US2813756A - Lift pot - Google Patents

Description

' Nov. 19, 1957 .l. M. BouRGUx-:T 2,813,755

' LIFT Po'r Filed Nov. 14, 1955 2 Sheets-Sheet 1 ATTORNEY Nov. 19, 1957 J. M. BOURGUET 2,813,755

LIFT POT Filed Nov. 14, 1955 2 Sheets--Sheml 2 zNvENToR BY A MORNEY w 2,813,756 Ice yPatented Nov. 19, 1957 LIFT POT Jean M. Bourguet, Woodbury, N. J., assignor to Socony Mobil Oil Company, Inc., a corporation of New York Application November 14, 1955, Serial No. 546,554

9 Claims. (Cl. 302-53) This invention relates to the transportation of particulate granular material and more particularly to the introduction into a dilute phase pneumatic lift of contact material of the type used in hydrocarbon conversion.

In the conversion of hydrocarbons by catalytic cracking and in various other operations of the petroleum industry, hydrocarbons are contacted with a compact moving bed of solid granular material which may function to catalyze a reaction or otherwise participate in a necessary physical or chemical modification of a hydrocarbon. These moving beds of granular material are formed by gravitating the particles in compact phase through a path which usually includes a reactor and a regenerator, the speed of the contact material movement being controlled by the rate at which it is removed from the bottom of the system.

Of course, a continuous gravity flow system presupposes some sort of a lift in order that the contact material can be recycled. With the compact moving bed type of contact material ow it is satisfactory to use a dilute phase pneumatic lift. This has been found to be capable of moving a large tonnage of contact material while at the same time keeping catalyst attrition at a desirably low level.

One of the problems of a dilute phase pneumatic lift is the continuous conversion of succeeding volumes of the compact solid phase bed into a dilute, less dense body capable of being lifted. Early efforts along this line involved passing the lift gas laterally through a body of contact material to cause succeeding portions of said body to move laterally into a lift pipe in which such portions Were vertically lifted by the same gas that effected the lateral movement. While this arrangement was operative in the sense that volumes of contact material could be moved thereby, it was found that the attrition rates were high probably due to the large and sudden changes in gas velocity brought about by breaking up a compact phase bed and then lifting the dilute phase material with the same gas.

In view of these diiculties, it was decided to introduce pneumatically the contact material into a lift gas stream by the use of a secondary gas stream separate from the stream which effects the lifting. This scheme has been successful but some Whipping and surging diculties and localized reversals of ilow in the main lift conduit are still present and cause some attrition and Wear on the lift conduit.

It is an object of this invention so to improve the introduction of contact material into an upwardly moving stream of primary lift gas by the use of a secondary lift gas that whipping and surging are eliminated with resulting reduction in catalyst attrition and Wear on the lift conduit.

It is proposed according to the present invention to introduce contact material into a pre-established column of lift gas by propelling it with a secondary gas through a smoothly curving annular zone which merges into the Vertical column of lift gas.

Other objects and advantages of this invention will be apparent from consideration of the following detailed description of several embodiments thereof in conjunction with the annexed drawings wherein:

Figure 1 is a schematic View in elevation of a moving bed hydrocarbon cracking system incorporating the lift equipment and procedures of the present invention; and

Figure 2 is a View in vertical section of one form of lift pot constructed according to the principles of the present invention.

Referring rst to Figure 1, the numeral 1t) represents a reactor in which hydrocarbons are reacted with a heated moving bed of solid granular particulate material. This material, which is gravitating as a moving bed through the system, enters the reactor through conduit 11. The moving bed of contact material leaves the reactor 10 through distribution conduits 12 and 13 and flows through additional distribution conduits 14 and 15 into an annular regenerator 16. From the regenerator 16 a pair of pipes 17 and 18 lead to a lift pot 19. From the lift pot 19 the contact material is pneumatically lifted through a conduit 21) into a separator 21 where the lift gas is separated from the contact material, the latter being recycled through conduit 11 to the reactor.

