Patent Description:
In process steps of manufacturing a semiconductor element, a liquid crystal panel, or a solar cell, a CVD (Chemical Vapor Deposition) process of depositing a film by using a chemical vapor reaction, an etching process, and the like are performed and, in a process chamber, various types of gases are used.

Examples of these gases include silane (SiH<NUM>), NH<NUM>, and H<NUM> which are film deposition material gases for the semiconductor element, the liquid crystal panel, and the solar cell, a gaseous fluoride such as NF<NUM>, CF<NUM>, C<NUM>F<NUM>, SF<NUM>, CHF<NUM>, or CF<NUM> to be used as a cleaning gas when a hermetically sealed chamber of a plasma CVD device or the like is to be internally cleaned with, e.g., a plasma, an inert gas such as nitrogen (N<NUM>), and the like. The H<NUM> gas reacts with oxygen to provide water vapor, which is also contained in exhaust gas.

In exhaust gases other than those from the semiconductor-related manufacturing process steps mentioned above, e.g., exhaust gas from a food manufacturing device for ham or the like or from a vacuum drying device also, water vapor is contained.

As illustrated in <FIG>, to a process chamber <NUM>, a turbo molecular pump <NUM> and a dry pump <NUM> are connected in series for evacuation so as to remove such toxic exhaust gas and water vapor. The process chamber <NUM> is configured such that, after evacuation is performed using the dry pump <NUM> to a degree when an operation is started, evacuation is further performed using the turbo molecular pump <NUM> until a required low pressure is reached. However, in a case of the CVD process or the like, it is a typical case that the turbo molecular pump <NUM> is omitted from a configuration of the process chamber.

The toxic exhaust gas output from the dry pump <NUM> is to be combusted/decomposed in a combustion-type detoxification device <NUM>. At this time, the exhaust gas is led into the combustion-type detoxification device <NUM>, while being decompressed to an extent by a central scrubber.

However, the combustion-type detoxification device <NUM> may not be disposed depending on a gas to be used in the process chamber <NUM>.

The exhaust gas that has passed through the dry pump <NUM> is usually at such a high temperature as <NUM> degrees due to compression heat during exhaust. Meanwhile, an outlet pipe connected to the dry pump <NUM> is in contact with outside air. Consequently, when passing through the outlet pipe, the exhaust gas is rapidly cooled at ambient temperature, and moisture (water vapor) in the exhaust gas condenses inside the outlet pipe to result in water droplets.

The outlet pipe may be communicating with an exhaust pipe for another treatment equipment in a factory and, due to the water droplets generated in the outlet pipe, a product may be generated at an unexpected place to adhere thereto. To prevent such water droplets, in the outlet pipe of the dry pump <NUM>, a cooling trap as described in <CIT> is disposed.

It is necessary to drain the moisture trapped by the cooling trap with attention to prevent the exhaust gas from leaking to the outside. Accordingly, an S-shaped bent pipe <NUM> as illustrated in <FIG> is conventionally disposed below the cooling trap in most cases, and the liquefied moisture (water droplets) is allowed to naturally fall. In this case, as long as the bent pipe <NUM> is internally filled with water, the exhaust gas is stopped by the water from leaking to the outside. Thus, in this case, a water sealing function can be performed by the bent pipe <NUM>.

However, it may be possible that the pipe is internally decompressed and, when the bent pipe <NUM> is to be installed, an installation space having a height of not less than a predetermined value including an allowance for the decompression and heights of spaces between bent portions of the pipe is required. In addition, when the bent pipe <NUM> is installed, due to the decompression, the water may be less likely to naturally fall. Another system is shown in <CIT>.

The present invention has been achieved in view of such conventional problems, and an object of the present invention is to provide a system for treating moisture in exhaust gas that can prevent, even in a case where there is not a space for disposing a pipe having a water sealing function, the exhaust gas from leaking to outside when the moisture or the like contained in the exhaust gas is removed, while preventing backflow of water resulting from liquefaction of the moisture in the removal process.

