Abstract:
A sparger includes a conduit for conducting an oxygen feed, a nozzle connected to the conduit for passage of the oxygen feed from the conduit to the outside of the sparger, the nozzle including an orifice and a shroud, and insulation surrounding the conduit and also the shroud substantially the full length of the shroud. A method is provided for producing acrylonitrile via propane ammoxidation, comprising introducing propane and ammonia feeds into a fluid bed of a fluid bed reactor, and introducing an oxygen feed into the fluid bed through at least one insulated and jacketed sparger nozzle for reacting with at least one of the propane feed and ammonia feed in the presence of a fluid bed catalyst.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to spargers and more particularly to a sparger and method for adding pure oxygen or relatively high concentrations of oxygen directly into a fluid bed reactor. 
     BACKGROUND 
     Significant economic advantages can be realized by using pure oxygen instead of air to form acrylonitrile via propane ammoxidation. The ammoxidation process typically consists of reacting propane, ammonia, and air in a fluid bed ammoxidation reactor containing a suitable ammoxidation catalyst to produce acrylonitrile. Also produced are high concentrations of unreacted starting materials, for example, unreacted hydrocarbons and other remaining flammable reactants. These unreacted materials are typically recycled, that is, mixed, in a recycle stream leading back to the fluid bed reactor. 
     Delivery of an oxygen feed comprising oxygen or high concentrations of oxygen into the fluid bed reactor is challenging because of the sensitivity of working with pure oxygen or oxygen-rich streams. By using an oxygen feed instead of an air feed, flammability envelopes are widened and oxidation reactions are accelerated. 
     Typically, one or more spargers are incorporated into the fluid bed reactor vessel for delivering into the interior thereof and agitating therein the reactants of the ammoxidation process. During a propane ammoxidation process, temperatures may vary within the reactor vessel from about 400 to 500° C. and, accordingly, spargers disposed within the reactor vessel will likewise vary in temperature as will the reactants carried by the sparger. As the temperature of a conventional sparger increases with increased reactor temperature, the flammability of a combustible material in the presence of an oxygen feed delivered therethrough would increase. As a consequence, spargers could exhibit undesirable burning because of their increased likelihood to ignite within the widened oxygen flammability limits. For example, spargers made of ordinary metals like carbon steels or even stainless steels, if used to inject pure oxygen or relatively high concentrations of oxygen, may ignite and locally burn inside a fluid bed reactor vessel for propane ammoxidation. 
     SUMMARY OF THE INVENTION 
     The present invention provides a sparger and method for injecting an oxygen feed into a fluid bed reactor. The sparger and method have particular application for injecting an oxygen feed into a fluid bed catalytic reactor for the ammoxidation of a propane feed and an ammonia feed. The oxygen feed may be oxygen enriched air (greater than 21% oxygen), pure oxygen (100% oxygen) or a high concentration of oxygen (greater than 50% oxygen). Other representative processes in which principles of the instant invention may be employed are the catalytic cracking of oils to produce gasoline and other light hydrocarbons, the coking of residua, coke gasification, the oxidation of benzene or n-butane or maleic anhydride, the ammoxidation of propylene to acrylonitrile, and the oxidation of hydrogen chloride to chlorine. 
     According to one aspect of the invention, the sparger and method are characterized by a feed conduit for conducting the oxygen feed and a nozzle connected to the feed conduit for passage of the oxygen feed from the feed conduit to outside the sparger. The nozzle includes an orifice and a shroud, and insulation surrounds the conduit and also surrounds the shroud substantially the full length of the shroud. In a preferred embodiment, a conduit jacket surrounds the conduit and a shroud jacket surrounds the shroud, and insulation is interposed between the conduit and conduit jacket and between the shroud and he shroud jacket. Also in a preferred embodiment, the shroud jacket terminates at a cheek plate at least partially closing an outer end of an annular space between the shroud and shroud jacket, which cheek plate closely surrounds the shroud but is radially spaced apart from the shroud by an amount sufficient to allow for differential expansion. 
