Abstract:
Smokeless burnout of regenerative thermal oxidizer systems is accomplished by isolating the incineration system from the process flow and drawing fresh air into the heating regenerator at approximately one-fourth of the normal process flow. A purge/burnout fan is employed to induce flow through an idle regenerator drawing high temperature gas from the retention chamber through the idle regenerator. Gas is directed from the purge/burnout fan back into the retention chamber to oxidize contaminants which has been volatilized from the media in the third regenerator. The reduced flow rate of the system and maintaining flow through the regenerator being burned out while continuing to cycle the remaining regenerators as heating and cooling regenerators builds the temperature in the burnout regenerator until volatilization of all contaminants is achieved. Upon completion of burnout of the first burnout regenerator, that regenerator enters the cycle as a cooling regenerator and the next idle regenerator enters the burnout cycle.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the removal of accumulated contaminant deposits on the heat transfer media of regenerative thermal oxidizers. More particularly, the present invention provides an apparatus and method for conducting a burnout of regenerator heat transfer media beds, while eliminating any discharge of visible unburned contaminants, which may be accomplished in an off-line condition for the oxidizer or a flow through on-line condition of the oxidizer. The present system is provided in combination with a purge system employed in normal operation of the oxidizer to preclude venting of unburned contaminants to the atmosphere during changeover between regenerators in a multiple regenerator system. 
     2. Description of the Prior Art 
     Regenerative incinerator systems use gas flow reversal to recapture heat, which would otherwise be lost to the atmosphere, during thermal oxidation of volatile contaminant compounds. A regenerative incinerator system consists of a gas heating regenerator which receives the processed gas from the system producing the volatile contaminants, a burner and retention chamber to oxidize the processed gas, and a regenerator which is heated by the exiting gas to cool the gas and reclaim the heat of the combustion process. After a period of time, flow of the gas through the system is reversed whereby the regenerator previously employed in heat recovery, now becomes the heating regenerator and the gas heating regenerator becomes the cooling regenerator through which gas passes prior to being released to the atmosphere thereby again raising the temperature of that regenerator bed. 
     Regenerator systems employing flow reversal in early systems allowed unburned gases in the inlet regenerator to be released to the atmosphere during the flow reversal. Use of multiple regenerator canisters with purge systems for removal of the unburned gas during flow reversals, eliminates this source of pollution. Certain prior art regenerative incinerator systems use positive pressure within the bottom of the idle regenerator to purge the unburned gases prior to flow reversal. Fresh air or incinerated air is introduced into the bottom of the idle regenerator which forces the residual gas through the media bed and into the combustion chamber. Use of positive pressure purging in this manner requires additional fan capability in the exhaust fan for the system and requires burning of recycled incinerated air thereby increasing fuel usage. 
     An improved system employing an induced draft purge is disclosed in U.S. Pat. No. 5,026,277 entitled REGENERATIVE THERMAL INCINERATOR APPARATUS, issued to James A. York on Jun. 25, 1991 which is assigned to the assignee of the present invention. The device disclosed in York uses negative pressure rather than positive pressure to purge the idle regenerator. The residual gas within the idle regenerator is removed by suction from the combustion air fan prior to flow reversal. 
     Operation of regenerative systems such as that disclosed in York and in U.S. Pat. Nos. 3,634,026 to Kuechler, issued Jan. 11, 1972, and U.S. Pat. No. 3,870,474 to Houston, require shutdown of the system to clean the regenerative beds of contaminant deposits which become entrapped in the heat transfer media. Removal of these contaminant deposits requires baking or burnout of the heat transfer media at temperatures sufficient to volitize the contaminant deposits on the heat transfer media. Previously, the volatilized contaminants were emitted to the atmosphere, thus causing a pollution problem. Typical prior art systems require removal of the heat transfer media from the beds in the regenerator canisters for burnout of the contaminant deposits. Alternative techniques such as that disclosed in Houston for removal of portions of the contaminated heat transfer media at the bottom of the regenerator with replacement of fresh heat transfer media at the top of the regenerator reduces the down time of the regenerator, and in some possible cases, could allow operation of the incinerator during media change out. The use of multiple canisters wherein one or more regenerators is idle during a process cycle, allows such operation. 
     The difficulty of performing such maintenance during operation of the system, including the potential hazards of an operating high temperature system, renders these methods less than ideal. 
