Abstract:
A valve for controlling the flow of a waste gas stream received from an industrial process is disclosed. The valve includes ducts to permit entry of the stream for removal of harmful VOCs and exit of the treated gas stream to the atmosphere. The valve includes several open frames extending radially from a central axis. A distribution blade mounted on the axis rotates between two positions to control the flow of the stream through the open frames during processing. A seal ring mounted to each open frame forms a seal with the distribution blade when in contact with the frame. Pressurized air delivered within the seal ring during contact with the blade acts to significantly reduce of the gas stream from within the valve to the atmosphere during operation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    (Not Applicable) 
       BACKGROUND OF THE INVENTION 
     Field of Invention 
       [0002]    The present invention relates to regenerative thermal oxidizers for destroying volatile organic compounds (VOCs) in emissions from industrial processes. More specifically, the present invention relates to a valve for controlling the flow of a waste gas stream through such an oxidizer that reduces the amount of waste gas streams that are leaked to the atmosphere. 
         [0003]    VOCs are found in significant amounts in waste gas streams created as a result of the implementation of industrial processes. Since VOCs are a precursor of smog, the amount of VOCs that are released into the atmosphere need to be substantially reduced or eliminated entirely. Increasingly stringent state and federal legislation impose the need to control the emission of Volatile Organic Compounds (VOCs) to the atmosphere. The industries and processes that need to control their output of VOCs include the printing, chemical, pharmaceutical manufacturing, automotive coating and painting, bakeries, can coating, wood manufacturing, medical device sterilization, soil remediation, and metal decorating industries, among others. Waste process gas streams must be passed through facilities that can eliminate the VOCs from the streams. 
         [0004]    Regenerative thermal oxidizers are conventionally used for destroying volatile organic compounds (VOCs) in high flow, low concentration emissions from industrial and power plants. Such oxidizers typically require high oxidation temperatures in order to achieve high VOC destruction. To achieve high heat recovery efficiency, the process gas that is to be treated is preheated before oxidation. A heat exchanger is typically provided to preheat these gases. The heat exchanger is usually packed with material having good thermal and mechanical stability and sufficient thermal mass. In operation, the process gas is fed through a previously heated heat exchanger, which, in turn, heats the process gas to a temperature approaching or attaining its VOC oxidation temperature. This pre-heated process gas is then directed into a combustion zone where any incomplete VOC oxidation is usually completed. The treated gas is then directed out of the combustion zone and through a second heat exchanger. As the hot oxidized gas continues through this second heat exchanger, the gas transfers its heat to the heat exchange media, cooling the gas and pre-heating the heat exchange media so that another batch of process gas may be preheated prior to the oxidation treatment. Usually, a regenerative thermal oxidizer has at least two heat exchangers, which alternately receive process and treated gases. This process is continuously carried out, allowing a large volume of process gas to be efficiently treated. 
         [0005]    The performance of a regenerative oxidizer may be optimized by increasing VOC destruction efficiency. Various manners for increasing VOC destruction efficiency have been addressed in the prior art. An important element of an efficient oxidizer is the valving used to switch the flow of process gas from one heat exchange column to another. Any leakage of untreated process gas through the valve system will decrease the efficiency of the apparatus and result in untreated process gas containing VOCs being released to the atmosphere. It therefore would be desirable to reduce or eliminate the amount of leakage of untreated process gas through the valving used to switch the flow of process gas from one heat exchanger to another. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    A valve for controlling the flow of a waste gas stream received from an industrial process is disclosed. The valve includes ducts to permit entry of the stream for removal of harmful VOCs and exit of the treated gas stream to the atmosphere. The valve includes several open frames extending radially from a central axis. A distribution blade mounted on the axis rotates between two positions to control the flow of the stream through the open frames during processing. A seal ring mounted to each open frame forms a seal with the distribution blade when in contact with the frame. Pressurized air delivered within the seal ring during contact with the blade acts to significantly reduce of the gas stream from within the valve to the atmosphere during operation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein: 
           [0008]      FIG. 1  is a perspective view of a regenerative thermal oxidizer, in which the control valve of the present invention is implemented; 
           [0009]      FIG. 2  is an elevational view of the control valve of the present invention; 
           [0010]      FIG. 3  is a top view of the control valve of the present invention; 
           [0011]      FIG. 4  is a cross-sectional view taken along line  4 - 4  of  FIG. 3 ; 
           [0012]      FIG. 5  is a top view of the control valve of the present invention illustrating rotational movement of the gas flow distribution blade mounted therein between first and second positions; 
           [0013]      FIG. 5A  is a cross-sectional view taken along line  5 A- 5 A of  FIG. 4 ; 
           [0014]      FIG. 6  is an enlarged broken view of the flow distribution blade in an abutting position with the frame of the control valve of the present invention; and, 
           [0015]      FIG. 7  is an enlarged view of the seal ring component of the control valve of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Referring now in detail to the various figures of the drawings wherein like reference characters refer to like parts, there is shown at  10  in  FIG. 1  a two-chamber regenerative thermal oxidizer, the operation of which will be explained and illustrated in detail. The oxidizer  10  includes a housing  14  in which there are first and second heat exchangers  18  and  22 , which include a heat recovery media, the heat exchangers being in communication with a centrally located combustion zone  26 . Each heat exchanger  18 ,  22  may also include filtration media for filtering VOCs from waste gas streams. A burner  30  may be located within the combustion zone  26  and a combustion blower (not shown) may be supported within the housing  14  to supply combustion air to the burner. A fan (not shown) is supported on the housing  14  for driving or drawing the process gas into the oxidizer  10 . The housing  14  includes a top chamber or roof  34 . Those skilled in the art will appreciate that the foregoing description of the oxidizer  10  is for illustrative purposes only; other designs are well within the scope of the present invention, including oxidizers with more or less than two chambers, oxidizers with horizontally oriented chamber(s), and catalytic oxidizers. 
