US2733993A

US2733993A - Elevation of granular solids

Info

Publication number: US2733993A
Authority: US
Publication date: 1956-02-07
Anticipated expiration: 1973-02-07

Description

Feb. 7, 1956 H. c. THOBER ET AL 2,733,993

ELEVATION OF GRANULAR SOLIDS I Filed Nov. 9, 1951 36 INVENTORS.

HERBERT C. THOBER BY WILLIAM L. MCCLURE AMW/w/ ATTORNEYS ELEVATION F GRANULAR-SOLIDS Herbert C. Timber and William L. McClure, Toledo, Ohio, assiguors to Sun Oil Company, Philadelphia, Pa.-, a corporation of New Jersey Application November 9, 1951, Serial No. 255,640

3 Claims. (Cl. 302-43) This invention relates to the elevation of granular'solids by means of a lifting gas and more particularly to a method of elevation whereby stabilized conditions are maintained in the elevation system with a minimum ofattrition of granular solids occurring.

In the so-called moving bed hydrocarbon=conversion process, whereby hydrocarbon materials are converted by contacting them with a moving compact bed of granular solids, it is known in the art to elevate the granular solids from a low point in the solids circulation system to a high point therein by suspending the solids in a liftingrg as I 5 and elevating the solids suspended in the gas to'the high point in the system. In this and other processes involving the pneumatic elevation of granular solids a frequently encountered disadvantage isthe high attrition undergone by the solids during the liftingoperationand the separation of solids from gas after the lifting operation; Attrition of solids is an effect which should be minimized in hydrocarbon conversion processes since it'results in disadvantageously high rates of loss of solids from-the system.

According to the present invention a highly stable-gas lifting operation is obtained with a minimum of attrition of granular solids. In the process of the presentinvention granular solids are elevated through a confined lift-conduit as a dense mass of solids, i. e., a mass'containinga high proportion of solids to gas in the mixtureof :gas and solids which passes upwardly through the lift conduit. In most prior art lifting operations the solids have been entrained by the lifting gas andpas sedupwardlythrough the lift conduit as a sparse suspension of solids ingas. The difference between the method of the present inven tion involving elevation of solids as a dense mass and such prior art sparse phase liftingoperations is readily apparent from a consideration of the behavior of the'solidsin the lift conduit if the supply of liftinggas to the lift conduit is abruptly shut ofi. In a dense phase lifting operation such as in the present invention, when the solids come to rest in'the lift conduit after abrupt shutting off of the lifting gas supply, the lift conduit is found to bemore than half full of solidsand'frequently it will be found to be completely full of solids. In a sparse phase lifting operation, on the other hand, when the solids come to rest after abrupt shuttting off of the lifting. gas supply the lift conduit is found to be generally'less than one-quarter fullof solids. The reasons for this difference in behavior; are that in a dense phase lifting operation the concentration of solids in the lift conduit is much higher than in a sparse phase lifting operation, and that the linear velocity of the solids in a dense phase operation is much lessthan the linear velocity of the solids in a sparse phase operation.

, As disclosed in copending applicatiomserial- No. 229,117, filed May 31, 1951, by Howard C. Passmore,,adense phase lifting operation can be obtained'by establishing an elongated compact mass of granular solids within a confined zone such as a lift conduit and supplying lift ing gas under pressure to the lower portion of the elon- States Patent 0 r ice gated compact mass, the rate of supply of lifting gas being sufiiciently low that=the granular solids in-the elongated co'mpact'mass are not entrained by the lifting gas, but are instead moved smoothly upwardly 'as a dense mass having a veryhighconcentration of solids therein. The granular solids should not beentrained to a substantial degree by the lifting gas because'if suchentrainrnent occurs, the lifting operationtends to become a sparsephase operation rather than a dense phase operation. As the granular solids-are'elevated in the'lift conduit additional solids'are supplied to a lower inlet to the'lift conduit to maintain the lift conduit full of solids.

According to the present inventiona highly stabilized dense phase lifting operation is provided by gradually laterallyexpandingthe dense'ma'ss of granularsolids-as it rises through the lift'conduit. As the lifting gas rises through the expanding dense mass it tends to decrease in linear upward velocity'because of the larger cross section through which it is enabled to flow. At th'esain'e time, however, the linear upward velocity'of the lifting gas tends to increasebecause ofthe decreasing pressure onthe lifting gas as'it'ris'es through the lift conduit; According to the present invention these two tendencies are caused to counterbalance each other so that the velocity of the lifting gas can be maintained substantially constant throughoutthe length of the lift conduit. Maintenance of such substantially constant velocity provides-a high degree of-stability ofthe lifting operation. The operation is stabilized in that there is no substantial tendency for the-lifting operation to become a sparse phase-operation through entrainment of solids'by the gas. In operation wherein the dense 'massis not laterally expanded as it rises'and wherein consequently, the velocity of the lifting gas-increases as it risesin the lift conduit, there isa tendency for the high velocity lifting gas in the upper portions of the lift conduit to entrain the solid particles and initiate asparse phase lift operation.