     It is, therefore, desirable to provide a system for burnout of the regenerator media beds without removal of the media and while allowing minimal system down time, or continued operation of the system in incineration of the processed gas during burnout of one or more of the regenerators. 
     The present invention provides the capability to conduct a burnout of the trapped contaminant compounds in the media of the regenerators without removal of the media. The combination of the burnout feature of the present invention with an induced draft purging system avoids redundancy in system elements and provides maximum efficiency. The primary feature of this invention is that burnout of the regenerators is accomplished without the discharge of visible unburned contaminants to the atmosphere and may be accomplished while incineration of process gas is continued. 
     SUMMARY OF THE INVENTION 
     The present invention is incorporated in a multiple canister regenerative thermal incinerator. Each regenerator contains heat exchange media which preheats incoming gas or cools oxidized gas prior to exhausting gas to the atmosphere. A first inlet regenerator receives process gas which is warmed while passing through the regenerator and transmitted to a combustion retention chamber. The combustion retention chamber incorporates an air-fuel system having at least one burner for elevation of the chamber temperature to oxidize the process gas. A second regenerator receives gas from the retention chamber for exhaust through an induced draft fan to the atmosphere. Gas passing from the retention chamber heats the media of the second regenerator. A third regenerator is idle during this process flow and is simultaneously purged of partially treated gas remaining from a previous cycle. The purged gas is drawn by either a dedicated purge fan or a combination purge/burnout fan from the third regenerator and directed to the process gas inlet of the system allowing processing and oxidation of the purged gas. The direction of flow of the gas through the system is periodically changed to enable heat recovered by cooling the process gas in the second regenerator to be used to heat incoming gas. The first regenerator becomes idle thereby allowing purging while the previously idle regenerator receives the gas from the retention chamber heating the regenerator and cooling the outlet gas. 
     Burnout of the system is accomplished in one mode by isolating the incineration system from the process flow and drawing fresh air into the heating regenerator at approximately one-fourth of the normal process flow as inlet gas into the system. The inlet gas is heated in the heating regenerator and cooled in the cooling regenerator and exhausted to the atmosphere. The purge/burnout fan is employed to induce flow through one of the idle regenerators drawing high temperature gas from the retention chamber through the idle regenerator. Gas is directed from the purge/burnout fan back to the retention chamber to oxidize contaminants which have been volatilized from the media in the third regenerator. The reduced flow rate of the system and maintaining flow through the regenerator being burned out, while continuing to cycle the remaining regenerators as heating and cooling regenerators, builds the temperature in the burnout regenerator until volatilization of the contaminants is achieved. Upon completion of burnout for the first burnout regenerator, that regenerator enters the cycle as a cooling regenerator and the next idle regenerator enters the burnout cycle. 
     Burnout of each regenerator is thereby accomplished to volatilize the contaminant compounds deposited in the heat transfer media beds. Direction of the volatilized contaminants through the retention chamber assures their incineration precluding soot or smoke in the gas exhausted from the system. 
     In the alternative, burnout of the system may be conducted by reducing the process gas flow to approximately one quarter of the normal flow for an &#34;on the fly&#34; burnout. Cycling of the regenerators into the burnout phase replaces purging of the regenerator brought to the idle condition for burnout. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a preferred embodiment of the invention showing three regenerator canisters of a multiple canister system. 
     FIG. 2 is a schematic diagram of the preferred embodiment of the system shown in FIG. 1 for a five canister system. 
     FIGS. 3a-c are schematic flow diagrams showing the various cycles of operation of the preferred embodiment of the invention for normal process gas flow with purging. 
     FIGS. 4a-c are schematic flow diagrams showing the various cycles of operation of the preferred embodiment of the invention during burnout operations. 
     FIGS. 5a-c are schematic flow diagrams showing the various cycles of operation of the preferred embodiment of the invention during &#34;on the fly&#34; burnout. 
     The advantages of the present invention may be best understood with reference to the drawings and the following detailed description of the invention. 
    
    
     DETAILED DESCRIPTION 
     The embodiment shown in FIG. 1 demonstrates the basic elements of the present invention. The invention is employed in a thermal incinerator system having multiple regeneration canisters. The embodiment described herein and disclosed in FIGS. 2-5 incorporates five regenerators. FIG. 1 shows three of the five regenerators for simplicity. The present invention is operable with three or more regenerators. 
