Patent Publication Number: US-2023158472-A1

Title: Heat transfer packing element

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Application Ser. No. 63/283,134 filed Nov. 24, 2021, and entitled “Heat Transfer Packing Element,” which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This present disclosure relates generally to heat transfer media, and more particularly to packing elements for use in packed beds of a heat-exchange apparatus. 
     BACKGROUND 
     Several operations in the chemical process industry require transferring a fluid medium through a process vessel to effect a change in the fluid medium. As used herein, a fluid medium may be a gas or a liquid. A process vessel may be filled with a quantity of packing elements to create a packed bed through which the fluid media is transferred during an operation. The shape and packing arrangement of the packing elements may have a significant impact several aspects of the process, including the pressure drop across the packed bed and the amount of heat exchanged between the fluid media and the packing elements. 
     An exemplary application for a packed bed is as a heat transfer media used with a regenerative thermal oxidizer (RTO). RTOs are commonly used to convert pollutants in a contaminated vapor stream into less harmful combustion products prior to discharge of the vapor stream to an environment. 
     Regenerative thermal oxidizers typically include a combustion chamber in which a contaminated vapor stream is subjected to a process where oxidization of the pollutants in the vapor stream occurs. In addition, RTOs typically include two or more heat transfer columns which increase the efficiency of the oxidation process in the combustion chamber by using the hot combusted vapor stream from the combustion chamber to preheat a first heat transfer column. The contaminated vapor stream is then passed through the preheated first heat transfer column prior to entering the combustion chamber so that heat is transferred from the packing elements in the first heat transfer column to the contaminated vapor stream. While the contaminated vapor stream is passing through the first heat transfer column, the hot combusted vapor stream is being directed through second heat transfer media in a second heat transfer column to cause heating thereof. The combusted and contaminated vapor streams may alternate between the first and second heat transfer columns. The packing elements absorb heat from the combusted vapor stream and subsequently transfer the heat to the contaminated vapor stream. 
     Desirable characteristics of the packing material used in a packed bed are a low pressure drop for the gas flowing through the bed and high efficiency in transferring heat to and from the gas stream. These characteristics are influenced by the surface area of the packing element for contact with the gas stream. In addition, a packing element design should not pack tightly together or nest closely to avoid restricting fluid flow through the packed bed. 
     SUMMARY OF THE EMBODIMENTS 
     A packing element optimizes surface area and packing behavior while maintaining mechanical strength of the packing element. 
     In a first aspect, a packing element for use in a heat exchange or mass transfer tower optimizes surface area and packing behavior while maintaining mechanical strength of the packing element. The packing element includes a barrel and a plurality of fins spaced around a circumference of the barrel, each fin having a height approximately equal to a height of the barrel and a length extending radially from the barrel, a proximate end of each fin attached perpendicularly to the barrel. 
     In a second aspect, a method for mass transfer includes passing fluids through a vessel packed with randomly arranged packing elements. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    is a fragmentary schematic side view of an exemplary regenerative thermal oxidizer with mass transfer columns, in embodiments. 
         FIG.  2    is a perspective view of a heat transfer packing element, in embodiments. 
         FIG.  3    is a top view of the heat transfer packing element of  FIG.  2   . 
         FIG.  4    is a side view of the heat transfer packing element of  FIG.  2   . 
         FIG.  5    is a side view of a exemplary mass transfer column with a packed bed of heat transfer elements, in embodiments. 
         FIG.  6    is a top view of the mass transfer column of  FIG.  2   . 
         FIG.  7    is a more detailed side view of the mass transfer column of  FIG.  5   . 
         FIG.  8    is a graph of pressure drop per air velocity for a packed bed of  FIG.  5   , in embodiments. 
         FIG.  9    is a perspective view of a heat transfer packing element, in embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The principles according to the present disclosure may have particular application to heat transfer media for regenerative thermal oxidizers, and thus will be described below chiefly in this context. It is also understood, however, that principles and aspects according to the present disclosure may be applicable to heat transfer media for other regenerative heat exchange systems, or other systems used to convert pollutants of a contaminated vapor stream into less harmful combustion products prior to discharge of the vapor stream to the environment, such as thermal oxidizers, flare thermal oxidizers, catalytic oxidizers, recuperative oxidizers, or the like. 
