Inlet assembly

Abstract

An inlet assembly for a an abatement burner includes: an inlet conduit operable to convey an effluent gas stream to be treated from an inlet aperture via a bore to an outlet aperture for treatment; and a lance conduit operable to convey a fuel gas from a gas inlet aperture via a gas bore to a gas outlet aperture positioned within the bore for mixing with the effluent gas stream, a cross-sectional area of the gas bore increasing towards the gas outlet aperture. In this way, the expansion caused by the increasing cross-sectional area of the gas bore enhances the mixing of the fuel gas with the effluent gas stream which provides for improved destruction and removal efficiencies (DRE), which enables the inlet assembly to be operated with reduced quantities of fuel gas, while still maintaining required levels of DRE.

Claims

1. An inlet assembly for an abatement burner, comprising: an inlet conduit operable to convey an effluent gas stream to be treated from an inlet aperture via a bore to an outlet aperture for treatment; and a lance conduit operable to convey a fuel gas from a gas inlet aperture via a gas bore to a gas outlet aperture positioned within said bore for mixing with said effluent gas stream, a cross-sectional area of said gas bore increasing towards said gas outlet aperture wherein said lance conduit comprises a taper section which tapers outwardly proximate said gas outlet aperture and wherein said taper section defines at least one void operable to convey gas between said bore and said gas bore.

2. The inlet assembly of claim 1, wherein a cross-sectional area of said gas outlet aperture is greater than a cross-sectional area of said gas inlet aperture.

3. The inlet assembly of claim 1, wherein said inlet conduit and said lance conduit are dimensioned to decrease a cross-sectional area of said bore towards said gas outlet aperture.

4. The inlet assembly of claim 1, wherein an external cross-sectional perimeter of said lance conduit increases towards said gas outlet aperture.

5. The inlet assembly of claim 1, wherein said taper section has a taper angle of up to around 60.

6. The inlet assembly of claim 1, wherein said at least one void is configured to direct said effluent gas stream from said bore radially inwards into said gas bore for pre-mixing therewithin.

7. The inlet assembly of claim 1, wherein said at least one void is configured to direct said fuel gas from said gas bore radially outwards into said bore for pre-mixing therewithin.

8. The inlet assembly of claim 1, wherein said taper section defines a plurality of voids.

9. The inlet assembly of claim 1, wherein said taper section defines an opposing pair of voids.

10. The inlet assembly of claim 1, wherein said taper section defines two opposing pairs of voids.

11. The inlet assembly of claim 1, further comprising a flow restrictor positioned within said bore proximate said lance conduit.

12. The inlet assembly of claim 11, wherein said flow restrictor extends along said axial length of said bore no further than said gas outlet aperture.

13. A method, comprising: conveying an effluent gas stream to be treated from an inlet aperture of an inlet conduit via a bore to an outlet aperture for treatment; and conveying a fuel gas from a gas inlet aperture of a lance conduit via a gas bore to a gas outlet aperture positioned within said bore for mixing with said effluent gas stream, a cross-sectional area of said gas bore increasing towards said gas outlet aperture wherein said lance conduit comprises a taper section which tapers outwardly proximate said gas outlet aperture and wherein said taper section defines at least one void operable to convey gas between said bore and said gas bore.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The embodiments will now be described further, with reference to the accompanying drawings, in which:

(2) FIG. 1 illustrates schematically an abatement burner according to one embodiment;

(3) FIG. 2A illustrates the configuration of a lance according to one embodiment;

(4) FIG. 2B is a view looking along a nozzle structure, showing the lance installed and a concentric conduit;

(5) FIG. 3A is a vector plot simulation showing fluid flow speed and direction taken on a plane through an opposing pair of slots;

(6) FIG. 3B is a vector plot simulation on a plane of 45 from FIG. 3A;

(7) FIGS. 4A and 4B illustrate streamlines showing fuel gas flow from a conventional lance; and

(8) FIGS. 4C and 4D illustrate streamlines showing fuel gas flow from the lance of FIG. 2.

