US2753221A

US2753221A - Elevation of granular solids

Info

Publication number: US2753221A
Application number: US223592A
Authority: US
Inventors: Clarence H Thayer
Original assignee: Sun Oil Co
Current assignee: Sunoco Inc
Priority date: 1951-04-28
Filing date: 1951-04-28
Publication date: 1956-07-03
Anticipated expiration: 1973-07-03

Description

July 3, 1956 c. H. THAYER ELEVATION OF GRANULAR SOLIDS Filed April 28, 1951 INVENTOR. CLARENCE H. THAYER ATTORNEYS United States Patent ELEVATION OF GRANULAR SOLIDS Clarence H. Thayer, Wallingford, Pa., assignor to Sun gfil Company, Philadelphia, Pa., a corporation of New ersey Application April 28, 1951, Serial No. 223,592 16 Claims. (Cl. 302-59) This invention relates to the elevation of granular solids by means of a lifting gas, and more particularly to the separation of solids from lifting gas after such elevation.

It is known in the art to elevate granular solids from a lower zone to a higher zone by suspending the solids in a lifting gas under pressure and passing the lifting gas having solids suspended therein upwardly through a lift conduit. In order to elevate solids through an elongated lift conduit, for example a conduit 50 feet or more in height, it is necessary to impart a relatively high velocity to the solid particles. When the solid particles reach the upper zone, it is necessary to decelerate the particles from this high velocity in order to collect the solids at the higher zone for further use. This is customarily accomplished by providing a disengaging vessel above and communicating with the outlet end of the lift conduit. The disengaging vessel having a greater cross sectional area than that of the lift conduit, the lifting gas expands after discharge from the lift conduit into the disengaging vessel and the solids suspended in that lifting gas decrease in velocity as a result of the decrease in velocity of the lifting gas as it expands. After the solids have risen a sufiicient distance in the disengaging zone, their upward velocity is decreased to zero and the solids then fall backwardly around the rising stream of gas and solids into the bottom of the disengager.

In operation as above described, the average .distance to which solids rise above the top of the lift conduit, before falling back into the bottom of the disengager, is necessarily large because of the high velocity which the solids have as they are discharged from the outlet end of the lift conduit. Because the granular solids are often subject to substantial attrition upon striking a rigid solid surface, it is generally desirable that the disengager be high enough to provide, above the outlet end of the lift conduit, a. free space in which the solids can reverse direction through loss of momentum without having struck while rising any rigid solid surface. If the height of rise of solids above the outlet end of the lift conduit is great, then the height of the disengager should be correspondingly great in order that the rising solids do not strike the top of the disengager. Another disadvantage of a large height of rise resides in the fact that the distance through which the solids fall in the disengager is a factor in determining the amount of attrition which the solids undergo when their fall is abruptly arrested. Generally, the greater the height of rise in the disengaging vessel, the greater is the attrition of the solids.

The present invention provides a manner of reducing the velocity and height of rise of granular solids after they have been elevated through an elongated lift conduit into a disengaging vessel. According to the present invention a stream of braking gas is discharged downwardly from a nozzle positioned directly above the outlet end of the lift conduit, and the braking gas which is thus discharged impinges directly upon the rising stream of gas and solids in direct opposition thereto. It has been found that the effect of this impingement is to decelerate the rising solids more rapidly than when no braking gas is used. It has also been found that this deceleration is accomplished, according to the invention, without excessive turbulence in the disengager. It is desirable to minimize turbulence in the disengager, because turbulence tends to cause the granular solids to strike against each other more than they would in the absence of turbulence, and such striking together of the solids causes additional attrition. By the method of the present invention, how ever, braking gas can be introduced into the disengager without causing excessive turbulence because the effect of the braking gas is merely to depress the fountainshaped stream of solids rather than to destroy the fountam-shaped pattern and disperse the particles.

Thus, the present invention provides a manner of decelerating granular solids rapidly and thereby decreasing the average height of rise of solids above the top of the lift conduit and decreasing the required height of the disengager while at the same time not causing excessive turbulence in the disengager.

According to the present invention braking gas is discharged downwardly in opposition to the rising stream of gas and solids at a relatively high velocity, preferably at a velocity greater than the lifting gas velocity, the volume rate of the braking gas on the other hand being preferably less than the volume rate of the lifting gas. The cross sectional area of the braking gas: nozzle through which the braking gas is discharged, is preferably less than the cross sectional area of the outlet end of the lift conduit. This makes it possible to obtain a relatively high braking gas velocity as the braking gas is discharged from the nozzle while still using a relatively small vol ume rate of braking gas. It is desirable to use relatively high velocity braking gas in order to obtain substantial depression of the rising stream of gas and solids. It is desirable, however, to use a relatively small volume rate of braking gas in order to minimize turbulence in the disengager and in order not to overload the equipment through which the lifting gas and the braking gas pass after they are removed from the disengager. It is customary to pass the lifting gas and braking gas through a cyclone separator, for example, in order that fine solid particles remaining in the gas may be removed, and it is preferred to minimize the volume rate of gas which such a cyclone separator must handle. It is also desirable to use a relatively small volume of braking gas in order to avoid any tendency to stall the lifting operation by creating an excessive back pressure on the lift conduit.

According to the present invention, even though a relatively high velocity braking gas stream is used, excessive turbulence in the disengager is avoided, since lifting gas and braking gas are removed from the disengager rapidly enough so that a satisfactorily smooth flow of lifting gas and braking gas through the disengager is obtained, and excessive mixing of braking gas with solids, which mixing would destroy the fountain-shaped solids pattern and result in excessive turbulence, is avoided.

According to the present invention, a single stream of braking gas may be discharged substantially vertically downwardly into the rising stream of gas and solids, the braking gas stream being coaxial with the rising stream, or a plurality of braking gas streams can be used, one of them being a central coaxial stream discharged substantially vertically downwardly and the other stream or streams being inclined annular streams discharged downwardly and laterally away from the longitudinal axis of the rising stream. An advantage of using a plurality of streams as described above resides in the fact that a greater decrease in the height of rise can be obtained with such a plurality of streams under otherwise similar operating conditions.

