Switching valve

Information

  • Patent Grant
  • 6261092
  • Patent Number
    6,261,092
  • Date Filed
    Wednesday, May 17, 2000
    24 years ago
  • Date Issued
    Tuesday, July 17, 2001
    23 years ago
Abstract
Switching valve and a regenerative thermal oxidizer including the switching valve. The valve of the present invention exhibits excellent sealing characteristics and minimizes wear. The valve has a seal plate that defines two chambers, each chamber being a flow port that leads to one of two regenerative beds of the oxidizer. The valve also includes a switching flow distributor which provides alternate channeling of the inlet or outlet process gas to each half of the seal plate. The valve operates between two modes: a stationary mode and a valve movement mode. In the stationary mode, a tight gas seal is used to minimize or prevent process gas leakage. The gas seal also seals during valve movement.
Description




BACKGROUND OF THE INVENTION




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 “dirty” process gas which is to be treated is preheated before oxidation. A heat exchanger column is typically provided to preheat these gases. The column is usually packed with a heat exchange material having good thermal and mechanical stability and sufficient thermal mass. In operation, the process gas is fed through a previously heated heat exchanger column, 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 now “clean” gas is then directed out of the combustion zone and back through the heat exchanger column, or through a second heat exchange column. As the hot oxidized gas continues through this column, the gas transfers its heat to the heat exchange media in that column, 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 exchanger columns 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 performance of a regenerative oxidizer may be optimized by increasing VOC destruction efficiency and by reducing operating and capital costs. The art of increasing VOC destruction efficiency has been addressed in the literature using, for example, means such as improved oxidation systems and purge systems (e.g., entrapment chambers), and three or more heat exchangers to handle the untreated volume of gas within the oxidizer during switchover. Operating costs can be reduced by increasing the heat recovery efficiency, and by reducing the pressure drop across the oxidizer. Operating and capital costs may be reduced by properly designing the oxidizer and by selecting appropriate heat transfer packing materials.




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. In addition, disturbances and fluctuations in the pressure and/or flow in the system can be caused during valve switchover and are undesirable. Valve wear is also problematic, especially in view of the high frequency of valve switching in regenerative thermal oxidizer applications.




One conventional two-column design uses a pair of poppet valves, one associated with a first heat exchange column, and one with a second heat exchange column. Although poppet valves exhibit quick actuation, as the valves are being switched during a cycle, leakage of untreated process gas across the valves inevitably occurs. For example, in a two chamber oxidizer during a cycle, there is a point in time where both the inlet valve(s) and the outlet valve(s) are partially open. At this point, there is no resistance to process gas flow, and that flow proceeds directly from the inlet to the outlet without being processed. Since there is also ducting associated with the valving system, the volume of untreated gas both within the poppet valve housing and within the associated ducting represents potential leakage volume. Since leakage of untreated process gas across the valves leaves allows the gas to be exhausted from the device untreated, such leakage which will substantially reduce the destruction efficiency of the apparatus. In addition, conventional valve designs result in a pressure surge during switchover, which exasperates this leakage potential.




Similar leakage potential exists with conventional rotary valve systems. Moreover, such rotary valve systems typically include many internal dividers which can leak over time, and are expensive to construct and maintain. For example, in U.S. Pat. No. 5,871,349, FIG. 1 illustrates an oxidizer with twelve chambers having twelve metallic walls, each of which can be a weak point for leakage.




It would therefore be desirable to provide a regenerative thermal oxidizer that has the simplicity and cost effectiveness of a two chamber device, and the smooth control and high VOC removal of a rotary valve system, without the disadvantages of each.




