Method for producing porous glass fine particle matter, equipment for producing porous glass fine particle matter, and method for producing optical fiber preform

Abstract

To provide a method for producing a porous glass particulate matter, the method enabling suppression of the occurrence of backfire by detecting decrease of the flow volume of a carrier gas when combustible raw material gas is used.SOLUTION: A method for producing a porous glass particulate matter is provided, which uses production equipment including: a burner 60 which ejects a premixed gas Gm including organosilicon compound gas and oxygen gas into flame Fa to generate glass fine particles; a burner line 20 transporting the organosilicon compound gas to the burner together with carrier gas; a carrier gas flow control unit 13a for measuring a flow of the carrier gas; a purge gas supply line 40 introducing the purge gas into the burner line via a purge value 41; and a control unit 50 controlling opening and closing of the purge value on the basis of the flow of the carrier gas measured by the carrier gas flow control unit. In the method for producing porous glass particulate matter, when the flow volume of the carrier gas is equal to or more than a predetermined value, the purge valve is closed, and when the flow volume of the carrier gas is less than the predetermined value, the purge valve is opened.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing porous glass particulate, an apparatus for producing porous glass particulate, and a method for producing an optical fiber preform. [Background technology]

[0002] Patent Document 1 discloses a method for producing porous glass particles by ejecting a raw material gas from a burner, reacting in a flame, and depositing the generated glass particles on a starting member. An optical fiber preform is obtained by subjecting the porous glass particles to a sintering process or the like. In Patent Document 1, an organic silicon compound is used as the raw material gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-94218 A Summary of the Invention [Problem to be solved by the invention]

[0004] When using a raw material gas such as an organosilicon compound, a gel-like substance (hereinafter simply referred to as gel) derived from the organosilicon compound may be generated in the pipe through which the gas containing the raw material gas passes. When gel is generated, the pipe becomes clogged, and when the flow rate of the mixed gas containing the raw material gas and the carrier gas mixed in the vaporization process of the organosilicon compound at the outlet of the burner is lower than the combustion speed of the premixed gas at the outlet of the burner, backfire is likely to occur in which the combustion surface penetrates into the pipe. In Patent Document 1, the generation of gel is suppressed by removing the moisture in the organosilicon compound, but it is difficult to completely suppress the generation of gel, and when gel is generated, backfire may occur.

[0005] The present invention has been made in consideration of the above circumstances, and aims to provide a method for manufacturing porous glass microparticles that is capable of detecting a decrease in the flow rate of carrier gas and suppressing the occurrence of flashback when a flammable raw material gas is used, an apparatus for manufacturing porous glass microparticles, and a method for manufacturing an optical fiber preform. [Means for solving the problem]

[0006] In order to solve the above problems, a method for producing porous glass particles according to a first aspect of the present invention is a method for producing porous glass particles using a production apparatus including a burner that releases a premixed gas containing an organosilicon compound gas and oxygen into a flame to generate glass particles, a burner line that transports the organosilicon compound gas together with a carrier gas to the burner, a carrier gas flow control unit that measures the flow rate of the carrier gas, a purge gas supply line that introduces a purge gas into the burner line via a purge valve, and a control unit that controls the opening and closing of the purge valve based on the flow rate of the carrier gas measured by the carrier gas flow control unit, wherein the purge valve is closed when the flow rate of the carrier gas is equal to or greater than a predetermined value, and the purge valve is opened when the flow rate of the carrier gas is less than the predetermined value.

[0007] When using a gas of a flammable organosilicon compound, by detecting a decrease in the flow rate of the carrier gas and opening the purge valve, it is possible to prevent the flow rate at the outlet of the burner from becoming lower than the combustion rate of the premixed gas at the outlet of the burner, thereby making it possible to suppress the occurrence of flashback in the burner.

[0008] Furthermore, in a second aspect of the present invention, in the method for producing porous glass microparticles of the first aspect, a burner valve provided in the burner line and provided between the purge valve and a vaporization unit that vaporizes the organosilicon compound is opened when the flow rate of the carrier gas is equal to or greater than the predetermined value, and the burner valve is closed when the flow rate of the carrier gas is less than the predetermined value.

[0009] In addition, in a third aspect of the present invention, in the method for producing porous glass microparticles according to the first or second aspect, the predetermined value is the flow rate of the carrier gas at which the flow velocity of the premixed gas released from the burner becomes 19 m / sec when the purge valve is closed.

[0010] Furthermore, in a fourth aspect of the present invention, in the method for producing porous glass microparticles according to any one of the first to third aspects, a flow rate of the purge gas is controlled by a purge gas flow rate control unit provided in the purge gas supply line so that the flow velocity of the gas released from the burner is 19 m / sec or more.

[0011] Furthermore, in a fifth aspect of the present invention, in the method for producing porous glass microparticles of any one of the first to fourth aspects, the specified value is 2% less than the set value of the flow rate of the carrier gas, and the set value is the flow rate of the carrier gas when the flow velocity of the premixed gas is 19 m / sec or more.

[0012] A manufacturing apparatus for porous glass microparticles according to a sixth aspect of the present invention includes a burner that releases a premixed gas containing an organosilicon compound gas and oxygen into a flame to generate glass microparticles, a burner line that transports the organosilicon compound gas together with a carrier gas to the burner, a carrier gas supply line having a carrier gas flow rate control unit that measures the flow rate of the carrier gas, and a vaporization unit that vaporizes the organosilicon compound in a liquid state mixed with the carrier gas, and is connected to the burner by the burner line, a purge gas supply line that introduces a purge gas into the burner line via a purge valve, and a control unit that controls opening and closing of the purge valve based on the flow rate of the carrier gas measured by the carrier gas flow rate control unit, and the control unit closes the purge valve when the flow rate of the carrier gas is equal to or greater than a predetermined value, and opens the purge valve when the flow rate of the carrier gas is less than the predetermined value.