The invention will be further described with reference to the attached drawing. Figure 1 of the drawing is a schematic diagram or" a system of apparatus through which granular solids are circulated, the apparatus including means for elevating granular solids by means of a lifting gas from a low point in the system to a high point therein. Figure 1 also shows means according to the invention by which granular solids can be rapidly decelerated after being elevated by means of lifting gas. In Figure 1 the braking gas nozzle illustrated is adapted to discharge a single central vertical stream of brak ing gas. In Figure 2 there is shown a sectional view of a disengaging vessel, for use in a solids circulation system, and of a braking gas nozzle positioned within the disengager, the nozzle being adapted to discharge a central vertical stream of braking gas and a plurality of inclined annular streams of braking gas.

In Figure 1 there are shown reaction vessels and 11 which may be, for example, a hydrocarbon conversion vessel and a solids regeneration vessel, respectively, for use in a process wherein hydrocarbon vapors are contacted with granular solids in the conversion vessel and wherein carbonaceous deposits are burned from the solids in the regeneration vessel. Also shown in Figure l are a gas lift engaging vessel 12, a lift conduit 13, a gas lift disengaging vessel 14, and a cylindrical braking gas conduit 15, the lower outlet end 22 of which constitutes a braking gas nozzle and is positioned within the disengaging vessel and directed substantially vertically downwardly toward the outlet end of lift conduit 13.

In operation granular solids gravitate downwardly from the bottom of disengager 14 through line 16 into reaction vessel 10. From reaction vessel 10, the solids gravitate through line 17 into reaction vessel 11 and from there through line 18 into engager 12. Lifting gas is introduced into engager 12 through line 19 and solids are suspended in the lifting gas and elevated through lift conduit 13 into disengager 14. Braking gas is passed through braking gas conduit and is discharged downwardly from the outlet end 22 thereof in direct opposition to the rising stream of gas and solids issuing from the outlet end of lift conduit 13. The solids in the rising stream are decelerated rapidly by the action of the braking gas and reverse their direction of vertical movement and fall back into the bottom of the disengager 14 from which they are removed through line 16 as previously described. Lifting gas and braking gas are commingled and pass upwardly around baffle and are removed from disengager 14 through line 21.

Turning now to Figure 2, there is shown therein a disengaging vessel 14 above and communicating with the outlet end of lift conduit 13. Positioned within disengager 14 is braking gas nozzle 30 communicating with braking gas conduit 31 which extends through the top of the disengager. Braking gas conduit 31 is slidably mounted through packing gland 32 and through the top of the disengager and through baffle plate 20, the latter being supported from the top of the disengager by means of support rods 33. The braking gas nozzle 30 is composed of three upper body members 34, and a lower body member 35. The

body members

34 and 35 are screwed onto the threaded lower end of the braking gas conduit 31 and are spaced vertically apart from each other to provide inclined annular spaces 36 between each pair of body members. Braking gas conduit 31 has four apertures 37 spaced equidistant from each other around the wall of braking gas conduit 31, these apertures providing communication between the interior of braking gas conduit 31 and the uppermost of the inclined annular spaces 36. The four apertures 38 in braking gas conduit 31 provide communication with the middle annular space 36 and the four apertures 39 provide communication with the lowermost of the annular spaces 36. The shape of the

body members

34 and 35 is .such that the overall shape of the braking gas nozzle 30 is that of an inverted cone. The lower body member 35 has a central vertical channel 40 therethrough providing communication between the lower end of braking gas conduit 31 and the' apex of the conical braking gas nozzle 30.

In operation lifting gas and solids are discharged from the outlet end of lift conduit 13 and rise through disengager 14. Braking gas is passed through braking gas conduit 31 and a portion of the braking gas passes therefrom into channel 40 and downwardly from the bottom thereof as a central vertical stream of braking gas. Other portions of braking gas pass through apertures 37, 38, and 39 and through the annular spaces 36 communicating therewith and are discharged from the lower ends of the annular spaces 36 as inclined annular streams of braking gas. The rising stream of gas and solids is diverted laterally by the central vertical stream of braking gas and passes upwardly in a diverging stream until the annular streams of braking gas impinge on the rising stream, whereupon the solids in the rising stream are decelerated by the annular braking gas streams and reverse direction and fall back into the bottom of disengager 14. The braking gas discharged through channel 40 and through the annular spaces 36 commingles with the lifting gas and passes with that lifting gas around and above bathe 20 and is removed with the lifting gas from disengager 14 through line 21. The solids which collect in the bottom of disengager 14 are removed therefrom through line 16.

In the drawing, the braking gas nozzles shown are adapted to discharge in the case of the nozzle shown in Figure l, a single central vertical stream of braking gas, or, in the case of the nozzle shown in Figure 2, a plurality of braking gas streams including a central vertical stream and three inclined annular streams. It is to be understood that a single annular braking gas stream or any number of annular braking gas streams within practical limits can be employed. The angle at which the annular stream or streams is discharged can vary widely; the annular stream should however be inclined, i. e., its angle with the vertical should not be less than, say, 5 nor greater than, say, Preferably, the angle with the vertical is within the approximate range 30 to 60. Lesser angles with the vertical tend to introduce the possibility of solids escaping laterally from the effect of the annular braking gas stream. Greater angles with the vertical decrease the downward component of the force exerted by the braking gas stream against the rising solids and thus tend to reduce the effectiveness of the braking gas stream to decrease the height of rise.

