CN104941536B - Air grid system for oxidation reactor and method of accommodating deflection therein - Google Patents

Abstract

When the distance between the sparger system 16 and the air grid 14 is controlled within 6 to 24 inches (-15 to 61cm), preferably 8 to 12 inches (-20 to 30.5cm), inadequate reactant mixing and localized reactor hot spots in commercial acrylonitrile reactors can be significantly mitigated. Furthermore, the problems of movement of the air grid into or out of contact with the support and mechanical failure of the air grid can be substantially completely eliminated by means of an improved system for attaching the air grid to the wall of the reactor and the support beams inside it.

Description

Air grid system for oxidation reactor and method of accommodating deflection therein

Background

In the commercial manufacture of acrylonitrile, propylene, ammonia and oxygen are reacted together according to the following reaction scheme:

CH₂=CH-CH₃ + NH₃ + 3/2 O₂ → CH₂=CH-CN+ 3 H₂O

this process, commonly referred to as ammoxidation, is carried out in the vapor phase at elevated temperature in the presence of a suitable fluidized bed ammoxidation catalyst.

Figure 1 shows a typical ammoxidation reactor used to carry out the process. As shown in this figure, the reactor 10 includes a reactor wall 12, an air grid 14, a feed distributor (spearger) 16, cooling coils 18, and cyclones 20. During normal operation, process air is charged into reactor 10 through air inlet 22, and a mixture of propylene and ammonia is charged into reactor 10 through feed distributor 16. Both at a flow rate high enough to fluidize the bed 24 of ammoxidation catalyst inside the reactor, in which the catalytic ammoxidation of propylene and ammonia to acrylonitrile takes place.

Product gases resulting from the reaction exit the reactor 10 through a reactor effluent outlet 26. Before doing so, the product gases pass through cyclone 20, which cyclone 20 removes any ammonia oxidation catalyst that these gases may entrain, to be returned to catalyst bed 24 via diplegs 25. Ammonia oxidation is highly exothermic and therefore cooling coils 18 are used to carry away excess heat to maintain the reaction temperature at a suitable level.

Propylene and ammonia can form explosive mixtures with oxygen. However, at normal operating temperatures, the explosion is prevented inside the reactor 10 by a fluidized ammoniation catalyst which preferentially catalyzes the ammoxidation reaction before explosion can occur. Accordingly, reactor 10 is designed and operated such that the only place that process air is allowed to contact propylene and ammonia during normal operation is within the fluidized bed of ammonia oxidation catalyst 24, and thus only when the temperature of the catalyst is high enough to catalyze the ammonia oxidation reaction.

To this end, the conventional manner of feeding propylene and ammonia to reactor 10 uses a feed distributor system 16 such as that shown in U.S. 5, 256,810, the disclosure of which is incorporated herein by reference. As shown in fig. 1 and 2 of the' 810 patent (which are renumbered as fig. 2 and 3 of this document), the feed distributor 16 takes the form of a series of supply pipes or tubes that include a main header 30 and branch pipes (laterals) 32, the branch pipes 32 being attached to the header 30 and branching off from the header 30. A series of downwardly facing feed nozzles 34 are defined in the header 30 and branch 32, and the mixture of propylene and ammonia is charged through the feed nozzles 34 during normal reactor operation. The number and spacing of the legs 32 and feed nozzles 34 is such that a total of about 10 to 30 feed nozzles per square meter are positioned generally uniformly across the entire cross-sectional area of the reactor 10.

Typically, each feed nozzle 34 is surrounded by a feed shroud 36, the feed shroud 36 taking the form of a short section of pipe having an internal diameter several times the diameter of the nozzle 34. The feed shroud 36 enables the velocity of the gas exiting the nozzles 34 to be significantly slowed prior to exiting into the catalyst bed 24, which prevents catalyst disintegration that could otherwise occur.

The process air typically enters the catalyst bed 24 (fig. 1) after passing through the air grid 14, the air grid 14 being located below the feed distributor 16. As is well known, the air grille 14 typically takes the form of a continuous sheet of metal that defines a series of air holes or nozzles therein. The diameter of the air nozzles, the mass flow of process air through the air grid 14 and the mass flow of the propylene/ammonia mixture through the feed distributor 16 are selected so that the ammonia oxidation catalyst in the catalyst bed 24 is fully fluidized by these gases during normal operation.