         [0017]    In operation, a stream of gas  38  containing contaminants such as VOCs flows into a process gas inlet conduit  42  of the oxidizer  10  and thereafter into a control valve  50  which alternately directs flow of the gas stream  38 . In a first direction, the control valve  50  directs the process gas  38  out of the control valve  50  and through the heat exchanger  18 , which has been previously heated, thus increasing the temperature of the gas stream  38  to a temperature approaching or attaining its VOC oxidation temperature. This pre-heated gas stream  38  is then directed into the combustion zone indicated generally at  26  where any incomplete VOC oxidation is usually completed by the gas stream  38  passing over the burner  30 . Within the combustion zone  26 , the gas stream  38  is further heated to the required oxidation temperature and held for a predetermined period of time, e.g., up to one second, at that temperature to allow for adequate destruction of the VOCs. The treated gas stream  38  is then directed out of the combustion zone  26  and through the second heat exchanger  22 , whereupon the gas stream  38  transfers its heat to the media of the heat exchanger  22 , cooling the gas  38  and pre-heating the media of the heat exchanger  22  so that another batch of process gas  38  directed by the control valve  50  in the opposite direction may be preheated prior to the oxidation treatment. Thereafter, the cooled and treated gas stream  38  is directed into the control valve  50  and then to an exhaust stack  54  where it is released to the atmosphere. 
         [0018]    Periodically, the control valve  50  reverses the direction of flow and the gas stream  38  flows in an opposite route. That is, with the heat exchanger  22  preheated, the control valve  50  switches to direct flow of the gas stream  38  along an opposite route. Along this opposite route, the gas stream  38  flows into the control valve  50  from the inlet  42  and flows out of the control valve  50  over the pre-heated heat exchanger  22  to increase the temperature of the gas stream  38  to a temperature approaching or attaining its VOC oxidation temperature. The pre-heated gas stream  38  is then directed into the combustion zone  26  where VOC oxidation is completed. The treated gas  38  is then directed out of the combustion zone  26  and through the heat exchanger  18 , whereupon the process gas  38  transfers its heat to the heat exchanger  18 , cooling the gas  38  and pre-heating the heat exchanger  18 . Thereafter, the cooled gas stream  38  is directed back through the control valve  50  and out to the exhaust stack  54 , where it is released to the atmosphere. 
         [0019]    As explained above, usually, a regenerative thermal oxidizer  10  has at least two heat exchangers, which alternately receive process and treated gases. This process is continuously carried out, allowing a large volume of process gas to be efficiently treated. The back and forth switching between heat recovery beds  18  and  22  occurs every three to six minutes in most cases. In the embodiment shown, flow through the heat exchangers  18  and  22  is vertical wherein contaminated gas enters the heat exchangers from below or above. However, those skilled in the art will appreciate that other orientations are suitable including a horizontal arrangement. 
         [0020]    Referring now to  FIGS. 4 ,  5  and  5 A, the details and operation of the control valve  50  are discussed. As best shown in  FIGS. 5 and 5A , the control valve  50  includes a housing  60  having a plurality of walls  64 , e.g., four walls, a floor  68 , and a ceiling  72  (best shown in cut-away in  FIG. 3 ). An L-shaped angle iron  76  having a plurality of through mounting holes (best shown in  FIGS. 6 and 7 ) is affixed to interior surface of each wall  64  by any suitable means, e.g., welding. The angle irons  76  affixed to the four walls  64  extend vertically approximately the height of the wall  64  from the floor  68  to the ceiling  72 . As best shown in  FIG. 4 , a plurality of angle irons  76 , e.g., four angle irons, are affixed to the ceiling  72  in like fashion and extend radially from a location in proximity to a vertical axis  80  to each of the four angle irons  76  affixed to the four walls  64 . Likewise, a plurality of angle irons  76 , e.g., four angle irons, are affixed to the floor  68  and extend radially from a location in proximity to the vertical axis  80  to meet with each of the four wall angle irons  76 . In this manner, as best shown in  FIGS. 4 ,  5  and  5 A, the angle irons  76  affixed to the floor, walls and ceiling form four frames  88 ,  92 ,  96 , and  100  having large rectangular openings, wherein the angle irons  76  are suited for mounting a seal assembly  104  thereto. 
