US3115370A

US3115370A - Disengagement and elutriation of pneumatically elevated solids

Info

Publication number: US3115370A
Application number: US103828A
Authority: US
Inventors: Jr Willis J Cross
Original assignee: Air Products and Chemicals Inc
Current assignee: Air Products and Chemicals Inc
Priority date: 1961-04-18
Filing date: 1961-04-18
Publication date: 1963-12-24
Anticipated expiration: 1980-12-24

Description

Dec. 24, 1963 w. J. CROSS, JR 3,115,370

DISENGAGEMENT AND ELUTRIATION OF PNEUMATICALLY ELEVATED souns Filed April 18, 1961 Z/Fr ans s a f F a L/FT P/PES & 0 P. z m 0 MW r B A D United States Patent 3,115,370 DISENGAGEMENT AND ELUTRTATIGN 0F PNEUMATICALLY ELEVATED SGLTDS Willis J. Cross, .l'r., Media, Pa, assignor to Air Products and Chemicals, Inc, a corporation of Delaware Filed Apr. 18, 1%1, Ser. No. 103,828 8 Claims. (Cl. 3e2 5a This invention relates to processing systems for effecting hydrocarbon or other chemical conversions, and particularly those systems wherein a body of frangible, granular solid contact material, such as catalyst in the form of pellets, beads, etc, is circulated within a closed path including a plurality of treating zones wherein the reactants in gaseous state are contacted with granular material or solids gravitating in the form of a compact moving mass to effect the desired reactions. More specifically, the invention is directed to those processing systems wherein a continuous circulation of the granular material is maintained by gravitational free fall and/or compact flow thereof through a confined downflow path and subsequent pneumatic elevation of the granular material through an upright confined lift path. Such circulation causes a gradual attrition of the solids, producing fines whose removal continuously or periodically, is necessary for efficient operation. The invention is concerned particularly with the problems of disengaging the granular contact material from the lift gas at the top of the lift path and of removing the small attrited particles of granular material, or fines, from the circulating body of solids.

A typical processing system to which the method and apparatus of the invention may be applied is disclosed in an article entitled Houdrifiow: New Design in Catalytic Cracking, appearing in the Oil and Gas Journal, page 78, January 13, 1949.

The invention may be applied to a disengager servicing either a single lift pipe or a plurality of lift pipes. In any case, the trajectory of the discharging stream or streams of solids should be such as to cause the disengaged solids to fall freely as a relatively dense mass or curtain of solids in a low region of the disengaging zone which is laterally removed from any rapidly rising solids discharging from one or more lift pipes. In a multiple lift disengager the discharge ends of the lift pipes may be closely grouped in one small horizontal area of the total disengager cross section or they may be distributed uniformly about the peripheral region of the disengager, for example, in a circle concentric to its vertical axis.

Typical of the last-mentioned type are those disclosed in U.S. Patents 2,813,757 to R. M. Shirk, and 2,887,341 to W. 1. Cross, In, each of which discloses a multiple litt disengager comprising an elongated cylindrical vessel, the upper portion of which contains a disengaging zone. A plurality of lift pipes discharge streams of lift gas and solids upwardly into the lower peripheral region of the disengaging zone. The decrease in gas velocity resulting from the sudden expansion of flow area upon discharge from the lift pipes into the disengager vessel causes the substantial major portion of the solids to completely decelerate before reaching the top region of the disengaging zone and to settle or fall freely to the bottom of the vessel.

Because of the high lift gas velocities employed, such as a velocity of 50100 ft./sec., the disengager vessel is necessarily of considerable elongation in order to provide sufficient disengaging height, that is, vertical distance in which to effect the complete gravitation deceleration of the granular material and reversal of its direction of travel.

Lift disengagers of the type referred to herein are generally provided with lift gas outlet means at their 3,l 15,379 Patented Dec. 24, 1863 upper end to continuously discharge lift gas relatively free of solids, especially solids of a size suitable for continued use by recirculation. It is also a common practice to install one or more battles in the top region of the disengager vessel just below the lift gas outlet in order to deflect random particles of solids which may have sufiicient momentum to carry them above the main stream of solids undergoing deceleration and direction reversal and which may be carried out of the system with the discharging lift gas it they approach too closely to the lift gas outlet through which the lift gas moves at high velocity.

