JPS5832030A - Electric melting furnace for glass - Google Patents

Abstract

PURPOSE:To titled upright melting furnace enabling the uniform heating and the proper convection, by placing electrodes at opposing positions at regular intervals perpendicular to a pair of opposing peripheral walls of a furnace with a square cross section, differentiating the phase of electrodes to each other between neighboring electrodes. CONSTITUTION:A glass raw material is fed from the feed opening at the top of the electric melting furnace 1 to it, and the batch layer 7 is formed on the molten glass 6 in the furnace. The glass 6 is heated by the electricity from the two-phase powder systems 10 and 11 for the bar electrodes 9 set perpendicular to each of the peripheral wall 2 of the longer side at regular intervals, extending nearly to the central part of the furnace. Namely, the difference of phase between neighboring electrodes is 90 deg. and the opposing electrodes are in the same phase. The layer 7 is melted by the rising flow of the molten glass heated by the above-mentioned method, the molten glass made into low temperature and high density is changed into a downward flow, and the vigorous circulating flows A are formed. The incomplete glass fairly purified in the melt and convection zone 4 is gradually transferred to the purifying zone 5 of laminar flow, the complete and uniform purification and temperature uniformity of the glass are attained, and the glass is fed to the outlet opening 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vertical electric melting furnace, more specifically a vertical electric melting furnace with a rectangular cross section, in which electricity is applied directly to the molten glass itself, and the raw glass batch is melted, homogenized and clarified by its Genieal heat. Applicable to such an electric melting furnace with a shape and a specific electrode arrangement adapted to it.

Glass products, such as glass fibers, are produced industrially by melting and clarifying a powdered raw glass batch by flame in an open hearth melting furnace made of a refractory material, and passing the molten glass through a channel into a melting furnace made of a refractory material. It is manufactured by spinning the platinum material from a plurality of platinum bushings arranged at the bottom of the forehearth while controlling the temperature by heating resistance by energizing the constituent platinum material while conditioning the material. (Refer to Koshoro No. 9-5219 and Koshoro No. 46-64941)
.

In recent years, a vertical electric melting furnace has been developed for melting, fining, and forming yarn, which consists of the open hearth and four-hearth melting furnaces. In this vertical electric melting furnace, the electrodes are appropriately placed relatively at the upper part of the furnace, and when electricity is applied directly to the molten glass in the furnace, an appropriate vertical temperature distribution is generated in the molten glass, and at the same time, the electrodes are placed in the upper part of the furnace. The relatively high temperature, low density molten glass is difficult to mix into the relatively low temperature, high density molten glass region below, even against the force of gravity. It is based on the simple principle that a region of heating convection is formed in the molten glass while a region of laminar flow of molten glass is formed relatively below. In this way, the electric melting furnace achieves melting, stirring, and diffusion of a glass batch naturally and functionally in the same furnace, and achieves homogeneous and clarified molten glass near the bottom of the furnace, compared to the conventional open hearth furnace. It has a clarity of melting theory and a simplicity of process that are not found in conventional systems, thus achieving miniaturization of equipment and improvement of thermal efficiency. The use of electrical energy used to be expensive compared to fossil fuels, even when efficiency was taken into account.
The simplicity and high efficiency of the electric melting furnace process, combined with the recent rise in the price of fossil fuels, has gradually increased its advantages, and it is establishing itself as a new glass melting technology.

As such an electric melting furnace, for example, the
No. 884 discloses that at least one part of the upper part of the dissolution tank is
having a three-phase alternating current electrode arrangement for generating thermal energy by energizing the molten glass in at least two levels in one melting zone, thereby creating and maintaining a circulating flow of molten glass in opposing directions in the levels; An electric melting furnace and melting method are disclosed.

Japanese Patent Application Laid-open No. 47-13618 discloses that in a glass electric melting furnace having electrode groups on multiple planes in the furnace, the inner end of the electrode group on one plane is connected between the ends of the electrode groups on the upper and lower planes. an electric melting furnace located in the gap, thus causing the ascending glass stream of each lower plane to meet the descending glass stream of each upper plane at the interface with the upper plane, and preventing each glass stream from penetrating into the other plane; and a melting method.

Furthermore, Japanese Patent Publication No. 56-9455 discloses that an unmelted glass batch or an incompletely melted glass batch deposited on molten glass in an electric melting furnace is equipped with electrodes.

In order to minimize convection toward the nearby furnace wall, a batch warping plate means was attached to the furnace wall above the electrode immersed in the molten glass and at a position where it did not come into contact with the molten glass. Discloses an electric melting furnace.

