Patent Publication Number: US-2009227826-A1

Title: System and method for vaporizing a cryogenic liquid

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This U.S. application is a divisional patent application claiming priority to U.S. patent application Ser. No. 11/037,034, filed on Jan. 18, 2005, which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a system and method for vaporizing a cryogenic liquid and, more particularly, a system for providing heat for cryogenic liquid vaporization. 
     BACKGROUND OF THE INVENTION 
     It is often necessary or desirable to vaporize a cryogenic liquid (i.e., to bring about vaporization of a cryogenic liquid to a vaporized state). For example, and though a wide variety of applications exist for liquid vaporization, it is often necessary or desirable to vaporize liquid natural gas (LNG) so that it can be handled and distributed as a fuel source. 
     Many vaporization systems operate with burners in order to produce the necessary vaporization heat. For example, evaporators of the submerged combustion type comprise a water bath in which a flue gas tube of a gas burner is installed as well as an exchanger tube bundle for the vaporization of the liquefied gas. The gas burner discharges the combustion flue gases into the water bath, which heat the water and provide the heat for the vaporization of a liquefied gas that flows through the tube bundle. Such vaporization systems are provided, for example, by T-Thermal Company, a division of Selas Fluid Processing Corporation, under the registered trademark SUB-X. 
     Evaporators of this type are reliable and of compact size, but they may become expensive to operate. For example, in order to reduce emissions of nitrogen oxide (NOx) from such systems, a current practice utilizes a gaseous fuel burner in combination with water injection to reduce NOx emissions. In such systems, NOx emissions can be reduced to approximately 30 ppmvd, corrected to 3 volume percent oxygen (dry basis). 
     Further reduction of NOx emissions may require post combustion catalytic treatment. For example, a catalytic treatment system may be located at the outlet of a submerged liquid bath. Such treatment utilizes a portion of the burner exhaust to reheat the gases that are exiting the liquid bath, so as to reduce the moisture content of the gases before they enter the post combustion catalytic system. The corresponding use of this portion of the burner exhaust can, however, reduce the energy efficiency of the system, since this portion of the burner gases are not used to heat the cryogenic fluid. 
     Accordingly, there remains a need for an improved method and system for cryogenic liquid vaporization. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a flameless thermal oxidizer is provided. The flameless thermal oxidizer includes a matrix bed containing media, an inlet tube extending into the matrix bed and having an outlet positioned to deliver reacting gases into the matrix bed. The matrix bed defines a void proximal the outlet of the inlet tube. In the oxidizer, a disc is optionally positioned adjacent the outlet of the inlet tube and configured to direct reacting gases away from the inlet tube. The void defined in the matrix bed is optionally substantially cylindrical. 
     According to another aspect, this invention provides a method of reducing pressure losses in a flameless thermal oxidizer, the method including introducing reacting gases from an inlet tube into a void defined by a matrix bed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention will be described with reference to several embodiments selected for illustration in the drawing, of which: 
         FIG. 1  is a schematic, block diagram of a vaporization system according to one exemplary embodiment of this invention; 
         FIG. 2  is a schematic diagram of an embodiment of a flameless thermal oxidizer capable of use in the vaporization system illustrated in  FIG. 1 ; 
         FIG. 3  is a schematic diagram of another embodiment of a flameless thermal oxidizer capable of use in the vaporization system illustrated in  FIG. 1 ; 
         FIG. 4  is a perspective view of yet another embodiment of a flameless thermal oxidizer capable of use in the vaporization system illustrated in  FIG. 1 ; 
         FIG. 5  is a perspective view of still another embodiment of a flameless thermal oxidizer capable of use in the vaporization system illustrated in  FIG. 1 ; 
         FIG. 6A  is an elevation view of another embodiment of a vaporization system according to this invention; 
         FIG. 6B  is a plan view of the vaporization system illustrated in  FIG. 6A ; 
         FIG. 6C  is an elevation view of the vaporization system shown in  FIG. 6A , with portions removed to reveal internal details; 
         FIG. 7A  is an elevation view of an embodiment of a manifold and distributor assembly capable of use in the vaporization system illustrated in  FIG. 6A ; 
         FIG. 7B  is an end view of the manifold and distributor assembly illustrated in  FIG. 7A ; 
         FIG. 7C  is a cross-sectional, end view of the manifold and distributor assembly illustrated in  FIG. 7A ; 
         FIG. 7D  is a plan view of a portion of the manifold and distributor assembly illustrated in  FIG. 7A ; 
         FIG. 8A  is an elevation view of an embodiment of a tube bundle assembly capable of use in the vaporization system illustrated in  FIG. 6A ; and 
         FIG. 8B  is a cross-sectional end view of the tube bundle assembly illustrated in  FIG. 8A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will next be illustrated with reference to the Figures. Such Figures are intended to be illustrative rather than limiting and are included herewith to facilitate explanation of the present invention. The Figures are not to scale, and are not intended to serve as engineering drawings. 
