Regenerative thermal oxidizer

Abstract

A regenerative thermal oxidizer system (20) for use in processing a contaminated fluid. The system includes a combustion chamber (22), a contaminated fluid feed duct (39), and at least a first (24) and a second (26) regenerator chambers in fluid communication with the combustion chamber (22). A regenerator half-chamber (21) is provided in fluid and thermal communication with the combustion chamber (22). A first flow control element (44) is provided for controlling a flow of fluid from the system fluid feed duct (39) to the first regenerator chamber (24), and a second flow control element (46) is provided for controlling a flow of fluid from the system fluid feed duct (39) to the second regenerator chamber (26). An intermittent supply duct (60) connects the system fluid feed duct (39) to the regenerator half-chamber (21). A third flow control element (62) controls flow of system feed fluid through the intermittent supply duct (60). Feed fluid is directed either to one of the first (24) and second (26) regenerator chambers or to the half-chamber (21) prior to flowing into the combustion chamber (22) so that the fluid is are pre-heated prior to entering the combustion chamber (21).

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional application Ser. No. 60/632,907, filed on Dec. 3, 2004.

BACKGROUND OF THE INVENTION

The present invention relates to the treatment of contaminant laden industrial process emissions and, more particularly, to a ducting and valving system that directs and controls the flow of such emissions to and through a regenerative oxidizer.

Industrial process emissions often contain combustible contaminants and/or odors that, if released to atmosphere, have a potential for polluting the environment. Thermal and/or catalytic oxidizers increase the temperature of such process emissions to a temperature above the ignition temperature of the contaminants therein so as to oxidize the contaminants.

One type of thermal oxidizer is a regenerative thermal oxidizer (“RTO”). The basic components of a regenerative thermal oxidizer are a combustion chamber, at least two separate beds (or chambers) of a heat exchange medium having a high heat capacity, and a valving and ducting system sufficient to convey contaminated emissions to and from the combustion chamber, via the heat exchange chambers. In a regenerative thermal oxidizer, hot gases leaving the combustion chamber are directed over a first, relatively cooler one of the beds of heat exchange medium. The temperature difference between the hot gases and the relatively cooler bed results in heat transfer from the gases to the heat exchange medium, thereby heating the medium. At the same time, relatively cooler contaminated emissions entering the oxidizer are directed over a previously heated second bed of heat exchange media prior to entering the combustion chamber, in order to preheat the emissions to a temperature close to the combustion temperature of the contaminants. Transfer of heat from the second bed to the incoming emissions leads to a gradual cooling of the second bed. Any remaining heat required to bring the emissions to contaminant combustion temperature is provided by a burner located in or near the combustion chamber.

When the first bed has absorbed as much heat as possible from hot gases exiting the combustion chamber, flow of the hot gases is redirected by a valve to flow over the second bed to reheat (or “regenerate”) the second bed. At the same time, flow of the contaminated emissions is redirected by a valve to flow over the first bed, which was recently heated by the hot processed gases. The incoming emissions are now heated by thermal communication with the first bed. Thus, a first bed of heat exchange medium is used as a heat source for emissions, while the second bed is used as a heat sink for hot gases exiting the combustion chamber.

One problem that materially affects the efficiency of regenerative thermal oxidizers is short circuiting of the oxidizer by contaminated emissions incident to opening and closing of the valves required for control of fluid flow to and from the regenerators. As the regenerative chambers of known two-chamber regenerative oxidizers switch from inflow to outflow, there is both a momentary change in system pressure due to simultaneous opening and closing of all valves, and a momentary period where incoming contaminant-laden emissions short circuit the common oxidation chamber. The resulting pressure variations place excessive loads on the fluid moving equipment and are unacceptable in processes being controlled via the regenerative oxidizer. Also, short circuiting of emissions between flow control valves in the partially open condition seriously compromises the efficiency of the oxidizer.

An additional problem may arise where a two-chamber thermal oxidizer is employed without a purge circuit incorporated therein. In this case, the reversal of air flow direction within the unit may cause a volume of contaminated air located within and around the heat sink media to be discharged to the atmosphere.

