WO2000001465A1

WO2000001465A1 - System and method for oxidizing toxic, flammable, and pyrophoric gases

Info

Publication number: WO2000001465A1
Application number: PCT/US1999/015103
Authority: WO
Inventors: Earl C. Vickery
Original assignee: Techarmonic, Inc.
Priority date: 1998-07-07
Filing date: 1999-07-01
Publication date: 2000-01-13
Also published as: AU5313699A; WO2000001465A9

Abstract

A process exhaust gas treatment system (PEGTS) that eliminates or reduces exhausted toxic, flammable and pyrophoric gases in accordance with embodiments of the present invention is provided. The PEGTS has an enclosure (28) for mixing a stream of a first gas with a stream of a second gas to form a mixed gas stream. At least some components of the first gas are oxidized. The PEGTS of the present invention also has a second enclosure (50) that receives the mixed gas stream. The second enclosure (50) has an apparatus for accelerating a gas flow (58) for entraining abrasive particles (90). The entrained abrasive particles (90) can dislodge any solid-phase reaction products that may deposit on internal surfaces of the PEGTS. Some or all of this dislodged particulate matter is then removed from the PEGTS by the entraining air flow. In some embodiments of the present invention, the PEGTS directs the gas stream through a water-based scrubber (74) prior to exhausting to atmosphere.

Description

SYSTEM AND METHOD FOR OXIDIZING TOXIC, FLAMMABLE, AND

PYROPHORIC GASES

Earl C . Vickery

BACKGROUND

1. Field of the Invention

The present invention relates to an exhaust gas treatment system and method, and more particularly to a system for reducing or eliminating emissions of toxic, flammable and/or pyrophoric gases contained in process exhaust gas streams and the method thereof.

2. Description of Related Art

The semiconductor industry and others, utilize a variety of gaseous compounds as reactants during typical manufacturing processes such as chemical vapor deposition or plasma etching. Many of these compounds are toxic (i.e. tungsten hexafluoride (WF₆) ) , flammable (i.e. hydrogen (H₂) ) or even pyrophoric (i.e. silane (SiH₄)) . As only small portions of each of the reactants are generally consumed during most manufacturing processes, unreacted gaseous compounds necessarily exit the processing equipment in a waste gas or process exhaust gas stream. Thus where the process exhaust gas stream encompasses gaseous compounds with dangerous or noxious properties, it is desirable and often required to treat the exhaust gas stream prior to discharge into the atmosphere .

A number of commercially available systems for treating process exhaust gas streams are known. For example, one such system, the Flawamat E 300 K2 ("Flawamat"), is manufactured by Centrotherm of Germany. The Flawamat is a partial abatement system that utilizes a natural gas/oxygen flame to generate a high- temperature environment through which the process exhaust gas stream is passed. Generally, certain exhaust gas components entering the Flawamat, for example silane, are oxidized to silicon dioxide and water (SiH₄ + 20₂ - Si0₂ + 2H₂0) , while others are pyrolytically decomposed. Problematically however, H_2, a typical exhaust gas component, is generally left unreacted by the Flawamat to avoid system overheating. Hence the Flawamat provides only partial abatement of some hazardous and/or toxic gaseous compounds. Another commercially available system, manufactured by the EcoSys division of Advanced Technology and Materials, located in San Jose, California, ("EcoSys") is also a partial abatement system. The EcoSys provides for passing the process exhaust gas stream through an extended conduit. Electrical heaters heat the conduit in order to generate a temperature sufficiently high for pyrolytic decomposition and/or oxidation of the components of the gas stream. However, the EcoSys also allows most of the H₂ present to exit unreacted to avoid system overheating.

Another problem often experienced with presently known process exhaust gas treatment systems is deposition of solid-phase reaction products on the system's internal surfaces. Some oxidation products, particularly Si0₂ and tungsten oxide (W0₃), and some pyrolysis products, particularly Si, are stable even at the elevated temperatures that exist within systems such as the Flawamat and EcoSys. This stability allows for these solid-phase products to deposit on any internal surfaces the gas stream accesses. Over time accumulations of these deposits lead to operational problems such as corrosion, clogging of the gas flow path, and in some cases structural damage to the system. As a result, system lifetime is shortened, system efficiency decreased and system downtime increased. In currently known systems, removal of the accumulated deposits to avoid these problems is typically difficult and expensive.