Operation according to'the present invention is further stabilized-in that there is no substantial tendency for the lifting operation to become stalled, i. e., for the solids to stop moving inthe lift conduit and come to rest; operation according to the present invention is particularly free from any tendency for the lifting operation to'stall if the rate of expansion-of the dense mass as it rises through the lift conduit is maintained at a suitably low level. Preferably, to obtain thisresult, the lift conduit is so constructed that in one foot of vertical height of the lift' conduit the average increase in cross sectional area of the lift conduit is not greater than 0. 1 square feet. A generally preferred rate of increase of cross section according to the present invention is one within the approximate range 0.001 to 0.1 square feet per foot of lift condun height. 7

In a' further preferred embodiment of the present invention, in addition to a main lift conduit portion having an average rate of increase of cross section as specified above, a short upper lift conduit section is provided which has a substantially greater rate of increase of cross section, for example, a rate within the approximate range 0.1 to 1.5 square feet per vertical foot of lift conduit height. The total vertical height'of such an upperportion is preferably within the approximate range 02-10 times the major dimension of the lift conduit cross sectionat the bottom of the upper portion. The advanta e 7 of the provision of such an uper portion resides in the fact that it provides at the top of the'solids lift path a short section wherein the linear velocity of the lifting gas is somewhat lower than the velocity of the liftinggas in the main" portion of the lift conduit. This-somewhatlower velocity provides an additional safeguard against initiation of a sparse phase lifting operation.

According to a further preferred embodiment of the present invention granular solids are fed into the lower portion of the lift conduit through an annular passageway, the cross sectional area of the central area surrounded by the annular passageway gradually decreasing as the compact mass of solids rises through the annular passageways. The cross sectional area of the central area ultimately decreases to zero at a level above which the rising dense mass is no longer annular. As the solids rise through the annular passageway the cross sectional area of the rising solids mass increases since the total area enclosed by the periphery of the annular mass does not decrease as the solids rise, whereas the central area does decrease as the solids rise. Operation according to this preferred embodiment of the invention is advantageous in that it provides a particularly smooth flow of solids into the lift conduit.

The invention will be further described with reference to the attached drawing. Figure l of the drawing is a schematic diagram of apparatus wherein granular solids are gravitated from a high point in the system to a low point therein and elevated as a dense mass by means of a lifting gas from the low point in the system to the high point therein. Figure 1 does not illustrate any of the details of the present invention and is provided merely to show a type of system to which the present invention is advantageously applied. Figure 1 is a sectional elevati tional view of the gas lift engaging vessel, lift conduit, and disengaging vessel which are indicated schematically in Figure 1. Figure 2 illustrates details according to the present invention.

Turning now to Figure 1 there are illustrated therein reaction vessels and 11, pressuring

vessels

12 and 13, gas lift engaging vessel 14, lift conduit 15, and gas lift disengaging vessel 16. In operation granular solids are gravitated from disengager 16 through line 17 into reaction vessel 10 which may be, for example, a hydrocarbon conversion vessel. From vessel 10 solids are gravitated as a compact mass through line 18 into reaction vessel 11, which may be, for example, a solids regeneration vessel. From vessel 11 solids are gravitated either through line 19 or through line 20, depending upon the setting of the

valves

21 and 22. The manipulation of the

valves

21 and 22 is such that when one is open the other is closed. Assuming that solids are gravitating from vessel 11 through line 19 into pressuring vessel 13, the latter being at a relatively low pressure, the valve 23 is kept closed to provide a seal between pressuring vessel 13 and engager 14 which is always at a higher pressure. Assuming further that valve 21 has just been closed, pressuring vessel 12 is first pressured until its pressure is equal to the pressure in engager 14, and then solids flow from vessel 12 through line 24 into engager 14. Lifting gas is introduced into engager i i through line 31. The lifting gas thus introduced passes through a compact mass of solids in engager 14 and forces solids from the compact mass into and through lift conduit as a dense mass of solids propelled by lifting gas. The dense mass of solids and lifting gas is discharged from the upper end of lift conduit 15 into disengager 16. Lifting gas is withdrawn from disengager 16 through line 26 and granular solids are gravitated again through line 17.