The various feed lines to the reactor bear legends in Figure 1 as do the air flue gas lines to the regenerator. The lower part of the regenerator contains a cooling section in which the contact material is adjusted as to tem* perature to the value required in the reactor. It will be recalled that the cracking of hydrocarbons is an endothermic reaction and that heat is supplied to the reactor from the catalyst. During the reaction, a coky hydrocarbon deposit forms on the active surface of the particles of contact material and the regeneration of the contact material is accomplished by burning off this coky deposit. The burning of of the coky deposit is a strongly eXothermic reaction with the result that at the bottom of the regenerator the temperature of the contact material is acually higher than it needs to be to provide the proper amount of heat in the reactor. It is for this reason that the cooling zone is provided. Although the lift pipe 20 passes from the center of the annular regenerator, the flow of the catalyst from the lift pipe is so rapid and the spacial relation is such that the catalyst is not appreciably reheated from the regenerator.

The contact material flows from the separator 21 to the feed pot 19 as a compact moving bed, all parts of which are moving at a rate determined by the rate of Withdrawal or removal of material from the lift pot. On the other hand, the contact material in the lift conduit 211 is not in compact form but is somewhat dispersed in what might be described as a dilute phase. The solid body of contact material in the pot 19 is propelled by secondary air entering through a line 22 into an upwardly moving column of lift gas provided through the conduit 23. Conduits 22 and 23 are provided with control valves 24 and 25, respectively.

The lift pot 19 shown in Figure 1 is illustrated to an enlarged scale in Figure 2. Note that the conduits 17 and 18 are full of contact material which is part of the continuous moving bed that is gravitating from the top to the bottom of the system. Conduits 17 and 18 enter an eX- ternally cylindrical chamber 26 which is provided with a base 27. Within the space defined by the walls 26 and 27, there is an annular secondary air space 29 which is defined in part by the wall 26, in part by the wall 27 and by an annular wall 30 Within the pot. The secondary air space 29 communicates with and is supplied by the conduit 22, see again Figure 1.

The lift pipe 20 structurally terminates near the top of the lift pot but the contact material passageway is continued by a section of a conduit 31 which is outwardly flared at 32 near the mouth'thereof. Projecting coaxially up through the conduit 31 and into the conduit 20 is a generally conical hollow fairing 33. The interior of the vcone 33 constitutes an extension of the conduit 23. The conical element 33 terminates at its apex end in an opening 34 equal to about 50% of the lift pipe area from which as much as 60% of the primary air can be supplied to conduit 20. Around the base of the conical element 33 there are a plurality of apertures at 35 leading to an annular space 36 whichsupplies primary air to the bottom of the annular space 37 defined between the outer sur- -face of the vcone 33 and the inner surface of the conduit section 31. The bottom of the annular space 36 has an outlet 38 which may function as a drain or pressure probe connection.

At the bottom of the pot 19 lbetween the base 27 and the wall of the conical member 33 there is disposed an annular body 39, the upper surface 40 of which is smoothly curved. The surface 40 is complementary in curvature to the curvature of the flared portion 32 of the conduit 31 so as to define with the portion 31 a smoothly and regularly curving mouth 41 leading inwardly and upwardly to the annular space 37. Spaced radially from the mouth 41 at circumferentally spaced points thereabout are a series of baiiies 42 which subdivide into compartments 43 the space defined by an annular vertical baffle 44. Each compartment has an aperture 45 therein for the admission of secondary air.

The contact material which enters the lift pot from conduits 17 and 18 and forms a compact body in the annular space defined by the liared pipe portion 32, the base 27, the wall 3l) and the wall 26; lies across the mouth 41 which leads to the space 37 and across the mouth of the compartments 43. In both cases, the material enters the mouths to an extent determined by its angle of repose. On the other hand, the shape of the mouth 41 is such that unless secondary air is supplied to the chamber 29, no amount of flow of primary air in the annular conduit 37 will cause contact material to be sucked into the lift conduit. The secondary air enters the compartments 43 through apertures at 4S and the partitions 4Z keep the air from moving in an annular lsense to a point of low resistance so that each compartment 43 is fed with an equal amount of air which is forced to go out under the edge of the baffie 44 to propel the contact material into the mouth 41. This structure for controlling the admission of secondary air to the bed of material in the litt pot is shown in Patent 2,694,815.