[0013] A seventh aspect of the present invention is a method for producing an optical fiber preform, comprising a step of sintering the porous glass particles obtained by the production method of any one of the first to fifth aspects. Effect of the Invention

[0014] According to the above aspect of the present invention, when a flammable source gas is used, it is possible to detect a decrease in the flow rate of the carrier gas and suppress the occurrence of flashback. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a schematic diagram showing a configuration of a supply device in the manufacturing apparatus according to the present embodiment. [Diagram 2] 2 is a view for explaining opening and closing of a valve of the supplying device shown in FIG. 1 when production of glass particles is stopped. FIG. [Diagram 3] 3 is a flowchart showing a manufacturing method according to the present embodiment. [Figure 4] FIG. 13 is a diagram showing a supply device according to a modified example of the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The manufacturing method of the porous glass particles of this embodiment will be described below with reference to the drawings. The porous glass particles obtained by this embodiment can be used to obtain an optical fiber preform by applying, for example, the outside vapor deposition method (OVD method) or the vapor phase axial deposition method (VAD method).

[0017] The OVD method is a method in which glass particles are deposited on the outer surface of a starting member such as a glass rod to form a glass soot layer, and then the glass soot layer is sintered by heating to obtain transparent glass. The VAD method is a method for obtaining transparent glass by starting deposition of glass particles from the tip of a starting member such as a glass rod to form cylindrical glass soot, and then sintering the glass soot by heating. In this embodiment, SiO 2 The glass particles containing the above are generated by heating and vaporizing an organic silicon compound and burning it together with oxygen in a burner. Hereinafter, a method for generating glass particles in a burner will be described with reference to FIG. 1.

[0018] (Feeding device) As shown in Fig. 1, the supply device 1 includes a raw material supply line 10, a burner line 20, a vent line 30, a purge gas supply line 40, and a control unit 50. The raw material supply line 10 is provided with a raw material valve 11, a raw material flow rate control unit 12, a vaporization unit 14, and a thermometer 16. In addition, the raw material supply line 10 is connected to a carrier gas supply line 13 and an oxygen supply line 15. The carrier gas supply line 13 is provided with a carrier gas flow rate control unit 13a. The oxygen supply line 15 is provided with an oxygen flow rate control unit 15a. A burner 60 is connected downstream of the burner line 20 .

[0019] The upstream side of the raw material supply line 10 is connected to a supply source (not shown) of the liquid raw material. The supply source of the liquid raw material supplies the liquid raw material to the raw material supply line 10. The supply source may include, for example, a container that contains the liquid raw material and is connected to the raw material supply line 10, and a pressurized gas pipe that supplies a pressurized gas having a low solubility in the liquid raw material to the container. In this case, by supplying pressurized gas from the pressurized gas pipe to the container, the pressure inside the container can be increased, and the liquid raw material can be supplied from the container to the raw material supply line 10. A degassing device that degasses dissolved gas from the liquid raw material may be provided between the sealed container and the raw material flow rate control unit 12.

[0020] In this embodiment, an organic silicon compound is used as the raw material. The organic silicon compound includes alkylcyclosiloxanes, and octamethylcyclotetrasiloxane (OMCTS) is particularly suitable. OMCTS is also called "D4", and "D" stands for (CH 3 ) 2 D4(C 8 H 24 O 4 S 4 ) is widely used industrially and is easily available, but D3(C 6 H 18 O 3 S 3 ), D5(C 10 H 30 O 5 S 5 ) may be used. D3, D4, and D5 may be used alone or in combination. The organosilicon compounds do not generate hydrochloric acid even when they are oxidized, which contributes to reducing the environmental load and reducing production costs by eliminating the need for hydrochloric acid treatment equipment.

[0021] The downstream end of the raw material supply line 10 branches off towards a burner line 20 and a vent line 30 . The raw material valve 11 is located upstream of the raw material flow rate control unit 12 and the vaporization unit 14, and switches between allowing and not allowing the liquid raw material to flow through the raw material supply line 10. Raw material flow rate control unit 12 is located between raw material valve 11 and vaporization unit 14, and adjusts the flow rate of the liquid raw material flowing toward vaporization unit 14. Raw material flow rate control unit 12 is an MFC (Mass Flow Controller) or the like.

[0022] The carrier gas supply line 13 is connected to the raw material supply line 10 at a connection J1 between the raw material flow rate control unit 12 and the vaporization unit 14, and supplies a carrier gas to the raw material supply line 10. The carrier gas may be argon (Ar), helium (He), nitrogen (N2 ), or oxygen (O 2 The carrier gas may contain a plurality of types of gases. The carrier gas supply line 13 has a carrier gas flow rate control unit 13a provided upstream of the connection part J1. The carrier gas flow rate control unit 13a adjusts the flow rate of the carrier gas flowing through the raw material supply line 10. The carrier gas flow rate control unit 13a is an MFC or the like. The upstream side of the carrier gas supply line 13 is connected to a carrier gas supply source (not shown).

[0023] The oxygen supply line 15 is connected to the raw material supply line 10 at a connection J2 between the vaporization unit 14 and the thermometer 16, and supplies oxygen (O 2 ) is supplied to the raw material supply line 10. This produces a premixed gas Gm in which the raw material gas, carrier gas, and oxygen are mixed. Oxygen is required to make the raw material gas combustible. The oxygen supply line 15 has an oxygen flow rate control unit 15a provided upstream of the connection J2. The oxygen flow rate control unit 15a adjusts the flow rate of oxygen flowing through the raw material supply line 10. The oxygen flow rate control unit 15a is an MFC or the like. The upstream side of the oxygen supply line 15 is connected to an oxygen supply source (not shown).

[0024] The thermometer 16 measures the temperature of the premixed gas Gm. The thermometer 16 is provided downstream of the connection part J2 in the raw material supply line 10. For example, the thermometer 16 may measure the temperature of the premixed gas Gm by measuring the temperature of the piping. The thermometer 16 does not necessarily have to be provided. When the thermometer 16 is not provided, the temperature of the gas or the piping may be measured by the vaporization unit 14 or each flow rate control part.

[0025] The burner line 20 has an upstream end connected to a downstream end of the raw material supply line 10, and a downstream end connected to the burner 60. The burner line 20 supplies the premixed gas Gm to the burner 60. The burner line 20 is provided with a burner valve 21. The burner valve 21 is configured to open and close the burner line 20. When the burner valve 21 is open, the premixed gas Gm can flow toward the burner 60. A purge gas supply line 40 is connected to a portion of the burner line 20 between the burner valve 21 and the burner 60.