     According to another aspect of the invention, a fluid bed reactor comprises a reactor vessel for containing a fluid bed and a sparger disposed within the reactor vessel for delivery of an oxygen feed into the fluid bed. The sparger includes at least one nozzle for directing a stream of the oxygen feed into the fluid bed. The nozzle is at least partially thermally insulated for inhibiting heat transfer from the interior of the reactor to the interior of the nozzle in order to maintain, at a fluid bed temperature greater than about 400° C., the temperature of the oxygen feed below a temperature at which the materials of construction of the nozzle (or any combustible impurities therein) would ignite. 
     According to yet another aspect of the invention, a method is provided for introducing an oxygen feed into a fluid maintained at a temperature of about 400° C. or higher, the method comprising the use of a sparger disposed within the fluid bed for introducing the oxygen feed into the fluid bed through at least one sparger nozzle. 
     According to a further aspect of the invention, a method is provided for the production of acrylonitrile via propane ammoxidation comprising the steps of introducing propane and ammonia into a fluid bed reactor, introducing an oxygen feed into the fluid bed reactor through a sparger to react the propane, ammonia and oxygen feed in the presence of a fluid bed catalyst to produce the corresponding acrylonitrile, and maintaining the temperature of the oxygen feed while inside the sparger below the temperature at which the materials of construction of the sparger (or any combustible impurities therein) would ignite. 
     The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail one or more illustrative embodiments of the invention, such being indicative, however, of but one or a few of the various ways in which the principles of the invention may be employed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified schematic cross-sectional illustration of a fluid bed reactor including a sparger constructed in accordance with the invention. 
     FIG. 2 is a cross-sectional view of the fluid bed reactor as viewed from the plane  2 — 2  in FIG.  1 . 
     FIG. 3 is a cross-sectional view of a header pipe of the sparger as viewed from the plane  3 — 3  in FIG.  2 . 
     FIG. 4 is a partial cross-sectional view of an end of the header pipe as viewed from the plane  4 — 4  in FIG.  2 . 
     FIG. 5 is a cross-sectional view of a lateral pipe of the sparger as viewed from the plane  5 — 5  in FIG.  2 . 
     FIG. 6 is a partial cross-sectional view of a portion of the sparger where the header pipe and lateral pipe intersect as viewed from the plane  6 — 6  in FIG.  2 . 
     FIG. 7 is a partial cross-sectional view of a portion of the sparger where the header pipe, a lateral pipe and a nozzle intersect as viewed from the plane  7 — 7  in FIG.  2 . 
     FIG. 8 is a cross-sectional view of a portion of the sparger where the header pipe, a lateral pipe, a nozzle and the feed line intersect as viewed from the plane  8 — 8  in FIG.  2 . 
     FIG. 9 is a partial cross-sectional view of an end of a lateral pipe of the sparger as viewed from the plane  9 — 9  in FIG.  2 . 
     FIG. 10 is a cross-sectional view of a nozzle extending from a lateral pipe of the sparger as viewed from the plane  10 — 10  in FIG.  2 . 
     FIG. 11 is a cross-sectional view of a feed line for the sparger. 
     FIG. 12 is a cross-sectional view of the feed line as viewed from the plane  12 — 12  in FIG.  11 . 
    
    
     DETAILED DESCRIPTION 
     Referring now in detail to the drawings and initially to FIG. 1, a fluid bed reactor is designated generally by reference number  8 . The fluid bed reactor  8  includes a reaction or reactor vessel  12  in which a gas-solid or liquid-solid contacting process occurs. In the reactor, a bed of finely divided solid particles (e.g. a fluid bed catalyst) is lifted and separated by using a stream of process gas or liquid. Fluid bed reactors exist in all shapes and sizes. Typically the reactors are equipped with a grid near the bottom of the reactor which supports a catalyst bed while allowing process feed to pass through. The remainder of this description focuses in the practice of the instant invention in gas-solid contacting processes and particularly an ammoxidation process that typically consists of reacting propane, ammonia, and a source of oxygen in the reactor containing a suitable ammoxidation catalyst to produce acrylonitrile. However, the apparatus and methods described herein are equally applicable to other processes, including liquid-solid contacting processes. 