Conventional electric melting furnaces, including these publications, have a horizontal cross-sectional shape of a regular 6n square with n = '1 or more, usually 6~
They have a common feature in that they have a dodecagonal, typically hexagonal structure. For example, the aforementioned Japanese Patent Publication No. 52-26884 has 6
Discloses a furnace structure consisting of a rectangular upper vertical part and an inverted hexagonal pyramidal funnel-shaped bottom part connected to the upper vertical part, and also discloses the above-mentioned Japanese Patent Application Laid-Open No.
13618 and Japanese Patent Publication No. 56-9455 are both 6
A rectangular prismatic structure is disclosed.

Glass melting furnaces require a temperature of several hundred degrees to melt a batch of glass, so they are constructed of refractory materials such as refractory bricks that can withstand such temperatures, but as is well known, these refractory materials Corrosion caused by molten glass cannot be avoided, and its service life is said to be about 2 to 6 years. After the end of its useful life, the furnace is refurbished or a new one is built.
The furnace cost accounts for a large portion of the production cost of glass products. On the other hand, corrosion of the refractory material by molten glass does not pose a practical problem in the early stages of operation, but as it approaches the later stages of operation, it becomes a serious problem for the safe operation of the furnace.

Therefore, the simplicity of the furnace form and the stability of the furnace structure not only guarantee the ease of furnace construction or support and reinforcement work for the furnace, but also increase the durability of the furnace and ensure the operational safety of the furnace. is also an important factor. When considering conventional electric melting furnaces from these viewpoints, the polygonal shape increases the technical difficulty of furnace construction, makes external support and reinforcement work complicated and difficult, and makes it difficult to use refractory materials based on the polygonal shape. The large number of joints between the molten glass leads to an increase in the number of eroded areas where erosion by the molten glass progresses rapidly, and this, coupled with the fact that the depth of the furnace is several times that of an open hearth, impairs the overall structural stability of the furnace. This is a hindering factor.

This regular polygonal furnace structure is related to the fact that the main power sources of the power supply system are three-phase AC power sources whose phases are shifted by 1200 degrees from each other. That is, the current must flow evenly through the glass in the plane containing the electrodes to create proper convection that does not affect the glass in the laminar fining region at the bottom of the furnace, but in a three-phase power system. In order to achieve an even flow of current when using a power system, it is most rational to arrange the electrodes connected to the three phases of the power system so as to form an equilateral triangle within the same plane. The polygonal furnace structure has n = '1 for this electrode arrangement.
This is because the above-mentioned regular 6n-gonal cross-sectional structure is suitable for the purpose.

However, in order to achieve uniform heating and formation of proper convection with such a three-phase electrode arrangement, it is difficult to create a furnace with a complicated current pattern, for example, as typically disclosed in Japanese Patent Publication No. 52-26884. A triangular energization pattern that forms the shortest current path on the side of a triangle with each electrode as the apex within the plane of the level that includes the electrodes arranged on the wall, and a triangular current path that forms the shortest current path around the furnace wall between adjacent electrodes. It is necessary to form a complicated energization pattern around the furnace wall, or a pattern in which the two patterns are superimposed on each other at a plurality of levels, and the control technology accordingly becomes complicated. Especially when the electric melting furnace becomes large, it is very difficult to achieve uniform heating and proper convection formation and control over a wide area using such a current pattern, and from the aspect of heating control. However, there are limits to the size of the furnace.

Therefore, the present invention has a simple furnace configuration, has high structural stability, enables uniform heating and formation of proper convection through a simple current flow pattern, and has a vertical electrode arrangement that can be applied to furnaces of any size. The purpose is to provide a type electric melting furnace.

According to the present invention, which achieves the above objects, the basic structure consists of: a melting convection zone for the raw glass batch having a receiving opening for the raw glass batch at the top; a laminar flow clarification zone of molten glass adjoining vertically downwardly with respect to the convection zone; electrodes disposed through at least said molten convection zone in at least one horizontal level on a peripheral wall defining said zone; and in an electric glass melting furnace, the molten glass take-out opening is connected to a feeder through an arbitrary flow path: the furnace has a set of circumferential walls having a rectangular cross-sectional shape; - arranged substantially perpendicularly, equidistantly, and in opposing relation, with adjacent electrodes being out of phase with each other, and opposing electrodes being in phase with each other; An electric melting furnace is provided.

