Patent Publication Number: US-2005139272-A1

Title: Rotary air distributor

Description:
CROSS-REFERNCE TO RELATED APPLICATION  
      This application is entitled to and claims the benefit of Provisional Patent Application Ser. No. 60/515,133, filed on Oct. 28, 2003. 
    
    
     BACKGROUND OF THE INVENTION  
      The present invention relates generally to oxidizer systems for the abatement of process emissions and more particularly, to a rotary valve assembly for controlling flow of contaminated process emissions to and from chambers of a regenerative oxidizer.  
      Process emissions often contain combustible contaminants that, if released to the atmosphere, have the potential of polluting the environment. However, the amount of combustible material contained in such emissions is generally below several thousand ppm and, accordingly, will not ignite or propagate a flame at ambient temperature.  
      Oxidizers increase the temperature of such process emissions to a level above the ignition temperature of the combustible contaminants by the use of heat derived from a supplemental energy source, therefore allowing for oxidation of the emissions. Regenerative oxidizers recover heat remaining in the cleansed exhaust gas to increase the temperature of emissions entering the oxidizer thereby minimizing the amount of supplemental energy required to raise the emission to its ignition temperature.  
      Known regenerative oxidizers typically comprise a plurality of conventional regenerator beds that communicate with a combustion chamber. The regenerator beds contain conventional ceramic heat exchange elements. Admission of emissions into each regenerator bed is controlled by a valve network. During operation of a regenerative oxidizer that contains, for example, three regenerator beds, emissions pass through a first regenerator bed to pick up heat therefrom, thence to the combustion chamber for oxidation. Following oxidation to CO 2  and H 2 O, the cleansed air then passes through a second regenerator bed, which is operating in the regenerative, or heat receptive, mode for discharge to atmosphere or to a purified air duct which conducts purified air to a third regenerator bed to purge the bed of contaminants. Thus, each regenerator bed performs three modes of operation: a feed mode, a heat receptive mode, and a purge mode.  
       FIG. 1  shows an example of a prior art regenerative oxidizer. The oxidizer  510  utilizes a plurality of valves  512  to control the flow of contaminated emissions and cleansed air to and from the oxidizer  510 , respectively. The oxidizer  510  comprises a plurality of conventional regenerator beds  514 ,  516  and  518  that communicate with a combustion chamber  520 . Fuel, for example natural gas, is supplied to the combustion chamber  520  from a fuel control and burner  521 . Emissions are conducted to the oxidizer  510  from an inflow duct  522 . Cleansed air is conducted away from the oxidizer  510  by an outflow duct  524  that is in fluid communication relationship with an exhaust blower  526 . Exhaust air may be vented to atmosphere or conducted through a conduit  528  to ducts to selectively purge the regenerator beds  514 ,  516  or  518 . After passing the selectively opened valves  512 , the contaminated fluids are ducted to the regenerative beds  514 ,  516  and  518  by ducts  530 ,  532  and  534 , respectively.  
      However, a problem with the arrangement described above is that the use of three separate valve assemblies to control emissions flow to and from the three regenerative beds increases the production and maintenance costs of the oxidizer system and complicates assembly and control of the system.  
     SUMMARY OF THE INVENTION  
      The present invention includes a rotary valve having a central shaft with a longitudinal axis, and a plurality of gas flow plenums extending along the shaft, at least a portion of each plenum extending around a portion of the shaft in a spiral configuration. The rotary valve is incorporated into a rotary valve assembly comprising an inner housing enclosing the valve, the inner housing being fixed with respect to the valve so as to rotate in correspondence with the valve.  
      A plurality of windows is formed along the inner housing, at least one window of the plurality of windows being in fluid communication with a corresponding one of the valve plenums.  
      An outer housing encloses the inner housing and has at least two fluid flow apertures formed therealong, each of the fluid flow apertures being in fluid communication with a corresponding one of a pair of regenerative chambers in a regenerative oxidizer.  
      The inner housing is rotatable with respect to the outer housing to bring an inner housing window into alignment with an outer housing fluid flow aperture, thereby bringing the inner housing window into fluid communication with the outer housing aperture and correspondingly enabling fluid communication between the plenum that is in fluid communication with the window, and the regenerative chamber that is in fluid communication with the outer housing flow aperture.  
