JP5304031B2 - Porous glass base material dehydration sintering apparatus and exhaust control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent exhaust defect, quality defect and the corrosion of ambient equipment, to prevent the reduction of operation rate due to the exchange of the exhaust pipe and to reduce the maintenance cost by preventing clogging of an exhaust pipe, the entrainment of the air and the indoor leakage of a dehydrated process gas. <P>SOLUTION: In a dehydration sintering apparatus 100 of the porous glass preform 1 for supplying a process gas for dehydration or fluorine addition to the porous glass preform to a heating furnace 3 and heating, an exhaust pathway 5 for introducing an exhaust gas in the heating furnace 3 to the outside of the furnace is constituted of two lines of a first pathway 61 through which an exhaust gas containing a suspended substance flows when the process gas producing the suspended substance by the reaction with water content or the like in the air is passed and a second pathway 63 for passing the exhaust gas when the process gas producing no suspended substance or the exhaust gas when a plant is under the standby, wherein the first and the second pathways 61, 63 are opened or closed corresponding to the process gas. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a dehydration sintering apparatus for a porous glass base material that heats the porous glass base material in a heating furnace by supplying a process gas for dehydration and fluorine addition to the porous glass base material, and an exhaust control method thereof.

The glass base material of the silica-based glass optical fiber is manufactured by subjecting a glass fine particle deposit body (porous glass base material) to heat treatment, dehydration and transparent vitrification. In the heat treatment step, an atmospheric gas is selected according to the heat treatment content such as dehydration and transparent vitrification. For example, the porous glass base material is dehydrated using He and O ₂ and dehydrating gas (chlorine gas, thionyl chloride, fluorosilane, etc.) in the first heat treatment, and then He and O ₂ or He in the second heat treatment. A cylindrical glass rod called a preform is made by vitrification into a transparent vitreous atmosphere. Thereafter, the preform is heated and drawn while being melted to finish an optical fiber having a predetermined thickness.

As a pretreatment for preforming, transparent glass is obtained by performing dehydration sintering by bringing a heated porous glass base material into contact with a gas such as SiCl ₄ or SiF ₄ as a dehydrating agent. Thus, similar dimensions and refractive index are given to the core and clad of the optical fiber to be finally finished. FIG. 3 shows an example of an apparatus for dehydrating and sintering a porous glass base material used for manufacturing such a preform (see, for example, Patent Document 1).

  The dehydration and sintering apparatus 500 described in Patent Document 1 includes a heating furnace 501 and an exhaust gas treatment apparatus 505 equipped with an exhaust pipe 503 connected to the heating furnace 501. The heating furnace 501 has a cylindrical furnace core tube 507 whose axis is directed in the vertical direction, a furnace core tube upper cover 509 that covers the upper part of the furnace core tube 507, and a center of the furnace core tube upper cover 509 that can be moved up and down. A support rod 513 for suspending the porous glass preform 511 in the furnace core tube 507, a ring heater 515 for heating the porous glass preform 511 from the outer periphery of the furnace core tube 507, the ring heater 515, and the furnace core tube And a furnace casing 517 covering the periphery of 507.

The dehydration and sintering apparatus 500 supplies Cl ₂ , SiCl ₄ , SiF _4, etc. in the form of gas from the lower part of the furnace core tube 507 into the furnace core tube 507 at a predetermined pressure, as indicated by an arrow G in the figure. These gases are used for dehydration treatment and refractive index adjustment. A gas containing Si such as SiCl ₄ gas or SiF ₄ gas reacts with moisture in the furnace core tube 507 to generate SiO ₂ soot. . This SiO ₂ soot accumulates in the low temperature part of the furnace core tube 507 or floats in the exhaust gas and is discharged from the exhaust pipe 503 to the exhaust gas treatment device 505.

  The exhaust gas processing device 505 includes an exhaust pipe 503 that guides excess gas in the furnace core tube 507 to the outside of the heating furnace 501 as exhaust gas, and a gas processing means 515 that collects and processes the exhaust gas discharged from the exhaust pipe 503. I have. The gas processing means 515 has a suction fan 519 for sucking the exhaust gas in order to efficiently recover the exhaust gas.