The braking gas nozzle shown in Figure 2 is illustrative of nozzles which can be used to provide central and annular braking gas streams. Other suitable nozzles having a substantially vertically downwardly directed outlet and one or more inclined annular downwardly directed outlets can be used according to the invention. An annular outlet, as the term is used here, is intended to indicate not only a continuous annular channel such as the annular spaces 36 in Figure 2, but also a plurality of downwardly inclined apertures spaced apart around the circumference of the braking gas nozzle cross section, the number and positioning of the apertures being such as to provide a nozzle adapted to discharge braking gas which will impinge on substantially all portions of the horizontal cross section of the rising stream of gas and solids. The horizontal distance of the annular outletsof the braking gas nozzle from the longitudinal axis of the nozzle can vary, but it is to be understood that sufficient horizontal distance should be provided between such outlets and the disengager wall in order to avoid the possibility of the annular braking gas stream driving solids against that wall with resulting high attrition. In the example given subsequently, apparatus is described having dimensions such that no excessive impingement of solids against, the disengager wall occurs at ordinary operating conditions. Front this disclosure, 2 person skilled in the art can determine the proper dimensions of apparatus for a given set of operating conditions. Generally, it is preferred that the horizontal distance of the lowest annular outlet of the braking gas nozzle from the longitudinal axis of the nozzle should not be greater than the major dimension of the cross section of the lift conduit outlet.

The present invention is generally applicable to the elevation of granular solids which are subject to substantial attrition upon having their motion at relatively high velocity abruptly arrested. Examples of such solids are the widely used hydrocarbon conversion catalysts, e. g. natural or synthetic silica-alumina catalyst, and also inert refractory granular materials such as are used as heat transfer material in non-catalytic hydrocarbon conversion.

The invention is used in the elevation of mixtures of coarse granular solids, e. g. mixtures of solids a major proportion of which are large enough to be retained on a 20 mesh U. S. sieve series screen. Such mixtures are widely used in hydrocarbon conversion systems wherein a moving compact bed of solids gravitates through the conversion and regeneration vessels, whereas mixtures of more finely divided solids are employed in the so-called fluid type of hydrocarbon conversion operation. When employed in the elevation of mixtures of coarse granular solids, the present invention is particularly advantageous, since the momentum of the large particles traveling at high velocities is large and the problem of decelerating the particles is a more important one to be solved when the particles have such large momentum.

Any suitable lifting gas can be used according to the present invention. The lifting gas can be inert with respect to the solids elevated, as in the case of steam, air, or flue gas used to elevate regenerated hydrocarbon conversion supporting granular solids, or the lifting gas can be capable of undergoing a chemical reaction upon contact with the solids, as in the case of hydrocarbon vapors used to elevate regenerated, hydrocarbon conversion-supporting granular solids under conversion-supporting conditions. Any suitable braking gas can be used according to the present invention. The braking gas can be the same as, or different from the lifting gas.

In the use of braking gas according to the present invention, certain ranges of operating variables are preferred in that they provide particularly advantageous operation. The variables involved include, among others:

Braking gas volume ratio or ratio of the braking gas volume rate to the lifting gas volume rate.

Braking gas nozzle area ratio, or ratio of the cross sectional area of the braking gas nozzle outlet to the cross sectional area of the lift conduit outlet.

The vertical distance of the braking gas nozzle central outlet above the lift conduit outlet, sometimes expressed as the ratio of that distance to the normal maximum height of rise of solids above the lift conduit outlet, or maximum height of rise obtained under the same conditions but without the use of braking gas. Maximum height of rise is subsequently defined.

The following example illustrates the invention and illustrates the advantages to be obtained from using the preferred ranges of variables, as subsequently set forth:

A series of operations was performed in each of which a mixture of granular solids was suspended in lifting gas and elevated thereby at a rate of about 42 tons per hour through a vertical cylindrical gas lift conduit 67 feet high and 8 inches in diameter into a disengaging vessel generally similar in construction to that illustrated in Figure 1 and having a 4 foot square cross section. The solids consisted of pellets of hydrocarbon conversion catalyst, substantially all of which pellets were small enough to pass through a 3 mesh U. S. sieve series screen, and a major proportion of which pellets were large enough to be retained on a 20 mesh U. S. sieve series screen. The lifting gas was compressed air.

In runs 1, 2, 3, 5, and 6 below, the lift conduit had secured to the upper end thereof a frustoconical conduit section as disclosed in the example given in my copending application, Serial No. 202,306, filed December 22, 1950, now Patent No. 2,704,228, issued March 15, 1955, and as claimed in that application. In the following reporting of these runs, the outlet end of the lift conduit is considered to be the top of the frustoconical conduit section, and all heights of rise and distances of braking gas nozzle outlets from the outlet end of the lift conduit are measured from the top of the frustoconical conduit section. However, in the case of solids velocities, the velocities calculated as subsequently described are velocities at the bottom of the frustoconical conduit section.

In runs 4 and 7 below, there were supported, adjacent and outside the space directly above the top of the lift conduit, three vertically spaced apart bathe plates as disclosed in the example given in my copending application, Serial No. 221,285, filed April 16, 1951, now Patent No. 2,674,499, April 6, 1954, and as claimed in that application. In the following reporting of the results obtained, the outlet of the lift conduit is considered to be at the upper end of the lift conduit beneath the lowermost bafile plate.

When operated without braking gas, the apparatus having three baffle plates provides about the same height of rise as the apparatus having the frustoconical conduit section secured to the top of the lift conduit, so that the heights of rise obtained with braking gas in the two types of apparatus can be compared to show the relative merits of the braking gas nozzles used.

In each of the following operations, the lifting gas and braking gas were removed from the disengager by passi g them downwardly together with the falling solids around the central rising stream of gas and solids and laterally into an annular gas removal space beneath the lift conduit outlet through which space the lifting gas and braking gas were removed separately from the bulk of granular solids. an alternative to the manner nection with the drawings.

In the series of gas lifting operations the performance when various types of gas braking arrangements according to the invention were used was compared with the performance when no gas braking was employed, and it was found that the gas braking was effective to decrease the maximum height of rise of solids in the disengager, without causing excessive turbulence in the solids as they rose, reversed direction, and fell to the bottom of the disengager. In each run of the series, the rates of lifting gas and of braking gas used, and the maximum height of rise of solids were measured, the latter by visual observation of the level of the top of the rising stream of solids.