According to the present invention, the rectangular cross-sectional structure facilitates the construction of the furnace and its supporting and reinforcing work, and also reduces the number of joints between the refractory material phases where erosion by molten glass is more likely to proceed. In addition to significantly improving the overall structural stability of the furnace, the electrode arrangement perpendicular to the peripheral wall and at equal intervals does not require complicated heating control technology, and regardless of the size of the furnace / h. The invention will now be further explained with reference to the drawings, which make it possible to form a uniform current carrying pattern in the plane containing the electrodes, thus creating a balanced thermal convection in the melt convection zone.
The illustrated electric melting furnace is a preferred embodiment of the invention and includes:
Of course, the present invention is not limited to these.

In the accompanying drawings, FIG. 1 shows a side sectional view of the rectangular electric melting furnace of the present invention, and FIG. 2 shows a cross-sectional view taken along the plane ■-■ of FIG. 1, showing the electrode arrangement and the power system therefor. . In these figures, an electric melting furnace 1 is defined by a peripheral wall 2 made of refractory bricks and a furnace bottom wall 3, the relative upper part of which constitutes a melting convection area 4 of the molten glass, and the relative lower part of which constitutes a melting convection area 4 for the molten glass. A laminar flow clarification zone 5 of the glass is constituted.

The top of the melting convection zone 4 is entirely open for receiving the raw glass batch and forming a deposited layer 7 of glass batch on top of the furnace molten glass 6.

Although not shown, a feeding device for raw glass batches is disposed above the top opening, so that glass batches are continuously or intermittently fed into the opening, preferably by being scattered. It has become.

The glass batch is melted in this melting convection zone 4,
A certain degree of clarification and homogenization takes place under thermal convection.

On the other hand, the laminar flow clarification zone 5 is directly connected vertically downward from the melt convection zone 4 and is closed by the furnace bottom wall 3. In this laminar flow clarification zone 5, the melt continuously supplied from the melt convection zone 4 is substantially completely homogenized and clarified. The homogeneous, clarified glass is removed through a removal opening 8 formed in the bottom end of one of the peripheral walls. Although not shown, a feeder provided with a forming device is usually connected to the take-out opening 8 through a riser or any other flow path. The number of extraction openings 8 is not limited to one as shown in this figure, but a plurality of extraction openings may be formed in a plurality of peripheral walls.

The electric melting furnace 1 of the present invention has a rectangular cross-sectional structure. In this rectangular furnace, its cross-sectional shape can be rectangular or square. In the case of a rectangular cross-sectional shape, the ratio of the length of the short side to the long side can vary considerably, for example the short side can be 1/3 of the long side or less. This is because the electrical conductivity of molten glass to which electricity is applied varies greatly depending on the glass composition.

In Figures 1 and 2, the number 9 represents a group of main electrodes, and electricity is applied directly to the molten glass in the furnace through these electrodes, and the Joule heat generated transforms the glass batch in the glass batch layer on the molten glass into the molten glass. The glass is sequentially melted and vitrified at the contact interface with the molten glass, and thermal convection is caused in the molten glass. In order for the electrode group 9 to function in this way, these electrodes -
are typically arranged at one horizontal level at a depth of about 10 to 60 cm below the liquid surface of the molten glass, but in the present invention, as in the conventional method, the main electrode group including this primary electrode group is They can also be placed on multiple levels.

In the present invention, the electrode groups 9 are arranged on a pair of opposing circumferential walls of the rectangular cross-section furnace of the present invention, in at least one horizontal level, perpendicular to the circumferential walls and substantially equally spaced, and in opposing relationship. It penetrates and is installed in those surrounding walls.

In the case of a rectangular cross-section furnace, the electrode group is preferably arranged on the long side of the circumferential wall, but in the case of a small furnace it can be arranged on the short side of the circumferential wall.

In the above electrode arrangement, the electrodes are arranged so that adjacent electrodes have mutually different phases, and electrodes facing each other have the same phase. Most commonly, the phase difference between the electrodes is 90° or 120°.

In the present invention, the electrode is a rod-shaped electrode.

These rod-shaped electrodes are preferably extended and placed near the center of the furnace in order to heat a wide area. Also,
In a plurality of electrode groups arranged on each peripheral wall,
9. The inner phase electrodes sandwiched between the electrodes at both ends have electrodes with different phases on both sides, so the current density is high.9. Since the consumption of the electrodes is large, in order to prevent this, it is preferable to construct each electrode with two electrodes as shown in the embodiments shown in FIGS. 3 and 4, which will be described later.

In the present invention, the electrodes themselves may be made of known materials, such as molybdenum electrodes, and in the above electrode arrangement, the phase difference between the electrodes is, for example, 90° or 12°.
A phase relationship of 0° can be achieved using known two-phase or three-phase power systems.