When pressuring vessel 12 becomes empty of granular solids valve 25 is closed. Then pressuring vessel 12 is vented through means not shown to reduce the pressure to approximately the level of the pressure at the bottom of vessel 11. Then valve 21 is opened and substantially simultaneously valve 22 is closed. Valve 23 is opened and pressuring of vessel 13 is begun. The operation is continued in cycles with pressuring

vessels

12 and 13 alternately in communication with vessel 11 and with engager 14. Such operation is generally necessary in a dense phase lifting system because the lifting gas pressures, which are required for a dense phase operation, are quite high so that means such as described above for sealing the engaging vessel from the reaction vessels are required.

The above description refers to an on-stream operation. The manner of starting up an operation of the type described above is not described in detail here, but a known manner of starting up which can advantageously be used is that disclosed in application Serial No. 229,117, of Howard C. Passmore referred to above. In order to obtain a dense phase operation, it is necessary to first establish an elongated compact mass of solids, e. g., a mass having vertical height within the approximate range 50-300 times the average major dimension of the lift conduit cross section in a confined zone, and then supply lifting gas to a lower portion of the confined zone. For example, a dense phase operation according to the present invention can be obtained by partially or completely filling a lift conduit to obtain an elongated compact mass therein and supplying lifting gas to the bottom of the mass, whereas sparse phase operation is obtained in prior art operations where solids are carried from a supply vessel by lifting gas into a lift conduit which was substantially empty of solids when the lifting gas supply was started.

Turning now to Figure 2 there are shown therein engager 14, lift conduit 15, and disengager 16. Engager 14 has an inlet 30 for granular solids and an inlet 31 for lifting gas under pressure. The lowest portion 32 of lift conduit 15 has its lower end 33 positioned within engager 14. Concentric with lift conduit 15 is a conical baffle 34 having its apex positioned within lift conduit 15 and having its base positioned below the lower end 33 of lift conduit 15. An annular passageway is provided between the baffle 34 and the inner wall of lower portion 32 of lift conduit 15. The cross sectional area of this annular passageway increases toward the apex of the bafile 34 since the central area of the annulus, i. e. the cross sectional area of the bafile 34, decreases toward the apex of baffle 34, whereas the total cross sectional area enclosed by the inner Wall of lower portion 32 of lift conduit 15 remains substantially constant. Secured to the center of the base of conical baffle 34 is a support rod 35 extending vertically downwardly through the bottom of the engager and through packing gland 36. The support rod 35 is slidably mounted in order that the vertical level of bafi le 34 can be adjusted from outside the engager 14.

As shown in Figure 2 lift conduit 15 consists of four conduit sections, 32, 37, 38, and 39, which have increasing cross sectional area in the order named.

Conduit sections

32, 37, and 38 have substantially constant cross section throughout their lengths and conduit section 39 is an inverted frustoconical conduit section.

Conduit sections

32, 37, and 38 constitute a main portion of lift conduit 15 according to the present invention. The dimensions of these conduit sections are so chosen that the average rate of increase of cross section through the entire length of the main portion of lift conduit 15, which main portion consists of the three conduit sections, is substantially less than the rate of increase of cross section of frustoconical conduit section 39; and preferably the rates of increase in cross sectional area per vertical foot of height of the main conduit portion consisting of

conduit sections

32, 37, and 38, and for the upper portion consisting of frustoconical conduit section 39, are within the ranges previously given for the main portion and the upper portion respectively, of the lift conduit according to the present invention. Although in Figure 2 the main portion of the lift conduit 15 is shown as consisting of a series of three conduit sections, each having substantially constant cross sectional area somewhat greater than the cross sectional area of the adjacent lower conduit section, it is to be understood that according to the present invention any suitable number of such conduit sections can be used or, instead of a series of conduit sections each having substantially constant cross section, a single conduit section having ihvert'ed frustoconicalshapecan-be used. Inthelatter case, 'if'the upperportion of the lift conduit such as the upper portion 39 of lift conduit is employed, the angle with the vertical of th'e side' of the 'fru'stoconical conduit section, constituting the main portion of the'lift'conduit, will be less than the angle with the vertical of the side of the frustoconical conduit section constituting the upper portion of the lift conduit.

