System and method for supplying liquid raw material to vaporizer

Abstract

To provide a liquid raw material supply system and a liquid raw material supply method for a vaporizer that enable a liquid raw material filter to be replaced without stopping manufacturing a soot body while grasping how much the liquid raw material filter gets clogged in supply of liquid raw material to a soot body manufacturing vaporizer.SOLUTION: The present invention relates to a supply system for liquid raw material to a vaporizer used to manufacture a soot body, and the supply system for liquid raw material includes at least: first and second raw material supply mechanisms which each have a liquid raw material introduction line for introducing the liquid raw material into a vaporization tank of the vaporizer and a liquid raw material filter provided to the liquid raw material introduction line; liquid raw material introduction speed measuring equipment for monitoring the introduction speed of the liquid raw material into the vaporization tank of the vaporizer; and a valve mechanism which switches a liquid raw material supply mechanism that the liquid raw material flows through between the first and second liquid raw material supply mechanisms.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a liquid source supply system and a liquid source supply method for a vaporizer used to manufacture a SiO2 soot body. [Background technology]

[0002] Synthetic quartz glass, with its high purity and excellent chemical resistance, has been widely used as a material for semiconductor processing, optics, laboratory equipment, decoration, and other applications. The typical process for producing synthetic quartz glass is to produce a SiO2 soot body (also called a porous quartz glass base material) and then sinter it to make it transparent. The soot body is produced by vaporizing a silicon-containing liquid glass raw material and depositing fine SiO2 particles on a target through flame hydrolysis or pyrolysis.

[0003] As a vaporizer (also called a vaporizer) which is a raw material vaporization supply device used to vaporize the liquid glass raw material, there is a vaporizer 120 as described in Patent Document 1, for example.

[0004] If foreign matter gets into the vaporization tank of such a vaporizer, impurities may get mixed in when the liquid raw material is vaporized. For this reason, a liquid raw material filter is installed in the introduction line of the liquid raw material to the vaporizer to prevent impurities, foreign matter, crystals, etc. from getting into the liquid raw material. However, if the liquid raw material filter becomes clogged, the introduction rate of the liquid raw material into the vaporizer will decrease. In this specification, the term "line" refers to the piping through which liquids and gases pass.

[0005] Figure 9 shows a conventional liquid raw material supply system for a vaporizer. In Figure 9, reference numeral 100 denotes a conventional liquid raw material supply system for a vaporizer. Liquid raw material supply system 100 is a liquid raw material supply system for sending SiCl4, a liquid raw material, from SiCl4 inlet line 104 through liquid raw material inlet line 108, which has liquid raw material filter 106 installed midway, to vaporizer 110. Also provided is N2 inlet line 102, through which N2, a purge gas for purging liquid raw material inlet line 108, passes. Valves 112, 114, and 116 are provided on N2 inlet line 102, SiCl4 inlet line 104, and liquid raw material inlet line 108, respectively.

[0006] A vaporizer 110, which is a raw material vaporization supply device, is provided at the end of the liquid raw material supply system 100. The vaporizer 110 has a vaporization tank 118 for vaporizing a liquid raw material such as SiCl4 sent from a liquid raw material inlet line 108, and has a gas raw material inlet line 124 provided with a gas raw material filter 120 and a mass flow controller 122 midway.

[0007] A growth furnace 126 is provided beyond the vaporizer 110. The growth furnace 126 is provided with an oxyhydrogen burner 128, and soot deposition is carried out in the growth furnace 126 by supplying vaporized SiCl gas from a gas source introduction line 124 to a concentric tube in the oxyhydrogen burner 128, thereby producing a soot body.

[0008] When liquid raw material filter 106 is installed in the line that supplies the liquid raw material to the vaporization tank in vaporizer 110, impurities contained in the liquid raw material accumulate in liquid raw material filter 106 and gradually become clogged. Therefore, when clogging progresses, liquid raw material filter 106 needs to be replaced, but in the past, there was no way to detect clogging of liquid raw material filter 106, so liquid raw material filter 106 needed to be replaced well before clogging progressed, which increased the frequency of replacement. However, even so, when a large amount of impurities flow in from the upstream side, clogging progresses rapidly, and replacement may be required at an unexpected time, which can have a significant impact on soot body production activities.

[0009] Furthermore, it is necessary to thoroughly remove the liquid source and its residual gas from the piping of the introduction line when replacing the liquid source filter 106. SiCl4 generates HCl, a corrosive gas, when it comes into contact with air, which can cause problems in maintaining the equipment and can be harmful to humans. Therefore, sufficient purging with N2 is required, but purging for more than 120 hours is required to make the liquid raw material introduction line 108 and the liquid raw material filter 106 sufficiently safe, and after replacing the liquid raw material filter 106, purging for more than 48 hours is required to replace the air that has become mixed into the piping of the liquid raw material introduction line 108. Combining the purging and replacement work, replacing the liquid raw material filter 106 once results in a loss of more than 170 hours of soot production activity. Furthermore, because replacement is required frequently and each replacement takes a long time, the impact on production activity is significant.