One of the major problems encountered in systems which maintain continuous circulation of a body of granular solids is that of attrition, resulting in the production of fines. Efficient operation requires the discharge from the circulating body of solids of substantially all or at least a major portion of those attrited particles which are of a size smaller than the minimum acceptable size. To this end a side stream of the circulating solids is generally withdrawn at some suitable location in the circulatory system, and the withdrawn stream of solids is subjected to known elutriation treatment to eliminate the fines while retaining the larger particles for return to the circulaing body of granular material. A location which has been found particularly suitable for withdrawal of solids to supply the elutriator is in the disengager vessel itself, and various methods for effecting such withdrawal and elutriation treatment are well known in the art.

In accordance with the invention the total lift gas discharging into the disengaging zone from the plurality of lift paths is withdrawn from the disengaging zone at a plurality of locations. The main stream of withdrawn lift gas, constituting a substantial major portion of the total lift gas, is withdrawn at a low level within the disengaging zone and from a location wholly within a region laterally removed from the rapidly rising streams of solids discharging from the confined lift paths. This main portion of lift gas is conveyed upwardly as a confined stream to and through the upper end of the disengaging zone.

The inlet end of the confined path for withdrawing the major portion of lift gas from the disengaging zone is so sized as to provide a gas velocity sufiicient to entrain the unwanted fines. Since the inlet is situated to one side of the upwardly moving, high velocity stream of solids the region immediately adjacent to or surrounding the inlet will contain a concentration of free-falling solids. The confined lift paths are arranged to discharge into the disengaging zone at a slight angle, such as up to about 15, to the vertical so that each stream of solids emerging from a lift path will have not only the normal conical pattern of discharge but also a slight trajectory toward the location of the main gas withdrawal path. Thus, a group of lift paths may be arranged to discharge so that all have a slight trajectory in the same general direction, as from one side of the disengager vessel to the other or from a central location to a side of the vessel, or a group of lift paths may be arranged to discharge at spaced points along a peripheral circle concentric to the vertical axis of the vessel, with a slight trajectory toward the axis.

As the disengaged solids descend through the region immediately adjacent to or surrounding the inlet of the main gas Withdrawal path the gas moving laterally under the perimeter of the inlet and into the Withdrawal path entrains the smaller solids and carries them upwardly out of the vessel. Solids elu-tn'ation thus takes place in the region surrounding and immediately below the inlet.

The other stream or streams of lift gas, constituting, in all, a minor portion of the total lift gas, are withdrawn from the upper end of the disengaging zone. These secondary streams are provided with suitable flow conts trol means whereby the portion of the total lift gas so withdrawn may be regulated at will, thereby enabling a predetermined gas velocity to be maintained within the elutriatiug zone at the bottom of the main gas withdrawal ath.

p For a further understanding of the invention reference may be had to the following description and claims taken in connection with the accompanying drawing showing a sectional elevation of a combination lift disengager and elutriator representing one arrangement of apparatus for carrying out the method of the invention, particularly as applied to the type of disengager referred to in the aforementioned patents.

Referring to the single FIGURE of the drawing, rising streams of lift gas and granular material are discharged from the upper ends of a plurality of lift pipes into the lower region of an elongated cylindrical disengager vessel 6 having a dished head 7 at its upper end and a dished tray or partition 8 at an intermediate level defining the upper and lower boundaries of a disengaging zone 9. The upper ends of lift pipes 5 converge slightly toward the axis of the vessel 6 so as to direct the streams of solids discharging from the confined lift paths toward the central or axial region of the disengaging zone in order that the substantial major portion of the descending sol-ids will fall in the axial region andhave minimum interference with the rapidly rising particles of solids in the peripheral region of the disengaging zone 9.

A vertical pipe 16 extends downwardly into disengaging Zone 9 through a central opening in dished head 7 and terminates at a low level therein, slightly above and concentrically within the circle of lift pipes 5. The lower end of pipe 10 is provided with an outwardly flared or tapered section 11 which is located well within the envelope formed by the merging streams of solids rising from the lift pipes 5. The flared section, however, is not essential to the successful carrying out of the invention, and a slightly larger straight pipe providing the desired inlet velocity may be employed. A pair of addi tional lift gas outlet pipes 12 and 13 are provided at the top of the disengaging zone 9 to either side of the central discharge pipe 10. Pipes 12 and 13 have

control valves

14 and 15, respectively, by which the proportion, and hence velocity, of the lift gas Withdrawn through pipe 10 may be regulated.

