JP6292090B2 - Melting kiln, melting method, and alkali-free glass plate manufacturing method - Google Patents

Description

The present invention, melting furnace, dissolution method, and relates to the production how the non-alkali glass plate.

  The melting furnace melts a raw material of alkali-free glass. The melting furnace includes a first chamber in which raw materials are charged, a first chamber burner that forms a flame in the upper space of the first chamber, a second chamber in which molten glass obtained by melting the raw materials is supplied from the first chamber, A second chamber burner that forms a flame in the upper space of the two chambers; and a throat that connects the lower portion of the first chamber and the lower portion of the second chamber.

  The first chamber burner and the second chamber burner form a flame by burning a fuel such as natural gas or heavy oil mixed with gas. A burner that mainly uses air as a gas is called an air combustion burner, and a burner that mainly uses oxygen as a gas is called an oxyfuel burner.

In the case of an air combustion burner, nitrogen gas occupying most of the air is exhausted outside the melting furnace without contributing to combustion. On the other hand, in the case of an oxyfuel burner, since the amount of exhaust is smaller than in the case of an air combustion burner, the thermal efficiency is high, and the amount of CO ₂ emission and NO _x emission is small.

A burner using a mixed gas in which air and oxygen gas are mixed can also be used (see, for example, Patent Document 1). In this case, of course in the case of oxygen-fired burners, as compared with the case of air combustion burner, sometimes NO _x emissions increased (e.g., see Non-Patent Document 1). Specifically, when the oxygen concentration in the mixed gas is less than 93% by volume and more than 25% by volume, the amount of NO _x emission increases as compared with the case of the air combustion burner.

JP 2000-128549 A

R & D Kobe Steel Engineering Reports, Vol. 51, no. 2 (Sep. 2001), p. 8-12, "Research on energy saving and low NOx combustion by oxygen-enriched air"

In the case of alkali-free glass, the melting temperature of the raw material is higher than in the case of general soda lime glass, and a foam layer is likely to stick to the liquid surface of the molten glass in the first chamber. The bubble layer is an aggregate of small bubbles, and the bubbles are caused by the generation of gas by thermal decomposition of the raw material. The foam layer is particularly easily formed when the alkali-free glass has a SiO ₂ content of 54 to 73 mass%.

  When there is a foam layer, the surface of the molten glass is not directly exposed to the atmosphere of the upper space. Therefore, the heat radiation from the flame of the burner to the molten glass was blocked, and the heating efficiency of the molten glass was low.

In the case of a glass containing a general alkali component, B ₂ O ₃ in the molten glass tends to volatilize as the alkali content in the molten glass increases. B ₂ O ₃ is volatilized, for example, as a sodium compound.

On the other hand, in the case of non-alkali glass in which alkali components such as Na are hardly contained in the molten glass, the higher the moisture concentration in the atmosphere of the upper space, the easier the B ₂ O ₃ in the molten glass volatilizes.

The amount of moisture in the atmosphere of the upper space depends on the type of burner. In the case of an oxyfuel burner, the concentration of water contained in the gas after combustion is higher than in the case of an air combustion burner, and B ₂ O ₃ in the molten glass is likely to volatilize. B ₂ O ₃ is considered to volatilize as a hydrogen compound.

The present invention was made in view of the above problems, can efficiently heat the molten glass through the foam layer, and the volatiles of B ₂ O ₃ in the molten glass can be suppressed, such as melting furnace The main purpose is provision.

In order to solve the above problems, according to one aspect of the present invention,
A melting furnace for melting an alkali-free glass material having a SiO ₂ content of 54 to 73 mass% and a B ₂ O ₃ content of 0.1 to 12 mass%,
A first chamber into which the raw material is charged;
A first chamber burner for forming a flame in the upper space of the first chamber;
A second chamber in which a molten glass obtained by melting the raw material is supplied from the first chamber;
A second chamber burner for forming a flame in the upper space of the second chamber;
A throat connecting the lower portion of the first chamber and the lower portion of the second chamber;
For each of the first chamber burners and each of the second chamber burners, either an oxyfuel burner or an air combustion burner is used,
50-100% of the total combustion heat per hour of all the first chamber burners is due to the oxyfuel burner,
A melting furnace is provided wherein 75-100% of the total combustion heat per hour of all the second chamber burners is due to the air combustion burner.

According to one embodiment of the present invention, there is provided a melting kiln that can efficiently heat a molten glass through a foam layer and can suppress volatilization of B ₂ O ₃ in the molten glass.

