Exhaust gas moisture treatment system

Abstract

To provide a treatment system for moisture in exhaust gas, capable of inhibiting leakage of exhaust gas outside while preventing backflow of water or the like being a liquid generated in a moisture removal process even if there is no space for installing a pipe having a seal water function when removing the moisture or the like included in the exhaust gas.SOLUTION: In a treatment system for moisture in exhaust gas, whether or not the water accumulating in a tank 60 exceeds a high water level H is determined by a valve control part 81. When the valve control part 81 determines that the water exceeds the level H, an opening signal is sent to a drain valve 80, and the drain vale 80 is opened. Thereby, the water in the tank 60 is discharged. The water level lowers following the discharge of water, and whether or not the water level becomes equal to or less than a low water level L set by the valve control part 81 is determined by the above part 81. When the valve control part 81 determines that it becomes the low water level L or less, a closing signal is sent to the drain valve 80 and thereby the valve 80 is closed. By setting the low water level L, the exhaust gas becomes hard to get mixed inside a drain pipe 70.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a moisture treatment system for exhaust gas, and in particular to a moisture treatment system for exhaust gas that can prevent the exhaust gas from leaking to the outside while preventing the backflow of water that has become liquid during the removal process, even when there is no space to install piping with a water sealing function when removing moisture contained in the exhaust gas. [Background technology]

[0002] In the manufacturing processes of semiconductor devices, liquid crystal panels, and solar cells, processes such as CVD (Chemical Vapor Deposition), which uses chemical vapor reactions to form films, and etching are performed, and various gases are used in the process chambers.

[0003] Examples of such gases include silane (SiH4), NH3, and H2, which are used as film-forming material gases for semiconductor elements, liquid crystal panels, and solar cells, as well as gaseous fluorides such as NF3, CF4, C2F6, SF6, CHF3, and CF6, which are used as cleaning gases when using plasma to clean the inside of a sealed chamber such as a plasma CVD device, and inert gases such as nitrogen (N2).H2 gas reacts with oxygen to become water vapor, which is contained in the exhaust gas. In addition to the above-mentioned semiconductor-related manufacturing processes, water vapor is also contained in exhaust gases from, for example, food manufacturing equipment for ham and the like and vacuum drying equipment.

[0004] 10, a turbomolecular pump 3 and a dry pump 5 are connected in series to the process chamber 1 to evacuate the chamber and remove the harmful exhaust gases and water vapor. The dry pump 5 evacuates the chamber to a certain degree at the start of operation, and then the turbomolecular pump 3 evacuates the chamber to the required low pressure. However, in the case of CVD processing and the like, the turbomolecular pump 3 is generally omitted from the configuration.

[0005] The harmful exhaust gas output from the dry pump 5 is combusted and decomposed in the combustion type detoxification device 10. At this time, the exhaust gas is guided into the combustion type detoxification device 10 while being slightly decompressed by the central scrubber 11. However, the combustion type abatement device 10 may not be installed depending on the gas used in the process chamber 1.

[0006] The exhaust gas that has passed through the dry pump 5 is usually at a high temperature of around 150°C due to the heat of compression during exhaust. On the other hand, the outlet pipe connected to this dry pump 5 is exposed to the outside air. For this reason, the exhaust gas is rapidly cooled to room temperature as it passes through this outlet pipe, and the moisture (water vapor) in the exhaust gas condenses into droplets inside the outlet pipe.

[0007] This outlet piping may be connected to the exhaust piping of other processing equipment within the factory, and water droplets generated in the outlet piping may cause products to be generated or adhere to unexpected locations. In order to prevent this water droplets, a cooling trap as shown in Patent Document 1 is provided on the outlet pipe of the dry pump 5. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-16215 Summary of the Invention [Problem to be solved by the invention]

[0009] Incidentally, the moisture captured by the cooling trap must be drained while taking care not to leak the exhaust gas to the outside. For this reason, conventionally, an S-shaped bent pipe 51 as shown in Figure 11 was installed below the cooling trap, and the liquefied moisture (water droplets) often fell naturally. In this case, if the bent pipe 51 is filled with water, the water will stop the exhaust gas and prevent it from leaking to the outside. Therefore, in this case, the bent pipe 51 can function as a water seal.