In view of the foregoing discussion, there is a need for improved systems, and methods thereof, for treating process exhaust or waste gas streams. For example, waste or exhaust gases that are emitted from semiconductor manufacturing processes. Such improved methods and systems will advantageously provide more complete abatement of hazardous and or toxic gaseous compounds than is currently known. In particular, such essentially total abatement systems will provide for the reduction and/or elimination of unreacted H₂ released into the atmosphere. In addition, such methods and systems will include elements for preventing or reducing the deposition of solid-phase oxidation products and/or pyrolytic decomposition products on internal surfaces of the systems. Advantageously, such elements and the methods of use thereof will result in a reduction in the deposition of solid-phase reaction products. In this manner, such^' improved systems, and methods thereof, will maintain long system lifetimes, high efficiencies and will reduce system downtime for cleaning.

SUMMARY

An emissions control device, hereinafter a process exhaust gas treatment system (PEGTS) , and method of use, in accordance with embodiments of the present invention, are provided. The PEGTS encompasses a mixing conduit or _ first enclosure for mixing a first gas with a second gas . In some embodiments of the present invention the PEGTS is configured such that the first gas and the second gas are mixed in an essentially coaxial manner within the first enclosure. In this manner a coaxially mixed gas stream is formed which, advantageously, results in a rapid combination of the components of the first and second gases. In addition, the coaxially mixed gas stream is essentially uniformly directed toward a second enclosure or vessel, thus minimizing contact with inner surfaces of the first enclosure. Where the second gas is an oxidizing gas heated to a first temperature, generally at least some toxic, flammable or pyrophoric components of the first gas stream are oxidized within the first enclosure.

In accordance with embodiments of the present invention, the second enclosure of the PEGTS has an apparatus for accelerating an entraining gas flow. Generally, the accelerating apparatus is positioned at a first end of the second enclosure and forms an array of high-velocity gas jets. Each high-velocity gas jet has a velocity sufficient to entrain abrasive particulate matter contained within the second enclosure. The entraining gas flow and entrained abrasive particles mix with the coaxially mixed gases as the coaxially mixed gases enter the second enclosure. Advantageously, as a result of this mixing, entrained abrasive particulate matter impinges on various internal surfaces of the PEGTS. In this manner solid-phase reaction products that may become deposited on these various internal surfaces are mostly dislodged, and build-up of these reaction products slowed or in some cases substantially eliminated. In addition, the entraining gas flow cools and dilutes the mixed gas flow. Advantageously, the possibility of any down stream reactions and resulting deposition of reaction products on down stream internal surfaces by the cooled, diluted gas stream are substantially reduced. In addition, the aforementioned cooling effect of the entraining gas flow also serves to cool the first and second enclosures of the PEGTS.

In preferred embodiments of the present invention, the velocity of the entraining gas flow from each of the high-velocity gas jets decreases sufficiently, prior to reaching a second end of the vessel, so that the abrasive particles are no longer entrained therein.

Thus the abrasive particles are returned to a lower portion of the second enclosure to replenish the supply of abrasive particles. As particles of dislodged solid-phase reaction products are generally less dense and significantly smaller in diameter than the abrasive particles, most of these dislodged reaction product particles are removed from the PEGTS by remaining entrained within the gas flow.

Some embodiments of the present invention provide additional process exhaust gas treatment by using one or more water scrubbers. Thus, the gas flow exiting from the second enclosure is directed through a water scrubber where essentially all particulate matter entrained therein is removed along with at least a portion of the highly water soluble components of the gas flow. In some embodiments, the water scrubbers use a water based acidic or basic solution that is tailored to the react with and thus remove some components of the gas flow entering the scrubber. In addition, the one or more water scrubbers can contain filtering and/or vapor condensing material to enhance removal of particulate matter and reduce the water content of the gas flow prior to release into the environment.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic representation of a process exhaust gas treatment system (PEGTS) in accordance with an embodiment of the present invention; Fig. 2 is an enlarged view of a portion of the