The following table shows the results obtained in a series of runs illustrating the effect of different types of gas braking arrangements. In run No. 1, there was no braking gas nozzle operating in the disengager. In run No. 2, there was a vertical braking gas nozzle consisting of a 2 inch pipe having a lower open end. This nozzle was positioned substantially similarly to the braking gas nozzle shown in Figure 1. In run No. 3, a 4 inch I. D. braking gas nozzle was employed similarly to the 2 inch nozzle in run No. 2. In run No. 4, a braking gas nozzle similar to that illustrated in Figure 2 was employed similarly to the nozzles in runs 2 and 3. The nozzle in run No. 4 consisted of a inch pipe threaded at the lower end and having three downwardly tapered annulusforming upper body members and a downwardly tapered lower body member about 5% inches long screwed onto the inch pipe. The lower body member had a central inch hole therethrough coaxial and communicating with the lower end of the inch pipe. The /1 inch pipe communicated with each of the three .annuli formed by the body members, through three sets of four holes having inch diameter drilled through the wall of the inch pipe. The three downwardly and outwardly inclined annuli, which constituted the lateral gas discharge previously described in con- This manner of removing gas represents .7 outlets of the nozzle each were 0.05 inches wide. The three lateral outlets were vertically spaced apart from each other a distance of about inch. The cross sectional areas of the three lateral outlets were about 0.37, 0.33, and 0.28 square inch respectively, from top to bottom. The cross sectional area of the central vertical outlet at the bottom of the lower body member was about 0.028 square inch. The four body members were so shaped that the overall shape of the nozzle was substan- It is noted that-the conical nozzle in run 4above, under the other existing conditions, was positioned at a distance, above the lift conduit outlet, at which the height of rise was about equal to the distance of the braking gas nozzle 5 central outlet above the lift conduit outlet. This condition enables the disengager height to be the minimum obtainable under the other existing conditions. As shown subsequently in run 7, if the nozzle central outlet is closer to the lift conduit outlet, the solids rise higher than t y conical, the nozzle being 8% inches long and 10 they do when the height of rise is equal to the height mg an PPP 2 lnches dlametefl and a lower of the braking nozzle. If the nozzle central outlet is apex %6mc h aX1a 1Out 1et' farther from the lift conduit outlet, the solids do not Tliie SOllClS ilelocitiesfgigen in the teltlbdle below are 51 i e as high as when the height of rise is equal to the age fg ve cuties e i z height of the braking nozzle, but the disengager must Passe. eupper en 0 6 cy m ma 1 con e e 0 nevertheless be higher since the braking nozzle outlet is velocities were calculated as subsequently described. In d h r all of the following runs, in both tables, the lifting gas ai i th t f th b velocity at the upper end of the lift conduit was about 6 6 set 0 varymg IS O 1 fa mg 02S 55 feet per second, calculated from the gas rate and lift nozzle outlet above the conduit Quflet 15 Shown by conduit cross section. The braking gas velocities given compal'lson of the follqvlflng t l Wlth Tabla Thfl in the tables were calculated from braking gas rates and r w m at condltlons sl 0 runs above, braking nozzle discharge outlet cross sections. except that the outlets of the 2 inch and 4 Inch pipes were Table 1 Lifting Braking Braking Solids Height Run N0. Braking Gas Nozzle Gas Rate, Gas Rate, Gas Velocity, of Rise,

S. O. S. 0. Velocity, ft./sec. ft. F. M. F. M. ft./sec.

None 1,150 0 o 29.5 11 2 pipe-5 feet above 1, 150 695 495 29.5 9

lift outlet. 4" pipe-5 feet above 1,160 645 120 29.8 8

lift outlet. Conical-4 feet above 1, I 600 1,430 30.8 4

lift outlet.

In each of runs 2, 3, and 4 the solids stream in the disengager, though depressed by the braking gas stream, followed a satisfactorily smooth path, without excessive in each case 11 feet above the lift conduit outlet, and the central outlet of the conical nozzle was 18 inches above the lift conduit outlet.

turbulence, and reversed direction in a satisfactorily regular fountain-shaped stream.

In each of the above runs, the braking gas volume ratio was in the general neighborhood of 0.55 varying from 0.52 to 0.61. The vertical distance from the lift conduit outlet upwardly to the braking gas nozzle outlet was 0.36 times the normal height of rise in run 4, and 0.55 times the normal height of rise in runs 2 and 3. The braking gas nozzle area ratio varied from run to run, being 0.0625 in run No. 2, 0.25 in run No. 3, and in run No. 4, 0.00055 for the central outlet of the braking gas nozzle and 0.0195 for the sum of the three annular outlets, or a total of about 0.02.

The above table shows that the use of braking gas with all three forms of braking gas nozzle is effective to substantially decrease the height of rise of solids above the lift conduit outlet. Under the particular conditions used, the 4 inch pipe was more effective than the 2 inch pipe in decreasing the height of rise. However, as shown subsequently, the 2 inch pipe, under other conditions giving greater decrease in the height of rise, is more effective than the 4 inch pipe. The above table shows that under the conditions employed the conical nozzle having both a central axial discharge outlet and annular inclined discharge outlets is more effective in decreasing the height of rise than the nozzles having only a central axial outlet.

In each of these runs, as in runs 24, the reversal of the solids was satisfactorily smooth, without excessive turbulence.

In runs 5 and 6 the braking gas volume ratio was in the general neighborhood of 0.6, being 0.565 in run 5, and 0.625 in run 6; in run 7, the ratio was 0.17. Even at this lower braking gas volume ratio, the conical nozzle was as effective in decreasing the height of rise as the other nozzles, which lacked the lateral discharge outlets, at higher braking gas volumes. It is noted, however, that the conical nozzle 18 inches above the lift conduit outlet caused an increase in pressure drop over the length of the lift conduit when braking gas rates substantially greater than 200 S. C. F. M. were used. Therefore, care should be taken, when the nozzle outlet is near to the lift conduit outlet, not to use a braking gas rate high enough to stall the lift. It is within the ability of a person skilled in the art to determine, in the light of the present specifications, the proper braking gas rate for any set of other conditions, and suitable braking gas rates may be found even when the central discharge outlet of a nozzle similar to the conical nozzle described above is positioned within the lift conduit and adjacent and below the outlet thereof.