[0010] The liquid raw material filter 106 installed in the piping of the liquid raw material introduction line 108 before the vaporization tank 118 is installed in the liquid raw material transport route to prevent impurities mixed in the liquid raw material from entering the vaporization tank 118.

[0011] Liquid SiCl4 is introduced into vaporization tank 118, vaporized, and then discharged. However, small amounts of solid impurities that are mixed in during manufacturing, transportation, storage, etc. gradually accumulate without vaporizing in vaporization tank 118, and so over long periods of use, the impurities in vaporization tank 118 become concentrated, resulting in a high impurity concentration. Furthermore, if a substance that is solid at room temperature but melts at the temperature inside the vaporization tank (70°C to 80°C) is mixed in, there is a concern that it could be mixed into the vaporized SiCl4 gas if there is even a slight vapor pressure. In high-purity synthetic quartz glass, where impurity concentration must be controlled at the ppb level, even a small amount of impurity mixed into the SiCl4 gas can pose significant quality problems for synthetic quartz glass products.

[0012] Furthermore, it is complicated and difficult to identify where impurities in liquid SiCl4 are mixed in, such as during production, transportation, or storage, and investigating the cause and taking measures is costly. Therefore, filtering the liquid before it enters the vaporization tank is practical and cost-effective.

[0013] For this reason, conventionally, an operator needs to grasp the degree of clogging of the liquid raw material filter and replace the liquid raw material filter at the appropriate timing while the liquid raw material can still be supplied to the vaporizer. However, the degree of clogging of the liquid raw material filter varies, making it difficult to predict when to replace the liquid raw material filter.

[0014] Furthermore, when replacing the liquid raw material filter, if the liquid raw material generates corrosive and harmful substances, thorough purging is required, and replacing the liquid raw material filter takes a long time before and after replacement, which poses the problem that soot body production operations on the line must be stopped during that time.

[0015] For example, Patent Document 2 discloses a method for shortening the replacement time of a gas filter in a flow path of raw material gas sent from a vaporizer that vaporizes glass raw material to a burner. However, Patent Document 2 merely relates to a technology related to a gas filter in a flow path of raw material gas sent from a vaporizer to a burner, and does not solve the problem of clogging of the liquid raw material filter. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] Special Publication No. 2015-502316 [Patent Document 2] Patent Publication No. 2021-8391 Summary of the Invention [Problem to be solved by the invention]

[0017] The present invention has been made in consideration of the problems of the conventional technology described above, and aims to provide a liquid raw material supply system and a liquid raw material supply method for a vaporizer that, when supplying liquid raw material to a vaporizer used to manufacture a soot body, which is a synthetic quartz glass base material, enables the liquid raw material filter to be replaced while keeping track of the degree of clogging of the liquid raw material filter and without stopping the manufacture of the soot body. [Means for solving the problem]

[0018] The liquid raw material supply system to a vaporizer of the present invention is a system for supplying a liquid raw material containing a silicon-containing compound to a vaporizer used to manufacture a soot body, which is a synthetic quartz glass base material, and includes at least: a first liquid raw material supply mechanism having a first liquid raw material introduction line for introducing the liquid raw material into the vaporization tank of the vaporizer and a first liquid raw material filter provided on the first liquid raw material introduction line; a second liquid raw material supply mechanism having a second liquid raw material introduction line for introducing the liquid raw material into the vaporization tank of the vaporizer and a second liquid raw material filter provided on the second liquid raw material introduction line; a liquid raw material introduction rate measuring device for monitoring the introduction rate of the liquid raw material into the vaporization tank of the vaporizer; and a valve mechanism for switching whether the liquid raw material flows through the first liquid raw material supply mechanism or the second liquid raw material supply mechanism.

[0019] It is preferable that each of the first liquid source supply mechanism and the second liquid source supply mechanism further includes a purge inert gas introduction line and a purge exhaust line for purging.

[0020] It is preferable that each of the first liquid source supply mechanism and the second liquid source supply mechanism further includes an inert gas inlet for leak detection for detecting whether there is a leak of the liquid source, and a vacuum pump connection port for replacing air in a liquid source introduction line.

[0021] The introduction rate of the liquid raw material is preferably γ expressed by the following formula (1). γ = (introduction mass rate of liquid raw material) ÷ ​​(exit mass rate of gas raw material from vaporizer) (1)

[0022] It is preferable that the γ is 4≦γ<20.

[0023] It is preferable that in addition to the first liquid source supply mechanism and the second liquid source supply mechanism, a further liquid source supply mechanism is included, and the valve mechanism is a valve mechanism that switches through which of the liquid source supply mechanisms the liquid source flows.

