Glass melting tank

Abstract

The invention relates to a tank for fully electric heating of a glass melt located in a tank interior, said tank comprising a stepped bottom, a plurality of electrodes, and a lateral wall, and being capable of achieving a throughput of 80 to 450 tonnes / day and a good glass quality. The hot chamber side of the lateral wall forms, above the raised bottom portion, a polygon with at least five sides, a circle or an ellipse in horizontal cross-section. The bottom has a raised bottom portion extending around at least 70% of the periphery of the tank interior and a central homogenising bottom portion that is surrounded by and lower than the raised bottom portion, wherein: the raised bottom portion extends laterally from the hot chamber side of the lateral wall in the direction of the tank interior and has a width which is greater than or equal to 0.25 x D (D is the mean diameter); in the transition from the raised bottom portion to the homogenising bottom portion, a transition wall is formed extending perpendicularly with respect to the surface of the glass melt; and a first group of the plurality of electrodes projects into the glass melt in a region adjacent to the lateral wall and a second group of the plurality of electrodes is located in the raised bottom portion in a region adjacent to the transition wall.

Description

[0001] Glass melting tank

[0002] The present invention relates to a glass melting tank for fully electric heating of the glass melt in the production operating state, a glass melting plant and a method for producing a glass melting tank.

[0003] Tanks for the production of molten glass (glass melting tanks) usually have a floor and a side wall surrounding the interior of the tank. During production, the molten glass is arranged in the interior of the tank and is defined by the floor below and the wall to the sides. The interior of the tank is also often at least partially covered at the top by a roof to reduce the loss of thermal energy and / or the release of exhaust gases and dust. During a melting, refining, and homogenization process, the molten glass flows in the interior of the tank in a flow direction from a melting area, in which raw material mixture and, if applicable, cullet are fed into the interior of the tank, to at least one outlet opening through which the molten glass is drawn off.The drawn-off molten glass can be used, for example, to produce container glass, flat glass, rolled glass, fiberglass, glass fibers, household glass or technical glass.

[0004] So-called cold-top furnaces typically have a complete covering of unmelted starting materials (raw material batch and / or cullet) arranged on top of the glass melt. The temperature of this covering is significantly lower than the temperature of the glass melt and is therefore referred to as "cold." This "cold" covering has the well-known advantage of being thermally insulating and serving as a resource-saving condensate trap. With cold-top technology, the glass flows vertically, i.e., from top to bottom, and is drawn off at the bottom or from the sides. Fully electrically heated glass melting furnaces are well known and are used today, especially for smaller glass throughputs (conveyor capacity / melting capacity / tonnage) for high-quality glass in the range of a maximum of 250 t of glass melt per day.From document US 3,520,979, a glass melting tank with electrical heating is known, in which the tank interior has the shape of a complete 6-sided prism, with the electrodes extending from the side wall into the glass melt. The glass melting tank shown in document DE 34 05 273 C2 also has the same shape of the tank interior, with the electrodes in this variant being designed as top electrodes. An electrically heated, cuboid-shaped tank interior with a horizontal flow direction of the glass melt is disclosed in document US 3,885,945. Today, glass melting tanks with fully electric heating primarily operate according to the cold-top principle, i.e., with a "cold" blanket of raw material batch and / or cullet arranged on the glass bath.

[0005] US Pat. No. 3,683,093 discloses an electrically heated glass melting tank comprising four parallel rows of electrodes, each electrode being arranged on a raised base section and extending upwards into the molten glass. Between each of the two outer rows of electrodes, a feed channel is arranged parallel to the electrode rows, which are connected to a collecting channel arranged between the two central rows of electrodes. The collecting channel also runs parallel to the electrode rows and opens directly into the outlet of the glass melting tank, with the collecting channel having the same width as the outlet.

[0006] The publications JP S60-24055 B2 and JP S61-222928 A also describe electrically heated glass melting tanks whose tank interior is designed such that the glass melt is arranged in a wider upper section (with a larger diameter) and a narrower, lower section (with a smaller diameter). In both sections, including the narrower section, the glass melt is heated by means of electrodes.

[0007] The importance of climate protection and the associated social pressure for more energy-intensive processes used in the glass industry is growing. Currently available processes for generating renewable, so-called "green" energy predominantly produce electrical energy, the most energy-efficient option. High efficiency can be achieved by directly using electrical energy to melt glass, e.g., by heating it with electrodes based on the Joule effect. In contrast, converting renewably generated electrical energy into another energy source (e.g., hydrogen) and heating it by, for example, burning this energy source would result in significantly higher overall losses.Therefore, there is great interest in increasing the use of direct electrical heating of a glass melting tank, especially for glass melting tanks that are intended to achieve higher conveying capacities.

[0008] Further factors influencing the further development of glass melting tank technology are the desired glass quality and the size of the glass melting tank. In many cases, the glass quality should be high, i.e. the bubble density in the final product should be less than 60 small bubbles per 100 g of glass. On the other hand, the daily throughput should be increased by larger units while maintaining a reasonable level of expenditure in terms of the space required for the glass melting tank. The object of the present invention is therefore to create a compact glass melting tank which is fully electrically heated in production mode, delivers good glass quality, and is suitable for medium to large glass throughputs. Furthermore, the object is to provide a cost-effective and simple process for producing such a glass melting tank.