That is, FIG. 2 shows the arrangement of the rod-shaped electrode group 9 in a two-phase power system in which adjacent electrodes have a phase difference of 90 degrees from each other, while opposing electrodes have the same phase. It consists of a regulator 10 connected to a three-phase power source and a two-phase output transformer 11 with Scott connection. Control of the current density in the molten glass and therefore the glass temperature by this power system is performed by a regulator 10.

FIG. 6 shows another example of a two-phase electrode arrangement, which has a two-phase power system and a mutual phase relationship between the electrodes as in FIG. are each composed of two electrodes.

FIG. 4 shows a polarity reversal arrangement using a three-phase power system consisting of a regulator 10' and a transformer 11' with a three-phase output 5, and each electrode 9' has a phase of 120 degrees with respect to the other as shown in the figure. It has different R, S, and T phases.

The glass melting and fining process using the vertical rectangular electric melting furnace of the present invention described above will be explained with reference mainly to FIGS. 1 and 2.

In the electric melting furnace 1 shown in FIGS. 1 and 2, a raw glass batch is distributed and supplied to the top opening of the furnace, and is deposited on the molten glass 6 in the furnace to form a batch layer 7. This batch layer 7 blocks heat radiation from the molten glass in the furnace. The glass batch of layer 1 receives heat from the molten glass at the contact interface with the molten glass 6 and is gradually melted and vitrified.

At this time, most of the gas generated by the vitrification reaction passes through the batch layer 1 and is dissipated into the atmosphere.

The molten glass 6 in the furnace is heated by a two-phase electrode group 9 extending perpendicularly to the opposing peripheral walls forming the long sides of the furnace and arranged at regular intervals to near the center of the furnace. This is achieved by energizing from the power system 10°611. Adjacent electrodes have a phase difference of 90°, while opposing electrodes have the same phase. When electricity is applied to the electrodes arranged in this way, the shortest current path is formed between adjacent parallel electrodes,
In addition, a current density gradient decreases in the direction of adjacent electrodes around each electrode, and a uniform highest current density region is formed in a band shape along the electrode. Along with the formation of the highest current density region, a band-shaped highest temperature region is similarly formed in the vicinity thereof, and thus a temperature distribution appears between the electrodes, which is high near the electrodes and decreases as the distance from the electrodes increases. The highest current density and therefore the highest temperature is provided by the regulator 10.

The molten glass heated to a high temperature in this way has a relatively high temperature, and the low-density glass in the highest temperature region mainly forms a large upward flow toward the batch layer T, and a part of the heat is used to melt the glass batch. , supplied to the vitrification reaction, loses heat and cools down, becoming low temperature and high density. This low-temperature, high-density glass mixes with the coarsely molten glass produced as a result of the glass batch melting and vitrification reaction, flows downward, and when it reaches the vicinity of the electrode, it is heated again and rises. do. Due to the existence of this series of cycles, an intense circulating flow A as thermal convection is formed between the vicinity of the stain and the glass batch layer.

Since this electric melting furnace 1 uses only the heating by the electrode group 9 as its heat source, the glass temperature gradually decreases as it moves downward from the vicinity of the electrode group 9. Therefore, the circulating flow only exerts its influence up to a certain position below the electrode group. Even if the heat convection area of this glass corresponds to the melting convection area 4, the depth of the heat convection area of this glass will vary depending on various factors, such as the set temperature, and will vary from case to case, but will usually depend on the depth of the furnace. It is set to a position of about 1/2 to 315.

The crude molten glass is drawn into the circulating stream in the glass of the melting convection zone 4, and during the circulation, its heterogeneous portions are stretched and homogenized through physical stirring, mixing and diffusion, and the batch is Most of the remaining gas that was not degassed near the layer floats to the surface during this circulation and is degassed.

In contrast to the rectangular furnace and electrode arrangement shown in Figs. 1 and 2 above, when using a rectangular furnace with the electrode arrangement shown in Figs. 6 and 4,
Basically, the same current pattern and thermal convection as in FIGS. 1 and 2 are formed.

Thus, according to the rectangular electric melting furnace of the present invention, vertically and equally spaced from a pair of opposing circumferential walls of the furnace that are parallel to each other,
A natural and simple in-plane energization pattern can be formed between adjacent parallel electrodes disposed in opposing relation, and mutually uniform between each electrode, thus covering the entire area of the melting convection area. It can be covered to create well-balanced heat convection. In addition, this in-plane energization pattern can basically be formed covering the entire horizontal plane by arranging the electrodes at only one horizontal level, and therefore, for larger furnaces, the number of electrodes can be increased. You can respond with

In this melting convection zone 4, the melted and mixed glass is refined to a slight degree, but there are still some bubbles, non-uniform striae and temperature irregularities. As it progresses to the bottom of the furnace, complete homogeneity, clarification, and temperature uniformity are achieved.