      The single rotary valve described herein is designed to replace the multiple valves currently used in regenerative oxidizers such as the prior art device previously described. By reducing the number of valves needed for control of gas flow to and from the regenerative chambers, the production and maintenance costs of the oxidizer system and the complexity of the flow control system are reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the drawings illustrating embodiments of the present invention:  
       FIG. 1  is a cross-sectional side view showing a regenerative oxidizer incorporating a rotary valve and valve assembly in accordance with the present invention;  
       FIG. 2  is a cross-sectional side view showing a the rotary valve and valve assembly of  FIG. 1 ;  
       FIG. 3  is a cross-sectional end view of the valve assembly of  FIG. 2  taken along line  3 - 3  of  FIG. 2 ;  
       FIG. 4  is a cross-sectional end view of the valve assembly of  FIG. 2  taken along line  44  of  FIG. 2 ;  
       FIG. 5  is a cross-sectional end view of the valve assembly of  FIG. 2  taken along line  5 - 5  of  FIG. 2 ;  
       FIG. 6  is an exploded perspective view of the valve assembly of  FIG. 2 ; and  
       FIG. 7  is a perspective view of an example of a prior art regenerative oxidizer; 
    
    
     DETAILED DESCRIPTION  
      Referring to the figures, a rotary oxidizer valve  10  is shown as associated with an exemplary regenerative oxidizer  12 . As known in the art, depending on the purity required, two or more chambers  12   a - 12   b  are included in the regenerative oxidizer  12 . Exemplary regenerative oxidizers include those described in the U.S. Pat. Nos. 5,612,005; 5,643,539; 5,967,771; 5,000,422, incorporated herein by reference.  
      The rotary oxidizer valve  10  is contained within a fixed valve housing  16 . Housing  16  has a first end  18  and a second end  20 . In a preferred embodiment, a plurality of gas apertures or slots  17   a - c  are evenly spaced across the length of an outer wall  19  of the housing  16 , thereby providing fluid flow to and from the interior of housing  16  and the interior of oxidizer  12 . A plurality of regenerative chambers  12   a    12   c  extends from the oxidizer  12 , whereby each chamber is ducted to the outer wall  19  to provide fluid communication with gas apertures  17   a - 17   c,  respectively. A first or inlet end  18  of the housing  16  communicates with an inlet source of gas or air to be purified. A second or outlet end  20  of the housing  16  communicates with an oxidizer exhaust stream and serves to exhaust cleansed air to the environment. An inlet plenum  22  is defined by a first cap  24  at the first end  18  and receives an inlet gas stream to be fed to the oxidizer  12 . The first cap  24  is sealed to the stationary housing  16  except where directed to the gas inlet stream, thereby preventing any release of inlet gas and ensuring a steady flow of gas to the valve  10 .  
      An outlet plenum  26  is defined by a second cap  28  and fluidly communicates with an exhaust stream from the oxidizer  12 , thereby ducting the exhaust stream to the environment. The second cap  28  is also sealed to the fixed housing  16 . If desired, a purge conduit  30  fluidly communicates with the outlet plenum  26  and, as explained below, is routed back within the valve  10  thereby providing a source of purge air to the valve  10 .  
      A hollow shaft  32  longitudinally extends through the valve  10  and is journaled on bearings  34  thereby facilitating rotation of the valve  10  within the housing  16 . The shaft  32  extends through the first and second end caps  24  and  28 , respectively; through a corresponding apertures  36  in end caps  24 .  
      An actuator  40  (not shown) drives the shaft  32  and may be electrically, hydraulically, or pneumatically powered. The actuator  40  incorporates intermittent gearing as exemplified by a Geneva Wheel, for example. Accordingly, the valve  10  may be indexed over a predetermined time wherein the valve  10  rotates over a predetermined arcuate length (e.g. 60 degrees) each time the valve  10  is indexed. It should be emphasized, however, that the actuator employed will be designed to accommodate the desired cycle time, six to twelve minutes for example. An exemplary cycle generally consists of six periods, each about one to two minutes, wherein a first period is a first purge, second and third periods are outlets, a fourth period is a second purge, and fifth and sixth periods are inlets to the regenerative oxidizer  12 . Other known or suitable actuators may be employed and are also contemplated as useful in the present invention.  
      An annular channel  42  is defined by an inner wall  44  of the shaft  32  and receives a purge stream from the purge conduit  30 . The purge conduit  30  is fixed to secondary bearings  45  attached to a corresponding end of the shaft  32 , thereby facilitating independent rotary movement of the shaft  32  while conduit  30  remains fixed in place.  