[0009] The above object is achieved by a glass melting tank having the features of claim 1 and a method for its production having the features of claim 14. The above object is further achieved by a glass melting plant having the features of claim 13.

[0010] In particular, the above object is achieved by a glass melting tank for fully electric heating of a glass melt arranged in a tank interior in the production operating state, with a stepped bottom and with a lateral wall, wherein the bottom delimits the tank interior at the bottom and the lateral wall encloses the tank interior laterally, wherein in the production operating state the glass melt is arranged in the tank interior, wherein the hot space side of the lateral wall above a raised bottom section forms in horizontal cross-section an at least 5-sided polygon, for example at least a 6-sided polygon, a circle or an ellipse, wherein the bottom comprises the raised bottom section running around at least 70% of the circumference of the tank interior, preferably around at least 80% of the circumference of the tank interior, and a central, surrounded by the raised bottom section,with respect to this lower homogenization base section, wherein the raised base section extends laterally from the hot space side of the lateral wall towards the tank interior and has a width B which is greater than or equal to 0.25 x D, where D is the mean diameter of the tank interior above the raised base section, wherein in the transition from the raised base section to the homogenization base section a transition wall is formed which runs perpendicularly or almost perpendicularly with respect to the surface of the glass melt, wherein the glass melting tank has a plurality of electrodes which heat the glass melt in the production operating state,wherein, in the production operating state, the surface of the glass melt lies above the raised bottom section and a first group of the plurality of electrodes projects into the glass melt in an area adjacent to the lateral wall above the raised bottom section or from the raised bottom section, and a second group of the plurality of electrodes is arranged in an area adjacent to the transition wall in the raised bottom section and projects into the glass melt from the raised bottom section, so that a melting and refining chamber is formed for the glass melt in the interior of the tank above the level of the raised bottom section and a homogenization chamber is formed below this level, wherein the homogenization chamber is surrounded laterally by the transition wall and below by the homogenization bottom section. (The specification 0.25 x D includes the multiplication of the number 0.25 by D,In the following, multiplications are presented in an analogous manner.),

[0011] The glass melting tank according to the invention has a tank interior that is bounded at the bottom by the floor and, along the largest extent of the glass melting tank, laterally by the wall, each made of refractory material. The lateral wall comprises all outermost side walls of the glass melting tank, but not the transition wall arranged between the raised floor section and the homogenization floor section. In production mode, the glass melt is arranged in the tank interior. According to the invention, a hot chamber side of the lateral wall above the raised floor section, facing the glass melt, has, in horizontal cross-section, the shape of at least a 5-sided polygon (i.e., not a rectangular shape), a circle, an ellipse, or a shape approximating these geometric shapes."Essentially" here means that the hot chamber side of the side wall may have recesses and steps that are not taken into account in this consideration of the general shape of these surfaces. This shape is assumed by the side wall particularly in the vertical section of the glass melting tank, which lies in the area of ​​the glass level and the coverage of the molten glass above the raised floor section. It is important to note that, from a macroscopic perspective / overall, the flow direction of the molten glass during production operation is essentially from top to bottom, i.e., from the surface of the molten glass to the bottom of the glass melting tank (specifically, to the bottom in the area of ​​the homogenization floor section).

[0012] The "in production" state of the glass melting furnace means that the glass melted in the glass melting furnace and drawn off through at least one outlet opening is used for the production of flat glass, hollow glass, fiberglass, or specialty glass. This is to be distinguished from operations in which, for example, before or after a maintenance phase or commissioning, glass production is slowly ramped up or down (tempering or cooling down).

[0013] The hot chamber side of the lateral wall or the transition wall can, with respect to a horizontal cross-section above the raised base section, either have a curved shape (i.e., the shape of a (partial) cylindrical surface) or run straight in sections, i.e., form the shape of a (partial) prism side surface. In particular, the lateral wall above the raised base section has, in horizontal cross-section, essentially the shape of at least a 5-sided polygon, a circle, or an ellipse, or a shape approximating these geometric shapes. The base of the glass melting tank has at least one step and is therefore referred to above as "stepped." The step is formed by the raised base section, the transition wall, and the homogenization base section, with the step running along at least 70% of the circumference of the tank interior (i.e., along the lateral wall).The bottom of the glass melting tank thus has the homogenization floor section, which is surrounded by the raised floor section. It is very advantageous for the glass quality if the step runs along a larger proportion of the circumference of the tank interior, e.g. along at least 80% of the circumference, or along the entire circumference of the tank interior and thus surrounds the entire homogenization floor section. In the latter case, the step is uninterrupted. The step can be shaped as a single, uninterrupted step or formed in two or more than two sections running along the circumference, particularly if the glass melting tank has more than one exit opening for withdrawing the molten glass. The step can be interrupted / divided, for example, by a channel to the exit opening, which connects the homogenization space to a more external exit opening.