The secondary air issuing under the edge of the baffie 44 from the compartments 43 propels the contact material radially inwardly and into the mouth 41. At this point it flows in smoothly curving fashion through the annular aperture at 41 and into the annular space 37 where it is acted upon by the upwardly moving primary air issuing from the annular zone 36. As the primary air contacts the granular material it commences to lift and, as the section of the lift pipe increases at the apex of conical element 33, added air is furnished through the opening at 34. The lift conduit 20 is tapered in order that the velocity of the air can be kept somewhat lower at the upper end of the conduit to prevent excessive attrition in the separator. structurally speaking, the part 39 is spaced from the outer wall of the cone 33 by radially extending circumferentially spaced baffle plates 46, two of which show in Figure 2.

ln reference to Figure 2 it should be noted that the main body of lift gas, which is the primary lift gas, is introduced into the lower end of the lift pipe 20 through an inwardly and upwardly extending annular space or passageway 37, the passage being rather steep with respect to the vertical and the lateral or radial thickness of the passage or space remaining substantially constant from bottom to top, although this is not necessarily required and the lateral thickness of the passage may, in some in- 4 stances, increase and other instances decrease from bottom to top. The catalyst is gravitated as a compact mass in the pot 19 which surrounds the passageway 37 and the secondary small stream of lift gas is introduced into this mass of catalyst to move the catalyst through the smoothly curving annular zone 41 which merges into the zone 37 and in turn into lthe vertical column 20 in which the lift gas is moving. The introduction of solid particles is effected at a level at which the lateral thick- `ness of the rising stream of primary gas is thin relative to the 'size of the particles, so that the particles are substantially confined to an upward direction during the acceleration period. The particles accelerate very rapidly in the annular passage 37 so that when they enter the lower end of the lift pipe 20 and are free to move laterally or radially, they have reached a velocity high enough to prevent the whipping which formerly occurred in the inlet section.

Any roughness of the wall of the passage through which the particles travel is refiected immediately in excessive attrition and wear. The catalyst path, particularly through the inlet annulus 41, must change gradually and smoothly. While the velocity of the particles is low they can curve rapidly but at the upper end of the passageway and at the base of the main pipe only Very gradual curvature can be tolerated. For this reason the passage through which the main or primary gas is passed should be at an angle of about 60-85 with the horizontal. Preferably, this angle is about 77-80 with the horizontal.

The total lift gas fiow through the lift pipe is fixed by the permissible catalyst velocity for the particular pipe and conditions. There is a critical velocity for the catalyst in the annular passageway which varies in accordance with changing conditions. While it may be theoretically possible to design a lift pot for fixed conditions to give the proper critical velocity in most cases, it appears desirable to build some adjustment into the pot and this can be obtained by varying the portion of the lift gas through the opening 34 at the top of the central conical member 33. The primary air that passes into the lift pipe through opening 34 is isolated from the annular fiow of primary air by the centrally located coaxial conduit 49. A plug valve 47 at the lower end of conduit 49 and adjustable orifice 48 permits the operator to distribute the primary lift gas as desired.

It is desirable to provide at least enough gas ow through the opening 34 to substantially prevent any sudden changes in gas velocity because of sudden change in cross-section of the gas passage.

As a broad range, 0.5 %-50% of the total gas fiow may be passed through the top of the cone at 34. When employing a 16 inch lift pipe, for example, 12 to 27% of the primary gas flow would be optimum. From about 27% to 46% of the primary gas fiow would be optimum for a 32 inch lift over a range of catalyst concentration averaging from l to 3 pounds per cubic foot.