An inverted curved or dished bathe plate 16 is concentrically supported by struts 17 from the underside of dished head 7 and is spaced from the top and sides of the vessel 6. Baffle 16 is provided with a central opening to accommodate the pipe 10 in a close fit. Thus, the total lift gas rising from the lift pipes 5 into the disengaging zone 9 is withdrawn from the disengaging zone as three separate streams. The major portion of the lift gas passes through the tapered section 11 and pipe 10, while the remaining pontion of the lift gas passes upwardly around and over the sides of baflie 16 and is withdrawn in two separate streams through valve-controlled discharge pipes 12 and 13. Although two outlets 12 and 13 for secondary lifit gas withdrawal are disclosed, more or even a single outlet may be employed.

For any given total flow of lift gas through the disengager vessel the gas velocity in the elutriating zone 11 may be controlled by adjusting the discharge rate of the lift gas passing through pipes 12 and 13. Since the particle-size range of the fines removed from the solids stream descending through the region immediately about the lower perimeter of section 11 is a function of the gas velocity in that region, it is possible to determine the maximum size particles to be removed from the system by such control of the gas velocity in the elutriating region.

In a typical installation embodying the method and apparatus of the invention, the disengager vessel 6 may be about l525 feet in diameter and the lift pipes 5 may 4 be 8-12 inches in diameter. Main draw-off pipe 10 may be 34 feet in diameter with a 6-10 foot diameter at the mouth of the elutriator sectioh 11. Secondary gas outlet conduits l2 and 13 may be 12. inches in diameter.

Typical gas velocities at the top of the lift pipes 5 are in the order of about 55 ft./sec., the top of the lift being considered as the bottom of any decelerato-r section that may be provided to reduce the gas velocity before discharge into the disengaging zone 9.

At the base or inlet end of the elutriator section 11 the gas velocity may be in the range of about 9-15 ft./sec., increasing the velocities in the range of about 28-47 ft./sec. at the top of pipe 10.

It is contemplated that proper elutriation may be effected by controlling

valves

14 and 15 so that they with draw up to about 40% of the total lift gas from the zone 9.

Gbviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

What is claimed is:

l. A combination disengager-elutriator for a multiple pneumatic solids lift system comprising an upright elongated cylindrical vessel adapted at its lower end to receive the upper ends of a plurality of lift pipes; an elongated main outlet conduit extending along the axis of said vessel from a level above the discharge ends of said lift pipes through the upper end of said vessel; secondary as outlet means at the top of said vessel provided with control means for regulating the flow of gas therethrough; and an inverted dished bafile extending across the upper region of said vessel with its perimeter just short of the walls of said vessel to provide an annular peripheral passageway for flow of lift gas from the main disengaging region of said vessel to said secondary gas outlet means, said baffle having a central opening to receive said main outlet conduit.

2. Apparatus as in claim 1 in which said main conduit is outwardly flared at its lower end.

3. A combination disengager-elutriator for a pneumatic solids lift system comprising an upright elongated vessel; lift path means for discharging pneumatically elevated solids and the accompanying lift gas upwardly within the lower region of said vessel; said vessel being of such increased horizontal flow area with respect to said lift path means as to cause complete gravitational deceleration of the solids and free fall thereof through a low region within said vessel laterally removed from the widening cone of rapidly moving solids discharging from said lift path means; a pipe providing a main path for lift gas withdrawal directly upward from a location within said laterally-removed region to the exterior of said vessel; means at the top of said vessel for withdrawing a secondary portion of said lift gas; a baffle in the upper region of said vessel to deflect rising solids away from the means for withdrawing said secondary portion of lift gas; and means for controlling the flow of gas through the secondary lift gas withdrawal means to thereby control the proportion of the total lift gas flowing in said main lift gas withdrawal path and consequently its inlet velocity, whereby the particle size range of solids withdrawn from said. vessel by said main gas stream is determined.

4. A combination solids disengager and elutriator for a pneumatic solids lift system adapted to circulate granular solids comprising: an upright elongated vessel arranged to receive upwardly discharging and laterally expanding streams of lift gas and solids within the lower peripheral region thereof, said vessel being of such horizontal dimensions as to reduce the lift gas velocity to below the solids supporting velocity and of such height as to effect substantially total disengagement of said solids from said lift gas through gravitational deceleration, and said discharging strcams of lift gas and solids being so directed as to cause the substantial major portion of said disengaged solids to fall freely to the bottom of said vessel through a region of high solids concentration laterally remote from the expanding cones of discharged solids; a main conduit extending upwardly through said vessel from a low level within said region of high solids concentration but above the discharge level of said streams, said main conduit being adapted to withdraw upwardly from said vessel the major portion of said lift gas while providing a gas velocity in the zone surrounding and immediately below the main conduit inlet suflicient to entrain and remove from said vessel the unwanted solids fines; controllable secondary gas withdrawal means at the upper end of said vessel adapted to withdraw from said vessel such portion of the total lift gas as will maintain the desired gas velocity in the elutriation zone at the inlet end of said main conduit; means directly below said secondary gas withdrawal means for shielding the inlet thereto against the admission of the highest rising solids; and means for draining the disengaged solids from the bottom of said vessel.