     A flameless thermal oxidizer (FTO) has been coupled with a cryogenic heat exchanger according to one aspect of this invention to vaporize a liquid such as liquefied natural gas prior to injection into a utility distribution system. The resulting vaporization system minimizes oxides of nitrogen (NOx) emissions to the environment normally associated with conventional combustion processes. The thermal reaction of commercial fuel gas with air in a matrix bed of porous inert media is accomplished using the flameless thermal oxidizer. The reaction is optionally conducted in an apparatus that is capable of establishing and maintaining a non-planar reaction wave within the matrix bed. 
     Generally, and according to one exemplary embodiment, the vaporization system includes a vessel that contains a matrix bed; one or more feed tubes that extend into the matrix bed; a burner or other matrix bed preheat system; connecting ductwork to a heat exchanger (such as the Sub-X® heat exchanger provided by T-Thermal Company of Blue Bell, Pa.); process controls; and an exhaust outlet to the atmosphere. A non-planar reaction wave (such as the one formed by the oxidizer shown in  FIG. 3 , for example) is established by heating at least a portion of the matrix bed to the minimum reaction temperature of a commercial fuel gas/air mixture and feeding said mixture at controlled rates into the feed tube(s). Upon exiting the feed tube(s), the commercial fuel gas/air mixture is reacted in a non-planar reaction wave to produce heat and non-toxic combustion products. 
     The heat generated in the non-planar reaction wave maintains the interior surfaces of the vessel at a temperature of at least 1600 degree F. but less than 2400 degree F. during the entire operation, which minimizes the formation of NOx emissions. The hot exhaust gases are directed from the vessel through ductwork to a specialized cryogenic heat exchanger submerged in a water bath. Cryogenic liquids are directed through tubes in the interior of the heat exchanger as the quenched exhaust gases contact the exterior surfaces of the tubes via the water bath. The cryogenic fluid inside the heat exchanger completes a phase change to a gaseous product resulting from the flow of heated gases within the water bath. Exhaust gases exit the water bath and are released to the atmosphere via a stack. 
     The natural gas vaporization capacity of the system ranges from about 150 to 200 million cubic feet per day, dependent on operating pressure conditions. Heat release rate for the flameless thermal oxidizer is 120 MMBtu/hr, and the emission rate of nitrogen oxides is reduced. 
     The emissions of nitrogen oxides from the flameless oxidation process are approximately 2 ppmvd (corrected to 3 volume percent oxygen (dry basis)), which is significantly lower than the nitrogen oxide emissions from the burner exhaust of the current practice. The use of the flameless oxidation eliminates the need for water injection, as well as the post combustion catalytic NOx reduction treatment system. This elimination of the catalytic treatment system in turn eliminates the reoccurring use of both the catalyst and associated reducing agent (such as ammonia). Catalyst has a limited operating lifetime and is expensive to replace. The elimination of the reducing agent may make the system safer to operate by eliminating the storage and handling of ammonia. The elimination of the post catalytic treatment system along with the necessary heat input required to reheat the exhaust gases will increase the system energy efficiency by utilizing all of the flameless oxidation exhaust to heat the cryogenic fluid. 
     Referring to the Figures generally, and according to one aspect of this invention, a system  1 ,  100  is provided for vaporizing a cryogenic liquid. To heat or vaporize fluids such as cryogenic liquids, the system  1 ,  100  utilizes flameless oxidation to provide the heat input into a submerged heat exchanger coil. 