[0026] The vent line 30 is provided with a vent valve 31. The vent valve 31 is configured to open and close the vent line 30. A treatment device (not shown) is provided downstream of the vent line 30. When the vent valve 31 is open and the burner valve 21 is closed, the premixed gas Gm flowing from the raw material supply line 10 flows through the vent line 30 toward the treatment device.

[0027] The purge gas supply line 40 supplies a purge gas to the burner 60. As the purge gas, an inert gas such as nitrogen can be used. The purge gas supply line 40 is connected to the burner line 20 between the burner valve 21 and the burner 60. A purge valve 41 is provided in the purge gas supply line 40. The purge valve 41 is configured to open and close the purge gas supply line 40. When the purge valve 41 is open, the purge gas can flow toward the burner 60. Furthermore, the purge gas supply line 40 has a purge gas flow rate control unit 42 provided upstream of the purge valve 41. The purge gas flow rate control unit 42 adjusts the flow rate of the purge gas flowing through the burner 60. The purge gas flow rate control unit 42 is an MFC or the like. The upstream side of the purge gas supply line 40 is connected to a purge gas supply source (not shown).

[0028] The control unit 50 is electrically connected to the raw material valve 11, the burner valve 21, the vent valve 31, the purge valve 41, the raw material flow rate control unit 12, the carrier gas flow rate control unit 13a, the oxygen flow rate control unit 15a, the purge gas flow rate control unit 42, and the thermometer 16. The control unit 50 outputs signals for switching the opening and closing of the valves 11, 21, 31, and 41, and signals for instructing the set values ​​of the flow rates by the flow rate control units 12, 13a, 15a, and 42. The control unit 50 may also control the temperature of each gas in the raw material supply line 10 and the temperature of a temperature adjustment device (not shown) provided in the piping of the raw material supply line 10, based on temperature information measured by the thermometer 16. The control unit 50 may be a part of any one of the flow rate control units 12, 13a, 15a, and 42. Alternatively, the control unit 50 may be configured to control not only the supply device 1 but also the entire porous glass microparticle manufacturing device. The control unit 50 may have a determination unit that determines whether or not there is an abnormality in the manufacturing apparatus based on the flow rate data from the flow rate control units 12, 13a, 15a, and . The control unit 50 may be, for example, a microcontroller, an integrated circuit such as an IC (Integrated Circuit), an LSI (Large-scale Integrated Circuit), or an ASIC (Application Specific Integrated Circuit), or a programmable logic controller (PLC).

[0029] The burner 60 has a premixed gas port to which the burner line 20 is connected and from which the premixed gas Gm is ejected, a port to which a piping for a combustible gas Gf is connected, and a port to which a piping for oxygen is connected. Note that instead of the port to which the piping for the combustible gas Gf is connected and the port to which the piping for oxygen is connected, the burner 60 may have a port to which a piping for a mixed gas of the combustible gas Gf and oxygen is connected. The combustible gas may be, for example, hydrogen (H 2 ) and methane (CH 4 ) etc.

[0030] (Generation of glass particles) The liquid raw material is introduced into the vaporization unit 14 together with the carrier gas, with the flow rate being controlled by the control unit 50 and the raw material flow rate control unit 12, and is vaporized. The liquid raw material is then mixed with oxygen to form a premixed gas Gm. The premixed gas Gm is supplied to the burner 60 from the burner line 20. At the outlet 60a of the burner 60, the combustible gas Gf and oxygen are mixed and burned to generate a combustible gas combustion flame Fa (sometimes simply referred to as flame Fa). The premixed gas Gm is ignited by the combustible gas combustion flame Fa, generating a raw material combustion flame Fb. The raw materials react in the raw material combustion flame Fb to generate glass particles.

[0031] When D3, D4, or D5 is used as the raw material, the number of D units contained in the premixed gas Gm is n1, and the amount of oxygen is n2. The mixing ratio R (molar ratio) of the number of D units to oxygen in the premixed gas Gm is expressed as R=n1 / n2.

[0032] The mixture ratio R is preferably 0.68≦R≦1.00. If the mixture ratio R exceeds 1.00, the oxygen required for burning the raw material is insufficient, resulting in incomplete combustion and soot generation. If the mixture ratio R is below 0.68, the combustion reaction becomes unstable, the raw material combustion flame Fb becomes turbulent, the deposition efficiency of the glass particles decreases, and the glass particles adhere to the burner 60. If oxygen is contained in the carrier gas, the substance amount n2 of oxygen at the mixture ratio R is the combined value of the substance amounts of oxygen supplied from the carrier gas supply line 13 and the oxygen supply line 15.

[0033] For example, if the raw material is D4, 1 mole of the raw material contains 4 D units, so if the amount of substance of the raw material is m, note that n1 = m x 4. If the mixing ratio R' of the premixed gas Gm is expressed by the amount of substance m of D4, it is R' = m / n2. Therefore, in order to obtain 0.68 ≦ R ≦ 1.00, 0.17 ≦ R' ≦ 0.25 is required. Similarly, if the raw material is D3, n1 = m x 3, and if the raw material is D5, n1 = m x 5. In addition, when raw materials with different numbers of D units such as D3, D4, and D5 are mixed and used, the value of n1 is calculated taking into account the number of D units relative to the amount of substance of each raw material.

[0034] (Porous glass microparticle manufacturing equipment) The porous glass particle manufacturing apparatus of this embodiment includes a burner 60, a supply device 1, a reaction vessel, a pair of rotating chucks, and a rail. The number of burners 60 provided in the porous glass particle manufacturing apparatus may be one or more. When the manufacturing apparatus includes a plurality of burners 60, the burners 60 may be arranged at predetermined intervals in the longitudinal direction of the starting member. A pair of rotating chucks support both ends of the starting member, and the starting member is rotated within the reaction vessel by the rotating chucks.

[0035] The burner 60 is movable along a rail extending in the same direction as the longitudinal direction of the starting member. That is, the burner 60 is movable along the longitudinal direction of the starting member. All or part of the supply device 1 may also move together with the burner 60 along the rail. The burner 60 moves back and forth along the rail in the longitudinal direction. For example, the rail may be formed into a ring shape, and a plurality of burners 60 may be moved in a circulating manner along the rail in one direction. The manufacturing apparatus may be configured to reciprocate the starting member along the longitudinal direction, rather than the burner 60 .