JP 2003-246628 A

However, in the sintering furnace using a Si-based process gas having different properties and Cl ₂ gas such as a gas of SiF _4, SiCl _4, when evacuating the SiF _4, SiCl ₄ gas in the furnace core tube, the moisture in the air By reacting, SiO ₂ (silica) which is a suspended substance in the exhaust gas is generated. This SiO ₂ is also generated by the reaction of moisture in the air drawn into the furnace core tube 507 with the suction pressure of the exhaust gas from the insertion hole 521 through which the support rod 513 is inserted, and the SiCl ₄ gas or SiF ₄ gas. It is thought. The generated SiO ₂ accumulates in the exhaust pipe 503 and causes the exhaust pipe to be blocked, resulting in exhaust failure. When exhaust becomes poor, the furnace core tube internal pressure becomes unstable. In addition, if the dehydration process gas leaks into the equipment installation chamber, the peripheral equipment is corroded and the human body is affected. The previously closed exhaust pipe 503 is cutting and replacing the closed portion. For this reason, the operating rate declined by exchanging the exhaust pipe 503, and the repair cost also increased.
The present invention has been made in view of the above situation, and provides a dehydration sintering apparatus for a porous glass base material that prevents clogging of the exhaust pipe and does not cause indoor leakage of the dehydration process gas, and an exhaust control method therefor, The purpose is to prevent exhaustion defects, quality defects, and corrosion of peripheral equipment, to prevent a reduction in operating rate due to exhaust pipe replacement, and to reduce repair costs.

The above object of the present invention is achieved by the following configuration.
(1) A dehydration sintering apparatus for a porous glass base material that heats the porous glass base material in a heating furnace by supplying a process gas for dehydration or fluorine addition to the porous glass base material,
An exhaust path for guiding exhaust gas in the heating furnace to the outside of the furnace,
A first path for flowing an exhaust gas containing the suspended solid when flowing the process gas that reacts with moisture in the air to generate the suspended solid;
The exhaust gas when flowing the process gas that does not generate the suspended matter, or a second path for flowing exhaust gas during standby of equipment, and two systems,
An intake passage for adjusting the furnace pressure is connected only to the second passage,
An apparatus for dehydration and sintering of a porous glass base material, wherein the first and second paths are opened and closed according to the type of the process gas.

According to this porous glass base material dehydration and sintering apparatus, an exhaust line (first path) dedicated to SiF ₄ and SiCl ₄ gas is provided to prevent reaction to SiO ₂ as an exhaust line that does not take in air such as excess air. doing. In addition, when Cl _{2 is} added to the heating furnace or when the equipment is on standby, switching to the other exhaust line (second path) prevents the air from entering the SiF ₄ and SiCl ₄ lines (first path). The reaction to ₂ can also be suppressed. By preventing the SiF ₄ and SiCl ₄ gas from the heating furnace from mixing with air (moisture), an exhaust environment in which SiO ₂ is not generated is formed, and the piping is not blocked.
Furthermore, the amount of surplus air introduced into the second path is controlled by opening and closing the intake path, and fine adjustment of the heating furnace pressure, which cannot be performed by the rotation control of the suction fan provided downstream of the exhaust path, becomes possible. The first passage is not provided with an intake passage, and the internal pressure of the heating furnace can be finely adjusted while preventing reaction to SiO ₂ .

(2) The porous structure according to (1), wherein an opening / closing valve is provided in each of the first and second paths, and the opening degree of the opening / closing valve is controlled according to the internal pressure of the heating furnace. Glass base material dehydration and sintering equipment.

  According to this porous glass base material dehydration and sintering apparatus, the first and second paths can be switched by individually controlling the opening degrees of the on-off valves provided in the first and second paths. Can be switched, and the exhaust amount of the first and second paths can be gradually decreased and increased.

(3) A washing tower is connected downstream of the first path,
The porous glass preform dehydration and sintering apparatus according to (1) or (2), wherein an electric dust collector is interposed between the on-off valve and the washing tower.