SUMMARY OF THE INVENTION

A regenerative thermal oxidizer system for use in processing a contaminated fluid. The system includes a combustion chamber, a system fluid feed duct, and at least a first and a second regenerator chambers in fluid communication with the combustion chamber. A regenerator half-chamber is provided in fluid and thermal communication with the combustion chamber. A first flow control element is provided for controlling a flow of fluid from the system fluid feed duct to the first regenerator chamber, and a second flow control element is provided for controlling a flow of fluid from the system fluid feed duct to the second regenerator chamber. An intermittent supply duct connects the system fluid feed duct to the regenerator half-chamber. A third flow control element controls flow of system feed fluid through the intermittent supply duct. Feed fluid is directed either to one of the first and second regenerator chambers or to the half-chamber prior to flowing into the combustion chamber so that the fluid is are pre-heated prior to entering the combustion chamber, even during reversal of fluid flow direction within the oxidizer.

The system may also include a fourth flow control element for controlling a flow of fluid from the first regenerator chamber to a system exhaust, and a fifth flow control element for controlling a flow of fluid from the second regenerator chamber to the system exhaust. A control system is provided for opening and closing the flow control elements, selectively, in a prearranged sequence whereby one of the fourth flow control element or fifth flow control element and either the third flow control element or one of the first and second flow control elements is open at all times to maintain the pressure of fluid flow through the regenerative thermal oxidizer relatively constant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-12 are similar schematic representations of a two-chamber regenerative thermal or catalytic oxidizer showing the sequence of flow control element operation in the present invention.

DETAILED DESCRIPTION

FIGS. 1-12 show a schematic representation of one embodiment of a regenerative thermal oxidizer system in accordance with the present invention, although the present invention is applicable to oxidizer systems having other known configurations. As seen in FIGS. 1-12, a two chamber regenerative oxidizer 20 comprises a common combustion chamber 22 overlying a pair of conventional segregated regenerative chambers 24 and 26. The combustion chamber 22 is provided with one or more conventional burners 30a and 30b. In the embodiment shown, a first burner 30a is provided in combustion chamber 22 proximate regenerative chamber 24 and a second burner 30b is provided in combustion chamber 22 proximate regenerative chamber 26. While the embodiment of the oxidizer disclosed herein shows burners 30a and 30b positioned proximate chambers 24 and 26, the burners are not necessarily positioned proximate chambers 24 and 26, and may be positioned at any of a variety of alternative locations within the combustion chamber. The regenerative chambers 24 and 26 are provided with heat exchange media (for example, known ceramic matrix heat exchange media such as ceramic saddles) 32 and 34, respectively.

A regenerative half-chamber 21 is positioned so as to be in fluid and thermal communication with combustion chamber 22. Chamber 21 is termed a “half-chamber” because it is smaller that more conventional regenerative chambers 24 and 26 and because gas flow to the chamber is controlled by a single flow control element 62. Half-chamber 21 is also provided with a heat exchange medium similar to those provided in regenerative chambers 24 and 26. In the embodiment shown, half-chamber 21 is positioned along an upper portion of the oxidizer system between conventional chambers 24 and 26 and in close proximity to combustion chamber 22. However, half-chamber 21 may be located in any position where it can receive contaminated emissions via an intermittent supply duct (as described below) prior to entering either of conventional chambers 24 or 26, and in any position where the heat exchange medium contained in chamber 21 will be exposed to radiant and/or convective heat emanating from combustion chamber 22. The heat exchange medium in half-chamber 21 is constantly regenerated with heat received from hot gases which traverse the combustion chamber between chambers 24 and 26. This enables pre-heating of contaminated emissions flowing vertically through half-chamber 21. The emissions are pre-heated to a temperature near the oxidation temperature of the contaminants prior to entering combustion chamber 22.

A contaminated emission duct or system fluid feed source 39 feeds a system fluid to regenerative chambers 24 and 26 of oxidizer 20 through a pair of inlet ducts 36 and 38, respectively. Outlet ducts 40 and 42 lead from chambers 24 and 26, respectively to the low pressure side of an exhaust blower 43.

The various ducts of the oxidizer system are operatively coupled to flow control elements for regulating the flow of fluid along the ducts between the various regenerative chambers and blowers comprising the oxidizer system. In the embodiment of the oxidizer described herein, the flow control elements are in the form of individual valves positioned along respective ones of the ducts for controlling flow therethrough. Specifically, inlet ducts 36 and 38 are provided with valves 44 and 46, respectively, and outlet ducts 40 and 42 are provided with valves 48 and 50, respectively, for control of flow to the exhaust blower 43.