[0024] The method for supplying a liquid raw material to a vaporizer of the present invention is a method for supplying a liquid raw material to a vaporizer using a liquid raw material supply system for the vaporizer, and includes the steps of: introducing the liquid raw material into a vaporization tank of the vaporizer by either the first liquid raw material supply mechanism or the second liquid raw material supply mechanism; monitoring the introduction rate of the liquid raw material into the vaporization tank of the vaporizer; and switching, using a valve mechanism, through which liquid raw material flows, either the first liquid raw material supply mechanism or the second liquid raw material supply mechanism, depending on a decrease in the introduction rate of the liquid raw material.

[0025] It is preferable to include a step of replacing the liquid source filter of the liquid source supply mechanism from which the liquid source has stopped flowing after switching by the valve mechanism.

[0026] It is preferable that the method further includes a purging step of purging the liquid raw material introduction line of the liquid raw material supply mechanism through which the liquid raw material has stopped flowing, before or after the step of replacing the liquid raw material filter after switching by the valve mechanism.

[0027] It is preferable that the method further comprises, after the replacing step, a leak detection step of detecting whether there is a leak in the liquid source introduction line of the liquid source supply mechanism through which the liquid source has stopped flowing, and a substitution step of substituting air in the introduction line after the leak detection step.

[0028] The introduction rate of the liquid raw material is preferably γ expressed by the following formula 1. γ = (introduction mass rate of liquid raw material) ÷ ​​(exit mass rate of gas raw material from vaporizer) (1)

[0029] It is preferable that the γ is 4≦γ<20.

[0030] It is preferable that the system further includes a liquid source supply mechanism in addition to the first liquid source supply mechanism and the second liquid source supply mechanism, the valve mechanism is a valve mechanism that switches which of the liquid source supply mechanisms the liquid source flows through, and the step of switching using the valve mechanism includes a step of switching to one of the liquid source supply mechanisms using the valve mechanism.

[0031] The method for producing a soot body of the present invention is a method for producing a soot body that is a synthetic quartz glass base material using the liquid raw material supply system to the vaporizer.

[0032] The method for producing a soot body of the present invention is a method for producing a soot body that is a synthetic quartz glass base material using the method for supplying a liquid raw material to a vaporizer. [Effects of the Invention]

[0033] According to the present invention, it is possible to provide a significant effect of providing a liquid raw material supply system and a liquid raw material supply method for a vaporizer that, when supplying a liquid raw material to a vaporizer used to manufacture a soot body, which is a synthetic quartz glass base material, enables the liquid raw material filter to be replaced without stopping the manufacture of the soot body while keeping track of the degree of clogging of the liquid raw material filter. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a configuration diagram of a liquid source supply system to a vaporizer, a vaporizer, and a growth furnace according to the present invention. [Figure 2] 10 is a graph showing the change in the value of γ over time. [Figure 3] FIG. 10 is a schematic diagram showing switching to a first liquid raw material introduction line. [Figure 4] FIG. 4 is a schematic diagram showing the next step of FIG. 3. [Figure 5]FIG. 10 is a schematic diagram showing switching to a second liquid raw material introduction line. [Figure 6] FIG. 6 is a schematic diagram showing the next step of FIG. 5. [Figure 7] 10 is a flowchart showing a flow before filter replacement when switching the liquid raw material introduction line. [Figure 8] 10 is a flowchart showing the flow after filter replacement when switching the liquid raw material introduction line. [Figure 9] FIG. 1 is a configuration diagram of a conventional liquid source supply system to a vaporizer, a vaporizer, and a growth furnace. DETAILED DESCRIPTION OF THE INVENTION

[0035] The following describes embodiments of the present invention, but these embodiments are shown by way of example only, and it goes without saying that various modifications are possible without departing from the technical concept of the present invention.

[0036] A configuration diagram of a liquid raw material supply system to a vaporizer, a vaporizer, and a growth furnace according to the present invention is shown in Figure 1. A liquid raw material supply system 10 to a vaporizer according to the present invention is a system for supplying a liquid raw material containing a silicon-containing compound to a vaporizer used to produce a soot body, which is a synthetic silica glass base material.

[0037] In FIG. 1 , liquid raw material supply system 10 to a vaporizer includes at least: first liquid raw material supply mechanism 16 having first liquid raw material inlet line 12 and first liquid raw material filter 14 provided on first liquid raw material inlet line 12 for introducing the liquid raw material into vaporization tank 118 of vaporizer 110; second liquid raw material supply mechanism 22 having second liquid raw material inlet line 18 and second liquid raw material filter 20 provided on second liquid raw material inlet line 18 for introducing the liquid raw material into vaporization tank 118 of vaporizer 110; liquid raw material introduction rate measuring device 24 for monitoring the introduction rate of the liquid raw material into vaporization tank 118 of vaporizer 110; and valve mechanism 25 for switching whether the liquid raw material flows through first liquid raw material supply mechanism 16 or second liquid raw material supply mechanism 22. As the valve mechanism 25, an example in which valves 26a to 26f are provided is shown.