     The system  1 ,  100  includes means for producing an exhaust gas by flameless thermal oxidation of a fuel/air mixture. For example, the means for producing an exhaust gas optionally includes an oxidizer  2 ,  10 ,  40 ,  70 ,  108  having a matrix bed  29 ,  42 ,  72 , 112 ; a fuel/air mixture inlet  4 ,  54  positioned to deliver the fuel/air mixture to the matrix bed  29 ,  42 ,  72 , 112 ; and an exhaust outlet  5 ,  45 ,  78 A,  78 B,  114  positioned to deliver the exhaust gas from the oxidizer  2 ,  10 ,  40 ,  70 ,  108 . 
     The system  1 ,  100  also includes means for transferring heat from the exhaust gas to the cryogenic liquid. For example, the means for transferring heat optionally includes a vaporizer  3  having a receptacle  122  configured to hold a heat transfer medium; a conduit  118 ,  144  for cryogenic liquid extending into the receptacle; and a sparger  138  positioned to deliver exhaust gas from the exhaust gas producing means to the receptacle  122 . 
     The heat transferring means of the system  1 ,  100  is coupled to receive the exhaust gas from the exhaust gas producing means. In this manner, the products of reaction or oxidation in the exhaust gas producing means are delivered to the heat transferring means. Such heat transfer brings about vaporization of a cryogenic liquid. 
     In use of system  1 ,  100 , a fuel/air mixture is oxidized in a flameless thermal oxidizer  2 ,  10 ,  40 ,  70 ,  108  to produce an exhaust gas. Heat is then transferred from the exhaust gas to the cryogenic liquid, thereby vaporizing the cryogenic liquid. The oxidizing step optionally includes delivering fuel/air mixture into a matrix bed  29 ,  42 ,  72 , 112 , and the transferring step optionally includes introducing exhaust gas into a heat transfer medium such as water. 
     To modify or retrofit a vaporizer of cryogenic liquid according to one aspect of this invention, a flameless thermal oxidizer  2 ,  10 ,  40 ,  70 ,  108  is coupled to the vaporizer  3 , and the flameless thermal oxidizer  2 ,  10 ,  40 ,  70 ,  108  is configured to deliver exhaust gas to the vaporizer  3 . The coupling step optionally includes coupling an exhaust outlet  5 ,  45 ,  78 A,  78 B,  114  of the flameless oxidizer  2 ,  10 ,  40 ,  70 ,  108  to a sparger  138  of the vaporizer  3 . 
     To reduce NOx emissions according to another aspect of the invention, a fuel/air mixture is oxidized using a flameless thermal oxidizer  2 ,  10 ,  40 ,  70 ,  108 , and heat from exhaust gases generated by the oxidizing step is transferred to a cryogenic liquid. The NOx emissions can be reduced to less than about 5 ppmvd NOx, preferably about 4 ppmvd NOx or less, or more preferably about 2 ppmvd NOx or less, corrected to 3 volume percent oxygen (dry basis). The reduction of NOx emissions is optionally performed without catalytic treatment. 
     According to another aspect of this invention, a flameless thermal oxidizer  70  has a matrix bed  72  containing media, an inlet tube  80  extending into the matrix bed  72  and having an outlet positioned to deliver reacting gases into the matrix bed  72 . The matrix bed  72  defines a void  73  proximal the outlet of the inlet tube  80 . A disc  82  is optionally positioned adjacent the outlet of the inlet tube  80  and configured to direct reacting gases away from the inlet tube  80 . The void  73  is optionally substantially cylindrical. 
     To reduce pressure losses in a flameless thermal oxidizer, reacting gases can therefore be introduced from an inlet tube  80  into a void  73  defined by a matrix bed  72 . Also, plural exhaust outlets  78 A,  78 B can be provided to exhaust reacted gases from the oxidizer  70 . 
     It has been discovered that this invention provides an efficient vaporization technology with very low oxides of nitrogen emissions (NOx) resulting from the combustion of natural gas fuel. For example, a typical burner system may operate with up to 40 percent excess air in a LNG vaporizer as compared to approximately 175 percent excess air with a flameless thermal oxidizer. Such excess air is beneficial in that it limits the maximum adiabatic temperature achieved in the oxidizer to less than the Zeldovich reaction mechanism requirements for high levels of NOx production. Fuel consumption is unchanged when the burner and flameless thermal oxidizer technologies are compared, but the volume of gases handled by the equipment is significantly larger for a flameless thermal oxidizer system according to this invention. 