The preferred vertical level at which braking gas is discharged from the braking gas nozzle depends upon the 75 normal height of rise of solids above the outlet end of 9 the lift conduit, that is the height of rise which is obtained under the other existing conditions when no braking gas is employed. When a single braking gas stream is used, the distance between the outlet end of the lift conduit and the outlet end of the braking gas nozzle is prefer ably within the approximate range 0.3 to 1.5 times the normal maximum height of rise of solids above the outlet end of the lift conduit. Maximum height of rise as the term is used here, is intended to indicate the distance from the outlet end of the lift conduit to the top of the rising stream of gas and solids. It is to be understood that some solids will rise a greater distance than this maximum height of rise, but these are considered to be stray solids and the maximum height of rise can be determined by visual observation of the apparent level of the top of the rising stream of gas and solids. It is preferred that the braking nozzle outlet should be at least 0.3 times the normal height of rise above the outlet end of the lift conduit in order that the braking gas after discharge from the nozzle will be able to expand laterally a sufficient amount so that it can provide opposition to the rising solids over a relatively wide cross section. If the braking gas nozzle is closer to the outlet end of the lift conduit it has been found that the rising solids can escape laterally from the decelerating effect of the braking gas before the latter has time to expand, with the result that the braking gas does not have a substantial effect on the height of rise of the solids. It is preferred that the distance of the braking gas nozzle outlet above the lift conduit outlet should not be substantially more than 1.5 times the normal height of rise; otherwise the required height of the disengager is disadvantageously great. When a central-annular combination of braking gas streams is used, it has been found that the braking gas nozzle outlet can be positioned closer to the lift conduit outlet than when a single braking gas stream is used. In fact, it is possible to have a central braking gas stream discharged at a point within the lift conduit and below the outlet end thereof provided that simultaneously an annular braking gas stream is discharged at a level above the outlet end of the lift conduit.

In each of runs and 6 above, the vertical distance from the lift conduit outlet upwardly to the braking gas nozzle outlet was 1.0 times the normal height of rise, and in run 7 the distance was about 0.14 times the normal height of rise. Comparing run 5 with run 2 in Table 1 shows that increasing the distance from 0.45 to 1.0 times the normal height of rise, in the case of the 2 inch pipe, substantially decreases the height of rise. The 4 inch pipe, however, was apparently more effective closer to the lift conduit outlet, for in run 3 an 8 foot height of rise was obtained with a lesser braking gas rate than was required in run 6 to obtain the same height of rise. For the 4 inch pipe, since the height of rise is depressed to about 0.73 times the normal height of rise, both when the distance from the lift conduit outlet to the braking gas nozzle outlet is about 0.45 and when it is 1.0 times the normal height rise, it appears that the height of rise would be about equal to the distance from the lift conduit outlet to the braking gas nozzle outlet when the latter distance is about 0.73 times the normal height of rise. For the 2 inch pipe, the same relationship is probably approximately true. If when using a braking gas nozzle having an area ratio less than about 0.2, it is desired to achieve maximum depression in the height of rise, rather than a height of rise approximately equal to the distance from the lift conduit outlet to the braking gas nozzle outlet, it is generally preferred that the distance from the lift conduit outlet to the braking gas nozzle outlet should be greater than about 0.8 times the normal height of rise, when a single central braking gas stream is used, or greater than about 0.3 times the normal height of rise when a plurality of braking gas streams including an annular stream are used. When the braking gas nozzle area ratio is greater than about 0.2, for example in the case of the 4 inch pipe, the height of rise is less sensitive to the positioning of the nozzle outlet.

It is noted that the optimum height of the braking gas nozzle outlet varies with the braking nozzle area ratio, as described above, and also with the braking gas velocity. Preferably, if the braking gas velocity is above 400 feet per second, the distance from the lift conduit outlet to the braking gas nozzle outlet is at least 0.4 times the normal height of rise. The height of the braking gas nozzle outlet should be great enough so that no tendency to stall the lift is encountered at the otherwise existing operating conditions. Selection of combinations of nozzle height with other conditions which will avoid stalling the lift is, in the light of the present specification within the ability of a person skilled in the art.

The optimum height in feet of the braking gas nozzle above the lift conduit outlet, varies with the velocity of the solids issuing from the lift conduit outlet. When the solids velocity is in the neighborhood of 30 feet per second and a single central braking gas stream is used, the preferred distance of the braking gas nozzle outlet above the lift conduit outlet is within the approximate range 416 feet.

It is noted that nozzle heights can be: chosen which make possible a disengager of minimum height. For example, if the distance from the lift conduit outlet to the braking gas nozzle outlet is sufliciently less than the normal height of rise and sufliciently greater than 0.3 times the normal height of rise, a braking gas volume ratio can be found at which the height of rise obtained using braking gas is equal to the height of the braking gas nozzle outlet above the lift conduit outlet, and such braking gas nozzle height and volume ratio make possible a disengager of minimum height for the otherwise existing operating conditions. It is to be understood, however, that it is generally advisable to construct a disengager with great enough height to allow for possible changes in operating conditions. Also, Where minimum height of rise of solids rather than minimum required disengager height is desired, it is generally preferred to position the braking gas nozzle outlet above the level at which the height of rise obtained using braking gas is equal to the height of the braking gas nozzle above the lift conduit outlet.

It is to be noted that when a central-annular combination of braking gas streams is used according to the present invention an important function of the central stream is to divert laterally the rising stream of gas and solids into the path of the inclined annular braking gas streams so that the latter can effect their deceleration action more effectively. Thus, a central braking gas stream which would be unsatisfactory for use alone as a braking gas stream can be effectively used in conjunction with inclined annular braking gas streams. For example, the braking nozzle area ratio of the central braking gas stream can be less when the central stream is used in conjunction with an annular stream than when the central stream is used alone.