The air holes 76 (in fig. 5) are typically provided with their own protective air shield (not shown) which is typically located below the air grill 14. Further, in many cases, the feed nozzles 34 are disposed in a one-to-one relationship with the air nozzles in the air grille 14, with each feed shroud 36 directly aligned with its corresponding air nozzle to promote rapid and thorough mixing of the gases passing out of the two different nozzles. For the purposes of this application, such air nozzles are referred to as capless. See U.S. 4,801,731. In other cases, the air nozzles may have a cap mounted directly above them to distribute air horizontally (in a directional or uniform manner) preferentially along the grate rather than vertically directly against the feed shroud. These caps may be small metal caps welded over such air nozzles. The design of the legs attaching the cover to the grid may be selected to optimize the horizontal gas distribution pattern. These caps above the air holes may also be designed to prevent the catalyst in a refluxed state from (i) falling through the air holes and/or (ii) settling on the cap itself (e.g., by having a sloping surface or being made of angle iron).

While this general type of propylene/ammonia feed system works well, it can suffer from certain disadvantages. For example, the mixing of the propylene/ammonia feed mixture exiting the feed distributor 16 with the air exiting the air grill 14 may be inadequate. This can reduce reactor performance, leading to less than ideal conversion of reactants to products.

In addition, molybdenum scale (molybdenum scale) produced by the ammonia oxidation catalyst may cause a small pile of such molybdenum scale plus an additional amount of entrained catalyst to accumulate on the upper surface of the air grid 14 in the form of a small catalyst pile. These stacks function like miniature stationary or "fixed" catalyst beds in which the ammonia oxidation reaction continues to occur. Because the heat transfer inside a fixed catalyst bed is much weaker than in a fluidized bed, these catalyst stacks create local hot spots that are high enough in temperature to damage any fluidized catalyst that just reaches the vicinity. For example, such temperatures are high enough to calcine to the surface of any nearby fluidized catalyst, which in turn reduces the surface area and thus the catalyst activity. Also, over time, these hot spots can damage all charges of fluidized bed catalyst in the reactor, as the individual catalyst particles forming the fluidized catalyst bed are free to circulate through their entire volume.

Additional disadvantages include mechanical problems with the construction of the acrylonitrile reactor. Typical commercial acrylonitrile reactors operate at relatively constant temperatures of about 400 to 550 ℃, but do fluctuate. In addition, the ammoxidation reactor must be periodically shut down for normal maintenance, catalyst replacement, etc., and due to sudden failures such as, for example, power failures. With normal operating temperatures so high, the temperature inside the reactor can vary as much as 500 ℃ or more as the reactor transitions between ambient and normal operating temperatures. This cycling between low and high temperatures can place considerable stresses on the structural members forming the reactor, especially where they are connected to each other, as the inherent expansion and contraction of these structural members occurs in response to temperature changes. Over time, these stresses can lead to mechanical failure, especially at joints formed by welding.

For example, the normal manner in which the air grille 14 is attached to the wall 12 of the reactor 10 is shown in FIG. 4. As shown, the air grille 14 is attached to the side wall 12 of the reactor by a dog-ear (knuckle)44, the air grille 14 taking the form of a substantially flat metal plate 40 having a series of holes therein. As shown in this figure, the break angle 44 is in the form of a concave section of metal in cross-section, with its upper end 46 substantially flush with the side wall 12 and welded to the side wall 12 by a weld 48, and its lower end 50 substantially coplanar with and welded to the facing edge of the air grille plate 40 by a weld 52.

In a large commercial acrylonitrile reactor of 31 feet in diameter (-9.4 meters), for example, the air grid plate 40 can expand and contract horizontally for nearly as inches (1.27cm) in response to temperature changes experienced during reactor startup and shutdown. This creates significant stress on the break angle 44, and particularly in the welds 48 and 52 used to attach the break angle 44 to the air grid plate 40 and the reactor sidewall 12. Unfortunately, over time, these stresses can lead to mechanical failure, which in turn requires long down time for repair and/or replacement.