     A LNG vaporizer burner system together with water injection can produce NOx emissions in the range from 35 to 50 ppmvd. A LNG vaporizer using a flameless thermal oxidizer as the heat source according to this invention can produce NOx emissions in the range from 2 to 4 ppmvd, though NOx emissions lower than 2 ppmvd and greater than 4 ppmvd are contemplated as well (the foregoing NOx emissions values being corrected to 3 volume percent oxygen on a dry basis). 
     In order to reduce NOx emissions (e.g., to comply with NOx emission regulations), burner systems typically use post-combustion treatment processes involving a catalyst and injection of a reducing agent chemical. These post-combustion control systems tend to be expensive, difficult to maintain, and require periodic shutdowns for catalyst cleaning and replacement. 
     Referring specifically to the embodiments selected for illustration in the figures,  FIG. 1  provides a schematic illustration of an embodiment of a vaporization system, generally indicated by the numeral  1 , according to one aspect of this invention. Vaporization system  1  includes a flameless thermal oxidizer  2  that is coupled to a vaporizer  3 . The flameless thermal oxidizer  2  is configured to receive a fuel/air mixture  4  for reaction within the flameless thermal oxidizer  2 . Flameless thermal oxidizer  2  is also configured to deliver exhaust gases  5  that are produced as a result of the oxidation or reaction of the fuel/air mixture  4 . 
     The vaporizer  3  is configured to receive the exhaust gases  5  from the flameless thermal oxidizer  2 . The vaporizer  3  is also configured to receive a cryogenic liquid  6  and to deliver a vaporized gas  7 . Vaporizer  3  is also configured to deliver emissions  8 . 
     The hot exhaust gases  5  delivered from the flameless thermal oxidizer  2  to the vaporizer  3  causes vaporization of the cryogenic liquid  6  into a vaporized gas  7 . Accordingly, the heat from exhaust gases  5  provides a heat source for the vaporization of the cryogenic liquid  6 , and the exhaust gases  5  received in the vaporizer  3  from the flameless thermal oxidizer  2  are discharged from the vaporizer  3  in the form of emissions  8  either for further treatment or discharge to the atmosphere. 
       FIG. 2  illustrates an exemplary embodiment of a flameless matrix bed reactor, generally designated by the numeral  10 , which can be used in the vaporization system  1  illustrated in  FIG. 1  as a component of the flameless thermal oxidizer  2 . 
     Referring to  FIG. 2 , there is shown a schematic of the internal temperature zones in a flameless matrix bed reactor  10  that contains a planar reaction wave  22 . Additional details of the flameless matrix bed reactor  10  can be found in U.S. Pat. No. 6,015,540, which is incorporated herein by reference in its entirety. 
     The flameless reactor  10  includes a vessel  25 , having a matrix bed of porous inert media  29 . The vessel is lined with a refractory material. Prior to the planar reaction wave, there is typically a cool zone  27  that has a temperature below the uniform reaction temperature. After the planar reaction wave  22 , there will be a hot region  26  that is typically at least above 1200 degree F. By using temperature sensors  20 , the planar reaction wave  22  may be located within the matrix and moved to a desired point by controlling the output end of a process controller  28 . 
     While this planar reaction wave temperature profile is effective for oxidation, corrosive products or reactants (such as acid gases or their pre-cursors) can tend to condense in the cool zone  27  on the interior surfaces  23  of the vessel  25 . This condensation can occur when the corrosive products or reactants migrate through the lining of refractory material  24  adjacent to the interior surfaces  23  of the vessel  25 . Additionally, if the vessel is constructed of heat resistant metal alloys, and there is no internal lining of refractory material, corrosive products or reactants can still condense on the interior surfaces of the vessel in the cool zone  27 . This condensation in turn can lead to corrosion of the interior surfaces of the vessel. Consequently, the life of the vessel can be reduced and/or more expensive materials of construction may be needed to improve corrosion resistance 
       FIG. 3  shows another embodiment of a flameless matrix bed reactor  40 , which can be used to oxidize one or more chemicals. Additional details of the flameless matrix bed reactor  40  can be found in U.S. Pat. No. 6,015,540. 
     Referring to  FIG. 3 , a flameless matrix bed reactor, generally designated by the numeral  40 , is capable of use in the vaporization system  1  illustrated in  FIG. 1  as a component of the flameless thermal oxidizer  2 . 