According to this porous glass base material dehydrating and sintering apparatus, in the exhaust pipe used for the process gas that reacts with moisture in the air to generate SiO ₂ , that is, in the first path, the exhaust gas is discharged from the electric dust collector. After removing SiO ₂ , neutralization is performed in a washing tower.

(4) An exhaust control method for a dehydration and sintering apparatus according to any one of (1) to (3),
An exhaust control method for a dehydration and sintering apparatus, characterized in that, when the first and second paths are switched, the switching is performed after an exhaust state occurs in both paths.

  According to the exhaust control method of the dehydration and sintering apparatus, the moment when both the first and second paths are closed can be eliminated. This can prevent the furnace core tube internal pressure from becoming unstable or prevent the exhaust gas from leaking indoors when there is an abnormality in the on-off valve.

(5) An exhaust control method for a dehydration sintering apparatus according to any one of (1) to (3),
When it is detected that the internal pressure of the heating furnace is a pressure target value and the opening / closing valve provided in the first path is detected to be opened, supply of a process gas for generating the floating substance in the heating furnace is started. An exhaust gas control method for a dehydration sintering apparatus.

According to the exhaust control method of this dehydration sintering apparatus, it is possible to avoid erroneous supply of process gas in the event of insufficient process environment when the pressure gauge or the on-off valve breaks down at the start of the dehydration sintering process. Even if the exhaust system component fails due to corrosive gas, leakage of SiF ₄ and SiCl ₄ gas from the heating furnace (upper lid of the furnace core tube) can be prevented.

(6) The exhaust control method for the dehydration and sintering apparatus according to any one of (1) to (3),
Exhaust control of the dehydration sintering apparatus characterized in that the on-off valve of the second path is opened when the on-off valve provided in the first path is open and the exhaust pressure of the first path becomes close to zero. Method.

According to the exhaust control method of this dehydration and sintering apparatus, when exhaust abnormality occurs in the first path due to the accumulation of suspended solids, alternative exhaust by the second path is possible, and SiF ₄ and SiCl ₄ gas in the heating furnace Leakage due to positive pressure can be prevented.

(7) An exhaust control method for a dehydration sintering apparatus according to any one of (1) to (3),
An exhaust control method for a dehydration and sintering apparatus, wherein a valve opening degree of an on-off valve provided in each of the first and second paths is controlled to 2.5% or more.

According to the exhaust control method of this dehydration and sintering apparatus, it is possible to prevent the on-off valve from being erroneously controlled and fully closed due to a pressure gauge failure during the dehydration and sintering process. It is possible to reduce the burden on the exhaust system parts due to the exhaust path being fully closed and pressure fluctuations. Leakage of SiF ₄ and SiCl ₄ gas from the heating furnace (the upper lid of the furnace core tube) due to the positive pressure in the heating furnace can also be prevented.

According to the dehydration and sintering apparatus for a porous glass base material according to the present invention, a process gas (SiF ₄ , SiCl ₄ gas, etc.) that reacts with moisture or the like to generate a suspended substance flows through the exhaust path. This system consists of two systems: a first path for flowing exhaust gas, and a second path for flowing exhaust gas when a process gas (such as Cl ₂ -based gas) that does not generate suspended substances is flowing, or exhaust gas that is waiting for equipment. 1. Since the second path is opened and closed according to the process gas to be flown, the exhaust gas when Si containing gas such as SiF ₄ and SiCl ₄ is flowing is separated and exhausted through an independent path. Air can be prevented from being involved. As a result, the exhaust gas containing Si does not react with moisture in the air, so that exhaust failure due to clogging of the exhaust pipe can be prevented, quality failure due to air entrainment, and peripheral equipment due to indoor leakage of dehydrated process gas can be prevented. Corrosion can be prevented. In addition, it is possible to prevent a reduction in operating rate due to replacement of the exhaust pipe, and to reduce repair costs.

  According to the exhaust control method of the dehydration and sintering apparatus according to the present invention, when switching between the first and second paths, the switching is performed after the exhaust state occurs in both paths, and therefore the pressure at which both paths are closed. The burden on exhaust system parts (exhaust path, on-off valve, suction fan, etc.) due to fluctuations can be reduced.

