RADIANT BURNER FOR NOXIOUS GAS INCINERATION

Abstract

A radiant burner and method are disclosed. The radiant burner is for treating an effluent gas stream from a manufacturing process tool, the radiant burner comprises: a sintered metal fibre sleeve through which combustion materials pass for combustion proximate to an inner combustion surface of the sintered metal fibre sleeve; and an insulating sleeve surrounding the sintered metal to fibre sleeve and through which the combustion materials pass. In this way, a radiant burner is provided which does not crack due to rapid cycling caused by frequent idle steps during which the burner is extinguished. Also, by providing an insulating sleeve, the temperature within the radiant burner and the temperature of an outer surface of the radiant burner remain comparable with existing ceramic burners. This enables the radiant burner to be substituted in place of existing ceramic burners as a line-replaceable unit which does not suffer from cracking during such frequent and short-duration periods of process tool inactivity.

Claims

1. A radiant burner for treating an effluent gas stream from a manufacturing process tool, said radiant burner comprising: a sintered metal fibre sleeve through which combustion materials pass for combustion proximate to an inner combustion surface of said sintered metal fibre sleeve; and an insulating sleeve surrounding said sintered metal fibre sleeve and through which said combustion materials pass.

2. The radiant burner of claim 1, wherein said sintered metal fibre sleeve has at least one of a porosity of 80-90%, an air permeability of 150-300 cc/min/cm.sup.2 and a density of 690-1110 kg/m.sup.3.

3. The radiant burner of claim 1, wherein said insulating sleeve is a ceramic fibre blanket.

4. The radiant burner of claim 1, wherein said insulating sleeve has at least one of a density of 100-150 Kg/m.sup.3 and a density which provides a 40-60 Pa pressure drop as said combustion materials pass therethrough.

5. The radiant burner of claim 1, wherein said sintered metal fibre sleeve is retained concentrically within said insulating sleeve.

6. The radiant burner of claim 1, further comprising a support operable to retain said sintered metal fibre sleeve and said insulating sleeve.

7. The radiant burner of claim 1, wherein said insulating sleeve is retained concentrically within said support.

8. The radiant burner of claim 1, wherein said sintered metal fibre sleeve comprises a pleat extending circumferentially.

9. The radiant burner of claim 1, further comprising a temperature sensor thermally coupled with said sintered metal fibre sleeve and operable to provide an indication of a temperature of said sintered metal fibre sleeve.

10. The radiant burner of claim 1, wherein said temperature sensor is thermally coupled with said sintered metal fibre sleeve on an outer surface.

11. The radiant burner of claim 10, further comprising a source operable to supply said combustion materials in one of a plurality of mix ratios selected in response to said temperature.

12. The radiant burner of claim 11, wherein said source is operable to supply said combustion materials in a substantially stoichiometric mix ratio when said temperature of said sintered metal fibre sleeve fails to exceed an operating temperature.

13. The radiant burner of claim 11, wherein said source is operable to supply said combustion materials in a substantially lean mix ratio when said temperature of said sintered metal fibre sleeve exceeds an operating temperature.

14. A method of operating a radiant burner for treating an effluent gas stream from a manufacturing process tool, said method comprising: determining a temperature of an outer surface of a sintered metal fibre sleeve of said radiant burner through which combustion materials pass for combustion proximate to an inner combustion surface of said sintered metal fibre sleeve; and supplying said combustion materials in one of a plurality of mix ratios selected in response to said temperature.

15. The method of claim 14, wherein said supplying comprises supplying said combustion materials in a substantially stoichiometric mix ratio when said temperature of said sintered metal fibre sleeve fails to exceed an operating temperature.

16. The method of claim 14, wherein said supplying comprises supplying said combustion materials in a substantially lean mix ratio when said temperature of said sintered metal fibre sleeve exceeds an operating temperature.

17. The method of claim 14, wherein said supplying comprises supplying said combustion materials in said substantially stoichiometric mix ratio for a selected time period.

18. The method of claim 14, wherein said supplying comprises supplying said combustion materials in said substantially lean mix ratio upon expiry of said selected time period.

19. (canceled)

20. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0032] FIG. 1 illustrates a radiant burner according to one embodiment; and

[0033] FIG. 2 illustrates in more detail the arrangement of the foraminous burner liner shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0034] Before discussing the embodiments in any more detail, first an overview will be provided. Embodiments provide a radiant burner which is particularly suited to operate in a so-called “green mode”, where the burner is extinguished during periods of processing tool inactivity (for example, during idle steps), these periods may be frequent and of short duration. The radiant burner liner has a sintered metal fibre sleeve which is surrounded by an insulating sleeve, which replaces a typical ceramic radiant burner liner. The combination of the sintered metal fibre sleeve and the insulating sleeve provides a radiant burner which operates under almost identical conditions and with improved efficiency compared with existing radiant burners, but which is able to resist shocks due to thermal cycling. Also, in order to improve the warm-up time of the radiant burner from cold, the mix of the combustion materials may be adjusted to make the mixture rich before reverting to lean conditions during normal operation.