It is a flowchart which shows the manufacturing method of the alkali free glass plate by one Embodiment of this invention. It is sectional drawing which shows the melting furnace used in the melting | dissolving process of FIG. It is sectional drawing which shows the melting kiln by a 1st modification. It is sectional drawing which shows the melting kiln by a 2nd modification. It is sectional drawing which shows the melting kiln by a 3rd modification.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In the drawings, the same or corresponding components are denoted by the same or corresponding reference numerals, and description thereof is omitted. In this specification, “to” representing a numerical range means a range including numerical values before and after the numerical range.

  FIG. 1 is a flowchart showing a method for producing an alkali-free glass plate according to an embodiment of the present invention. The method for producing an alkali-free glass plate includes a melting step S12 and a forming step S14.

The alkali-free glass is a glass that does not substantially contain an alkali metal oxide such as Na ₂ O, K ₂ O, or Li ₂ O. The alkali-free glass according to the present invention has a total content of alkali metal oxides of 0.2% by mass or less.

The alkali-free glass is, for example, in mass percentage display based on oxide,
SiO _2: 54~73%
Al ₂ O ₃ : 10 to 23%
B ₂ O ₃ : 0.1 to 12%
MgO: 0 to 12%
CaO: 0 to 15%
SrO: 0 to 16%
BaO: 0 to 15%
MgO + CaO + SrO + BaO: 8-26%
Containing.

When obtaining a high strain point, the B ₂ O ₃ content of the alkali-free glass is preferably 9% by mass or less, more preferably 5% by mass or less, further preferably 3% by mass or less, and particularly preferably 2% by mass or less. is there.

In addition, the B ₂ O ₃ content of the alkali-free glass is preferably 0.3% by mass or more, more preferably 0.5% by mass or more, and further preferably 1% by mass or more in order to obtain high solubility.

  The strain point of the alkali-free glass is preferably 650 ° C. or higher, more preferably 670 ° C. or higher, and further preferably 700 ° C. or higher.

T _{2 of the} alkali-free glass (a temperature that is a standard for melting and corresponding to a viscosity of 10 ² dPa · s) is 100 ° C. or more higher than T ₂ of a general soda lime glass. T ₂ of the alkali-free glass is preferably 1600 to 1820 ° C, more preferably 1610 to 1770 ° C, and further preferably 1620 to 1720 ° C.

Β-OH indicating the water content of the alkali-free glass plate is preferably 0.2 to 0.4 mm ⁻¹ , more preferably 0.2 to 0.35 mm ⁻¹ . The higher the value of β-OH, the greater the amount of water. This value increases when dissolved in an atmosphere with a high moisture concentration. The value B of β-OH is calculated by measuring the thickness C and transmittance T of the alkali-free glass plate and substituting the measurement result into the following equation. A common Fourier transform infrared spectrophotometer (FT-IR) is used for measuring the transmittance of the alkali-free glass plate.
B = (1 / C) log ₁₀ (T1 / T2)
T1: Transmittance of non-alkali glass plate at a reference wave number of 4000 / cm (unit:%)
T2: Minimum transmittance of non-alkali glass plate in the vicinity of hydroxyl absorption wave number 3570 / cm (unit:%)
The alkali-free glass plate is used as a substrate for a display such as a liquid crystal display or a substrate for a magnetic disk. The use of the alkali-free glass plate may vary widely. As will be described in detail later, according to the present embodiment, a homogeneous alkali-free glass plate having few defects such as bubbles can be obtained. Therefore, it is suitable for a substrate for a liquid crystal display that requires particularly high quality.

  In the melting step S <b> 12 shown in FIG. 1, a non-alkali glass raw material is put into a melting furnace, and the raw material is melted to obtain molten glass.

  In the forming step S14 shown in FIG. 1, the molten glass is formed into a plate shape. The molding method may be a common one, and examples thereof include a float method and a fusion method.

  In the float process, molten glass is continuously supplied onto a molten metal (for example, molten tin), and the molten glass is flowed in the horizontal direction on the molten metal to be formed into a strip shape.

  The fusion method is also called the overflow down draw method. The molten glass overflowing from the left and right sides flows down along the left and right side surfaces of the bottle, and the molten glass joined at the lower end of the bottle flows further downward. To form a strip.

  A clarification device (for example, a vacuum degassing device) or a stirring device (for example, a stirring stirrer) may be provided between the dissolving step S12 and the forming step S14.

  FIG. 2 is a cross-sectional view showing a melting furnace used in the melting step of FIG. The melting furnace includes a first chamber 21, a first chamber burner 26, a second chamber 31, a second chamber burner 36, a throat 41, and the like.