     In the discussion above and to follow, the terms “upper”, “lower”, “top”, “bottom,” “end,” “inner,” “left,” “right,” “above,” “below,” “horizontal,” “vertical,” “longitudinal,” “lateral,” etc. refer to an exemplary stackable plate, or an exemplary heat transfer block, as viewed in a horizontal position, for example. This is done realizing that these units, such as when used in a regenerative thermal oxidizer, can be packed sideways or on various ends, or can be provided in various other positions. Furthermore, it is understood that the terms “upstream,” “downstream,” “leading,” and “trailing” refer to the arrangement of an exemplary stackable plate or an exemplary heat transfer block as fluid flows in an overall direction through a heat transfer column of a regenerative thermal oxidizer. Such an overall direction of fluid flow is shown generally in the various figures with reference to the directional arrows designated “F.” This is done realizing that fluid may flow in various other directions depending on the orientation of the units in the heat transfer column, or the direction of flow through the heat transfer column. 
     Turning now to  FIG.  1   , a representative regenerative thermal oxidizer (RTO)  10  is shown. RTO  10  is used to remove pollutants contained in a vapor stream by oxidizing them, and typically converting them into carbon dioxide and water. The regenerative thermal oxidizer  10  comprises a single combustion chamber  12  containing a burner  14  which causes oxidation of the pollutant-laden or contaminated vapor stream to form a clean vapor stream. RTO  10  also includes three separate heat transfer columns  16 ,  18  and  20  which are in fluid flow communication with the combustion chamber  12  and through which the contaminated vapor stream and clean vapor stream alternately flow on their way to and from the combustion chamber. 
     The contaminated vapor stream may be directed from its source to each of the heat transfer columns  16 ,  18  and  20  through a supply line  21  and separate inlet lines  22  containing flow control valves  24 . The clean vapor stream may be removed from the heat transfer columns by separate outlet lines  26  which also contain flow control valves  28  and feed a common discharge line  29 . A purge gas may also be directed to the heat transfer columns through separate inlet purge lines  30  containing flow control valves  32  and connected to a common supply line  33 . A portion of the clean vapor stream may be used as the source of the purge gas and a tap line  34  is provided between the clean vapor stream discharge line  29  and purge gas supply line  33  for this purpose. 
     The contaminated vapor stream flows through supply line  21  and is fed through inlet line  22  into the center heat transfer column  18 . The contaminated vapor stream flows through the heat transfer column  18  and undergoes heat exchange before it enters the combustion chamber  12  where it is combusted to form the clean vapor stream. The clean vapor stream is removed from combustion chamber  12  through the adjacent heat transfer column  16  and is then removed from the column through outlet line  26  and discharge line  29 . Purge gas may be concurrently fed to the other heat transfer column  20  through supply line  33  and purge line  30 . As the purge gas passes through the heat transfer column  20 , it removes any contaminated vapor from the column  20  and carries it to the combustion chamber  12  for cleaning. The flow paths of the vapor streams as described above are regulated by selective opening and closing of the flow control valves  24 ,  28  and  32 . 
     Because the clean vapor stream leaves the combustion chamber  12  at a high temperature, it is desirable to transfer heat from the clean vapor stream to the contaminated vapor stream to improve process efficiency. This is achieved by manipulating the flow control valves  24 ,  28  and  32  to cause the contaminated vapor stream to be redirected from heat transfer column  18  to the heat transfer column  16  which has been heated by the clean vapor stream. As the contaminated vapor stream flows through the heated column  16  it increases in temperature until it exits the column and enters the combustion chamber  12  at a much hotter temperature than when it entered the column. At the same time, the clean vapor stream is redirected from heat transfer column  16  to heat transfer column  20  which has been purged of contaminated vapor. The clean vapor stream enters heat transfer column  20  from combustion chamber  12  at a very high temperature and then exits the opposite end of the column  20  at a reduced temperature, having undergone heat exchange within the column  20 . Purge gas is in turn directed through column  18  to remove residues of the contaminated vapor stream. 
     It will be appreciated that after a period of time, column  16  through which the contaminated vapor stream is flowing will have cooled as a result of heat exchange such that it does not provide the desired degree of preheating of the contaminated vapor stream. The contaminated vapor stream must then be switched to column  20  which has been heated by the clean vapor stream. The clean vapor stream is concurrently redirected to the purged heat transfer column  18  and purge gas is directed to the cooled column  16  to remove residue of the contaminated vapor stream. This repeated cycling of the vapor streams among the heat transfer columns allows the regenerative thermal oxidizer to be continuously operated while providing for indirect heat exchange between the respective vapor streams. 