     As shown in  FIG. 3 , the flameless matrix bed reactor includes a vessel  41 , containing a matrix bed  42  of porous inert media; a vessel refractory lining  63 , located adjacent to the vessel interior surfaces  64 ; a feed tube  43  for receiving a reactable process stream  44 , where a portion of the feed tube  43  that passes through the vessel is insulated with a refractory lining  62 ; an exhaust outlet  45  for removing reacted process stream  46 ; and a void space  47  located above the matrix bed  42 . The matrix bed  42  is heated by introducing a heated medium (flue gases generated by a conventional fuel gas burner)  48 , such as air, through a heating inlet  49 . The reactable process stream is formed by combining in a mixing device  50  a fume stream  51  containing an oxidizable material, an optional oxidizing agent stream  52  (such as air or oxygen), and an optional supplementary fuel gas stream  53 . 
     After the reactable process stream is formed, it is fed into a feed inlet  54  of the feed tube  43 . The reactable process stream is then directed to the exit  55  of the feed tube  43 . A non-planar reaction wave  56  is established in the matrix bed located in a region approximately around the exit  55  of the feed tube  43  and the bottom  57  of the vessel. The reactable process stream  44  is reacted (in this embodiment oxidized) in the non-planar reaction wave  56  to produce the reacted process stream  46 . The reacted process stream  46  is directed through the matrix bed  42 , through the void space  47 , and out the exhaust outlet  45 . 
     The exhaust outlet  45  is positioned so that the reacted process stream  46  prior to exiting the vessel  41  flows countercurrent to the flow direction in the feed tube  43 . The exhaust outlet  45  may be connected to either the void space  47  or matrix bed  42 . However, it is preferred that the exhaust outlet be connected to the void space  47 . Temperature sensors  58  may be used for monitoring the temperature in the flameless matrix bed reactor  40 . A process controller  59  may be used for accepting input from the temperature sensors  58  and, in response thereto, controlling the flow rate of the reactable process stream  44 , the fume stream  51 , the optional oxidizing agent stream  52 , the optional supplementary fuel gas stream  53 , and/or the heated medium  48  (e.g., flue gases generated by a conventional fuel gas burner). 
       FIG. 4  shows a schematic, perspective view of a flameless thermal oxidizer, generally indicated by the numeral  70 , that can be used as a component of the flameless thermal oxidizer  2  of the vaporization system  1  illustrated in  FIG. 1 . Flameless thermal oxidizer  70  includes a matrix bed  72  that extends upwardly to a top surface  74 . The top surface  74  of the matrix bed  72  at least partially defines an oxidizer head space  76 . 
     Dual, opposed exhaust ducts  78 A and  78 B are positioned to exhaust reacted gases from the oxidizer head space  76 . Specifically, reacted gases that enter the oxidizer head space  76  from the matrix bed  72  are delivered from the flameless thermal oxidizer  70  via exhaust ducts  78 A and  78 B. The provision of dual, opposed exhaust ducts such as ducts  78 A and  78 B has been discovered to reduce the pressure losses encountered by the flameless thermal oxidizer  70 . 
     Flameless thermal oxidizer  70  also includes a premixed gas dip tube  80  that extends downwardly into the matrix bed  72  in order to deliver a premix of gas into the matrix bed  72  at a location below the top surface  74  of the matrix bed  72 . The dip tube  80  has a dip tube outlet diverter disc  82  positioned adjacent the outlet of the premixed gas dip tube  80 . The disc  82  helps to divert reaction gases away from the wall of the dip tube. 
     Referring now to  FIG. 5 , a modification to the flameless thermal oxidizer  70  illustrated in  FIG. 4  is shown. Specifically, as illustrated in  FIG. 5 , the flameless thermal oxidizer  70  is provided with a modification to its matrix bed  72  in order to improve the performance of the flameless thermal oxidizer  70 . A void is created in the ceramic media bed or matrix bed  72  just beneath the dip tube outlet SO that gases can flow with less restriction into the matrix bed  72  to lower pressure losses in the flameless thermal oxidizer  70 . The void is provided in the form of a cylindrical voidage  73 . In one exemplary embodiment, the voidage  73  has a diameter of about 8 feet (corresponding roughly to the diameter of the dip tube outlet diverter disc  82 ) and a depth of about 3 feet. 
