Patent Publication Number: US-6698469-B2

Title: Cylinder cabinet and method of purging remaining gas in the pipe thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for and a method of purging remaining gas in the pipe of a cylinder cabinet. 
     2. Description of the Related Art 
     A conventional cylinder cabinet will be described making use of FIG. 1 because it is the same as that according to a first embodiment of the present invention. 
     Conventionally, a method of purging gas remaining in a primary pipe  14  of a cylinder cabinet is mainly executed manually. That is, leaving-pipe-in-pressurized-state purge is repeated manually to pressurize the inside of the primary pipe  14  by inert gas  15  and to leave it in the pressurized state for 5 to 30 seconds and to evacuate the primary pipe  14  by a vacuum generator  11  for about 20 seconds. Further, when gas  22  in a cylinder  1  is exhausted on the delivery side  16 , it is replaced with a new cylinder filled with gas. At the time, the inside of the primary pipe  14  is pressurized by the inert gas  15  for at least 10 seconds and then evacuated for about 20 seconds once manually just before a filling pipe  2  is removed from the cylinder  1 . 
     This conventional method of purging remaining gas in the primary pipe  14  cannot sufficiently accomplish an intended end. That is, when the cylinder  1  is replaced, the inside of the pipe is corroded by the reaction of water in the atmosphere with the remaining gas. As a result, troubles are caused in parts such as respective air-operated valves and a pressure reducing valve. Further, actually, the filling pipe  2  is removed from the cylinder  1  in the state that gas is left and liberated in the primary pipe  14  for a long time because the cylinder  1  cannot be replaced just after the completion of purge of the remaining gas in the primary pipe  14 , thereby leakage of gas is caused. Furthermore, the vacuum generator  11  is operated at all times while the inside of the primary pipe  14  is pressurized in the leaving-pipe-in-pressurized-state purge and the just-before-replacement purge, which increases the consumption of the nitrogen gas  17  for start. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a cylinder cabinet capable of purging remaining gas in a primary pipe with high-efficiency and stopping a vacuum generator while the inside of the primary pipe is pressurized in leaving-pipe-in-pressurized-state purge and just-before-replacement purge and to provide a method of purging the remaining gas in the primary pipe. 
     According to the present invention, there is provided a cylinder cabinet comprising a cylinder containing gas and having a valve, a filling pipe, a primary pipe, a first air-operated valve, a pressure reducing valve, a secondary pipe, and a second air-operated valve through which the cylinder is connected to a supply side, a third air-operated valve through which inert gas flows into the primary pipe, and a vacuum generator to which the primary pipe is connected through a fourth air-operated valve and a pipe, wherein remaining gas in the primary pipe is purged by automatically repeating leaving-pipe-in-pressurized-state purge for pressurizing the inside of the primary pipe by the inert gas and leaving the pipe in the pressurized state for 2 to 10 minutes and evacuating the pipe for 20 seconds. 
     Further, according to the present invention, there is provided a method of purging remaining gas in a pipe in a cylinder cabinet comprising a cylinder cabinet containing gas and having a valve, a filling pipe, a primary pipe, a first air-operated valve, a pressure reducing valve, a secondary pipe, and a second air-operated valve through which the cylinder is connected to a supply side, a third air-operated valve through which inert gas flows into the primary pipe, and a vacuum generator to which the primary pipe is connected through a fourth air-operated valve and a pipe, the method comprising the step of purging remaining gas in the primary pipe by automatically executing leaving-pipe-in-pressurized-state purge for repeatedly pressurizing the inside of the primary pipe by the inert gas and leaving the pipe in the pressurized state for 2 to 10 minutes and evacuating the pipe for 20 seconds. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a cylinder cabinet according to a first embodiment of the present invention; 
     FIG. 2 is a flowchart for exhausting remaining gas and executing leaving-pipe-in-pressurized-state purge according to the first embodiment of the present invention; 
     FIG. 3 is a flowchart for executing just-before-replacement purge according to the first embodiment of the present invention; 
     FIG. 4 is a flowchart for exhausting remaining gas and executing leaving-pipe-in-pressurized-state purge according to a second embodiment of the present invention; and 
     FIG. 5 is a flowchart for executing just-before-replacement purge according to the second embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Two embodiments of the present invention will be described. 
     First, a first embodiment of the present invention will be described with reference to FIGS. 1 to  3 . 
     In FIG. 1, a cylinder  1  is connected to a filling pipe  2 . When a cylinder valve  23  is opened, gas  22  in the cylinder  1  is introduced into a primary pipe  14 . When an air-operated valve  6  is opened, the pressure of the gas  22  is reduced by a pressure reducing valve  7 , and an air-operated valve  10  is opened, the gas  22  is supplied to a delivery side  16  through a secondary pipe  19 . A pressure gauge  4  can detect the pressure in the primary pipe  14 , whereas a pressure gauge  8  can detect the pressure in the secondary pipe  19 . When an air-operated valve  3  is opened, inert gas  15  such as nitrogen gas is introduced into the primary pipe  14 . When an air-operated valve  12  is opened, nitrogen gas  17  flows into a vacuum generator  11  through a pipe  21 , thereby the inside of a pipe  20  can be evacuated. 