SUMMARY OF THE INVENTION




The problems of the prior art have been overcome by the present invention, which provides a single switching valve and a regenerative thermal oxidizer including the switching valve. The valve of the present invention exhibits excellent sealing characteristics and minimizes wear. The valve has a seal plate that defines two chambers, each chamber being a flow port that leads to one of two regenerative beds of the oxidizer. The valve also includes a switching flow distributor which provides alternate channeling of the inlet or outlet process gas to each half of the seal plate. The valve operates between two modes: a stationary mode and a valve movement mode. In the stationary mode, a tight gas seal is used to minimize or prevent process gas leakage. The gas seal also seals during valve movement. The valve is a compact design, thereby eliminating ducting typically required in conventional designs. This provides less volume for the process gas to occupy during cycling, which leads to less dirty process gas left untreated during cycling. Associated baffling minimizes or eliminates untreated process gas leakage across the valve during switchover. The use of a single valve, rather than the two or four conventionally used, significantly reduces the area that requires sealing. The geometry of the switching flow distributor reduces the distance and number of turns the process gas goes through since the flow distributor can be located close to the heat exchange beds. This reduces the volume of trapped, untreated gas during valve switching. Since the process gas passes through the same valve ports in the inlet cycle as in the outlet cycle, gas distribution to the heat exchange beds is improved.




Valve switching with minimal pressure fluctuations, excellent sealing, and minimal or no bypass during switching are achieved. In view of the elimination of bypass during switching, the conventional entrapment chambers used to store the volume of unprocessed gas in the system during switching can be eliminated, thereby saving substantial costs.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a perspective view of a regenerative thermal oxidizer in accordance with one embodiment of the present invention;





FIG. 2

is a perspective exploded view of a portion of a regenerative thermal oxidizer in accordance with one embodiment of the present invention;





FIG. 3

is a perspective view of the cold face plenum in accordance with the present invention;





FIG. 4

is a bottom perspective view of the valve ports in accordance with the present invention;





FIG. 5

is a perspective view of the flow distributor switching valve in accordance with the present invention;





FIG. 5A

is a cross-sectional view of the flow distributor switching valve in accordance with the present invention;





FIG. 6

is a perspective view of the switching valve drive mechanism in accordance with the present invention;





FIGS. 7A

,


7


B,


7


C and


7


D are schematic diagrams of the flow through the switching valve in accordance with the present invention;





FIG. 8

is a perspective view of a portion of the flow distributor in accordance with the present invention;





FIG. 9

is a top view of the seal plate in accordance with the present invention;





FIG. 9A

is a cross-sectional view of a portion of the seal plate of

FIG. 9

;





FIG. 10

is a perspective view of the shaft of the flow distributor in accordance with the present invention;





FIG. 11

is a cross-sectional view of the rotating port in accordance with the present invention; and





FIG. 12

is a cross-sectional view of the lower portion of the drive shaft in accordance with the present invention.











DETAILED DESCRIPTION OF THE PRESENT INVENTION




Turning first to

FIGS. 1 and 2

, there is shown a two-chamber regenerative thermal oxidizer


10


(catalytic or non-catalytic) supported on a frame


12


as shown. The oxidizer


10


includes a housing


15


in which there are first and second heat exchanger chambers in communication with a centrally located combustion zone. A burner (not shown) may be associated with the combustion zone, and a combustion blower may be supported on the frame


12


to supply combustion air to the burner. The combustion zone includes a bypass outlet


14


in fluid communication with exhaust stack


16


typically leading to atmosphere. A control cabinet


11


houses the controls for the apparatus and is also preferably located on frame


12


. Opposite control cabinet


11


is a fan (not shown) supported on frame


12


for driving the process gas into the oxidizer


10


. Housing


15


includes a top chamber or roof


17


having one or more access doors


18


providing operator access into the housing


15


. Those skilled in the art will appreciate that the foregoing description of the oxidizer 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.




A cold face plenum


20


forms the base of housing


15


as best seen in FIG.