[0014] Viewed three-dimensionally, the interior of the tank essentially has the shape of two solid-shaped spaces arranged one above the other, whereby each of the two spaces can have the shape of a prism (horizontal cross-section corresponds to a polygon) or a cylinder (horizontal cross-section corresponds to a circle or an ellipse) or a shape approximating these shapes. The shapes of these spaces can be combined as desired and thus adapted to the specific conditions of the glass melting tank. For example, the melting and refining chamber can have the shape of a prism and the homogenization chamber the shape of a cylinder, or vice versa. The combination of similar shapes (cylinder - cylinder or prism - prism) is also possible. The side walls and the transition wall are designed accordingly.The areas of the outlet opening(s) and any channel(s) upstream of them (in the flow direction of the molten glass) are not taken into account in this consideration (dividing the tank interior into two spaces). The space (or volume) formed further up, above the raised floor section by the tank interior is the melting and refining space and has an average diameter D (measured from the hot space side of the side wall). The raised floor section thus defines a level above which the melting and refining space is formed by the tank interior. In one embodiment, the average diameter D of the tank interior above the raised floor section (i.e. the average diameter of the melting and refining space) is at least 5 m. The maximum average diameter D of the tank interior above the raised floor section can be, for example, 16 m.The space (or volume) formed for the glass melt directly below the level of the raised floor section is the homogenization space, which is bounded laterally by the transition wall, upwards by the melting and refining space, and downwards by the homogenization floor section, and whose upper end is approximately at the level of the raised floor section. The homogenization space has an average diameter d, where d < D / 2. The homogenization space has a significantly smaller diameter d than the melting and refining space (d = D - 2 x B, where B > 0.25 x D). In one embodiment, the average diameter d of the homogenization space is at least 1.6 m and a maximum of 8 m. In other words, the raised floor section extends laterally from the hot space side of the lateral wall toward the interior of the tank and has a width B that is greater than or equal to 0.25 x D = D / 4.In one embodiment, the width B is less than or equal to D / 3 in order to create sufficient volume for good homogenization of the molten glass through a sufficiently large lateral extension of the homogenization chamber. The above definition further implies that the two chambers (melting and refining chamber and homogenization chamber) are arranged essentially concentrically, i.e. the two vertically running axes of these chambers lie one above the other or parallel, wherein in the latter case the axes are only a small distance apart in the horizontal direction, i.e. a distance of at most 0.5 m. The mean diameter d is determined as the mean diameter in the region of the homogenization chamber, i.e. as the mean diameter of the glass melting tank below the raised floor section. In addition, the homogenization chamber is arranged directly, i.e. immediately below the melting and refining chamber.The starting materials are melted and refined after being fed into the melting and refining chamber, preferably from above, and then pass into the homogenization chamber directly below.

[0015] The homogenization chamber can also have the shape of a circle, an ellipse, or a polygon with at least three sides, for example, a polygon with at least five sides or a polygon with at least six sides, in its horizontal cross-section. This means that, depending on the shape of the homogenization chamber, the raised floor section may not have the same width throughout the horizontal direction. This width depends on the shapes of the melting and refining chamber and the homogenization chamber.

[0016] Each of the two chambers can take the form of a rotationally symmetrical body, whereby rotational symmetry is understood to mean that the respective body is mapped onto itself by rotation through certain, predetermined angles around the longitudinal axis. In one embodiment, the rotationally symmetrical body is a substantially straight body, since a chamber in the form of a straight body is more cost-effective in the realization of such a glass melting tank. In the vertical direction, the tank interior has a predetermined height, with the height being measured from the bottom of the homogenization floor section to the upper edge of the side wall.In one embodiment, the vertical height of the tank interior is a maximum of 3.5 m, since deeper tanks would endanger the operational safety of the system due to the temperature-related length change behavior of the refractory material forming the lateral wall and the transition wall and the vitrostatic pressure of the glass.

[0017] In one embodiment, the height difference h between the raised floor section and the homogenization floor section is at least 0.5 m. This creates a sufficiently large homogenization space in the vertical direction and also in terms of volume (taking into account the horizontal expansion), so that good glass quality can be achieved. This height difference simultaneously forms the vertical height of the homogenization space. The height difference (regardless of any inclined design of the transition wall) is measured in the vertical direction relative to the surface of the molten glass. In one embodiment, the height difference between the raised floor section and the homogenization floor section is a maximum of 2.7 m. When considering the height difference h, the collar described below, which can be arranged on the raised floor section, is not taken into account.

[0018] The height of the glass melt in the interior of the tank during production is also referred to as the glass level depth. Here, the glass level depth only includes the height of the melt, but not the covering of cold raw material mixture and / or cullet arranged above the melt. The glass level depth is a value assigned to the interior of the glass melting tank and can, for example, be measured indirectly using the bath depth in the riser, which adjoins the glass melting tank after the outlet opening and the passage channel in the direction of flow. In the area of ​​the raised floor section, the glass level depth T can be a minimum of 0.8 m and a maximum of 2.7 m, while in the area of ​​the homogenization floor section, the glass level depth can be a minimum of 1.3 m and a maximum of 3.2 m.