[0010] However, since the pressure inside the piping is reduced, an installation space with a height equal to or greater than a predetermined value, including the reduced pressure and the height between the bent portions of the piping, is required when installing the bent pipe 51. Furthermore, due to this reduced pressure, there is a risk that water will not fall naturally when the bent pipe 51 is installed.

[0011] The present invention has been made in consideration of such conventional problems, and aims to provide a system for treating moisture in exhaust gas that can prevent the backflow of water that has become liquid during the removal process and prevent the exhaust gas from leaking to the outside, even when there is no space to install piping with a water sealing function when removing moisture and other substances contained in the exhaust gas. [Means for solving the problem]

[0012] Therefore, the present invention (claim 1) provides a moisture treatment system for exhaust gas that uses a cooling trap to remove moisture contained in exhaust gas discharged from a process, the system comprising: a tank that stores the moisture that flows out of the cooling trap as liquid water; water level measuring means that measures the water level in the tank; a pipe connected to a drain outlet for discharging the water stored in the tank to the outside; a valve disposed in the pipe; and valve control means that opens the valve to start discharging the water when the water level in the tank measured by the water level measuring means exceeds a first water level, and starts closing the valve when the water level reaches a second water level set closer to the drain outlet than the first water level, wherein the first water level is a water level set to prevent backflow from the tank to the cooling trap, and the second water level is a water level set to seal the exhaust gas so that it is not discharged from the pipe to the outside during the draining, and the second water level is set at a position higher than the drain outlet, the piping includes a discharge amount adjustment mechanism that adjusts the amount of water discharged from the tank to the outside, The water passes through the valve during the period from when the valve control means starts to close the valve until the valve is completely closed, and the second water level is maintained at a level that is equal to or lower than the first water level even if there is a negative pressure downstream of the valve during the period from when the valve control means starts to close the valve until the valve is completely closed. The aforementioned The water is set to remain above the drain.

[0013] When the water level in the tank measured by the water level measuring means exceeds the first water level, the valve opens and drainage begins. This prevents backflow of water in the tank even when the pipe diameter is small. On the other hand, when the water level in the tank reaches the second water level, the valve closes and drainage stops. The reason for setting the second water level in this way is to prevent exhaust gas from entering the drain pipe and leaking out. In other words, the second water level is set for sealing the water. Therefore, this second water level must always be set higher than the drain outlet so that the opening of the drain outlet can be completely covered with water. The water level in the tank is always kept filled with water, and it will not fall below the second water level even when draining. In addition to storing water, the tank can also serve as a seal for the drain line. By providing a discharge volume adjustment mechanism, even if negative pressure is applied to the discharge side, the water level in the tank is always maintained at a certain level higher than the discharge outlet from the time the valve control means issues a command to close the valve until the valve is completely closed, thereby reliably maintaining a water seal in the drain line.

[0014] The present invention (claim 2) is characterized in that the cooling trap and the tank are connected by a piping that has no curves.

[0015] Because the tank can be used for water sealing, exhaust gas will not leak to the outside even if a straight pipe is installed between the cooling trap and the tank. Even if there is not enough installation space between the cooling trap and the tank to connect a curved pipe, a straight pipe can be used. Therefore, it is low cost because there is no need to install expensive curved pipes, and water will fall naturally easily even if the pressure inside the straight pipe is reduced. [Effects of the Invention]