     FIG. 1 displays three regenerators 1, 2, and 3 each consisting of a gas permeable support structure 6 above a closed plenum 8. Heat transfer media 10 such as ceramic, porcelain, quartz gravel, or metal is contained within the support structure. 
     Connected to the base of regenerators 1, 2, and 3 are inlet conduits 12, 14, and 16 respectively, which communicate with the plenum in the base of each regenerator. Damper valves 22, 24, and 26 in each of inlet conduits respectively, may be positioned open or closed for selectively connecting the regenerators with an intake conduit 32 connected to the inlet conduits. 
     Also connected to the base of regenerators 1, 2, and 3, are outlet conduits 34, 36, and 38 respectively, which also communicate with the plenum. Damper valves 44, 46, and 48 are contained in the outlet conduits which may be positioned open or closed for selectively communicating the regenerators with an exhaust conduit 56. An induced draft exhaust fan 58 is connected to the exhaust conduit for venting of the processed effluent to the atmosphere. 
     Additionally, connected to the base of regenerators 1, 2, and 3 are purging conduits 60, 62, and 64 respectively, which also communicate with the plenum. Damper valves 70, 72, and 74 may be opened or closed for connecting the plenum of the respective regenerator through the associated purging conduit and through purge/burnout fan 80 into a common conduit with a first branch 82 connected to the intake conduit. The exhaust from fan 80 is also connected through a common conduit 84 to a retention combustion chamber 86, which extends over and interconnects the top of the regenerators. Damper valves 88 and 90 control flow of the gas from the purge/burnout fan through conduits 82 and 84, respectively. 
     The combustion chamber is heated by burners 92 and 94, which receive combustion air from fan 100 through conduit 102. Conduit 104 delivers fuel to the burners through valves 106 and 108, respectively. 
     Control of the process gas for burnout of the system is accomplished through isolation damper valve 110 in the intake conduit. A fresh air conduit 112 connected to the intake conduit downstream of isolation valve 110 allows the intake of fresh air through inlet damper valve 114. 
     FIG. 2 illustrates the present invention for a five regenerator system. Regenerators 4 and 5, not shown in FIG. 1, are shown schematically in FIG. 2 with associated intake conduits 18 and 20, intake damper valves 28 and 30, outlet conduits 40 and 42, outlet damper valves 50 and 52, purged conduits 66 and 68, and purged damper valves 76 and 78, all components operating as previously described for comparable elements associated with regenerators 1-3. Additional burners 96 and 98 with associated gas control valves 110 and 112 are shown in the combustion retention chamber 86 with raw gas injection nozzles 120, 122, and 124, not shown for simplicity in FIG. 1, which provide for additional temperature control and uniformity in the retention chamber. 
     Operation of the present invention in the normal gas processing mode is exemplified in Table I and FIG. 3a-c. As shown in the Table, two regenerators operate in the inlet mode and two regenerators operate outlet mode while the fifth regenerator is purged. 
     
                       TABLE I______________________________________REGENERATOR   1        2     3      4   5______________________________________Normal        I        I     O      O   PCycling;      P        I     I      O   O         O        P     I      I   O         O        O     P      I   I         I        O     O      P   I______________________________________ I = INLET O = OUTLET P = PURGE 
    
     Referring to FIG. 3a, and the first line of Table I, regenerators 1 and 2 begin operation in the inlet mode. Valves 22 and 24 are open allowing process gas flowing through the intake conduit through inlet conduits 12 and 14 into the regenerators. Process gas flows through the regenerator media beds into retention chamber 86. In operation, the media beds of regenerators 1 and 2 have been warmed in a previous cycle, and now warm the process gas flowing through them to the retention chamber. The burners in the retention chamber maintain the retention chamber at an oxidation temperature of approximately 1450° F., which oxidizes the contaminant compounds present in the process gas. Regenerators 3 and 4 are the outlet regenerators with valves 48 and 50 in the open condition allowing the oxidized gas from the retention chamber to be drawn through the media beds in regenerators 3 and 4 through outlet conduits 38 and 40 into exhaust conduit 56. Reduced pressure in exhaust conduit 56 is provided by an induced draft fan 58, which exhausts the gas to atmosphere through an oxidizer stack. Gas flowing from the retention chamber through the media beds of regenerators 3 and 4 heats the heat transfer materials in those beds. 
