IMPROVED HIGH EFFICIENCY REGENERATOR APPARATUS

Abstract: Disclosed is a high efficiency catalyst regenerator employing a barrier separating upper and lower regenerator sections which minimizes structural damage caused by thermal stress in portions of the barrier subject to different degrees of heating. In one embodiment a hot internal cone portion of the regenerator forming the barrier is spaced from a cooler regenerator vessel sidewall. The space may be an unfilled void space or it may be filled with an insulation material. In another embodiment the regenerator vessel is physically separated into upper and lower sections with the barrier being formed by an upper section containing a concave dish head at its bottom and the lower section containing a convex dish head at its top which are connected by an extension of a riser interconnecting the concave and convex dishes.

Description: IMPROVED HIGH EFFICIENCY REGENERATOR APPARATUS The present invention provides a regenerator for regenerating catalyst used in the fluidic catalytic cracking of hydrocarbons. More particularly, the invention is directed to an improved construction for a high efficiency regenerator which minimizes problems of material damage due to thermal stress. A conventional high efficiency catalyst regenerator is illustrated in Fig. 1. The regenerator 11 is divided into an upper regenerator section 13, commonly known as a disengager section and a lower regenerator section 15, commonly known as a combustor section. Spent catalyst, received typically from a fluidized catalytic cracking (FCC) apparatus, is introduced into the lower regenerator section 15 through a reactor standpipe 45. The catalyst contained within the lower regenerator section 15 is illustrated as a catalyst bed 37. The catalyst received through the reactor standpipe 45 is at a high temperature, typically at 538°C (1,000°F). An air inlet 49 is used to introduce air into the catalyst bed, with the air entering at a temperature within the range of 204 to 260°C (400° to 500°F). The introduced air passes through an air distributor 47 having a plurality of holes therein and into the catalyst bed 37. The mixing of the air and catalyst causes a combustion of carbonaceous material deposited on the catalyst particles, thus regenerating them. The mixture of air and catalyst particles is typically at a temperature of 732 to 760°C (1350 to 1400°F). The heated air entering at inlet 49 also forms a fluidized mixture of air and catalyst above the catalyst bed 37 which passes upwardly through an internal cone 17 and into a riser 19. The riser 19 is provided in the upper (disengager) regenerator section 13 and allows a more complete combustion of the carbonaceous material on the catalyst. The mixture of air and catalyst exiting riser 19 enters a serial connection of cyclones 21 wherein the catalyst particles are separated from the air and deposited in a catalyst bed 39 located at the bottom of the upper disengager regenerator section 13. In addition, the atmosphere of the upper regenerator section 13, which also contains a mixture of air and catalyst particles, passes through the inlet of a cyclone 23 which is in turn connected in series to a cyclone 25 for further separation of catalyst particles. The respective diplegs 27 and 29 from the cyclones 23 and 25 are embedded within the catalyst bed 39. Exhausted gas from the cyclones 21 are conducted into a plenum 31 at the top of the upper regenerator section 13 and from there into a conduit 34 and through orifice chamber 33 containing a plurality of spaced perforated plates 35 therein. The orifice chamber 33 serves as a pressure dropping device and the output thereof goes to a boiler or conventional flue gas stack. Catalyst from the catalyst bed 39 is supplied through a regenerator standpipe 43 to the bottom of an FCC reactor where it is admixed with fluidized hydrocarbons and passed through a riser of an FCC cracking unit. In addition, a portion of the catalyst from catalyst bed 39 passes through a catalyst recirculation standpipe 41 and into catalyst bed 37 of the lower regenerator section 15. The lower regenerator section 15 is considered a combustor since most of the combustion which removes the carbonaceous deposits from the catalyst occurs within this section of the regenerator. The upper regenerator section 13 is called the disengager because it serves primarily to separate the regenerated catalyst from the airstream in which it is entrained. While the regenerator structure depicted in Fig. 1 serves to regenerate catalyst particles with great efficiency, it has been discovered that the internal cone 17 tends to prematurely fail by buckling, cracking and/or sagging under normal use conditions. EP-A-0142275 and US-A-4283273 disclose conventional regenerators for fluidizable catalyst particles. No provisions are made for relieving the stresses which may cause premature failure in these regenerators. The problem of severe overstressing of the internal cone has been observed within a period as short as one or two years following an initial startup of a new regenerator unit. Cone damage requires expensive repairs and removal of the regenerator and its associated FCC cracking unit from use for repair. The premature failure