     It is understood that the placement of the combustion chamber  12  in relation to the heat transfer columns  16 ,  18  and  20  can be varied from the illustrated embodiment. For example, the combustion chamber  12  could be placed below or to either side of the heat transfer columns. When the combustion chamber is to one side of the columns the flow through the columns is generally horizontal. 
     As a representative example of a regenerative thermal oxidizer, each of transfer columns  16 ,  18  and  20  include heat transfer blocks  36 . Generally, a heat transfer block  36  includes solid surfaces that define fluid flow passages  38  for enabling fluid passing therethrough to undergo heat exchange as the fluid flows through the passages. However, other arrangements of heat transfer media are possible, such as a packed bed of packing elements. 
       FIG.  2    is a perspective view of a heat transfer packing element.  FIG.  3    is a top view and  FIG.  4    is a side view of the heat transfer packing element of  FIG.  2   .  FIGS.  2 - 4    are best viewed together in the following discussion. 
     Packing element  200  includes a barrel  202  having a central axis  212  and a radial axis  214  perpendicular to central axis  212 . A plurality of fins  204  are positioned around the circumference of barrel  202 . In an embodiment, packing element  200  is depicted with five fins  204  but any number between three and seven may be used. Barrel  202  is generally cylindrical with a height H B  along central axis  212 . Barrel  202  is open on both ends, with an interior cavity  210 . In embodiments, height H B  is approximately one inch but any height between approximately 0.5 and 2 inches may be used. 
     Fins  204  have a height H F  and a length L along radial axis  214 . Height H F  is approximately the same as height H B  but may be greater or less than H B , ranging from approximately 0.25 inches to 2 inches. In embodiments, length L is approximately 0.5 inches but any length between approximately 0.25 inches to 1 inch may be used. A proximate end of each fin  204  relative to central axis  212  is attached to barrel  202  perpendicularly to a tangent of a circumference of the barrel at the attachment point. In embodiments, fins  204  are spaced evenly around the circumference of barrel  202 . Each fin  204  has a thickness T 1  along most of its length L. In embodiments, fin  204  has a slightly larger thickness T 2 &gt;T 1  where it is attached to barrel  202 . The extra thickness provides a stronger attachment between fin  204  and barrel  202  to help prevent fins from breaking off. In embodiments, thickness T 1  may be approximately 0.125 to 0.375 inches. 
     The distal end of each fin  204  has a protrusion  206  which may extend away from fin  204  in a direction perpendicular to radial axis  214 . In embodiments, protrusion  206  may extend along the full height of fin  204 . As depicted in  FIGS.  2 - 4   , protrusion  206  has a generally oval cross-section along the height H F  of fin  204 , and a thickness T 3  the extends perpendicularly from both sides of fin  204 . In embodiments, T 3  may be approximately equal to T 1  up to about 2.5 times T 1 . Protrusion  206  assists with vapor flow through a packed bed of packing elements  200 . Without protrusion  206 , fins  204  would be flat and thus, packing elements  200  may load in a way that fins from different packing elements  200  could rest against each other without a gap between. This may make the faces that touch less ineffective since it would be more difficult for vapor to flow between them. Protrusions  206  prevent this face-to-face contact. Additionally, protrusions  206  make fins  204  stronger and more resistant to breakage. 
     Although protrusions  206  are shown in  FIGS.  2 - 4    with a certain cross-section, this is for the purposes of illustrating principles disclosed herein. In embodiments, protrusions  206  may have other cross-sections, such as a circle or diamond, for example. In embodiments, packing elements  200  may not include protrusions  206 , as shown for packing element  900  shown in  FIG.  9   , which is an example of the packing element  200 . Packing element  900  includes all of the features of packing element  200  except protrusions  206 , and thus the description of packing element  200  applies equally to packing element  900 . For clarity of illustration, axis  214  and various dimensions are shown for one of fins  204  but may apply to all fins  204  attached to barrel  202 . 
     In embodiments, barrel  202  includes radial holes  208  between fins  204 . Radial holes  208  provide a passage between interior cavity  210  and the exterior of packing element  200 . As shown, radial holes  208  are centered at approximately a midpoint of height H B  and have an oblong shape, although any shape for radial holes  208  may be used. Radial holes  208  provide an additional flow path through a packed bed of packing elements  200 . These additional flow paths ensure that all parts of packing element  200  take part in the heat transfer process, and also reduce the pressure drop across the packed bed. As shown in  FIG.  3    the number of radial holes  208  is the same as the number of fins  204 , but more or fewer radial holes may be used. 