2


. Suitable support grating


19


is provided on the cold face plenum


20


and supports the heat exchange matrix in each heat exchange column as is discussed in greater detail below. In the embodiment shown, the heat exchange chambers are separated by separation walls


21


, which are preferably insulated. Also in the embodiment shown, flow through the heat exchange beds is vertical; process gas enters the beds from the valve ports located in the cold face plenum


20


, flows upwardly (towards roof


17


) into a first bed, enters the combustion zone in communication with the first bed, flows out of the combustion zone and into a second chamber, where it flows downwardly through a second bed towards the cold face plenum


20


. However, those skilled in the art will appreciate that other orientations are suitable including a horizontal arrangement, such as one where the heat exchange columns face each other and are separated by a centrally located combustion zone.




Turning now to

FIG. 3

, the details of the cold face plenum


20


will be discussed. The plenum


20


has a floor


23


which is preferably sloped downwardly from outside walls


20


A,


20


B towards the valve ports


25


to assist in gas flow distribution. Supported on floor


23


are a plurality of divider baffles


24


, and chamber dividers


124


. The divider baffles


24


separate the valve ports


25


, and help reduce pressure fluctuations during valve switching. The chamber dividers


124


separate the heat exchange chambers. Chamber dividers


124


A and


124


D, and


124


E and


124


H, may be respectively connected with each other or separate. Valve port


25


A is defined between chamber divider


124


A and baffle


24


B; valve port


25


B is defined between baffles


24


B and


24


C; valve port


25


C is defined between baffle


24


C and chamber divider


124


D; valve port


25


D is defined between chamber divider


124


E and baffle


24


F; valve port


25


E is defined between baffles


24


F and


24


G; and valve port


25


F is defined between baffle


24


G and chamber divider


124


H. The number of divider baffles


24


is a function of the number of valve ports


25


. In the preferred embodiment as shown, there are six valve ports


25


, although more or less could be used. For example, in an embodiment where only four valve ports are used, only one divider baffle would be necessary. Regardless of the number of valve ports and corresponding divider baffles, preferably the valve ports are equally shaped for symmetry.




The height of the baffles is preferably such that the top surface of the baffles together define a level horizontal plane. In the embodiment shown, the portion of the baffles farthest from the valve ports is the shortest, to accommodate the floor


23


of the cold face plenum which is sloped as discussed above. The level horizontal plane thus formed is suitable for supporting the heat exchange media in each heat exchange column as discussed in greater detail below. In the six valve port embodiment shown, baffles


24


B,


24


C,


24


F and


24


G are preferably angled at about 45° to the longitudinal centerline L—L of the cold face plenum


20


as they extend from the valve ports


25


, and then continue substantially parallel to the longitudinal centerline L—L as they extend toward outside walls


20


A and


20


B, respectively. Baffles


24


A,


24


D,


24


E and


24


H are preferably angled at about 22.5° to the latitudinal centerline H—H of the cold face plenum


20


as they extend from the valve ports


25


, and then continue substantially parallel to the latitudinal centerline H—H as the extend toward outside walls


20


C and


20


D, respectively.




Preferably the baffles


24


B,


24


C,


24


F and


24


G, as well as the walls


20


A,


20


B,


20


C and


20


D of the cold face plenum


20


, include a lip


26


extending slightly lower than the horizontal plane defined by the top surface of the baffles


25


. The lip


26


accommodates and supports an optional cold face support grid


19


(FIG.


2


), which in turn supports the heat exchange media in each column. In the event the heat exchange media includes randomly packed media such as ceramic saddles, spheres or other shapes, the baffles


24


can extend higher to separate the media. However, perfect sealing between baffles is not necessary as it is in conventional rotary valve designs.





FIG. 4

is a view of the valve ports


25


from the bottom. Plate


28


has two opposite symmetrical openings


29


A and


29


B, which, with the baffles


26


, define the valve ports


25


. Situated in each valve port


25


is an optional turn vane


27


. Each turn vane


27


has a first end secured to the plate


28


, and a second end spaced from the first end secured to the baffle


24


on each side (best seen in FIG.