When a single braking gas stream is used the braking nozzle area ratio, that is the ratio of the cross sectional area of the discharge outlet of the braking gas nozzle to the cross sectional area of the outlet end of the lift conduit, is preferably within the approximate range 0.01 to 0.9. This area ratio is preferably not less than 0.01; otherwise the required pressure of the braking gas would be inconveniently high. It is preferred that the area ratio should not be greater than 0.9; otherwise it might be inconveniently difficult to obtain a high braking gas velocity while still using a relatively low volume of braking gas. When a central-annular combination of braking gas strealns is used the braking gas nozzle area ratio is preferably within the approximate range 0.001 to 0.9. The area ratio can be less when a centralannular combination of braking gas streams is used since as previously described, greater velocities can be used 16 with such combination.

Although in the above runs, volume ratios ranging from about 0.17 to about 0.625 were used, it is to be understood that other volume ratios can be used with good effect. Generally, relatively low volume ratios give relatively little decrease in the height of rise, and when the braking nozzle has only a central vertical outlet the volume ratio preferably is at least 0.1. When the braking nozzle has annular inclined outlets also, the volume ratio is preferably at least 0.91. It is further preferred that the volume ratio not exceed 0.9 whether the braking nozzle has annular inclined outlets or not, otherwise some tendency for stalling of the lift, for excessive turbulence in the disengager, for overload of cyclone separators, or for other undesirable effect may be encountered.

Comparison of Table l with Table 2 shows that, at similar braking gas volume ratios, at 2 inch pipe gives better results than the 4 inch pipe in decreasing the height of rise when the outlets are relatively far from the lift conduit outlet, but gives poorer results than the 4 inch pipe when the outlets are closer to the lift conduit outlet. Generally, it is belived that the effectiveness of a braking gas nozzle in decreasing the height of rise depends on the momentum of the braking gas discharged from the nozzle outlet or outlets. Thus the effectiveness depends both on the rate of braking gas, and on its velocity. Braking gas nozzles having discharge outlets with large cross sectional area in some instances require higher gas rates to achieve a given degse'of effectiveness than a nozzle having a smaller area outlet since at equal rates, the gas velocity is lower in thelarge area outlet. This is generally true when the braking gas nozzle outlets are relatively far from the lift conduit outlet as shown in Table 2. However, where the braking gas nozzle outlet is relatively close to the lift conduit outlet, the effectiveness of the smaller nozzle may be decreased, as in run 2 above, by another factor, i. e. the tendency of the rising solids to escape laterally from the narrow braking gas stream, rather than being directly opposed and depressed by the braking gas.

The solids velocities given in the above tables refer to the average linear vertical upward velocity of the solid particles as they pass the upper end of the cylindrical lift conduit. These velocities were calculated from measured lifting gas rates, average solid particle diameters, and gas and solid densities by means of the following formula:

rl U,-U 9.9 dz where Us is solids velocity in feet per second, Ug is gas velocity obtained by dividing the measured gas rate in cubic feet per second by the average cross sectional area of the lift conduit in square feet, D5 is average particle diameter of the'solids in feet, and ds/dg is the ratio of densities of the lifted solids and of the lifting gas. The subtracted term in the equation represents the slip velocity of the solids, i. e. the velocity at which they tend to fall through the surrounding gas.

Although in each of the above runs, the solids velocity was about feet per second, it is to be understood that the use of braking gas according to the invention is effective to decrease the height of rise when other solids velocities are used. Generally, it is preferred that the solids velocity should not be less than 15 feet per second when braking gas is employed according to the invention; otherwise, some tendency for the lift to stall may be encountered. Generally, it is preferred that the solids velocity should not be greater than 60, feet per second when braking gas is employed according to the invention; otherwise some tendency for excessive turbulence to occur when the braking gas impinges on the. gas-solids stream may be encountered.

In the above runs, the braking gas velocities used varoutlets of the braking nozzle.

led from'l40 to 1430 feet per second. Thesewere linear velocities at the discharge outlet or outlets of the braking nozzle and were'calculated by dividing the braking gas volume rate by the cross sectional area of the outlet or Braking gas velocities higher or lower than those used in the above runs can be employed. It is preferred that the braking gas velocity be greater than 50 feet per second, in order that an advantageous amount of depression of the height of rise can t be effected. It is further preferred that, when using only a central vertical braking gas jet, the braking gas velocity should not be greater than 600 feet per second; otherwise a tendency for excessive turbulence in the disengager may be encountered, and also the braking gas stream may tend to laterally expand too little after discharge from the above the lift conduit outlet, it is preferred that velocities below 600 feet per second he used with the braking gas nozzle positioned at a level as described subsequently. When a central braking gas stream is used in combination with an annular stream as described above, it is preferred that the braking gas velocity in each stream should be within the approximate range 50 to 1500 feet per second. Higher braking gas velocities can be used with a centralannular combination of braking gas streams, because even at velocities over 600 feet per second, the annular stream effectively opposes the rising solids over a wide cross section, and the function of the central stream when used in combination with an annular stream is, as subsequently described, merely to divert the rising stream of gas and solids, rather than to oppose it over a wide cross section. Braking gas velocities above about 1500 feet per second are avoided lest some tendency to stall the lift should be encountered.

The present invention is advantageously applied to lifting operations wherein granular solids are elevated through elongated confined lift conduits whose heights may be, for example, 50 to 300 times the major dimension of the cross section of the lift conduit. Lift conduits of such height are used, for example, in hydrocarbon conversion operations wherein granular particles of the conversion-supporting contact material are elevated from a low point in the conversion apparatus system to a high point therein. The lifting gas velocities through lift conduits as used in such operations are generally within the approximate range 25 to feet per second as calculated by dividing the volume rate of the lifting gas by the crosssectional area of the lift conduit.

