DEVICE AND METHOD FOR CLEANING A GAS STREAM

Abstract

A device, such as a wet scrubber for cleaning a stream of gas by removing gaseous, liquid and solid impurities, has a gas inlet and a gas outlet. At the gas inlet there is a first structured packing. A spray-scrubber area with atomizing nozzles is provided above the first structured packing. A first demister is provided for separating larger drops above the spray-scrubber area. A woven fabric is above the first demister, and spray nozzles are arranged around this woven fabric to spray washing liquid in the direction of the gas stream onto the surface of the woven fabric. A final demister is located above the woven fabric and has a demister rinsing apparatus. The device may be used to dispose of industrial waste gases encountered in the semiconductor industry, particularly for the disposal of waste gases stemming from CVD processes in microelectronics production.

Claims

1. A device for cleaning a stream of gas by removing gaseous, liquid and solid impurities, including but not limited to fine and ultrafine solid particles, comprising: a gas inlet; a gas outlet; a first structured packing at the gas inlet; a spray-scrubber area with atomizing nozzles above the first structured packing; a first demister for separating larger drops above the spray-scrubber area; a woven fabric above the first demister, two or more spray nozzles arranged around the woven fabric and configured to spray a washing liquid in the direction of the gas stream onto the surface of the woven fabric; and a final demister above the woven fabric, said final demister having a demister rinsing apparatus.

2. The device according to claim 1, wherein the first structured packing is charged with a first washing liquid in the form of water containing a sodium hydroxide solution or a potassium hydroxide solution.

3. The device according to claim 1, wherein one or more of the atomizing nozzles of the spray-scrubber area are configured to spray a second washing liquid in the form of water.

4. The device according to claim 1, wherein the atomizing nozzles are configured as two-fluid nozzles which are operated with washing liquid and a gas comprising compressed air or nitrogen.

5. The device according to claim 1, wherein the woven fabric is placed on a cylindrical support element.

6. The device according to claim 5, wherein the woven fabric is a textile material that is placed radially symmetrically on the support element in the form of a woven-fabric cylinder.

7. The device according to claim 5, wherein the support element has a bottom, and the bottom of the support element is closed.

8. The device according to claim 5, wherein the woven fabric has a specific surface area, and the specific surface area of the woven fabric is greater than 500 m.sup.2/m.sup.3.

9. The device according to claim 5, wherein the woven fabric is placed in the vertical direction.

10. The device according to claim 5, wherein the gas that is to be cleaned is deflected horizontally above the first demister and then flows in the horizontal direction through the woven-fabric cylinder.

11. The device according to claim 10, wherein the woven-fabric cylinder has an upper end and a bottom end opposite the upper end, and wherein the upper end of the woven-fabric cylinder is connected to the entrance of the final demister, and at least three spray nozzles are arranged horizontally around the woven-fabric cylinder.

12. A method for cleaning a stream of gas by removing gaseous, liquid and solid impurities, including but not limited to fine and ultrafine solid particles, comprising: directing the gas through a first structured packing at a gas inlet; passing the gas through a spray-scrubber area with atomizing nozzles above the first structured packing; separating larger drops with a first demister that is above the spray-scrubber area; passing the gas through a woven fabric above the first demister, spraying a washing liquid in the direction of the gas stream onto the surface of the woven fabric with two or more spray nozzles arranged around the woven fabric; and separating drops with a final demister above the woven fabric, said final demister having a demister rinsing apparatus.

13. The method of claim 12, wherein the first structured packing is charged with a first washing liquid in the form of water containing a sodium hydroxide solution or a potassium hydroxide solution.

14. The method according to claim 12, wherein one or more of the atomizing nozzles of the spray-scrubber area are configured to spray a second washing liquid in the form of water.

15. The method according to claim 12, wherein the atomizing nozzles are configured as two-fluid nozzles which are operated with washing liquid and a gas comprising compressed air or nitrogen.

16. The method according to claim 12, wherein the woven fabric is placed on a cylindrical support element.

17. The method according to claim 12, wherein the woven fabric is a textile material that is placed radially symmetrically on the support element in the form of a woven-fabric cylinder.

18. The method according to claim 12, wherein the support element has a bottom, and the bottom of the support element is closed.

19. The method according to claim 17, wherein the woven fabric has a specific surface area, and the specific surface area of the woven fabric is greater than 500 m.sup.2/m.sup.3.

20. The method according to claim 17, wherein the woven fabric is placed in the vertical direction.

21. The method according to claim 17, wherein the gas that is to be cleaned is deflected horizontally above the first demister and then flows in the horizontal direction through the woven-fabric cylinder.

22. The method according to claim 21, wherein the woven-fabric cylinder has an upper end and a bottom end opposite the upper end, and wherein the upper end of the woven-fabric cylinder is connected to the entrance of the final demister, and at least three spray nozzles are arranged horizontally around the woven-fabric.

Description

DESCRIPTIONOF THE DRAWINGS

[0019] The invention will be described in greater detail below on the basis of drawings and embodiments, without being limited thereto. The preceding and subsequently described features of the device according to the invention and of the method according to the invention can be freely combined, either individually or with several features, without being associated to a given embodiment.

[0020] There is shown in the Figures:

[0021] FIG. 1 schematically shows a burner-scrubber installation of the type known from the state of the art. The washing segment (6) to which the present invention relates has a structured packing (19) which is charged with a washing liquid by means of spray nozzles (15), a demister (10) with a demister rinsing apparatus (20) and a gas outlet (9).

[0022] FIG. 2 likewise shows a burner-scrubber installation in which the washing segment (6) is configured as a device according to the invention.

[0023] FIG. 3 lastly schematically shows the washing segment or device (6) according to the invention in a preferred embodiment containing additional components.

[0024] Elements having the same function are provided with identical reference numerals in FIGS. 1 to 3.

DETAILED DESCRIPTION

[0025] The washing segment (6) according to the invention or the device (6) according to the invention for cleaning a gas stream preferably has a cylindrical tube which, below a first structured packing (19; not shown here), has an inlet for the gas stream that is to be cleaned. The gas stream comes from a thermal reactor (3) equipped with a burner (1), passes through a quenching zone (4) and then enters the washing segment (= device) through the inlet. The washing segment can have at its bottom an additional opening (not shown here) through which the washing liquid can run off into the tank (5) located underneath.

[0026] After entering the washing segment (6), the gas flows upwards through a first structured packing (19). This structured packing (19) preferably consists of a corrosion-proof metallic packed bed and is rinsed by the washing liquids from the areas of the washing segment situated above this structured packing. Preferably, packing bodies having a specific surface area of at least 200 m.sup.2/m.sup.3 and a free volume of at least 95% are employed. In the structured packing (19), the gas comes into contact with the washing liquid and the soluble and/or reactive compounds are then washed out. Only a small fraction of very fine particles, that is to say, particles with a diameter of considerably less than 1 .Math.m, are separated in this first structured packing (19).

[0027] Above the first structured packing (19), the gas flows through a spray-scrubber area where a washing liquid is atomized to form very fine drops. The liquid is atomized by spray nozzles or atomizing nozzles (18) that can generate liquid drops having a diameter of less than 1 mm, preferably less than 100 .Math.m. These spray nozzles or atomizing nozzles (18) can be configured as two-fluid nozzles which are supplied with washing liquid and compressed air or nitrogen via appropriate feed lines (8, 17).

[0028] As an alternative, it is also possible to use high-pressure nozzles which are supplied with the washing liquid by means of a high-output pump with a high initial pressure. In order to prevent the spray nozzles (18) from becoming clogged in this stage with solid particles that might be contained in the recirculating washing liquid, these nozzles (18) are supplied with a second washing liquid, preferably fresh water or particle-free filtered spent water. The spray nozzles are selected and arranged in such a way that the entire cross section of the washing segment is covered with drops so that all of the particles in the gas stream come in close contact with drops and can collide with them. Naturally, the drops also pick up soluble gases.

[0029] Above the spray-scrubber area, there is an area for separating the drops and fine particles out of the gas. This area has a first demister (16) for the separation of larger drops. This demister is preferably configured as an additional structured packing (16) having a low height, for example, it is configured as a packed bed having only a few layers of tower packings which are preferably of the same type as in the first structured packing (19). This structured packing (16) is rinsed from above with washing liquid by means of spray nozzles (15) in order to wash out the separated particles and also so as to function as a gas scrubber. This washing liquid can be recirculated out of a washing liquid tank (5). Water, preferably set to an alkaline pH value by means of the addition of a sodium hydroxide solution or a potassium hydroxide solution, is used as the washing liquid.

[0030] The gas passes from the bottom to the top through the first demister or through the second structured packing (16) and is then deflected horizontally, after which it flows in the horizontal direction through a woven fabric (11). This woven fabric (11) can be a textile material having a pore size that is considerably smaller than that of the first demister packing. The specific surface area of the woven fabric (11) is preferably greater than 500 m.sup.2/m.sup.3, especially greater than 1000 m.sup.2/m.sup.3. The woven fabric (11) is a flat material that is placed in the vertical direction. Examples of suitable materials are those classified as MERV 8 according to ASHRAE 52.5 (American Society of Heating, Refrigerating, and Air Conditioning Engineers) or as M5 according to European Standard EN 779. Washing liquid is continuously sprayed by means of spray nozzles (12) in the direction of the gas flow onto the surface of the woven fabric (11). Some of the liquid or all of it penetrates into the woven fabric (11) and flows downwards in the woven fabric or on its surfaces. As a result, the fine drops and particles that are separated in the woven fabric are continuously washed out. In order to optimize the surface of the woven fabric (11) in the cylindrical washing segment, the woven fabric is placed radially symmetrically on a cylindrical support element (11) in the washing segment. The bottom of the support element is closed so that the gas can only enter via the woven fabric. The upper end of the support element (11) is connected to the entrance of a final demister stage (10). The first demister packing (16) can be configured as a ring around the support element together with the woven fabric. At least three, preferably six, spray nozzles (12) are arranged around the woven-fabric cylinder (11) for purposes of attaining a uniform and complete wetting of the woven fabric. A closed circular line on the exterior or in the interior of the washing segment can serve to ensure a uniform supply of washing liquid to the spray nozzles.

[0031] In order to rinse off accumulated solids, the demister stage (10) can additionally be discontinuously charged with additional washing liquid, preferably fresh water, by means of a demister rinsing apparatus (20) installed above in the gas outlet (9).

[0032] The specific surface area is defined as the geometric surface of the packing bodies, or as the surface of the fibers or filaments in the volume of the packed bed or of the structured packing. If A.sub.F stands for the surface of the packing bodies or for the surface of the fibers, and V.sub.s stands for the volume of the packed bed or of the structured packing, then the specific surface area is A.sub.F/V.sub.S. The free volume is defined as the portion of volume of the packed bed or structured packing that is not filled up by the packing bodies or fibers. If V.sub.F stands for the volume of the packing bodies and Vs stands for the volume of the entire packed bed, then the free volume is defined as (V.sub.S—V.sub.F)/V.sub.s. The same applies analogously for fibers or filaments. As a reference source for the use of these parameters (specific area, void fraction), see the definitions presented, for example, in H.T. El-Dessouky et al.: Chemical Engineering and Processing 39 (2000) 129-139.

TABLE-US-00001 List of reference numerals 1 burner 2 noxious gas feed line 3 reactor 4 quenching zone 5 washing liquid tank 6 washing segment 7 washing liquid circulation system 8 feed line for particle-free washing liquid 9 gas outlet 10 demister 11 woven-fabric cylinder / woven fabric 12 spray nozzle 13 feed line for washing liquid 14 feed line for washing liquid 15 spray nozzle 16 second structured packing / demister 17 feed line for compressed air 18 atomizing nozzle 19 first structured packing 20 demister rinsing apparatus