3


). Each turn vane


27


widens from its first end toward its second end, and is angled upwardly at an angle and then flattens to horizontal at


27


A as shown in

FIGS. 3 and 4

. The turn vanes


27


act to direct the flow of process gas emanating from the valve ports away from the valve ports to assist in distribution across the cold face plenum during operation. Uniform distribution into the cold face plenum


20


helps ensure uniform distribution through the heat exchange media for optimum heat exchange efficiency.





FIGS. 5 and 5A

show the flow distributor


50


contained in a manifold


51


having a process gas inlet


48


and a process gas outlet


49


(although element


48


could be the outlet and


49


the inlet, for purposes of illustration the former embodiment will be used herein). The flow distributor


50


includes a preferably hollow cylindrical drive shaft


52


(FIGS


5


A,


10


) that is coupled to a drive mechanism discussed in greater detail below. Coupled to the drive shaft


52


is a partial frusto-conically shaped member


53


. The member


53


includes a mating plate formed of two opposite pie-shaped sealing surfaces


55


,


56


, each connected by circular outer edge


54


and extending outwardly from the drive shaft


52


at an angle of 45°, such that the void defined by the two sealing surfaces


55


,


56


and outer edge


54


defines a first gas route or passageway


60


. Similarly, a second gas route or passageway


61


is defined by the sealing surfaces


55


,


56


opposite the first passageway, and three angled side plates, namely, opposite angled side plates


57


A,


57


B, and central angled side plate


57


C. The angled sides plates


57


separate passageway


60


from passageway


61


. The top of these passageways


60


,


61


are designed to match the configuration of symmetrical openings


29


A,


29


B in the plate


28


, and in the assembled condition, each passageway


60


,


61


is aligned with a respective openings


29


A,


29


B. Passageway


61


is in fluid communication with only inlet


48


, and passageway


60


is in fluid communication with only outlet


49


via plenum


47


, regardless of the orientation of the flow distributor


50


at any given time. Thus, process gas entering the manifold


51


through inlet


48


flows through only passageway


61


, and process gas entering passageway


60


from the valve ports


25


flows only through outlet


49


via plenum


47


.




A sealing plate


100


(

FIG. 9

) is coupled to the plate


28


defining the valve ports


25


(FIG.


4


). Preferably an air seal is used between the top surface of the flow distributor


50


and the seal plate


100


, as discussed in greater detail below. The flow distributor is rotatable about a vertical axis, via drive shaft


52


, with respect to the stationary plate


28


. Such rotation moves the sealing surfaces


55


,


56


into and out of blocking alignment with portions of openings


29


A,


29


B as discussed below.




Turning now to

FIG. 6

, a suitable drive mechanism for driving the flow distributor


50


is shown. The drive mechanism


70


includes a base


71


and is supported on frame


12


(FIG.


1


). Coupled to base


71


are a pair of rack supports


73


A,


73


B and a cylinder support


74


. Cylinders


75


A,


75


B are supported by cylinder support


74


, and actuate a respective rack


76


A,


76


B. Each rack has a plurality of grooves which correspond in shape to the spurs


77


A on spur gear


77


. The drive shaft


52


of the flow distributor


50


is coupled to the spur gear


77


. Actuation of the cylinders


75


A,


75


B causes movement of the respective rack


76


attached thereto, which in turn causes rotational movement of spur gear


77


, which rotates the drive shaft


52


and flow distributor


50


attached thereto about a vertical axis. Preferably the rack and pinion design is configured to cause a back-and-forth 180° rotation of the drive shaft


52


. However, those skilled in the art will appreciate that other designs are within the scope of the present invention, including a drive wherein full 360° rotation of the flow distributor is accomplished. Other suitable drive mechanisms include hydraulic actuators and indexers.





FIGS. 7A-7D

illustrate schematically the flow direction during a typical switching cycle for a valve having two inlet ports and two outlet ports. In these diagrams, chamber A is the inlet chamber and chamber B is the outlet chamber of a two column oxidizer.