[0038] The liquid raw material can be any liquid raw material containing a known silicon-containing compound used in the production of synthetic quartz glass base materials, and is not particularly limited, but for example, SiCl4 is preferably used. Figure 1 shows an example of SiCl4 as the liquid raw material.

[0039] The first liquid source supply mechanism 16 and the second liquid source supply mechanism 22 each further include purge inert gas introduction lines 28, 30 and purge exhaust lines 52, 54 for purging. The purge exhaust lines 52, 54 refer to piping through which the purge inert gas is exhausted. While N2 is used as the purge inert gas, any known inert gas used for purging can be used, and N2, argon, and the like are preferably used. The purge exhaust lines 52, 54 are connected to the purge inert gas introduction lines 28, 30 for venting.

[0040] The first liquid source supply mechanism 16 and the second liquid source supply mechanism 22 each further include inert gas inlet ports 32 and 34 for leak detection to detect leaks of the liquid source and vacuum pump connection ports 36 and 38 for replacing air in the liquid source introduction lines. Reference numerals 48 and 50 denote vacuum pumps. As the inert gas for leak detection, any known inert gas that can be used to check for leaks in piping can be used, and for example, He shown in FIG. 1 is preferably used.

[0041] Furthermore, the first liquid source supply mechanism 16 and the second liquid source supply mechanism 22 are provided with drain lines 40 and 42 each having drains 41 and 43 for draining liquid.

[0042] Valves 44a to 44h and 46a to 46h are provided on the purge inert gas introduction lines 28 and 30 and the leak detection inert gas introduction ports 32 and 34 on each side of the first liquid source supply mechanism 16 and the second liquid source supply mechanism 22, as well as on the drain lines 40 and 42 and the purge exhaust lines 52 and 54, respectively.

[0043] As described above, in the present invention, two parallel series of liquid raw material supply mechanisms each equipped with a liquid raw material filter, an inlet for a purge inert gas (nitrogen in the illustrated example), an inlet for a leak detection inert gas (helium in the illustrated example), a vacuum pump, a drain, and various valves are installed on the line for introducing a liquid raw material containing a silicon-containing compound (SiCl4 in the illustrated example) into vaporization tank 118 of vaporization device 110, and the line passing through first liquid raw material filter 14 is designated first liquid raw material supply mechanism 16, and the line passing through second liquid raw material filter 20 is designated second liquid raw material supply mechanism 22.

[0044] Furthermore, a liquid raw material introduction rate measuring device 24 was installed upstream of the vaporization tank 118 to measure the introduction rate of the liquid raw material (FIG. 1). A liquid mass flow meter is optimal as the liquid raw material introduction rate measuring device 24, but an ultrasonic type or flow meter may also be used as long as it is a flow meter that can withstand corrosive materials such as SiCl4. In addition to the example shown in the figure, the liquid raw material introduction rate measuring device 24 may also be configured such that a load cell is installed below the vaporization tank 118 and the mass of the introduced liquid raw material and the elapsed time are measured to calculate the mass flow rate per unit time. In the example shown in the figure, a liquid mass flow meter is used as the liquid raw material introduction rate measuring device 24.

[0045] Metal filters made of stainless steel are suitable for the first liquid raw material filter 14 and the second liquid raw material filter 20. For example, it is preferable to use a material that can withstand corrosion such as SiCl4 as the filtering material. For example, a metal filter made of SUS316L, which is more corrosion-resistant and chemically resistant than ordinary stainless steel, can be used. Furthermore, a filter with a filtration accuracy of 0.5 μm or less, more preferably 0.3 μm or less, is suitable.

[0046] By installing the liquid raw material introduction rate measuring device 24, it is possible to grasp the degree of clogging of the first liquid raw material filter 14 and the second liquid raw material filter 20 over time, and to carry out replacement work according to the actual state of clogging.

[0047] The introduction rate of the liquid raw material is preferably γ expressed by the following formula (1). γ = (introduction mass rate of liquid raw material) ÷ ​​(exit mass rate of gas raw material from vaporizer) (1)

[0048] As described above, the γ value is defined as the value obtained by dividing the mass velocity of the liquid source introduced into the vaporization tank 118 by the mass velocity of the gas source discharged from the vaporization tank 118 .

[0049] When calculating the γ value, when valve 26d (FIG. 1) that introduces the liquid raw material into vaporization tank 118 is in the "open" position, the mass of the liquid raw material introduced per unit time is measured using a liquid mass flow meter, which is liquid raw material introduction rate measuring device 24, and the γ value can be obtained by dividing this value (introduction mass rate of the liquid raw material) by the mass of the gas raw material discharged per unit time from gas mass flow controller 122, which supplies the gas raw material to burner 128 as a raw material gas (discharge mass rate of the gas raw material from the vaporizer).