The maximum catalyst equilibrium velocity through the annular passage 37 has been found to approximate the following values:

16 inch, 115 foot air lift at 230 t./hr.=65 ft./sec. 32 inch, 115 foot air lift at 300 t./hr.=54 ft./sec. 32 inch, 115 foot air lift at 450 t./hr.===65 ft./sec. 32 inch, 115 foot air lif't at 600 t./hr.=75 ft./sec.

Controlling the amount of air through the apex of the cone, gives control of the proper velocity in the annular passage.

As an example of the invention a feed pot was built similar to that shown in Figure 2 and it was attached to a vertical lift pipe of about 32 inches average internal diameter and feet tall. The capacity of this lift pipe was from 50 to 600 tons per Ihour of granular silicaalumina cracking catalyst of the synthetic bead type (size range 4-12 mesh by Tyler screen, average diameter about 0.13 inch).

A lift pot constructed according to the principles disclosed in Figure 2 has the smoothly .curving mouth 41 defined by an upper surface curved on a radius of inches while its lower defining surface is curved on a radius of 12% inches. This means that the mouth is 1% inches wide and regularly curved so as to enter the annular lift zone tangentially as viewed in radial section. It is very important that the surface defining the mouth 41 be free of rough spots or other factors tending to impede or resist iiow. The annular space or passageway 37 is of constant cross-section throughout its length, the radial distance between the interior surface of the conduit 31 and the exterior surface of the cone 33 being 6 inches. The radial distance between the exterior surface of the cone 33 and the part 39 is 5 inches. This relationship causes an increase in the primary air velocity adjacent the inside wall 33 of passageway 37.

When the device of Figure 2 is operated primary air is supplied to the conduit 23 and discharged upwardly through the conduit 20. No material is lifted at this stage until the secondary air is admitted to the annular conduit 29. The amount of secondary air supplied determines the rate of propulsion of contact material into the mouth 41 for entrainment of the stream of primary air.

What is claimed is:

l. An improved method for feeding granular solid material into an upwardly-extending lift passage through which it is lifted by a lift gas to an elevated receiving zone, which method comprises: flowing a lift gas stream of annular cross-section upwardly and inwardly through a passage of restricted radial thickness which terminates at its upper end at the inner periphery of the bottom of the lift passage, said annular passage being of substantial length relative to its restricted radial thickness, maintaining a substantially compact bed of said solid material surrounding at least the lower end of said annular passage and in communication with the interior of said passage through a smoothly curving passage of annular crosssection and restricted thickness which passage merges with the outer periphery of said upwardly and inwardlyextending passage near the lower end thereof, introducing a sucient amount of gas into the bed of solid material surrounding the lower end of said annular' passage to move the solid particles through the curving passage into the upwardly and inwardly-extending passage to merge smoothly with the lift gas and enter the lift passage without whipping and surging, whereby attrition is minimized.

2. An improved method for feeding granular solid material into an upwardly-extending lift passage through which it is lifted by a lift gas to an elevated receiving zone, which method comprises: flowing a iirst stream of lift gas of annular cross-section upwardly and inwardly through a first passage of restricted radial thickness which terminates at its upper end at the inner periphery of the bottom of the lift passage, said annular passage being of substantial length relative to its restricted radial thickness, maintaining a substantially compact bed of said solid material surrounding at least the lower end of said rst annular passage and in communication with the interior of said passage through a smoothly curving passage of annular cross-section and restricted thickness, said second annular passage merging with the outer periphery of said first annular passage near the lower end thereof, introducing a second stream of lift gas into the bed of solid material surrounding the lower end of said annular passage to move the solid particles smoothly through the curving passage into the upwardly and inwardly-extending passage to merge smoothly with the lift gas and enter the lift passage without whipping and surging, the total of the first and second gas streams being adjusted to propel the particles through the first annular passage at at least substantially the critical velocity required for smooth flow with minimum attrition, introducing a third gas-stream into the lower end of the lift passage through a centrally aligned passage located below the lift passage and within the first annular passage, the flow rate of the third gas stream being adjusted to combine with the first and second gas streams and propel the particles through the lift passage at at least substantially the critical velocity required for smooth flow with minimum attrition.