Preferred embodiments of a porous glass base material dehydration and sintering apparatus and its exhaust control method according to the present invention will be described below with reference to the drawings.
In this specification, the distinction between “process gas”, “atmosphere gas”, “pressure adjusting gas”, and “seal gas” is defined as follows. “Process gas”: Gas used for the process. SiCl ₄ , SiF ₄ , Cl ₂ etc. “Atmosphere gas”: Gas that flows during each process, including process gas. Including He, N _{2 and the} like. “Pressure adjusting gas”: A gas used for adjusting the furnace pressure among the atmospheric gases. In this embodiment, He. “Sealing gas”: Gas used for sealing among atmospheric gases. N _{2 in} this embodiment.
FIG. 1 is a block diagram of a dehydration and sintering apparatus according to the present invention.
The dehydration and sintering apparatus 100 according to the present embodiment includes a heating furnace 3 that supplies a process gas for dehydration and fluorine addition to heat-treat the glass fine particle deposit (porous glass base material) 1, and the heating furnace 3. And an exhaust device 7 having an exhaust path 5 for guiding the exhaust gas to the outside of the furnace.

  The heating furnace 3 includes a cylindrical core tube 9 arranged in a vertical shape and a cylindrical heater 11 serving as a heating source arranged on the outer peripheral side of the core tube 9. The heater 11 is made of carbon, and a heat insulating material 13 is disposed around the heater 11. Furthermore, the core tube 9 and the heat insulating material 13 are covered with a furnace body 15 that forms the outer shell of the furnace.

  The core tube 9 is made of quartz, and the temperature of the core tube 9 is raised mainly by a portion of the core tube 9 located inside the heater 11 due to heat generated by the heater 11. And the porous glass preform | base_material 1 can be accommodated in the in-furnace space 17 inside the furnace core tube 9, and can be heated. The porous glass base material 1 is integrally formed with the support bar 19 so as to be suspended by the support bar 19, and can be moved up and down by an elevating device 21 to which the support bar 19 is attached. Further, the elevating device 21 can also rotate the porous glass base material 1 together with the support rod 19 around its axis. Further, an upper lid 23 for opening and closing the opening at the time of introduction and removal of the porous glass base material 1 can be attached to and detached from the upper end of the core tube 9, and it can be attached to the lower end of the core tube 9 as appropriate. A possible lower lid 25 is provided.

The dehydration and sintering apparatus 100 also includes a gas supply control device 27 that supplies a gas used when the porous glass base material 1 is heat-treated and controls the supply amount. The gas supply control device 27 supplies the atmospheric gas into the core tube 9 from the atmospheric gas introduction unit 29 provided near the lower end of the core tube 9. As the atmospheric gas, He and O ₂ and dehydrated gas (chlorine gas, thionyl chloride, fluorosilane, etc.) are used during dehydration, and only He and O ₂ or He are used during transparent vitrification. Alternatively, after dehydration, a gas containing SiF ₄ or the like is used as the atmospheric gas for adjusting the refractive index of the glass base material.

  Further, a reactor core pressure monitor 31 is provided in the vicinity of the upper end of the reactor core tube 9 so that the pressure in the reactor space 17 can be monitored in a timely manner. Data measured by the reactor core pressure monitor 31 is sent to the gas supply control device 27 and used to adjust the supply amount of the atmospheric gas to the atmospheric gas introduction unit 29.

  The atmospheric gas in the furnace space 17 is exhausted to the exhaust device 7 through the space provided in the upper lid 23. The upper lid 23 covers the support rod insertion port 35 formed in the approximate center of the lid portion 33 and the support rod 19 penetrating the support rod insertion port 35 on the upper surface of the lid portion 33 facing the furnace space 17. A short cylindrical pressure regulation chamber 37 is provided. A side of the pressure regulation chamber 37 is provided with a regulation gas introduction section 39 for introducing a pressure regulation gas, and the pressure regulation gas from the gas supply control device 27 passes through the regulation gas introduction section 39 and the pressure regulation chamber 37. Supplied to. For example, He gas may be used as the pressure adjusting gas.