[0050] A γ value of 1 or greater is preferable. If the production of the soot body continues when the γ value is below 1, the liquid raw material in the vaporization tank 118 will run out, making it difficult to supply the vaporized raw material to the burner 128. A γ value of γ≧4 is more appropriate for stable production of the soot body, and γ<4 is suitable as a guideline for filter replacement.

[0051] Conversely, if γ ≥ 20, the liquid raw material will be introduced into the vaporization tank too quickly, causing a temporary drop in the temperature of the liquid raw material in the tank and making stable vaporization impossible. Therefore, it is preferable to control the γ value within the range of 4 ≤ γ < 20.

[0052] 2 shows the change in the γ value over time after the installation of a liquid mass flow meter, which is the liquid raw material introduction rate measuring device 24. When γ became ≦4, the liquid raw material filters were switched between the line of the first liquid raw material supply mechanism 16 and the line of the second liquid raw material supply mechanism 22, and the first liquid raw material filter 14 and the second liquid raw material filter 20 were alternately replaced and used.

[0053] In Figure 2, the timing when the line of the first liquid raw material supply mechanism 16 and the line of the second liquid raw material supply mechanism 22 were switched, i.e., the timing when the first liquid raw material filter 14 and the second liquid raw material filter 20 were switched and replaced, have been added to the transition of the γ value shown in Figure 2. As shown in Figure 2, the cycle in which γ<4 was achieved was irregular and varied greatly from time to time. However, because the γ value could be determined using the liquid raw material introduction rate measuring device 24, it was possible to determine the appropriate timing for replacing the first liquid raw material filter 14 and the second liquid raw material filter 20.

[0054] In addition, by providing two parallel systems of liquid raw material supply mechanisms equipped with liquid raw material filters 14, 20 and the inlet for purge inert gas (nitrogen in the illustrated example) required for purging and replacing them, a vacuum exhaust port, a purge exhaust port, an inert gas (helium in the illustrated example) inlet for leak detection, a vacuum pump, a drain, and various valves, it was possible to replace the liquid raw material filters 14, 20 without stopping the production of the soot body.

[0055] In the illustrated example, two lines, the first liquid raw material supply mechanism 16 and the second liquid raw material supply mechanism 22, are installed in parallel and an example is shown in which each line is switched, but it is also possible to provide an additional liquid raw material supply mechanism in addition to the first liquid raw material supply mechanism 16 and the second liquid raw material supply mechanism 22 and use a valve mechanism to switch through which of these liquid raw material supply mechanisms the liquid raw material flows.

[0056] The method for supplying a liquid raw material to a vaporizer of the present invention is a method for supplying a liquid raw material to a vaporizer using the liquid raw material supply system 10 to a vaporizer described above.

[0057] The method for supplying a liquid raw material to a vaporizer of the present invention includes a step of monitoring the introduction rate of the liquid raw material into the vaporizer 110, and a step of switching, using a valve mechanism 25, through which liquid raw material flows, either the first liquid raw material supply mechanism 16 or the second liquid raw material supply mechanism 22, depending on a decrease in the introduction rate of the liquid raw material.

[0058] When switching to either the first liquid source supply mechanism 16 or the second liquid source supply mechanism 22 through which the liquid source flows, it is preferable to carry out a purge step of purging the next liquid source supply mechanism through which the liquid source flows.

[0059] Furthermore, when switching to either the first liquid source supply mechanism 16 or the second liquid source supply mechanism 22 through which the liquid source flows, it is preferable to perform a leak detection step of detecting whether there is a leak of the liquid source for the next liquid source supply mechanism through which the liquid source flows, and a substitution step of substituting the air in the introduction line for the next liquid source supply mechanism through which the liquid source flows.

[0060] <Replacing the second liquid raw material filter 20> The steps for replacing the liquid raw material filter 20 in the liquid raw material supply device to the vaporizer of the present invention will be described below with reference to FIGS. 3, 4, 7 and 8.

[0061] When the second liquid raw material filter 20 provided in the second liquid raw material introduction line 18 of the second liquid raw material supply mechanism 22 is being used (i.e., when the valves 26a, 26f, 26e, and 26d are open and the valves 26b, 26c, 46f, 46e, and 46a are closed), and it is determined that the liquid raw material filter 20 is becoming increasingly clogged based on the measurement value of the liquid raw material introduction rate measuring device 24, the following procedure is carried out.

[0062] First, in order to switch from the liquid raw material filter 20 of the second liquid raw material introduction line 18 to the liquid raw material filter 14 of the first liquid raw material introduction line 12 of the first liquid raw material supply mechanism 16, the valves 44f, 44e, and 44a are closed, and the valves 26b and 26c are opened and the valves 26f and 26e are closed by the valve mechanism 25.