Disengager l6h'as an outlet 17 for granular solids and an outlet'26for' lifting gas. Suspended from the top of disengager 16 by means o'f ha'nger's 40 is a cylindrical disc-shaped baffle 41. In operation granular solids are introduced through line intoen a'ger 14 in order to establish a compact bed of granular solids surrounding the inlet end 33 of lift conduit 15 Generally the introduction of solids through line 30 is not continuous, but intermittent; however, the frequency and rate at which solids are introduced through line 30 is sufficient to maintain the top of the compact bed of solids in engager 14 at a level above the inlet end 33 of lift conduit 15. Lifting gas under pressure is introduced under pressure into engager 14 through line 31, and passes into and through the compact bed in engager 14. The lifting gas passes downwardly then horizontally toward the lower part of the side of conical baffie 34, then upwardly between bafiie 34 and the inner wall of lower portion 32 of lift conduit 15. Lifting gas then rises past the apex of baffie 34 and through the remaining length of conduit section 32 and then through

conduit sections

37, 38, and 39. Throughout this entire path of travel lifting gas passes through a compact or dense mass of granular solids. After its reversal of direction of flow adjacent inlet end 33 of lift conduit 15, the lifting gas provides an upward force which propells the compact mass of solids through which it moves upwardly in lift conduit 15.

As the lifting gas passes from conduit section 32 into conduit section 37, its linear upward velocity tends to decrease because of the lateral expansion permitted by the greater cross section of conduit section 37. Such tendency for the lifting gas velocity to decrease counteracts the tendency of the lifting gas velocity to increase as the gas rises through decrease of pressure on the gas. A similar effect is obtained when lifting gas passes through conduit section 37 into conduit section 38. As the lifting gas passes through conduit section 39 its velocity tends to decrease at a greater rate than the average rate of decrease during its passage through the main portion of the lift conduit. This decrease in velocity in the conduit section 39 reduces the possibility of entrainment of solids by the lifting gas in that conduit section.

As the granular solids pass upwardly above the top of conduit section 39 they move laterally over the upper edge of conduit section 39 and then move downwardly through the annular space in disengager 16 surrounding

conduit sections

39 and 38. The lifting gas disengages from the upper surface of the dense or compact mass of solids as the latter reverses direction and the disengaged lifting gas passes upwardly around bafile plate 41 and out of disengager 16 through outlet 26. Granular solids are removed as a compact mass from disengager 16 through outlet 17.

Operation as above-described is particularly advantageous in a number of features. First, the reversal of direction of granular solids in the disengager is accomplished so smoothly that very little attrition of granular solids occurs in the disengager. In sparse phase lifting operations, on the other hand, high degrees of attrition are frequently encountered in the disengager since the solids rise to a high level in the disengager and fall onto the surface of a compact bed in the lower portion of the disengager; upon striking the surface of the compact bed substantial attrition of the solids tends to occur. According to the present invention the height of rise of solids above the top of the lift conduit is so slight compared to "the heights of rise obtained in sparse phase liftin'g'o'pen ations, that'att'rition is minimized. Operation according to the present invention is further advantageous in'tha't a particularly stable dense phase lifting operation is obtained, the velocity of the lifting gas being maintained much nearer a constant velocity throughout the main portion of the lift conduit than has been obtained in prior-art lifting operations. In operation according to the present invention little or no tendency for entrainmentof granular solids by lifting gas occurs and thepossibility of a sparse phase lift being initiated is therefore minimized or eliminated. With the above advantages there is combined the additional advantage that little or no tendency of the lift to stall occurs. The manner of introducing gra'ndular Solids and lifting gas into the lower inlet end of the lift conduit according to the preferred embodiment of thepresent invention is particularly advantageous in that it provides a smooth introduction of'solid's and gas into the lift conduit with little or no tendency for aggregates of granular solids separated by lifting gas pockets to be formed in the rising stream of gas and solids.

Granular solids which are elevated according to the present invention are mixtures of solids a major proportion of which are large enough to be retained on a 20 mesh U. S. Sieve Series screen. Preferably the mixture of solids is substantially free from granular solids which are large enough to be retained on a 3 mesh'U. S. Sieve Series screen. Examples of solids to which the invention is advantageously applied are granular catalysts, such as silica-alumina cracking catalyst, and granular inert, refractory heat-transfer materials such as are used in noncatalytic hydrocarbon conversion processes. The solid particles can be any suitable shape, e. g., spherical or cylindrical or such intermediate shapes as result from attrition of cylindrical particles, etc. The present invention, as applied to solids which are subject to substantial attrition upon striking solid surfaces, has the particular advantage of minimizing such attrition.

