US2836902A - Grid support for fluidized solids vessels - Google Patents

Description

June 3, 1958 1-1. c. NORTH GRID SUPPORT FOR FLUIDIZED SOLIDS VESSELS Filed Dec. 14, 1955 mmawt i. H mmzwt 9% MSEA N Inventor I Howard C. North By 1 M Attorney atent 2,836,902 Patented June 3, 1958 fiice GRID SUPPORT FOR FLUIDIZED SOLIDS VESSELS Howard C. North, Westfield, N. J., assignor to Esso Research and Engineering Company, a corporation of Delaware Application December 14, 1955, Serial N 0. 552,997

2 Claims. (Cl. 34-57) This invention relates to an improved apparatus for contacting fluidized solids with gasiform fluids. The invention pertains more particularly to a vessel wherein finely divided solids, either catalytic or non-catalytic, are fluidized and treated or reacted with liquid or gaseous fluids, for example, for regenerative and/ or heat production purposes at temperatures above about 900 F. This invention proposes an improved grid or gas distributor plate design for supporting, and uniformly distributing a gasiform reactant throughout, a high temperature fluidized solids bed within a reaction vessel.

This invention will find use in various fluidized solids processes such as ore roasting, drying of wet solids, coal carbonization or burning for power generation, shale retorting, catalytic cracking of gas oils, reforming of heavy naphthas, and coking of heavy oils. It has particular utility in the burning of carbon-containing solids wherein relatively high temperatures are encountered, such as in the regeneration of spent cracking or hydroforming catalyst. It is especially adapted to the partial burning of particulate fluid coke used as a heat carrier in a hydrocarbon oil fluid coking process, for supplying heated solids to the reaction zone, and will be described in relation to this fluid coking process.

In the fluid coking process, as used in the petroleum industry, a heavy oil-usually a low value residual oil, shale oil, asphalt, etc., is converted by pyrolysis to relatively lighter hydrocarbons and coke by contact with fluidized finely divided heat carrying solids maintained at a coking temperature in the range of 850 to 1600 F., or above. The coke produced by the pyrolysis deposits on the fluidized solids, layer by layer, and becomes a part thereof. The heat carrying solids normally used are coke particles produced by the process, but other types of solids can be used such as sand, spent catalyst, and metal particles.

Heat is supplied to the coking zone by withdrawing carbon containing solids from the coking zone and partially burning them as a fluidized bed in a burning zone, whereby their temperature is raised 100 to 400 F. above the coking temperature. The solids so heated are then returned to the coking zone.

This invention is concerned with an improved grid design for supporting the fluid bed within the burning zone, and for uniformly distributing the combustion air throughout the bed.

In fluidized solids vessels, it has been found desirable to provide a grid or foraminous plate to uniformly disperse the fluidizing gas or gasiform reactant throughout the bed. In early designs, this gas distributing means was placed within the bed and operated at the temperature ofv the bed. At high temperatures this required special alloys, usually non-weldable, to be used to resist the severe erosive and corrosive conditions. In later designs, the grid was utilized to also support the bed so that the fluidizing gas, which is usually at a lower temperature than the temperature of the bed, when passing up through the grid would cool the grid. The perforations or open ings in the grid were designed to create a pressure drop (gas velocity) over the grid sufliciently high to prevent any significant amount of the fluidized solids from passing down through the grid. By this means, it was found, for example, in the regeneration of catalyst from a gas oil catalytic cracking process, that the grid temperature could be maintained below 600 F. This permitted carbon steels to be used. Also, it became the practice to internally insulate the vessels to maintain low vessel shell temperature, e. g., about 300 to 500 F.

In the design Where the grid supports the fluid bed, it was conventional practice to support the grid on a series of clips or lugs around the circumference of the vessel, the clips being welded to the shell of the vessel. The grid was bolted to the clips with the bolt holes being slotted to permit thermal movement between the grid and the relatively cool metal shell of the vessel. it was not feasible to combine the separate support clips into a continuous support ring because at high temperatures, undesirable high thermal stresses would occur, both in the ring and in the vessel shell, particularly with internally insulated vessels.

Because the clips were separate from one another, a grid sealing device has been necessary to prevent air or fluidized solids from passing through the spaces between the clips and the periphery of the grid, and also from passing through the vessel insulation. To accomplish this, a thin flexible membrane of stainless steel, Welded to a vapor stop attached to the vessel shell and extending over and fastened to the grid, has been used. The grid sealing device in one design had an inverted V shape in cross section. A positive mechanical seal was thus formed which prevented any leakage around the grid or through clearances that existed in the grid support bolt holes.