     Collectively, fins  204  define an outer circumference OC and an outer diameter OD of packing element  200 . Outer diameter OD may be between approximately 0.5 and 6 inches. The ratio of outer diameter OD to height H B  defines an aspect ratio for packing element  200 . The aspect ratio of packing element  200  affects the way the packing element loads into a bed, which affects the performance. In embodiments, an aspect ratio of packing element  200  is 1:1 but any aspect ratio up to 3:1 may be used. 
     In embodiments, packing element  200  is a ceramic product. Ceramic has performance advantages over plastic and metal, for example, in that it can withstand higher temperatures and has a greater capacity to absorb and release heat, however, any suitable material may be used depending on the fluid media and expected operational temperatures. 
     The barrel and fin configuration of packing element  200  provides several advantages. By providing fins with a shaped protrusion on the distal ends, a plurality of packing elements  200  may be randomly installed in a packed bed or transfer column to provide minimum pressure drop during a heat transfer process while maximizing the available surface area for contact with a fluid medium. In addition, the construction of packing element  200  accomplishes these objectives without sacrificing the strength of the element. Radial holes through the barrel are sized to facilitate drainage of a fluid medium through the packed bed without weakening the barrel and increasing the likelihood that the element will break during use. 
       FIG.  5    is a side view of a mass transfer column with a packed bed of heat transfer packing elements  200 .  FIG.  6    is a top view of the mass transfer column of  FIG.  5   .  FIG.  7    is a more detailed view of  FIG.  5   , in embodiments.  FIGS.  5 - 7    are best viewed together in the following discussion. The mass transfer column of  FIGS.  5 - 7    is an example of columns  16 ,  18  and  20  of  FIG.  1   . Embodiments discussed herein are exemplary and it should be understood that packing element  200  may be used similarly in a wide variety of industrial applications where it is desirable to transfer heat from one fluid to another. 
     Mass transfer column  500  as depicted is generally cylindrical, with a perimeter wall  502 . In embodiments, a circular cross-section is not required, and other cross-sections are contemplated. Mass transfer column  500  may also include additional components and structural features that are not shown in  FIGS.  5 - 7   . A quantity of packing elements  200  are randomly arranged through a height of mass transfer column  500  by generally placing them into mass transfer column  500  and leveling by any suitable method. A fluid medium may be passed through mass transfer column  500  in either an upward or a downward direction relative to the axis of the column. In embodiments, a fluid medium may enter mass transfer column  500  from a side of the column. The quantity of packing elements  200  depicted in  FIGS.  5  and  6    is representative and any quantity may be used. 
     Packing elements  200  have a barrel and fin arrangement that provides mechanical strength with reduced nesting which improves fluid flow through mass transfer column  500 . Packing elements  200  are randomly placed in mass transfer column  500  such that there is no common orientation for adjacent packing elements  200  or groups of packing elements. Any two adjacent packing elements  200  may have different spatial orientations as explained in connection with  FIG.  7   . 
       FIG.  7    illustrates a quantity of packing elements  200 , and specifically identifies packing elements  702 ,  704 ,  706 ,  708  and  710  to illustrate how the structure of packing element  200  reduces nesting and packing density. To illustrate principles discussed herein, five packing elements are identified but all packing elements in  FIG.  7   , as well as  FIGS.  5  and  6   , are examples of packing element  200 . As shown, packing element  702  has a central axis  712 , packing element  704  has a central axis  713 , and packing element  706  has a central axis  716 . Likewise, packing element  708  has a central axis  718  and packing element  710  has a central axis  720  Central axes  710 ,  712 ,  714 ,  716  and  720  are examples of central axis  212 . As shown in  FIG.  7   , axes  710 ,  712 ,  714 ,  716  and  720  have random orientations with respect to three-dimensional axis  714  in that their orientations different in all three dimensions relative to each other. 
     Once placed in a packed bed, packing elements having different design parameters may be compared to each other based on their specific surface area, which may be evaluated based on the pressure drop across the packed bed in the direction of fluid flow. The lower the pressure drop across the bed; the less energy is required to force fluid through the bed and operate the unit. 
       FIG.  8    is a graph of pressure drop (dP, mmHg/ft) versus air velocity (Fs, (ft/s)(lb/ft 3 ) 0.5 ) for a packed bed of packing elements  200  as compared with a prior art packing element, for example the packing element disclosed in U.S. Pat. No. 6,547,222.  FIG.  8    shows the performance of packing element  200  as line  802  and the performance of a prior art packing element as line  804 . As shown in the graph of  FIG.  8   , packing element  200  has a 15% lower pressure drop and 15% greater efficiency than a prior art packing element. Data supporting the graph of  FIG.  8    is shown in Table 1: 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Prior Art Packing Element 
                   