     With additional reference to FIG. 2, the reactor vessel  12  has disposed therein, for delivery of an oxygen feed, an exemplary sparger  10  constructed in accordance with the present invention. The sparger  10  generally includes a header pipe  14 , one or more lateral pipes  16  and one or more nozzles  18 , all of which are thermally insulated and are preferably made of metals that have high resistance to burning in oxygen. The lateral pipes  16  extend transversely outwardly from the header pipe  14 . That is, the lateral pipes  16  extend in a perpendicular, or T-shaped, relation to the header pipe  14 . The nozzles preferably are positioned along the lengths of the header and lateral pipes in a triangular-like pattern (or pitch) for uniform distribution of the oxygen feed across the cross-section of the vessel, although other nozzle and/or pipe configurations may be employed. 
     During the process of manufacture of acrylonitrile, an oxygen feed is fed through the header pipe  14  into the lateral pipes  16  for dispersion through the nozzles  18  into a fluid bed catalyst  20  contained in the reactor vessel  12 . As used herein, an oxygen feed is a feed having an oxygen concentration higher than the normal percentage concentration of oxygen in air, such as, oxygen enriched air (greater than 21% oxygen), pure oxygen (100% oxygen) or a high concentration of oxygen (greater than 50% oxygen). The oxygen feed is mixed with propane and ammonia feeds delivered by any suitable means (not shown). For example, the ammonia feed may be delivered by a similar sparger upstream, downstream or at the same level as the oxygen sparger, and the propane feed may be introduced via an inlet at the upstream end of the vessel  12 . Together, the propane, ammonia and oxygen feeds react to produce acrylonitrile. 
     The hereinafter described construction of the sparger  10  maintains the temperature of the oxygen feed passing through the sparger  10  at a temperature below which the metal of the pipes  14  and  16  and particularly the nozzles  18  would ignite. These and other advantages, as well as the structure, function, and other features of the invention are described in greater detail below. 
     As shown in FIG. 3, the header pipe  14  is surrounded by a conduit jacket  24  spaced apart from the header pipe  14  by spacers  26 . The spacers  26 , which may be three equally circumferentially spaced apart pins or ribs having rounded ends, maintain the header pipe  14  centered in and thus concentric with the conduit jacket  24 . The spacers  26  are located along the length of the header pipe, for example at locations midway between the connections of the header pipe  14  with the lateral pipes  16 . As shown in FIG. 4, the header pipe  14  is closed at its ends  28  preferably by end plugs  30  inserted therein and welded thereto. The conduit jacket  24  is also closed at its ends  32  preferably by plate discs  34  welded thereto. The annular space between the header pipe  14  and conduit jacket  24  is filled with thermal insulation to cover the exterior surface  36  of the header pipe  14 . A preferred insulation is a ceramic paper insulation. 
     Like the configuration of the header pipe  14 , the lateral pipes  16  are surrounded by respective conduit jackets  40  spaced apart from the lateral pipes  16  by spacers  42  as seen in FIG.  5 . The spacers  42 , which may be three equally circumferentially spaced apart pins or ribs having rounded ends, maintain the lateral pipes  16  centered and thus concentric with the respective conduit jackets  40 . The spacers  42  are located along the length of each lateral pipe, for example at locations approximately midway between the connections of the lateral pipe and nozzles  18 . 
     As shown in FIGS. 6-9, the lateral pipes  16  and lateral conduit jackets  40  are sealingly connected, preferably by welding, to the header pipe  14  and header conduit jacket  24 , respectively. The lateral pipes  16  and conduit jackets  40 , similar to the header pipe  14  and conduit jacket  24 , are closed at their distal ends  44  and  45  by end plugs  46  and plate discs  48 , respectively. The annular space between the lateral pipes  16  and conduit jackets  40  are filled with thermal insulation to cover the exterior surface  50  of the lateral pipes  16 . Again, a preferred insulation is a ceramic paper insulation. 
     As seen in FIGS. 7,  8  and  10 , each nozzle  18  includes an orifice  52 . The orifices of the nozzles are configured preferably to provide for even distribution of the oxygen feed transversely across the fluid bed reactor  12 . As above noted, the nozzles, and thus the orifices, are arranged in a triangular pattern (FIG.  2 ). That is, the orifices are equidistant from one another and form a repeated pattern across the sparger  10 . For example, any three neighboring orifices  52  form an equilateral triangle of the same size as an adjacent equilateral triangle formed by another three neighboring orifices  52 . The orifices  52  are sized to provide a desired pressure drop and flow velocity that prevents or substantially reduces the probability of backflow of any reactant gases into the header pipe  14  or the lateral pipes  16 . 
