GB2588909A - Inlet assembly for an abatement apparatus - Google Patents

Abstract

An inlet assembly 100 for an abatement apparatus comprises an effluent stream inlet conduit 120 extending between an inlet 130 receiving an effluent stream 220 and an outlet 140 in fluid communication with a treatment chamber of the abatement apparatus. A lance 150 is located within the inlet conduit, with a lance wall 160 defining a lance conduit 170 extending between a lance inlet 180 receiving a combustion reagent 230 and a lance outlet 190. The lance wall comprises an aperture 210 delivering a first proportion of combustion reagent into the inlet conduit to pre-mix with the effluent stream. The lance outlet delivers a second proportion of combustion reagent into the inlet conduit to mix with the pre-mixed effluent stream before it is delivered to the treatment chamber. The lance may be coaxially located within the inlet conduit and may share an elongate axis with the effluent stream inlet. The apertures may be located closer to the lance inlet than the lance outlet. The apertures may be located circumferentially around the lance wall and at different positions along the elongate axis. The lance conduit may narrow at a discontinuity 200 in the lance wall.

Description

INLET ASSEMBLY FOR AN ABATEMENT APPARATUS

FIELD OF THE INVENTION

The present invention relates to an inlet assembly for an abatement apparatus.

BACKGROUND

Abatement apparatus, such as radiant burners are known and are typically used for treating an effluent gas stream from a manufacturing process tool used in, for example, the semiconductor or flat panel display manufacturing industry. During io such manufacturing, residual perfluorinated compounds (PFCs) and other compounds exist in the effluent gas stream pumped from the process tool. PFCs are difficult to remove from the effluent gas stream and their release into the environment is undesirable because they are known to have relatively high greenhouse activity.

Known radiant burners use combustion to remove the PFCs and other compounds from the effluent gas stream. Typically, the effluent gas stream is a nitrogen stream containing PFCs and other compounds. Secondary, combustion reagent gases such as fuel gas and oxygen are mixed with the effluent gas stream and that gas stream mixture is conveyed into a combustion chamber that is laterally surrounded by the exit surface of a foraminous gas burner. Fuel gas and air are simultaneously supplied to the foraminous burner to affect flameless combustion at the exit surface, with the amount of air passing through the foraminous burner being sufficient to consume not only the fuel gas supplied to the burner, but also all the combustibles in the gas stream mixture injected into the combustion chamber.

The range of compounds present in the effluent gas stream and the flow characteristics of that effluent gas stream can vary from process tool to process 3o tool, and so the range of fuel gas and air, together with other gases or fluids that need to be introduced into the radiant burner will also vary. -2 -

Although techniques exist for processing the effluent gas stream, they each have their own shortcomings. Accordingly, it is desired to provide an improved technique for processing an effluent gas stream.

SUMMARY

According to a first aspect, there is provided an inlet assembly for an abatement apparatus, comprising: an effluent stream inlet having an inlet wall defining an inlet conduit extending between an inlet configured to receive an effluent stream and an outlet configured for fluid communication with a treatment chamber of the io abatement apparatus; and a lance at least partially positioned within the inlet conduit, the lance having a lance wall defining a lance conduit extending between a lance inlet configured to receive a combustion reagent and a lance outlet, the lance wall comprising at least one aperture configured to deliver a first proportion of the combustion reagent into the inlet conduit for premixing with the effluent stream, the lance outlet being configured to deliver a second proportion of the combustion reagent into the inlet conduit for mixing with the pre-mixed effluent stream prior to delivery to the treatment chamber.

The first aspect recognizes that in order to obtain a good destruction rate efficiency (DRE) of compounds in an effluent gas stream, high temperatures and/or good mixing with combustion reagents are required within the abatement apparatus. The first aspect also recognizes that although combustion reagents may be introduced into an effluent gas stream in order to improve the DRE, the DRE may still be less than is possible. In particular, the first aspect recognizes that the DRE may be less than is possible due to the type of mixing of the combustion reagents with the effluent gas stream prior to introduction into the abatement apparatus. In particular, poor pre-mixing leads to un-combusted combustion reagents, which reduces the temperature and/or increases the fuel consumption of the abatement apparatus. In contrast, highly mixed combustion 3o reagents lead to a very hot and short flame, which reduces the dwell time of the compounds in the effluent stream, which also reduces DRE. -3 -

