JPH09286620A - Method for supplying gaseous raw material and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which a gaseous raw material can be supplied at a stable flow rate even when some change in temp. of a raw material tank is caused and also to provide a device for the method. SOLUTION: This method comprises receiving a liquid raw material 3 of glass in a raw material tank 1 provided with a heater 2 and stably supplying the gaseous raw material 4 vaporized in the raw material tank 1 to a reactor. At this time, the liquid raw material 3 is continuously supplied to the raw material tank 1 so as to always maintain the gas volume occupied by the gaseous raw material 4 at a prescribed volume value and when the heating temp. of the raw material tank 1 is changed to cause a change in pressure inside the tank 1 whose vapor phase is occupied by the gaseous raw material 4, the volume of a closed body 6 communicated with the vapor phase of the raw material tank 1 is changed to keep the pressure inside the tank 1 constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for stably supplying a raw material gas.

[0002]

2. Description of the Related Art In order to manufacture an optical fiber, a method of forming a porous glass base material by an axial attachment method, an external attachment method, an internal attachment method or the like, and dehydrating / sintering this to draw it . In recent years, a method of continuously supplying a large amount of glass raw material has been adopted from the viewpoint of lengthening or increasing the efficiency of an optical fiber. The configuration of such a raw material supply device is shown in FIG.
As shown in, the raw material liquid 3 sent from the pipe 22 is temporarily stored in the service tank 20. Service tank 20
A pressurized gas is introduced through the supply line 21 and the raw material liquid 3 is pressure-fed to the raw material tank 1 through the pipe 23 by this gas pressure. The vaporized raw material gas 4 is sent to a glass reactor through a pipe 14 and a condenser 11 using an inert gas such as Ar as a carrier gas. The carrier gas is pressure-fed to the raw material tank 1 through the flow rate controller 12.

In order to obtain an optical fiber having a uniform structure, it is important to adjust the flow rate of the raw material gas. Therefore, conventionally, the temperature of the heater has been sufficiently controlled, and the condenser 11 and the flow control device 12 have been used. The flow rate of the raw material gas per unit time is determined by the flow rate of the carrier gas and the saturated vapor pressure in the raw material tank, that is, the temperature of the raw material gas. Therefore, theoretically, the flow rate of the raw material gas can be kept constant by keeping the flow rate of the carrier gas and the temperature of the raw material gas constant. Based on this idea, conventionally, when the temperature of the raw material tank is kept constant, or when the temperature of the raw material gas fluctuates, this temperature fluctuation is returned to the heating means through any control method to keep the raw material gas flow rate constant. I have been wondering if I can keep it. As a typical method, there is Japanese Patent Publication No. 7-72091.

[0004]

Using such a device, the temperature of the raw material tank has been controlled by proportional (P), integral (I), and derivative (D) control, but it is suppressed to 0.1 ° C. or less. Was almost impossible. However, the precision required for recent optical fibers is increasing more and more, and it is necessary to suppress the temperature control of the raw material tank to 0.1 ° C. or less. Therefore, it is an object of the present invention to provide a method and an apparatus for stably supplying a flow rate of a raw material gas even if there is a slight temperature fluctuation in the raw material tank.

[0005]

According to the method of supplying a raw material gas according to the present invention, a raw material liquid of glass is contained in a raw material tank equipped with a heater, and the raw material gas vaporized in the raw material tank is used as a reactor. A method of supplying a raw material gas to be delivered to a raw material tank, wherein the raw material liquid is continuously supplied to the raw material tank so that the volume occupied by the raw material gas is always kept at a predetermined value, and the raw material tank is heated. When the temperature fluctuates and the pressure in the tank occupied by the raw material gas changes, the volume of the sealed body communicating with the raw material tank changes, and the pressure in the tank is kept constant.

The raw material gas supply apparatus according to the present invention is a raw material tank in which a heater is attached to a raw material tank for containing a raw material liquid for glass, and the raw material gas vaporized in the raw material tank is sent to a reactor. And a mechanism for continuously supplying a raw material liquid to the raw material tank so that the volume occupied by the raw material gas is always a predetermined value. The sealed body is provided in communication with the raw material tank, and when the heating temperature of the raw material tank fluctuates and the pressure in the tank occupied by the raw material gas changes, the volume of the sealed body changes to keep the pressure in the tank constant. It is characterized by holding.

[0007]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. FIG. 1 is a diagram showing a configuration of a raw material gas supply device according to the present invention, which contains a raw material liquid 3 of glass, a raw material tank 1 having a heater 2 mounted on the outer periphery thereof, and vaporized in the raw material tank 1. A pipe 14, a condenser 11, and a carrier gas flow rate controller 12 for delivering the raw material gas 4 to the reaction device together with the carrier gas are provided. Then, a mechanism in which the raw material liquid 3 is continuously supplied to the raw material tank 1 so that the volume occupied by the raw material gas 4 is always a predetermined value: For example, the raw material gas 4 is consumed by the reaction device and the liquid of the raw material liquid 3 is consumed. When the surface is lowered, the raw material liquid 3 in the service tank 20 is automatically supplied to the raw material tank 1 through the pipe 23. Further, a variable volume sealing body 6 is connected to the raw material tank 1 via a communication pipe 7 and the raw material tank 1 is connected to the raw material tank 1 when the pressure in the tank occupied by the raw material gas 4 changes due to the temperature change of the heater 2. The volume of the communicating sealing body 6 is changed to keep the pressure in the tank constant.