An intermittent supply duct 60 extends from contaminated emission feed duct 39 to half chamber 21. As emissions pass through half-chamber 21, the emissions are pre-heated to a temperature near the oxidation temperature of the contaminants, prior to entering combustion chamber 22. The emissions then pass out of half chamber 21 to combustion chamber 22 of oxidizer 20.

The embodiment of the oxidizer 20 shown in FIGS. 1-12 is provided with a purge circuit comprising a duct 70 leading from the clean air output of the exhaust blower 43. Flow through the duct 70 is short circuited back to the blower 43 upon opening of a balancing valve 72 that communicates with the outlet 40 to the exhaust blower 43. The clean air duct 70 feeds the regenerative chamber 26 through a valve 74 and line 76 and feeds the regenerative chamber 24 through a valve 78 and duct 80. A purge blower 90 forces purge air through a purge air input duct 92, which directs purge air to chambers 24 and 26 based on the state (open or closed) of valves 74 and 78. Although the embodiment of the oxidizer described herein includes a purge circuit, an oxidizer incorporating a half-chamber as described herein may also be used without a purge circuit.

Purge system valves 72, 74, 78, and valves 44, 48, 46, 50, and 62 used to direct the emissions to the combustion chamber and the hot gases from the combustion chamber may be power-actuated, computer or electronically-controlled flow control valves typically used for such purposes. Examples of such valves and the types of electronic control systems usable for actuating the valves are disclosed in U.S. Pat. Nos. 5,000,422, 5,327,928, 4,347,869, 6,609,904, and in published U.S. Application No. 20040230402, all of which are incorporated herein by reference. Alternatively, rather than using individually actuated valves for flow control, two or more of the necessary flow control elements may be integrated into a single unit or structure (for example, an indexable rotary valve) which controls flow of fluid to the various elements of the oxidizer system. One or more such integrated flow control structures may be incorporated into the oxidizer system.

Operation of the oxidizer valving system and half-chamber will now be discussed. For purposes of description, it is assumed that heat exchange media 32 in regenerative chamber 24 has been fully “regenerated” with heat energy from emissions flowing from combustion chamber 22 to outlet duct 40. In operation, and as seen in FIG. 1, contaminated emissions flow through feed duct 39, open valve 44, and duct 36 to regenerative chamber 24 wherein the emissions are pre-heated. The emissions then flow through combustion chamber 22, then outwardly through regenerative chamber 26, duct 42, and open valve 50 to exhaust blower 43. Intermittent supply circuit control valve 62 is closed during the aforesaid phase of operation. Purge air is circulated through duct 70, blower 90, open valve 72, and duct 40 back to blower 43.

As seen in FIG. 2, inlet valve 44 begins to close and intermittent supply valve 62 beings to open. Thus, emission inlet flow is through both intermittent supply duct 60 and regenerator inlet duct 36. As emissions pass from intermittent supply duct through half-chamber 21, the emissions are pre-heated to a temperature near the oxidation temperature of the contaminants. The emissions then pass out of half chamber 21 to combustion chamber 22. Outlet flow continues through open valve 50 from regenerator 26. A level of heat is constantly maintained in the heat exchange media of half chamber 21 due to convective and radiative heat transfer thereto from combustion chamber 22. Thus, all emissions passing through intermittent supply duct 60 undergo a degree of pre-heating in half-chamber 21 prior to entering combustion chamber 22. Purge valve 78 begins to open to regenerative chamber 24 and purge balancing valve 72 begins to close.

As seen in FIG. 3, regenerative bed 24 is in an idle condition with both the inlet valve 44 and the outlet valve 48 closed. Intermittent supply circuit valve 62 is fully open resulting in 100% of inlet emissions flow through the intermittent supply duct 60 and through half chamber 21, where the emissions are pre-heated. Outlet flow remains through open outlet valve 50 from regenerator 26. Purge valve 78 to regenerative chamber 24 remains open thereby purging chamber 24. Purge balancing valve 72 is closed.

As seen in FIG. 4, inlet valve 44 to the regenerator 24 remains closed and outlet valve 48 begins to open. Simultaneously, outlet valve 50 from regenerator 26 begins to close. Inlet emission flow remains through open valve 62 and intermittent supply circuit 60. Outlet flow is through partially open valves 48 and 50 from regenerators 24 and 26, respectively. During the steps shown in FIGS. 1-4, heat exchange media 34 in regenerative chamber 26 is being “regenerated” with heat absorbed from emissions exiting chamber 26 through open valve 50. Purge valve 78 to regenerative chamber 24 begins to close and balancing valve 72 begins to open.

