Patent Publication Number: US-2003221725-A1

Title: Regenerative oxidizers with elliptical valve system

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates generally to regenerative thermal oxidizers. More specifically, the present invention relates to valve systems for two chamber regenerative thermal oxidizers.  
       BACKGROUND OF THE INVENTION  
       [0002] Regenerative thermal oxidizers (RTOs) are used in a number of industries to reduce the quantity of contaminants in process effluent gases. RTOs are unique in their ability to conserve fuel through the use of heat exchangers. In an RTO, the process effluent gases are oxidized in a combustion chamber. As the high-temperature combustion gases move to an exhaust stack, they flow through a heat exchanger, typically a chamber filled with ceramic saddles or the like. In the heat exchanger, up to 95% of the heat is transferred from the gases to the ceramic saddles. The flow of gases is then reversed such that the inlet process gases move through the heat exchanger toward the combustion chamber. Heat is transferred from the hot ceramic media to the process gases and consequently less energy is required to oxidize the process gases in the combustion chamber.  
       [0003] Several configurations of RTOs have been developed based on this heat recovery principle. In an RTO having three or more chambers, one heat exchanger sequentially serves as a standby chamber such that the continuous flow of process gas is not interrupted during flow reversal. In a two chamber RTO, however, neither of the heat exchangers can function as a standby chamber and thus the problem of handling a continuous process gas stream is more difficult. In a two chamber RTO both heat exchangers are separately attached to a shared combustion chamber. A flow path is thereby established that extends from the inlet of one heat exchanger, through the heat exchange medium, into the combustion chamber and then out via the second heat exchange chamber.  
       [0004] In order for the incoming process gas to capture heat from the heat exchangers, gas flow through the RTO must be periodically reversed. And, as will be appreciated by those skilled in the art, flow reversal must occur in a manner which minimizes discharge of unoxidized process gas to the atmosphere.  
       [0005] The prior art has used electronic and hydraulic controls to actuate valves in RTOs. It is difficult, however, to properly time the opening and closing of the valves associated with the heat exchange chambers and still maintain steady inlet pressures. Further, hydraulically opened and closed valves tend to significantly restrict the flow of gas through the valves when they first begin to close, but then slowly taper to zero. Accordingly, the valves are restricted in a manner which results in low flow percentages for a relatively long portion of the cycle.  
       [0006] Various types of cams and other mechanical actuation systems have also been used to open and close inlet and outlet butterfly/wafer valves in three chamber RTOs. These include mechanically operated means which have utilized eccentrically mounted secondary shafts driven by a main shaft.  
       [0007] In the case of two chamber RTOs the most frequently used valve system employs poppet valves actuated by hydraulic or air linear actuators connected to the valve shaft. Poppet valves go from zero flow to full flow quickly and the opening and closing of the poppets minimizes the tendency of foreign particles carried by the gases to be trapped in the valve. Gas moving through the valve is directed by the position of a disk or “poppet” which is fixed on a stem. The disk is moved linearly so that it seals one of two opposed valve seats.  
       [0008] In two chamber RTOs, two poppet valves are employed, each having its own hydraulic or pneumatic linear actuator. It will be appreciated that for efficient operation, both poppet valves must be timed so that they open and close as fast as possible, forming substantially airtight seals. While hydraulic or air linear actuated poppet valves have some advantages (i.e., the overall simplicity of poppet valves), for large RTOs such systems are not always reliable. For example, in a large RTO a poppet disk may weigh in excess of 300 pounds and may cycle 200,000 times per year. With disks of this size, poppet valves actuated hydraulically or by air linear means are inadequate to provide control and sealing force to the degree required for reliable operation. Moreover, due to the force with which the valves are closed, they may cause premature wear of valve seats, i.e. due to the “slamming” of the disk against the valve seat. Moreover, the lack of constant air pressure in RTOs, the temperature variability of many hydraulic fluids, as speed varies season to season due to ambient variances and occasional frozen air lines, and a number of other factors make these conventional systems less than optimum.  