[0019] As described above, according to the present invention, when the water level in the tank measured by the water level measuring means exceeds a first water level, the valve is opened to start draining, and when the water level reaches a second water level, the valve is closed to stop draining. This prevents backflow while also preventing exhaust gas from entering the drain pipe and leaking to the outside. This allows the tank to not only store water but also seal the drain line. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a block diagram of a system for treating moisture in exhaust gas according to an embodiment of the present invention; [Figure 2] Straight pipe [Figure 3] Side view of cooling trap [Figure 4] Front cross-sectional view of the cooling trap [Figure 5] Cross section taken along the arrow AA in Figure 4 [Figure 6] A diagram showing how exhaust gas gets mixed inside a drainage pipe and leaks out [Figure 7] An example of a drainage volume adjustment mechanism installed in a drain pipe [Figure 8]An example of a displacement adjustment mechanism configured with an orifice (side cross section) [Figure 9] Perspective view of the orifice plate [Figure 10] Exhaust gas treatment flow diagram [Figure 11] Bent piping DETAILED DESCRIPTION OF THE INVENTION

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described. A configuration diagram of a system for treating moisture in exhaust gas according to an embodiment of the present invention is shown in FIG. In Figure 1, a cooling trap 20 is installed in the outlet pipe 7 connected to the dry pump 5. This cooling trap 20 is a device that condenses water vapor in the exhaust gas to turn it into water. The water that flows out of the cooling trap 20 falls naturally through a straight pipe 50 as shown in Figure 2 and accumulates in a tank 60. Conventionally, a bent pipe 51 has been installed between the cooling trap 20 and the tank 60 instead of the straight pipe 50.

[0022] A water level sensor 61 is also provided inside the tank 60. Water collected in the tank 60 is drained by gravity through a drain pipe 70 connected to a drain outlet 63 provided on the bottom of the tank 60 into drainage equipment (not shown) provided in the factory. A drain valve 80 is provided midway along the drain pipe 70. The water level signal measured by the water level sensor 61 is input to a valve control unit 81, and the drain valve 80 is controlled based on the result determined by this valve control unit 81.

[0023] A side view of the cooling trap 20 is shown in Fig. 3, and a front cross-sectional view is shown in Fig. 4. Also, a cross-sectional view taken along the line AA in Fig. 4 is shown in Fig. 5. The cooling trap 20 has a cylindrical peripheral wall 21, and the outlet pipe 7 is connected to an inlet port 23 protruding from the peripheral wall 21. On the other hand, a discharge port 25 protruding from the peripheral wall 21 is connected to a pipe 9 leading to the factory exhaust facility.

[0024] A disk-shaped lid 27 is attached to the upper surface of the peripheral wall 21. Meanwhile, the bottom surface 29 of the peripheral wall 21 is formed in a spherical shape, so that water droplets that fall on the bottom surface are naturally collected in the center. A thin tube 33 having a water supply port 31 at one end penetrates the disk-shaped lid 27. Cooling water is supplied to the water supply port 31 from a water supply facility (not shown). As shown in Figures 4 and 5, the thin tube 33 descends vertically, then bends near the inlet port 23, changes direction by 180 degrees, and ascends. Thereafter, it again changes direction by 180 degrees near the outlet port 25 and descends. After repeating this downward and upward movement multiple times, the thin tube 33 again penetrates the disk-shaped lid 27. A water discharge port 35 is formed at the other end of the thin tube 33.

[0025] Baffles 37 and 39 are combined at regular intervals on the inside of the peripheral wall 21 so that their protruding directions change alternately, and are attached at an angle to the thin tube 33. A water outlet 41 is provided in the center of the bottom surface 29 and is connected to a straight tube 50.

[0026] Next, the operation of the embodiment of the present invention will be described. The high-temperature exhaust gas that has passed through the dry pump 5 enters the inlet port 23 of the cooling trap 20, and while its flow is obstructed by the baffles 37 and 39, it slowly rises, changing direction from side to side as shown by the dotted lines in the figure. At this time, the exhaust gas is cooled through the thin tube 33. As a result, water vapor condenses inside the cooling trap 20. The water droplets that condense in the cooling trap 20 accumulate on the bottom surface 29 of the cooling trap 20. The accumulated moisture (moisture here refers to the total amount of moisture removed, and is in the form of liquefied water) then falls naturally through the straight tube 50 into the tank 60.