In the preceding example, where a frustoconical conduit section was secured to the upper end of the lift conduit, that conduit section was concentric with thelift conduit and 23 inches high and had 8 inches base diameter and 20.5 inches top diameter. Where the three bafile plates were supported adjacent and outside the space directly above the top of the lift conduit, each baffle plate consisted of an inner inverted frustoconical portion and an outer upright frustoconical portion, the two portions being joined at their tops by a smoothly curved connecting portion. The sides of each frustoconical portion were inclined at a 45 angle. In each baffle, the base of the outer portion was about 2 /2 inches above the base of the inner portion. The baffles were vertically spaced apart, the base of the inner portion of the lowest bafile being about 2 /2 inches above the top of the lift conduit, and the base of the inner portion of each of the upper bafiies being about 4 inches above the base of the adjacent lower bafiie. The base diameters of the inner portions of the three baf- 13 fies were about 8.7, 9.7, and 10.7 inches respectively, from lowermost to uppermost, and the base diameters of the outer portions of the three batfles were about 20, 21, and 22 inches respectively, from the lowermost to uppermost. Each baffle was concentric with the lift conduit. The overall height of each bafile was a little less than 4 inches. The smoothly curved connecting portion of each baffle had the shape of a section of a torus of revolution about the longitudinal axis of the lift conduit, which section lay above a horizontal plane intersecting the torus.

Both the frustoconical conduit section and the set of bafl'le plates were effective in themselves to decrease the height of rise to about 13 feet above the top of the cylindrical pipe to which, in one case, the frustoconical conduit section was secured and above which, in the other case, the three bathe plates were supported. The various gas braking means employed were effective to decrease the height of rise still further, as shown in the preceding examples.

Although the frustoconical conduit section and the baffle plates each co-act with the gas braking means to obtain particularly effective operation according to the invention, it is to be understood that the gas braking means can be used in the absence of any such frustoconical conduit section or bafile plate. The frustoconical conduit section, when used with gas braking means, decelerates the solids in the rising stream shortly after they issue from the top of the cylindrical lift conduit, and the effectiveness of the braking gas stream in opposing the already partially decelerated solids is unusually great. The baflle plates also decelerate the solids in the rising stream shortly after they issue from the top of the lift conduit, since the inner edge of each baffle plate interrupts the vertical upward movement of part of the lifting gas at the periphery of the rising stream and causes that part of the lifting gas to lose its ability to push solids upwardly.

The use of braking gas according to the invention is effective to decrease attrition of granular solids by decreasing the height of rise of solids above the top of a lift conduit, and also by imparting to the solids a large lateral component of motion relative to their downward component of motion as they fall after reversal of direction. The lateral component of motion serves to decrease the impact on the solids when their fall is abruptly arrested in a lower portion of the disengager.

The invention claimed is:

1. Apparatus for elevating granular solids by means of a lifting gas and for separating solids from gas after such elevation which comprises: an elongated lift conduit; a disengaging vessel communicating with the top of said lift conduit and providing a space thereabove for deceleration and reversal of direction of granular solids and pro viding a communicating space therebeneath for receiving granular solids; a braking gas nozzle having a lower substantially vertically downwardly directed outlet substantially coaxial with said lift conduit and having an upper annular downwardly directed outlet substantially above said top of said lift conduit and inclined downwardly away from the longitudinal axis of said lift conduit; a solids supply source communicating with a lower portion of said lift conduit; means for introducing braking gas into said nozzle; and means for introducing lifting gas and solids from said supply source into said lift conduit for passage upwardly therethrough as a stream of solids suspended in lifting gas.

2. Apparatus according to claim 1 wherein said braking gas nozzle is downwardly tapered and has said vertically downwardly directed outlet at its apex, and wherein said braking gas nozzle has a plurality of vertically spaced apart, inclined annular downwardly directed outlets.

3. Method for elevating granular solids which comprises: suspending such solids in a lifting gas; passing solids and gas upwardly through an elongated confined Zone; discharging solids and gas upwardly from said confined zone into an expansion zone as a rising stream; discharging downwardly into said expansion zone in sub stantially direct opposition to said rising stream a central stream of braking gas, substantially coaxial with said rising stream, and an annular stream of braking gas inclined downwardly away from the longitudinal axis of said rising stream, said annular stream of braking gas being substantially coaxial with said rising stream, the ratio of the braking gas volume rate to the lifting gas volume rate being not substantially greater than 0.9; maintaining the maximum height of rise of solids in said expansion zone at a level beneath the upper boundary of said expansion zone and withdrawing braking gas and lifting gas from said expansion zone substantially separately from solids.

4. Method according to claim 3 wherein a plurality of vertically spaced apart, coaxial, annular inclined streams, substantially coaxial with said rising stream, are discharged downwardly into said rising stream each annular stream other than the lowest being discharged at a location farther removed from the axis of said annular inclined streams than the location at which the adjacent lower annular stream is discharged.

5. Method according to claim 3 wherein the average velocity of said lifting gas in said confined zone is within the approximate range 25 to feet per second, and wherein the velocity of said braking gas at discharge is within the approximate range 50 to 600 feet per second, the lifting gas velocity being less than the braking gas velocity.

6. In apparatus for circulation of granular solids which are subject to substantial attrition as a result of pneumatic elevation, which apparatus comprises a reaction vessel, an elongated vertical lift conduit extending beneath the solids outlet from said reaction vessel and extending above the solids inlet to said reaction vessel, the height of said lift conduit being at least 50 times as great as the major dimension of its horizontal cross section, means for introducing granular sol-ids into said lift conduit after said granular solids have gravitated through said reaction vessel, and means for introducing lifting gas into said lift conduit to elevate said granular solids therethrough, the improvement which comprises: a disengaging vessel communicating with the top of said lift conduit and providing a space thereabove for deceleration and reversal of direction of granular solids and providing a communicating space therebeneath for receiving granular solids; a braking gas nozzle communicating with said disengaging vessel and substantially coaxial with said lift conduit and having a downwardly directed outlet positioned substantially above said top of said lift conduit; and means for introducing braking gas into said nozzle.

7. Apparatus according to claim 6 wherein said braking gas nozzle has a lower substantially vertically downwardly directed outlet and an upper annular downwardly directed outlet inclined downwardly away from the longitudinal axis of said lift conduit.

8. Apparatus according to claim 7 wherein said braking gas nozzle is downwardly tapered and has said vertically downwardly directed outlet at its apex, and wherein said braking gas nozzle has a plurality of vertically spaced apart, inclined annular downwardly directed outlets.

