FR2553300A1 - METHOD FOR UNIFORMING AN INCREASED CURRENT OF GAS AND LIQUID IN A FLUIDIZED BED REACTOR AND A FLOW DISTRIBUTION GRID FOR THE ITS IMPLEMENTATION - Google Patents

Abstract

A MIXTURE OF GAS AND LIQUID MOUNTS FROM AN INLET SPACE 15 FROM THE LOWER PART OF A REACTOR 10 TO A FLUIDIZED BED 25 ABOVE A DISTRIBUTION GRID. THE GRID CONSISTS OF TWO SUPERIMPOSED PLATES 12, 30 WITH PASSAGES DEFINED BY TUBES 16, 32. THE TOTAL FLOW SECTION OF THE SECONDARY PLATE 30 AT THE BOTTOM IS LARGER THAN THAT OF THE PRIMARY PLATE 12 AT THE TOP. A NEW MIXING AND A NEW DISTRIBUTION (ESSENTIALLY HORIZONTAL) THUS OCCURRED IN THE SPACE 35 BETWEEN THE TWO PLATES. THE MIXTURE ENTERS THE FLUIDIZED BED 25 BY PASSING UNDER BELLS 18 COVERING THE TUBES OF THE PRIMARY PLATE. THE INVENTION IS APPLICABLE IN PARTICULAR TO THE CATALYTIC HYDROGENATION OF HEAVY OILS OR OF COAL AND OIL SLUDGE UNDER HIGH TEMPERATURE AND PRESSURE.

Description

This invention relates to an improved assembly of grid trays

  flow distribution apparatus and method for uniformly distributing or distributing an upward flow of gas and liquid in fluidized bed catalytic reactors More particularly, it relates to a method and a gate for a step flow distribution, the grid substantially horizontal including a primary tray and under it a secondary tray, each containing a large

  number of vertical flow tubes.

  In fluidized catalyst bed reactors operating at high temperatures and pressures, problems of poor flow distribution sometimes exist below the distribution grid plate and in the catalyst bed. This poor distribution is usually due to abnormal operating conditions, such as clogging coke openings in the tray, or excessive coke deposits on the catalyst particles in the bed. If there is such blockage of openings in the tray, the distribution of The flow and fluidization of the bed become irregular, which is highly undesirable. The upflow tubes and split end pipes currently employed in the reactor grate trays generally provide adequate distribution of the recycle liquid streams. and feeding

  and hydrogen gas in the fluidized catalyst bed.

  However, it has been found that the grid plate currently used does not make it possible to control a very poor distribution of the flow in the reactor overpressure inlet space; in fact, it can only moderately improve the flow distribution beneath the plateau, but it is unable to avoid the formation of "chimneys" or major disturbances that lead to an irregular depth of hydrogen in the inlet chamber, which may have the consequence that some risers are exposed to hydrogen over a greater length of their extreme slotted portion, thereby increasing the flow of hydrogen in these tubes. Flow conditions with poor distribution in the inlet space of a reactor may be more or less constant depending on how feed and recycle streams are introduced into the inlet space. the flow can also result from an oscillation effect of the liquid surface in the inlet space, under the distribution grid, the surface of the liquid constantly inclining in one direction and the other. The use in these fluidized bed catalytic reactors of conventional cylindrical upflow tubes covered by cylindrical bubble bells is described in US Pat. Nos. 3,197,286, 3,197,288 and 3,475,134. shows however that the flows of gas and liquid in these

  reactor types have inadequate distribution.

  The applicant has therefore sought to improve the flow distribution in the fluidized bed catalytic reactors 15 and has succeeded in developing an improved step grid which ensures a more efficient redistribution of gas and liquid under the primary grid tray Whenever a poor distribution exists under this tray, which provides more uniform fluidization of the catalyst bed in the reactor to help maintain a "smooth" liquid surface in the inlet space and thereby ensure that A substantially equal slit length is exposed on each upflow pipe for gas entry into this pipe, a secondary grid plate is provided under the primary plate. This secondary plate is similar to the single grid tray currently being used. for the distribution of the flow in the fluidized bed reactors, but the tubes it contains do not carry bells or water. similar elements on the upper side of the plate; the secondary plateau contains only

  tubes with slots and extends to a short distance from the inner wall of the reactor.

  According to the invention, gas and liquid pass from bottom to top of the secondary bottom plate and then the primary plate and then enter the fluidized bed of the reactor. The flow tubes provided in the lower plate are spaced apart uniformly and they have a larger diameter and a greater total flow section than the top-deck primary flow tubes, so that the largest and most regulating pressure drop occurs on the primary plateau, together providing a more uniform flow upwardly into the fluidized bed This staged construction of the grid allows its upper deck to work more efficiently, with the result that the fluidized catalyst bed is traversed by an upward flow of gas and liquid having a

  more uniform distribution over the entire cross section of the reactor.

  The primary plate at the top of the grid according to the invention 10 can be supported by the bottom or the wall of the reactor; the secondary grid tray located at the bottom will usually be supported by the primary plate, for example by a large number of spacer rods extending between the two plates. The secondary plate may also be supported separately by the bottom of the reactor, or by its wall. but it can also be made in one piece with the upper plate to contribute to the resistance to the difference in total pressure produced in the rising fluid flow between the inlet and the outlet of the whole grid II It is also possible to fix the lower plate rigidly to the upper plate by the upper tray flow tubes, which for this purpose are extended to the bottom plate, so that the weight of the fluidized catalyst bed and the total pressure difference on the two trays of the

  grid are supported by the set.

  According to a particular embodiment, the gate is installed near the lower end of the reactor; the primary tray carries primary flow tubes of equal dimensions, which are uniformly spaced in the tray and which each carry a bell covering their upper end, this bell 30 being fixedly attached to the upper end of the tube, above the plate, and being laterally spaced from this end, so as to allow the fluid to go up through each tube and then escape outside in the fluidized bed, passing under the lower edge of the bell; the secondary grid tray, located at a distance below the primary plate, contains secondary tubes of uniform diameter and spacing, but does not

carrying no bells.

  According to the process of the invention, gas and liquid streams are introduced into an inlet space at the lower end of a reactor, under a flow distribution grid, the flow of gas and liquid from this entrance space through a large number of tubular passages located in a secondary grid tray, up to an intermediate zone above this secondary plateau and below a plateau of primary grid, a new mixture and a new distribution of gas and liquid flow is produced in this intermediate zone and the gas and liquid are then raised through a large number of tubular passages located in the primary plateau then under sparge bells, rec each of which drains one of these flow passages upwards, and

  in a fluidized bed of catalyst particles of the reactor.

  Other features and advantages of the invention

  will become more clearly apparent from the following description of several nonlimiting exemplary embodiments, as well as

  FIGS. 1 is a partial vertical section of the lower portion of a reactor vessel, containing a stepped grid with a large number of upward flow tubes, according to the invention; Figure 2 is an enlarged vertical section of a portion of the primary plate of this grid, containing a large number of flow tubes each covered by a single bubble bell and each containing a ball check valve; Figure 3 is a partial vertical section of a stepped grid according to an alternative embodiment of the invention, o the two trays of the grid are supported by the bottom of the reactor; and FIG. 4 is a similar view of still another variant, where the trays of the grid are assembled in a single

  unit supported by the reactor wall.

  In liquid-phase catalytic reactors where liquids, gases and solids in the form of particles have to be brought into contact, it is very important for the complete and efficient catalytic reactions that the upward mixture of liquid and gas be obtained. is uniformly distributed over the entire horizontal section of the reactor, in order to keep the bed of solids or particulate catalyst in a uniform expansion state, with random but generally uniform swirling motions of the catalyst particles For certain reactions, such as that the catalytic hydrogenation of heavy oils or of coal and oil sludge or hydrocracking of heavy hydrocarbon feed streams at high temperatures and pressures, of the order of 250-480 or 550 C and 35-350 bars for example, for the production of liquid fractions with a lower boiling point, a poor distribution of the flow through The flow distributor or grate plate assembly of the reactor can create relatively inactive areas in the bed where the catalyst particles do not perform a random but globally uniform swirling motion. undesired agglomeration of catalyst particles by coking oil or hot sludge. The desired uniform flow through the grate tray in the fluidized catalyst bed may be disturbed either by obstructions formed in the flow tubes as a result of coking or by the entry of catalyst particles into the tubes. The invention provides an effective solution to these problems of poor flow distribution in the fluidized catalyst bed. The flow distributor or grate according to the invention should also prevent catalyst particles from flowing downwardly through the dispenser when the reactor is shut down, while most of the liquid contained in the catalyst bed is then If catalyst particles are allowed to flow back through the flow distributor, they may clog the flow passages thereof and hinder subsequent operations, so that the formation of a new fluidized catalyst bed becomes very difficult because the flow passages are at least partially clogged. Moreover, such obstructions can lead to poor flow distribution in the catalyst bed itself. flow comprises a ball check valve to prevent such reflux of catalyst particles. The invention provides for the superposition of two grid trays, which are thus arranged in series with each other for fluid flow, thereby providing a more uniform distribution of upward fluid flow into the bed.

  fluidized catalyst over the primary tray of the grid.

  A basic element of the invention is that the trays contain a large number of flow tubes having uniform dimensions and spacings in each tray, but only the tubes of the upper tray are covered at the top by bells. The tubes of the secondary plate have a larger diameter and a larger total flow section than the tubes of the primary top plate. It is not essential that the secondary tubes have a cylindrical shape; they may also have a square, rectangular, triangular, or substantially any other desired cross-sectional shape. However, the combination of the effective diameter of the tubes and the number of tubes must provide the desired uniform flow and must produce the desired differential pressure on them. the secondary plateau, which should be between about 0.1 and 0.9 times the differential pressure on the top primary plateau. Moreover, the length / diameter ratio of the secondary tubes should be at least about 1; usually, it is not necessary for this report to be superior

& about 5.

  During operation, the mixture of gas and liquid that passes through the tubes of the secondary tray is subjected to a new distribution in the horizontal space between the two trays. Thus, the flow of the mixture of gas and liquid through the many tubes of the upper tray in the

  fluidized bed will be more uniform than if there was only one grate tray.

  As generally shown in FIG. 1, a reactor 10 contains a primary or upper gate tray 12 which is rigidly supported in the reactor, usually by its outer edge, by means of a cylindrical support skirt 13 attached to the bottom bottom 14 of the reactor; the primary plate 12 is sealed with respect to the side wall of the lower part of the reactor, so that an inlet space 15 is formed under a lower gate tray 30 The reactor feed stream enters through a conduit 11 and it is deflected radially outwardly by a fixed deflector 11a. The plate 12 serves to support a catalyst bed 25 and contains a large number of tubes 16 for upward flow of the fluid. FIG. that each tube 16 has at least one cutout or slit 17 at its upper end and is covered by a bell 18 which is fixed rigidly to the upper end of the tube 16 by a suitable fastening means 19, such as For example, a threaded stud and a nut The side wall of the bell 18 is located radially outside the tube 16, so as to allow uniform flow of the fluid, upwardly through

  each tube 16 of the tray 12, through the slot 17 and then into the bed of catalyst particles 25.

  It is preferable that the lower edge of the bell 18 has, as shown in FIG. 2, notches 18a for locating the gas exhaust from the bottom of the bell and promoting the formation of small gas bubbles in the bed. notches are therefore especially 25 intended to let the gas escape from below the bells

  in the form of small discrete bubbles instead of large masses.

  Generally, the notches should have a width corresponding to 5-10 times the effective diameter of the catalyst particles. The notches 18a, distributed all around the lower edge of the bells, can be combined with individual covers which can have any desired cylindrical shape. For example, to prevent backflow of catalyst particles from the bed 25 into the inlet space 15 under the grate, following a reactor shutdown, or an interruption in the flow of liquid. recycle, each tube 16 usually has, preferably in its upper end, a ball check valve 20, as can be seen in Figure 2 Besides the ball 20, the valve comprises a seat 22 formed in the upper end of the tube 16 To facilitate the entry of gas such as hydrogen into the lower end of the tube 16, openings such as holes 23 or vertical slots 24 are formed in the tube

under the plate 12.