of cone 17 is believed to be caused by thermal stress at the connection between the internal cone 17 and the sidewalls of the lower regenerator section 15. This connection is more clearly illustrated in Fig. 2 which shows an enlarged view of a portion of Fig. 1. As illustrated in Fig. 2, the riser 19 includes a downwardly extending sidewall 51 which is a continuation of the internal cone 17. The sidewall 51 is attached, usually by welding, at area 55 to the sidewall 61 of the lower regenerator section 15. As also shown in Fig. 2, the inside surfaces of the reactor and cone 17 are covered with a refractory lining 57. The lower portion of riser and upper portion of cone 17 are also covered on their inside and outside surfaces with a hexmesh supported refractory lining 59. Despite the presence of the refractory lining 57, considerable stress at the connection between internal cone 17 and the reactor sidewall 61 is caused by differential thermal expansion between the hot internal cone 17 and cooler regenerator sidewall 61, causing, in turn, cone damage. In addition, failure of the internal cone may be attributed to reduce strength of the internal cone 17 at process temperatures, and the high bending and buckling stresses in the internal cone encountered during normal and upset operations. In accordance with the invention, there is provided a catalyst regenerator apparatus as defined in claim 1. The advantages and structural features of the invention will be more clearly understood from the following detailed description of the invention which is provided in connection with the accompanying drawings. In the drawings, Fig. 1 illustrates in cutaway view a conventional high efficiency catalyst regenerator; Fig. 2 illustrates in greater detail a side sectional view of a portion of the regenerator illustrated in Fig. 1; Fig. 3 illustrates in side-sectional view a portion of the regenerator of Fig. 1 containing the first embodiment of the invention; and Fig. 4 illustrates in side-cutaway view a regenerator employing the second embodiment of the invention. The invention will first be described in connection with a first embodiment thereof illustrated in Fig. 3. As shown therein, an internal cone 17a of regenerator 11 is provided with a cylindrical downwardly extending skirt 63. Internal cone 17a is mounted within regenerator 11 so that the cylindrical skirt 63 is spaced from the sidewall 61 of the reactor vessel by about 50 to 203 mm (2" to 8"). A support bar ring 69 is fastened to the internal periphery of the sidewall 61 and the cylindrical cone skirt 63 is fastened to the support ring 69. Fastening of the bar ring 69 to wall 61 of regenerator vessel, and of the cylindrical skirt 63 to the bar ring 69 may be accomplished by any suitable fastening arrangement, for example, by welding. The space provided between the cylindrical cone skirt 63 and sidewall 61 of the regenerator vessel is preferably filled with a commercially available bulk ceramic fiber layer 65 or the space may be left void of any fill. The bulk ceramic fiber layer 65 or the void space serves to insulate the cylindrical skirt 63 and conical portion 53 of the internal cone from the reactor vessel sidewall 61 and also permits a certain amount of flexure of the cylindrical skirt 63 and associated conical portion 53. A commercially available ceramic fiber blanket 67 is also preferably provided on both the upper and lower surfaces of the conical portion 53. The fiber ceramic blanket provided on the under surface extends from a point along the lower portion of the conical portion 53 down along the inside periphery of the cylindrical cone skirt 63. The ceramic fiber blanket 67 provided on the upper surface of conical portion 53 extends along conical portion 53, terminating at the bulk ceramic fiber layer 65 or void space. The void space, or ceramic fiber blanket 65, if used, also provides the cylindrical skirt 63 and the lower end of conical portion 53 with a certain amount of room for flexure. A refractory lining 57 is also provided on the interior periphery of the regenerator vessel sidewall 61 and over the ceramic fiber blanket 67, both on the inner surface of the cylindrical cone skirt 63 and cone portion 53 and may also be on the outer surface of cone portion 53. In addition, a hexmesh supported refractory lining 59 is provided along the inner and outer peripheral surfaces of the upper portion of cone portion 53 and a lower portion of the riser 19. With the construction illustrated in Fig. 3, thermal stress caused by the interface of the hot internal cone 17a with the cooler regenerator shell 61 is considerably reduced. Moreover, the ceramic fiber blanket 67 provides a certain degree of flexibility for the internal cone 17a. The bulk ceramic fiber in the space between the cylindrical cone skirt 63 and the regenerator sidewall 61, or the void space, whichever is used further reduces stress and allows for differential expansion between the internal cone 17a and regenerator vessel sidewall 61. If the bulk ceramic fiber 65 is used for insulation, it also reduces heat flow to the regenerator sidewall 61 and serves to minimize the intrusion of FCC catalyst from catalyst bed 39 into the space between the cylindrical skirt 63 and regenerator