Accordingly, an aspect of the present invention (claim <NUM>) is a system for treating moisture in exhaust gas, the system using a cooling trap to remove the moisture contained in the exhaust gas discharged by a process and including: a tank that stores, as liquid water, the moisture flown out of the cooling trap; a water level measurement means that measures a water level in the tank; a pipe connected to a drainage port for draining the water stored in the tank to outside; a valve disposed in the pipe; and a valve control means that opens the valve to start drainage when the water level in the tank measured by the water level measurement means exceeds a first water level and closes the valve to stop the drainage when a second water level set lower than the first water level is reached, the second water level being provided at a position higher than the drainage port. A warning is further issued when a third water level set lower than the second water level is reached.

When the water level in the tank measured by the water level measurement means exceeds the first water level, the valve is opened to start the drainage. Thus, it is possible to prevent backflow of the water in the tank even when the pipe has a small pipe diameter. Meanwhile, when the water level in the tank reaches the second water level, the valve is closed to stop the drainage.

Thus, the second water level is set so as to prevent the exhaust gas from entering the drain pipe and leaking to the outside. In other words, the second water level is a water level set to seal water. Accordingly, to allow water to completely cover the drainage port, the second water level is required to be provided at a position constantly higher than the drainage port. The tank is in a state where the water is constantly stored therein, and the water level in the tank is kept from becoming not higher than the second level even during the drainage.

The tank can also function to seal water in a drainage line in addition to functioning to store water.

In the system according to the aspect of the present invention (claim <NUM>), the cooling trap and the tank are connected to each other by an unbent pipe.

Since the tank is used to allow water to be sealed, even when the unbent pipe is disposed between the cooling trap and the tank, there is no leakage of the exhaust gas to the outside. Even when there is not an installation space sufficient to allow a bent pipe to be connected between the cooling trap and the tank, the unbent pipe can be used instead. This eliminates need to provide a high-cost bent pipe, and cost is accordingly lower. Even when the unbent pipe is internally decompressed, the water naturally falls with ease.

In the system according to the present invention, the pipe includes a drainage amount adjustment mechanism that adjusts, of the water stored in the tank, an amount of the water to be drained to the outside.

Since the drainage amount adjustment mechanism is included, even if a negative pressure is placed on a drain side, during a period from a time when an instruction to close the valve was given by the valve control means until the valve is completely closed, the water level in the tank is maintained at a position constantly higher than the drainage port by a given value or more. Therefore, the sealing of water in the drainage line is reliably maintained.

The first water level may be a water level set to prevent backflow from the tank toward the cooling trap, and the second water level is a water level set to seal water such that, during the drainage, the exhaust gas is not discharged from the pipe to the outside.

As described above, according to the present invention, the system is configured such that, when the water level in the tank measured by the water level measurement means exceeds the first water level, the valve is opened to start the drainage and, when the second water level is reached, the valve is closed to stop the drainage. Therefore, it is possible to prevent the exhaust gas from entering the drain pipe and leaking to the outside, while preventing the backflow.

Consequently, the tank can also function to seal water in the drainage line in addition to functioning to store water.

A description will be given below of an embodiment of the present invention. <FIG> illustrates a configuration diagram of a system for treating moisture in exhaust gas as the embodiment of the present invention.

In <FIG>, an outlet pipe <NUM> connected to a dry pump <NUM> is provided with a cooling trap <NUM>. The cooling trap <NUM> is a device that condensates water vapor in the exhaust gas into water. The water flown out of the cooling trap <NUM> passes through a straight pipe <NUM> as illustrated in <FIG> and naturally falls to be stored in a tank <NUM>. Conventionally, between the cooling trap <NUM> and the tank <NUM>, not the straight pipe <NUM>, but a bent pipe <NUM> has been disposed.