  In the first chamber 21, the alkali-free glass material 12 is charged. The first chamber 21 melts the raw material 12 and stores the molten glass 14. The first chamber 21 is surrounded by a horizontal bottom wall 22, an upstream side wall 23 perpendicular to the bottom wall 22, a downstream side wall 24 parallel to the upstream side wall 23, a ceiling 25 (for example, an arched ceiling), and the like. . The downstream side wall 24 reaches the ceiling 25 as shown in FIG. 2, but may be higher than the foam layer 16, and may not reach the ceiling 25 as shown in FIG. 3. An inlet 23 a for the raw material 12 is formed in the upstream side wall 23.

  The first chamber burner 26 forms a flame by mixing and burning a fuel such as natural gas or heavy oil with a gas. The first chamber burner 26 forms a flame in the upper space of the first chamber 21 and heats the raw material 12 and the like charged from the charging port 23a. The raw material 12 is melted by the radiant heat of the flame formed by the first chamber burner 26 and gradually melts into the molten glass 14.

  The first chamber burner 26 ejects a flame into the first chamber 21 from the openings on the left and right side walls that connect the upstream side wall 23 and the downstream side wall 24. The first chamber burner 26 may eject the flame continuously or may eject the flame intermittently.

  The first chamber burner 26 is disposed on each of the left and right side walls. The first chamber burners 26 may be arranged symmetrically across the first chamber 21, may be arranged staggered across the first chamber 21, or partly arranged symmetrically and partly. A staggered arrangement may be used.

  For each first chamber burner 26, either an air combustion burner or an oxyfuel burner is used. Of the plurality of first chamber burners 26, all may be oxyfuel burners, some may be oxyfuel burners, and the remainder may be air combustion burners.

  In this specification, an air combustion burner refers to one that mainly uses air as a gas mixed with fuel, and refers to one having an oxygen concentration of 25% by volume or less. If the oxygen concentration of the gas is 25% by volume or less, a mixed gas of air and oxygen gas may be used, or only air may be used.

  In the present specification, the oxyfuel burner refers to a gas mainly using oxygen gas as a gas mixed with fuel, and a gas having an oxygen concentration of 93% by volume or more. If the oxygen concentration of the gas is 93% by volume or more, a mixed gas of oxygen gas and air may be used, or only oxygen gas may be used.

Each first chamber air combustion burner to the burner 26, for either oxygen combustion burner is used, can be reduced NO _x emissions.

  For the purpose of assisting heating of the molten glass 14 by the first chamber burner 26, an electrode for energizing and heating the molten glass 14 may be provided in the molten glass 14 of the first chamber 21.

  It is preferable not to introduce a dry gas such as nitrogen gas into the upper space of the first chamber 21. A decrease in thermal efficiency and an increase in the amount of exhaust gas can be prevented.

  In the second chamber 31, molten glass 14 obtained by melting the raw material 12 is supplied from the first chamber 21. The second chamber 31 clarifies the molten glass 14 or adjusts the temperature. The second chamber 31 is surrounded by a horizontal bottom wall 32, an upstream side wall 33 perpendicular to the bottom wall 32, a downstream side wall 34 parallel to the upstream side wall 33, a ceiling 35, and the like. An outlet 34 a for the molten glass 14 is formed at the lower portion of the downstream side wall 34.

  The bottom wall 32 of the second chamber 31 and the bottom wall 22 of the first chamber 21 are integrated as shown in FIG. 2, but may not be integrated as shown in FIG. Further, as shown in FIG. 4, there may be a step D between the bottom wall 32 of the second chamber 31 and the bottom wall 22 of the first chamber 21. Note that the bottom wall 32 of the second chamber 31 and the bottom wall 22 of the first chamber 21 may be higher.

  Although the upstream side wall 33 of the second chamber 31 and the downstream side wall 24 of the first chamber 21 are integrated, they may not be integrated as shown in FIG.

  Although the ceiling 35 of the second chamber and the ceiling 25 of the first chamber 21 are integrated, they may not be integrated. As a case where the ceiling 35 of the second chamber and the ceiling 25 of the first chamber 21 are not integrated, for example, the downstream side wall 24 of the first chamber 21 and the upstream side wall 33 of the second chamber 31 are formed as shown in FIG. The case where it is not integrated is mentioned.

  The second chamber burner 36 forms a flame by mixing a fuel such as natural gas or heavy oil with the gas and burning it. The second chamber burner 36 forms a flame in the upper space of the second chamber 31 and heats the molten glass 14 supplied from the first chamber 21.