Accordingly, an inlet assembly is provided. The inlet assembly may be an abatement apparatus inlet assembly. The inlet assembly may comprise an effluent stream inlet. The effluent stream inlet may have a wall or tube which defines an inlet conduit having an inlet and an outlet. The inlet may receive, or be provided with, an effluent stream. The outlet may be coupled with a treatment chamber of the abatement apparatus. The assembly may comprise a lance which may be located within the inlet conduit. The lance may be provided with a wall or tube having a lance inlet and a lance outlet. The lance inlet may receive or be provided with a combustion reagent. The lance wall may have one or more io apertures or openings. The openings may be arranged to deliver some of the combustion reagent into the inlet conduit to mix with the effluent stream. The lance outlet may provide the remainder of the combustion reagent into the inlet conduit to be mixed with the premixed effluent stream before being conveyed into the treatment chamber. In this way, extended mixing of the combustion reagent with the effluent stream prior to delivery to the treatment chamber is achieved. In particular, the provision of the combustion reagent from the apertures increases the volume of effluent stream containing the combustion reagent, which extends the burning volume and availability of combustion reagent, which assists in heating and extends the dwell time of the compounds in the effluent stream within the combustion volume, which increases the DRE.

The lance may be coaxially located within the inlet conduit and share an elongate axis with the effluent stream inlet which extends along a major direction of flow of the effluent stream. Accordingly, the lance and the inlet conduit may be co-25 located to share the same elongate access.

The lance may extend at least partially along the inlet conduit along the major direction of flow of the effluent stream.

3o The at least one aperture may be located to deliver the first proportion of the combustion reagent into the inlet conduit upstream of the lance outlet. Accordingly, some of the combustion reagent may be conveyed from the lance to -4 -the inlet conduit at a position which is upstream of the lance outlet to enable premixing.

The aperture may be located between the lance inlet and the lance outlet.

Accordingly, the aperture may be positioned somewhere between the lance inlet and the lance outlet.

The aperture may be located closer towards the lance inlet than the lance outlet. Accordingly, the aperture may be proximate the lance inlet and distal the lance io outlet.

The aperture may extend through the lance wall for fluid communication between the lance conduit and the inlet conduit. Accordingly, the aperture may be defined by the lance wall to enable the combustion reagent to be conveyed from the lance conduit to the inlet conduit.

The aperture may be orientated transverse to major direction of flow. This helps to increase mixing.

The aperture may be orientated to extend at least partially along the major direction of flow of the effluent stream. Accordingly, the aperture may be tilted in the direction of flow of the effluent stream which helps to reduce turbulence and reduce the probability of powder gathering in the aperture.

The inlet assembly may comprise plurality of the apertures. Accordingly, more than one aperture may be provided.

The plurality of the apertures may be located circumferentially around the lance wall. Accordingly, the apertures may be positioned around the lance wall to 3o facilitate mixing of the combustion reagents with the effluent stream. -5 -

The plurality of the apertures may be located at different positions along the elongate axis. Accordingly, the apertures may be positioned at different locations along the length of the lance.

The apertures may have an area which is larger than the lance outlet. Accordingly, the area of each or the total number of apertures may be larger than that of the lance outlet to facilitate pre-mixing of the combustion reagents.

An area of the plurality of the apertures may vary along the elongate axis.

to Accordingly, the apertures at different positions along the length of the lance may have different areas.

The plurality of the apertures may increase in area towards the lance outlet. Accordingly, the apertures may increase in size towards the lance outlet.

The lance conduit may narrow between the lance inlet and the lance outlet. Narrowing the cross-sectional area of the lance conduit provides backpressure to encourage the combustion reagent to exit the lance through the apertures.

The lance conduit may narrow at a discontinuity in the lance wall.

The lance conduit may narrow at a plurality of discontinuities in the lance wall.

According to a second aspect, there is provided an abatement apparatus comprising the inlet assembly of the first aspect.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in 3o combinations other than those explicitly set out in the claims. -6 -

Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which: Figure 1 is a schematic cross-sectional view of an inlet assembly according to one embodiment; io Figure 2 illustrates the mole fraction of combustion reagent within an effluent stream for a conventional lance; and Figure 3 illustrates the mole fraction of methane distributed in the effluent stream for the inlet assembly of Figure 1.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided. Embodiments provide one or more inlet assemblies which provide for distributed premixing of combustion reagents with an effluent stream prior to delivery to the abatement apparatus, in order to increase temperature and dwell time of compounds in the effluent stream. Typically, the inlet assembly has one or more apertures positioned along the length of a lance which provides for initial premixing of the combustion reagents prior to subsequent mixing with combustion reagents flowing from the outlet of the lance. This arrangement leads to increases in the DRE of the abatement apparatus, due to more distributed mixing of the combustion reagents with the effluent gas stream.