[0019] In one embodiment, the transition wall can run vertically with respect to the surface of the molten glass. Alternatively, the transition wall can run at a small angle to this vertical, for example at a maximum angle of 30° to this vertical. In this case, the slope of the transition wall can be selected such that the diameter of the homogenization chamber is larger at the top than at the bottom, in the region of the homogenization base section, or vice versa. In the simplest embodiment, the surface of the raised base section runs parallel to the surface of the molten glass; in one embodiment, the surface of the raised base section can run at an angle, for example such that the glass level depth above the raised base section increases radially towards the center of the glass melting tank, i.e. it is designed to slope downwards towards the center of the glass melting tank.

[0020] The electrodes that are active in the production operating state and project into the glass melt are arranged in two groups in the glass melting tank according to the invention. A first group of electrodes is used as a top electrode, bottom electrode and / or side electrode in an area adjacent to the lateral wall, and a second group of electrodes is used as a bottom electrode in an area adjacent to the transition wall in the production operating state. These two groups are located in the area of ​​the raised bottom section, i.e., in or above the raised bottom section. In particular, in one embodiment, no electrodes that are active in the production operating state are arranged in the homogenization chamber. This means that in the production operating state, the glass melt in the homogenization chamber is not heated. Rather, the energy input (i.e.,the heat input) into the glass melt only in the region of the melting and refining chamber above the level of the raised bottom section. The electrodes of the first group and the electrodes of the second group are spaced apart from one another, for example, in the radial direction, wherein the distance between the electrodes is selected such that it is as large as possible, taking into account the width of the raised bottom section and a minimum distance (for top and bottom electrodes) from the lateral wall in the first group and a minimum distance from the transition wall. In one embodiment, no further electrodes, which heat the glass melt in the production operating state, are provided between these two groups.Alternatively, at least one further group of electrodes can be provided between these two groups, which supply heat energy to the glass melt in the production operating state, whereby this further group is also arranged in the melting and refining chamber and heats the glass melt above the raised floor section.

[0021] The inventive design of the tank interior in the stepped shape described above and the specific arrangement of the electrodes as electrodes near the side wall (first group of electrodes) and as bottom electrodes protruding from the raised bottom section and arranged near the transition wall (second group of electrodes) allow a significant increase in the diameter of the glass melting tank and thus in the glass throughput compared to previous solutions with all-electric heating, while simultaneously achieving very good glass quality. The glass throughput, as shown by the examples below, is particularly in the range between 80 t / day and 450 t / day.This throughput is achieved on the one hand by the fact that in the area of ​​the melting and refining chamber above the raised floor section, due to the two spaced-apart electrode groups arranged there and the resulting flows in the molten glass, good melting of the starting materials (batch and / or cullet) which are preferably placed on top and good refining (i.e. expulsion of bubbles) of the molten glass is achieved. The distance between the electrodes of the first electrode group and the electrodes of the second electrode group causes the formation of a strong, easily controllable flow in the molten glass in the area of ​​the melting and refining chamber. In particular, the distance between the electrodes of the first group and the nearest electrodes of the second group orThe distance between the oppositely arranged electrodes of the second group is roughly comparable, so that even in the central area of ​​the glass melt arranged in the melting and refining chamber, a corresponding, sufficient flow dynamic is achieved in the glass melting tank, which differs little from the flow in the outer area of ​​the melting and refining chamber (see explanations below for Figs. 2b and 2c). Furthermore, due to the essentially vertical arrangement of the bottom electrodes, the flows have a significant vertical component, which promotes good melting and refining in the melting and refining chamber.In addition, the glass melt in the homogenization chamber, which is located below the melting and refining chamber, is provided with sufficient volume to ensure homogenization and stabilization of the glass melt to the extent required for good gas quality, preventing the direct escape of solid starting materials or bubbles into an outlet opening. This is achieved in particular because no energy is input into the homogenization chamber during production, as the glass melt is not heated by electrodes.