     When an air-operated valve  9  is opened in this state, the inside of the secondary pipe  19  can be evacuated. Further, when an air-operated valve  5  is opened, the inside of the primary pipe  14  can be evacuated. The quantity of flow of the nitrogen gas  17  flowing to the vacuum generator  11  is detected by a mass flow meter  13  in terms of weight. Exhaust gas  18  exhausted from the vacuum generator  11  contains the nitrogen gas  17  and gas  22 . 
     When the gas  22  in the cylinder  1  is exhausted by being consumed on the delivery side  16 , the cylinder  1  must be replaced with a new cylinder filled with the gas  22 . Unless the gas in the primary pipe  14  is removed when the cylinder  1  is replaced with the new cylinder, it leaks into the atmosphere because the filling pipe  2  is removed from the cylinder  1 . Operation for purging the gas  22  in the primary pipe  14  with high-efficiency will be described with reference to FIGS. 1 to  3 . 
     1. Exhaust of Remaining Gas (Step A1) 
     First, when the cylinder valve  23  is closed, the gas  22  in the cylinder  1  is not exhausted (step A3). At this time, the air-operated valves  3 ,  5 , and  6  are closed. When the air-operated valve  12  is opened and the vacuum generator  11  is started, and then the air-operated valve  5  is opened for about 20 seconds, the gas  22  remaining in the primary pipe  14  is exhausted (steps A4 and A5). Thereafter, the air-operated valve  5  is closed and further the air-operated valve  12  is closed, thereby the vacuum generator  11  is stopped (steps A6 and A7). Thereafter, leaving-pipe-in-pressurized-state purge will be executed (step A2). 
     The leaving-pipe-in-pressurized-state purge will be described below. 
     2. Leaving-pipe-in-pressurized-state Purge (Step A2) 
     When the air-operated valve  3  is opened for five seconds, the inert gas  15  such as nitrogen gas of at least 0.2 MPa pressurizes the inside of the primary pipe  14  closed by the air-operated valves  5  and  6  and the cylinder valve  23  (step A8). After the completion of pressurization, the air-operated valve  3  is closed, and the primary pipe  14  is left in the pressurized-state for 2 to 10 minutes (step A9). After the primary pipe  14  has been left for 2 to 10 minutes, the air-operated valve  12  is opened and the vacuum generator  11  is started, and then the air-operated valve  5  is opened, thereby the inert gas  15  such as nitrogen gas pressurized in the primary pipe  14  is exhausted, and then the primary pipe  14  is evacuated for 20 seconds (steps A10 and A11). 
     After the pressurized inert gas  15  such as nitrogen gas has been exhausted from the primary pipe  14  for about 20 seconds and the primary pipe  14  has been evacuated, the air-operated valves  5  and  12  are sequentially closed, thereby the vacuum generator  11  is stopped (steps A12 and A13). The series of operation is the leaving-pipe-in-pressurized-state purge executed at a time, and the leaving-pipe-in-pressurized state purge is executed 50 to 100 times (steps A14 and A15). It was confirmed in an experiment executed using hydrogen bromide gas as the gas  22  that the remaining concentration (ppm) of the hydrogen bromide gas in this embodiment was one-several to one-several tenth that of a conventional technology. Thereafter, just-before-replacement purge is executed (step B1). The just-before-replacement purge will be described below. 
     3. Just-before-replacement Purge (Step B1) 
     When the cylinder  1  is replaced with the new cylinder, the air-operated valve  3  is opened for five seconds, and the primary pipe  14 , which is closed by the air-operated valves  5  and  6  and the cylinder valve  23 , is filled with the inert gas  15  such as nitrogen gas of at least 0.2 MPa (step B2) to remove the filling pipe  2  from the cylinder  1 . After the completion of filling, the air-operated valve  3  is closed, and the primary pipe  14  is for at least to 10 seconds (step B3). After the primary pipe  14  has been left for at least 10 seconds, the vacuum generator  11  is started by opening the air-operated valve  12 , and then the air-operated valve  5  is opened, thereby the inert gas  15  such as nitrogen gas filled in the primary pipe  14  is exhausted and the primary pipe  14  is evacuated (steps B4 and B5). After the pressurized inert gas  15  such as nitrogen gas has been exhausted from the primary pipe  14  for about 20 seconds and the primary pipe  14  has been evacuated, the air-operated valves  5  and  12  are sequentially closed, thereby the vacuum generator  11  is stopped (steps B6 and B7). The series of operation is the just-before-replacement purge executed at a time, and the just-before-replacement purge is executed about 10 times (step B8 and B9). It was confirmed in the experiment executed using the hydrogen bromide gas as the gas  22  that the concentration (ppm) of the hydrogen bromide gas was 0.3 ppm while it was 2 ppm after the leaving-pipe-in-pressurized-state purge and 27 ppm in 30 minutes after the leaving-pipe-in-pressurized-state purge. 