As seen in FIG. 5, regenerator 26 is in an idle position with both inlet valve 46 and outlet valve 50 closed. Emissions inlet flow is solely through valve 62 and intermittent supply circuit 60. Thus, emissions are preheated only by half-chamber 21. Outlet flow is solely through fully open valve 48 from regenerator 24. Purge air is circulating through open balancing valve 72.

As seen in FIG. 6, outlet valve 50 from regenerator 26 remains closed, while inlet valve 46 begins to open and intermittent supply circuit valve 62 begins to close. Emission inlet flow is through both the intermittent supply circuit 60 to regenerator 24 and through valve 46 to regenerator 26. Thus, emissions are preheated by both regenerator 26 and by half-chamber 21. Outlet flow from regenerator 24 is through open valve 48. Purge air circulates through the open balancing valve 72.

As seen in FIG. 7, intermittent supply circuit valve 62 and the intermittent supply circuit 60 are closed. Emission inlet flow is through open valve 46 to regenerator 26. Outlet flow is through valve 48 from regenerator 24. Purge air is circulating through open valve 72.

As seen in FIG. 8, the inlet valve 46 to regenerator 26 begins to close and intermittent supply circuit valve 62 begins to open. Outlet flow is through valve 48 from regenerator 24. Emission inlet flow is shared between the intermittent supply circuit 60 and valve 46 to regenerator 26. Balancing valve 72 begins to close off recirculation of purge air and purge air valve 74 begins to open to admit air to regenerative chamber 26.

As seen in FIG. 9, regenerator 26 is in an idle position with both the inlet valve 46 and the outlet valve 50 closed. Inlet emission flow is solely through the intermittent supply circuit valve 62 and intermittent supply circuit 60. Outlet flow is through valve 48 from regenerator 24. Purge valve 74 to regenerator chamber 26 is open and said chamber is being purged.

As seen in FIG. 10, the inlet valve 46 to regenerator 26 is closed and outlet valve 50 therefrom begins to open. Regenerator 24 outlet valve 48 begins to close. Emission inlet flow is solely through valve 62 and the intermittent supply circuit 60. Outlet flow is shared between valves 48 and 50 from regenerators 24 and 26, respectively. Purge valve 74 to regenerative chamber 26 is closing and balance valve 72 is opening.

As seen in FIG. 11, regenerator 24 is in an idle position with both the inlet valve 44 and the outlet valve 48 closed. Emission inlet flow is solely through valve 62 and the intermittent supply circuit 60. Outlet flow is solely through valve 50 from regenerator 26. Purge air circulates through open balancing valve 72.

As seen in FIG. 12, the outlet valve 48 from regenerator 24 is closed and the inlet valve 44 thereto begins to open. The intermittent supply circuit valve 62 in the intermittent supply circuit 60 begins to close conditioning the system 20 for operation as discussed with respect to FIG. 1. Purge air circulates through open balancing valve 72.

From the above description, it may be seen that all contaminated emissions entering combustion chamber 22 undergo some degree of preheating, either from one of regenerators 24 and 26, or from half-chamber 21. It may also be seen from the above description that process efficiency is increased by using convective and radiant heat from combustion chamber 22 to constantly regenerate half chamber 21, and by using chamber 21 to pre-heat contaminated emissions prior to flow of the emissions into combustion chamber 22. From the foregoing it should also be apparent that the intermittent supply circuit 60 results in an operating circuit and sequence that precludes contaminated emissions from short circuiting the oxidation chamber 22 of the oxidizer 20. Static pressure variations are minimized by the intermittent supply duct and intermittent supply valve in intermittent supply circuit 60. Purging of regenerator chambers 24 and 26 is also accomplished in a manner that minimizes static pressure variations.

As described herein, the present invention is applied to a regenerative thermal oxidizer; however, it is not limited thereto. The system described herein may also be employed in any system where a half-chamber as described can be placed in thermal and fluid communication with a combustion chamber, to preheat any suitable working fluid prior to combustion or oxidation thereof.

