108, a Foxboro Recorder Controller as SRC-112, a Foxboro 58P4 controller- 5412 PS recorder as instrument 114, a heat-balance computer-recorder as disclosed in S.N. 683,662 and in U.S. Patent 2,974,017, as computer 120, and a Foxboro pneumatic speed transmitter, type 16A Speed 02400 RPM, without integral speed changer, C.W. rotation-locking at shaft end, and a Boston Gear reducer No. TW113 W/400-1 ratio, as reductor 98. This apparatus arrangement is highly effective in maintaining relatively uniform production in the reactor system.

While pneumatic instruments have been illustrated in the apparatus arrangement of FIGURE 4, electrical instruments with corresponding functions can be purchased commercially and arranged for use in the disclosed invention.

A broad aspect of the method of the invention comprises controlling a catalytic reaction in which a fluid feed, such as a normally gaseous l-olefin (ethylene) is continuously fed, along with an inert liquid diluent, to a catalyatic reactor and particulate catalyst is continuously fed in increments to the reactor, as with a rotary pocket type feeder, so as to polymerize said olefin. The control is effected by measuring, sensing, or computing a value representing a variable function of the process and varying the rate of adding catalyst to the reactor in response to said value so as to maintain a substantially constant reaction rate. A fluid effluent is continuously withdrawn from the reactor with catalyst suspended or entrained therein.

The process is applicable to other catalytic reactions than polymerization, such as isomerization, alkylation, cracking, hydrogenation, dehydrogenation, etc. Any

variable -function of the process being controlled may be utilized as the control.

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

We claim:

1. A feeder for particulate solids comprising a shaft having on one end thereof a coaxial truncated conical rotor, the end of said rotor of larger diameter being adjacent said one end, and said one end of said shaft terminating at said rotor; at least one pocket in said rotor intermediate its ends for picking up solids fed thereto; means for attaching said rotor to said shaft for rotation with said shaft; a housing around said shaft and rotor open at the rotor end so that the shaft and rotor assembly is insertable thru the open-ended housing, said housing providing a tapered bearing surface for sealably engaging said rotor; bearing means in said housing for said shaft spaced from said rotor; a cap detachably affixed to and covering the open end of said housing; flexible means in said cap for applying pressure on the outer end of said rotor to hold same in sealing engagement with said bearing surface; a solids inlet thru said housing leading to the path of said pocket when revolving; and a solids outlet thru said housing leading from said path and spaced circumferentially from said solids inlet.

2. The feeder of claim 1 wherein said rotor is formed of a solid resin and said tapered bearing surface is metal.

3. The feeder of claim 2 wherein said resin is Teflon (polytetrafiuoroethylene) 4. The feeder of claim 2 wherein said resin is high density polyethylene.

5. The feeder of claim 2 wherein said resin is nylon.

6. The feeder of claim 2 wherein said resin is polyolefin.

7. The feeder of claim 1 wherein said rotor is bored for and mounted on said shaft in longitudinally slidable engagement therewith for longitudinal movement of said rotor on said shaft during rotation thereof, said rotor extends beyond said shaft to leave a short open space in said bore, and said flexible means comprises a plate covering said space and aifixed to said rotor and a spring plunger axially positioned in said cap so as to press against said plate.

8. The feeder of claim 7 wherein said rotor is fabricated of Teflon (polytetrafluoroethylene).

9. The feeder of claim 1 wherein said rotor is fabricated of a solid resin, has an axial bore closely fitting said shaft, and is slidably keyed to said shaft by a plurality of radially extending keys uniformly spaced around said shaft and bore to permit longitudinal movement of said rotor on said shaft during rotation thereof.

10. The feeder of claim 1 including a removable metal sleeve on the inside of said housing forming said bearing surface for said rotor.

11. A catalyst feeder for particulate solid catalyst comprising a steel shaft having on one end thereof a coaxial truncated conical rotor formed of solid resin and having an axial bore for said shaft, the end of said rotor of larger diameter extending beyond said one end to provide a short open space in said bore; a plurality of pockets spaced apart in circumferential alignment in said rotor for receiving and delivering solids; a plurality of keys fixed longitudinally in said shaft and extending into corresponding slots in said rotor extending from end to end thereof to provide for sliding said rotor longitudinally on said shaft during rotation thereof; a housing around said shaft and rotor having a removable cap on the rotor end thereof to permit insertion and withdrawal of said shaft and rotor thru said end, said shaft extending thru the other end of said housing; a tapered bearing surface in said housing for sealably engaging said rotor; bearing means in said housing for said shaft spaced from said rotor; means for preventing axial displacement of said shaft away from said rotor; a cover on the open end of said rotor; an axial spring-actuated plunger in said cap biased against said cover to hold said rotor in engagement with said tapered bearing surface; and openings thru said housing for introducing said catalyst to and removing same from said pockets.