     The respective operations described above for exhausting the remaining gas and executing the leaving-pipe-in-pressurized-state purge and the just-before-replacement purge are automatically carried out by sequence control. 
     Next, a second embodiment of the present invention will be described with reference to FIGS. 1,  4 , and  5 . The second embodiment will be described only as to points different from those of the first embodiment, omitting the description of the points similar to those of the first embodiment. 
     A first different point is as described below. That is, when the air-operated valve  12  is opened, the nitrogen gas  17  flows into the vacuum generator  11  to thereby start the vacuum generator  11 . However, the mass flow meter  13  confirms whether or not the quantity of flow in terms of weight of the nitrogen gas  17  permits the vacuum generator  11  to sufficiently exhibit a vacuum generating capability. The vacuum generator  11  can exhibit the vacuum generating capability with the quantity of flow of the nitrogen gas of about 40 l/min or more. Thus, steps are added to confirm whether or not the quality of flow of the nitrogen gas flowing through the second flow path connecting pipe  13  is 40 l/min or more (steps C1, C7, and D3). When the quantity of flow of the nitrogen gas is less than 40 l/min, the air-operated valve  12  is closed (steps C2, C8, and D4). 
     A second different point is as described below. That is, the air-operated valve  5  is opened and the primary pipe  14  is evacuated, the pressure gauge  4  confirms whether or not it is reliably evacuated. Steps are added to confirm, when evacuation is stared, whether or not the pressure gauge  4  indicates a value of 0 MPa or less (steps C3, C9, and D5). The addition of these steps permits the evacuation to be executed reliably. When the value indicated by the pressure gauge  4  is not equal to or less than 0 MPa, the air-operated valves  5  and  12  are closed (steps C4, C10, and D6). 
     A third different point is as described below. That is, when the inert gas  15  such as nitrogen gas is introduced into the primary pipe  14  by opening the air-operated valve  3 , the pressure gauge  4  confirms the pressure of the pressurized inert gas  15  such as nitrogen gas. When the pressure of the pressurized inert gas  15  such as nitrogen gas is less than 0.2 MPa, purge efficiency is reduced. Thus, steps are added to confirm that the pressure of the pressurized inert gas  15  is equal to or more than 0.2 MPa by the pressure gauge  4  (steps C5 and D1). When the pressure of the pressurized inert gas  15  such as nitrogen gas is less than 0.2 MPa, the air-operated valve  3  is closed (steps C6 and D2). 
     As apparent from the above description, the present invention accomplishes the following advantages. 
     1. Since the pipe can be purged with high-efficiency by executing the leaving-pipe-in-pressurized-state purge, the corrosion of the pipe in the cylinder cabinet can be prevented, and further the troubles of parts such as the air-operated valves and the pressure reducing valve can be reduced. A reason why the pipe can be purged with the high-efficiency is as described below. In general, the molecules in gas can be purged more promptly by vacuum purge. This is because lower pressure more increases the diffusing speed of the molecules, thereby the molecules can be diffused promptly and discharged. However, when the cylinder cabinet is used ordinarily, the molecules of gas are absorbed by the inside wall of the pipe because the gas is in contact with the pipe for a long time. The molecules of the gas having been absorbed by the inner wall of the pipe are not released unless physical energy is applied thereto. When the inside of the pipe is pressurized by nitrogen gas and left, nitrogen molecules collide against the molecules of the gas to be purged. As a result, the molecules of the gas absorbed by the inner wall of the pipe are discharged into a gas phase, thereby the inside of the pipe can be sufficiently purged. 
     2. Actually, the cylinder cannot be replaced just after the completion of leaving-pipe-in-pressurized-state purge. Thus, when the cylinder is left for a long time, the gas molecules absorbed by the inner wall of the pipe are released. The released gas molecules are discharged from the vacuum generator by executing the just-before-replacement purge, thereby the leakage of the gas caused when the cylinder is removed from the filling pipe when it is replaced can be prevented. 
     3. The amounts of inert gas used for purge and nitrogen gas used to start the vacuum generator can be reduced. This is because that the number of times of purge can be reduced due to the high-efficiency in purge and that the vacuum generator is stopped while the inside of the primary pipe is pressurized by the leaving-pipe-in-pressurized-state purge and the just-before-replacement purge.