5. Apparatus as in claim 4 in which the vertical distance 6 between the surface upon which the free-falling disengaged solids are deposited and the inlet end of said main conduit is such as to preclude the rebound of the larger-size solids from said surface into the high velocity stream of gas entering said main conduit.

6. Apparatus as in claim 4 in which said secondary gas withdrawal means comprises a plurality of controllable flow conduits having their inlet ends communicating with said vessel through its upper end at locations uniformly distributed around said main conduit.

7. Apparatus as in claim 4 in which the maximum total flow area of said controllable secondary gas withdrawal means is such as to permit withdrawal therethrough of up to about 40% of the total lift gas.

8. Apparatus as in claim 4 in which said main gas withdrawal conduit is sharply divergent over a relatively short portion of its lower end.

Elkin Dec. 31, 1957 Claunch 'Oct. 31, 1961

Claims

4. A COMBINATION SOLIDS DISENGAGER AND ELUTRIATOR FOR A PNEUMATIC SOLIDS LIFT SYSTEM ADAPTED TO CIRCULATE GRANULAR SOLIDS COMPRISING: AN UPRIGHT ELONGATED VESSEL ARRANGED TO RECEIVE UPWARDLY DISCHARGING AND LATERALLY EXPANDING STREAMS OF LIFT GAS AND SOLIDS WITHIN THE LOWER PERIPHERAL REGION THEREOF, SAID VESSEL BEING OF SUCH HORIZONTAL DIMENSIONS AS TO REDUCE THE LIFT GAS VELOCITY TO BELOW THE SOLIDS SUPPORTING VELOCITY AND OF SUCH HEIGHT AS TO EFFECT SUBSTANTIALLY TOTAL DISENGAGEMENT OF SAID SOLIDS FROM SAID LIFT GAS THROUGH GRAVITATIONAL DECELERATION, AND SAID DISCHARGING STREAMS OF LIFT GAS AND SOLIDS BEING SO DIRECTED AS TO CAUSE THE SUBSTANTIAL MAJOR PORTION OF SAID DISENGAGED SOLIDS TO FALL FREELY TO THE BOTTOM OF SAID VESSEL THROUGH A REGION OF HIGH SOLIDS CONCENTRATION LATERALLY REMOTE FROM THE EXPANDING CONES OF DISCHARGED SOLIDS; A MAIN CONDUIT EXTENDING UPWARDLY THROUGH SAID VESSEL FROM A LOW LEVEL WITHIN SAID REGION OF HIGH SOLIDS CONCENTRATION BUT ABOVE THE DISCHARGE LEVEL OF SAID STREAMS, SAID MAIN CONDUIT BEING ADAPTED TO WITHDRAW UPWARDLY FROM SAID VESSEL THE MAJOR PORTION OF SAID LIFT GAS WHILE PROVIDING A GAS VELOCITY IN THE ZONE SURROUNDING AND IMMEDIATELY BELOW THE MAIN CONDUIT INLET SUFFICIENT TO ENTRAIN AND REMOVE FROM SAID VESSEL THE UNWANTED SOLIDS FINES; CONTROLLABLE SECONDARY GAS WITHDRAWAL MEANS AT THE UPPER END OF SAID VESSEL ADAPTED TO WITHDRAW FROM SAID VESSEL SUCH PORTION OF THE TOTAL LIFT GAS AS WILL MAINTAIN THE DESIRED GAS VELOCITY IN THE ELUTRIATION ZONE AT THE INLET END OF SAID MAIN CONDUIT; MEANS DIRECTLY BELOW SAID SECONDARY GAS WITHDRAWAL MEANS FOR SHIELDING THE INLET THERETO AGAINST THE ADMISSION OF THE HIGHEST RISING SOLIDS; AND MEANS FOR DRAINING THE DISENGAGED SOLIDS FROM THE BOTTOM OF SAID VESSEL.