12. The feeder of claim 11 wherein a metal sleeve fixed in and insertable and removable from said housing, provides said bearing surface.

13. In combination, a catalyst feeder constructed in accordance with claim 1; an air motor operatively connected with said feeder; an air supply line connected with said air motor and with an air supply; a motor valve in said air supply line; a set-point speed controller operatively connected with said motor valve; a controller operatively connected with said speed controller to change the set point thereof; and a speed transmitter sensitive to the speed of said air motor and adapted to emit a signal to said controller proportional to the speed of said motor.

14. The combination of claim 13 wherein said controller, said speed controller, said motor valve, and said speed transmitter are pneumatic.

15. A feeder for catalyst particles and the like comprising in combination:

(a) a horizontal shaft having means at one end for applying rotational torque thereto;

(b) a tapered rotor in the form of a truncated cone having an axial bore extending therethru, positioned coaxially on the other end of the shaft of (a) in longitudinally slidable relation therewith by means of symmetrically placed longitudinal keys and keyways in said shaft and said rotor, the larger end of said rotor being adjacent said other end;

(0) a housing around the shaft of (a) and the rotor of (b) provided with shaft bearing means and a tapered bearing surface engaging said rotor, said bearing surface extending longitudinally substantially beyond the smaller end of said rotor, and said shaft terminating short of the larger end of said rotor;

(d) closure means on the end of said housing adjacent the rotor of (b);

(e) a biasing means in the housing of (c) urging the rotor of (b) toward said one end of the shaft of (a) as take-up means; and

(f) catalyst transport means thru said feeder comprising at least one pocket in the tapered surface of the rotor of (b), an inlet thru the housing of (c) above said rotor, and an outlet thru said housing below said rotor.

16. The feeder of claim 15 wherein the keys and keyways of (b) comprise blind keyways in said shaft in which said keys are fixed and corresponding keyways in said rotor extending from end to end thereof, said keys being slidable in said rotor.

References Cited by the Examiner UNITED STATES PATENTS 941,024 11/1909 Mantius 222-368 X 1,402,184 1/ 1922 Sinclair 222-368 X 1,943,376 1/ 1934 Dilling 302-42 1,944,902 1/ 1934 Pettibone 302-42 2,420,557 5/ 1947 Mueller.

2,428,241 9/1947 Pootjes 222-368 2,663,465 12/1953 Hogin 222-368 2,766,911 10/1956 Greaves et al. 222-368 X 2,885,246 5/1959 De Haven 302-49 2,909,413 lO/ 1959 Hildyard 23-230 3,078,265 2/1963 Berger et a1. 23-285 X MORRIS O. WOLK, Primary Examiner.

LOUIS I. DEMBO, LAVERNE D. GEIGER, DEL- BERT E. GANTZ, Examiners.

Claims (2)

1. A FEEDER FOR PARTICULATE SOLIDS COMPRISING A SHAFT HAVING ON ONE END THEREOF A COAXIAL TRUNCATED CONICAL ROTOR, THE END OF SAID ROTOR OF LARGER DIAMETER BEING ADJACENT SAID ONE END, AND SAID ONE END OF SAID SHAFT TERMINATING AT SAID ROTOR; AT LEAST ONE POCKET IN SAID ROTOR INTERMEDIATE ITS ENDS FOR PICKING UP SOLIDS FED THERETO; MEANS FOR ATTACHING SAID ROTOR TO SAID SHAFT FOR ROTATION WITH SAID SHAFT; A HOUSING AROUND SAID SHAFT AND ROTOR OPEN AT THE ROTOR END SO THAT THE SHAFT AND ROTOR ASSEMBLY IS INSERTABLE THRU THE OPEN-ENDED HOUSING, SAID HOUSING PROVIDING A TAPERED BEARING SURFACE FOR SEALABLY ENGAGING SAID ROTOR; BEARING MEANS IN SAID HOUSING FOR SAID SHAFT SPACED FROM SAID ROTOR; A CAP DETACHABLY AFFIXED TO AND COVERING THE OPEN END OF SAID HOUSING; FLEXIBLE MEANS IN SAID CAP FOR APPLYING PRESSURE ON THE OUTER END OF SAID ROTOR TO HOLD SAME IN SEALING ENGAGEMENT WITH SAID BEARING SURFACE; A SOLIDS INLET THRU SAID HOUSING LEADING TO THE PATH OF SAID POCKET WHEN REVOLVING; AND A SOLIDS OUTLET THRU SAID HOUSING LEADING FROM SAID PATH AND SPACED CIRCUMFERENTIALLY FROM SAID SOLIDS INLET.

13. IN COMBINATION, A CATALYST FEEDER CONSTRUCTED IN

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