In the tank <NUM>, a water level sensor <NUM> is disposed. The water stored in the tank <NUM> is to be drained by natural fall into drainage equipment disposed in a factory and not shown through a drain pipe <NUM> connected to a drainage port <NUM> disposed in a bottom surface of the tank <NUM>. Halfway in the drain pipe <NUM>, a drain valve <NUM> is disposed.

A water level signal resulting from measurement by the water level sensor <NUM> is input to a valve control unit <NUM> and, on the basis of a result of determination made by the valve control unit <NUM>, the drain valve <NUM> is controlled.

<FIG> illustrates a side profile view of the cooling trap <NUM>. <FIG> illustrates a front cross-sectional view of the cooling trap <NUM>. <FIG> illustrates a cross-sectional view taken along an arrow line A-A in <FIG>.

The cooling trap <NUM> includes a cylindrical peripheral wall <NUM>. The outlet pipe <NUM> is connected to a flow-in port <NUM> protruding from the peripheral wall <NUM>. Meanwhile, a discharge port <NUM> protruding from the peripheral wall <NUM> is connected to a pipe <NUM> extending to factory exhaust equipment.

To an upper surface of the peripheral wall <NUM>, a disk-shaped lid <NUM> is attached. Meanwhile, a bottom surface <NUM> of the peripheral wall <NUM> is formed in a spherical shape such that water droplets that have fallen to the bottom surface are collected by natural fall to a center thereof. Through the disk-shaped lid <NUM>, a thin pipe <NUM> having one end portion provided with a water supply port <NUM> extends. To the water supply port <NUM>, cooling water is supplied from water supply equipment not shown. As illustrated in <FIG> and <FIG>, after extending downward in a vertical direction, the thin pipe <NUM> is bent in the vicinity of the flow-in port <NUM> by making a <NUM>-degree directional change to extend upward. Then, the thin pipe <NUM> makes a <NUM>-degree directional change again in the vicinity of the discharge port <NUM> to extend downward. After repeatedly extending downward and upward a plurality of times, the thin pipe <NUM> extends again through the disk-shaped lid <NUM>. The thin pipe <NUM> has another end portion formed with a water discharge port <NUM>.

On an inner side of the peripheral wall <NUM>, baffles <NUM> and baffles <NUM> are alternately combined at regular intervals so as to protrude in different directions and attached obliquely to the thin pipe <NUM>. At the center of the bottom surface <NUM>, a water discharge port <NUM> is disposed to be connected to the straight pipe <NUM>.

Next, an operation of the embodiment of the present invention will be described.

The high-temperature exhaust gas that has passed through the dry pump <NUM> enters the cooling trap <NUM> from the flow-in port <NUM> thereof to slowly flow upward, while having the flow thereof interrupted by the baffles <NUM> and the baffles <NUM> and changing a direction of the flow leftward and rightward, as indicated by the dotted line in the drawing. At this time, the exhaust gas is cooled through the thin pipe <NUM>. As a result, the water vapor condensates within the cooling trap <NUM>. Then, the water droplets resulting from the condensation in the cooling trap <NUM> collect at the bottom surface <NUM> of the cooling trap <NUM>. Then, the moisture (the moisture means a total amount of the removed moisture herein, and results in a state of liquefied water) collected herein naturally falls into the tank <NUM> through the straight pipe <NUM>.

Since the drain valve <NUM> is closed, the moisture is stored in a state of liquid water in the tank <NUM>. Then, whether or not a water level of the water stored in the tank <NUM> exceeds a higher water level H set by the valve control unit <NUM> is determined by the valve control unit <NUM>. The higher water level H is equivalent to a first water level. Upon determining that the higher water level H is exceeded, the valve control unit <NUM> transmits an open signal to the drain valve <NUM> to open the drain valve <NUM>.

As a result, the water in the tank <NUM> is drained. The higher water level H is a water level set so as to prevent the water stored in the tank <NUM> from overflowing and flowing backward toward the dry pump <NUM>. Since the straight pipe <NUM> and the outlet pipe <NUM> have small pipe diameters, backflow is easy to occur. Accordingly, the higher water level H is set with a predetermined margin.