     While the embodiment of the voidage  73  illustrated in  FIG. 5  is substantially cylindrical in shape, it is contemplated that the voidage may have a wide variety of geometric shapes (e.g., spherical or semi spherical, elliptical, rectangular, or other geometric configurations). 
     Referring now to  FIGS. 6A and 6B , another embodiment of a vaporization system, generally indicated by the numeral  100 , is illustrated. Vaporization system  100  includes a blower  102  configured to urge air into the vaporization system  100 . Downstream from the blower  102  is a start-up burner  104  used during start-up of the vaporizer system  100  to preheat the matrix bed (described later). Also downstream from the blower  102  is a fuel-air mixer  106  configured to mix fuel with the air introduced by the blower  102 . 
     The vaporization system  100  also includes a flameless thermal oxidizer vessel  108  configured to receive the fuel-air mix provided by the fuel-air mixer  106 . The flameless thermal oxidizer vessel  108  generates the heat that is used to vaporize liquid in the vaporization system  100 . Specifically, hot gas is delivered from the flameless thermal oxidizer vessel  108  via a hot gas duct  114 . 
     From hot gas duct  114 , hot gas is introduced into an SCV tank  122 . Gases are then delivered from the SCV tank  122  by means of an exhaust separator  124  and an exhaust stack  126 . 
       FIG. 6C  is another elevation view of the vaporization system  100 , with wall portions removed to reveal internal details of the flameless thermal oxidizer vessel  108  and the SCV tank  122 . The illustration in  FIG. 6C  also indicates the flow pattern of flue gases, indicated by arrows, in the flameless thermal oxidation vessel  108 . 
     The flameless thermal oxidation vessel  108  includes a dip tube  110  that extends downwardly into a ceramic packing  112 . A mix of fuel and air is delivered through the dip tube  110  into the ceramic packing  112  for oxidation or reaction within the ceramic packing  112 . The flue gases resulting from the reaction oxidation of the mixture of fuel and air travels upwardly through the ceramic packing  112  into a space above the ceramic packing  112  within the flameless thermal oxidation vessel  108 , as indicated by the arrows in  FIG. 6C . The flue gases are then urged outwardly from the flameless thermal oxidation vessel  108  and into the hot gas duct  114  for delivery to the SCV tank  122 . The hot gas duct  114  is preferably insulated in order to reduce loss of heat from the flue gases. 
     The SCV tank  122  is at least partially filled with a heat transfer medium such as water or other suitable medium. In operation, hot flue gases from the flameless thermal oxidizer vessel  108  are introduced into the heat transfer medium such that it bubbles through the heat transfer medium, heats the heat transfer medium, and brings about heat transfer from the heat transfer medium to cryogenic liquid flowing through a tubing bundle situated in the heat transfer medium. 
     More specifically, the SCV tank  122  includes a manifold and distributor system such as assembly  116  connected to receive hot flue gases from the hot gas duct  114 . Details of the manifold and distributor assembly will be described later with reference to  FIGS. 7A-7D . The SCV tank  122  also includes a tube bundle  118  through which cryogenic liquid is circulated for vaporization. Further details of the tube bundle  118  will be described later with reference to  FIGS. 8A and 8B . Liquid natural gas inlet and natural gas outlet manifolds are provided in the SCV tank  122  as indicated by numeral  120 . It is by means of the inlet and outlet manifolds  120  that liquid natural gas is introduced into the tube bundle and the resulting natural gas is discharged from the tube bundle. 
     Referring now to  FIGS. 7A through 7D , details of an embodiment of a manifold and distributor assembly are illustrated. The manifold and distributor assembly, such as assembly  116 , is configured to receive hot gases from the hot gas duct  114  and to deliver those hot gases into the heat transfer medium (e.g., water) in the SCV tank  122 . More specifically, the manifold and distributor assembly  116  receives a stream of heated gas and divides that gas for substantially even distribution into the SCV tank to encourage heat transfer between the hot gases, the heat transfer medium, and ultimately the cryogenic liquid such as liquid natural gas circulating within the tube bundle  118 . 