PEGTS of FIG. 1, in accordance with an embodiment of the present invention;

Fig. 3 is an enlarged view of another portion of the PEGTS of Fig. 1, in accordance with an embodiment of the present invention; and

Fig. 4 is a schematic representation of another PEGTS in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Reference is initially directed to FIG.l, which schematically depicts an emissions control device or process exhaust gas treatment system 10 (PEGTS) constructed in accordance with an embodiment of the present invention. A first enclosure, or gas mixing enclosure 20 is shown joined and fluidically coupled to a second enclosure or gas entrainment enclosure 50 at an attachment region 52. A first enclosed angle 54 is formed between entrainment enclosure 50 and mixing enclosure 20. Enclosure 50 is also joined and fluidically coupled to an air conduit 70 at one end and to a convergent section 72 at another, opposing end. Convergent section 72 is fluidically coupled to a water scrubber 80, as depicted, via a scrubber conduit 74.

Thus, process exhaust gases are directed into treatment system 10 through an inner or exhaust gas conduit 22 having an open or distal end 23, these gases are treated, as will be more fully discussed, and the treated exhaust gases are directed out of system 10 via a scrubber outlet 82.

Turning now to Fig. 2, an enlarged view of a portion of PEGTS 10 of FIG. 1 is shown. Fig. 2 shows gas mixing enclosure 20 as an essentially "Y" shaped structure comprising a first or process exhaust gas portion 24, a second or oxidizing gas portion 26 and a mixed gas or connecting portion 28. A second enclosed angle 25 is seen formed between first gas portion 24 and second gas portion 26. While other configurations for mixing enclosure 20 are possible, it has been found that the configuration shown, with each portion having an essentially circular cross-section and where second angle 25 is an acute angle, is advantageous as both promote the mixing and then flow of the gases from first and second gas portions 24 and 26 into connecting portion 28.

Exhaust gas conduit 22 is fluidically coupled to a manufacturing process system (not shown) for directing exhaust gases from the manufacturing system into gas mixing enclosure 20. Generally, exhaust gas conduit 22 is joined to and positioned within first gas portion 24 in a substantially coaxial manner, i.e., conduit 22 and gas portion 24 essentially share a first central axis 30. An oxidizing gas conduit 32 is fluidically coupled to an oxidizing gas source (not shown) at one end and to a heater or heating apparatus 34 at another end. As the oxidizing gas flows through heater 34, the oxidizing gas is heated to a first temperature. Once heated, the heated oxidizing gas 42 is directed through a second or oxidizing gas conduit 36 to second gas portion 26. This first temperature is generally within the range of between approximately 100 to 1000 degrees Centigrade (°C). The actual temperature selected depends on the operational conditions and requirements needed for optimum treatment of the specific process exhaust gas from the processing system (not shown) . For example, where the process exhaust gas contains hydrogen (H₂), the first temperature employed is generally at least 600°C, and where the process exhaust gas contains nitrogen trifluoride (NF₃), the first temperature selected is generally at least 750°C. It will be understood that operational conditions include factors other than exhaust gas stream composition that can influence selection of an appropriate first temperature. Exemplary factors include exhaust gas flow rate and pressure as well as the composition of the oxidizing gas^' used.

Heating apparatus 34 is preferably of the cartridge type (electrical resistance) , but may alternatively comprise a plasma torch, a natural gas-fired heater or any other suitable heater consistent with the temperature required. In addition, some embodiments in accordance with the present invention comprise two or more heaters 34, where the two or more heaters 34 are all of one type or of a combination of heater types. It will be understood that where an exhaust gas treatment system 10 (Fig. 1) with multiple heaters 34 is provided (not shown) , heaters 34 can be fluidically coupled to the oxidizing gas stream in a variety of configurations. For example, either fluidically parallel or fluidically serial gas flow configurations are possible with multiple heaters. In other embodiments of the present invention, a multiple heater configuration can encompass the use of a plurality of second gas conduits, each coupled to one of a plurality of second gas portions, as will be described hereinafter. Thus, it will be understood that the configuration shown in Fig. 2, including heater 34, oxidizing gas conduit 32, second gas conduit 36 and second gas portion 26 is illustrative only and other configurations of these and additional components, e.g. any of the multiple heater/multiple second gas conduit designs previously discussed, are within the scope and spirit of the present invention.