[0022] The above-described dimensions of the melting and refining chamber and the homogenization chamber (achieved by dimensioning the raised floor section, transition wall, and homogenization floor section), as well as the above-explained arrangement of the electrodes on the raised floor section, result in convection bands rotating in opposite directions (relative to a vertical section) being formed in the glass melt in the melting and refining chamber between opposing electrodes. Each convection band has a large vertical, upward component in an area near the respective electrode and a large vertical, downward component in a central area between opposing electrodes. Between an area near an electrode and the adjacent central area, each convection band has a large horizontal component. The convection bands are shown in Fig.2b and 2c are shown by way of example in connection with an embodiment and are explained below. The convection bands, as described above, ensure thorough mixing of the starting materials, which are preferably applied from above, and promote the complete dissolution of the more difficult-to-melt components of the starting materials. This convection takes place in the melting and refining chamber. In contrast, in the homogenization chamber during production, no energy is introduced by electrodes, so that the glass melt there has a significantly lower flow velocity, for example, at least one order of magnitude lower, with the exception of an upper transition section of the homogenization chamber, which is located in the immediate vicinity of and in the transition to the melting and refining chamber. In this transition section, the glass melt flows at a somewhat higher velocity.The height of this transition section, measured in the vertical direction from the level of the raised floor section, is not greater than 0.25 xh, for example not greater than 0.15 xh, whereby the transition section has a lower height (measured vertically from the level of the raised floor section) on the sides (i.e. viewed in the radial direction) of the homogenization chamber than in the central region. In a main section of the homogenization chamber, which lies below this transition region and occupies by far the largest part of the homogenization chamber, the glass melt is characterized in that at the points in this region the vertical component of the glass flow velocity, i.e. the average sinking velocity of the glass melt towards the outlet opening, is approximately of the order of magnitude of the buoyancy velocity of the gas bubbles enclosed in the melt or is less than this buoyancy velocity of the gas bubbles.The main section of the homogenization chamber has a greater height on the sides (i.e., viewed in the radial direction) than in the central area. The respective settling speed and the respective buoyancy-related speed are related to the corresponding glass chemistry (i.e., the respective composition of the molten glass or the respective glass type (borosilicate glass, water glass, container glass, fiber glass)). This means that in the homogenization chamber, the molten glass is at rest, as described above, and any gas bubbles still present are not drawn downwards toward the outlet opening by the settling molten glass, but migrate upwards into the melting and refining chamber due to their buoyancy.It is also important that the vertical height of the homogenization chamber h is dimensioned such that the outlet opening is vertically spaced sufficiently from the melting and refining chamber to provide the gas bubbles with sufficient time and volume to rise. In one embodiment, the outlet opening is arranged such that, when the glass melting tank is new, its upper edge has a vertical distance from the level of the raised floor section that is greater than x h. The convection bands and the temperatures and flow velocities present in the glass melt are explained in more detail below using an embodiment and a corresponding simulation.

[0023] For particularly good results in terms of glass quality, the electrodes of the first group are arranged in a region of the melting and refining chamber so that they are at a maximum distance (in the horizontal direction) of 800 mm from the hot chamber side of the side wall. The electrodes of the first group can be designed as top electrodes and / or side electrodes and / or bottom electrodes. As a top electrode, the respective electrode protrudes from the surface of the molten glass into it; as a side electrode, the respective electrode protrudes from the side wall into the molten glass; and as a bottom electrode, the respective electrode protrudes from the raised bottom section into the molten glass.For example, the top electrode can have a minimum (horizontal) distance from the side wall of 150 mm, while the bottom electrode can have a minimum (horizontal) distance from the side wall of 150 mm (each relative to the hot space side of the side wall). The side electrode can have a distance from the raised floor section of a maximum of 2.5 m and / or a minimum of 200 mm, whereby the distance also depends on the glass stand depth above the raised floor section.

[0024] The electrodes of the second group are designed as floor electrodes, for example, and are spaced at a minimum distance of 500 mm from the edge of the raised floor section where the transition wall begins (hereinafter also referred to as the inner edge). They also have a predetermined distance from the electrodes of the first group. Consequently, the horizontal diameter of the arrangement formed by the second group of electrodes is larger than the diameter d of the homogenization chamber, for example, by at least 1 m.

[0025] In one embodiment, the electrodes within the respective group (i.e., within the first group and within the second group) can be arranged individually or as a pair along a line that runs parallel to a horizontal cross-sectional line of the lateral wall (for the first group of electrodes) or the transition wall (for the second group of electrodes), evenly distributed / equidistantly. Alternatively, the electrodes of the first group can, for example, as explained below, be arranged in subgroups of three individual electrodes or three electrode pairs that are closer together in the direction along the line. The distance between the two outermost of the three electrodes / electrode pairs is approximately comparable to the distance between the middle electrode / electrode pair and an opposite electrode / electrode pair of the second group.

[0026] In one embodiment, all electrodes of the first group have the same distance (in the horizontal direction) from the lateral wall (if they are designed as top or bottom electrodes) and / or all electrodes of the second group have the same distance (in the horizontal direction) from the transition wall. Alternatively, the distance from the lateral wall or the transition wall can vary within the respective group, which can also be caused by the specific shape of the lateral wall or the transition wall.

[0027] For good glass quality, it is important that the electrodes are arranged in such a way that the entire volume of the melting and refining chamber is heated and that no dead zone is created. With the inventive dimensioning of the glass melting tank and arrangement of the electrodes, such a dead zone is avoided. As shown below in the exemplary embodiment using Figs. 2b and 2c, the convection introduced by the electrodes of the second group generates convection bands that extend across the central region of the melting and refining chamber.