     Each nozzle  18  includes a protective shroud  54  for directing the oxygen feed into the fluid bed catalyst  20  contained in the reactor vessel  12  (FIG.  1 ). In the illustrated embodiment, each protective shroud  54  extends downwardly from, and are sealingly connected to, preferably by welding, the header pipe  14  (FIGS. 7 and 8) or the lateral pipes  16  (FIG.  10 ). 
     In accordance with the invention, shroud jackets  56  surround the shrouds. The shroud jackets are spaced apart from the respective shrouds  54  and are connected to the corresponding conduit jackets  24 ,  40  of the header pipe  14  or lateral pipe  16 , preferably by welding. The annular space between the shrouds  54  and shroud jackets  56  is filled with thermal insulation, preferably a ceramic paper insulation, to cover the exterior surface  58  of the shrouds  54 . 
     The ends of the shroud jackets  56  are substantially closed by cheek plates  60 . The cheek plates  60  are connected to the respective bottom ends  66  of the shroud jackets  56  and have a center opening  62 , or aperture, through which the protective shrouds  54  extend. The openings  62  are sized larger than the diameters of the shrouds  54  to enable the cheek plates  60  and shrouds  54  to expand and/or contract relative to one another. The cheek plates  60  retain and protect the thermal insulation within the annular space between the shrouds  54  and shroud jackets  56 . As is preferred, the shrouds extend only a short distance beyond the respective cheek plates as shown. 
     Referring now to FIG. 11, an oxygen feed line is generally indicated by reference numeral  70 . The feed line  70  is connected to and in fluid communication with the sparger  10  at the header pipe  14 . In the illustrated embodiment, the feed line  70  generally includes tube couplings  72  and  74  respectively connecting opposite ends  90  and  92  of an elbow pipe  76  to an oxygen feed source conduit  94  and a transition conduit  104 . However, other means, such as welding, may be used to connect the elbow pipe to the conduits  94  and  104 . Like the header pipe  14 , lateral pipes  16  and nozzles  18 , the elbow pipe  76  is surrounded by a jacket  78  spaced apart from the elbow pipe  76 . Spacers  80  (FIG. 12) maintain the annular space between the elbow pipe  76  and conduit jacket  78 . The annular space is filled with thermal insulation, preferably a ceramic paper insulation, to cover the exterior surface  82  of the elbow pipe  76 . Cheek plates  84  are connected to the respective ends  86  of the conduit jacket  78 . 
     The oxygen feed source conduit  94  extends through an opening  96  in a side wall  98  of the reactor vessel  12 . A penetration coupling  100  connected to the reactor vessel wall  98  surrounds the oxygen feed source conduit  94  for protection. The transition conduit  104  is sealingly connected, preferably by welding, to the header pipe  14 . The transition conduit  104  is disposed in and spaced apart from a conduit jacket  106  that is connected to the conduit jacket  24  surrounding the header pipe  14 , preferably by welding. The transition conduit  104  and conduit jacket  106  form an annular space therebetween in which thermal insulation, preferably a ceramic paper insulation, is filled to cover the exterior surface  108  of the transition conduit  104 . A plate disc  110  is connected to the end  112  of the conduit jacket  106 . The plate disc  110  has an opening  114  through which the transition conduit  104  extends. 
     The tube couplings  72  and  74  are disposed in respective outer casings  120  and  122 . The spaces within the casings  120  and  122  and around the tube couplings  72  and  74  are filled with thermal insulation, preferably a ceramic paper insulation, to cover the exterior surfaces  124  and  126  of the tube couplings  72  and  74 , as well as portions  130  of the transition conduit  104 , elbow pipe  76  and oxygen feed source conduit  94 . The casing  122  includes a cheek plate  132  that has an opening  134  through which the elbow pipe  76  extends. The casing also includes a cheek plate  136  that has an opening  138  through which the transition conduit  104  and conduit jacket  106  extend. The cheek plates  132  and  136  are preferably welded to the respective ends  140  and  142  of the outer casing  122  and are operative to maintain the thermal insulation in the annular space. The casing  120  also has cheek plates  146  and  148  connected at its ends  150  and  152 , preferably by welding. The cheek plate  146  has an opening  154  through which the elbow pipe  76  extends. Likewise, the cheek plate  136  has an opening  156  through which the oxygen feed source conduit  94  extends. 