DESCRIPTION OF THE EMBODIMENTS

(9) Overview

(10) Before discussing the embodiments in any more detail, first an overview will be provided. Embodiments provide an inlet assembly for an abatement burner, such as a ring burner, which is used to abate an effluent gas stream. The inlet assembly has a lance co-located within an inlet nozzle which delivers the effluent gas stream for abatement by the ring burner. The lance delivers fuel gas for premixing with the effluent gas stream prior to delivery to the ring burner. The lance is configured its gas outlet aperture to enhance mixing between the effluent gas stream and the fuel gas. Typically, the lance has a discontinuity, for example a taper, step or other arrangement, which enhances this premixing. A flow restrictor may be provided around the lance in order to further enhance such pre-mixing. The flow restrictor may be arranged to extend no further than the lance along the inlet nozzle, in order that a near-laminar flow is re-established before the mixed effluent gas stream and fuel gas exits the inlet nozzle to provide for stable combustion as the mixture exits the inlet nozzle. Such premixing has been found to provide more than acceptable DRE levels when using a ring burner with lower ratios of effluent stream gas to fuel gas than used in conventional abatement burners.

(11) Abatement BurnerGeneral Configuration and Operation

(12) FIG. 1 illustrates schematically an abatement burner, generally 8, according to one embodiment. The abatement burner 8 treats an effluent gas stream pumped from a manufacturing processing tool (not shown) such as a semiconductor or flat panel display process tool, typically by means of a vacuum-pumping system.

(13) The effluent stream is received by an inlet structure 10. The effluent stream is conveyed by the inlet structure 10 to a nozzle structure 12. In this embodiment, the abatement burner 8 comprises four inlet structures 10 arranged circumferentially, each conveying an effluent gas stream pumped from a respective tool by a respective vacuum-pumping system. Alternatively, the effluent stream from a single process tool may be split into a plurality of streams, each one of which is conveyed to a respective inlet structure 10. Each nozzle structure 12 is located within a respective bore 16 formed in a ceramic top plate 18 which defines an upper or inlet surface of a combustion ring 14.

(14) The combustion ring 14 has sidewalls defined by an exit surface 21 of a foraminous element 20. The foraminous element 20 is cylindrical and is retained within a cylindrical outer shell 24. A plenum volume 22 is defined between an entry surface 23 of the foraminous element 20 and the outer shell 24. A mixture of fuel gas, such as natural gas or a hydrocarbon, and air is introduced into the plenum volume 22 via inlet nozzles (not shown). The mixture of fuel gas and air passes from the entry surface 23 of the foraminous element 20 to the exit surface 21 of the foraminous element 20 for combustion within the combustion ring 14.

(15) The inlet structure 10 has an inlet portion 10A which couples with a gallery portion 10B, which in turn couples with the nozzle structure 12. The elongate axis of the inlet portion 10A and the nozzle structure 12 are offset to facilitate the introduction of a lance 30, which is retained within the nozzle structure 12. In this embodiment, the lance 30 is concentrically and coaxially positioned within the nozzle structure 12. As will be explained in more detail below, the lance 30 introduces fuel gas for premixing with the effluent gas stream within the nozzle structure 12 prior to exiting from the nozzle structure 12. The nozzle structure 12 is surrounded concentrically by a fuel conduit 13 (not shown in FIG. 1, but illustrated in FIG. 2B) which also supplies fuel as the effluent gas stream and fuel gas exits from the nozzle structure 12. A helical spring 50 is located concentrically and coaxially around the lance 30, between the lance 30 and the nozzle structure 12. The helical spring 50 is coupled with an actuator (not shown) which provides for reciprocal displacement of the helical spring 50 in the axial direction of the lance 30 and the nozzle structure 12 to clean any deposits forming on the nozzle structure 12. In this embodiment, the helical spring 50 when at its shown rest position extends no further than the lance 30 in the axial direction, along the nozzle structure 12.

(16) The effluent gas stream flows from the inlet portion 10A, through the gallery portion 10B and into the nozzle structure 12, which injects the premixed fuel gas and effluent stream into a cylindrical combustion ring 14. Fuel gas is introduced by the lance 30 into the nozzle structure 12 for premixing with the effluent gas stream. The configuration of the lance 30 and its relationship with the helical spring 50 provides for particularly effective premixing, as will be explained in more detail below. The mixed effluent gas stream and fuel gas exits the nozzle structure 12 where it is surrounded by fuel gas from the fuel conduit 13 and heated and combusted within the combustion ring 14. The combustion provides combustion products, such as oxygen, typically within a nominal range of 7.5% to 10.5%, depending on the fuel air mixture (CH.sub.4, C.sub.3H.sub.8, C.sub.4H.sub.10) and the firing rate of the combustion burner 14. The heat and combustion products react with the effluent gas stream and fuel gas mixture to clean the effluent gas stream. For example, SiH.sub.4 and NH.sub.3 may be provided within the effluent gas stream, which reacts with O.sub.2 within the combustion chamber to generate SiO.sub.2, N.sub.2, H.sub.2O, NO.sub.x. Similarly, N.sub.2, CH.sub.4, C.sub.2F.sub.6 may be provided within the effluent gas stream, which reacts with O.sub.2 to generate CO.sub.2, HF and H.sub.2O. The ratio of the mixture of fuel gas and air is varied to vary the nominal temperature within the combustion ring 14 to that which is appropriate for the effluent gas stream to be treated. The exhaust 15 of the combustion ring 14 is open to enable the combustion products to be output from the abatement burner 8.