Still referring to Fig. 2, second gas conduit 36 is shown mechanically and fluidically coupled to second portion 26 via a coupling flange 38 such that a second central axis 40 intersects first central axis 30. In this manner coaxial mixing of the gas streams is provided. It will be understood, that flange 38 can have any one of the generally accepted flange configurations that are compatible with the gases and temperatures employed. Alternatively, a unitary configuration for second gas portion 26 incorporating second conduit 36 can be employed. It is seen therefore, that the specific manner of construction, unitary or with a coupling, is a design choice. As this design choice is not critical to the description of embodiments of the present invention, they will not be hereinafter described. However, it will be understood that there are typically several methods to effect the joining or coupling of the various components of

PEGTS 10 (Fig. 1) and that each of these methods is within the scope and spirit of the present invention.

In addition to various methods of coupling the various parts of PEGTS 10 (Fig. 1), these various components can be formed or manufactured from a variety of materials. Mixing enclosure 20 may be fabricated from any one several stainless steel alloys, e.g. 304, 309, 316, or KOVAR™, an Inconel™ alloy, or the like (any of which may be passivated to enhance chemical resistance to the various exhaust gas components and reaction products) . In addition to various stainless steel alloys, other materials such as ceramic, glass and/or plastic materials are used in some embodiments of the present invention where appropriate. Thus where microwave or radio frequency (Rf) energy is used for heating, ceramic components are often employed to provide electrical isolation. Plastic materials such as " polyvinyl chloride (PVC) or polyethylene or any of the various Teflon® materials, among others, can also used in some embodiments. For example, it is often advantageous to use such a plastic material in constructing water scrubber 80, as such plastic materials are generally inexpensive, easy to work and form and compatible with the low temperatures and generally dilute concentrations of chemicals present in such a water based scrubber. Therefore it will be understood, that the specific materials selected for each of the various components of the embodiments of the present invention can and will vary. These variations are design choices influenced by the specific process exhaust gases and treatment process employed, as well as other factors such as materials cost and ease of construction.

Turning again to Fig. 2, a flow of heated oxidizing gas 42, directed along second central axis 40, mixes with process exhaust gas flow 44, directed along first central axis 30 and through open or distal end 23 of exhaust gas conduit 22. This mixing of heated oxidizing gas 42 and process exhaust gas flow 44 forms a mixing region 46, shown for illustrative reasons as a circular region. As exhaust gas flow 44 is essentially coaxial to central axis 30, the mixing of the aforementioned gases is hereinafter referred to as coaxial mixing. In some embodiments of the present invention, this coaxial mixing displaces mixing region 46, such that open end 23 is not centered therein. This displacement is often advantageous as many of the oxidizing reactions occurring within mixing region 46 result in the formation solid-phase reaction products, e.g. silane to silicon dioxide or tungsten hexafluoride to tungsten oxide which can clog open end 23. Hence, the coaxial mixing employed can minimize the extent to which open end 23 is within mixing region 46, reducing the possibility of clogging.

Typically, it is desirable to maximize the oxidation of the oxidizable exhaust gas components within mixing enclosure 20. Therefore, a sufficiently long transit time through a region capable of supporting the oxidation of these components is necessary. In some embodiments of the present invention, this sufficiently long transit time is achieved by forming connecting portion 28 with a sufficient length and diameter. In some embodiments, the position of open end 23 along central axis 30 is varied to adjust the transit time. It will be understood that in addition to adjusting physical dimensions and positions, embodiments of the present invention can also adjust gas flow rates, temperatures and the concentration of the oxidizer and/or oxidizable material supplied to mixing region 46, among other things, to obtain the transit time needed. Finally, it will be understood that in some embodiments in accordance with the present invention, the reaction of process exhaust gases with the oxidizing gases continues into entrainment enclosure 50. Referring to Table 1, the percent removal for several typical exhaust gas components is shown for a variety of oxidizing gas temperatures. In some embodiments, for example where the

Table 1

target component in the exhaust gas stream is NF₃ , complete abatement of the target component is obtained by injecting H₂, or any other material that provides a highly exothermic oxidation reaction, into the exhaust gas stream prior to mixing the exhaust gas stream with the oxidizing gas. Thus the exothermic oxidation of the injected material is used to increase the temperature of the mixed gases and provide essentially complete removal of the target component.