[0027] Because the drain valve 80 is closed, this moisture is stored in the tank 60 in the form of liquid water. The valve control unit 81 then determines whether the level of the water stored in the tank 60 exceeds the high water level H set by the valve control unit 81. The high water level H corresponds to the first water level. When the valve control unit 81 determines that the water level has exceeded the high water level H, an open signal is sent to the drain valve 80, and the drain valve 80 opens.

[0028] This causes the water in the tank 60 to be drained. This high water level H is set so that the water accumulated in the tank 60 does not overflow and flow back into the dry pump 5. Backflow is likely to occur easily because the pipe diameters of the straight pipe 50 and the outlet pipe 7 are small. Therefore, this high water level H is set with a certain margin of error.

[0029] The water level drops as the water is drained, and the valve control unit 81 determines whether this water level has fallen below the low water level L set in the valve control unit 81. The low water level L corresponds to the second water level. When the valve control unit 81 determines that the water level has fallen below the low water level L, a close signal is sent to the drain valve 80, and the drain valve 80 is closed. After that, water is again stored in the tank 60.

[0030] The reason for setting the low water level L in this way is to prevent exhaust gas from entering the drain pipe 70 and leaking out, as shown in Figure 6. In other words, the low water level L is a water level set for sealing the water. Therefore, this low water level L must always be set at a position higher than the drain outlet 63 so that the opening of the drain outlet 63 can be completely covered with water. The water level in the tank is always in a state where water is stored, and it does not fall below the low water level L even when draining.

[0031] Because the tank 60 can be used for sealing the water, exhaust gas will not leak to the outside even if a straight pipe 50 is installed between the cooling trap 20 and the tank 60 instead of a bent pipe 51 as in the past. If the distance between the cooling trap 20 and the tank 60 is, for example, about 20 cm, and the distance from the bottom of the cooling trap 20 to the floor 83 is about 30 to 50 cm, it would normally be impossible to install a bent pipe 51 at this distance, but even in this case, a straight pipe 50 can be used between the cooling trap 20 and the tank 60.

[0032] Therefore, it is not a problem if there is not enough installation space for the bent pipe 51, and the cost can be reduced since there is no need to install the expensive bent pipe 51. Also, because it is a straight pipe 50, water falls freely even when the pressure inside is reduced. In this way, the tank 60 can serve not only as a water storage facility but also as a sealant for the drain line.

[0033] Furthermore, the valve control unit 81 issues an abnormal high water level alarm when the signal from the water level sensor 61 exceeds the high water level HH, which is the limit value for the water level height, and issues an abnormal low water level alarm when the signal falls below the low water level LL, which is the limit value for the low water level.

[0034] Next, the adjustment of the amount of water discharged will be described. As described above, when the valve control unit 81 determines that the water level in the tank 60 has fallen below the low water level L, a close signal is sent to the drain valve 80, and the drain valve 80 is closed. After that, water is again stored in the tank 60.

[0035] However, if the negative pressure on the drain side is large, there is a risk that the speed of the drain water flowing through the drain pipe 70 will be faster than in the case of natural fall. In such a case, there is a time lag between when the valve control unit 81 sends a close signal to the drain valve 80 and when the drain valve 80 is completely closed, and during this time lag, there is a possibility that a certain amount of drain water will flow through the drain pipe 70. In this case, it is also possible that the water level in the tank 60 will fall below the low water level LL. To avoid such a problem, the drain pipe 70 is provided with a drainage amount adjustment mechanism to limit the force of the water accumulated in the tank 60.

[0036] Next, the displacement adjusting mechanism will be described. In Fig. 7, a discharge amount adjustment mechanism 90 is provided downstream of the drain valve 80. However, the discharge amount adjustment mechanism 90 may also be provided upstream of the drain valve 80. Fig. 8 shows an example in which the discharge amount adjustment mechanism 90 is configured as an orifice. As shown in Fig. 8, this orifice has an orifice plate 93 sandwiched between flanges 91A and 91B and made of, for example, the same material as the drain pipe 70, polyvinyl chloride. Fig. 9 shows a perspective view of this orifice plate 93.