(17) Lance Configuration

(18) FIG. 2 illustrates the configuration of the lance 30, according to one embodiment. As can be seen, the lance 30 has an inlet coupling 32 which couples with a conduit (not shown) which supplies the fuel gas from a gas inlet aperture 37 via a bore 35 defined by a cylindrical section 36 to a gas outlet aperture 39 defined by a tapered portion 34. The tapered portion is frustoconical, having a conical sidewall 38 within which slots 33 are formed. In this embodiment, the conical sidewall 38 extends at an angle of around 45 from the elongate axis of the lance 30. However, angles less than this and up to around 60 have been found to improve mixing. Also, in this embodiment there are provided four slots 33, but fewer or more than this may also be provided. Also, the slots 33 need not fully extend along the whole length of the tapered portion 34 and instead individual holes within the tapered portion 34 are sufficient to facilitate mixing.

(19) Fluid Flow and Mixing

(20) FIG. 3A is a vector plot simulation showing fluid flow speed and direction taken on a plane through an opposing pair of slots 33. As can be seen, the velocity of the effluent gas stream is increased in the vicinity of the gas outlet aperture 39 by the presence of the helical spring 50 and the tapered portion 34 of the lance 30.

(21) Some of the effluent gas stream is then forced through the opposing pair of slots 33 and mixes with the fuel gas travelling from the bore 35 into the tapered portion 34 of the lance 30.

(22) FIG. 3B is a vector plot simulation on a plane of 45 from FIG. 3A. As can be seen, the gas stream mixture within the tapered portion 34 exits the gas outlet aperture 39 and mixes with the effluent gas stream which has been accelerated by the outer surface of the tapered portion 34 and the helical spring 50.

(23) Fuel Gas Flow and Mixing

(24) FIGS. 4A and 4B illustrate the streamlines showing the fuel gas flow (in this example, propane) from a conventional lance (which omits the tapered portion 34). These streamline illustrations assume the flow through the inlet structure 10 is 50 standard litres per minute of nitrogen, 18 standard litres per minute oxygen and the flow rate of fuel gas through the lance 30 is 3.2 standard litres per minute. In particular, FIG. 4A shows the streamlines of the fuel gas flow where the helical spring 50 extends in the axial direction past the lance within the nozzle structure 12, whilst FIG. 4B shows the streamlines of the fuel gas flow when the helical spring 50 extends in the axial direction no further than the lance. As can be seen, the fuel gas stays generally within a central, axial region of the nozzle structure 12 and is surrounded coaxially by an outer sheath of effluent gas stream. The mole fraction of fuel gas drops due to dilution in the effluent gas stream.

(25) FIGS. 4C and 4D illustrate the streamlines of fuel gas flow (in this example, propane) from the lance 30. In particular, FIG. 4C illustrates the streamlines of fuel gas flow from the lance 30 when the helical spring 50 extends in the axial direction beyond the lance 30, within the nozzle structure 12. These streamline illustrations assume the flow through the inlet structure 10 is 50 standard litres per minute of nitrogen, 18 standard litres per minute oxygen and the flow rate of fuel gas through the lance 30 is 3.2 standard litres per minute. As can be seen, enhanced mixing occurs due to the presence of the tapered portion 34, but the fuel gas flow is more turbulent. However, as can be seen in FIG. 4D, increased mixing occurs due to the presence of the tapered portion 34, but the turbulent flow is minimized by terminating the helical spring 50 such that it extends in the axial direction into the nozzle structure 12 no further than the gas outlet aperture 39 of the lance 30. The mole fraction of fuel gas drops due to dilution in the effluent gas stream.