Turning now to Fig. 3, an enlarged view of another portion of PEGTS 10 (FIG. 1) , is shown. Mixed gas flow 48 is directed through connecting portion 28, of gas mixing enclosure 20 (Fig. 2), to gas entrainment enclosure 50 at attachment region 52. As previously mentioned, gas entrainment enclosure 50 is coupled to air conduit 70, which serves to provide air flow 76 to a velocity plate 56. Velocity plate 56 comprises a substantially flat plate, joined around its periphery to gas entrainment enclosure 50, which has a pattern of through-holes 60 formed therein. The open area (the ratio of aggregate through-hole area to total plate area) of velocity plate 56 is typically only about 15 percent (%) . Thus air flow 76 is restricted by velocity^' plate 56 which results in an increase in pressure at a first side 55. Air flow 76 is forced through the pattern of through-holes 60 to a second side 57 where as the flow expands from the restriction of through-holes 60 it has an increased velocity. Thus a plurality of high-velocity jets 58, corresponding to the pattern of through-holes 60 is created, where the velocity of the gas flow of each high-velocity jet 58 is significantly larger than the velocity of air flow 76. The amount of this increase in velocity is a function velocity plate open area. It has been found that for the useful range of open areas between a relatively open approximately 60% to a much more restricted approximately 10%, the velocity of air flow 76 is decreased from approximately 10 to 3 times, respectively. For example, a desirable open area of 15% creates a velocity of approximately 85 feet per second (ft/sec), where air flow 76 has a velocity of approximately 10 ft/sec.

A quantity of particulate matter or particles 90 is disposed within gas entrainment enclosure 50, above velocity plate 56 and an optional protective screen 62. Particles 90 are an abrasive material such as silicon dioxide, aluminum oxide, or washed, cleaned sand particles that have a nominal mean size in the range of approximately 0.01 to 0.2 inches (in.). Particles 90 are entrained in the air flow of high-velocity jets 58. That is to say, each particle of particles 90 is drawn into the air flow of high-velocity jets 58 and carried with that air flow upward from velocity plate 56.

It is advantageous to select a single particular abrasive material having a particular nominal size and shape for particles 90. For example, in some embodiments particles 90 are washed, cleaned sand particles with a specific mean size of approximately

0.1 in. It will be understood that such an essentially homogeneously sized composition of particles 90 facilitates selection of an appropriate velocity of the entraining air flow. That is to say a velocity that is sufficiently high to entrain essentially all of particles 90 while not being high enough to allow any significant number of particles 90 to exit gas entrainment enclosure 50. In some embodiments, the cooling effect and dilution of the mixed gas stream by the entraining air flow is determined and the composition and size of particles 90 selected to be appropriate for that entraining air flow.

It will be appreciated that as particles 90 are carried upward in the entraining flow, away from second surface 57, the velocity of the entraining air flow will decrease. Therefore, at some distance above second surface 57, this initial velocity will have decreased below the velocity needed to entrain abrasive particles 90. Particles 90 will necessarily fall, under the influence of gravity until the entraining air velocity is sufficient to re-establish entrainment. In this manner, abrasive particles 90 are continuously circulated within enclosure 50. As these abrasive particles circulate within enclosure 50, they necessarily impinge upon the inner surfaces of enclosure 50 as well as extending into connecting portion 28 and impinging upon the inner surfaces thereof. These impinging, entrained particles 90 create a scouring action on these inner surfaces which dislodges portions of any solid-phase reaction products that may have formed thereon. Thus any buildup of these products is reduced or eliminated. It will be appreciated that where first enclosed angle 54 is an acute angle, this desirable scouring action is enhanced due to the turbulence of mixing occurring proximate to attachment region 52.