  Further, the upper lid 23 is short so that the upper surface of the pressure adjustment chamber 37 covers the support rod insertion port 41 provided on the upper wall of the pressure adjustment chamber 37 and the support rod 19 through which the support rod insertion port 41 is inserted. A cylindrical exhaust chamber 43 is provided. An exhaust part 45 for exhausting the gas in the exhaust chamber 43 is provided on the side of the exhaust chamber 43, and the gas exhausted from the exhaust chamber 43 is exhausted to the exhaust device 7 through the exhaust part 45. The exhaust device 7 cleans the exhausted gas.

  In the heating furnace 3, since the exhaust chamber 43 is provided on the upper surface of the pressure adjustment chamber 37, even when the exhaust pressure of the exhaust device 7 fluctuates, the fluctuation of the pressure is adjusted by the pressure adjustment gas in the pressure adjustment chamber 37. Thus, the influence of the pressure fluctuation on the furnace internal space 17 is suppressed to a low level.

  An exhaust pressure monitor 47 is provided at the side of the exhaust chamber 43 so that the exhaust pressure to the exhaust device 7 can be monitored by monitoring the pressure in the exhaust chamber 43 in a timely manner. Data measured by the exhaust pressure monitor 47 is sent to the gas supply control device 27 to adjust the supply amount of the pressure adjusting gas supplied to the pressure adjusting chamber 37 in accordance with the measured fluctuation of the exhaust pressure. Used for

A short cylindrical seal chamber 51 is provided on the upper surface of the exhaust chamber 43 so as to cover the support rod insertion port 49 and the support rod 19 through which the support rod insertion port 49 is inserted. A seal gas introduction portion 53 for introducing a seal gas is provided at a side portion of the seal chamber 51, and the seal gas from the gas supply control device 27 is supplied to the seal chamber 51 through the seal gas introduction portion 53. The seal gas supplied to the seal chamber 51 stays in the seal chamber 51, but a part of the seal gas flows out of the apparatus through the support rod insertion port 55 on the upper wall of the seal chamber 51 or exhausts through the support rod insertion port 49. Flows into chamber 43. By introducing the seal gas, it is possible to prevent the outside air from getting into the furnace and the process gas from leaking out of the furnace. An inert gas such as N ₂ gas may be used as the seal gas.

In the present embodiment, the exhaust path 5 is composed of two systems, a first path 61 and a second path 63. The first path 61 flows exhaust gas containing suspended substances when a process gas (SiF ₄ , SiCl ₄ gas) that reacts with moisture in the air to generate suspended substances is flowing. On the other hand, the second path 63 flows exhaust gas when a process gas (Cl ₂ gas) that does not generate suspended substances is flowing, or exhaust gas during equipment standby.

  Motor opening / closing valves 65 and 67 are provided in the first and second paths 61 and 63, respectively. The opening and closing timings of the opening and closing valves 65 and 67 are controlled by a control means (PLC) 69. A pressure gauge 71 for detecting the pressure in the exhaust part 45 and a pressure gauge 73 for detecting the internal pressure of the core tube 9 are connected to the control means 69. These pressure gauges 71 and 73 send the detected pressure value to the control means 69 as a detection signal. It is possible.

  In the exhaust path 5, on-off valves 65 and 67 are provided in the first and second paths 61 and 63, respectively, and the opening degrees of the on-off valves 65 and 67 are controlled according to the internal pressure of the core tube 9. By individually controlling the valve opening degree of the on-off valves 65 and 67 provided in the first and second paths 61 and 63, the first and second paths 61 and 63 can be switched. The first and second paths 61 and 63 can be switched to gradually decrease or increase the exhaust amount.

Further, the control means 69 can switch the first and second paths 61 and 63 by controlling the on-off valves 65 and 67 according to the type of process gas to be used. When the SiF ₄ or SiCl ₄ gas is exhausted, the first path 61 is switched, and when the Cl ₂ gas is exhausted, the second path 63 is switched. The type of process gas can be determined by sending a gas type signal from the gas supply control device 27 to the control means 69. In addition, the gas type may be manually input to the control means 69.