  The second chamber burner 36 jets a flame into the second chamber 31 from the openings on the left and right side walls that connect the upstream side wall 33 and the downstream side wall 34. The second chamber burner 36 may eject the flame continuously, or may eject the flame intermittently.

  The second chamber burner 36 is disposed on each of the left and right side walls that connect the upstream side wall 33 and the downstream side wall 34. The second chamber burners 36 may be arranged symmetrically with respect to the second chamber 31, or may be arranged in a staggered manner with respect to the second chamber 31. A staggered arrangement may be used.

  For each second chamber burner 36, either an air combustion burner or an oxyfuel burner is used. Of the plurality of second chamber burners 36, all may be air-burning burners, some may be air-burning burners, and the remaining may be oxygen-burning burners.

Each second chamber air combustion burner to the burner 36, for either oxygen combustion burner is used, can be reduced NO _x emissions.

  An electrode for energizing and heating the molten glass 14 may be provided in the molten glass 14 in the second chamber 31 for the purpose of assisting the heating of the molten glass 14 by the second chamber burner 36.

  It is preferable not to introduce a dry gas such as nitrogen gas into the upper space of the second chamber 31. A decrease in thermal efficiency and an increase in the amount of exhaust gas can be prevented.

  The throat 41 connects the lower part of the first chamber 21 and the lower part of the second chamber 31. The throat 41 is filled with the molten glass 14. A plurality of throats 41 may be provided. The molten glass 14 in the first chamber 21 is supplied to the second chamber 31 via the throat 41.

  Although the inlet of the throat 41 is formed in the downstream side wall 24 of the first chamber 21 in FIG. 2, it may be formed in the bottom wall 22 of the first chamber 21. Similarly, the outlet of the throat 41 is formed on the upstream side wall 33 of the second chamber 31 in FIG. 2, but may be formed on the bottom wall 32 of the second chamber 31.

Meanwhile, T ₂ of the non-alkali glass is higher 100 ° C. or higher than T ₂ of the general soda-lime glass. Therefore, in this embodiment, the molten glass 14 is heated using both the first chamber burner 26 and the second chamber burner 36.

In the case of alkali-free glass, the melting temperature of the raw material 12 is higher than in the case of general soda lime glass, and the foam layer 16 tends to stick to the liquid surface of the molten glass 14 in the first chamber 21. The bubble layer 16 is an aggregate of small bubbles, and the bubbles are caused by generation of gas due to thermal decomposition of the raw material 12. The foam layer 16 is particularly easily formed when the alkali-free glass has a SiO ₂ content of 54 to 73 mass%. The foam layer 16 blocks heat radiation from the flame of the first chamber burner 26 to the molten glass 14.

  Therefore, in this embodiment, 50 to 100% (preferably 55 to 100%, more preferably 60 to 100%) of the total combustion heat amount per hour of all the first chamber burners 26 is due to the oxyfuel burner. To do.

In the case of an air combustion burner, nitrogen gas occupying most of the air is exhausted outside the melting furnace without contributing to combustion. On the other hand, in the case of an oxyfuel burner, since the amount of exhaust is smaller than in the case of an air combustion burner, the thermal efficiency is high, and the amount of CO ₂ emission and NO _x emission is small.

  If 50 to 100% of the total combustion heat amount per hour of all the first chamber burners 26 is due to the oxyfuel combustion burner, the molten glass 14 can be efficiently heated even through the foam layer 16, and the amount of fuel can be reduced. The molten glass 14 can be heated to a desired temperature. The total amount of combustion heat is obtained by adding the amount of heat generated when the fuel used in each burner is completely burned.

  Molten glass 14 melted in the first chamber 21 is supplied to the second chamber 31. Since the molten glass 14 is supplied to the second chamber 31 through the throat 41, the homogeneous molten glass 14 is supplied to the second chamber 31 almost without being affected by the foam layer 16 of the first chamber 21. Unlike the first chamber 21, the foam chamber 16 is hardly formed in the second chamber 31.

  In the second chamber 31, the liquid surface of the molten glass 14 is exposed, and the molten glass 14 is exposed to the atmosphere in the upper space of the second chamber 31. The gas in the atmosphere of the upper space of the second chamber 31 melts into the molten glass 14.

By the way, in the case of general alkali-containing glass, the greater the alkali content in the molten glass, the easier it is for B ₂ O ₃ in the molten glass to volatilize. B ₂ O ₃ is volatilized, for example, as a sodium compound.