     Referring specifically to  FIG. 7A , the manifold and distributor assembly  116  includes a shell  128  that is substantially cylindrical in shape, though other cross-sectional shapes are contemplated as well. Shell  128  is coupled to the hot gas duct  114  by means of a flange  130 . The opposite end of the shell  128  is capped by a plate  132 . Plural lifting lugs  134  are provided along a top surface of the shell  128  in order to facilitate the handling of the shell  128  during assembly, disassembly, modification and/or maintenance. Plural supports  136  are provided to support the shell  128  against a foundation of the SCV tank  122  (not shown). 
     In order to facilitate the distribution of hot gases from within the shell  128  to the heat transfer medium, the manifold and distributor assembly  116  is provided with plural spargers  138 . Each sparger  138  extends outwardly from the shell  128  and is connected to the shell  128  in order to receive hot gases from the shell  128  and to deliver the hot gases to the heat transfer medium within the SCV tank  122 . 
     Referring to  FIG. 7B , which provides an end view of the manifold and distributor assembly  116 , the relationship between the sparger  138  and the shell  128  of the manifold and distributor assembly  116  can be seen. Specifically, each sparger  138  extends outwardly from a lower portion of the shell  128  at an angle substantially transverse to the axis of the shell  128 . 
     Referring to  FIG. 7C , which provides a cross-sectional end view of the manifold and distributor assembly  116 , each sparger  138  is provided with a closed end  140  and a plurality of openings  142  (generally positioned along its upper surface) to permit the flow of hot gases from within the sparger  138  to the heat transfer medium in the SCV tank  122 . 
       FIG. 7D  provides a plan view of a portion of a sparger  138 . Each sparger  138  includes plural rows of openings  142  (two such row shown in  FIG. 7D ). By means of openings  142 , hot gas flows from within each sparger  138  and into the heat transfer medium in the SCV tank  122 . 
     While a specific embodiment of a manifold and distributor assembly  116  is shown in the Figures for purposes of illustration, a wide variety of configurations can be used in order to deliver hot gases to a heat transfer medium. Depending on a particular application or size constraints for a vaporization system, the manifold and distributor assembly can have a wide variety of shapes, sizes, and configurations. Preferably, however, the assembly will be configured to distribute hot gases substantially evenly into heat transfer medium so that heat can be substantially evenly distributed for the vaporization of cryogenic liquid. 
     Referring now to  FIGS. 8A and 8B , an exemplary embodiment of a tube bundle configured for use in the SCV tank  122  is illustrated. The tube bundle  144  illustrated in  FIG. 8A  includes four (4) tubes, each extending from an inlet  146  for liquid natural gas (or other cryogenic liquid) to an outlet  148  for vaporized natural gas (or other gas). The inlet  146  and outlet  148  of tube bundle  144  correspond to the inlet and outlet manifolds  120  illustrated in  FIG. 6C . 
     As illustrated in  FIG. 8B , which provides a cross-sectional end view of tube bundle  144  (with the tubes removed for clarification), the inlet  146  and outlet  148  are provided with a plurality of openings for connection to tube bundles such as tube bundle  144 . Accordingly, a plurality of tube bundles  144  are positioned next to each other and are connected for fluid flow communication with the inlet  146  and outlet  148  in order to provide a dense population of flow passages through which a cryogenic fluid can be passed for vaporization. For example, inlet  146  and outlet  148  can accommodate up to fifteen (15) or more tube bundles  144 , each tube bundle  144  including four (4) tubes. In such an embodiment, the tube bundle assembly will provide sixty (60) tubes for the flow of cryogenic liquid such as liquid natural gas (LNG). Each tube bundle  144  can also have fewer or more than four tubes, and the tube bundle assembly can have fewer or more than fifteen (15) rows of tube bundles. 
     EXAMPLE 
     According to one aspect of this invention, a flameless thermal oxidizer can be modified to create a cylindrical void at the diptube outlet. Also, a flat disc can be added to the end of the diptube to direct reacting gases away from the diptube walls. These modifications were run on a CFD model and resulted in a significant reduction in pressure losses and also changed the shape of the reaction wave to force improved containment of the reaction gases within the ceramic media bed. 