  Under the primary grid tray 12 is located a secondary grid tray 30 which contains a large number of parallel flow tubes 32, each having openings 10 such as holes 33 or one or more vertical slots 34 in their lower end. Secondary tray 30 is located some distance beneath primary tray 12 and is usually supported by it, for example by means of a large number of rods 36 each surrounded by a tube 15 to 37 to maintain a space 35 of the desired height between the two trays, as can be seen in Figure 1 The secondary tray 30 can extend laterally to come into contact with the support skirt 13, but it can also, which is preferable forming a small annular space 38 between itself 20 and the supporting skirt 13 and being provided with a circumferential skirt 40 directed downwards from the plate 30. The skirt 40 should be located substantially at the same height as the lower ends of the secondary flow tubes 32. The skirt 40 is further provided with openings such as holes 39 or slots 41, which are similar to the holes 33 respectively at slots 34 of the tubes 32 The flow section of the annular space 38 between the plate 30 and the support skirt 13 should not exceed about 10% of the total flow section of the openings of the secondary plate, that is, to say of the

  section resulting from both the tubes 32 and the annular space 38.

  During the operation of the gate, the mixture of gas and liquid introduced into the inlet space 15 forms a sheet of gas 15a under the secondary plateau 30 The mixture of gas and liquid in the space 15 rises through the tubes 32 and the annular passage 38 in the space 35 between the lower plate and the upper plate In the space 35, the mixture of gas and liquid is redistributed, mainly in the direction

  horizontal, and the gaseous fraction rises and forms a layer of gas 35a above a layer of liquid whose surface is designated by 35b.

  The level 35 b of this liquid is determined by the height position of slots 24 in the lower ends of the tubes 16 and the flow rate of the fluid through the grid. The invention thus has the advantage, in particular, that the secondary plateau situated at the bottom produces a lateral redistribution of the fluid flow under the primary plateau and thus tends to correct any poor distribution in the flow under the primary plateau. which can be caused by problems of

  poor distribution on the bottom side of the grate Fluidization of the reactor bed will generally be uniform unless some risers become plugged due to coke formation or for other reasons.

  FIG. 3 shows an alternative embodiment of the invention where the upper plate 12 and the lower plate 30 are supported separately by the lower bottom 14 of the reactor, by means of an outer cylindrical support skirt 13 for the primary plate 12 and an inner cylindrical skirt 45 for supporting the secondary plate 30 at the bottom. The support rods 36 and the spacer tubes 37 used in the example of FIG. 1 are not necessary with this construction. The tubes 32 of the plate 30 are also provided. holes 33 or slots 34 to facilitate the entry of gas such as hydrogen into the tubes, and the same for the tubes 16 of the upper plate 12 If desired, separate gas supply streams and liquid can be introduced

  in the space 15 by two ducts 11 with two deflectors lla.

  Another important advantage provided by the invention is that the two trays forming the grid can be assembled so that the overall pressure difference on the grid, resulting from the current flowing through it from bottom to top, and the weight of the bed of These constructions are supported by the two plates together. Such a construction is shown in FIG. 4, where the tubes 42 for the primary plate 12 are extended downwards and fixed rigidly, for example by welding, to the secondary plate 30 located at the bottom. in the preceding examples, the lower portion of each tube 42 has openings such as holes 43 or slots 44 to allow the entry of gas such as hydrogen into the tube. The upper plate 12 can be conveniently supported by the internal wall of the reactor, as shown for this example, by means of a continuous ring 26 welded to the wall The upper plate 12 is fixed to the ring 26 by means of a In this grid construction, the periphery of the bottom plate 30 may be located at a short distance from the inner wall of the reactor 10, so as to define a small annular space 46 therewith. , and this plate may be provided with a peripheral skirt 48 directed downwards and having holes 49 or similar openings, as already

described for the example of Figure 1.

  The utility and efficiency of the stepped flow distribution grid according to the invention is illustrated by the following specific example, which should not be considered as

  a limitation of the scope of the invention.

Example

  In a fluidized bed catalytic hydrogenation reactor, intended to be fed with a petroleum product, a double gate having the following characteristics and dimensions is used: Reactor temperature 400-455 C Reactor pressure 70-210 bar Inner diameter of the reactor reactor 3.65 m Vertical distance between the primary and the secondary grid plates 0.4 m Primary tube diameter 33 mm Diameter of the bubble bells 76 mm Length of the primary tubes under the primary plate 230 mm flow of the primary tubes 14 cm Diameter of the secondary tray flow tubes 100 mm Dimension of the secondary tubes under the secondary tray 125 mm

Z553300

  Secondary tube flow section 17.4 cm Pressure difference between the lower and upper sides of the primary plate 0.35-0.56 bar Pressure difference between the lower side and the upper side of the secondary plate 0.07 -0.21 bar The fluidization of the catalyst particles in the reactor is uniform over a wide range of liquid and gas flow rates from the inlet to the top

into the reactor bed.