As previously mentioned, some embodiments employ an optional screen 62 disposed in proximity to and above velocity plate 56. Such a screen 62 generally is mostly open area so that gas flow is not restricted, yet with an array of openings sufficiently small to prevent particles 90 from reaching second surface 57. Screen 62 is advantageous when particles 90 can cause one or more of through-holes 60 to become clogged under conditions of no or inadequate entrainment air flow or where the flow distribution across velocity plate 56 is non-uniform.

In addition to the previously mentioned scrubbing action of entrained particles 90, particles 90 provide a grinding-like action upon particles of the dislodged solid-phase reaction products. As a result, dislodged particles of solid-phase reaction products are generally much smaller than particles 90. Often, the mean diameters of such solid-phase reaction product particles are only about 1/100 of the mean diameters of the abrasive particles. Therefore, the velocity required to entrain these particles is substantially lower than for particles 90. Hence, when particles 90 begin falling downward as previously described, these small dislodged particles remain entrained in the gas flow and are carried out of entrainment enclosure 50. For example, as depicted in Fig. 3, a plurality of dislodged particles 92 are shown within convergent section 72.

Convergent section 72 is advantageously designed to accelerate the gas stream leaving entrainment enclosure 50. This increased gas stream velocity, as high as 430 ft/sec, provides high shear forces at internal surfaces 76 thus reducing or even eliminating any accumulation of the solid-phase reaction products 92 on surfaces 76 as well as into scrubber conduit 74.

Returning to Fig. 1, venturi water scrubber 80 is depicted therein. As known, venturi scrubbers are useful for the removal of particles and soluble gases including those having acidic components (such as hydrogen fluoride (HF) ) and cooling of gas streams prior to release to the atmosphere. The operation of venturi water scrubbers is well known in the art and need not be described in detail herein. Essentially, the gas stream enters scrubber 80 through a scrubber inlet 84 and is therein contacted by a spray of fine water droplets. The gas stream and water droplets then pass through a venturi section 86. Acid gas components, such as HF or hydrogen chloride (HC1) are absorbed by the water droplets, and thus removed from the gas stream. In addition, as the gas stream passes through the water spray, substantially all of the entrained dislodged particles 92 (Fig. 3) are removed. For example, a venturi scrubber having a throat diameter of 0.75 inches and a gas load of 25 standard cubic feet per minute (scfm) will remove approximately 93% of particles 1 micron (μm) or less in diameter from the gas stream. It will also be realized that the spray of fine water droplets provides for enhanced evaporation which provides a cooling effect to further reduce the temperature of the gas stream prior to exit. Thus, the cooled gas stream, with acidic and particulate components removed, then exits venturi scrubber 80 via outlet 82. In some embodiments where the exhaust gas stream entering scrubber 80 is particularly acidic, a neutralizing compound such as ammonia (NH₃) is added to the water spray to neutralize the acidic component. In a similar manner, for an alkaline or basic exhaust gas stream, an acidic neutralizing agent is sometimes employed, i.e. HCl .

Some embodiments of the present invention can also encompass multiple water scrubbers 80 and/or other vessels (not shown) generally coupled to an outlet 86 of the last water scrubber 80. One type of water scrubber 80 or vessel employed provides a path for the gas stream that contains fibrous materials to present the gas stream with additional surface area to coalesce small droplets into larger drops. When the drops become large enough, they will drop out of the gas stream thus reducing the liquid content of the gas stream before releasing it to the environment. In other embodiments, a filtering vessel is employed as a final vessel to enhance the removal of very small particles.