Providing apertures in the lance enables the lance to maintain an unvarying external diameter, which prevents the accumulation of any powder deposits which may be present in the effluent stream.

3o Inlet Assembly -General Arrangement Figure 1 is a schematic view of an inlet assembly 100 according to one embodiment. The inlet assembly 100 is typically located in an end plate of an -7 -abatement apparatus and extends into its combustion chamber. Typically, more than one inlet assembly 100 is provided, arranged at positions in the endplate, each extending into the combustion chamber. The inlet assembly 100 has an effluent stream inlet 110, which in this example is a cylindrical tube extending along an elongate axis A. The effluent stream inlet 110 defines an inlet conduit which extends between an inlet 130 and an outlet 140. Located concentrically and coaxially within the effluent stream inlet 110 is a lance 150. The lance 150 has a lance wall 160 which defines a lance conduit 170 which extends between a lance inlet 180 and a lance outlet 190. The lance wall 170 io has a variable thickness and has a narrowing portion 200 located proximate the lance outlet 190. A number of apertures 210 are formed and extend through the lance wall 160. The lance apertures are located towards the lance inlet 180 and away from the lance outlet 190. In this embodiment, four lance apertures are provided which are arranged circumferentially around the lance wall. Each has the same cross-sectional area. The apertures are orientated to extend through the lance wall 160 in a direction which is transverse to the elongate axis A. In operation, an effluent stream 220 is provided via the inlet 130 and travels in a major flow direction, along the elongate axis A towards the outlet 140. A combustion reagent 230, such as methane, is provided to the lance inlet 180 and also flows along the elongate axis A towards the lance outlet 190. A proportion of the combustion reagent 230 exits the apertures 210 in a direction transverse to the major direction of flow of the effluent stream. This causes premixing between the combustion reagent 230 and the effluent stream 220 in the vicinity of the apertures 210 and this premixing continues as the combined effluent stream 230 and combustion reagent 230 travel along the elongate axis A towards the lance outlet 190. Ejection of some of the combustion reagent 230 through the apertures 210 is encouraged by the backpressure caused by the narrowing of the lance conduit in the region 200. The remainder of the combustion reagent 230 3o exits the lance outlet 190 and also mixes with the pre-mixed effluent stream 220 and combustion reagent 230. The resultant mixed effluent stream 220 and combustion reagent 230 and exits the outlet 140 into the combustion chamber. -8 -

Figure 2 illustrates the mole fraction of combustion reagent (in this example, methane) within an effluent stream for a conventional lance.

Figure 3 illustrates the mole fraction of methane distributed in the effluent stream for the inlet assembly 100. As can be seen, the combustion reagent 230 exiting the apertures 210 forms a widening curtain which extends around the downstream length of the lance 150. This, in combination with the combustion reagent exiting the lance outlet 190, creates a distributed volume of combustion io reagent 230 within the effluent stream 220. This helps to facilitate combustion and increases dwell time of compounds within the effluent stream 220 since the combustion reagent 180 is more distributed and can be scavenged.

Although the embodiment mentioned above has multiple circular apertures 1.5 arranged at one position around the circumference of the lance 150, it will be appreciated that this need not be the case and that apertures may be positioned at different locations along the length of the lance 150. Furthermore, the apertures need not be circular but may be of a different shape. Furthermore, the lance wall may be tapered rather than providing a discontinuity and more than one taper or discontinuity may be provided in order to vary the backpressure at a particular location. Additionally, although the apertures are arranged transversely to the elongate axis A, it will be appreciated that they may be provided with a different orientation, such as being tilted with a tilt component along the elongate axis A. Hence it can be seen that some embodiments provide an alteration to the geometry of the inlet lance to improve the mixing of the lance gas with the bulk flow. Side holes and a restricted outlet result in the upstream lance gas pressure driving the lance gas into the bulk flow.