This grid seal type of arrangement, besides being cumbersome and expensive, has proved to be somewhat unsatisfactory. It is amenable to erosion and while accommodating horizontal movement between the grid and the vessel shell, it will accommodate only very little vertical movement without rupture. Because by necessity this grid seal arrangement is thin, it will not stand a very high pressure diiferential over the grid, which pressure diflerential in fluid coke burners may be considerable.

The present invention proposes an improved grid and grid sealing arrangement which overcomes these and other difliculties. This novel grid design adequately allows for diiferences in thermal expansion and contraction in the equipment, while providing support for the grid and preventing passage of gases around the periphery of the grid.

In the drawings:

Figure I illustrates a fluidized solids vessel containing a grid arrangement designed in accordance with the teachings of this invention. Figure ll illustrates an alternative embodiment of this invention.

In brief compass, this invention proposes a grid in the lower portion of a fluidized solids vessel in horizontal spaced relation to the Walls of the vessel, for uniformly distributing a gasiform medium throughout a fluidized bed of high temperature, particulate solids contained therein, and for supporting the bed; in combination with 'an in-part vertically disposed gas impervious skirt or definite upper level 3.. For purposes of illustration, the fluid bed may comprise fluid. coke particles being oxidatively reheated'to supply heated solids to a hydrocarbon oilfluidcoking vessel. Cool solids from the fluid coking .vessel are circulated andintroduced into burning" vessel 1 by line 4, and rehe'a ted solids at a temperature of 100 to 400 F.'above thecoking temperature are circulated to the coking zone via line 5, in a manner known by the art.

Air is admitted to the base of the burner vessel 1,

which preferably has a cone bottom, by line 6 and fiuidizes and burns the coke within the vessel tomaintain a temperature therein of about 900 to 2000? F. Flue gases from the burner are vented overhead via line-7 after having entrained solids removed in cyclone system 8.

Accordingto this invention, the fluid bed 2 is supported, and-the combustion air is uniformly distributed throughout" the fluid bed, by a gasiform' distributing" means, i. e.,. a perforated circular-grid 9. The grid is horizontally spaced from the vessel walls, usually 1 V 'to 3 inches, suflicient to permit thermal expansion'of the sufficiently long to keep thermal bending-stresses plus pressure stresses to an allowable value. Thelen'gth and thickness of the. skirt are selected depending on the specific'design conditions, the actual dimensions being such that the combined pressure and bending stress is 7 within the allowable for the material used." It is essential that the skirt have a minimum length determined by temperature gradient over the skirt, D=diameter of the skirt, l=thickness of the skirt, L=length of the skirt, and T :the temperature of the skirt. For most vessels, the vertical height of the skirt is at least 18 to 30 inches. To provide a reasonably smooth .and low value of the temperature gradient over the skirt, it is also essential that insulationll within the vessel extends part way, usually 18' to 24 inches, along the skirt from the vessel walls, as shown. This reduces the bending stresses in the skirt.

Another important feature of this'designi is that the skirt is welded to the vessel shell; preferably with a continuous full penetration weld, to prevent passage of air and fluidized solids around the skirt. The -.skirt can also be welded to the grid, although other fastening arrangements can be used here. i

In vessels over about 10 ftfin diameter, grid 9 is slightly dished in order to give it the membrane strength associated with curved surfaces, thus making it selfsupporting and eliminating the framework of beams required to support flat grids. A downward, rather than an upward, dish is employed toreduce the volume of 'waste (unoccupied) space below thergrid.

The amount of dish in the grid (radiusof curvature) represents a compromise between mechanical and process considerations. If the radius of curvature is too small, the depth of the dish causes asignificant ditference in the hydrostatic head of the fluidized solids acting in the center of the grid, compared with points near'its 4 supportthe mass of solids'in an unfluidized condition at the operating temperatures. 7

Figure II illustrates another embodiment of the invention wherein the grid, instead of being dependent or hanging from the skirt, is superposed on the skirt.- The design of Figure I is preferred: because it permits place-' ment of the grid lower down in the vessel space below the grid is minimized.

whereby waste.

In Figure II, dished grid is supported by a vertical continuous circular ring or skirt 21.: The skirt initiates from and is welded to the cone bottom of vessell22. As is essential, refractory lining or insu1ation23 'of the vessel extends part way over the'skir't to create a uniform temperature differential.