  Although the invention has been described generally and with reference to some of its preferred embodiments, it is self-evident that modifications and changes may be made to the described devices and that certain elements may

  be used without others, without departing from the spirit and scope of the invention.

Claims (11)

  A method for distributing or evenly distributing, in the horizontal direction, an upward flow of gas and liquid in a fluidized bed reactor, characterized in that: a) introducing gas and liquid streams into an entrance space (15) located at the lower end of a reactor (10), under a flow distribution grid; b) the gas and liquid flow of this inlet space (15) is passed through a large number of tubular passages (32) of a secondary grid tray (30), located at the bottom, to in an intermediate zone (35) located above this secondary plateau and below a primary grid plate (12); c) producing a new mixture and a new distribution of the gas and liquid flow in this intermediate zone (35); and d) the gas and the liquid are passed through a large number of tubular passages of the primary plate (12) and then under bubbling bells (18), each covering one of these   upper flow passages and, uniformly, in a fluidized bed of catalyst particles of the reactor.   Method according to Claim 1, in which the differential pressure of the fluid forming the upward flow on the primary plateau situated at the top is greater than the differential pressure.   of this fluid on the secondary plateau located at the bottom.   Method according to claim 1 or 2, wherein the gas and supply liquid streams are introduced into the inlet space (15) through separate ducts (11) and must each bypass a deflector (11a) at the output of each leads in said space (15).   Process according to one of Claims 1 to 3,   o the liquid is a liquid hydrocarbon and the gas is hydrogen.   Process according to any one of claims 1 to 4,   o the liquid temperature is about 250-480 C and the pressure   the liquid is about 35-350 bar.   A tray-step grid for distributing or evenly distributing, in the horizontal direction, a flow of a mixture of gas and liquid rising in a fluidized bed formed in a reactor, for carrying out the process according to any one of   Claims 1 to 5, characterized in that it comprises:   a) a top gate tray (12), which is supported in the reactor (10) near the lower end of the reactor, which primary tray contains multiple flow distribution tubes (16) which pass through the platen substantially vertically, said primary tubes (16) having uniform dimensions and being uniformly spaced in the platen; b) a bell (18) covering the upper end of each tube (16) of the primary plate (12), the bell being rigidly attached to the upper end of the tube (16), spaced laterally from this end and located at the above the primary plate (12), so as to allow upward fluid flow, through the tubes (16) and outwardly in the fluidized bed passing under the lower edge of the bells (18); and c) a secondary gate tray (30) located at a distance below the primary tray (12), the secondary tray containing multiple flow distribution tubes (32) which traverse the tray substantially in the vertical direction said secondary tubes (32) having uniform diameters and spacings so that the fluid rises through the tubes (32) of the secondary tray (30) and then through the tubes (16) of the primary tray (12) and then flows uniformly outwardly into the fluidized bed (25) of the reactor (10) passing under the   lower edges of the bells (18).   Grid according to claim 6, wherein the total flow section of the secondary flow tubes (32) of the secondary tray (30) is greater than that of the flow tubes.   primary (16) of the primary plate (12).   8 grid according to claim 6 or 7, o each tube (32)   the secondary tray has a larger flow section than each tube (16) of the primary tray.   Grid according to one of Claims 6 to 8,   the length / diameter ratio of the tubes (32) of the secondary plateau is between about 1 and about 5.   Grid according to one of Claims 6 to 9,   the secondary plate (30) is supported by the primary plate (12) by means of multiple support rods (36), which can be individually surrounded by spacer tubes (37).   Grid according to one of Claims 6 to 10,   the primary plate (12) is attached to the bottom of the reactor (10) by means of a skirt (13) which extends downwards to a point   fastener located under the secondary tray (30).   Grid according to one of Claims 6 to 10,   the primary platen (12) and the secondary platen (30) are structurally integrated to withstand the weight of the catalyst bed and the total differential pressure on the assembly of the grid (Figure 4).   13 grid according to any one of claims 6 to 12,   the primary tubes (16) contain non-return valves (20, 22) for preventing the reflux of catalyst particles from the zone 20 above the primary plate to an area under this plate, each valve consisting in particular of a ball (20) and a seat (22) located in the upper part of a tube (16) primary plateau (12).