FIG. 7A

illustrates the valve in its fully open, stationary position. Thus, valve ports


25


A and


25


B are in the full open inlet mode, and valve ports


25


C and


25


D are in the full open outlet mode. Process gas enters chamber A through valve ports


25


A and


25


B, flows through the heat exchange media in chamber A where it is heated, flows through a combustion zone in communication with chamber A where any volatile components not already oxidized are oxidized, is cooled as it flows through chamber B in communication with the combustion zone, and then flows out valve ports


25


C and


25


D into an exhaust stack opening to atmosphere, for example. The typical duration of this mode of operation is from about 1 to about 4 minutes, with about 3 minutes being preferred.





FIG. 7B

illustrates the beginning of a mode change, where a valve rotation of 60° takes place, which generally takes from about 0.5 to about 2 seconds. In the position shown, valve port


25


B is closed, and thus flow to or from chamber A is blocked through this port, and valve port


25


C is closed, and thus flow to or from chamber B is blocked through this port. Valve ports


25


A and


25


D remain open.




As the rotation of the flow distributor continues another 60°,

FIG. 7C

shows that valve ports


25


A and


25


D are now blocked. However, valve port


25


B is now open, but is in an outlet mode, only allowing process gas from chamber A to flow out through the port


25


B and into an exhaust stack or the like. Similarly, valve port


25


C is now open, but is in an inlet mode, only allowing flow of process gas into chamber B (and not out of chamber B as was the case when in the outlet mode of FIG.


7


A).




The final 60° rotation of the flow distributor is illustrated in FIG.


7


D. Chamber A is now in the fully open outlet mode, and chamber B in the fully open inlet mode. Thus, valve ports


25


A,


25


B,


25


C and


25


D are all fully open, and the flow distributor is at rest. When the flow is to be again reversed, the flow distributor preferably returns to the position in

FIG. 7A

by rotating 180° back from the direction it came, although a continued rotation of 180° in the same direction as the previous rotation is within the scope of the present invention.




The six valve port system of

FIG. 3

would operate in an analogous fashion. Thus, each valve port would be 45° rather than 60°. Assuming valve ports


25


A,


25


B and


25


C in

FIG. 3

are in the inlet mode and fully open, and valve ports


25


D,


25


E and


25


F are in the outlet mode and fully open, the first step in the cycle is a valve turn of 45° (clockwise), blocking flow to valve port


25


C and from valve port


25


F. Valve ports


25


A and


25


B remain in the inlet open position, and valve ports


25


D and


25


E remain in the outlet open position. As the flow distributor rotates an additional 45° clockwise, valve port


25


C is now in the open outlet position, valve port


25


B is blocked, and valve port


25


A remains in the open inlet position. Similarly, valve port


25


F is now in the open inlet position, valve port


25


E is blocked, and valve port


25


D remains in the open outlet position. As the flow distributor continues another 45°, valve ports


25


C and


25


B are now in the open outlet position, and valve port


25


A is blocked. Similarly, valve ports


25


F and


25


E are now in the open inlet position, and valve port


25


F is blocked. In the final position, the flow distributor has rotated an additional 45° and come to a stop, wherein all of valve ports


25


A,


25


B and


25


C are in the open outlet position, and all of valve ports


25


D,


25


E and


25


F are in the open inlet position.




As can be seen from the foregoing, one substantial advantage of the present invention over conventional rotary valves is that the instant flow distributor is stationary most of the time. It moves only during an inlet-to-outlet cycle changeover, and that movement lasts only seconds (generally a total of from about 0.5 to about 4 seconds) compared to the minutes during which it is stationary while one of chamber A or chamber B is in the inlet mode and the other in an outlet mode. In contrast, many of the conventional rotary valves are constantly moving, which accelerates wear of the various components of the apparatus and can lead to leakage. An additional benefit of the present invention is the large physical space separating the gas that has been cleaned from the process gas not yet cleaned, in both the valve itself and the chamber (the space


80


(

FIG. 3

) between chamber dividers


124


E and


124


D, and dividers


124


H and


124


A), and the double wall formed by chamber dividers


124


E,


124


H and


124


A,


124


D. Also, since the valve has only one actuation system, the valve will successfully function if it moves fast or slow, unlike the prior art, where multiple actuation systems must work together. More specifically, in the prior art, if one poppet valve is sluggish relative to another, for example, there could be leakage or loss of process flow or a large pressure pulse could be created.