[0028] The advantageous spatial arrangement of the electrodes of the first group near the lateral wall and the electrodes of the second group near the transition wall described above results in flow dynamics in the melting and / or refining chamber that are particularly uniform in the horizontal direction and can thus be set to be comparatively stable. The interior of the furnace represents the space designated for melting the added raw material mixture and / or the supplied cullet, refining the molten glass, and homogenizing it. As already explained above, it can be divided into an upper melting and refining chamber and a homogenizing chamber located below. The interior of the furnace thus has a compact shape that is also easily accessible from the outside. This shape is usually created by palisade sections made of refractory material that are placed and secured next to and / or on top of one another.The refractory material can be, for example, inorganic, non-metallic materials (ceramics, glass, glass ceramics, mineral fibers) and can include, for example, the oxides silicon oxide, aluminum oxide, magnesium oxide, calcium oxide, zirconium oxide, chromium oxide. Carbon and silicon carbide can also be used as components. One material used, for example, is fused cast AZS (aluminates, zirconates, silicates, also aluminum, zirconium and silicon oxides). Furthermore, the refractory material can have at least one coating on the hot space side, for example made of platinum or a platinum alloy. With or without the specified coating, the refractory material can be composed of one layer, at least two or more than two layers with different compositions, e.g. with different zirconium contents.

[0029] The cold room sides of the side wall and the transition wall of the glass melting tank, each facing away from the tank interior, can run essentially parallel to the respective hot room side. The cold room sides can be at least partially or completely insulated.

[0030] In one embodiment, a collar can be arranged directly on the transition wall in the region of the raised base section, which collar is at least 50 mm high and / or at least 50 mm wide. The height is specified as the height above the raised base section. The width is the extent of the collar in the horizontal direction. The collar begins at the transition wall and represents a protrusion that projects vertically upwards from the raised base section. The end wall of the collar opposite the transition wall (sill) is arranged radially further inward in the tank interior than the electrodes of the second group. The collar effects an additional mechanical separation of the moving zone in the melting and refining chamber from the calm zone in the homogenization chamber.

[0031] In one embodiment, the glass melting tank is configured to operate according to the cold-top principle. This means that the raw material mixture and / or cullet are fed from above toward the surface of the glass melt, which is preferably completely covered for most of the time during production. In one embodiment, the diameter or area of ​​the surface of the glass melt covered with raw material mixture and / or cullet is larger than the diameter d or the cross-sectional area of ​​the homogenization chamber during production.As described above, the heating of the glass melt during production is carried out exclusively by means of electrodes that protrude from above into the surface of the glass melt (top electrodes), from the raised bottom section into the glass melt (bottom electrodes), or from the side wall (side electrodes) into the glass melt, and only into the glass melt located in the melting and refining chamber. In addition, at least one burner can be provided for fossil heating (e.g., for tempering the glass melting tank), which, however, is not used during production.

[0032] In one embodiment, the top of the tank interior is covered by a ceiling which seals it off almost completely in dust-tight fashion. In other words, the tank interior is sealed off so completely in dust-tight fashion that, during production, a negative pressure is created in the central region of the tank interior above the glass melt compared to a location in the vicinity of the glass melting tank where exhaust gases from the tank interior are released. Accordingly, the dust-tight seal ensures that practically no dust originating from the tank interior reaches the area around the glass melting tank. In addition, the seal can significantly reduce heat losses. The openings for the electrodes and any burners are sealed off in dust-tight fashion during normal operation; this is only not guaranteed when changing the electrodes.Furthermore, during production, the openings for feeding the batch and / or the cullet are sealed gas-tight. If necessary, a venting device is provided (e.g., in a side wall) through which gas generated during melting can be removed. The gas is filtered by appropriate filters (e.g., for toxic gases and dust) to ensure compliance with applicable environmental regulations. The exhaust gas is released into the environment.

[0033] In one embodiment, the ceiling is designed as a rotating ceiling, which essentially has the shape of a disc and is preferably designed as a suspended rotating ceiling. The use of a rotating ceiling in the form specified above enables simple covering of the interior of the furnace, so that heat losses and the release of exhaust gases and / or dust can be avoided or reduced. At the same time, the rotating ceiling, which is designed to rotate over at least 90°, preferably over at least 180°, allows simple, uniform, and easily controlled feeding of raw material mixture and / or cullet to the glass melt.

[0034] The side wall, the transition wall, and the floor of the glass melting tank can be at least partially supported by an external steel frame arranged on a cold room side. The external steel frame supports the side wall, the transition wall, and the floor (i.e., the raised floor section and the homogenization floor section). The external steel frame can also each have an annular rail element on its upper side. Each rail element serves to support and guide the rotating ceiling, with the rotating ceiling having at least three corresponding wheels or pairs of wheels that roll along the respective rail element.

[0035] In one embodiment, the sealing of the glass melting tank in the area of ​​the side wall is achieved by means of an apron (collar) projecting vertically downwards from the rotating ceiling, which engages a guide containing a sealing material, e.g., sand (also referred to as a sand pocket). The guide can be arranged on the upper side of the outer steel frame, approximately horizontally, next to the respective rail element.