[0063] Next, as indicated by the solid arrows in FIG. 3, while the first liquid raw material filter 14 provided on the first liquid raw material introduction line 12 of the first liquid raw material supply mechanism 16 is in use (i.e., valves 26a, 26b, 26c, 26d are open, and valves 44a, 44e, 44f, 26f, 26e are closed), the liquid raw material in the second liquid raw material filter 20 on the second liquid raw material introduction line 18 is pumped with N2, an inert purge gas, and discharged from the drain 43, while valves 46c, 46h, 46d, 46g, 46e are closed and valves 46f, 46a, 46b are opened (FIG. 3).

[0064] Furthermore, to purge the second liquid material filter 20 and its piping, N2, a purge inert gas, is allowed to flow through the filter with valves 26e and 26f closed, valves 46c, 46h, 46d, and 46f closed, and valves 46b, 46a, 46e, and 46g open, thereby purging the area indicated by the dotted arrows in Figure 3 (Figure 7). Note that in this specification, "flow purging" refers to "flow purging." Furthermore, nitrogen batch purging is performed by opening and closing valve 46g.

[0065] Furthermore, with valves 26e and 26f closed, valves 46c, 46h, 46g, and 46f closed, and valves 46b, 46a, and 46e open, nitrogen vacuum batch purging is performed by opening and closing valve 46d and using vacuum pump 50 to purge the route indicated by the dotted arrows in Figure 4 to a sufficiently safe condition, and valve 46d is then closed. Next, with valves 26e and 26f closed, valves 46c, 46d, 46g, and 46f closed, and valves 46b, 46a, and 46h open, the second liquid raw material filter 20 is replaced while flowing inert purge gas N2 from the liquid raw material inlet and outlet sides of the second liquid raw material filter 20, i.e., from both the upstream and downstream sides of the second liquid raw material filter 20.

[0066] After replacing the second liquid raw material filter 20, the valve 46d is opened again, and the inert purge gas N2 is flowed in to purge the filter. The valve 46d is also opened and closed, and a batch purge is performed using the vacuum pump 50 to completely replace the air in the second liquid raw material filter 20 and the air that was mixed in during replacement (FIG. 8).

[0067] Furthermore, the above-mentioned purging and replacement of the second liquid raw material filter 20 can be carried out while the first liquid raw material introduction line 12 of the first liquid raw material supply mechanism 16 is in use, so that the work can be carried out safely over a sufficient period of time.

[0068] An example of the procedure for pre-exchange purging before replacing the liquid source filter is shown in Figure 7. As shown in Figure 7, in the pre-exchange purging, the remaining liquid source is collected from the drain (S110), an inert gas (N2 in the illustrated example) is purged (S102), and the liquid source filter is then replaced (S108). The conditions for each purge process can be selected appropriately depending on the configuration and size of the piping, and are not particularly limited, but the process conditions described below are preferred. Note that the more times and for how long the purge process is performed, the more gas is replaced, which is preferable from the standpoint of gas replacement. There are no particular upper limits on the number of times and duration of each purge process, and these can be determined appropriately taking into account factors such as cost. The flow-through purge (S102) is preferably carried out for 30 minutes or more, and more preferably for 10 hours or more. 7, after the flow-through purge (S102), it is preferable to perform a batch purge in which pressurization and depressurization are repeated multiple times. For example, as shown in Fig. 7, after the flow-through purge (S102), a batch purge (S104) using an inert gas (N2 in the illustrated example) is performed in which the inert gas is filled into the passage under pressurized conditions (preferably pressurized to a gauge pressure of 0.1 MPa or more) with the valve closed, and then the valve is opened to return to atmospheric pressure. This batch purge is repeated multiple times (preferably 20 times or more), and then a vacuum batch purge (S106) using an inert gas (N2 in the illustrated example) is performed in which the inert gas is filled into the passage under pressurized conditions (preferably pressurized to a gauge pressure of 0.1 MPa or more) with the valve closed, and then the passage is depressurized using a vacuum pump to return to a depressurized condition (preferably depressurized to a gauge pressure of -0.05 MPa or less). This inert gas vacuum batch purge is repeated multiple times (preferably 5 times or more). The replacement of the liquid raw material filter (S108) is preferably carried out while purging with an inert gas (N2 in the illustrated example) from both sides (upstream and downstream sides) of the liquid raw material filter. In the example shown in Figure 7, this can be safely performed over a total of 50 hours.