       [0009] Therefore it would be desirable to provide a two chamber RTO valve system which addresses the problems inherent in the prior art. A two chamber RTO having a valve system which meets the above-noted objectives is described in Greco, U.S. Pat. No. 6,039,927. It is desirable to bring forth a two chamber RTO having a valve system which takes the improvements brought forth by Greco to a higher level. The present invention meets these objectives.  
       SUMMARY OF THE INVENTION  
       [0010] In one aspect the present invention provides a first heat exchanger defining a first flow path. A first inlet/outlet in association with the first flow path is provided with the first inlet/outlet providing flow access to the first flow path. In like manner, a second heat exchanger defining a second flow path is provided. The second heat exchanger is associated with a second inlet/outlet. Additionally, a valve assembly is provided having a valve body having process flow inlet and outlets and first and second ports connected to the first and second inlet/outlets of the heat exchanger.  
       [0011] The valve assembly has an elliptical valve disk having an outer perimeter for sealably engaging the cylindrical body. The valve disk is pivotally mounted within the valve body having a first position connecting the process flow inlet with the first side port and process flow outlet with the second side port. In a second position, the disk connects the process flow outlet with the first port and a process flow inlet with the second port. Accordingly, only a single valve disk is required, unlike many prior RTOs which required separate valve disks.  
       [0012] In another aspect, a valve disk is provided which has a pivotal axis at an angle with its plane of extension. The valve disk seals directly against an interior surface of the valve body and can be rotated unidirectionally or bidirectionally.  
       [0013] Further aspects, features and advantages of the present invention will become more apparent to those skilled in the art after a review of the invention as it shown in the accompanying drawings and detailed description. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014]FIG. 1 diagrammatically illustrates the components and operation of the present invention.  
     [0015]FIG. 2 is a partial sectional view illustrating a disk sealably engaged with a valve body in the RTO shown in FIG. 1.  
     [0016]FIG. 3 is a diagrammatic illustration of the present invention in another embodiment in which the valve disk is pivotally mounted within the valve body at an angle with respect to a plane extension of the valve disk and wherein the valve disk is driven unidirectionally.  
     [0017]FIG. 4 is a partial sectional view of the RTO almost identical to that shown in FIG. 3 with a motor and linkage arrangement to give reciprocating motion to the valve disk.  
     [0018] FIGS.  5 - 7  are views taken along lines  5 - 5 ,  6 - 6 , and  7 - 7  of FIG. 4, respectively.  
     [0019]FIG. 8 is a view taken along lines  8 - 8  of FIG. 7. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0020] Referring now to FIG. 1 of the drawings, regenerative thermal oxidizer or incinerator  20  is shown diagrammatically having common combustion chamber  21  in flow communication with first and second heat exchangers  22 ,  24 . As will be appreciated by those skilled in the art of regenerative incinerators, heat exchangers  22 ,  24  define chambers which house a heat exchange element  25  such as ceramic saddles or porous ceramic monoliths. Heat exchanger  22  has inlet/outlet  26  through which gas enters and exits the combustion chamber  21 . Similarly, heat exchanger  24  has inlet/outlet  28  which provides flow access. The opposite ends of heat exchangers  22 ,  24  are attached to combustion chamber  21  in the standard fashion; that is, a flow passage is created by which process gases can flow into one of the heat exchangers, into the combustion chamber (which is equipped with a burner  30 ) and then out through the opposite heat exchanger. As described in the background section of this application, as the hot combustion gases flow through the exit heat exchanger heat is transferred to the ceramic heat exchange element. The path of gases through heat exchangers  22 ,  24  and combustion chamber  21  are shown by the arrows marked “A” in FIG. 1 in one mode of operation.  
     [0021] Still referring to FIG. 1 of the drawings, the duct and valve assembly of the invention will now be described. There are essentially four ducts or passages for gas from the heat exchangers to the valve body  31  of valve assembly  32 . The first is transfer duct  34  which is in flow communication with heat exchanger  22 . Transfer duct  34  extends between heat exchanger  22  and valve port  36 . A second transfer duct  38  extends from heat exchanger  24  to port  40  of valve body  31 . Inlet or process gas duct  42  extends from the source of process gas (not shown) to process flow inlet  44  of valve body  31 . Finally, outlet or exhaust gas duct  46  extends from process flow outlet  48  of valve body  31  to exhaust stack  50 .  