Lifting gas used according to the present invention can be any suitable gas; it can be inert, i. e. chemically unreactive with the solids lifted, or it can be capable of undergoing a reaction upon contact with the solids, as in the case of hydrocarbon vapors used to elevate contact material having the ability to promote a hydrocarbon conversion reaction. Examples of inert lifting gas which can be advantageously used to elevate contact material used in hydrocarbon conversion are steam, air, flue gas, etc.

The dense masses of granular solids which rise through confined lifting zones according to the invention are generally characterized by high bulk density, i. e., at a given moment the weight of solids in a unit volume of the confined zone is high. In a dense phase lifting operation, the bulk density of a rising dense mass of solids is generally greater than 0.5 times and frequently almost as great as the bulk density of a loose-packed compact bed of the same solids at rest, whereas in a sparse phase lifting operation, the bulk density of the same solids is much less, e. g., about 0.15 times the bulk density of a loose-packed stationary bed. The above bulk densities are given as examples; they vary with average particle size and size distribution and other factors.

The pressures at which lifting gas is supplied to a lower portion of an elongated compact mass of solids according to the present invention are high relative to the pressures employed in sparse phase lifting operations. For example, in a sparse phase lifting operation, the differential gas pressure over a lift conduit feet high might be five pounds per square inch gauge, whereas in a dense phase lifting operation, the differential gas pressure over a lift conduit 100 feet high might be seventy pounds per square inch gauge. These pressures vary, however, with the other conditions in the respective operations.

The invention claimed is:

1. Method for elevating a mixture of granular solids, a

7 major proportion of which are coarse particles too large to pass a-20 mesh U. S. Sieve Series screen which comprises: passing such a mixture and lifting gas upwardly through a feeding zone as an annular mass having gradually upwardly increasing cross-sectional area and thence into a confined lifting zone and therethrough as a non-annular mass, the cross-sectional area of the solids mass at any level in the feeding zone and lifting zone being at least approximately as great as the cross-sectional area at any lower level in the feeding zone and lifting zone; maintaining in the lifting Zone a dense mass having average bulk density greater than one-half the static bulk density of the mixture of solids; gradually laterally expanding said dense mass as it rises through said lifting zone; introducing lifting gas into the feeding zone only at the lower end thereof; and discharging solids and gas from the lifting zone into a relatively expanded collection Zone.

2. Method according to claim 1 wherein the crosssectional area of said annular mass at a given horizontal level is changed during the elevating operation.

3. Method according toclaim 1 wherein the rate of References Cited in the file of this patent UNITED STATES PATENTS 788,741 Trump May 2, 1905 1,339,977 Pruden May 11, 1920 1,390,974 Von Porat Sept. 13, 1921 2,304,827 Jewell Dec. 15, 1942 2,398,759 Angeli Apr. 23, 1946 2,487,961 Angel] Nov. 15, 1949 2,684,870 Berg July 27, 1954 2,684,873 Berg July 27, 1954 FOREIGN PATENTS 180,397 Great Britain May 11, 1922

Claims

1. METHOD FOR ELEVATING A MIXTURE OF GRANULAR SOLIDS, A MAJOR PROPORTION OF WHICH ARE COARSE PARTICLES TOO LARGE TO PASS A 20 MESH U.S. SIEVE SERIES SCREEN WHICH COMPRISES: PASSING SUCH A MIXTURE AND LIFTING GAS UPWARDLY THROUGH A FEEDING ZONE AS AN ANNULAR MASS HAVING GRADUALLY UPWARDLY INCREASING CROSS-SECTIONAL AREA AND THENCE INTO A CONFINED LIFTING ZONE AND THERETHROUGH AS A NON-ANNULAR MASS, THE CROSS-SECTIONAL AREA OF THE SOLIDS MASS AT ANY LEVEL IN THE FEEDING ZONE AND LIFTING ZONE BEING AT LEAST APPROXIMATELY AS GREAT AS THE CROSS-SECTIONAL AREA AT ANY LOWER LEVEL IN THE FEEDING ZONE AND LIFTING ZONE; MAINTAINING IN THE LIFTING ZONE A DENSE MASS HAVING AVERAGE BULK DENSITY GREATER THAN ONE-HALF THE STATIC BULK DENSITY OF THE MIXTURE OF SOLIDS; GRADUALLY LATERALLY EXPANDING SAID DENSE MASS AS IT RISES THROUGH SAID LIFTING ZONE; INTRODUCING LIFTING GAS INTO THE FEEDING ZONE ONLY AT THE LOWER END THEREOF; AND DISCHARGING SOLIDS AND GAS FROM THE LIFTING ZONE INTO A RELATIVELY EXPANDED COLLECTION ZONE.