9. In a process for circulation of granular solids which are subject to substantial attrition as a result of pneumatic elevation, which process comprises gravitating granular solids through a reaction zone, suspending said solids, after passage through said reaction zone, in a lifting gas, and passing solids and gas vertically upwardly through an elongated confined zone as a confined stream to a level above said conversion zone, the distance of travel through said confined zone being at least 50 times as great as the major dimension of the horizontal cross section of said confined stream, the improvement which comprises: discharging solids and gas upwardly from said confined zone into an expansion zone as a rising stream; discharging braking gas downwardly into said expansion zone in substantially direct, opposition to said rising stream, the ratio of the braking gas volume rate to the lifting gas volume rate being not substantially greater than 0.9; and maintaining the maximum height of rise of solids in said expansion zone at a level beneath the upper boundary of said expansion zone.

10. Process according to claim 9 wherein a central stream of braking gas, substantially coaxial with said rising stream, and an annular stream of braking gas inclined downwardly away from the longitudinal axis of said rising stream, said annular stream of braking gas being substantially coaxial with said rising stream, are discharged downwardly into said rising stream.

11. Process according to claim 10 wherein a plurality of vertically spaced apart, coaxial, annular inclined streams, substantially coaxial with said rising stream, are discharged downwardly into said rising stream, each annular stream other than the lowest being discharged at a location farther removed from the axis of said annular inclined streams than the location at which the adjacent lower annular stream is discharged.

12. Process according to claim 9 wherein the average velocity of said lifting gas in said confined zone is within the approximate range to 100 feet per second, and wherein the velocity of said braking gas at discharge is within the approximate range 50 to 600 feet per second, the lifting gas velocity being less than the braking gas velocity.

13. Process according to claim 9 wherein solids are discharged from said confined zone at a velocity of at least about 25 feet per second.

14. Apparatus for elevating granular solids by means of a lifting gas and for separating solids from gas after such elevation which comprises: an elongated lift conduit; a disengaging vessel communicating with the top of said lift conduit and providing a space thereabove for deceleration and reversal of direction of granular solids and providing a communicating space therebeneath for receiving granular solids; a braking gas nozzle substantially coaxial with said lift conduit and having an annular downwardly directed outlet substantially above said top of said lift conduit and inclined downwardly away from the longitudinal axis of said lift conduit; a solids supply source communicating with a lower portion of said lift conduit; means for introducing braking gas into said nozzle; and means for introducing lifting gas and solids from said supply source into said lift conduit for passage upwardly therethrough as a stream of solids suspended in lifting gas.

16 15. Method for elevating granular solids which comprises: suspending such solids in a lifting gas; passing solids and gas upwardly through an elongated confined zone; discharging solids and gas upwardly from said confined zone into an expansion zone as a rising stream; discharging downwardly into said expansion zone in opposition to said rising stream an annular stream of braking gas inclined downwardly away from the longitudinal axis of said rising stream, said stream of braking gas being substantially coaxial with said rising stream, the ratio of the braking gas volume rate to the lifting gas volume rate being not substantially greater than 0.9; maintaining the maximum height of rise of solids in said expansion zone at a level beneath the upper boundary of said expansion zone and withdrawing braking gas and lifting gas from said expansion zone substantially separately from solids.

16. In a process for circulation of granular solids which are subject to substantial attrition as a result of pneumatic elevation, which process comprises gravitating granular solids through a reaction zone, suspending said solids, after passage through said reaction zone, in a lifting gas, and passing solids and gas vertically upwardly through an elongated confined zone as a confined stream to a level above said conversion zone, the distance of travel through said confined zone being at least times as great as the major dimension of the horizontal cross section of said confined stream, the improvement which comprises: discharging solids and gas upwardly from said confined zone into an expansion zone as a rising stream; maintaining the velocity of said solids at discharge within the approximate range from 15 to feet per second; discharging braking gas downwardly into said expansion zone in substantially direct opposition to said rising stream, the ratio of the braking gas volume rate to the lifting gas volume rate being not substantially greater than 0.9; and maintaining the maximum height of rise of solids in said expansion zone at a level beneath the upper boundary of said expansion zone.

' References Cited in the file of this patent UNITED STATES PATENTS 2,054,441 Peebles Sept. 15,1936

2,106,869 'Falkenstein Feb. 1, 1939 2,358,497 Egloif Sept. 19, 1944 2,460,546 Stephanoff Feb. 1,1949

FOREIGN PATENTS 360,968 Germany Oct. 9, 1922

Claims

1. APPARATUS FOR ELEVATING GRANULAR SOLIDS BY MEANS OF A LIFTING GAS AND FOR SEPARATING SOLIDS FROM GAS AFTER SUCH ELEVATION WHICH COMPRISES: AN ELONGATED LIFT CONDUIT; A DISENGAGING VESSEL COMMUNICATING WITH THE TOP OF SAID LIFT CONDUIT AND PROVIDING A SPACE THEREABOVE FOR DECELERATION AND REVERSAL OF DIRECTION OF GRANULAR SOLIDS AND PROVIDING A COMMUNICATING SPACE THEREBENEATH FOR RECEIVING GRANULAR SOLIDS; A BRAKING GAS NOZZLE HAVING A LOWER SUBSTANTIALLY VERTICALLY DOWNWARDLY DIRECTED OUTLET SUBSTANTIALLY COXIAL WITH SAID LIFT CONDUIT AND HAVING AN UPPER ANNULAR DOWNWARDLY DIRECTED OUTLET SUBSTANTIALLY ABOVE SAID TOP OF SAID LIFT CONDUIT AND INCLINED DOWNWARDLY AWAY FROM THE LONGITUDINAL AXIS OF SAID LIFT CONDUIT; A SOLIDS SUPPLY SOURCE COMMUNICATING WITH A LOWER PORTION OF SAID LIFT CONDUIT; MEANS FOR INTRODUCING BRAKING GAS INTO SAID NOZZLE; AND MEANS FOR INTRODUCING LIFTING GAS AND SOLIDS FROM SAID SUPPLY SOURCE INTO SAID LIFT CONDUIT FOR PASSAGE UPWARDLY THERETHROUGH AS A STREAM OF SOLIDS SUSPENDED IN LIFTING GAS.