Radiant Burner—General Configuration and Operation

[0035] FIG. 1 illustrates a radiant burner, generally 8, according to one embodiment. The radiant burner 8 treats an effluent gas stream pumped from a manufacturing process tool such as a semiconductor or flat panel display process tool, typically by means of a vacuum-pumping system. The effluent stream is received at inlets 10. The effluent stream is conveyed from the inlet 10 to a nozzle 12 which injects the effluent stream into a cylindrical combustion chamber 14. In this embodiment, the radiant burner 8 comprises four inlets 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. Each nozzle 12 is located within a respective bore 16 formed in a ceramic top plate 18 which defines an upper or inlet surface of the combustion chamber 14. The combustion chamber 14 has side walls defined by an exit surface 21 of a foraminous burner element 20, which is illustrated schematically and shown in more detail in FIG. 2. The burner element 20 is cylindrical and is retained within a cylindrical outer shell 24.

[0036] A plenum volume 22 is defined between an entry surface of the burner element 20 and the cylindrical 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. The mixture of fuel gas and air passes from the entry surface 23 of the burner element to the exit surface 21 of the burner element for combustion within the combustion chamber 14.

[0037] The nominal ratio of the mixture of fuel gas and air is varied to vary the nominal temperature within the combustion chamber 14 to that which is appropriate for the effluent gas stream to be treated. Also, the rate at which the mixture of fuel gas and air is introduced into the plenum volume 22 is adjusted so that the mixture will burn without visible flame at the exit surface 21 of the burner element 20. The exhaust 15 of the combustion chamber 40 is open to enable the combustion products to be output from the radiant burner 8.

[0038] Accordingly, it can be seen that the effluent gas received through the inlets 10 and provided by the nozzles 12 to the combustion chamber 14 is combusted within the combustion chamber 14 which is heated by a mixture of fuel gas and air which combusts near the exit surface 21 of the burner element. Such combustion causes heating of the chamber 14 and provides combustion products, such as oxygen, typically with 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 surface firing rate of the burner, to the combustion chamber 14. The heat and combustion products react with the effluent gas stream within the combustion chamber 14 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 within the combustion chamber to generate CO.sub.2, HF, H.sub.2O.

Foraminous Burner Liner Arrangement

[0039] Turning now to the arrangement of the foraminous burner liner 20, its construction is shown in more detail in FIG. 2. In this arrangement, the foraminous burner liner 20 is constructed by rolling and seam welding a sintered metal fibre sheet 100 to a perforated screen 110, retained between flanges 120A, 120B.

[0040] The sintered metal fibre sheet 100 may be any suitable sintered metal fibre, such as SFF1-35, or SFFE-30 supplied by the FiberTech Company of South Korea alternatively S-mat or D-mat supplied by Micron Fiber-Tech Company of USA. Typically, such sintered metal fibre has a porosity of between 80% and 90%, an air permeability of 150-300 cc/min/cm.sup.2, and a sheet density of around 694 to 1111 kg/m.sup.3.

[0041] Referring now to Table 1, it has been found that a foraminous burner liner having the sintered metal fibre sheet welded to the perforated support 110 operates under identical conditions to existing ceramic foraminous burner liners. In this example, a 152.4 mm (6 inch) internal diameter by 304.8 mm (12 inch) axial length foraminous burner liner having the sintered metal fibre sheet (and another example with a ceramic fibre blanket mentioned below) with a surface area of 145,931 mm.sup.2 (226 inch.sup.2) was fired using 36 slm of natural gas in 610 slm of air, which provided a surface burning rate of approximately 80 kW/m.sup.2 (50,000 BTU/hr/ft.sup.2) and a residual oxygen concentration of 9% (as measured when no effluent stream is present). Combustion emissions were measured in the presence of a simulated effluent stream of 200 l/min of nitrogen. As can be seen the combustion emissions (sintered metal fibre sheet/sintered metal fibre sheet+ceramic fibre blanket) when the effluent stream was then introduced are better than existing burners (ceramic).

TABLE-US-00001 TABLE 1 Concentration (ppm) sintered metal sintered metal fibre sheet + Species ceramic fibre sheet ceramic fibre blanket CO 22 18 7 NO 3 3 3 NO.sub.2 2 1 1

[0042] However, the warm-up time from cold for such an arrangement can be approximately 15 minutes. This can be shortened to less than 10 seconds by lighting off under stoichiometric conditions, before reverting to lean conditions after a short period such as, for example, 10 seconds.