[0036] In one embodiment, the glass melting tank is designed such that the raw material mixture and / or cullet are fed into the glass melting tank from above through at least one corresponding, dust-tight opening in the ceiling, such that the raw material mixture and / or cullet are continuously deposited over a large area on the surface of the molten glass, for example, in the form of one or more annular strips. This ensures a uniform distribution of the starting materials (raw material mixture and glass cullet) over the surface and more effectively realizes the advantageous operation of the glass melting tank according to the cold-top principle. "Large-area" deposit means that the raw material mixture and / or glass cullet are deposited on at least 40% of the surface of the molten glass, which^) is distributed over the entire surface of the molten glass due to the forming cones of material and the movement of the coating on the molten glass.

[0037] In one embodiment, the feed device and the rotating ceiling are designed such that the raw material mixture and / or cullet are fed into the glass melting tank through a plurality of dust-tight openings in the rotating ceiling. The feed can in particular take place through two or more openings, e.g. arranged next to one another in the radial direction of the rotating ceiling, which results in a more even distribution of the raw material mixture and / or cullet on the surface of the molten glass. In a further embodiment, at least two groups of openings arranged next to one another in the radial direction can be provided for the feed of raw material mixture and / or cullet, which further evens out the distribution and possibly reduces the angle of rotation required when rotating the rotating ceiling.The feed device can, for example, be designed such that at least one stationary storage container for raw material mixture and / or cullet is provided above the glass melting tank, from which raw material mixture and / or cullet is fed by means of a dosing device at appropriately coordinated times to at least one storage container movable with the rotating ceiling. For example, the raw material mixture and / or cullet can be fed in sufficient quantities if, along the rotational movement of the rotating ceiling, the movable storage container is located below the stationary storage container. Alternatively, a flexible feed pipe can be provided which, during the rotation of the rotating ceiling, connects the outlet of the dosing device to the inlet of the storage container movable with the rotating ceiling.From the storage container, which is movable with the rotating ceiling, the raw material mixture and / or cullet is then further distributed to the openings in the rotating ceiling, for example, by means of an additional transport and / or dosing device (e.g., a vibrating chute or screw). If at least two groups of openings are provided, the openings of one group are arranged radially offset from the openings of the other group, so that the surface of the molten glass can be evenly coated with the supplied raw material mixture / glass cullet.The transport and / or dosing device can, for example, be designed in such a way that the at least one opening located radially further inwards receives a smaller quantity of raw material mixture and / or cullet than the at least one opening located radially further outwards, since the area on the surface of the glass melt to be covered by the respective opening during rotation of the rotating cover differs accordingly.

[0038] As already explained above, the overall flow direction of the glass is from top to bottom (vertical), i.e. from the surface of the molten glass towards the homogenization floor section of the tank interior, with at least one outlet opening through which the molten glass is drawn off being arranged in the region of the homogenization floor section, the lower end of the transition wall and / or the lower end of the lateral wall. The outlet opening can be located at the height of the lower end of the transition wall or below in the vertical direction, i.e. approximately at the height of the homogenization floor section. The lower edge of the outlet opening can, for example, be at the height of the homogenization floor section or below in the vertical direction.In one embodiment, one, two or three outlet openings are provided next to or opposite one another at the lower end of the transition wall and / or at the lower end of the lateral wall. In one embodiment, a corresponding depression / notch can be provided in the homogenization base section, e.g. with a width of at least 400 mm, which extends in the direction of the outlet opening. In this embodiment, the outlet opening lies at least partially or completely below the vertical height of the homogenization base section. In another case, in which the outlet opening is located at the bottom of the lateral wall, the lateral wall extends in the region of the outlet opening as far as the homogenization base section. In this case, the raised base section is interrupted in a region running radially to the axis of the melting and refining chamber / homogenization chamber.In other words, in this embodiment, a radially extending channel is provided upstream of the outlet opening in the flow direction of the glass melt, which channel runs essentially radially from the homogenization base section to the (downwardly drawn) lateral wall. The channel has at least a width corresponding to the width of the outlet opening, for example, at least 400 mm. In one embodiment, the outlet opening has a maximum width of 1 / 2x d (d = diameter of the homogenization chamber). In another embodiment, the vertical height of the outlet opening in the new state is less than x h. The maximum width that the channel can assume in one embodiment is the maximum diameter of the homogenization chamber.

[0039] In one embodiment, the outlet openings are arranged opposite one another when using two outlet openings (corresponds to a distance of 1800 relative to the circumference of the raised base section or the homogenization section, depending on where the outlet opening is provided - in the radial direction -), if three outlet openings are used, these are spaced apart by 120 °, for example.