[0036] At the outlet 60a of the burner 60, the premixed gas Gm is released into the combustible gas combustion flame Fa produced by the combustible gas Gf supplied to the burner 60, generating a raw material combustion flame Fb. The raw material gas contained in the premixed gas Gm reacts in the raw material combustion flame Fb to generate glass particles. The glass particles are deposited on the surface of the starting material to form a deposition layer (soot) of glass particles. This results in a porous glass particle body. When the formation of soot is completed, the raw material combustion flame Fb is extinguished. More specifically, as shown in Fig. 2, the burner valve 21 is closed, the vent valve 31 is opened to discharge the premixed gas Gm toward the vent line 30, and the purge valve 41 is opened to supply the purge gas to the burner 60. This allows the premixed gas Gm remaining in the burner 60 and the burner line 20 to be discharged outside the burner 60.

[0037] The porous glass particles are sintered to obtain an optical fiber preform. In addition to the sintering, the optical fiber preform may be subjected to a dehydration treatment or a doping treatment, if necessary. Moreover, an optical fiber can be obtained by drawing the optical fiber preform.

[0038] Here, in this embodiment, an organic silicon compound is used as the raw material gas. The organic silicon compound is flammable. For example, the flash point (about 51°C) of D4 is lower than the boiling point (about 175°C). Therefore, there is a risk of ignition in a gas (premixed gas Gm) in which vaporized D4 and oxygen are mixed at a certain ratio. When such an organic silicon compound is used, the premixed gas Gm remaining in the burner 60 or the burner line 20 connected to the burner 60 is ignited, and the raw material combustion flame Fb is likely to backfire inside the burner 60 or piping. Furthermore, for example, when D4 is used as a raw material, high boiling point impurities such as D5 and D6 contained in D4 may cause gel formation in the piping. Also, a part of D4 may decompose and polymerize, and may accumulate in the piping as gel. If the piping is narrowed by the gel and the flow rate of the gas discharged from the outlet 60a of the burner 60 (hereinafter referred to as the burner nozzle flow rate) becomes lower than the combustion rate of the premixed gas Gm at the outlet 60a of the burner 60, a backfire is likely to occur in which the combustion surface of the flame penetrates into the piping. Therefore, in this embodiment, the flow rate of the gas ejected from the burner 60 is set to a flow rate that does not cause flashback, and when an abnormality such as a decrease in the flow rate of the gas ejected from the burner 60 occurs due to adhesion of gel to the piping, creating conditions that make flashback likely to occur, the generation of the glass particles is controlled to be stopped before flashback occurs. Details of the control in the supply device 1 will be described below.

[0039] First, the generation of glass particles is started with the flow rate of the gas ejected from the burner 60 set to a flow rate at which no backfire occurs. That is, the generation of glass particles is started with the gas flow rate being higher than the combustion rate of the premixed gas Gm. If the flow rate of the gas ejected from the burner 60 is maintained during the formation of soot, the gas flow rate will not become higher than the combustion rate, so no backfire will occur. However, if gel adheres to the inside of the pipe, the pressure loss in the pipe increases, the gas flow rate decreases, and there is a possibility of backfire occurring. In this embodiment, backfire is suppressed by controlling the flow rate of the carrier gas in the premixed gas Gm so that it does not fall below a predetermined value.

[0040] (Carrier gas flow rate setting) The flow rate of the carrier gas is determined based on two factors: (A) the vaporization capacity of the organosilicon compound, and (B) the burner nozzle flow rate.

[0041] (A) Vaporization ability of organosilicon compounds The vaporization capacity of the organosilicon compound is affected by the stability of the flow rates of the liquid organosilicon compound to be vaporized and the vaporized organosilicon compound gas (raw material gas), the structure and set temperature of the vaporization unit 14, and the flow rate of the carrier gas. In particular, the higher the carrier gas flow rate, the more organosilicon compound can be vaporized. And, by increasing the flow rate of the vaporized organosilicon compound, the flow rate of the supplied raw material gas is less likely to increase or decrease, and the stability is also increased. However, since the inert gas contained in the carrier gas inhibits the reaction for producing glass particles, it is preferable that the flow rate of the carrier gas is small from the viewpoint of producing glass particles. Therefore, in this embodiment, the source gas flow rate is set to a flow rate necessary for producing a target amount of glass particles, and the carrier gas flow rate is set to a flow rate as low as possible within a range in which stability after vaporization of the source material can be maintained.

[0042] (B) Burner nozzle flow velocity The inventors' investigations have revealed that backfire is less likely to occur by adjusting the flow velocity of the premixed gas Gm discharged from the outlet 60a of the burner 60 to 19 m / sec or more. That is, the flow rates of the raw material gas, carrier gas, and oxygen are determined and the total amount of the premixed gas Gm is adjusted so that the flow velocity of the premixed gas Gm is 19 m / sec or more. First, the flow rates of the organosilicon compound and oxygen are determined, since the mixing ratio of the organosilicon compound and oxygen is preferably 0.68≦R≦1.00 as described above. Then, the flow rate of the carrier gas preferable for vaporizing the organosilicon compound is determined by the method described in (A). Under this condition, if the burner nozzle flow rate calculated from the total flow rate of the organosilicon compound, the carrier gas, and the oxygen is less than 19 m / sec, the flow rate of the carrier gas is increased so that the flow rate of the premixed gas Gm discharged from the outlet 60a of the burner 60 is 19 m / sec or more. When the amount of oxygen in the premixed gas Gm is small and the amount is outside the combustion range of the organic silicon compound, flashback will not occur even if the flow velocity is less than 19 m / sec. However, due to the lack of oxygen, soot will be mixed with the soot, resulting in a poor appearance after sintering.