[0037] A through hole 95 is formed in the center of the orifice plate 93. A sealing groove 97A is carved circumferentially on the left side of the orifice plate 93 where the end face of the flange 91A meets the left side of the orifice plate 93, and an O-ring 99A is embedded in this sealing groove 97A. Furthermore, a sealing groove (not shown) is carved circumferentially on the end face of the flange 91B where the end face of the flange 91B meets the right side of the orifice plate 93, and an O-ring 99B is embedded in this sealing groove. Furthermore, the through hole 95 in the orifice plate 93 has a diameter of, for example, 5 mm, while the inner diameter of the drain pipe 70 is 20 mm. In the case of such an orifice configuration, the installation work can be easily carried out even when the orifice is retrofitted after the facility is completed.

[0038] However, the discharge amount adjustment mechanism 90 may be configured to narrow the diameter of the drain pipe 70 in consideration of the degree of negative pressure. In this case, the diameter of the drain pipe 70 may be narrowed so that the water level in the tank 60 does not reach the low water level LL between the time the low water level L is detected and the time the drain valve 80 is completely closed. A certain amount of leeway may be provided in the pipe diameter. Even when the diameter of the drain pipe 70 is narrowed in this way, the piping can be easily replaced even after the installation is completed.

[0039] Alternatively, a separate valve may be provided as the drainage amount adjustment mechanism 90, and the drainage amount may be adjusted by the valve control unit 81. However, without providing a separate valve, the valve control unit 81 may adjust the drainage amount by throttling the drainage valve 80 when the low water level L is detected in the tank 60. As a result of the above, even if the negative pressure on the drain side is large, after the water level in the tank 60 falls below the low water level L and the valve control unit 81 sends a closure signal to the drain valve 80, there is no risk of the water level falling below the low water level LL during the time lag until the drain valve 80 is completely closed in response to this closure signal. Therefore, the water level in the tank is always maintained at a level higher than the drain outlet by a certain value, and the water seal of the drain line is reliably maintained.

[0040] In this embodiment, the water vapor is assumed to turn into water droplets in the cooling trap 20, but this embodiment is not limited to water vapor and can be similarly applied to exhaust gases containing alcohol, resist liquid, etc. Furthermore, the present invention can be modified in various ways without departing from the spirit of the present invention, and it goes without saying that the present invention also covers such modifications. [Explanation of symbols]

[0041] 5 Dry Pump 20 Cooling trap 23 Inlet port 25 Discharge port 31 Water supply outlet 33 tubules 35 Water outlet 37, 39 Baffles 50 Straight pipe 60 Tank 61 Water level sensor 63 Drain 70 Drain pipe 80 Drain valve 81 Valve control section 90 Drainage adjustment mechanism 93 Orifice Plate

Claims

1. In a moisture treatment system for exhaust gas that uses a cold trap to remove moisture contained in exhaust gas discharged from a process, a tank for storing the water flowing out of the cooling trap as liquid water; a water level measuring means for measuring the water level in the tank; a pipe connected to a drain outlet for discharging the water stored in the tank to the outside; a valve disposed in the piping; a valve control means for opening the valve to start draining water when the water level in the tank measured by the water level measuring means exceeds a first water level, and for starting to close the valve when the water level reaches a second water level set closer to the drain outlet than the first water level, the first water level is a water level set to prevent backflow from the tank to the cooling trap, the second water level is a water level set to seal the exhaust gas so that it is not discharged to the outside from the piping during the drainage; The second water level is set at a position higher than the drain outlet, a second water level set so that the water remains above the drain outlet even if there is negative pressure downstream of the valve, from the time the valve control means starts to close the valve until the valve is completely closed; and a second water level set so that the water remains above the drain outlet even if there is negative pressure downstream of the valve, from the time the valve control means starts to close the valve until the valve is completely closed.

2. 2. The system for treating moisture contained in exhaust gas according to claim 1, wherein the cooling trap and the tank are connected by a piping that has no curves.

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