Another disadvantage associated with the above-described conventional designs relates to air grille deflection. Since the air grid 16 must support the entire weight of the catalyst charge inside the reactor 10 when the reactor 10 is shut down, it is necessary to support the air grid plates 40 from below to accommodate this weight. Typically, this is accomplished by means of an I-beam system on which the air grille panel 40 rests. In some reactor designs, the air grid plates 40 rest only on these i-beams. Unfortunately, in these designs, the air grid plate 40 has a tendency to flutter during normal operation, not only due to the force of the air moving upwardly through the air grid plate, but also due to its inherent expansion as its temperature rises to normal operating temperatures. In other designs, the air grid plate 40 is welded to the top of these I-beams. Unfortunately, in these designs, the force of the upwardly moving air plus the inherent expansion of the air grid plates can cause mechanical failure of these welds.

Disclosure of Invention

In accordance with the presently disclosed technology, it has been found that the above-mentioned problems of reactant under-mixing and localized reactor hot spots can be significantly alleviated when the distance between the sparger system 16 and the air grid 14 is controlled to be within 6 to 24 inches (-15 to-61 cm), preferably 8 to 12 inches (-20 to-30.5 cm). Furthermore, it has been found that the above-mentioned problems of air grid flutter and air grid mechanical failure can be substantially completely eliminated by means of an improved system for attaching the air grid to the wall of the reactor and to the support beams inside it.

Accordingly, the present disclosure provides, according to one feature, an improved feed system for a commercial oxidation or ammoxidation reactor, such as an acrylonitrile reactor, comprising: a feed distributor for supplying a mixture of unsaturated and/or saturated C3 to C4 hydrocarbons and ammonia to the interior of the reactor; and an air grid system for supplying air to the interior of the reactor, the feed distributor comprising a main header conduit and branch conduits fluidly attached to and diverging from the main header conduit, the main header conduit and the branch conduits both defining downwardly facing feed nozzles, the feed distributor system further comprising feed shrouds associated with the respective feed nozzles, each feed shroud comprising a proximal end connected to the respective branch conduit or header conduit and arranged to direct C3 to C4 hydrocarbons and ammonia passing out of its respective feed nozzle downwardly into the interior of the reactor, the air grid system comprising a continuous metal plate arranged below the feed distributor system, the continuous metal plate defining a series of air holes therein for directing process air from below the continuous metal plate towards the distributor system to above the continuous metal plate, wherein the distance between the upper surface of the continuous metal sheet and the distal end of the feed shroud is selected to be between about 6 to 24 inches (15 to 61 cm). As used herein, mixtures of unsaturated and/or saturated C3 to C4 hydrocarbons refer to C3 to C4 hydrocarbons including propane, propylene, butane, butene, and mixtures thereof.

In another aspect, a process for feeding an oxidation or ammoxidation reactor is provided which includes supplying a mixture of saturated and/or unsaturated C3 to C4 hydrocarbons and ammonia to the interior of the reactor through a feed distributor. The feed distributor includes a main header conduit and a branch conduit fluidly attached to and branching off from the main header conduit, both the main header conduit and the branch conduit defining downwardly facing feed nozzles. The feed distributor system also includes feed shrouds associated with respective feed nozzles, each feed shroud including a proximal end connected to a respective branch or header conduit and arranged to direct saturated and/or unsaturated C3 to C4 hydrocarbons and ammonia exiting its respective feed nozzle downwardly into the interior of the acrylonitrile reactor. The method also includes supplying air to the interior of the reactor through an air grid system. The air grid system includes a continuous metal sheet disposed below the feed distributor system, the continuous metal sheet defining a series of air holes therein for directing process air from below the continuous metal sheet toward the distributor system to above the continuous metal sheet. In one aspect, the distance between the upper surface of the continuous metal sheet and the distal end of the feed shroud is between about 6 to about 24 inches (about 15 to about 61 cm).