[0043] Here, the flow velocity Fmix (m / sec) of the premixed gas Gm discharged from the outlet 60a of the burner 60 is expressed by the flow rate (m 3 / sec) by the cross-sectional area of ​​the outlet 60a of the burner 60. Fmix=[(F1 / M×22.4+F2+F3)×(T / 273) / 1000 / 60] / S …(1) In formula (1), F1 is the flow rate of the liquid organosilicon compound (g / min); M is the molecular weight of the organosilicon compound; F2 is the flow rate of the carrier gas (slm (Standard Litter per Minute)), F3 is the flow rate of oxygen (slm); T is the temperature of the premixed gas (K), S is the cross-sectional area (m 2 ). In this embodiment, F1 is the flow rate of the liquid raw material in the MFC of raw material flow rate control unit 12, F2 is the flow rate of the carrier gas in the MFC of carrier gas flow rate control unit 13a, and F3 is the flow rate of oxygen in the MFC of oxygen flow rate control unit 15a. Since the gas flow meter measures the flow rate (slm) at 0°C (273K), in formula (1), the flow rate at temperature T (K) of premixed gas Gm measured by thermometer 16 is calculated from the flow rate at 0°C. In addition, when the gas flow meter measures the flow rate (slm) at 20°C, equation (1) may be modified to calculate the volume of the premixed gas at a temperature (K) from the volume of each gas at 20°C.

[0044] F1, F2, and F3 may be values ​​output from the flow rate control units 12, 13a, and 15a, respectively, to the control unit 50. The flow velocity Fmix may be calculated in the control unit 50, or may be calculated based on a numerical value output from the control unit 50 to an external device (not shown).

[0045] When the judgment section of the control section 50 judges that the following condition 1 or 2 is satisfied, it is determined that the risk of backfire has increased and the porous glass particle manufacturing apparatus is stopped. Condition 1: When the carrier gas flow rate is 2% or more lower than the set value for one continuous second or more. Condition 2: The flow velocity Fmix of the premixed gas Gm is less than 19 m / sec. The set value in condition 1 may be the flow rate of the carrier gas calculated when determining the burner nozzle flow rate based on the above-mentioned elements (A) and (B), or it may be the flow rate of the carrier gas initially set by the control unit 50 and the carrier gas flow rate control unit 13a when starting deposition of glass microparticles in the manufacturing equipment.

[0046] When condition 1 or condition 2 occurs, it is considered that an abnormality has occurred in the manufacturing equipment due to, for example, the following causes. Cause 1: Abnormality in carrier gas flow control unit 13a. Cause 2: Pressure drop in the carrier gas supply. Cause 3: Gel derived from organosilicon compounds accumulates in the internal piping of the vaporization unit 14, reducing heat exchange performance and vaporization capacity, and increasing piping resistance due to liquid organosilicon compounds remaining in the piping. Cause 4: Increased piping resistance due to accumulation of gel derived from organic silicon raw materials in the piping and gas filters downstream of the vaporization unit 14. When condition 1 or 2 occurs due to any of the above causes 1 to 4, it is unlikely that the cause will be resolved even if the production of glass particles is continued, and therefore it is necessary to immediately stop the production equipment in order to prevent backfire.

[0047] In this manner, in this embodiment, backfire is suppressed by depositing glass particles while checking that the flow rate of the carrier gas in the premixed gas Gm is not less than a predetermined value. As described in Conditions 1 and 2, the "predetermined value" of the flow rate of the carrier gas is a value that is 2% less than the set value of the flow rate of the carrier gas, and the set value of the carrier gas can be said to be the flow rate of the carrier gas when the burner nozzle flow velocity is 19 m / sec or more.

[0048] (Shutdown of manufacturing equipment) When the condition 1 or the condition 2 is satisfied, a stop signal is sent from the control unit 50. Even in the process of stopping the manufacturing equipment, it is required to control the equipment so that flashback does not occur. In response to an emergency stop signal sent by the control unit 50, the valves 21, 31, and 41 are changed from the state shown in FIG. 1 to the state shown in FIG. 2 to send the purge gas to the burner 60. More specifically, the burner valve 21 is closed and the vent valve 31 is opened, and the premixed gas Gm is discharged while the purge valve 41 is opened to supply the purge gas to the burner 60. In this case, the flow rate of the purge gas may be adjusted so that the burner nozzle flow velocity of the purge gas discharged from the outlet 60a or the mixed gas of the purge gas and the premixed gas Gm is 19 m / sec or more. When the purge valve 41 is open, the purge gas flow rate may be adjusted by the purge gas flow rate control unit to make the burner nozzle flow velocity 19 m / sec or more. This allows the premixed gas Gm remaining in the burner 60 or the burner line 20 to be discharged outside the burner 60, so that the manufacturing equipment can be reliably prevented from being damaged by backfire even during extinguishing. After the manufacturing equipment is stopped, in order to eliminate the cause of the drop in carrier gas pressure, repairs may be made to carrier gas flow rate control unit 13a and the carrier gas supply source, and piping and filters clogged with gel may be cleaned.

[0049] The control unit 50 judges whether or not an abnormality that satisfies conditions 1 and 2 occurs while depositing the glass particles, based on the flow rates in the flow rate control units 12, 13a, and 15a. If an abnormality occurs while depositing the glass particles, the production of the porous glass particles is interrupted, and the porous glass particles may be judged to be defective. If no abnormality occurs and the desired amount of soot is deposited, a good porous glass particles that does not include an abnormal portion can be produced.

[0050] A method for producing porous glass particles using the porous glass particle production apparatus will be described with reference to the flow chart of FIG. Step S11: In each of the flow rate control units 12, 13a, and 15a, the flow rates of the raw material gas, carrier gas, and oxygen are set. The set flow rates of each gas may be values ​​determined based on the mixture ratio of each gas and the burner nozzle flow rate, as described above. Step S12: The flow rate control units 12, 13a, and 15a control the flow rate of each gas so that the flow rates of the source gas, carrier gas, and oxygen become the set flow rates. Step S13: The flow rates F1, F2, and F3 of the respective gases are measured, and the measurement results are output to the control unit 50. When the flow rate control units 12, 13a, and 15a are provided with flow meters for the respective gases, F1, F2, and F3 are output from the flow rate control units 12, 13a, and 15a to the control unit 50, respectively.