3. Claim 2 further characterized in that the thickness of the second annular passage is adjusted at at least substantially that critical thickness required by the contact material being conveyed to provide smooth introduction of the particles into the rst annular passage.

4. Claim 2 further characterized in that the walls of the iirst passage have no more than a slight curvature with each wall arranged to provide no more than slight change in cross-section from level to level, the slope of the passage being steep relative to the horizontal and the length of the passage being suflicient relative to the gas flow and particles being conveyed to introduce the particles upwardly into the lower end of the lift passage with substantially only a vertical component of velocity.

5. An improved apparatus for pneumatic transfer of granular contact material comprising a feed chamber adapted to confine a bed of contact material, conduit means to supply contact material into the upper section of said feed chamber, a receiving chamber positioned at a higher level than said feed chamber, a lift pipe extending upwardly to said receiving chamber from said feed chamber, an annular passageway of restricted radial thickness attached to the bottom of the lift pipe and adapted to supply gas and granular contact material to the inner periphery of said lift pipe, means for supplying lift gas to the bottom of said annular passageway, a second annular passageway located within the feed chamber following a curved path and merging with the outer periphery of said iirst annular passageway near the bottom thereof, means for feeding a second stream of lift gas into said feed chamber to pass through a substantial thickness of compact granular material in said feed chamber and propel the material through the second annular passage into the first annular passage, whereby the particles mix with the first stream of lift gas and are introduced into the lift pipe with minimum attrition and minimum wear of the feeding apparatus.

6. An improved apparatus for pneumatic transfer of granular contact material comprising a feed chamber adapted to confine a bed of contact material, conduit means to supply contact material into the upper section of said feed chamber, a receiving chamber positioned at a higher level than said feed chamber, a lift pipe extending upwardly to said receiving chamber from said feed chamber, an annular passageway of restricted radial thickness attached to the bottom of the lift pipe and adapted to supply gas and granular contact material to the inner periphery of said lift pipe, the inner walls of said passage having a steep slope with respect to the horizontal, no more than a slight change in curvature from level to level and no more than a slight change in horizontal cross-section from level to level, a second annular passageway located within the feed chamber following a curved path and merging with the outer periphery of said first annular passageway near the bottom thereof, means for feeding a second stream of lift gas into said feed chamber to pass through a substantial thickness of the bed of contact material in said feed chamber and propel the material through the second annular passage into the first annular passage, whereby the particles and second stream of lift gas mix with the first stream of lift gas and are introduced into the lift pipe with minimum attrition and minimum wear of the feeding apparatus.

7. Claim 6 further characterized in that the thickness of the second annular passageway is adjusted at at least substantially the critical thickness required to introduce Vflowing through the rst annular passageway with miniimum Whipping and surging.

8. Claim 6 further characterized in that the thickness :of the second annular passageway is set at about 1% inches iin width 'when conveying a granular V'craeking catia'lyst of ythe 'synthetic bead type (size range 4-12 .mesh by Tyler screen, average diameter :about v0.13 inch).

9. Claim I6 Ifurther lcharacterized in that .a gas pipe is connected withinthe first iannularipassageway, and means .is provided within the pipe to control the ow of a 'third 'stream of gars through the pipe .and `into the bottom of 8 `the lift pipe, :whereby the .total `gas Vow through the lift pipe may be adjusted to flow the particles through the lift pipe at substantially that-critical velocity .required yfor minimum attrition within the 'lift pipe.

References Cited in the itile of this patent UNITED STATES PATENTS v2,6'65,73"1 Bergstrom Jan. 19, 1954 2,687,372 i'Ray Aug. 24, 1954 2,723,180 Celani Nov. 8, 1955 2,744,793 `McKinney May 8, 1956

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