Information
-
Patent Grant
-
6261092
-
Patent Number
6,261,092
-
Date Filed
Wednesday, May 17, 200024 years ago
-
Date Issued
Tuesday, July 17, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Bittman; Mitchell D.
- Lemack; Kevin S.
-
CPC
-
US Classifications
Field of Search
US
- 432 179
- 432 180
- 432 181
- 110 245
- 110 345
- 137 309
- 137 311
-
International Classifications
-
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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