         [0021]    Referring now to  FIGS. 6 and 7 , a portion of the seal assembly  104  is illustrated therein as being mounted to an angle iron  76 . When mounted to the angle irons  76  locate on the floor  68 , walls  64 , and ceiling  72 , the seal assembly  104  forms a continuous seal thereover by utilizing mitered corners as illustrated in  FIG. 7 . Each seal assembly  104  includes an outer sealing leaf  108  and an inner sealing leaf  112 , the sealing leaves being similarly configured. Each sealing leaf  108  and  112  includes a plurality of regularly spaced mounting holes for mounting to a manifold bar  116  situated therebetween. The sealing leaves  108  and  112  are made of any suitable material, e.g., spring steel which may consist of a longitudinal ribbon or band of spring steel. The manifold bar  116  is disposed between the sealing leaves  108 ,  112  and is also provided with a plurality of regularly spaced mounting holes for securing the sealing leaves thereto on opposite sides thereof. As mounted, the sealing leaves  108  and  112  are spaced from one another to create a seal gap  120  therebetween ( FIG. 6 ). The sealing leaves are mounted utilizing suitable hardware, e.g., nuts  124  and bolts  128 . As best shown, the seal assembly  104  is affixed to the angle irons  76  at regularly spaced intervals within frame openings  92   a  and  100   a.    
         [0022]    As best shown in  FIG. 6 , the manifold bar  116  includes a second set of regularly spaced through openings  132  that are flared at one end  132   a . These flared openings  132   a  are arranged for attachment of hose segments  136  thereto by utilizing a suitable hose connector  140 . Other hose connectors  144  suitable for attaching the plurality of hose segments  136  to each other are also provided. The hose segments  136  are provided for delivering pressurized air from a source (not shown) through the flared openings  132   a  and into the seal gap  120  to increase the effectiveness of the seal as will be discussed below. A metal plate  148  is also included as part of the seal assembly  104  to increase rigidity. The sealing leaves  108  and  112  are similarly configured in that each includes a free end that bends at an angle approximating forty-five degrees and bends again so that the free end of the sealing leaves  108  and  112  extends in a direction that is approximately parallel to the gas flow distribution blade  176  when the blade  176  is in contact with the sealing leaves so as to form an effective seal in a manner to be discussed further below. 
         [0023]    Referring again to  FIGS. 5 and 5A , the housing  60  includes an inlet opening  152 , an opposed outlet opening  156 , and opposed ducts  160  and  164  for directing process gas in and out of the control valve  50  during operation. The inlet opening  152  is in communication with the inlet conduit  42  ( FIG. 1 ) and the outlet opening  156  is in communication with an outlet conduit  158  ( FIG. 1 ) which leads to the exhaust stack  54  ( FIG. 1 ). The duct  160  provides communication between control valve  50  and heat exchanger  18  through conduit  168  ( FIG. 1 ), while duct  164  provides communication between the control valve  50  and the heat exchanger  22  through conduit  172  ( FIG. 1 ). 
         [0024]    Located centrally within the housing  50  is a stationary vertical axis  80  on which a gas flow distribution blade  176  is rotatably mounted. The blade  176  includes a circular hub  180  disposed over the vertical axis  80  and first and second blade portions, indicated at  176   a  and  176   b , that extend in opposite directions from the hub  180 . Referring now to  FIGS. 4 ,  5 , and  5 A, the housing  60  of the control valve  50  includes the plurality of frames, indicated at  88 ,  92 ,  96 , and  100 . Each frame includes a seal assembly  104  mounted thereon, as described previously. As shown in these figures, each of these frames extends radially from a location in proximity to the central axis  80  towards the perimeter of the housing  60 . 