Some embodiments seek to provide a lance which does not provide perfect mixing, just improved mixing. This is because there is a need to improve the -9 -mixing of the gas from the lance, typically methane, into the bulk gas which is typically process gas from a process tool via a vacuum pump. An existing lance is a 6 mm outside diameter pipe with a 4 mm through hole. This injects the secondary gas axially into the centre of the flow of primary gas, and this results in gradual diffusion of the secondary gas into the primary gas. Perfect mixing of the two gases, when the secondary gas is methane and the primary gas contains PFCs, has been found to be ineffective, only 'improved' mixing is required.

In some embodiments, the lance has the hole down the middle of the lance io reduced to 3 mm in the upstream section of the lance and to 2 mm for the final 12 mm. This allows some gas to emerge from the end of the lance, but also creates a pressure build-up within the lance. Approximately halfway down the lance are four 2 mm holes, arranged radially around the lance, which allow flow of the secondary gas to pass into the primary gas perpendicular to the bulk flow. This arrangement encourages mixing of some of the lance gas flow, without making the mixing perfect. The core of secondary gas, in this case methane, emerging from the end of the lance is largely unchanged, just slightly reduced in the lance with side holes. The outer volume of the nozzle, around this central core, is the primary change. Without the side holes this volume of primary gas remains devoid of the secondary gas, whereas the introduction of the side holes greatly improves the mixing. It can be seen that introducing the secondary gas to a largely laminar flow of primary gas to cause some mixing without requiring or generating turbulence.

Variations are that the relative size of the side holes to the end hole can be modified so as to find the best combination for a given bulk flow of primary gas around the lance.

Although illustrative embodiments of the invention have been disclosed in detail 3o 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 -10 -from the scope of the invention as defined by the appended claims and their equivalents.

REFERENCE SIGNS

inlet assembly 100 effluent stream inlet 110 inlet conduit 120 inlet 130 outlet 140 lance 150 lance wall 160 lo lance conduit 170 lance inlet 180 lance outlet 190 narrowing portion 200 apertures 210 effluent stream 220 combustion reagent 230 elongate axis A

Claims (15)

1. -12 -CLAIMS1. An inlet assembly for an abatement apparatus, comprising: an effluent stream inlet having an inlet wall defining an inlet conduit extending between an inlet configured to receive an effluent stream and an outlet configured for fluid communication with a treatment chamber of said abatement apparatus; and a lance at least partially positioned within said inlet conduit, said lance having a lance wall defining a lance conduit extending between a lance inlet io configured to receive a combustion reagent and a lance outlet, said lance wall comprising at least one aperture configured to deliver a first proportion of said combustion reagent into said inlet conduit for premixing with said effluent stream, said lance outlet being configured to deliver a second proportion of said combustion reagent into said inlet conduit for mixing with said pre-mixed effluent stream prior to delivery to said treatment chamber.
2. 2. The inlet assembly of claim 1, wherein said lance is coaxially located within said inlet conduit and shares an elongate axis with said effluent stream inlet which extends along a major direction of flow of said effluent stream.
3. 3. The inlet assembly of claim 2, wherein said lance extends at least partially along said inlet conduit along said major direction of flow of said effluent stream.
4. 4. The inlet assembly of any preceding claim, wherein said aperture is located between said lance inlet and said lance outlet.
5. 5. The inlet assembly of any preceding claim, wherein said aperture is located closer towards said lance inlet than said lance outlet.
6. 3o 6. The inlet assembly of any preceding claim, wherein said aperture extends through said lance wall for fluid communication between said lance conduit and said inlet conduit.
7. -13 - 7. The inlet assembly of any one of claims 2 to 6, wherein said aperture is orientated to extend at least partially along said major direction of flow of said effluent stream.
8. 8. The inlet assembly of any preceding claim, comprising a plurality of said apertures.
9. 9. The inlet assembly of claim 8, wherein said plurality of said apertures are located circumferentially around said lance wall.
10. 10. The inlet assembly of claim 8 or 9, wherein said plurality of said apertures are located at different positions along said elongate axis. 15
11. 11. The inlet assembly of any one of claims 8 to 10, wherein said apertures have an area which is larger than said lance outlet.
12. 12. The inlet assembly of any one of claims 8 to 10, wherein an area of said plurality of said apertures varies along said elongate axis.
13. 13. The inlet assembly of any preceding claim, wherein said lance conduit narrows between said lance inlet and said lance outlet.
14. 14. The inlet assembly of any preceding claim, wherein said lance conduit narrows at a discontinuity in said lance wall.
15. 15. The inlet assembly of any preceding claim, wherein said lance conduit narrows at a plurality of discontinuities in said lance wall.