That is, in the molten glass in the laminar flow clarification zone 5, there is only a very slow downward laminar flow B based on the sufficiently small amount of glass drawn out compared to the large amount of molten glass. The molten glass from the molten convection zone 4 rides this laminar flow B and stays in the laminar flow clarification zone 5 for a long time, and while moving downward, the inhomogeneity and temperature unevenness are eliminated based on diffusion and heat conduction. . In addition, among the small bubbles remaining in the molten glass from the molten convection zone 4, lamps
The formula is % (where ■ is the flow velocity of the laminar flow B, g is the gravitational acceleration, and d is the diameter of the bubble), ρ is the density of the molten glass, and η is the molten glass. Bubbles larger than the diameter given by 0 (the viscosity of the glass) float upwards and are defoamed while the molten glass moves through the laminar flow clarification zone, while smaller bubbles increase as the glass moves downward. Under this pressure, most of it melts into the glass according to the law of vapor-liquid equilibrium. In fact, it has been found that there are virtually no air bubbles in the molten glass at the bottom of the furnace. Thus, near the bottom of the furnace there is a molten glass in a pressurized state that is chemically and thermally uniform, bubble-free, substantially completely homogeneous, clarified, and completely purified. Glass is fed into the glass removal opening 8 .

In this turbid stream clarification zone 5, an auxiliary electrode group 12 is provided through the peripheral wall for heating the glass in the bottom zone at the time of starting the furnace and/or for temperature correction of the refined glass supplied to the take-out opening during operation of the furnace. This auxiliary electrode group 1
The heating by 2 must be controlled so as not to cause new thermal convection in the molten glass which is in a laminar state.

[Brief explanation of the drawing]

FIG. 1 is a side cross-sectional view of the electric melting furnace of the present invention, FIG. 2 is a cross-sectional view taken along the plane ■-■ of FIG. 1 showing the electrode arrangement and the power system for the electrodes, and FIGS. FIG. 4 is a cross-sectional view of the furnace showing an alternative electrode arrangement and its associated power system. 1... Electric melting furnace, 2... Peripheral wall, 3... Bottom wall, 4
... Melt convection zone, 5... Laminar flow clarification zone, 6...
Molten glass, 7... Glass batch deposited layer, 8... Molten glass stack opening, 9.9'... Main electrode group, 10,
10'...Regulator, 11, 11'...Transformer, 12...Auxiliary electrode group, A...Circulating flow, B...
・Laminar flow. Agent Asamura Akira 4 people orer Fig. 12 Garden 2-3 Fig. 4 Fig. R2R -1-/

Claims (5)

[Claims] (1) A raw glass batch melting convection area having a receiving opening for the raw glass batch at the top; a molten glass convection area having a molten glass take-out opening at the bottom area and connecting vertically downward to the melting convection area; a laminar flow clarification zone; a set of electrodes extending through and disposed in at least one horizontal level in the circumferential wall defining the zone; and an outlet opening for the molten glass; In a glass electric melting furnace connected to a feeder via an arbitrary flow path: the furnace is formed in the shape of a rectangular cross section; and the electrode group is composed of rod-shaped electrodes, and each electrode A pair of opposing peripheral walls of a surface furnace are provided with electrodes substantially perpendicular to the peripheral walls, equidistantly spaced, and in opposing relation, with adjacent electrodes being out of phase with each other, and electrodes facing each other being An electric glass melting furnace characterized by being arranged in phase with each other. (2) The electric melting furnace according to claim (1), wherein the cross-sectional shape of the furnace is rectangular. (3) The electric melting furnace according to claim (2), wherein the electrode group is disposed on a peripheral wall forming a long side of the furnace. (4) The electric melting furnace according to any one of claims (1) to (3), wherein the phase difference between adjacent electrodes is 90°. (5) Any one of claims (1) to (3) above, wherein the phase difference between adjacent electrodes is 1200°.
The electric melting furnace described in Section. - (6) The electric melting furnace according to any one of claims (3) to (5), wherein the electrode extends and is arranged near the center of the furnace. (Force) The electric melting system according to any one of Claims (1) to (6), wherein the electrodes of each phase on the inside sandwiched between the electrodes at both ends are each composed of two electrodes. Furnace.