     Regenerator 5 undergoes purging by opening of damper valve 78, which allows purge/burnout fan 80 to draw any gas remaining in the media bed of regenerator 5 through purge conduit 68. The purged gas flows from the purge/burnout fan through damper valve 80 and through conduit 82 into the intake conduit where it joins the process gas for incineration in the system. 
     As shown in FIG. 3b for the next cycle of the system, regenerator 3 transitions from an outlet regenerator to an inlet regenerator by closing of valve 48 and opening of valve 26. Heat transferred to the media bed of regenerator 3, during the prior cycle, is then employed to heat the inlet process gas flowing into the retention chamber. 
     Regenerator 5, which was undergoing purging in the previous cycle, becomes an outlet regenerator by closing valve 78 and opening of valve 52 thereby allowing incinerator gas from the retention chamber to flow through the media bed to heat the heat transfer material therein. Regenerator number 1 previously transferring heat to the incoming process gas is now purged by the closing inlet valve 22 and opening outlet valve 70 thereby drawing any process gas remaining in regenerator number through the purge/burnout fan and into the intake conduit. 
     The next cycle change illustrated by the third line of Table I and FIG. 3c results in a transition of regenerator 4 from an outlet to inlet regenerator by the closing of valve 50 and opening of valve 28, and transitioning of regenerator 1 from its purge cycle to an outlet cycle by closing of valve 70 and opening of valve 44. 
     Regenerator 2 becomes the idle regenerator which is purged by closing valve 24 and opening valve 72 allowing any unoxidized process gas to be drawn out of regenerator 2 through the purge/burnout/fan and into the intake conduit. 
     Cycling of the thermal incinerator continues through the conditions shown in Table I with normal cycling at a period of approximately 45 to 65 seconds. Operation of the system with three regenerators is accomplished by eliminating duplicated inlet and outlet regenerators while operation of systems with greater numbers of regenerators can be accomplished adding paired inlet, outlet, and idle/purge regenerators as required for system flow rate and cycle timing. 
     Operation of the present invention in a first burnout mode is demonstrated in Table II and FIGS. 4a-c. To accomplish a burnout in this mode, the regenerative thermal oxidizer is removed from the incineration mode and isolated from the process flow by closing isolation damper 114. Fresh air inlet damper 118 is opened allowing air to be drawn through conduit 116 into the intake conduit. As shown in Table II, burnout is initiated on regenerator 1 at the completion of a normal incineration cycle in which regenerator number 1 has completed a cycle as the outlet regenerator. Consequently, regenerator number 1 already holds an elevated temperature in the media bed. In the sequence shown in Table II for the first line of the burnout mode and FIG. 4a, inlet valve 22 and outlet valve 44 for regenerator number 1 are placed in the closed condition and purge valve 70 is opened allowing gas to be drawn through the purge/burnout fan from the regenerator. Isolation damper 88 is closed, while isolation damper 90 is opened allowing gas to flow from the purge/burnout fan through conduit 84 into the combustion retention chamber. Regenerator 5 is operating as an inlet regenerator throughout the burnout of Regenerator 1 to cool down with valve 30 open and valves 52 and 78 closed. Regenerator 2 is also operating as the inlet regenerator with valve 24 open, and valves 46 and 72 closed. Air flowing through conduit 116 and the intake conduit to inlet conduit 14 is heated in regenerator 2 flowing through the combustion retention chamber to regenerator number 3, which is acting as the outlet regenerator having valves 26 and 74 closed with valve 48 open to discharge the air through the exhaust conduit 56 and induced draft fan 58. Regenerators 4 is idle with all valves closed throughout the burnout of regenerator 1. The regenerators will continue to cycle as shown in Table II until the temperature in the plenum below the media bed of regenerator 1 reaches burnout temperature and the contaminants trapped in the media bed have been volatilized. 