  Furthermore, the control means 69 provided in the exhaust device 7 controls the on-off valves 65 and 67 so that the internal pressure of the core tube 9 is set to the pressure target value. The pressure gauges 71 and 73 detect the internal pressure of the heating furnace and the pressure of the exhaust part 45, and the detected value is given to the control means 69, so that the detected value becomes a pressure target value given in advance. The opening and closing (valve opening, opening / closing timing) of 65 and 67 is feedback-controlled, and as a result, the internal pressure of the core tube 9 is controlled automatically to the pressure target value.

  A cleaning tower 77 is connected downstream of the second path 63, and the cleaning tower 77 neutralizes the exhaust gas from the exhaust path 5. In the figure, reference numeral 79 denotes a water circulation pump. A suction fan 81 is connected downstream of the cleaning tower 77, and the suction fan 81 sucks the exhaust gas in the exhaust path 5 through the cleaning tower 77. Exhaust gas in the exhaust path 5 is sucked into the cleaning tower 77, passed through the cleaning water dropping atmosphere, cleaned, and exhausted from the suction fan 81 to the outside of the exhaust path.

An intake passage 83 that adjusts the internal pressure of the core tube 9 is connected to the second path 63 between the on-off valve 67 and the cleaning tower 77. The exhaust path 5 controls the amount of surplus air introduced into the second path 63 by opening and closing the intake path 83, and the internal pressure of the reactor core tube 9 cannot be controlled by the rotation control of the suction fan 81 provided downstream of the exhaust path. Adjustment is possible. The first passage 61 is not provided with an intake passage, and the internal pressure of the core tube 9 can be finely adjusted while preventing reaction to SiO ₂ .

An electric dust collector 85 is inserted in the first path 61 downstream from the on-off valve 65. The exhaust side of the electric dust collector 85 is connected to a second path 63 between the intake path 83 and the cleaning tower 77. That is, the electric dust collector 85 is interposed between the on-off valve 65 and the cleaning tower 77. In the first path 61 used when supplying the process gas that generates SiO ₂ by reacting with moisture in the air, the exhaust gas is neutralized by the washing tower 77 after the SiO ₂ is removed by the electric dust collector 85. .

A method for heat-treating the porous glass base material 1 using the dehydration and sintering apparatus 100 described above to form a transparent glass base material will be described. FIG. 2 is a time chart of the dehydration and sintering process by the dehydration and sintering apparatus 100 shown in FIG.
With the top cover 23 removed from the top of the core tube 9, a support rod 19 suspending the porous glass base material 1 is attached to the lifting device 21, and the porous glass base material 1 is connected to the core tube from the upper end opening of the core tube 9. 9 is introduced. Then, the porous glass base material 1 is arranged so that the lower end portion of the porous glass base material 1 is positioned inside the portion of the core tube 9 heated by the heater 11. Next, the upper lid 23 is attached to the upper end of the core tube 9.

  In the standby state before starting the process operation, the on-off valve 65 is closed and the on-off valve 67 is opened. As the process operation starts, the closed on-off valve 65 is gradually opened. The pressure inside the core tube 9 that was the target pressure value gradually decreases. When the full open signal of the on / off valve 65 is turned on, the closing control of the on / off valve 67 in the second path 63 is started. The open / close valve 65 in the first path 61 is also fully opened and then gradually closed after the open / close valve 67.

  As described above, when the first and second paths 61 and 63 are switched, the switching is performed after the exhaust state occurs in both paths. As a result, the moment when both the first and second paths 61 and 63 are closed is eliminated, the furnace core tube internal pressure becomes unstable, or the exhaust gas leaks indoors when there is an abnormality in the on-off valve. Can be prevented.

When the opening / closing valve 65 provided in the first path 61 is detected to be open and the internal pressure of the core tube 9 is detected to be a pressure target value, a process gas (SiF ₄ , The supply of SiCl ₄ gas) is started. The supplied process gas does not flow to the second path 63 because the on-off valve 67 is closed. While the temperature of the heater 11 is raised to raise the temperature in the core tube 9, process gas (SiF ₄ , SiCl ₄ gas) is supplied into the core tube 9 from the atmosphere gas introduction unit 29 as the atmosphere gas. And in the state which filled the furnace space 17 in the furnace core tube 9 with the said atmospheric gas, the temperature of the furnace space 17 located inside the heater 11 is 1000 to 1350 degreeC (preferably 1100 to 1250 degreeC). ) And is heated for a predetermined time of about several tens of minutes for dehydration.