In addition, the present disclosure provides, according to another feature, an improved air grille system for use in a commercial oxidation or ammoxidation reactor, such as an acrylonitrile reactor, the improved air grille system comprising: a continuous metal sheet defining an upper surface, a lower surface, and a perimeter extending between the upper and lower surfaces, the continuous metal sheet further defining a series of air holes for directing process air from below the continuous metal sheet toward a distributor feed system located above the continuous metal sheet; and a support system for supporting the weight of the continuous metal sheet and any oxidation or ammonia oxidation catalyst that may rest on the continuous metal sheet, wherein the support system comprises a series of support beams each having an upper support surface that engages the underside of the continuous metal sheet and a series of support hold-downs fixedly attached to the underside of the continuous metal sheet, each support hold-down being arranged to engage a mating surface defined in the respective support beam below its upper surface in such a manner that the support hold-downs prevent the continuous metal sheet from being lifted off the series of support beams.

In another aspect, a method for reducing movement of an air grid system in a commercial oxidation or ammonia oxidation reactor is provided. The method includes providing an air grille system, the air grille system including: a continuous metal plate defining an upper surface, a lower surface, and a perimeter extending between the upper surface and the lower surface. The continuous metal sheet further defining a series of air holes for directing process air from below the continuous metal sheet to above the continuous metal sheet; and a support system for supporting the weight of the continuous metal sheet and any oxidation or ammonia oxidation catalyst that may rest on the continuous metal sheet. In one aspect, the support system includes a series of support beams each having an upper support surface that engages the underside of the continuous metal sheet and a series of support hold-downs fixedly attached to the underside of the continuous metal sheet. Each support presser is arranged to engage a mating surface defined below its upper surface in the respective support beam in such a way that the support presser prevents the continuous metal sheet from being lifted off the series of support beams.

In addition, the present disclosure provides, according to another feature, an improved air grille system for use in a commercial oxidation or ammoxidation reactor, such as an acrylonitrile reactor, the improved air grille system comprising: a continuous metal sheet defining an upper surface, a lower surface, and a perimeter extending between the upper and lower surfaces, the continuous metal sheet further defining a series of air holes for directing process air from beneath the continuous metal sheet toward a distributor feed system located above the continuous metal sheet; and a connection assembly for attaching the periphery of the continuous metal sheet to the side wall of the oxidation or ammonia oxidation reactor, wherein the connection assembly comprises a flexible plate and a cooperating diaphragm, the flexible plate and diaphragm each comprising an annular metal sheet defining a top and a bottom, the flexible plate and diaphragm each being arranged to be substantially congruent (consent) with the side wall of the oxidation or ammonia oxidation reactor, wherein the diaphragm is attached to the side wall of the oxidation or ammonia oxidation reactor, wherein the bottom of the flexible plate is attached to the periphery of the continuous metal sheet, and wherein the flexible plate is attached to the diaphragm in such a way that the flexible plate defines a lower portion that extends below the bottom of the diaphragm, such that deviations in the diameter of the continuous metal sheet due to temperature changes inside the reactor can be accommodated by flexing the lower portion of the flexible plate.

In another aspect, a method for accommodating deflection in an air grille system is provided that includes providing a continuous metal plate defining an upper surface, a lower surface, and a perimeter extending between the upper surface and the lower surface. The continuous metal sheet also defines a series of air holes for directing process air from below the continuous metal sheet to above the continuous metal sheet, and a connection assembly for attaching the perimeter of the continuous metal sheet to the side wall of the reactor. The coupling assembly includes a flex plate and a mating diaphragm, each including an annular metal sheet defining a top and a bottom. The flexplate and the baffle are each arranged to substantially conform to a sidewall of the reactor, wherein the baffle is attached to the sidewall of the reactor, wherein a bottom of the flexplate is attached to a periphery of the continuous metal sheet, and wherein the flexplate is attached to the baffle in a manner such that the flexplate defines a lower portion that extends below the bottom of the baffle, such that deviations in the diameter of the continuous metal sheet due to temperature changes inside the acrylonitrile can be accommodated by flexing the lower portion of the flexplate.