     In view of the foregoing, it will be appreciated that the sparger  10 , as well as the oxygen feed line  70  connected to the sparger  10 , are substantially entirely surrounded by thermal insulation. The insulation, in turn, is substantially entirely covered by the spaced apart conduit jackets and shroud jackets to stabilize and protect the insulation. The size of the spacing and the corresponding type and amount of insulation depends on such factors as the size and configuration of the reactor vessel, the inlet temperatures and flow rates of the ammonia feed, propane feed and oxygen feed, and the metal of which the sparger  10  and reactor  12  are constructed. 
     The thermal insulation blocks heat transfer, or substantially reduces the rate of heat transfer, from the interior of the reactor vessel  12 . As a result, the temperature of the oxygen feed is maintained below a temperature that prevents the header pipe  14 , lateral pipes  16  and shrouds  54  of the sparger  10 , or contaminants that may be in the stream of oxygen feed communicated therethrough, from igniting. In particular, because the insulation surrounding the shrouds  54  extends substantially the full length of the shrouds  54 , there is less likely a chance of premature or undesirable oxidation reactions from developing near the ends of the shrouds  54 . 
     To further reduce the chance of ignition of the sparger  10 , the header pipe  14 , lateral pipes  16 , and shrouds  54  are constructed of metals that have high resistance to combustion with the oxygen feed. Preferred metals include nickel and copper alloys, for example, nickel 200 or Monel 400, although other metals such as stainless steel may also be used. 
     During the process of manufacture of acrylonitrile, the reactants, i.e., an ammonia feed and propane feed, are fed into the fluid bed reactor  12 , which contains the fluid bed catalyst  20 , via a sparger or other delivery apparatus (not shown) upstream, downstream or at the same elevation as the oxygen feed sparger  10 . An oxygen feed, in the form of pure oxygen or a mixture containing a high concentration of oxygen, is fed through the oxygen feed sparger  10  for dispersion directly into the fluid bed catalyst  20 . The catalyst  20  in the path of the nozzle outlet streams is preferably comprised of finely divided catalyst solids, for example having an average particle size of 50 microns, that assists in resisting or retarding the formation or propagation of flames. The shrouds  54  are sized to maintain a gas jetting velocity, for example between 20-30 feet/sec, into the fluid bed reactor  12  without substantial attrition of the catalyst contained therein. The fluid bed pressure may by example be about 15-17 psig and at a temperature of about 490-500° C. 
     A model of the sparger  10  was constructed in accordance with the invention and, as illustrated in the Figures, includes the header pipe  14 , which communicates the oxygen feed to ten outwardly extending spaced apart lateral pipes  16 . The header pipe  14  or lateral pipes  16  communicate the oxygen feed to  19  nozzles which include the orifices  52  and shrouds  54  that extend downwardly (into the paper in FIG. 2) from the header pipe  14  or lateral pipes  16 . The feed line  70  is centrally disposed relative to the orifices  52  and are configured so as to distribute the oxygen feed uniformly across the fluid bed reactor  12 . 
     Tests conducted with such model have shown that with a fluid bed reactor temperature in the range of about 400 to about 500° C., the temperature of the oxygen feed can be maintained at about 90 to about 120° C. (as estimated by standard heat transfer calculations). The orifices were sized to maintain a velocity in the range of about 400 to about 600 ft/sec at the orifice and the shrouds were sized to attain a gas jetting velocity in the range of about 20 to about 30 ft/sec, with a fluid bed pressure of about 15-17 psig. 
     Although the invention has been shown and described with respect to certain preferred embodiments, equivalent alterations and modifications will occur to others skilled in the art upon reading and understanding this specification and the annexed drawings. In particular regard to the various functions performed by the above described integers (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such integers are intended to correspond, unless otherwise indicated, to any integer which performs the specified function of the described integer (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.