                 Packing Element 200 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Fs 
                 dP 
                 Fs 
                 dP 
               
               
                   
                   
               
               
                   
                 0.499 
                 0.069 
                 0.502 
                 0.046 
               
               
                   
                 1.009 
                 0.385 
                 1.002 
                 0.304 
               
               
                   
                 1.510 
                 0.885 
                 1.505 
                 0.722 
               
               
                   
                 2.013 
                 1.568 
                 2.005 
                 1.304 
               
               
                   
                 2.521 
                 2.452 
                 2.510 
                 2.068 
               
               
                   
                 3.027 
                 3.525 
                 3.016 
                 3.010 
               
               
                   
                   
               
            
           
         
       
     
     In embodiments, packing elements  200  have a higher specific surface area than the prior art packing element, as shown in Table 2. This contributes to the lower pressure drop across a packed bed of packing elements  200 , as shown  FIG.  8   . 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Piece 
                 Piece 
                 Piece 
                 Specific 
                   
               
               
                   
                 Area 
                 Volume 
                 Density 
                 Surface Area 
                 Void 
               
               
                 Name 
                 [in2] 
                 [in3] 
                 [pcs/ft3] 
                 [ft2/ft3] 
                 Fraction 
               
               
                   
               
             
            
               
                 Prior Art 
                 7.20 
                 0.356 
                 1230 
                 61.53 
                 0.747 
               
               
                 Packing 
                 7.13 
                 0.377 
                 1309 
                 64.82 
                 0.714 
               
               
                 Element 200 
               
               
                   
               
            
           
         
       
     
     Changes may be made in the above methods and systems without departing from the scope hereof. It should thus be noted that the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. Herein, and unless otherwise indicated: (a) the adjective “exemplary” means serving as an example, instance, or illustration, and (b) the phrase “in embodiments” is equivalent to the phrase “in certain embodiments,” and does not refer to all embodiments. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.