Drawings

FIG. 1 is a schematic diagram showing a reactor section of a conventional ammoxidation reactor for the production of acrylonitrile;

FIG. 2 is a plan view showing the underside of a conventional distributor system of the ammoxidation reactor of FIG. 1;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2, FIG. 3 showing a feed nozzle and associated feed shroud of the conventional distributor system of FIG. 2;

FIG. 4 illustrates a conventional manner of attaching an air grid of an acrylonitrile reactor to a wall of the reactor;

FIG. 5 is a partial cross-sectional view of an acrylonitrile reactor illustrating a first feature of the present disclosure wherein the performance of a conventional acrylonitrile reactor is improved by spacing the air grid and feed distributor a suitable distance from each other and reducing mechanical damage to certain components of the acrylonitrile reactor;

FIG. 6 illustrates a second feature of the present disclosure in which a novel support system for supporting an air grid of an acrylonitrile reactor is provided; and

fig. 7 illustrates a third feature of the present disclosure in which a unique connection assembly is provided for securing an air grid 14 of an acrylonitrile reactor to a sidewall of the reactor.

Detailed Description

FIG. 5 illustrates a first feature of the disclosed technology, wherein the air grille 14 is spaced a suitable distance from the feed distributor 16, particularly 6 to 24 inches (-15 to 61 cm). Specifically, as shown, the feed distributor 16 includes a plurality of feed shrouds 60, each associated with a respective feed nozzle defined in a header 30 or a branch 32 of the distributor system. Each feed shroud defines a proximal end 62 connected to its respective header 30 or branch 32 and a distal end 64 remote therefrom, with the feed shroud 60 being arranged to direct the propylene and ammonia feeds exiting its respective feed nozzles downwardly into the interior of the acrylonitrile reactor toward the air grid 14. Meanwhile, the air grille 14 is in the form of a continuous metal plate 70, the continuous metal plate 70 being disposed below the feed distributor 16 and defining an upper surface 72, a lower surface 74 and a series of air holes 76 extending between the upper and lower surfaces 72, 74 for directing process air entering the ammonia oxidation reactor from below the continuous metal plate upwardly toward the feed distributor 16.

According to this feature of the invention, the distal end 64 of the feed shroud 60 is disposed at a distance of 6 to 24 inches (15 to 61cm) from the upper surface 72 of the continuous metal sheet 70. Preferably, the distal end 64 of the feed shroud 60 is disposed at a distance of 8 to 12 inches (20 to 30.5cm) from the upper surface 72 of the continuous metal sheet 70. In accordance with this feature of the present disclosure, it has been found that not only can poor reactor performance resulting from inadequate reactant mixing be substantially eliminated by following the process, but damage to the ammonia oxidation catalyst and other problems resulting from localized reactor hot spots can also be eliminated or at least substantially reduced by following the process.

From a theoretical/conceptual point of view, it appears beneficial to minimize the distance between the air grid 14 and the feed distributor 16, as this appears to contribute to the greatest possible degree of mixing between the feed gas exiting the distributor 16 and the process air exiting the air grid 16. However, in practice it has been found that placing the air grid 14 too close to the feed distributor 16 helps to form the reactor hot spots, as described above. When the distance between the air grate 14 and the feed distributor 16 is too small, some of the air holes 76 in the continuous metal sheet 70 or the distal end 64 of the feed shroud 60, or both, become located within the catalyst/molybdenum scale pile that inherently builds up on the upper surface 72 of the continuous metal sheet 70. This results in the propylene, ammonia and air reactants contacting each other inside these catalyst stacks, which behave like a fixed catalyst bed where heat transfer is poor and therefore the temperature rises rapidly. Accordingly, the distance between the air grate 14 and the feed distributor 16, measured between the distal end 64 of the feed shroud 60 and the upper surface 72 of the continuous metal sheet, should be at least 6 inches (-15 cm) and preferably at least about 8 inches (-20 cm) to avoid this problem.

With respect to the maximum distance between the air grid 14 and the feed distributor 16, it has been found that at distances greater than about 24 inches (61 cm), a portion of the catalyst in the reactor, particularly the portion located between the air grid 14 and the feed distributor 16, cannot be effectively used in the reaction. This reduces the conversion of the propylene and ammonia reactants to the product acrylonitrile, which is clearly undesirable. Accordingly, the maximum distance between the air grille 14 and the feed distributor 16, as measured between the distal end 64 of the feed shroud 60 and the upper surface 72 of the continuous metal sheet 70, is maintained at no more than about 24 inches (-61 cm), preferably no more than 18 inches (-45.7 cm), on the other hand no more than 14 inches (-35.5 cm), and on the other hand no more than 12 inches (-30.5 cm), to prevent this from occurring.

Fig. 6 illustrates a second feature of the presently disclosed technology, wherein a novel support system, generally indicated at 80, is provided for supporting the weight of the continuous metal sheet 70 of the air grille 14, including the weight of any ammonia oxidation catalyst that may rest thereon. As shown in this figure, the support system 80 takes the form of a series of support beams 82, which in a particular embodiment are shown as conventional i-beams. Each i-beam 82 includes an upper transverse section 84 defining an upper surface 86 on which the continuous metal sheet 70 rests. In addition, the underside of each upper cross section 84 defines a mating surface 88 for engagement with a support hold-down carried by the continuous metal sheet 70 of the air grille 14, as discussed further below.

As further shown in fig. 6, a series of support rods 90 are welded to the underside of the continuous metal sheet 70, each end of the support rods defining a nose (nose) 92. As further shown in this figure, each tab 92 extends on the underside of the upper cross section 84 of the respective i-beam 82, where the tab 92 engages the mating surface 88. With this construction, each support bar 90 acts as a hold down for the continuous metal sheet 70 to remain in contact with the upper surfaces 86 of the i-beams 82, thereby preventing the continuous metal sheet from being lifted off the i-beams by the force of the process air flowing upwardly through the air holes 76 in the metal sheet.

As further shown in fig. 6, appropriate spaces 94 and 96 are disposed between the ends of each support rod 90 and the facing portions of the i-beams 82 for accommodating variations in the length of these support rods that inherently occur due to temperature variations experienced inside the reactor during start-up and shutdown.

With this arrangement, the continuous metal sheet 70 is firmly pressed against the upper surface 86 of the i-beam by the projections 92 of the support rods 90 engaging the corresponding mating surfaces 88 of the i-beam 82. It will be appreciated that other structures providing similar attachment means may be used in place of the support rods 90 and their associated tabs 92. In any event, due to the spaces 94 and 96 disposed between the ends of each support rod 90 and the facing portions of the i-beams 82, changes in the length of the support rods 90 that occur as a result of significant temperature changes occurring inside the reactor 10 during start-up and shutdown are readily accommodated by these spaces. Thus, mechanical failure of the support system 80 is substantially eliminated.

Fig. 7 illustrates a third feature of the disclosed technique in which a unique connection assembly is provided for securing the perimeter of the continuous metal sheet 70 of the air grille 14 to the sidewall 12 of the reactor 10. As shown in this figure, the connector assembly, generally designated 100, includes a flexible plate 102 and a mating spacer 104. The flexplate 102 comprises an elongated sheet of metal, the two ends of which are welded together so that the flexplate 102 assumes an annular shape, in particular a cylindrical shape. With this shape, the flexible plate 102 substantially conforms to the sidewall 12 of the reactor 10 to which the air grille 14 is attached, because the middle portion of the reactor 10 is also shaped into a cylindrical form. Likewise, baffle 104 also comprises an elongated sheet of metal, the two ends of which are welded together so that baffle 104 also assumes an annular shape.

As further shown in fig. 7, the baffle 104 is disposed between the flexible sheet 102 and the sidewall 12 of the reactor 10 such that the flexible sheet 102 defines a lower portion 114 that extends below the bottom 112 of the baffle 104. Preferably, the bottom 110 of the flexible sheet 102 extends a distance of about 6 to about 10 inches (about 15 to about 25cm), more desirably about 7 to about 9 inches (about 18 to about 23cm), below the bottom 112 of the baffle 104.