With the drainage, the water level gradually lowers, and whether or not the water level is not higher than a lower water level L set by the valve control unit <NUM> is determined by the valve control unit <NUM>. The lower water level L is equivalent to a second water level. Then, upon determining that the water level is not higher than the lower water level L, the valve control unit <NUM> transmits a close signal to the drain valve <NUM> to close the drain valve <NUM>.

Then, water is stored again in the tank <NUM>.

Thus, the lower water level L is set so as to prevent the exhaust gas from entering the drain pipe <NUM> and leaking to outside, as illustrated in <FIG>. In other words, the lower water level L is a water level set to seal water. Accordingly, to allow water to completely seal the drainage port <NUM>, the lower water level L is required to be provided at a position constantly higher than the drainage port <NUM>. The tank is in a state where water is constantly stored therein, and the water level in the tank is kept from becoming not higher than the lower water level L even during the drainage.

Since the tank <NUM> is used to allow water to be sealed, even when the straight pipe <NUM> is disposed between the cooling trap <NUM> and the tank <NUM> instead of the bent pipe <NUM> disposed conventionally, there is no leakage of the exhaust gas to the outside. If it is assumed that a distance between the cooling trap <NUM> and the tank <NUM> is, e.g., about <NUM> and a distance between the bottom surface of the cooling trap <NUM> and a floor <NUM> is about <NUM> to <NUM>, even in this case, the straight pipe <NUM> can be used between the cooling trap <NUM> and the tank <NUM>, though the bent pipe <NUM> cannot usually be disposed with these distances.

Therefore, even when there is not an installation space sufficient to allow the bent pipe <NUM> to be disposed, no problem occurs. In addition, since there is no need to provide the high-cost bent pipe <NUM>, the system can accordingly be configured at lower cost. Moreover, since the straight pipe <NUM> is disposed, even when the straight pipe <NUM> is internally decompressed, water naturally falls with ease. Thus, the tank <NUM> can also perform a function of sealing water in the drainage line in addition to a function of storing water in the tank <NUM>.

Additionally, when a signal from the water level sensor <NUM> represents that a highest water level HH corresponding to a highest limit value of the water level is exceeded, the valve control unit <NUM> issues warning of an abnormally high water level. Meanwhile, when the water level becomes not higher than a lowest water level LL corresponding to a lowest limit value of the water level, the valve control unit <NUM> issues warning of an abnormally low water level.

Next, a description will be given of adjustment of an amount of drainage.

As described previously, upon determining that the water level in the tank <NUM> is not higher than the lower water level L, the valve control unit <NUM> transmits the close signal to the drain valve <NUM> to close the drain valve <NUM>.

However, if a magnitude of a drain-side negative pressure is large, a speed of the drainage of water flowing in the drain pipe <NUM> may be higher than that in a case of natural fall. In such a case, there is a time lag between the transmission of the close signal from the valve control unit <NUM> to the drain valve <NUM> and complete closing of the drain valve <NUM>. As a result, a given amount of water may possibly flow through the drain pipe <NUM> to be drained during the time lag. In addition, at this time, the water level in the tank <NUM> may conceivably be not higher than the lowest water level LL.

To avoid such a drawback, in the drain pipe <NUM>, a drainage amount adjustment mechanism is provided to limit a force of the water stored in the tank <NUM>.

Next, a description will be given of the drainage amount adjustment mechanism.

In <FIG>, a drainage amount adjustment mechanism <NUM> is provided downstream of the drain valve <NUM>. However, the drainage amount adjustment mechanism <NUM> may also be provided upstream of the drain valve <NUM>. <FIG> illustrates an example in which the drainage amount adjustment mechanism <NUM> is configured of an orifice. As illustrated in <FIG>, in this orifice, between a flange 91A and a flange 91B, an orifice plate <NUM> formed of, e.g., polyvinyl chloride as the same material as that forming the drain pipe <NUM> is interposed. <FIG> illustrates a perspective view of the orifice plate <NUM>.