Turning now to Fig. 4, another embodiment in accordance with the present invention is depicted. The embodiment depicted has a mixing enclosure 20 that employs a pair of second gas portions 26, each having an oxidizing gas conduit 32 coupled to an oxidizing gas source (not shown) . While typically both gas conduits 32 are coupled to a single gas source, in some embodiments, different oxidizing gas sources are employed to provide different oxidizing gases or different concentrations thereof. Each oxidizing gas conduit is coupled to a heating apparatus 34 and subsequently to second gas conduit 36. This then allows for each heating apparatus 34 to have a different temperature and/or gas composition. Where temperatures are varied, oxidizing gas flow 43 can have a temperature appropriate for increasing the temperature of the exhaust gas stream within conduit 22. In addition, oxidizing gas flow 43 can enhance coaxial mixing by providing a directed gas flow at open end 23, toward entraining enclosure 50. Thus, oxidizing gas flow 45 can be more efficient at initiating a desired oxidation reaction while combined flows 43 and 45 displace mixing region 46 from open end 23 to minimize any potential clogging thereof. In embodiments of the present invention where oxidizing gas compositions are varied, the rate of forming solid-phase reaction products can also be minimized proximate to open end 23 by minimizing the concentration of the oxidizing agent in flow 43. In addition, the embodiment depicted employs a pair of water scrubbers 80, coupled in a fluidically serial manner .

In summary, it will be understood that a system for the removal or destruction of toxic, flammable and pyrophoric gases from a process exhaust gas stream has been described. The system provides for mixing a heated stream of an oxidizing gas with the exhaust gas stream, wherein toxic, flammable and pyrophoric components of the exhaust gas stream are oxidized. While generally, the oxidizing gas of choice is air as it is both effective and plentiful, other oxidizing gases or combinations of gases can be employed. In some embodiments of the present invention a first flow of air is combined with a second flow of oxygen to form a oxidizing gas having a higher oxygen concentration than air. In some embodiments employing an oxygen enriched oxidizing gas, the additional oxygen is added after the air is heated to the first temperature. In embodiments in accordance with the present invention, the process exhaust gas is directed to the system of the present invention from a manufacturing process system at the normal pressure and flow rate for the specific process system. As typically it is important to that process system to exhaust its waste gas stream at such a specific pressure and flow rate, embodiments of the present invention advantageously are designed to operate with essentially any pressure or flow rate that might be supplied. For example, the pressure and/or flow rate supplied by the high pressure end of a vacuum pump fluidically coupled to such a process system.

Systems of the present invention, advantageously provides for reducing or eliminating the buildup of solid-phase reaction products as might be formed by the oxidation of exhaust gas components such as silane and tungsten hexafluoride . Thus an enclosure for creating an entraining gas flow to entrain abrasive particles is provided, where the entrained abrasive particles impinge on inner surfaces of the system to remove at least some of any solid-phase reaction products that may deposit thereon. Additionally, the entraining gas flow both cools and dilutes the exhaust gas flow.

Finally, systems in accordance with the present invention, generally employ at least one water scrubber to provide additional cooling of the gas flow prior to release. In addition the water scrubbers provide for the removal of acidic or basic components through absorption into the water that is employed, or in some embodiments by providing a neutralizing reagent dissolved in that water. Advantageously, the water scrubbers also serves to remove particles entrained in the gas flow, where generally at least one water scrubber also comprises filtering media and or fibrous materials for removing water and/or particles from the gas flow prior to releasing the air flow to the environment .

It will be recognized by those skilled in the art that, while the invention has been described above in terms of the embodiments depicted, it is not limited thereto. Various features and aspects of the above described invention may be used individually or jointly. Further, although the invention has been described in the context of its implementation in a particular environment and for particular applications, e.g., semiconductor fabrication plants, those skilled in the art will recognize that its usefulness is not limited thereto and that the present invention can be beneficially utilized in any number of environments and implementations .

Claims

CLAIMSWhat is claimed is:

1. An emission control system for reducing toxic, flammable and pyrophoric gases in a process exhaust gas, ^"" comprising:

a gas mixing enclosure for mixing said process exhaust gas with an oxidizing gas; a gas entrainment enclosure fluidically coupled to said gas mixing enclosure; abrasive particles disposed in said gas entrainment enclosure; and an entraining gas flow for entraining said abrasive particles, wherein said entrained particles impinge upon inner surfaces of said emission control system whereby solid-phase reaction products as may form on said inner surfaces are removed.

2. The emission control system of Claim 1

comprising :

an oxidizing gas conduit for providing said oxidizing gas, said oxidizing gas conduit fluidically coupled to an oxidizing gas source; and a heating apparatus fluidically coupled to said oxidizing gas conduit, whereby said heating apparatus heats said oxidizing gas to a first temperature .