The embodiment described herein includes a half-chamber 21 operating in conjunction with a pair of regenerative chambers 24, 26. In an alternative embodiment, the RTO system may incorporate multiple half-chambers operating in conjunction with two or more regenerator chambers. In another alternative embodiment, the RTO system may include more than two regenerator chambers operating in conjunction with a single half-chamber.

It will also be understood that the foregoing description of an embodiment of the present invention is for illustrative purposes only. As such, the various structural and operational features herein disclosed are susceptible to a number of modifications commensurate with the abilities of one of ordinary skill in the art, none of which departs from the scope of the present invention as defined in the appended claims.

Claims

1. A regenerative thermal oxidizer system comprising:

a combustion chamber;

a system fluid feed duct;

at least a first and a second regenerator chambers in fluid communication with the combustion chamber;

at least one regenerator half-chamber in fluid and thermal communication with the combustion chamber;

a first flow control element for controlling a flow of fluid from the system fluid feed duct to the at least a first regenerator chamber;

a second flow control element for controlling a flow of fluid from the system fluid feed duct to the at least a second regenerator chamber;

a intermittent supply duct connecting the system fluid feed duct to the at least one regenerator half-chamber; and a third flow control element for controlling flow of system feed fluid through the intermittent supply duct.

2. The regenerative thermal oxidizer system of claim 1 further comprising:

a fourth flow control element for controlling a flow of fluid from the at least a first regenerator chamber to a system exhaust;

a fifth flow control element for controlling a flow of fluid from the at least a second regenerator chamber to the system exhaust; and

a control system for actuating the flow control elements, whereby one of the fourth flow control element or fifth flow control element and either the third flow control element or one of the first and second flow control elements is open at all times to maintain the pressure of fluid flow through the regenerative thermal oxidizer relatively constant.

3. The regenerative thermal oxidizer system of claim 1 wherein the third flow control element is open to permit feed fluid flow through the intermittent supply duct during actuation of the first and second flow control element.

4. The regenerative thermal oxidizer system of claim 1 wherein the third flow control element is open to permit feed fluid flow through the intermittent supply duct when both the first and second flow control elements are closed.

5. The regenerative thermal oxidizer system of claim 1 further comprising a control system for opening and closing the flow control elements whereby fluid is directed either to one of the at least a first and a second regenerator chambers or to the at least one half-chamber prior to flowing into the combustion chamber so that the fluid is are pre-heated prior to entering the combustion chamber.

6. The regenerative thermal oxidizer system of claim 1 further comprising a purge circuit for circulating a purge gas through the at least a first and second regenerator chambers.

7. The regenerative thermal oxidizer system of claim 1 wherein at least a first one of the first flow control element, the second flow control element, and the third flow control element, and a second one of the first flow control element, the second flow control element, and the third flow control element are incorporated into an integrated flow control structure.

8. The regenerative thermal oxidizer system of claim 7 wherein the integrated flow control structure comprises an indexable rotary valve.

9. A regenerative thermal oxidizer system comprising:

a combustion chamber;

at least a first and a second regenerator chambers in fluid communication with the combustion chamber;

at least one regenerator half-chamber in fluid and thermal communication with the combustion chamber;

a first outlet extending between the first regenerator chamber and a system exhaust; and

a second outlet extending between the at least a second regenerator chamber and the system exhaust, the at least one regenerator half-chamber having an outlet only to the combustion chamber and no outlet extending between the at least one regenerator half-chamber and the system exhaust.

10. The regenerative thermal oxidizer system of claim 9 further comprising:

an intermittent supply duct connecting a system fluid feed source to the regenerator half-chamber;

a flow control element for controlling flow of system feed fluid through the intermittent supply duct;

a first outlet flow control element for controlling a flow of fluid from the first outlet to the system exhaust; and

a second outlet flow control element for controlling a flow of fluid from the second outlet to the system exhaust, wherein the first and second outlet flow control elements are actuated substantially simultaneously, and wherein the intermittent supply flow control element is open to permit feed fluid flow through the intermittent supply duct during actuation of the first and second outlet flow control elements.

11. A fluid pre-heat system for a regenerative thermal oxidizer comprising a regenerator half-chamber in fluid and thermal communication with a combustion chamber of the regenerative thermal oxidizer, the regenerator half-chamber including:

a heat exchange media therein for absorbing heat from the combustion chamber;

an opening only for receiving feed fluid therein for processing by the combustion chamber; and

another opening only for emission of the feed fluid therethrough to the combustion chamber.