(26) Accordingly, it can be seen that the presence of the tapered portion 34, together with the shorter length of the spring 50, provides for increased mixing of the fuel gas with the effluent gas stream, while avoiding unnecessary turbulence and producing near laminar flow as the mixed effluent stream and fuel gas exits the nozzle structure 12.

(27) Table 1 shows experimental data for a variety of different lance configurations. In this arrangement, propane was provided to both the lance 30, the concentric fuel conduit 13 and the combustion ring 14, together with oxygen. As can be seen, the highest rates of DRE occurred with four slots 33 and a length of 45 mm.

(28) TABLE-US-00001 TABLE 1 Lance type C.sub.3H.sub.8 (lpm) 0.sub.2 (lpm) [CF.sub.4] Length Slits Angle Lance Concentric Total Premix (ppm) DRE Conventional 1.8 1.5 3.3 18 1400 53.3% 4 4 15 1.8 1.5 3.3 18 1150 61.7% 4.5 4 45 1.8 1.5 3.3 18 1040 65.3% 3.5 4 15 1.8 1.5 3.3 18 1085 63.8% 4 5 15 1.8 1.5 3.3 18 1125 62.5% 4 3 15 1.8 1.5 3.3 18 1120 62.7%

(29) Table 2 shows how increasing the amount of propane delivered by the lance 30 and decreasing the amount of propane delivered by the concentric fuel conduit 13 when using the lance 30 dramatically increases the DRE. Table 2 also shows that maximum DRE occurs when the helical spring 50 is present and when it does not extend further than the lance 30 within the nozzle structure 12.

(30) TABLE-US-00002 TABLE 2 Lance type C.sub.3H.sub.8 (lpm) 0.sub.2 (lpm) Spring [CF.sub.4] Length Slits Angle Lance Concentric Total Premix Length (mm) (ppm) DRE 4.5 4 45 3.2 0.6 3.8 18 0 235 92.2% 4.5 4 45 3.2 0.6 3.8 18 70 180 94.0% 4.5 4 45 3.2 0.6 3.8 17 50 130 95.7% 4.5 4 45 3.2 0.6 3.8 18 40 100 96.7% Conventional 3.2 0.6 3.8 18 40 530 82.3% Conventional 3.2 0.6 3.8 18 70 290 90.3% Conventional 3.0 1.8 4.8 19 70 150 95.0%

(31) Accordingly, it can be seen that embodiments provide an ultra-low fuel lance design that has a split end, which improves the fuel, processed gas and oxygen mixing which increases PFC gas abatement efficiency. Furthermore, embodiments enable a 30% injection fuel reduction while still achieving greater than 95% DRE. Embodiments provide for etch ultra-low fuel CF.sub.4 abatement which replaces radiant combustors with a horizontal chamber, which provide a constant flame ignition source for the effluent stream process gases and propane/air mix. A conventional lance with a 70 mm spring and inject settings of 3.3 standard litres per minute propane (1.8 standard litres per minute on lance, 1.5 standard litres per minute on coaxial (concentric fuel conduit), 18 standard litres per minute oxygen could only achieve 71% DRE).

(32) The ultra-low fuel propane lance is 40 mm long, with four, 4.5 mm depth slits 90 apart at the end of the lance angled 45 outward and cooperating with a 40 mm actuator spring. The spring creates some turbulence to the incoming mixture of process gas and oxygen which were mixed upstream at a premix port prior to entering the inlet head nozzle. As the 40 mm spring is the same length as the lance, it does not overlap the lance tip where the lance fuel inject exits into the nozzle. The propane exiting from the lance mixes with the process gas and oxygen mixture stream within the nozzle before exiting the end of the nozzle in a laminar flow. This mixing arrangement demonstrated enhanced destruction of PFC gases.

(33) In addition to being able to perform greater than 95% DRE with a total propane injection flow of 3.6 standard litres per minute (3 standard litres per minute on lance, 0.6 standard litres per minute on coaxial, 18 standard litres per minute oxygen) there is a fuel flow reduction of approximately 30% compared to the conventional lance configuration. The conventional lance requires 4.8 standard litres per minute propane (3 standard litres per minute on lance, 1.8 standard litres per minute on coaxial, 19 standard litres per minute oxygen) to achieve greater than 95% DRE.

(34) Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

(35) Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

(36) Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.