At a center of the orifice plate <NUM>, a through hole <NUM> is formed to extend therethrough. In addition, in a portion in which an end surface of the flange 91A and a left surface of the orifice plate <NUM> are in contact, a sealing groove 97A is circularly engraved in the left surface of the orifice plate <NUM> and, in the sealing groove 97A, an O-ring 99A is embedded. Meanwhile, in a portion in which an end surface of the flange 91B and a right surface of the orifice plate <NUM> are in contact, a sealing groove not shown is circularly engraved in the end surface of the flange 91B and, in the sealing groove, an O-ring 99B is embedded. The through hole <NUM> of the orifice plate <NUM> has a diameter of, e.g., <NUM>, while the drain pipe <NUM> has a pipe inner diameter of <NUM>.

Thus, when the drainage amount adjustment mechanism <NUM> is configured of the orifice, even when the orifice is attached after completion of equipment, an attaching operation can easily be performed.

However, the drainage amount adjustment mechanism <NUM> may also have a structure in which the drain pipe <NUM> has a reduced pipe diameter in consideration of the magnitude of the negative pressure. In this case, the pipe diameter of the drain pipe <NUM> may be reduced appropriately so as to prevent the water level in the tank <NUM> from reaching the lowest water level LL during a period from the detection of the lower water level L as the water level in the tank <NUM> until the complete closing of the drain valve <NUM>. It may also be possible to allow the pipe diameter to include a given allowance. When the pipe diameter of the drain pipe <NUM> is thus reduced also, even after the completion of the equipment, a pipe replacement operation is easy.

Alternatively, it may also be possible to separately dispose a valve as the drainage amount adjustment mechanism <NUM> and adjust an amount of drainage by using the valve control unit <NUM>. It is however at least required to adjust the amount of drainage in such a manner that, from a time when the lower water level L is detected as the water level in the tank <NUM>, the valve control unit <NUM> tightens the drain valve <NUM> without separately disposing a valve.

Thus, even when the magnitude of the drain-side negative pressure is large, there is no possibility that, after the water level in the tank <NUM> becomes not higher than the lower water level L and the close signal is transmitted from the valve control unit <NUM> to the drain valve <NUM>, the water level in the tank <NUM> becomes not higher than the lowest water level LL during the time lag until the drain valve <NUM> is completely closed in response to the close signal.

As a result, the water level in the tank is maintained at a position constantly higher than the drainage port by a given value or more, and the sealing of water in the drainage line is reliably maintained.

Claim 1:
A system for treating moisture in exhaust gas, the system using a cooling trap (<NUM>) to remove the moisture contained in the exhaust gas discharged by a process and comprising:
a tank (<NUM>) that stores, as liquid water, the moisture flown out of the cooling trap (<NUM>);
a water level measurement means (<NUM>) that measures a water level in the tank (<NUM>);
a pipe (<NUM>) connected to a drainage port (<NUM>) for draining the water stored in the tank (<NUM>) to outside;
a valve (<NUM>) disposed in the pipe (<NUM>); and
a valve control means (<NUM>) that opens the valve (<NUM>) to start drainage when the water level in the tank (<NUM>) measured by the water level measurement means (<NUM>) exceeds a first water level (H) and begins closing the valve (<NUM>) when a second water level (L) set lower than the first water level (H) is reached,
the second water level (L) being provided at a position higher than the drainage port (<NUM>), and
issues a warning when a third water level (LL) set lower than the second water level (L) is reached, characterized in that
the pipe (<NUM>) includes a drainage amount adjustment mechanism that adjusts, of the water stored in the tank (<NUM>), an amount of water to be drained to the outside, such that, during a period of time between when the valve control means (<NUM>) begins closing the valve (<NUM>) and the valve (<NUM>) being completely closed, the water level in the tank (<NUM>) remains above the drainage port (<NUM>).