sidewall 61. A void space instead in this location may be used to increase heat transfer between cone skirt 63 and sidewall 61 thereby reducing temperature differential and consequent stress. Another embodiment of the invention is illustrated in Fig. 4. In this embodiment the regenerator vessel is separated into two separate vessels, an upper regenerator vessel 13a and a lower regenerator vessel 15a. The lower regenerator vessel 15a has at a top portion thereof a convex dish head 73 which has a central aperture which is connected to a downward extension of the riser 19. The bottom of the upper regenerator vessel 13 contains a concave dish head 71 through which the extension of the riser 19 passes. The aperture in the concave dish head 71 and that in the convex dish head 73 are essentially in axial alignment and are further axially aligned with respect to the axis of the riser 19. The inner surfaces of the lower regenerator vessel 15a are coated with a refractory lining 57 which extends up the entire length of the riser 19. The refractory lining 57 is also provided on the outer peripheral surface of the riser 19 to a point above a nominal level of catalyst bed 39 and on the inner peripheral surface of the upper regenerator vessel 13a, at the bottom thereof, including the concave dish head 71. The remaining structures of Fig. 4 are the same as depicted in Fig. 1 and accordingly a detailed description thereof is omitted herein. During operation of the high efficiency regenerator in accordance with the invention, the operating performance is substantially the same as with the conventional high efficiency regenerator illustrated in Fig. 1. However, the problems due to thermal stress which cause bending buckling, cracking and/or sagging of the internal cone 17 are eliminated. While preferred embodiments of the invention have been described and illustrated, it should be apparent that many modifications can be made to the invention and accordingly, that the invention is not limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims: A catalyst regenerator apparatus comprising: a regenerator vessel having a sidewall; a first combustor section within the regenerator vessel for regenerating spent catalyst, the combustor section comprising a catalyst receiving portion and means for introducing a combustor gas into catalyst introduced into the receving portion; a second disengaging section within the regenerator vessel for receiving a mixture comprising catalyst particles and the combusting gas from the first section, the second section including at least one separation device for separating regenerated catalyst particles from the mixture; and means within the regenerator vessel for physically separating the first combustor section from the second disengaging section, the separating means defining a conduit providing a flow passage for the mixture from the first to the second section, the conduit having, at one end, a riser extending into the second section, and at another end a sidewall, and; means for supporting the separating means such that the sidewall of the conduit is spaced from the sidewall of the regenerator vessel. A catalyst regenerator as in Claim 1, wherein the sidewall of the separating means includes a cylindrical skirt extending downwardly from the internal cone and the regenerator vessel has a cylindrical sidewall, the space being defined at least between the cylindrical skirt and the cylindrical sidewall. A catalyst regenerator as in Claim 1, further comprising an insulating material provided in the space. A catalyst regenerator as in Claim 1, wherein the space is an unfilled void space. A catalyst regenerator as in Claim 2, wherein the support means comprises a bar ring attached to the inner periphery of the sidewall of the regenerator vessel and the cylindrical skirt is supported by the bar ring. A catalyst regenerator as in Claim 1, further comprising a refractory material covering at least a portion of an inner periphery of the conduit sidewall which is disposed closest to the second regenerator section. A catalyst regenerator as in Claim 6, further comprising a ceramic fiber material located between the inner periphery of the conduit and the refractory material. A catalyst regenerator as in Claim 7, wherein the refractory material also covers at least a portion of an outer periphery of the conduit sidewall. A catalyst regenerator as in Claim 8, further comprising a ceramic fiber material located between an outer periphery of the conduit and the refractory material. A catalyst regenerator as in Claim 6 wherein the refractory material extends from the inner periphery of the conduit to cover an inner periphery of the regenerator vessel within the combustion section. A catalyst regenerator as in Claim 1, wherein the conduit includes a first larger diameter cylindrical portion, a second smaller diameter cylindrical portion, forming the riser, and a frusto conical shaped intermediate portion interconnecting the larger and smaller diameter cylindrical portions.

Inventors: HUMBLE, JOHN DUNCAN, JACOBOWITZ, JUDAH LEON, RUGGLES, JOHN DAVID, SEARLES, RAYMOND CHARLES
Applicants: MOBIL OIL CORPORATION
Application year: 1988
Main classification: C10G11
IPC codes: B01J38, B01J8, C10G11