As a more specific structure of the sealing body 6, as shown in FIG. 2, one end surface of the cylinder 61 is connected to the raw material tank 1 through the communication pipe 7, and the other end surface thereof is in the axial direction of the cylinder 61. There is a damper 60 composed of an end surface 63 provided at the tip of a piston 62 that is movable to the inside. When the heating temperature of the raw material tank fluctuates and the pressure in the tank occupied by the raw material gas fluctuates, the fluctuation is fed back to the piston 62 via the control device 63 and the pressure in the tank is kept constant.

A simpler form of the closed body 6 is a bag-shaped balloon made of vinyl (not shown). The inlet of the balloon is connected to the raw material tank 1 via a communication pipe 7. The balloon is normally deflated, but when the pressure in the tank occupied by the raw material gas 4 rises and more raw material gas is supplied to the reactor, excess raw material gas flows into the balloon and the pressure in the tank increases. It moderates the rise.

The first requirement for stably supplying the raw material gas using the supply device having such a configuration is that the raw material liquid 3 is continuously supplied to the raw material tank 1 and the volume occupied by the raw material gas 4 is always predetermined. It is to hold so that it becomes a value. The second requirement is that the pressure in the tank occupied by the raw material gas 4 changes due to the slight temperature fluctuations left after the temperature control, so that this slight pressure change is sealed by the raw material tank 1. The pressure is kept constant by feeding back to the body 6.

Here, the volume occupied by the source gas 4 is to be maintained at a value selected from 30% or less and 5% or more of the volume of the source tank and the closed body. The smaller the space occupied by the raw material gas, the smaller the influence of the fluctuation of the heating temperature on the pressure change of the raw material gas is, which is preferable, but if the volume is too small, the supply to the reactor may be interrupted.

Since a carrier gas such as Ar coexists in addition to the raw material gas in the space above the raw material tank 1, it is more preferable to use the partial pressure control of the raw material gas together.

<Example> As shown in FIG. 1, a raw material tank 1
An optical fiber preform was produced by a supply device in which the damper 6 was connected to the upper part of the. At this time, the raw material liquid was continuously supplied into the raw material tank 1, and the volume of the raw material gas was maintained at 10% of the whole volume. The temperature of the heater 2 was controlled by the P, I, and D controls that are normally used, but the temperature fluctuation was 0.2 ° C. When the distribution of the relative refractive index difference of the optical fiber obtained by drawing the optical fiber preform manufactured by this apparatus was measured, the variation was 0.005% or less.

<Comparative Example 1> The same supply device as that of the embodiment was used, and the volume of the raw material gas was made three times as large as that of the embodiment. Other conditions are the same as those in the example. When the distribution of the relative refractive index difference of the optical fiber obtained by drawing the optical fiber preform thus manufactured was measured, the variation was 0.009.
I was able to suppress it to less than%.

<Comparative Example 2> An optical fiber preform was produced by the feeder shown in FIG. 3 from which the damper 6 of the raw material tank was removed. The raw material liquid is continuously supplied into the raw material tank,
The volume of the raw material gas was maintained so as to be 10% of the whole.
The temperature control of the heater 2 is the same as in the embodiment. When the distribution of the relative refractive index difference of the optical fiber obtained by drawing the optical fiber preform thus manufactured was measured, the variation was 0.03% or less.

[0016]

The present invention is embodied in the form described above and has the following effects.

A slight temperature fluctuation remains after the temperature control, and even if the pressure in the tank occupied by the raw material gas changes due to this temperature fluctuation, the pressure change is fed back to the sealed body communicating with the raw material tank. Therefore, the flow rate of the raw material gas can be controlled with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a source gas supply device according to the present invention.

FIG. 2 is a diagram showing a configuration of a damper applied to the present invention.

FIG. 3 is a diagram showing a configuration of a conventional supply device.

[Explanation of symbols]

 1: Raw material tank 2: Heater 3: Raw material liquid 4: Raw material gas 5: Carrier gas supply line 6: Sealed body 7: Communication pipe 11: Condenser 12: Flow control device 20: Service tank 60: Damper 61: Cylinder 62: Piston 63: End face of piston 64: Control device for damper 14, 22, 23: Pipe

Claims (6)

[Claims] 1. A raw material gas supply method in which a raw material gas for glass is contained in a raw material tank equipped with a heater and the raw material gas vaporized in the raw material tank is delivered to a reactor. The raw material liquid is continuously supplied to maintain the volume occupied by the raw material gas at a predetermined value at all times, and the heating temperature of the raw material tank varies so that the pressure in the tank occupied by the raw material gas is A method of supplying a raw material gas, characterized in that the volume of a sealed body communicating with the raw material tank is changed to change so that the pressure in the tank is kept constant. 2. The method for supplying a raw material gas according to claim 1, wherein the volume occupied by the raw material gas is a value selected from the range of 5 to 30% of the volume of the raw material tank and the sealed body. .. 3. The method for supplying a raw material gas according to claim 1, wherein the pressure in the tank occupied by the raw material gas is detected, and the volume of the sealed body is controlled so that the pressure becomes constant. 4. A raw material gas supply device comprising a raw material tank in which a heater is mounted in a raw material tank for containing a raw material liquid for glass, and a pipe for delivering the raw material gas vaporized in the raw material tank to a reactor. The raw material tank is provided with a mechanism for continuously supplying the raw material liquid so that the volume occupied by the raw material gas is always a predetermined value, and a variable volume sealed body is provided in communication with the raw material tank. When the heating temperature of the raw material tank fluctuates and the pressure in the tank occupied by the raw material gas changes, the volume of the sealed body changes to keep the pressure in the tank constant. apparatus. 5. The raw material gas supply device according to claim 4, wherein the closed body is a damper. 6. The raw material gas supply device according to claim 4, wherein the closed body is a balloon.