     
                       TABLE II______________________________________REGENERATOR 1     2     3   4   5______________________________________Normal      P     O     O   I   I   NormalCycling     O     O     I   I   P   Incineration                               ModeStart #1    B     I     O   C   I   This isRegenerator B     O     I   C   I   repeatedInlet       B     I     O   C   I   until theFlow        B     O     I   C   I   area below the(Maximum of B     I     O   C   I   bed reaches50% capacity)       .     .     .   .   .   burnout temp.       .     .     .   .   .       .     .     .   .   .       B     O     I   C   IStart #2    I     B     O   I   CRegenerator I     B     I   O   C       I     B     O   I   C       I     B     I   O   C       .     .     .   .   .       .     .     .   .   .       .     .     .   .   .Regenerator #2       I     B     O   I   Cat burnouttemp.Start #3    C     I     B   O   IRegenerator C     I     B   I   OBurnout     C     I     B   O   I       C     I     B   I   O       .     .     .   .   .       .     .     .   .   .       .     .     .   .   .Regenerator #3       C     I     B   O   Iat burnouttemp.Start #4    I     C     I   B   ORegenerator O     C     I   B   IBurnout     I     C     I   B   O       O     C     I   B   I       .     .     .   .   .       .     .     .   .   .       .     .     .   .   .Regenerator #4       I     C     I   B   Oat burnouttemp.Start #5    O     I     C   I   BRegenerator I     O     C   I   BBurnout     O     I     C   I   B       I     O     C   I   B       .     .     .   .   .       .     .     .   .   .       .     .     .   .   .Regenerator #5       O     C     C   I   Bat burnouttemp.Normal      P     O     O   I   I   Return toCycling     O     O     I   I   P   Normal                               Incineration                               Mode.______________________________________ I = INLET O = OUTLET P = PURGE B = BURNOUT C = CLOSED/IDLE 
    
     The next cycle of the burnout of regenerator number 1 is shown in the next line of Table II and FIG. 4b, wherein regenerator number 4 remains idled by closing all valves and regenerator number 3 becomes the inlet regenerator by opening valve 26 and closing valve 48. Regenerator number 2 operates as the outlet regenerator by opening valve 46 and closing valve 24. Regenerator number 5 remains an inlet regenerator throughout the burnout cycle for regenerator 1. 
     Cycling of regenerators 2 and 3 continues in the sequence, as shown in Table II, while gas flow from the retention chamber drawn by the purge/burnout fan through purge valve 70 of regenerator number 1 continues to increase the temperature of the media bed. When temperature in the plenum below the media bed of regenerator number 1 reaches burnout temperature, burnout is complete and the contaminant compounds trapped in the heat transfer media have been volitized and drawn through the purge/burnout fan to the combustion retention chamber for oxidation. 
     Upon completion of the burnout of regenerator number 1, regenerator 2 is placed in the burnout configuration with the closing of valves 24 and 46 and opening of valve 72 to allow drawing of gas from regenerator 2 through the purged burnout fan. It should be noted that the cycle immediately prior to the burnout configuration of regenerator 2 included regenerator 2 operating as the outlet regenerator. Regenerator 1 operates as an inlet continuously for cool down and regenerators 3 and 4 cycle as inlet and outlet regenerators for the system as shown in Table II. The first cycle of the regenerator 2 burnout is shown in FIG. 4c. Regenerator 1 is an inlet regenerator with valve 22 in the open position and valves 44 and 70 in the closed position. Regenerator 3 is the outlet regenerator with valves 26 and 74 in the closed position, and valve 48 in the open position. Regenerator is also an inlet with valves 50 and 72 closed and valve 28 open. Regenerator 5 is idle throughout the burnout cycle with all valves closed. 
     During the next cycle, as shown in Table II, regenerator 1 remains an inlet for cooling. Regenerator 3 becomes the inlet regenerator with valve 26 open and valves 48 and 74 closed, while regenerator 4 becomes the outlet regenerator with valve 50 open and valves 28 and 76 closed. Regenerator 5 remains idle with all valves closed. 
     Cycling of regenerators 3 and 4 continues until temperature in the plenum of regenerator 2 reaches burnout temperature as previously described with regenerator 1. Burnout of regenerators 3, 4, and 5 is then accomplished sequentially as described for regenerators 1 and 2 and as shown in Table II. 
     A damper 120 controls the inlet to the purge/burnout fan for adjustment of purge and burnout flows from the regenerators. The purge/burnout fan is sized to handle the flow volume required during normal purging of the media beds in a regenerator when the oxidizer is in the normal incineration mode. In the embodiment shown the purge cycle in the incineration mode lasts approximately 45 to 65 seconds for each regenerator, while in the burnout mode, the purge/burnout fan continues to exhaust the same regenerator for approximately 1 hour to reach the desired burnout temperature. 