It will be appreciated by those skilled in the art that this grid and grid support and seal arrangement may be used in multiple forms, thus one skirt can support two or more grids in vertical spaced arrangementpor; a

plurality of concentric'skirts can be used 1to supportla plurality of vertically'jspiaced grids; It is desirablein some applications to use a plurality or series of grids to permit a wide variation in operating conditions; For example, two grids can be used with the lower one having a lesser free area or smaller perforations; In this way,

' dual grid design, some of the ,air during normal ioperaedge. This will cause a greater air flow through the edge normally a condition where the grid is called upon to protected by Letters Patent is with reference to a'fluid coke burning-vessel, when the air rate. is normal, the coke bed 'will-be' supported on the ,upper grid having the larger openings. At low air.

rates or minimum capacity, when thejamo untof air passing through the upper grid is not suflicient to prevent coke from back-flowing through the grid, the coke bedwill be supported on the lowergrid having the smallerperforations or openings. -To otfset high pressure drops in this tion can beadmitted between the grids; g

The following specific example will serve to make this invention clear. The example describes .a burning vessel, wherein fluid coke front "a hydrocarbon oil'fluid coking process having a particle size in the range ,of about 40 to 800 microns is partially burned at a'temperature'of about 1125 F. V J; 1.

Example p Temperature, F

Vessel shell Internal h 7 7 1125 Pressure, p. s. i. g I 12' Air rate 300 F., MM std. cu. f t./SD (dry) 12.7 Coke rate to burner 950 R, tons/mini V 4.3 Coke burning rate, lbs./hr V 3500 Coke hold up, tons 21' Bed density, lbs/cu. ft j. 4 8 Gas velocity in bed, ft./sec i '2 .8 Internal vessel diameter, ft: I L

Shell -i. 5 12,5 Vessel liner f 11.75 Griddiameter, ft 7 M 111.5 Grid thickness, inches u 0.5 Radius of curvature of grid, ft 7 25 Free area of grid, percent 0.5 AP over grid,p. s. i.: V

Normal 1 r 7 Short time 7 7 p 1 1 Total height of skirt, inches; 7: 24

Having described this invention, what -is'sou ght tobe following claims. 7 7 What is'claimedis:

1. In an'apparatus for contacting solids and gases-ab temperatures'above about 900 F. which comprises a] vertically disposed circular vessel, outlet means in'the 1 7 upper portion for removing gases, gas inlet means in a qit t e; 1 C rb n st e succinctly set forth in the the bottom portion, a foraminous plate positioned within the lower portion of said vessel and adapted to support a bed of fluidized solids thereon, said plate being in horizontally spaced relationship to the walls of said vessel, and particle outlet means extending beneath said plate, the improvement which comprises employing a downwardly dished foraminous plate supported from above by an in-part vertically disposed, gas impervious, circular support, said support being attached to the Walls of said vessel only in the region of the upper end of said support, said support being further characterized as extending downwardly for the major portion of its length and inwardly away from said vessel walls in spaced relationship thereto, its lower end terminating at and encompassing said plate, whereby gas from beneath said plate is denied passage around the periphery of said plate, and the volume of reactor space below said plate and solids bed is reduced in amount.

2. The improvement of claim 1 wherein said circular support is at least in part insulated.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. IN AN APPARATUS FOR CONTACTING SOLIDS AND GASES AT TEMPERATURES ABOVE ABOUT 900*F. WHICH COMPRISES A VERTICALLY DISPOSED CIRCULAR VESSEL, OUTLET MEANS IN THE THE BOTTOM PORTION, A FORAMINOUS PLATE POSITIONED WITHIN THE LOWER PORTION, A FORAMINUOS PLATE POSITIONED WITHIN A BED OF FLUIDIZED SOLIDS THEREON, SAID PLATE BEING IN HORIZONTALLY SPACED RELATIONSHIP TO THE WALLS OF SAID VESSEL, AND PARTICLE OUTLET MEANS EXTENDING BENEATH SAID PLATE, THE IMPROVEMENT WHICH COMPRISES EMPLOYING A DOWNWARDLY DISHED FORAMINOUS PLATE SUPPORTED FROM ABOVE BY AN IN-PART VERTICALLY DISPOSED, GAS IMPERVIOUS, CIRCULAR SUPPORT, SAID SUPPORT BEING ATTACHED TO THE WALLS OF SAID VESSEL ONLY IN THE REGION OF THE UPPER END OF SAID SUPPORT, SAID SUPPORT BEING FURTHER CHARACTERIZED AS EXTENDING DOWNWARDLY FOR THE MAJOR PORTION OF ITS LENGTH AND INWARDLY AWAY FROM SAID VESSEL WALLS IN SPACED RELATIONSHIP THERETO, ITS LOWER END TERMINATING AT AND ENCOMPASSING SAID PLATE, WHEREBY GAS FROM BENEATH SAID PLATE IS DENIED PASSAGE AROUND THE PERIPHERY OF SAID PLATE, AND THE VOLUME OF REACTOR SPACE BELOW SAID PLATE AND SOLIDS BED IS REDUCED IN AMOUNT.

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