As further shown in FIG. 7, the bottom 110 of the flexible plate 102 is attached to the perimeter of the continuous metal plate 70 of the air grille 14, preferably by welding. With this structure, changes in the diameter of the continuous metal plate 70 of the air grid 14 that occur due to significant changes in temperature occurring inside the reactor 10 during start-up and shutdown are easily accommodated by flexing of the lower portion 114 of the flexplate 102 (i.e., the portion of the flexplate 102 that extends below the bottom 112 of the baffle 104). Thus, mechanical failure of the joints connecting the periphery of the continuous metal sheet 70 of the air grid 14 to the side wall 12 of the reactor 10 is largely eliminated.

Various aspects described herein, and more particularly those shown in FIGS. 4-7, may be used with reactors having various sized diameters. In a preferred aspect, the reactor can have an outer diameter of from about 5 to about 12 meters, in another aspect from about 8 to about 12 meters, and in another aspect from about 9 to about 11 meters. In another preferred embodiment, when using a reactor outer diameter of between about 8 to about 12 meters, or about 9 to about 11 meters, the air nozzles are uncovered and air is introduced vertically into the reactor, most preferably directed vertically towards the feed shroud. In an alternative embodiment, when using a reactor outer diameter of between about 8 to about 12 meters, or about 9 to about 11 meters, the air nozzles in the air grid are capped, with air preferentially distributed horizontally into the reactor by the cap.

Although only a few embodiments of the presently disclosed technology have been described herein, it should be understood that many modifications may be made without departing from the spirit and scope of the present technology. All such modifications are intended to be included within the scope of this technology as limited only by the following claims.

Claims (4)

1. An improved air grid system for use in an oxidation or ammoxidation reactor, said improved air grid system comprising:

a continuous metal sheet defining an upper surface, a lower surface and a perimeter extending between the upper surface and the lower surface, the continuous metal sheet further defining a series of air holes for directing process air from below the continuous metal sheet toward above the continuous metal sheet; and a connection assembly for attaching the periphery of the continuous metal sheet to the side wall of the reactor,

wherein the connection assembly comprises a flexible plate and a mating diaphragm, the flexible plate and diaphragm each comprising an annular sheet of metal defining a top and a bottom, the flexible plate and diaphragm each presenting a cylindrical shape so as to be arranged in line with the side wall of the reactor, wherein the diaphragm is attached to the side wall of the reactor, wherein the bottom of the flexible plate is attached to the periphery of the continuous sheet of metal, and wherein the flexible plate is attached to the diaphragm in a manner such that the flexible plate defines a lower portion that extends below the bottom of the diaphragm, such that deviations in the diameter of the continuous sheet of metal due to temperature changes inside the reactor can be accommodated by flexing of the lower portion of the flexible plate.

2. The improved air grill system of claim 1, wherein the bottom of the flexible plate extends 15cm to 25cm below the bottom of the partition.

3. A method for accommodating flexure in an air grille system, the method comprising:

providing a continuous metal sheet defining an upper surface, a lower surface and a perimeter extending between the upper surface and the lower surface, the continuous metal sheet further defining a series of air holes for directing process air from below the continuous metal sheet toward above the continuous metal sheet; and a connection assembly for attaching the periphery of the continuous metal sheet to the side wall of the reactor,

wherein the connection assembly comprises a flexible plate and a mating diaphragm, the flexible plate and diaphragm each comprising an annular sheet of metal defining a top and a bottom, the flexible plate and diaphragm each presenting a cylindrical shape so as to be arranged in line with the side wall of the reactor, wherein the diaphragm is attached to the side wall of the reactor, wherein the bottom of the flexible plate is attached to the periphery of the continuous sheet of metal, and wherein the flexible plate is attached to the diaphragm in a manner such that the flexible plate defines a lower portion that extends below the bottom of the diaphragm, such that deviations in the diameter of the continuous sheet of metal due to temperature changes inside the reactor can be accommodated by flexing of the lower portion of the flexible plate.

4. The method of claim 3, wherein the bottom of the flexible sheet extends 15cm to 25cm below the bottom of the separator.

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