Another advantage of the present invention is the resistance that is present during a switching operation. In conventional valving such as the poppet valving mentioned above, the resistance to flow approaches zero as both valves are partially open (i.e., when one is closing and one is opening). As a result, the flow of gas per unit time can actually increase, further exasperating the leakage of that gas across both partially opened valves during the switch. In contrast, since the flow director of the present invention gradually closes an inlet (or an outlet) by closing only portions at a time, resistance does not decrease to zero during a switch, and is actually increased. thereby restricting the flow of process gas across the valve ports during switching and minimizing leakage.




The preferred method for sealing the valve will now be discussed first with reference to

FIGS. 5

,


8


and


9


. The flow distributor


50


rides on a cushion of air, in order to minimize or eliminate wear as the flow distributor moves. Those skilled in the art will appreciate that gases other than air could be used, although air is preferred and will be referred to herein for purposes of illustration. A cushion of air not only seals the valve, but also results in frictionless or substantially frictionless flow distributor movement. A pressurized delivery system, such as a fan or the like, which can be the same or different from the fan used to supply the combustion air to the combustion zone burner, supplies air to the drive shaft


52


of the flow distributor


50


via suitable ducting (not shown) and plenum


64


. As best seen in

FIG. 8

, the air travels from the ducting into the drive shaft


52


via one or more apertures


81


formed in the body of the drive shaft


52


above the base


82


of the drive shaft


52


that is coupled to the drive mechanism


70


. The exact location of the apertures(s)


81


is not particularly limited, although preferably the apertures


18


are symmetrically located about the shaft


52


and are equally sized for uniformity. The pressurized air flows up the shaft as depicted by the arrows in

FIG. 8

, and a portion enters on or more radial ducts


83


which communicate with and feed one or more piston rings seals located at the annular rotating port


90


as discussed in greater detail below. A portion of the air that does not enter the radial ducts


83


continues up the drive shaft


52


until it reaches passageways


94


, which distribute the air in a channel having a semi-annular portion


95


and a portion defined by the pie-shaped wedges


55


,


56


.




The mating surface of the flow distributor


50


, in particular, the mating surfaces of pie-shaped wedges


55


,


56


and outer annular edge


54


, are formed with a plurality of apertures


96


as shown in FIG.


5


. The pressurized air from channel


95


escapes from channel


95


through these apertures


96


as shown by the arrows in

FIG. 8

, and creates a cushion of air between the top surface of the flow distributor


50


and a stationary seal plate


100


shown in FIG.


9


. The seal plate


100


includes an annular outer edge


102


having a width corresponding to the width of the top surface


54


of the flow distributor


50


, and a pair of pie-shaped elements


105


,


106


corresponding in shape to pie-shaped wedges


55


,


56


of the flow distributor


50


. It matches (and is coupled to) plate


28


(

FIG. 4

) of the valve port. Aperture


104


receives shaft pin


59


(

FIG. 8

) coupled to the flow distributor


50


. The underside of the annular outer edge


102


facing the flow distributor includes one or more annular grooves


99


(

FIG. 9A

) which align with the apertures


96


in the mating surface of the flow distributor


50


. Preferably there are two concentric rows of grooves


99


, and two corresponding rows of apertures


96


. Thus, the grooves


99


aid in causing the air escaping from apertures


96


in the top surface


54


to form a cushion of air between the mating surface


54


and the annular outer edge


102


of the seal plate


100


. In addition, the air escaping the apertures


96


in the pie-shaped portions


55


,


56


forms a cushion of air between the pie-shaped portions


55


,


56


and the pie-shaped portions


105


,


106


of the seal plate


100


. These cushions of air minimize or prevent leakage of the process gas that has not been cleaned into the flow of clean process gas. The relatively large pie-shaped wedges of both the flow distributor