[0069] Next, an example of the procedure for post-replacement purging after replacing the liquid source filter is shown in Figure 8. As shown in Figure 8, in the post-replacement purging, a flow-through purging (S110) of an inert gas (N2 in the illustrated example) is performed to make the filter usable (S118). The flow-through purging (S110) is preferably performed for 30 minutes or more, and more preferably for 5 hours or more. After the flow-through purge (S110), it is preferable to further perform a leak detection step of detecting whether there is a leak, and a substitution step of replacing the air in the introduction line after the leak detection step. As the substitution step, it is preferable to perform a batch purge in which pressurization and depressurization are repeated multiple times. Specifically, as shown in FIG. 8, after the flow-through purge (S110), an inert gas (He in the illustrated example) for leak testing is introduced into the piping, and the gas is filled into the path under pressurized conditions (preferably, pressurized to a gauge pressure of +0.1 MPa or more), and a leak check is performed using an inert gas (He in the illustrated example) detector (S114). Thereafter, as a vacuum batch purge (S116) using an inert gas (N2 in the illustrated example), the inert gas is filled into the path under pressurized conditions (preferably, pressurized to a gauge pressure of +0.1 MPa or more) with the valve closed, and then the path is depressurized using a vacuum pump (preferably, depressurized to a gauge pressure of -0.05 MPa or less), and this inert gas vacuum batch purge is preferably repeated multiple times (preferably, five or more times). In the example shown in Figure 8, these steps can be safely performed over a total of 30 hours.

[0070] <Replacing the first liquid raw material filter 14> The steps for replacing the first liquid raw material filter 14 in the liquid raw material supply device to the vaporizer of the present invention will be described below with reference to FIGS. 5, 6, 7 and 8.

[0071] As shown by the solid arrow in FIG. 5, when the first liquid raw material filter 14 provided in the first liquid raw material introduction line 12 of the first liquid raw material supply mechanism 16 is being used, and it is determined from the measurement value of the liquid raw material introduction rate measuring device 24 that the first liquid raw material filter 14 is becoming increasingly clogged, the following procedure can be carried out in the same manner as described above.

[0072] First, the valve mechanism 25 switches from the first liquid raw material filter 14 provided on the first liquid raw material introduction line 12 to the liquid raw material filter 20 provided on the second liquid raw material introduction line 18 .

[0073] Next, while the second liquid raw material filter 20 of the second liquid raw material introduction line 18 is still in use, the liquid raw material in the first liquid raw material filter 14 of the first liquid raw material introduction line 12 is pumped with N2, an inert purge gas, and discharged through the drain 41 (FIG. 5).

[0074] The first liquid raw material filter 14 and the first liquid raw material introduction line 12 are purged by flowing inert gas (N2 in the illustrated example) in the range indicated by the dotted arrow in Figure 5.

[0075] Furthermore, batch purging is performed by opening and closing valve 44g, and vacuum batch purging is performed by opening and closing valve 44d and using vacuum pump 48, and the route indicated by the dotted arrow in Figure 6 is purged to a sufficiently safe condition, and valve 44d is then closed.Then, the first liquid raw material filter 14 is replaced while flowing N2, an inert purge gas, from both the liquid raw material inlet and outlet sides of the first liquid raw material filter 14, i.e., from both the upstream and downstream sides of the first liquid raw material filter 14.

[0076] After replacing the first liquid raw material filter 14, N2 flow purging and batch purging using the vacuum pump 48 are again performed to completely replace the air in the first liquid raw material filter 14 and the air that has become mixed in during replacement.

[0077] As described above, by performing the above-described steps using the liquid raw material supply system 10 to the vaporizer, the liquid raw material filter 14 or 20 can be replaced without stopping the production of the soot body.

[0078] In the method using the conventional apparatus shown in Figure 9, replacing the liquid raw material filter required more than 170 hours of downtime for the production of the soot body. However, when the above-mentioned process is performed using the liquid raw material supply system 10 to the vaporization apparatus of the present invention, there is no need to stop the production of the soot body, and therefore the downtime for the production of the soot body is 0 hours.

[0079] The soot body manufacturing method of the present invention manufactures a soot body, which is a synthetic silica glass base material, using a liquid raw material supply system 10 to a vaporizer. Also, the soot body manufacturing method of the present invention manufactures a soot body, which is a synthetic silica glass base material, using the above-described method of supplying liquid raw material to a vaporizer of the present invention. [Explanation of symbols]

[0080] 10: Liquid raw material supply system to the vaporization apparatus of the present invention, 12: First liquid raw material introduction line, 14: First liquid raw material filter, 16: First liquid raw material supply mechanism, 18: Second liquid raw material introduction line, 20: Second liquid raw material filter, 22: Second liquid raw material supply mechanism, 24: Liquid raw material introduction rate measuring device, 25: Valve mechanism, 26a to 26f: Valves, 28, 30: Inert gas introduction line for purging, 32, 34: Inert gas introduction port for leak detection, 36, 38: Vacuum pump connection port, 40, 42: Drain line, 41, 43 : Drain, 44a to 44h, 46a to 46h: Valves, 48, 50: Vacuum pump, 52, 54: Purge exhaust line, 100: Conventional liquid raw material supply system to vaporizer, 102: N2 introduction line, 104: SiCl4 introduction line, 106: Liquid raw material filter, 108: Liquid raw material introduction line, 110: Vaporizer, 112, 114, 116: Valves, 118: Vaporization tank, 120: Gas raw material filter, 122: Mass flow controller, 124: Gas raw material introduction line, 126: Growth furnace, 128: Oxyhydrogen burner.