      The valve  10  has a longitudinal axis L and contains a plurality of valve helical plenums  46  each defining a substantially helical or spiral shape. A valve feed plenum  48  fluidly communicates with the inlet plenum  22  through at least one aperture  50  defined within the inlet plenum  22 . As the valve  10  is indexed, inlet flow to the oxidizer is thereby cyclically routed through the plenum  48  to respective ones of chambers  12   a - 12   c  within the oxidizer  10 .  
      A valve exhaust plenum  60  is symmetrically oriented opposite the valve feed plenum  48  and fluidly communicates with the outlet plenum  26  through at least one outlet aperture (not shown) defined within the outlet plenum  26 . As the valve  10  is indexed, exhaust flow from an associated regenerative chamber is cyclically routed through the exhaust plenum  60  and through the outlet plenum  26 . A first valve purge plenum  64  fluidly communicates with the annular channel  42  thereby providing a source of purge air to the oxidizer  12 . A first plurality of purge apertures  66  are radially formed in and through the shaft  32  and are contained within the first purge plenum  64  thereby facilitating a relatively high pressure fluid flow from the shaft  32  to the first purge plenum  64 .  
       FIGS. 3-5  show cross-sectional views of the valve assembly taken at various points along the length of valve  10 . These views show the alignments between the various plenums  60 ,  64 ,  68 ; the inner housing windows  80 ,  84 ,  86 ; and the outer housing flow apertures  17   a - 17   c.  Referring to  FIGS. 3-5 , the first purge plenum  64  is formed between the valve feed plenum  48  and the valve exhaust plenum  60  thereby providing an air seal between the valve inlet and valve exhaust plenums and comprises about half of the volume of the feed and exhaust plenums. As such, when the valve  10  is indexed, the purge plenum  64  comprises about half the arcuate length of the feed and exhaust plenums. Accordingly, the purge function established by rotation of the valve  10  is about half of the time dedicated to either the feed or exhaust plenums. A second valve purge plenum  68  fluidly communicates with the annular channel  42  thereby providing a source of purge air to the oxidizer  12 . A second plurality of purge apertures  70  are radially formed in and through the shaft  32  and are contained within the second purge plenum  68  thereby facilitating a relatively high pressure fluid flow from the shaft  32  to the second purge plenum  68 . As with the first purge plenum  64 , the second purge plenum  68  is formed between the valve feed plenum  48  and the valve exhaust plenum  60  (and opposite the first purge plenum  64 ), thereby providing an air seal between the valve inlet and valve exhaust plenums and comprises about half of the volume of the feed and exhaust plenums. As such, when the valve  10  is indexed, the purge plenum  68  also comprises about half the arcuate length of the feed and exhaust plenums. Accordingly, the purge function established by rotation of the valve  10  is about half of the time dedicated to either the feed or exhaust plenums.  
      In further accordance with the present invention, a second housing  72  is contained within the first housing  16  and encapsulates the rotary valve  10 , thereby facilitating fluid flow from the rotary valve  10  to the multi chamber regenerative chamber  12 . The housing  72  contains a first end  74  and a second end  76  corresponding to first and second ends  18  and  20  of housing  16 . A plurality of windows or gas flow apertures  78  are formed along the periphery of the housing  72 .  
      A first plurality of windows  80  are circumferentially aligned proximate to first end  74  along a plane extending orthogonal to longitudinal axis L. Each window in the plurality of windows  80  is located within a respective plenum.  
      Accordingly, at least one of a first window  80   a  is formed within the feed plenum  48  and thereby communicates inlet air to a first regenerative chamber  12   a,  as the valve  10  is rotated to align window  80   a  and regenerative chamber  12   a.  At least one of a second window  80   b  is circumferentially aligned with window  80   a  and is formed within the outlet plenum  60 , thereby providing fluid flow from regenerative chamber  12   a  when it functions to exhaust purified air from the regenerative oxidizer  12 . If desired, one or more additional windows P 1 , P 2  may be added over one or both purge sections to provide a purge stream through regenerative chamber  12   a  as the respective purge window is aligned with the chamber  12   a.    