In the exhaust control method of the dehydration sintering apparatus 100, the pressure gauges 71 and 73 and the on-off valves 65, 65, An erroneous supply of process gas when the process environment is inadequate when 67 fails can be avoided. Thereby, even if the exhaust system parts break down due to the corrosive gas, it is possible to prevent leakage of SiF ₄ · SiCl ₄ gas from the upper lid 23 or the like.

Further, since the internal pressure of the core tube 9 is set to a pressure target value of 0 to −200 Pa and the on-off valves 65 and 67 are controlled, it is possible to achieve both prevention of leakage of SiF ₄ / SiCl ₄ gas from the upper lid 23 and improvement of quality. it can.

  Further, when the pressure target value is not reached within a predetermined time (for example, 4 min) at the start of the dehydration sintering process, an abnormal signal is issued so that the abnormality of the on-off valves 65 and 67 at the start of the dehydration sintering process can be detected. It is preferable to do.

Further, when the internal pressure of the furnace core tube 9 continues at a predetermined pressure (abnormal pressure) for a predetermined time or longer, the supply of SiF ₄ or SiCl ₄ gas is stopped so that the on-off valve abnormality during the dehydration sintering process can be detected. preferable. In this case, the opening operation of the on-off valve 67 is started. Thereby, even if the exhaust system component breaks down with the corrosive gas, the alternative exhaust by the second path 63 is enabled, and the leakage of the process gas from the core tube 9 can be prevented.

Furthermore, it is preferable to open the on-off valve 67 of the second path 63 when the on-off valve 65 provided in the first path 61 is in an open state and the exhaust pressure of the first path 61 becomes near zero. As a result, when an exhaust abnormality occurs in the first path 61 due to the accumulation of floating substances, alternative exhaust through the second path 63 is enabled, and leakage of SiF ₄ and SiCl ₄ gas in the reactor core tube 9 due to positive pressure is prevented. it can.

When the process is stopped, the opening / closing valve 67 in the second path 63 is opened. Until the opening operation of the on-off valve 67 is started, the process gas in the core tube 9 is exhausted from the first path 61 to the exhaust device 7 as exhaust gas. At this time, since the on-off valve 67 is closed, SiF ₄ and SiCl ₄ gas do not enter the second path 63. When the full open signal of the on / off valve 67 is turned on, the closing operation of the on / off valve 65 in the first path 61 is started. By closing the on-off valve 65, air (moisture) does not mix in the first path 61.

In addition, it is preferable that the valve opening degree of the on-off valves 65 and 67 provided in the first and second paths 61 and 63 is controlled to 2.5% or more. It is possible to prevent the on-off valves 65 and 67 from being erroneously controlled and fully closed due to a failure of the pressure gauges 71 and 73 during the dehydration sintering process. As a result, it is possible to reduce the burden on the exhaust system components due to a sudden pressure fluctuation that causes the exhaust path 5 to be fully closed. In addition, leakage of SiF ₄ and SiCl ₄ gas from the upper lid 23 due to the positive pressure in the furnace core tube 9 can be prevented.

As described above, the dehydration sintering apparatus 100 is provided with an exhaust line (first path 61) dedicated to SiF ₄ and SiCl ₄ gas, and prevents reaction to SiO ₂ as an exhaust line that does not take in air such as excess air. . Further, when Cl _{2 is} added to the reactor core tube 9 or when the equipment is on standby, switching to the other exhaust line (second path 63) prevents air from entering the SiF ₄ and SiCl ₄ lines (first path 61). In addition, reaction to SiO ₂ can be suppressed. By preventing the SiF ₄ and SiCl ₄ gases from the furnace core tube 9 from being mixed with air (moisture), an exhaust environment in which SiO ₂ is not generated is formed, and the piping is not blocked.