On the other hand, in the case of non-alkali glass in which alkali components such as Na are hardly contained in the molten glass, the higher the moisture concentration in the atmosphere of the upper space, the easier the B ₂ O ₃ in the molten glass volatilizes.

The amount of moisture in the atmosphere of the upper space depends on the type of burner. In the case of an oxyfuel burner, the concentration of water contained in the gas after combustion is higher than in the case of an air combustion burner, and B ₂ O ₃ in the molten glass is likely to volatilize.

  Therefore, in this embodiment, 75 to 100% (preferably 80 to 100%, more preferably 85 to 100%) of the total amount of combustion heat per hour of all the second chamber burners 36 is due to the air combustion burner. To do.

If 75 to 100% of the total amount of combustion heat per hour of all the second chamber burners 36 is due to the air combustion burner, the upper space of the second chamber 31 compared to the moisture concentration of the upper space of the first chamber 21. The water concentration is low. Therefore, volatilization of B ₂ O ₃ in the molten glass can be suppressed.

  The distance L1 in the flow direction (left-right direction in FIG. 2) between the upstream end and the downstream end of the first chamber 21 is preferably 50 to 75% of the reference distance L0, more preferably 55 to 70% of the reference distance L0. . Further, the distance L2 in the flow direction (left and right direction in FIG. 2) between the upstream end and the downstream end of the second chamber 31 is preferably 10 to 40% of the reference distance L0, more preferably 15 to 35% of the reference distance L0. It is. The reference distance L0 is a distance in the flow direction between the upstream end of the first chamber 21 and the downstream end of the second chamber 31.

  If the distance L1 is 50 to 75 of the reference distance L0 and the distance L2 is 10 to 40% of the reference distance L0, the molten glass 14 can be heated in a balanced manner in the first chamber 21 and the second chamber 31. it can.

  As mentioned above, although the melting furnace, the melting method, the manufacturing method of the alkali-free glass plate, and the embodiment of the alkali-free glass have been described, the present invention is not limited to the above-described embodiment and departs from the scope of the present invention. Without limitation, various modifications and substitutions can be made to the above-described embodiment.

  For example, the melting kiln of the above embodiment includes the first chamber 21 and the second chamber 31, but may further include a third chamber to which the molten glass 14 is supplied from the second chamber 31. The number of melting kiln rooms may be four or more. In order to promote melting and homogeneity of the glass, for example, a bubbler or the like may be provided on the bottom wall of the first chamber 21 and / or the second chamber 31.

12 Non-alkali glass raw material 14 Molten glass 16 Foam layer 21 First chamber 22 First chamber bottom wall 23 First chamber upstream side wall 23a Raw material inlet 24 First chamber downstream side wall 25 First chamber ceiling 26 1st chamber burner 31 2nd chamber 32 2nd chamber bottom wall 33 2nd chamber upstream side wall 34 2nd chamber downstream wall 35 2nd chamber ceiling 36 2nd chamber burner 41 Throat

Claims (4)

A melting furnace for melting an alkali-free glass material having a SiO ₂ content of 54 to 73 mass% and a B ₂ O ₃ content of 0.1 to 12 mass%,
A first chamber into which the raw material is charged;
A first chamber burner for forming a flame in the upper space of the first chamber;
A second chamber in which a molten glass obtained by melting the raw material is supplied from the first chamber;
A second chamber burner for forming a flame in the upper space of the second chamber;
A throat connecting the lower portion of the first chamber and the lower portion of the second chamber;
For each of the first chamber burners and each of the second chamber burners, either an oxyfuel burner or an air combustion burner is used,
50-100% of the total combustion heat per hour of all the first chamber burners is due to the oxyfuel burner,
A melting furnace in which 75 to 100% of the total combustion heat per hour of all the second chamber burners is due to the air combustion burner. The alkali-free glass is expressed by mass% based on oxide,
SiO _2: 54~73%
Al ₂ O ₃ : 10 to 23%
B ₂ O ₃ : 0.1 to 12%
MgO: 0 to 12%
CaO: 0 to 15%
SrO: 0 to 16%
BaO: 0 to 15%
MgO + CaO + SrO + BaO: 8-26%
The melting kiln according to claim 1, comprising:   A melting method using the melting kiln according to claim 1. A melting step using the melting furnace according to claim 1 or 2,
The manufacturing method of an alkali free glass plate which has a shaping | molding process which shape | molds the molten glass melt | dissolved by the said melt | dissolution process in plate shape.

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