50


and the seal plate


100


provide a long path across the top of the flow distributor


50


that uncleaned gas would have to traverse in order to cause leakage. Since the flow distributor is stationary the majority of time during operation, an impenetrable cushion of air is created between all of the valve mating surfaces. When the flow distributor is required to move, the cushion of air used to seal the valve now also functions to eliminate any high contact pressures from creating wear between the flow distributor


50


and the seal plate


100


.




Preferably the pressurized air is delivered from a fan different from that delivering the process gas to the apparatus in which the valve is used, so that the pressure of the sealing air is higher than the inlet or outlet process gas pressure, thereby providing a positive seal.




The flow distributor


50


includes a rotating port as best seen in

FIGS. 10 and 11

. The frusto-conical section


53


of the flow distributor


50


rotates about an annular cylindrical wall


110


that functions as an outer ring seal. The wall


110


includes an outer annular flange


111


used to center the wall


110


and clamp it to the manifold


51


(see also FIG.


5


). An E-shaped inner ring seal member


116


(preferably made of metal) is coupled to the flow distributor


50


and has a pair of spaced parallel grooves


115


A,


115


B formed in it. Piston ring


112


A sits in groove


115


A, and piston ring


112


B sits in groove


115


B as shown. Each piston ring


112


biases against the outer ring seal wall


110


, and remains stationary even as the flow distributor


50


rotates. Pressurized air (or gas) flows through the radial ducts


83


as shown by the arrows in

FIG. 11

, through apertures


84


communicating with each radial duct


83


, and into the channel


119


between the piston rings


112


A,


112


B, as well as in the gap between each piston ring


112


and the inner ring seal


116


. As the flow distributor rotates with respect to stationary cylindrical wall


110


(and the piston rings


112


A,


112


B), the air in channel


119


pressurizes the space between the two piston rings


112


A,


112


B, creating a continuous and non-friction seal. The gap between the piston rings


112


and the inner piston seal


116


, and the gap


85


between the inner piston seal


116


and the wall


110


, accommodate any movement (axial or otherwise) in the drive shaft


52


due to thermal growth or other factors. Those skilled in the art will appreciate that although a dual piston ring seal is shown, three or more piston rings also could be employed for further sealing. Positive or negative pressure can be used to seal.





FIG. 12

illustrates how the plenum


64


feeding the shaft


52


with pressurized air is sealed against the drive shaft


52


. The sealing is in a manner similar to the rotating port discussed above, except that the seals are not pressurized, and only one piston ring need by used for each seal above and below the plenum


64


. Using the seal above the plenum


64


as exemplary, a C-shaped inner ring seal


216


is formed by boring a central groove therein. A stationary annular cylindrical wall


210


that functions as an outer ring seal includes an outer annular flange


211


used to center the wall


210


and clamp it to the plenum


64


. A stationary piston ring


212


sits in the groove formed in the C-shaped inner ring seal


216


and biases against the wall


210


. The gap between the piston ring


212


and the bore of the C-shaped inner seal


216


, as well as the gap between the C-shaped inner seal


216


and the outer cylindrical wall


210


, accommodates any movement of the drive shaft


52


due to thermal expansion or the like. A similar cylindrical wall


310


, C-shaped inner seal


316


and piston ring


312


is used on the opposite side of the plenum


64


as shown in FIG.


12


.