Therefore, according to the porous glass base material dehydration and sintering apparatus 100 according to the above-described embodiment, the process gas (SiF ₄ , SiCl ₄ gas) that reacts with moisture or the like to generate floating substances flows through the exhaust path 5. The first path 61 for flowing the exhaust gas when flowing, and the second path 63 for flowing the exhaust gas when flowing the process gas (Cl ₂ gas) that does not generate floating substances, or the exhaust gas during standby of the equipment Since the first and second paths are configured to open and close according to the process gas, the exhaust gas when the SiF ₄ or SiCl ₄ gas is flowing is separated and exhausted through an independent path so that air is not involved in the exhaust. Can be. As a result, exhaust failure due to clogging of the exhaust pipe can be prevented, and quality failure due to air entrainment can be prevented. Corrosion of peripheral equipment due to indoor leakage of dehydration process gas can be prevented. In addition, it is possible to prevent a reduction in operating rate due to replacement of the exhaust pipe, and to reduce repair costs.

  Further, according to the exhaust control method of the dehydration and sintering apparatus 100, when the first and second paths 61 and 63 are switched, switching is performed after an exhaust state occurs in both paths, so both paths are closed. The burden on exhaust system components (exhaust path 5, on-off valves 65 and 67, suction fan 81, etc.) due to pressure fluctuation can be reduced.

It is a block diagram of the dehydration sintering apparatus which concerns on this invention. It is a time chart of the dehydration sintering process by the dehydration sintering apparatus shown in FIG. It is a block diagram of the conventional dehydration sintering apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous glass base material 3 Heating furnace 5 Exhaust path 61 1st path 63 2nd path 65,67 On-off valve 69 Control means 77 Cleaning tower 83 Intake path 85 Electric dust collector 100 Dehydration sintering apparatus

Claims (7)

A dehydration and sintering apparatus for a porous glass base material that heats by supplying a process gas for dehydration or fluorine addition to the porous glass base material in a heating furnace,
An exhaust path for guiding exhaust gas in the heating furnace to the outside of the furnace,
A first path for flowing an exhaust gas containing the suspended solid when flowing the process gas that reacts with moisture in the air to generate the suspended solid;
The exhaust gas when flowing the process gas that does not generate the suspended matter, or a second path for flowing exhaust gas during standby of equipment, and two systems,
An intake passage for adjusting the furnace pressure is connected only to the second passage,
An apparatus for dehydration and sintering of a porous glass base material, wherein the first and second paths are opened and closed according to the type of the process gas.   2. The porous glass base material according to claim 1, wherein an opening / closing valve is provided in each of the first and second paths, and a valve opening degree of the opening / closing valve is controlled according to the pressure in the heating furnace. Dehydration and sintering equipment. A washing tower is connected downstream of the first path,
The apparatus for dehydration and sintering of a porous glass base material according to claim 1 or 2, wherein an electrostatic precipitator is interposed between the on-off valve and the washing tower. An exhaust control method for a dehydration and sintering apparatus according to any one of claims 1 to 3,
An exhaust control method for a dehydration and sintering apparatus, characterized in that, when the first and second paths are switched, the switching is performed after an exhaust state occurs in both paths. An exhaust control method for a dehydration and sintering apparatus according to any one of claims 1 to 3,
When supply of the process gas for generating the suspended solids into the heating furnace is started when the internal pressure of the heating furnace is detected to be a target value and an opening / closing valve provided in the first path is detected to be opened An exhaust gas control method for a dehydration and sintering apparatus. An exhaust control method for a dehydration and sintering apparatus according to any one of claims 1 to 3,
Exhaust control of the dehydration sintering apparatus characterized in that the on-off valve of the second path is opened when the on-off valve provided in the first path is open and the exhaust pressure of the first path becomes close to zero. Method. An exhaust control method for a dehydration and sintering apparatus according to any one of claims 1 to 3,
An exhaust control method for a dehydration and sintering apparatus, wherein a valve opening degree of an on-off valve provided in each of the first and second paths is controlled to 2.5% or more.

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