[0051] Step S14: The control unit 50 calculates a predetermined value for the flow rate of the carrier gas. The predetermined value is a value that is 2% less than the set value of the flow rate of the carrier gas, and the set value of the carrier gas is the flow rate of the carrier gas when the burner nozzle flow velocity is 19 m / sec or more. Step S15: The control unit 50 judges whether or not F2, which is the flow rate of the carrier gas, is equal to or greater than a predetermined value. If the judgment result indicates that F2 is equal to or greater than the predetermined value, the process proceeds to step S16. If the judgment result indicates that F2 is less than the predetermined value, the process proceeds to step SE. Step S16: If "F2≧predetermined value" is satisfied, that is, if the control unit 50 determines that no abnormality has occurred, the process returns to step S12 with the purge valve 41 kept closed, and the deposition of glass particles continues. Step SE: If "F2<predetermined value" is satisfied, that is, if it is determined that an abnormality has occurred, the control unit 50 transmits an emergency stop signal and opens the purge valve 41 to send purge gas to the burner 60. This prevents the gas flow rate at the outlet 60a of the burner 60 from decreasing below the combustion rate of the premixed gas Gm at the outlet 60a of the burner 60, and terminates the deposition of glass particles. The processes of steps S12 to S15 may be repeated at predetermined time intervals until a desired amount of soot is deposited.

[0052] As described above, the method for producing porous glass particles of this embodiment is a method for producing porous glass particles using a production apparatus including a burner 60 that releases a premixed gas Gm containing an organosilicon compound gas and oxygen into a flame Fa to generate glass particles, a burner line 20 that transports the organosilicon compound gas together with a carrier gas to the burner 60, a carrier gas flow control unit 13a that measures the flow rate of the carrier gas, a purge gas supply line 40 that introduces a purge gas into the burner line 20 via a purge valve 41, and a control unit 50 that controls the opening and closing of the purge valve 41 based on the flow rate of the carrier gas measured by the carrier gas flow control unit 13a, and when the flow rate of the carrier gas is equal to or greater than a predetermined value, the purge valve 41 is closed, and when the flow rate of the carrier gas is less than the predetermined value, the purge valve 41 is opened.

[0053] In this way, when a gas of a flammable organosilicon compound is used, by detecting a decrease in the flow rate of the carrier gas and opening the purge valve, it is possible to prevent the flow rate of the gas at the outlet 60a of the burner 60 from decreasing below the combustion rate of the premixed gas Gm at the outlet 60a of the burner 60. Therefore, it is possible to suppress the occurrence of flashback in the burner 60.

[0054] In addition, when the flow rate of the carrier gas is equal to or greater than a predetermined value, the burner valve 21, which is provided in the burner line 20 and is provided between the vaporization unit 14 that vaporizes the organic silicon compound and the purge valve 41, is opened, and when the flow rate of the carrier gas is less than the predetermined value, the burner valve 21 is closed. This makes it possible to prevent the premixed gas Gm containing flammable raw material gas from flowing into the burner 60 when conditions are favorable for flashback, thereby more reliably preventing the occurrence of flashback.

[0055] The predetermined value may be the flow rate of the carrier gas when the flow velocity of the premixed gas Gm discharged from the burner 60 becomes 19 m / sec when the purge valve 41 is closed. Furthermore, the flow rate of the purge gas may be controlled by a purge gas flow rate control unit 42 provided in the purge gas supply line 40 so that the flow velocity of the gas discharged from the burner 60 is 19 m / sec or more. This makes the burner nozzle flow velocity 19 m / sec or more, which is greater than the combustion velocity of the premixed gas Gm at the outlet 60a of the burner 60, thereby making it possible to suppress the occurrence of flashback.

[0056] Moreover, the predetermined value is a value that is 2% less than the set value of the flow rate of the carrier gas, and the set value is the flow rate of the carrier gas when the flow velocity of the premixed gas Gm is 19 m / sec or more. This allows the control unit 50 to determine whether or not an abnormality has occurred based on the predetermined value. If it is determined that an abnormality has occurred, the control unit 50 can quickly stop the manufacturing equipment, thereby reliably preventing the manufacturing equipment from being damaged by flashback.

[0057] The porous glass microparticle manufacturing apparatus of this embodiment includes a burner 60 that discharges a premixed gas Gm containing an organosilicon compound gas and oxygen into a flame Fa to generate glass microparticles, a burner line 20 that transports the organosilicon compound gas together with a carrier gas to the burner 60, a carrier gas supply line 13 having a carrier gas flow rate control unit 13a that measures the flow rate of the carrier gas, and a raw material supply line 10 that has a vaporization unit 14 that vaporizes the liquid organosilicon compound mixed with the carrier gas and is connected to the burner 60 by the burner line 20, a purge gas supply line 40 that introduces a purge gas into the burner line 20 via a purge valve 41, and a control unit 50 that controls the opening and closing of the purge valve 41 based on the flow rate of the carrier gas measured by the carrier gas flow rate control unit 13a, and the control unit 50 closes the purge valve 41 when the flow rate of the carrier gas is equal to or higher than a predetermined value, and opens the purge valve 41 when the flow rate of the carrier gas is less than the predetermined value.

[0058] Furthermore, by subjecting the porous glass particles obtained as described above to a sintering process or the like to produce an optical fiber preform, it is possible to provide a high-quality optical fiber preform that is free of abnormalities.

[0059] The above embodiment will be described below using specific examples, but the present invention is not limited to the following examples.

[0060] Under the conditions shown in Experiment Nos. 1 to 9 in Table 1, porous glass particles were produced using a production apparatus having the supply device shown in FIG.

[0061] [Table 1]

[0062] As shown in Table 1, Experimental Numbers 1 to 9 correspond to Examples 1 and 2, Comparative Examples 1 and 2, Example 3, Comparative Example 3, and Examples 4 to 6, respectively. The experimental conditions are described in detail below. The following description includes cases where the carrier gas supplied from the carrier gas supply line 13 is oxygen and cases where oxygen is supplied from the oxygen supply line 15. In the following, in order to distinguish between the two oxygens supplied from different supply lines, the oxygen supplied from the carrier gas supply line 13 and used as a carrier gas is called carrier gas oxygen, and the oxygen supplied from the oxygen supply line 15 is called premixed oxygen.

[0063] Example 1 D4 was used as the raw material, and the flow rate of D4 was 16 g / min. Ar was used as the carrier gas, and the flow rate of Ar was 4 slm. The flow rate of oxygen was 7.0 slm. The flow rate of the premixed gas calculated from formula (1) was 21.7 m / sec. In Example 1, no backfire occurred, and no soot was attached to the soot.