         [0025]    As shown in  FIGS. 3 ,  5 , and  5 A, the blade  176  is arranged for rotary movement from a first position to a second position. As best shown in  FIG. 5A , in the first position, the blade segment  176   a  is contacting frame  92  and blocking the passage of any gas stream  38  through frame  92  while blade segment  176   b  is contacting frame  100  to block the passage of any gas stream therethrough. As best illustrated in  FIG. 6 , to create an effective seal, when in this first position, blade segment  176   a  makes contact with the free end of leaves  108  and  112  of the seal assembly  104  extending around the periphery of frame  92  to create a seal at the seal gap  120  to significantly reduce or eliminate the amount of gas stream  38  leaking across frame  92  and inadvertently escaping to the atmosphere. Additionally, pressurized air pumped into the seal gap  120  through hose segments  136  and the openings  132  of the manifold bar  116 , contributes to significantly reducing the amount of gas stream  38  leaking across open frame  92  and escaping to the atmosphere. In similar fashion, blade segment  176   b  contacts the free ends of leaves  108  and  112  of the seal assembly  104  extending around the periphery of frame  100  to create a seal at its seal gap  120 , which in combination with the pressurized air pumped into the seal gap  120  acts to significantly reduce the amount of gas stream  38  leaking across open frame  100  and escaping to the atmosphere. 
         [0026]    Since in the first position blade segments  176   a  and  176   b  are not in contact with frames  88  and  96 , these frames remain open for the passage of gas streams therethrough. Thus, as indicted by arrows  224  and  228  in  FIG. 5A , process gas  38  entering the control valve  50  through the inlet conduit  42  flows through the opening of frame  88  and out of the control valve  50  through duct  160  and to the heat exchanger  18 . Once the gas stream  38  has been processed through heat exchanger  18 , combustion zone  26 , and heat exchanger  22 , as indicated by arrows  232  and  236 , the process gas  38  re-enters the control valve  50  through duct  164 , through the opening of frame  96 , and out through outlet opening  156 , where it is released to the atmosphere through the stack  54  ( FIG. 1 ). 
         [0027]    The back and forth switching of the blade  176  between the first and second positions controls the path of flow of the process gas  38  between heat exchangers  18  and  22 . After a predetermined amount of time, the blade  176  is arranged to rotate from this first position through approximately 90 degrees to a second position (not shown) whereby the blade segment  176   a  blocks open frame  96  while blade segment  176   b  blocks open frame  88 . In a similar manner, seal assemblies  104  extend around the periphery of open frames  88  and  96 . Blade segments  176   a  and  176   b  contact the free ends of leaves  108  and  112  of the seal assemblies  104  while pressurized air is pumped into the seal gap  120  of these seal assemblies  104  to significantly reduce the amount of gas stream  38  leaking across open frames  88  and  96 .  FIG. 5  best illustrates movement of blade  176  between the first and second blocking positions discussed above. 
         [0028]    Since in the first position blade segments  176   a  and  176   b  do not contact frames  92  and  100 , these frames remain open for the passage of gas streams therethrough. Thus, when the blade  176  is in the second position, the gas stream  38  will travel along the opposite route, as previously mentioned. That is, when in the second position, the flow of process gas  38  through frames  88  and  96  will be blocked in similar manner as described above. Thus, process gas  38  entering the control valve  50  through the inlet conduit  42  ( FIG. 1 ) and opening  152  flows through the opening of frame  100  and out of the control valve  50  through duct  164  and to the heat exchanger  22  previously heated by the gas stream  38  traveling in the first direction. Once the gas stream  38  has processed through the heat exchanger  22 , combustion zone  26 , and heat exchanger  18 , the process gas  38  re-enters the control valve  50  through duct  160 , passes through the opening of frame  92 , and out through outlet opening  156 , where it is released to the atmosphere through the stack  54  ( FIG. 1 ). 
         [0029]    Referring now to  FIGS. 2 and 3 , rotational movement of the blade  176  is controlled by an actuatable pneumatic assembly  200  positioned within a box  204  located above the housing  50  by attachment to brackets  205  extending upwardly from the housing  50 . The pneumatic assembly  200  includes lead wires  202  which connect in to a conventional source of power and control (not shown), from which the assembly  200  may be remotely actuated and controlled in known ways. In particular, the pneumatic assembly  200  includes a cylinder  208  and a piston  212  disposed therein. As best illustrated in  FIG. 3 , in response to actuation, the piston  212  is arranged to move between a retracted position (shown in solid lines) and an extended position (shown in dotted lines). The retracted and extended positions are limited by stops  216  affixed to the box  204 , so as limit movement of the piston  212  between the retracted and extended positions. In this manner, rotation of the blade  176  may be limited between the first and second positions. The piston  212  is affixed to an arm  220  which is affixed to the hub  180  of the blade  176 . In this manner rotational movement of the blade  176  between the first position through approximately 90 degrees to the second position may be controlled. 
         [0030]    It is understood that the control valve and its constituent parts described herein is an exemplary indication of a preferred embodiment of the invention, and is given by way of illustration only. In other words, the concept of the present invention may be readily applied to a variety of preferred embodiments, including those disclosed herein. While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.