3. The emission control system of Claim 2 wherein said heating apparatus comprises an electrical resistance cartridge heater.

4. The emission control system of Claim 2 wherein said heating apparatus comprises a plasma torch or natural gas-fired heater.

5. The emission control system of Claim 2 wherein said gas mixing enclosure comprises at least two oxidizing gas portions.

6. The emission control system of Claim 5 wherein the at least two oxidizing gas portions are fluidically coupled to a heating apparatus for providing a heated oxidizing gas flow.

7. The emission control system of Claim 2 wherein said abrasive particles are selected from the group of abrasive particles consisting of aluminum oxide, silicon dioxide and washed, cleaned sand.

8. The emission control system of Claim 2 wherein said abrasive particles are comprised of washed, cleaned sand.

9. The emission control system of Claim 2 wherein said gas entrainment enclosure comprises:

a velocity plate positioned at a first end and fluidically coupled to an entraining air conduit; and a convergent section positioned at a second end opposing said first end.

10. The emission control system of Claim 2 comprising at least one water based scrubber fluidically coupled to said gas entrainment enclosure.

11. An emission control system, comprising:

a first enclosure for mixing a process exhaust gas stream with a heated oxidizing gas stream to form a mixed gas stream, thereby causing components of the process exhaust gas stream to be oxidized; a second enclosure for receiving the mixed gas stream flowing from the first enclosure; a velocity plate, positioned within a lower portion of the second enclosure, for accelerating an entraining air flow to create an array of high-velocity jets; and abrasive particulate matter held substantially within the second enclosure and entrained by the array of high-velocity jets, for dislodging solid-phase reaction products deposited on internal surfaces of the first and second enclosures.

12. The emission control system of Claim 11 wherein said first enclosure comprises a process exhaust gas portion, an oxidizing gas portion fluidically coupled to a heating apparatus and a connecting portion.

13. The emission control system of Claim 11 comprising at least two oxidizing gas portions wherein each oxidizing gas portion is coupled to a heating apparatus .

14. The emission control system of Claim 13 wherein said abrasive particulate matter comprises washed, cleaned sand.

15. The emission control system of Claim 14 comprising at least one water based scrubber fluidically coupled to said second enclosure.

16. A method for oxidizing toxic, flammable and pyrophoric gases comprising:

providing a process exhaust gas stream comprising at least one toxic, flammable and/or pyrophoric gas; heating an oxidizing gas stream to a first temperature; mixing said process exhaust gas stream and said heated oxidizing gas stream to form a mixed gas stream in a first enclosure; oxidizing substantially all of said at least one toxic, flammable and/or pyrophoric gas within said mixed gas stream; creating a plurality of high-velocity jets in a second enclosure, said plurality of high-velocity jets forming an entraining gas flow directed to a convergent section, said entraining gas flow having abrasive particles entrained therein; and directing said mixed gas stream to said second enclosure wherein said entraining gas flow cools and dilutes said mixed gas stream;

17. The method of Claim 16 wherein heating an oxidizing gas stream to a first temperature comprises heating said oxidizing gas stream using an electrical resistance cartridge heater.

18. The method of Claim 16 wherein heating an oxidizing gas stream comprises heating a first oxidizing gas stream to a first temperature and a second oxidizing stream to a second temperature, said second temperature equal to or greater than said first temperature.

19. The method of Claim 18 wherein forming an entraining gas flow having abrasive particles entrained therein comprises selecting said abrasive particles comprising washed, cleaned sand particles.

20. The method of Claim 16 wherein forming an entraining gas flow having abrasive particles entrained therein comprises said abrasive particles providing a scrubbing action upon inner surfaces of said first and second enclosures, said scrubbing action dislodging portions of solid-phase reaction products form on said inner surfaces .

21. The method of Claim 20 wherein forming an entraining gas flow having abrasive particles entrained therein comprises said abrasive particles providing a grinding-like action, said grinding-like action reducing said dislodged portions of solid-phase reaction products to a size substantially smaller than said abrasive particles .