[0043] In addition, the steady state temperature of the outer face 105 of the sintered metal fibre sheet 100 is higher than that of a ceramic foraminous burner liner (at 120-140° C. compared to less than 50° C.). This temperature climbs much more slowly than the combustion chamber 14 and so whilst it may not be possible to use this parameter to directly control the rich start, the outer face 105 temperature may be used beneficially to inhibit the rich start function.

[0044] Constructing a three component structure, comprising a mechanical outer support such as, for example, the perforated screen 100 and the flanges 120A, 120B, a gas permeable ceramic fibre blanket 130 and the sintered metal fibre sheet 100, results in improved performance, as shown in Tables 2 and 3. In this example, a 152.4 mm (6 inch) internal diameter by 152.4 mm (6 inch) axial length foraminous burner liner having the sintered metal fibre sheet welded to the perforated support (and another example with the ceramic fibre blanket) having a surface area of 72,965 mm.sup.2 (113 inch.sup.2) was fired using 19 slm of natural gas in 310 slm of air, which provided a residual oxygen concentration of 9% (as measured when no effluent stream is present). Nitrogen trifluoride abatement was measured as part of a simulated effluent stream with 200 l/min of nitrogen. As can be seen the combustion emissions (bare metal/insulated metal) when the effluent stream was then introduced are better than existing burners (ceramic).

TABLE-US-00002 TABLE 2 NF3 out (ppm) sintered metal sintered metal fibre fibre sheet + sheet + perforated NF3 in perforated support + ceramic (SLM) ceramic support fibre blanket 0.25 69 57 38 0.5 108 96 59 0.75 158 173 91 1.00 183 208 110 1.25 219 202 116 1.50 215 192 126 1.75 201 205 121 2.00 219 275 122

TABLE-US-00003 TABLE 3 NF3 destruction efficiency (%) sintered metal sintered metal fibre fibre sheet + sheet + perforated NF3 in perforated support + ceramic (SLM) ceramic support fibre blanket 0.25 86.3 88.7 92.4 0.5 89.3 90.4 94.1 0.75 89.4 88.5 94.0 1.00 90.9 89.6 94.5 1.25 91.2 91.9 95.4 1.50 92.8 93.6 95.8 1.75 94.2 94.1 96.5 2.00 94.5 93.1 96.9

[0045] The ceramic fibre blanket 130 is chosen so as to have a minimal pressure drop at the surface flow rates equivalent to the surface firing rates mentioned above. Typically somewhere between 6 and 12 mm, and preferably 10 mm, of commercially available blanket material such as Isofrax 1260 (calcium to silicate) of 128 kg/m.sup.3 density or Saffil (alumina) have acceptable performance, in the range of 40-60 Pa pressure drop at 0.1 m/s face velocity with a linear pressure-flow relationship. Both of these materials are available from Unifrax Limited.

[0046] As shown in FIG. 2, a thermocouple 140 is provided which thermally couples with the outer surface 105 of the sintered metal fibre sheet 100. The thermocouple 140 or other temperature sensor measures the temperature of the sintered metal fibre sheet 100. When the thermocouple 140 indicates that the temperature of the sintered metal fibre sheet 100 is below a threshold value (which indicates that the operating temperature of the combustion chamber 14 is lower than the operating temperature), the ratio of fuel to air is increased. The ratio of fuel to air is decreased when the temperature reported by the thermocouple 140 exceeds the threshold value, which indicates that the operating temperature of the combustion chamber 14 exceeds the operating temperature.

[0047] It will be appreciated that whilst in this embodiment a perforated screen 110 and metal flanges 120A, 120B are used to provide mechanical support, other arrangements for retaining the sintered metal fibre sheet 100 and the ceramic fibre blanket 130 may be provided.

[0048] Although not illustrated in FIG. 2, a circumferential pleat may be provided within the sintered metal fibre sheet 100 to accommodate changes in the length of the sintered metal fibre sheet 100 at different temperatures.

[0049] 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.

LIST OF REFERENCE SIGNS

[0050] 8 radiant burner [0051] 10 inlets [0052] 12 nozzle [0053] 14 combustion chamber [0054] 15 exhaust [0055] 16 bore [0056] 18 ceramic top plate [0057] 20 foraminous burner element [0058] 21 exit surface [0059] 22 plenum volume [0060] 23 entry surface [0061] 24 outer shell [0062] 100 sintered metal fibre sheet [0063] 105 outer face [0064] 110 perforated screen [0065] 120A, 120B flanges [0066] 130 ceramic fibre blanket [0067] 140 thermocouple