     The flameless thermal oxidizer was setup in the CFD model with a 60 inch ID by 20 foot long diptube. The ceramic media was simulated as 1 inch saddles, such as those used in commercial applications, packed to a depth of 16 feet. The diptube was simulated as being immersed 8 feet into the ceramic media bed. Two rectangular exhaust ducts were simulated to be used to convey flue gases from the surface of the ceramic media bed. The ducts were simulated to be installed 180 degrees apart in the headspace above the ceramic media bed. Dimensions for the ducts were simulated to be 2.5 feet high by 15 feet wide by 10 feet in length. The outlet of the diptube was simulated to be fitted with an 8 foot diameter disc to divert reaction gases away from the diptube wall. A void was simulated to be created in the ceramic media bed directly beneath the diptube outlet so that gases could flow with less restriction in an attempt to lower pressure losses in the flameless thermal oxidizer. The void was simulated to be a cylindrical volume 8 feet in diameter and 3 feet in height. 
     The LNG vaporizer was simulated to exert a 60 inch water column back pressure on the heat source due to pressure losses in the heat exchanger tube bundle and water bath. Addition of the disc to the diptube outlet and the void constructed in the ceramic medial bed significantly reduced the pressure losses in the flameless thermal oxidizer. The reduction in pressure losses was simulated to be approximately 45 inches WC, yielding a total pressure loss across the flameless thermal oxidizer of only 17 inches WC. 
     According to the simulation, the velocity of the premixed gases traveling down the diptube is approximately 50 feet per second. The total mass flow rate is approximately 4400 lbs/min yielding a heat release of 122 MMBtu/hr HHV. Combustion air is supplied at the rate of 4311 lbs./min and fuel gas at the rate of 86.26 lbs/min and, according to the simulation, the composition of the flue gases in volume percent is as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Component 
                 Volume Percent 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Oxygen 
                 13.38 
               
               
                   
                 Nitrogen 
                 76.54 
               
               
                   
                 Carbon Dioxide 
                 3.32 
               
               
                   
                 Water Vapor 
                 6.77 
               
               
                   
                   
               
            
           
         
       
     
     The gas velocity profile has been discovered to be significantly different in the ceramic bed with the optional cylindrical voidage beneath the diptube outlet, which contributes to a significant reduction in static pressure losses. Specifically, the temperature profile within the flameless thermal oxidizer after having installed the diptube exit disc and the voidage beneath the diptube differs from that of a flameless thermal oxidizer having ceramic media packing at the diptube discharge point and no disc attached to the diptube outlet. Also, it has been discovered that less carbon monoxide is present in the headspace above the ceramic media surface as compared to the unmodified oxidizer model. Although carbon monoxide burnout is achieved prior to the exhaust ducts in both designs, this feature is an improvement and lends more operational flexibility to the process. 
     The CFD modeling results for a flameless thermal oxidizer with a diverter disc mounted on the discharge of the diptube and a cylindrical voidage located beneath the diptube discharge have indicated a significant reduction in static pressure losses across the oxidizer. This improvement benefits the operating economics for the flameless thermal oxidizer in the LNG vaporizer application. Pressure losses across the flameless oxidizer now amount to only 17 inches WC. 
     Assuming that the pressure loss across the LNG vaporizer heat exchanger is not impacted by the flameless thermal oxidizer flue gas flow rate, then the total system pressure loss has been reduced from 122 inches WC to 77 inches WC. This represents a 37 percent reduction in pressure losses with the flameless thermal oxidizer modifications presented here. The pressure loss reduction across the flameless thermal oxidizer alone is a significant 72.6 percent with the modified design. 
     The temperature profile indicates that the reaction wave is better confined to the ceramic media bed with the modified design. While it has been generally considered acceptable for there to be some cold gas breakout into the headspace without a loss in performance, the reaction wave should remain within the ceramic media bed in order to increase the robustness of the flameless thermal oxidizer and reduce any perception of loss in performance associated with cold gas breakout. 
     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. 
     For example, the specific structures of the vaporizer and the flameless thermal oxidizer are not critical to the invention and may be modified within the scope of this invention. A wide variety of heat sources and heat exchangers can be utilized according to aspects of this invention. Similarly, the orientation of a heat exchanger (such as a vaporizer) with respect to the heat source (such as a flameless thermal oxidizer) can be modified to meet specific operating parameters. 
     While preferred embodiments of the invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the spirit of the invention. Accordingly, it is intended that the appended claims cover all such variations as fall within the spirit and scope of the invention. 
     What is claimed: