Device and method for wet cleaning of a gas stream

Abstract

Device (1), preferably in the form of a wet scrubber, for cleaning a gas stream of gaseous, liquid and solid impurities, which has a gas inlet (3), at least one first washing section (6) for cleaning the gas stream with a washing liquid, a gas outlet (5) and gas supply lines (24), characterized in that the device (1) further has several gas inlets (3) for different gas streams, wherein the supply lines (24) connected to the gas inlets (3) have a continuous gradient towards the device (1) and preferably a liquid trap (14) upstream of the gas inlets (3), and the device (1) has a pre-wash chamber (16) with at least one spray nozzle (10) and, between a first washing section (6) and a second washing section (7) in the connecting line or after the washing section (6), at least one packing (9) with a specific surface area of ​​at least 400 m² / m³, preferably in the form of a textile packing.and has a spray nozzle (10) above the packing (9), whereby the washing liquid for the packing (9) and the gas flowing through the packing (9) flow in the same direction, and wherein the gas flow is directed from the upper end of the first washing section (6) via the preferably textile packing (9) downwards in the connecting line to the lower end of the second washing section (7) or to the gas outlet (5).

Description

[0001] The invention relates to a device and a method for wet cleaning of a gas stream, wherein solid, liquid and gaseous impurities are removed from a gas stream.

[0002] In the semiconductor industry, particularly in microelectronics manufacturing, processes are used to clean wafers with a sequence of different liquid chemicals. The exhaust gases from these processes are treated with wet scrubbers located near the process equipment to prevent undesirable reactions caused by the mixing of different exhaust streams in the exhaust ducts. However, solid particles or mists of very fine liquid droplets can also form within the process equipment or at the beginning of the exhaust ducts. Since these particles are formed from the gas phase, they typically have a diameter of less than 1 µm.

[0003] Various methods and devices are proposed in the prior art for separating small particles from a gas stream.

[0004] US Patent 2008 / 0271603 A1 describes an air purification system which includes a cleaning chamber containing an aqueous solution of a reaction medium capable of removing contaminating particles and / or gaseous pollutants from a gas stream. Furthermore, this particle removal system comprises inlet and outlet filters capable of separating particles with sizes between 3-100 µm and 0.3-3 µm from a gas stream.

[0005] DE 10 2018 127 371 A1 relates to a compact wet scrubber for cleaning, for example, an exhaust gas stream in the semiconductor industry from solid, liquid and gaseous impurities, wherein the scrubber has a bypass channel within the housing to bridge the gas flow path through the at least one existing scrubbing section.

[0006] Furthermore, the prior art describes Venturi separators (water jet or gap venturi), which have high energy consumption, and electrostatic precipitators, which operate at high voltage, for particle separation from gases. The latter are often unacceptable because ignition sources should be avoided in the context of gas purification.

[0007] Therefore, there remains a need for high-performance and compact gas scrubbers that are also suitable for separating the finest particles contained in the exhaust air.

[0008] This problem is solved according to the invention by the device described below and by a method using such a device.

[0009] Typical wet scrubbers preferably have two scrubbing stages arranged side by side and operating in countercurrent flow. Since the transition of the gas into the liquid phase depends on the effective surface area of ​​the liquid, these scrubbing stages are generally designed as packed columns. The packed column is usually achieved by a bed of suitable packing material on a screen tray or by a so-called structured packing, in which large blocks of a structured material are incorporated into the column.

[0010] Especially in the semiconductor industry, bypass lines are commonly used; these are installed outside of a wet scrubber. These bypass lines allow the gas flow to be routed around the wet scrubber, ensuring that the exhaust airflow is not interrupted when the wet scrubber needs to be opened for maintenance.

[0011] For effective gas separation in wet scrubbers, a large surface area of ​​the scrubbing liquid and a long residence time of the gas in contact with the liquid are advantageous. For the separation of very fine particles, a longer residence time or contact time of the gas and liquid can also improve separation by particle diffusion. This is often not feasible in semiconductor manufacturing, however, due to the size limitations of wet scrubbers caused by their required proximity to the production unit.

[0012] According to the invention, an increase in the relative velocity between the particles and the surface and a reduction in the distance between the particles carried in the gas phase and the surface of the packing material are used to improve particle separation. For this purpose, a section in the scrubber with a narrower cross-section can be provided to increase the flow velocity and is preferably equipped with a textile packing. This packing is rinsed with scrubbing liquid. The increased flow velocity enhances the separation of larger particles due to inertia. The smaller the pore size of the packing, the closer and more effective the contact of fine particles with the liquid surface due to the barrier effect. Therefore, it is provided that the pore size of this preferably textile packing is finer / smaller than that of the packing material in the gas scrubbing columns.In the gas scrubbing columns, packing materials are used with a free volume of preferably at least 90% and a specific surface area of ​​preferably at least 150m². 2 / m 3 In contrast, preferred textile packings for improving particle separation are designed as cushions made of fibers or wire, i.e., as tangles, nonwovens, woven fabrics, or preferably knitted fabrics. These packings have a free volume of preferably at least 85% and a specific surface area of ​​preferably at least 400 m². 2 / m 3 .

[0013] The specific surface area is defined as the geometric surface area of ​​the fill material, or the surface area of ​​the fibers or wires within the volume of the bulk material or packing. If A F the surface of the filler material or the surface of the fibers is and V s The volume of the bulk material or packing is then the specific surface area A. F / V SThe free volume is defined as the portion of the volume of the bulk material or packing not filled by the filler material or fibers. If V F If the volume of the packing material and Vs is the volume of the entire packing, then the free volume is defined as (V S -V F ) / V S The same applies to fibers or wires. For a reference on the use of these parameters (specific area, void fraction), see the definitions, for example, in HT El-Dessouky et al: Chemical Engineering and Processing 39 (2000) 129-139.

[0014] With a reduced pore size, the pressure drop across the packing also increases, as does the risk of liquid buildup within the packing. Therefore, the described measure is better suited for a section of the scrubber where gas and scrubbing liquid flow in the same direction (downwards).

[0015] If the emission of particles into the ambient air is to be avoided, it is advantageous to prevent the formation of the particles in the first place. To this end, it is beneficial to feed the gases from the various sources of the production process to the scrubber separately and allow them to come into contact with the scrubbing liquid before the different gas streams mix and react with each other to form particle-forming substances.

[0016] The scrubber according to the invention is therefore preferably equipped with a modular front panel or front box that can be easily adapted to the individual situation, i.e., the number and size of the exhaust gas lines to be connected, in the respective production facility. This front panel is mounted to the scrubber body and forms the connection to a pre-wash chamber. The gas inlets with the connections for the exhaust gas feeds are located on the front panel. These gas inlets are preferably designed with a gradient into the scrubber to allow liquid that is injected into the lines to flow back into the scrubber. Spray nozzles can be provided in the area of ​​the gas inlets, arranged so that scrubbing liquid is sprayed into the gas inlets. This reduces the concentrations of water-soluble gases even before the gas streams from the various feeds mix.

[0017] Since upstream processes, particularly in semiconductor production, are often wet processes, it is possible for liquids to condense on the walls of the gas supply lines from the process plant to the scrubber, or even for liquids to be discharged from the process plant through the gas supply lines. For example, water may be deliberately flushed into the lines to remove solid deposits. Therefore, the lines from the process plants to the scrubber should preferably be designed with a continuous gradient and no dead spots. To prevent these liquids, which may also contain reactive chemicals, from entering the scrubber and the scrubbing liquid and impairing the scrubber's effectiveness, liquid traps can be installed at the supply lines or in the lines shortly before the gas inlets. These can be, for example, a depression in the line.Designed in the form of a funnel or a cylindrical container, these traps collect liquid. To prevent the liquid flowing down the inlet from overflowing the trap's recess, a projection can be incorporated into the pipe wall before or after the recess to slow down or retain the liquid. The traps may have a drain at the bottom, which leads via a gas barrier (traps) into a suitable collection container or liquid waste collection system. Such liquid traps can also prevent liquid from entering the pre-wash chamber when it is not in operation, for example, when a bypass around the scrubber is used and the connection to the scrubber is closed.This also prevents the liquid level from rising above the maximum permissible level during a scrubber shutdown or maintenance, thus blocking the passage for gas and therefore the suction of the process tool.

[0018] It is possible that during operation of the scrubber, packings or droplet separators within the scrubber may become blocked by solids or biological growth. In these cases, these components must be cleaned. For this purpose, it is advantageous to have a bypass around the scrubber, allowing the process plants to continue operating or at least continue to be drawn through the exhaust gas lines when the gas can no longer flow freely through the scrubber, or when the scrubber needs to be opened for maintenance.

[0019] The switch between the bypass and the path through the washer can be implemented with a flap, as described in DE 10 2018 127 371 A1. When using a modular front panel with multiple feeds at the pre-wash chamber, it is advantageous to choose a design with two bypass flaps. One bypass flap is located below the pre-wash chamber and a second flap above it. Both flaps are preferably connected to a common actuator to guarantee synchronous switching. Switching with two separate flaps allows for more stable pressure control in the pre-wash chamber during the switching process.

[0020] In a preferred embodiment, a controlled fan or a controlled throttle valve is also arranged in the bypass line to regulate the pressure at the inlet of the scrubber.

[0021] The invention is described in more detail below with reference to exemplary embodiments, without being limited by this. The features of the device and method according to the invention described above and below can be freely combined – individually or in groups – without being bound to a specific embodiment.

[0022] According to the invention, the scrubber housing is preferably made of stainless steel, which additionally has a corrosion protection layer on the inside. The advantages of this embodiment are: increased mechanical stability, low risk of damage during transport, especially at low ambient temperatures, in contrast to plastics, no functional risk due to load input when connecting the gas supply lines, and no temperature sensitivity to heat input from hot process exhaust gas or from reaction heat generated in the scrubber.

[0023] The scrubber according to the invention has a bypass line, which ensures the suction of the upstream process plant even during maintenance or in the event of a malfunction of the scrubber. Furthermore, the following embodiment is preferred according to the invention: The connecting pipe between the two washing stages runs from the top of the first washing stage downwards to the bottom of the second. The cross-section of this connecting pipe is smaller than the cross-section of the columns in the washing stages, resulting in a higher flow velocity. Packing material (e.g., packing material, structured packing, fabric) is inserted into this connecting pipe.

[0024] Washing fluid is supplied to the packing via spray nozzles located above it. Since the gas and washing fluid flow in the same direction, the washing fluid cannot accumulate within the packing. Therefore, smaller pore sizes are possible than in the washing stages. While the unidirectional flow is somewhat less efficient for gas separation, the higher gas velocity and deflection within the packing are highly advantageous for the preferred particle separation. Consequently, a small pore size and dense packing are preferred, and the downward flow, despite its small volume and the short residence time of the gas within the packing, can be used to improve particle separation.

[0025] The Fig. 1 to Fig.Figure 4 schematically shows different embodiments of the present invention. Identical or equivalently functioning components are designated with the same reference numerals in these figures.

[0026] The system 1 according to the invention has several separate inlets 3 for exhaust gases to prevent the mixing of exhaust gases from different process chambers and the resulting reactions with particle formation. Gas supply lines 24 lead from the upstream process system 25 with a continuous downward slope to the gas inlets 3 of the device 1. The gas supply lines 24 can have a liquid trap 14 upstream of the gas inlets 3. Spray nozzles 10 are provided in the inlets 3 or in the pre-wash chamber 16 directly after the inlets open to rapidly reduce the concentrations of water-soluble components in the exhaust gases. This reduces the rate of particle formation. A packing 9 can also be arranged at the lower end of the pre-wash chamber 16, which is wetted by the washing liquid from the spray nozzles 10 in the pre-wash chamber 16.This works similarly to the packing in the connecting line between washing stages 6 and 7, or after the washing stage, mainly for the separation of particles.

[0027] Due to the fine packings 9 used for particle separation, a slightly greater pressure drop across the system is to be expected. Deposits can also accumulate more quickly in the finer packings 9, leading to blockages in the system. Therefore, monitoring the pressure differential across the washing stages and the particle separation packings is crucial for the system's reliability. Consequently, a differential pressure measurement 17 is preferably provided between the pre-wash chamber 16 and the outlet of the second washing stage 5.

[0028] High particle loads from upstream processes or high concentrations of reactive gases can cause the pressure measurement port in the pre-wash chamber to become blocked. This can lead to particles entering the measuring port and distorting the pressure reading. Therefore, the measuring ports can be equipped with a purge gas port (22) through which, for example, dry air or nitrogen is supplied to keep particles out of the ports. However, this can also cause saline wash solution to dry on the ports and impede the pressure measurement. Therefore, the measuring line must be cleaned occasionally. To enable cleaning without interrupting the upstream process, two ports 18 are provided for pressure measurement, which can be used alternatively. For this purpose, the connecting line between the pressure gauge 19 and the ports 18 is branched and fitted with two shut-off valves 20.To clean a measuring port, the corresponding branch of the measuring line can then be shut off and removed without disturbing the pressure measurement, which continues via the second port.

[0029] To compensate for the pressure drop across the washing stages and the particle separation packs, the system can be equipped with an integrated fan 21 downstream of the washing stages and downstream of a demister 23. The pressure at the system inlet can be used to control the fan 21's speed to maintain a constant inlet pressure. The controlled fan 21 consumes more energy at high speed than at low speed. The pressure drop across the system also depends on the rinsing of the packs 8 and 9, particularly the finer packs 9 for particle separation. To reduce the energy consumption of the fan 21, the rinsing of the fine packs 9 can be controlled to minimize it when the upstream processes are not generating particles.

[0030] The waste disposal system can receive signals from the upstream process plant. These signals can provide information about the state of the process plant or the states of the individual process chambers. Based on these signals, the waste disposal system decides whether improved particle separation is required. Alternatively, the signals can request particle separation. These signals can be transmitted, for example, via switching contacts or standard serial interfaces such as Ethernet or RS485.

[0031] Such signals can also be used to indicate that no gas and particle disposal is required during a specific period. Based on this information, the system can then route the exhaust gases through the bypass, thereby saving energy for pumps and fans. Signals can also be used to adjust the pressure at the inlet of the disposal system to adapt to varying process plant requirements.

[0032] For safety reasons, it is common practice for waste disposal facilities to also transmit signals back to the process plant in a similar manner, indicating the plant's status, e.g., that the plant is fully operational, or that it is undergoing maintenance, or that a warning or alarm is issued if monitored parameters are outside the specified range.

[0033] The present invention thus comprises a device, preferably in the configuration as a wet scrubber, for cleaning a gas stream of gaseous, liquid and solid impurities, as described in the preceding description and in the following patent claims.

[0034] Furthermore, the present invention comprises a method for purifying a gas stream from gaseous, liquid and solid impurities, in which the device according to the invention is used, and finally the use of the device according to the invention in the said method or for purifying a gas stream from gaseous, liquid and solid impurities. Reference symbol list 1 device / wet scrubber 2 Front panel 3 Gas inlet (with slope towards the scrubber) 4 Bypass lines 5 Gas outlet 6 First wash cycle / wash stage 7 Second wash cycle / wash stage 8 packing elements in the washing lines 9 textile packing in the gas flow or connecting pipes 10 spray nozzles 11 Guide element 12 Collection tank for first wash fluid 13 Collection tank for second washing fluid 14 Liquid trap 15. Liquid trap process 16 Pre-wash chamber 17 Arrangement for differential pressure measurement 18 connections for differential pressure measurement 19 Pressure gauge 20 shut-off valves 21 fans 22 Purge gas connection for pressure measuring connections 23 droplet separators 24 gas supply lines 25 Process plant QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2008 / 0271603 A1

[0004] DE 102018127371 A1 [0005, 0019]

Claims

[1] Device (1), preferably in the form of a wet scrubber, for cleaning a gas stream of gaseous, liquid and solid impurities, which has a gas inlet (3), at least one first scrubbing section (6) for cleaning the gas stream with a scrubbing liquid, a gas outlet (5) and gas supply lines (24), characterized by that the device (1) further comprises several gas inlets (3) for different gas flows, wherein the supply lines (24) connected to the gas inlets (3) have a continuous gradient towards the device (1) and preferably a liquid trap (14) upstream of the gas inlets (3), and the device (1) has a pre-wash chamber (16) with at least one spray nozzle (10) and, between a first washing section (6) and a second washing section (7) in the connecting line or after the washing section (6), at least one packing (9) with a specific surface area of ​​at least 400 m² 2 / m 3, preferably in the form of a textile packing, and preferably has a spray nozzle (10). [2] Device (1) according to claim 1, characterized by , that the gas flow is directed from the upper end of the first washing section (6) via the preferably textile packing (9) in the connecting line downwards to the lower end of the second washing section (7) or to the gas outlet (5). [3] Device (1) according to claim 1 or 2, characterized by , that the device (1) has an interchangeable front panel (2) which is provided with the gas inlets (3). [4] Device (1) according to any one of claims 1 to 3, characterized by , that the pore size of the preferably textile packing (9) in the connecting lines is smaller than the pore size of the packing (8) in the washing section (6) or in the washing sections (6) and (7). [5] Device (1) according to any one of claims 1 to 4, characterized by that the liquid trap (14) is provided with a drain (15). [6] Device (1) according to any one of claims 1 to 5, characterized by , that the device (1) is equipped with an integrated fan after the washing sections (6), (7) and a droplet separator. [7] Device (1) according to any one of claims 1 to 6, characterized by that this has an arrangement for differential pressure measurement (17) between the pre-wash chamber (16) and the exit of the last wash section (7). [8] Device (1) according to any one of claims 1 to 7, characterized by , that the pre-wash chamber (16) has two connections (18) for differential pressure measurement (17) which can be used alternatively. [9] Device according to any one of claims 1 to 8, characterized by that this also has a packing (9) in the pre-wash chamber (16), preferably in the form of a textile packing which has a specific surface area of ​​at least 400 m² 2 / m 3 exhibits. [10] Method for purifying a gas stream from gaseous, liquid and solid impurities, characterized by , that a cleaning device (1) according to one of claims 1 to 9 is used. [11] Use of a device (1) according to any one of claims 1 to 9 in a method according to claim 10. [12] Use of a device (1) according to any one of claims 1 to 9 for cleaning a gas stream of gaseous, liquid and solid impurities.