     [0022] Referring also to FIG. 2, valve body  31  has interior surface  52 . Affixed to interior surface  52  is valve seat  54 . Valve seat  54  has compound sealing surfaces  56 ,  58 . Pivotally mounted within valve body  31  is disk  62 . Disk  62  has a pivotal axis that is generally coterminous with a pivot shaft  64 . Disk  62  is elliptical in shape. Disk  62  has an outer perimeter  66 . Both sides of the outer perimeter  66  have affixed thereto an elastomeric seal  68 . Elastomeric seal  68  has a head  70 , typically sized to compress 50% when sealably engaged with sealing surfaces  56 ,  58 .  
     [0023] Disk  62  has a first position as shown in FIG. 1 connecting process inlet  44  with port  36  and inlet  26 . Simultaneously, disk  62  connects ports  36 ,  40  with outlet  48  which connects with exhaust stack  50 . In a second position shown in phantom in FIG. 1, disk  62  connects inlet  44  with port  40  and inlet/outlet  28  and additionally, connects inlet/outlet  26  and port  36  with outlet  48  and exhaust stack  50 .  
     [0024] Elliptical disk  62  also has an upper conic semi-hemisphere  74  and a lower conic semi-hemisphere  76 . Valve seat  54  is formed in a spiral on surface  52  to project a semi-elliptical valve seat surface for disk  62 . Additionally, there is provided a valve seat  78  to sealably engage with the seal  68  when disk  62  is in its second position. In a similar manner, two addition valve seats are provided (not shown) for sealably engaging with the lower semi-hemisphere  76  of the disk  62 .  
     [0025] Referring now to FIGS.  3 - 6 , another embodiment RTO  120  is shown with items performing similar functions to those in FIGS. 1 and 2 being given like reference numerals. RTO  120  has a valve assembly  122  and valve body  124 . Mounted for pivotal movement within valve body  124  is valve disk  126 . Valve disk  126  has a first position sealably engaged with interior surface wall  128  of the valve body wherein process flow inlet  44  is connected with a first port  36 . In like manner, process flow outlet  48  is connected with port  40 . In a second position shown in phantom, port  36  is connected with outlet  48  and port  40  is connected with inlet  44 . Valve disk  126  is connected with a shaft  130  at an angle, typically, 30 degrees to 60 degrees with a plane of extension of valve disk  126 . Valve disk  126  has seals  132  that directly sealably engage valve body interior surface  128 . Valve disk  126  may be pivoted in a reciprocating manner by a motor and linkage arrangement as shown in FIGS. 4, 7 and  8  and as previously described for valve disk  62 . Valve disk  126  may also be pivoted in a constant angular direction by a motor  141  as shown in FIG. 3. Valve disk  126  may also be programmed to pivot unidirectionally or bi-directionally.  
     [0026] Referring now to FIGS.  7 - 8 , to reciprocally rotate valve disk  62  or  126  there is provided a motor  140 . Motor  140  rotates shaft  142 . Connected at an end of shaft  142  is a disk  144 . Disk  144  adjacent its outer perimeter  146  is pivotally connected with rod  148 . Rod  148  opposite its pivotal connection with disk  144  is slidably encircled by pivot washer  150 . Pivot washer  150  is pivotally connected with pivot arm  152 . Pivot arm  152  is connected with shaft  64  or shaft  130 . Positionally locked on rod  148  are set washers  154 ,  156 . Each set washer  154 ,  156  captures between itself and pivot washer  150  at a spring  158 . Springs  158  act as compliance members to absorb shock in the opening and closing of the disk.  
     [0027] While preferred embodiments of the present invention have been disclosed, it is to be understood that they have been disclosed by way of example only and that various modifications can be made without departing from the spirit and scope of the invention as it is explained by the following claims.