[0064] Example 2 The conditions were the same as in Example 1, except that the flow rate of Ar was 3.5 slm. The flow rate of the premixed gas calculated from formula (1) was 20.8 m / sec. In Example 2, no flashback occurred, and no soot was attached to the soot.

[0065] Comparative Example 1 The conditions were the same as in Example 1, except that the flow rate of Ar was 2 slm. The flow rate of the premixed gas calculated from formula (1) was 18.1 m / sec. In Comparative Example 1, the occurrence of flashback was observed.

[0066] Comparative Example 2 The flow rate of Ar was 8 slm, and the flow rate of oxygen was 0 slm. Other points were the same as in Example 1. The flow rate of the premixed gas calculated from the formula (1) was 16.4 m / sec. In Comparative Example 2, although no flashback was observed, adhesion of soot to the soot was observed.

[0067] Example 3 The flow rate of D4 was 25g / min, the flow rate of carrier gas oxygen was 3.5slm, and the flow rate of premixed oxygen was 6.5slm. The flow rate of premixed gas calculated by formula (1) was 22.1m / sec. In Example 3, no flashback occurred, and no soot was attached to the soot.

[0068] Comparative Example 3 The conditions were the same as in Example 3, except that the flow rate of the premixed oxygen was 3.5 slm. The flow rate of the premixed gas calculated from formula (1) was 16.5 m / sec. In Comparative Example 3, the occurrence of flashback was observed.

[0069] Example 4 The flow rate of D4 was 25g / min, Ar was used as a carrier gas, the flow rate of Ar was 3slm, and the flow rate of premixed oxygen was 7.0slm. The flow rate of the premixed gas calculated from formula (1) was 22.1m / sec. In Example 4, no backfire occurred, and no soot was attached to the soot.

[0070] Example 5 The flow rate of D4 was 44g / min, the flow rate of carrier gas oxygen was 3.5slm, and the flow rate of premixed oxygen was 14.1slm. The flow rate of premixed gas calculated by formula (1) was 38.9m / sec. In Example 5, no flashback occurred, and no soot was attached to the soot.

[0071] Example 6 The flow rate of D4 was 20g / min, the carrier gas was Ar and oxygen, and the flow rate of each was 2slm, and the flow rate of premixed oxygen was 6.0slm. The flow rate of the premixed gas calculated from formula (1) was 21.4m / sec. In Example 6, no flashback occurred and no soot was attached to the soot.

[0072] Example 7 When the generation of glass particles was continued under the conditions of experiment number 1 in Table 1, the flow rate of Ar decreased from 4 slm to 3.5 slm. The control unit 50 detected that the flow rate of the carrier gas had changed by 2% or more, transmitted a flow rate abnormality signal, and changed the open / close state of each valve to stop the deposition of soot. More specifically, the burner valve 21 was closed and the vent valve 31 was opened to change from the state shown in FIG. 1 to the state shown in FIG. 2, and the premixed gas Gm was discharged while the purge valve 41 was opened to supply purge gas to the burner 60. Furthermore, the air valves for supplying D4, Ar, and oxygen were closed, and the manufacturing equipment was stopped. From the time when a change in the flow rate of the carrier gas of a predetermined amount or more was detected until the manufacturing equipment was stopped, no backfire occurred, and the manufacturing equipment could be stopped without causing damage due to backfire.

[0073] Comparative Example 4 In Example 7, soot deposition continued even after the flow rate of the carrier gas changed by 2% or more. The flow rate of Ar continued to decrease, causing flashback, and damage was observed in the burner of the production equipment.

[0074] Comparative Example 5 When the production of glass particles was continued under the conditions of Experiment No. 1 in Table 1, the flow rate of Ar decreased from 4 slm to 3.5 slm. The control unit detected that the flow rate had changed by 2% or more, and closed the burner valve 21 and opened the vent valve 31. However, the purge valve 41 was kept closed. That is, in Example 7, the manufacturing apparatus was stopped while purge gas was flowing into the burner, whereas in Comparative Example 5, the manufacturing apparatus was stopped without flowing purge gas into the burner. After the shutdown, white soot was confirmed in the tube between the burner and the second valve of the burner line.

[0075] As described above, the results of Comparative Examples 1 and 3 show that when condition 2 is satisfied, the flow rate of the premixed gas is lower than the combustion rate of the premixed gas, making flashback more likely to occur. In Comparative Example 2, although the flow rate of the premixed gas satisfied condition 2, flashback did not occur. This is because the premixed gas does not contain oxygen, and the oxygen required for burning the raw materials is insufficient, resulting in incomplete combustion, and adhesion of soot to the soot was observed. From the results of Comparative Example 4, it is considered that when condition 1 is satisfied, an abnormality that is unlikely to be resolved even if soot accumulation is continued, such as pipe clogging due to gel, occurs, and further deterioration of conditions occurs, such as an increase in the amount of gel accumulation due to continued production, causing flashback. In contrast, in Examples 1 to 7, soot deposition was carried out under conditions that did not satisfy Condition 1 or 2, and therefore the occurrence of flashback could be suppressed. Furthermore, compared to Comparative Example 5, in which purge gas was not flowed through the burner when the manufacturing equipment was shut down, in Example 7, when conditions 1 or 2 were not satisfied, flammable gas was discharged from the burner and then the manufacturing equipment was shut down, thereby suppressing the occurrence of flashback.

[0076] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0077] For example, in the above embodiment, the case where an organosilicon compound is used as the raw material for the glass particles has been described, but the above embodiment can also be suitably applied to the case where other flammable raw materials are used.

[0078] Furthermore, the configuration of the supplying device 1 may be changed as appropriate. 4, oxygen supply line 15 may be connected to the upstream side of vaporization unit 14. In this case, carrier gas supply line 13 and oxygen supply line 15 may be joined together and then connected to raw material supply line 10 between raw material flow rate control unit 12 and vaporization unit 14. Furthermore, oxygen may be supplied from carrier gas supply line 13 to raw material supply line 10 together with the carrier gas. In this way, it is sufficient that the oxygen is mixed into the raw material gas at least upstream of the burner 60 .