     The burnout cycles described in Table II are used in an alternate mode for continuing flow of process gas at a reduced flow rate. Valve 114 is throttled but remains open and valve 118 remains closed. Cooling rate is approximately 50% of that in the next mode to be described, however, it remains much faster than the burnout rate. 
     A second mode for burnout of the system allowing continued flow of process gas through the system is demonstrated in Table III and FIGS. 5a-c. This burnout mode for regenerator 5 valves 30 and 52 are closed, while valve 78 is open allowing gas to be drawn from regenerator 5 through the purge/burnout fan for return to the combustion retention chamber. Process gas continues to flow through the intake conduit with regenerators 2 and 4 acting as inlet regenerators having valves 24 and 28 open, respectively, while regenerators 1 and 3 act as outlet regenerators with valves 44 and 48 open, respectively. This configuration is shown in FIG. 5a and the first line of Table III. Regenerators 2 and 3 cycle to outlet and inlet regenerators, respectively as shown in line 2 of Table III, wherein valve 24 is closed and valve 46 is opened for regenerator 2 and valve 26 is opened and valve 48 closed for regenerator 3. This configuration is shown in FIG. 5b. Regenerators 1, 2, 3, and 4 continue cycling as shown by Table III with regenerator 5 in the burnout mode until burnout temperature is reached in the plenum at the bottom of regenerator 5. 
     
                       TABLE III______________________________________REGENERATOR 1     2     3   4   5______________________________________Inlet flow  I     I     O   O   P   Normalat max.     P     I     I   O   O   Incinerationcapacity                            ModeRegenerator #5       O     I     O   I   B   BurnoutMaximum inlet       O     O     I   I   B   Modeflow up to  I     O     O   I   B   (continuesmax. capacity       O     I     O   I   B   until burnout       O     O     I   I   B   temp. reached       .     .     .   .   .   then advance       .     .     .   .   .   to next media       .     .     .   .   .   bed)       O     O     I   I   BRegenerator #1       B     O     I   O   I       B     O     O   I   I       B     I     O   O   I       B     O     I   O   I       B     O     O   I   I       .     .     .   .   .       .     .     .   .   .       .     .     .   .   .       B     O     O   I   IRegenerator #2       I     B     O   I   O       I     B     O   O   I       I     B     I   O   O       I     B     O   I   O       I     B     O   O   I       .     .     .   .   .       .     .     .   .   .       .     .     .   .   .       I     B     O   O   IRegenerator #3       O     I     B   O   I       I     I     B   O   O       O     I     B   I   O       O     I     B   O   I       I     I     B   O   O       .     .     .   .   .       .     .     .   .   .       .     .     .   .   .       I     I     B   O   ORegenerator #4       I     O     I   B   O       O     I     I   B   O       O     O     I   B   I       I     O     I   B   O       O     I     I   B   O       .     .     .   .   .       .     .     .   .   .       .     .     .   .   .       O     I     I   B   O       O     P     I   I   O   Normal       O     O     P   I   I   Cycling       I     O     O   P   I______________________________________ I = INLET O = OUTLET B = BURNOUT 
    
     Regenerator 1 then becomes the burnout regenerator at the conclusion of an outlet cycle, while regenerator 5 becomes an inlet regenerator as shown in the first line of the regenerator 1 burnout cycle of Table III. This flow configuration is shown in FIG. 5c, wherein valves 22 and 44 are closed and valve 70 is open with respect to regenerator 1 allowing gas to be drawn through the purge/burnout fan and into the retention chamber. Regenerator 2 is configured as an outlet regenerator with valves 24 and 72 closed and valve 46 open. Regenerator 3 is an inlet regenerator with valves 48 and 74 closed and valve 26 open. Regenerator 4 is an outlet regenerator having valves 28 and 76 closed with valve 50 open, while regenerator 5, which has just completed its burnout cycle, becomes an inlet regenerator for cool down, having valves 52 and 78 closed, with valve 30 open to receive process gas. Operation of the present invention in the burnout mode, as shown in Table III requires absence of a purge cycle thereby allowing release of unoxidized process gas during flow reversal. 
     A controller source program for operation of the system, as embodied in the drawings, for system burnout is attached hereto as Appendix A. 
     Having now described the invention in detail as required by the patent statute, those skilled in the art will recognize modifications and substitutions to the embodiments disclosed herein for specific process applications. Such modifications and substitutions are within the scope and intent of the present invention as defined in the following claims. ##SPC1##