In operation, in a first mode, untreated (“dirty”) process gas flows into inlet


48


, through passageway


61


of the flow distributor


50


, and into which ever respective valve ports


25


that are in open communication with the passageway


61


in this mode. The untreated process gas then flows up through the hot heat exchange media supported by cold face plenum


20


and through the combustion zone where it is treated, and the now clean gas is then cooled as it flows down through the cold heat exchange media in a second column, through the valve ports


25


in communication with passageway


60


, and out through plenum


47


and outlet


49


. Once the cold heat exchange media becomes relatively hot and the hot heat exchange media becomes relatively cold, the cycle is reversed by activating the drive mechanism


70


to rotate drive shaft


52


and flow distributor


50


. In this second mode, untreated process gas again flows into inlet


48


, through passageway


61


of the flow distributor


50


, which passageway is now in communication with different valve ports


25


that were previously only in fluid communication with passageway


60


, thus directing the untreated process gas to the now hot heat exchange column and then through the combustion zone where the process gas is treated. The cleaned gas is then cooled as it flows down through the now cold heat exchange media in the other column, through the valve ports


25


now in communication with passageway


60


, and out through plenum


47


and outlet


49


. This cycle repeats itself as needed, typically every 1-4 minutes.



Claims
  • 1. A regenerative thermal oxidizer for processing a gas, comprising:a combustion zone; a first heat exchange bed containing heat exchange media and in communication with said combustion zone; a second heat exchange bed containing heat exchange media and in communication with said combustion zone; a valve for alternating the flow of said gas between said first and second heat exchange beds, said valve comprising: a first valve port in fluid communication with said first heat exchange bed and a second valve port separate from said first valve port and in fluid communication with said second heat exchange bed; a flow distributor having an inlet passageway and an outlet passageway, said flow distributor being movable with respect to said first and second valve ports between a first position in which gas entering said inlet passageway flows into said first heat exchange column through said first valve port and out of said outlet passageway through said second heat exchange column and said second valve port, and a second position in which gas entering said first passageway flows into said second heat exchange column through said second valve port and out said outlet passageway through said first heat exchange column and said first valve port; said flow distributor comprising a blocking portion for blocking the flow of gas through a portion of said first and second valve ports when said flow distributor is between said first and second positions.
  • 2. The regenerative thermal oxidizer of claim 1, further comprising a cold face plenum comprising at least one baffle for dividing said first and second valve ports into a plurality of chambers.
  • 3. The regenerative thermal oxidizer of claim 2, wherein each of said chambers is congruent.
  • 4. The regenerative thermal oxidizer of claim 1, wherein said flow distributor is housed in a manifold having a manifold inlet and a manifold outlet, and wherein said manifold inlet is in fluid communication with said first passageway of said flow distributor, and said manifold outlet is in fluid communication with said second passageway of said flow distributor.
  • 5. The regenerative thermal oxidizer of claim 1, further comprising a drive shaft coupled to said flow distributor; at least one radial duct in fluid communication with and extending radially from said drive shaft; and a rotating port comprising: an outer ring seal, an inner ring seal spaced from said outer ring seal and having a plurality of bores, and at least one piston ring, said at least one piston ring positioned in a respective one of said plurality of bores in said inner ring seal and biasing against said outer ring seal.
  • 6. The regenerative thermal oxidizer of claim 5, further comprising means for causing gas to flow into said drive shaft, into said at least one radial duct, and between said at least one piston ring and said inner ring seal.
  • 7. The regenerative thermal oxidizer of claim 1, further comprising a sealing plate, and wherein said flow distributor further comprises a mating surface having a plurality of apertures through which gas flows, creating a cushion of gas between said mating surface and said sealing plate.
  • 8. The regenerative thermal oxidizer of claim 7, wherein said sealing plate comprises at least one annular groove aligned with some of said plurality of apertures.
  • 9. The regenerative oxidizer of claim 1, further comprising drive means for moving said flow distributor between said first and second positions.
  • 10. The regenerative oxidizer of claim 9, wherein said drive means comprises a gear coupled to said flow distributor, said gear having a plurality of spurs, and at least one rack having a plurality of grooves into which said plurality of spurs fit, whereby movement of said rack causes a corresponding movement of said gear, which rotates said flow distributor.
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