[0079] Although flow control units 12, 13a, 15a, and 42 have an MFC and adjust the flow rate of each material by the MFC, the device for adjusting the flow rate is not limited to an MFC and may be other flow rate adjustment devices.

[0080] In the above-mentioned condition 1, the reason for the condition where the carrier gas flow rate is 2% or more lower than the set value for one second or more is as follows. In the measurement results of a general MFC (for example, an MFC with a full scale of 20 slm), a deviation of less than ±2% from the set value may be observed even when the flow rate is constant, and it is determined that if the deviation in the flow rate is less than ±2%, no abnormality has occurred and the product has been manufactured under normal conditions. In addition, the reason for the requirement that the state where the value is 2% or more lower continues for more than one second is that flow rate changes that occur in less than one second are likely to be noise, and therefore noise-causing flow rate changes must be excluded in the determination.

[0081] In this way, condition 1 is determined to eliminate errors and noise in the measurement by the MFC. Therefore, when the method of measuring the flow rate of the carrier gas is changed, condition 1 may be appropriately changed in consideration of errors and noise in the changed method of measuring the flow rate. Also, the control unit 50 may transmit a stop signal when a tendency for the flow rate of the carrier gas to decrease is detected. For example, the carrier gas flow rate may be measured at regular intervals, and it may be determined that an abnormality has occurred when the rate of decrease in the flow rate of the carrier gas per unit time exceeds a predetermined threshold.

[0082] Further, in the method for determining the flow rate of the carrier gas based on (A) and (B) described above, when the burner nozzle flow velocity of the premixed gas calculated by Equation (1) is less than 19 m / s, an example was described in which the flow rate of the carrier gas is increased to make the burner nozzle flow velocity 19 m / s or more. However, the gas added when the burner nozzle flow velocity is less than 19 m / s is not limited to the carrier gas. For example, the flow rate of the purge gas may be increased so that the total flow velocity of the premixed gas Gm and the purge gas discharged from the outlet 60a of the burner 60 is 19 m / s or more. In this case, the purge valve 41 is opened so that the required flow rate of the purge gas that compensates for the insufficient flow rate flows, and the flow rate of the purge gas is adjusted by the control unit 50 and the purge gas flow rate control unit 42. Note that both the carrier gas and the purge gas may be used to compensate for the shortage of the burner nozzle flow velocity.

[0083] Further, when the determination unit of the control unit 50 determines that the above-described condition 1 or 2 is satisfied, the purge valve 41 is opened from the state shown in FIG. 1, and the purge gas is added to the premixed gas Gm flowing into the burner 60, and the burner nozzle flow velocity is increased, thereby suppressing the occurrence of flashback. In this case, regardless of the opening and closing states of the raw material valve 11, the burner valve 21, and the vent valve 31, the purge valve 41 can be opened immediately after an abnormality is detected, so that the occurrence of flashback can be suppressed, and thus the response speed to an abnormality in the burner nozzle flow velocity can be increased. Therefore, even when an abnormality occurs in which the risk of flashback suddenly increases, the occurrence of flashback can be reliably prevented.

[0084] In addition, within the scope not departing from the gist of the present invention, it is possible to appropriately replace the components in the above-described embodiments with well-known components, and the above-described embodiments and modification examples may be appropriately combined.

Explanation of Reference Numerals

[0085] 1...Supply device 10...Raw material supply line 13...Carrier gas supply line 13a...Carrier gas flow rate control section 14...Vaporization unit 20...Burner line 21...Burner valve 40...Purge gas supply line 41...Purge valve 42...Purge gas flow rate control section 50...Control section 60...Burner 60a...Outlet Gm...Premixed gas

Claims

1. a burner for discharging a premixed gas containing an organosilicon compound gas and oxygen into a flame to generate glass particles; a burner line for transporting the organosilicon compound gas together with a carrier gas to the burner; A carrier gas flow rate control unit that measures a flow rate of the carrier gas; a purge gas supply line for introducing a purge gas into the burner line through a purge valve; a control unit that controls opening and closing of the purge valve based on the flow rate of the carrier gas measured by the carrier gas flow rate control unit; A method for producing porous glass particles using a production apparatus comprising: When the flow rate of the carrier gas is equal to or greater than a predetermined value, the purge valve is closed, and when the flow rate of the carrier gas is less than the predetermined value, the purge valve is opened. A method for producing porous glass particles.

2. When the flow rate of the carrier gas is equal to or greater than the predetermined value, A burner valve provided in the burner line and between a vaporization unit for vaporizing the organosilicon compound and the purge valve is opened; When the flow rate of the carrier gas is less than the predetermined value, the burner valve is closed. The method for producing the porous glass particles according to claim 1.

3. the predetermined value is a flow rate of the carrier gas when the flow velocity of the premixed gas discharged from the burner becomes 19 m / sec when the purge valve is closed; The method for producing porous glass particles according to claim 1 or 2.

4. A flow rate of the purge gas is controlled by a purge gas flow rate control unit provided in the purge gas supply line so that the flow velocity of the gas discharged from the burner is 19 m / sec or more. The method for producing the porous glass particles according to claim 1 or 2.

5. the predetermined value is 2% less than the set value of the flow rate of the carrier gas; The set value is a flow rate of the carrier gas when the flow velocity of the premixed gas is 19 m / sec or more. The method for producing the porous glass particles according to claim 1 or 2.

6. a burner for discharging a premixed gas containing an organosilicon compound gas and oxygen into a flame to generate glass particles; a burner line for transporting the organosilicon compound gas together with a carrier gas to the burner; a carrier gas supply line having a carrier gas flow rate control unit for measuring a flow rate of the carrier gas, and a vaporization unit for vaporizing the organosilicon compound in a liquid state mixed with the carrier gas, the raw material supply line being connected to the burner by a burner line; a purge gas supply line for introducing a purge gas into the burner line through a purge valve; a control unit that controls opening and closing of the purge valve based on the flow rate of the carrier gas measured by the carrier gas flow rate control unit, The control unit closes the purge valve when the flow rate of the carrier gas is equal to or greater than a predetermined value, and opens the purge valve when the flow rate of the carrier gas is less than the predetermined value. An apparatus for manufacturing porous glass particles.

7. 3. A method for producing an optical fiber preform, comprising the step of sintering the porous glass particles obtained by the method according to claim 1.

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