      A second plurality of windows  84  are circumferentially aligned intermediate of first end  74  and second end  76  along a plane extending orthogonal to longitudinal axis L. Each window in the plurality of windows  84  is also located within a respective plenum. Accordingly, a third window  84   a  is formed within the inlet plenum  48  and thereby communicates inlet air to a second regenerative chamber  12   b,  as the valve  10  is rotated to align window  84   a  and regenerative chamber  12   b.  A fourth window  84   b  is circumferentially aligned with window  84   a  and is formed within the outlet plenum  60 , thereby providing fluid flow from regenerative chamber  12   b  when it functions to exhaust purified air from the regenerative oxidizer  12 . If desired, one or more additional windows P 3 , P 4  may be added over one or both purge sections to provide a purge stream through regenerative chamber  12   b  as the respective purge window is aligned with the chamber  12   b.    
      A third plurality of windows  86  are circumferentially aligned proximate to the second end  76  along a plane extending orthogonal to longitudinal axis L. Each window in the plurality of windows  86  is also located within a respective plenum. Accordingly, a fifth window  86   a  is formed within the inlet plenum  48  and thereby communicates inlet air to a third regenerative chamber  12   c,  as the valve  10  is rotated to align window  86   a  and regenerative chamber  12   b.  A sixth window  86   b  is circumferentially aligned with window  86   a  and is formed within the outlet plenum  60 , thereby providing fluid flow from regenerative chamber  12   c  when it functions to exhaust purified air from the regenerative oxidizer  12 . If desired, one or more additional windows P 5 , P 6  may be added over one or both purge sections to provide a purge stream through regenerative chamber  12   c  as the respective purge window is aligned with the chamber  12   c.  Additional pluralities of circumferentially aligned windows may be added as the size of the regenerative oxidizer  12  is increased. For example, given a five chamber regenerative chamber, a rotary valve  10  would include five pluralities of circumferentially aligned windows thereby providing intermittent or continuous fluid flow to each regenerative chamber.  
      In yet another aspect of the present invention, a plurality of wire brush seals  88  is employed, wherein each wire brush seal  88  is fixed about the periphery of each window  80 ,  84 ,  86  on an outer surface  90  of the housing  72 . An annular gap or clearance  92  exists between the outer wall  90  of housing  72  and an inner wall  15  of housing  16 . The wire brush seals  88  radially extend from the outer wall  90  to the inner wall  15 , thereby defining an annular and arcuate sweep against the inner wall  15  upon rotation of the housing  72 . When windows  78  are not aligned with gas apertures  17   a    17   c,  the wire brush seals  88  inhibit the flow from each respective window within the housing  16  and within the gap  92 .  
      In operation, as the valve  10  and the housing  72  are periodically rotated by the actuator, the various air/gas streams to and from the regenerative oxidizer  12  are alternated from chamber to chamber. For example, if at one point in time chamber  12   a  functioned as an inlet chamber, and chamber  12   b  functioned as an outlet chamber, then chamber  12   c  would either be inactive or functioning as a purge chamber depending on design choice. Upon valve  10  rotation, chamber  12   c  might then function as the outlet, chamber  12   a  as a purge chamber, and chamber  12   b  as an inlet.  
      Accordingly, in a first embodiment, the windows  80 ,  84 ,  86  are formed within the outer wall  90  to facilitate an ordered function of each chamber whereby each chamber functions as an inlet, two purges, and an outlet in a six period cycle of operation as the valve  10  is rotatably indexed. Stated another way, while one chamber functions as an inlet, the other chambers will preferably reflect other functions such as a gas outlet or purge. As such, in any given moment, each chamber will preferably have a unique function or will be inactive; no two chambers will reflect the same function at the same time. Of course, as the size of the regenerative oxidizer increases, it may be desirable to design the windows  80 ,  84 ,  86  so that two chambers, rather than just one chamber, functions as a gas inlet rather than just one, for example. In that case, two windows  80 ,  84 ,  86  aligned with chambers  12   a  and  12   b,  for example, would fluidly communicate with the inlet plenum  22  thereby providing a greater inlet flow to the oxidizer  12 . One of ordinary skill in the art will appreciate the myriad of other design permutations depending on the oxidizer size and requirements.  
      It will be understood that the foregoing description of an embodiment of the present invention is for illustrative purposes only. As such, the various structural and operational features herein disclosed are susceptible to a number of modifications commensurate with the abilities of one of ordinary skill in the art, none of which departs from the scope of the present invention as described above and as defined in the appended claims.