Claims

1. A supply system for supplying a liquid raw material containing a silicon-containing compound to a vaporizer used to manufacture a soot body that is a synthetic quartz glass base material, a first liquid source supply mechanism including a first liquid source introduction line for introducing the liquid source into a vaporization tank of the vaporization device and a first liquid source filter provided on the first liquid source introduction line; a second liquid source supply mechanism including a second liquid source introduction line for introducing the liquid source into the vaporization tank of the vaporization device and a second liquid source filter provided on the second liquid source introduction line; a liquid raw material introduction rate measuring device for monitoring the introduction rate of the liquid raw material into the vaporization tank of the vaporization device; a valve mechanism for switching whether the liquid source flows through the first liquid source supply mechanism or the second liquid source supply mechanism; and At least an introduction rate of the liquid raw material into a line through which the liquid raw material flows is γ expressed by the following formula (1), and γ is controlled so as to satisfy the following relationship: 4≦γ<20; γ = (introduction mass rate of liquid raw material) ÷ ​​(exit mass rate of gas raw material from vaporizer) (1) A liquid raw material supply system to a vaporizer, wherein a guideline for replacing a filter in a line through which the liquid raw material flows is γ<4.

2. 2. The liquid source supply system to a vaporizer according to claim 1, wherein each of the first liquid source supply mechanism and the second liquid source supply mechanism further comprises a purge inert gas introduction line and a purge exhaust line for purging.

3. 3. The liquid source supply system to a vaporizer according to claim 1, wherein each of the first liquid source supply mechanism and the second liquid source supply mechanism further comprises an inert gas inlet for leak detection for detecting whether there is a leak of the liquid source, and a vacuum pump connection port for replacing air in a liquid source introduction line.

4. 4. The liquid source supply system to a vaporization device according to claim 1, further comprising, in addition to the first liquid source supply mechanism and the second liquid source supply mechanism, a further liquid source supply mechanism, and the valve mechanism is a valve mechanism for switching through which of the liquid source supply mechanisms the liquid source flows.

5. A method for supplying a liquid raw material to a vaporizer using the liquid raw material supply system to a vaporizer according to any one of claims 1 to 4, introducing the liquid source into a vaporization tank of the vaporizer by either the first liquid source supply mechanism or the second liquid source supply mechanism; monitoring the rate at which the liquid source is introduced into the vaporization tank of the vaporization device; switching, by a valve mechanism, through which liquid source flows, the first liquid source supply mechanism or the second liquid source supply mechanism, in response to a decrease in the introduction speed of the liquid source; Including, an introduction rate of the liquid raw material into a line through which the liquid raw material flows is γ expressed by the following formula (1), and γ is controlled so as to satisfy the following relationship: 4≦γ<20; γ = (introduction mass rate of liquid raw material) ÷ ​​(exit mass rate of gas raw material from vaporizer) (1) A method for supplying a liquid raw material to a vaporizer, wherein a guideline for replacing a filter in a line through which the liquid raw material flows is γ<4.

6. 6. The method for supplying a liquid source to a vaporizer according to claim 5, further comprising the step of replacing the liquid source filter of the liquid source supply mechanism through which the liquid source no longer flows after switching by the valve mechanism.

7. 7. The method for supplying a liquid raw material to a vaporization device according to claim 6, further comprising a purging step of purging the liquid raw material inlet line of the liquid raw material supply mechanism through which the liquid raw material no longer flows, before and after the step of replacing the liquid raw material filter after switching by the valve mechanism.

8. After the replacing step, a leak detection step of detecting whether there is a leak in the liquid source introduction line of the liquid source supply mechanism through which the liquid source has stopped flowing; a replacement step of replacing the air in the introduction line after the leak detection step; 8. The method for supplying a liquid raw material to a vaporizer according to claim 6, comprising:

9. a liquid source supply mechanism in addition to the first liquid source supply mechanism and the second liquid source supply mechanism, and the valve mechanism switches through which of the liquid source supply mechanisms the liquid source flows; 9. The method for supplying a liquid source to a vaporizer according to claim 5, wherein the step of switching using the valve mechanism includes the step of switching using the valve mechanism to one of the liquid source supply mechanisms.

10. A method for producing a soot body, which is a synthetic silica glass base material, using the liquid raw material supply system for a vaporizer according to any one of claims 1 to 4.

11. A method for producing a soot body, which is a synthetic silica glass base material, using the method for supplying a liquid raw material to a vaporizer according to any one of claims 5 to 9.

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