[0040] In one embodiment, each electrode of the first group can be designed as a top electrode such that, in the production operating state, it is perpendicular to the surface of the glass melt or at a small angle to this vertical direction, e.g., a maximum of 30°, preferably between 5 0and 20°, obliquely from above, i.e. from the surface of the glass melt, into the glass melt and heats the glass melt from above. In one exemplary embodiment, the top electrode can additionally be designed so that it can be pivoted in and out of the interior of the tank. This allows each electrode to be easily replaced or renewed. The electrodes arranged in / on the side wall are accessible from the outside. Each top electrode has a corresponding, pivotable holder. In one exemplary embodiment, each electrode of the second group can be designed as a bottom electrode such that, in the production operating state, it protrudes perpendicular to the surface of the glass melt or at a small angle to this vertical direction, e.g. a maximum of 30°, preferably between 5° and 20°, obliquely from below, i.e. from the raised bottom section, into the glass melt and heats the glass melt from below.In one embodiment, the bottom electrode can also be designed to be retractable into the interior of the tank. This allows each electrode to be easily replaced. The electrodes located in the raised bottom section are accessible from below.

[0041] In one embodiment, at least one step and / or at least one recess is provided on or in the lateral wall on the respective hot chamber side. The at least one recess in / on the lateral wall of the glass melting tank can be provided, for example, for the arrangement or the pivoting in and / or out of the at least one top electrode. A step arranged, for example, above the lateral wall can be designed in such a way that it reduces or increases the annular width of the tank interior compared to the width below the step.

[0042] According to the invention, the glass melting tank is provided with a plurality of electrodes for heating the glass melt, wherein the required number of electrodes heating the glass melt in the production operating state and their energy supply are determined on the basis of the melting and refining energy required for a given glass throughput. The total number of electrodes can be, for example, 18, 24, 36, or 42, wherein the first group and the second group can have a different or the same number of electrodes. For this purpose, the resulting average current density on the surface of the respective electrode, which has a value of 3 A / cm 2 should not be exceeded. Furthermore, the current carrying capacity of the electrode holder system should not exceed approximately 3,600 A.

[0043] Due to the arrangement of the electrodes in the first group near the side wall and in the second group near the transition wall, the electrodes are arranged, for example, on at least two circumferential, concentric circles or circular lines (viewed in horizontal cross-section) and interconnected in such a way that a voltage of 500 V (for safety reasons) and a current of 3,600 A are not exceeded. The outer (larger) circle / line is located on the side wall or at a radial distance of 150 to 800 mm, typically 330 mm, from the hot space side of the side wall, while the inner (smaller) circle / line is arranged at a distance of at least 500 mm, typically 750 mm, from the transition wall, each on the raised floor section and at a predetermined distance from the circle / circular line of the first group of electrodes.The electrodes can be arranged individually or in pairs, evenly distributed / equidistantly along the circumference of the respective circle / line. To achieve the most even current distribution possible and thus even wear of the electrodes, three electrodes or electrode pairs located adjacent to each other on the line or circle, as explained above, can be provided on the outer circle with a smaller distance from each other than from the respective nearest electrode / electrode pair. In this case, the distance between the outer two of the three electrodes / electrode pairs is advantageously approximately comparable to the distance between the middle electrode / electrode pair and an opposite electrode / electrode pair of the second group.

[0044] A good distribution of the flows in the melting and refining chamber can be achieved if the ratio of the diameter DEG2 of the circle or circular line of the second group of electrodes to the diameter DEG1 of the circle or circular line of the first group of electrodes DEG2 / DEG1 is in the range between 0.45 and 0.7. This is especially true if the electrodes of the first group are designed as top or bottom electrodes.

[0045] In one embodiment, in order not to exceed the above-mentioned limits of electrode current density and electrode current per electrode, an installation of two electrodes arranged closely next to each other and connected electrically in parallel can be used. This achieves a high number of electrodes. The closely arranged and parallel-connected electrodes electrically form, in a sense, a coherent "virtual electrode." Alternatively, a single electrode can be used for each electrode pair.

[0046] A power supply unit is provided to supply the electrodes with power, implementing a circuit that ensures a uniform, symmetrical load on the electrodes. Suitable electrical circuits map the arrangement of the pointers in the electrical pointer diagram to a geometrically similar arrangement of the electrodes in the respective new type of glass melting tank. The number and arrangement of the pointers in the electrical pointer diagram results from the number and configuration of the transformers provided in the power supply unit. These can be implemented in various electrical circuits, for example:

[0047] • Scott-T circuit - here the number of connected electrodes is a multiple of four,

[0048] • Interlinked three-phase system - here the number of connected electrodes is a multiple of three,

[0049] • Open three-phase system - here the number of connected electrodes is a multiple of 6. The open three-phase system offers advantages in terms of lower load on the melting electrodes and is therefore preferred.

[0050] Further variation options exist, especially in the open three-phase system, in the different connection configurations of the primary side of the transformers – in particular, delta connection and star connection are possible. These connection configurations can also be combined.

[0051] Furthermore, it is conceivable to divide the electrodes arranged in the tank interior into two or more tank interior segments. The electrodes in each segment then form their own heating circuit.

[0052] The above object is further achieved by a glass melting plant with a glass melting tank as described above, wherein the glass melting plant further comprises a feed system for supplying raw material mixture and / or glass cullet and a power supply device for the plurality of electrodes, wherein the power supply device is connected to each electrode. The glass melting plant has the advantages explained above for the glass melting tank.

[0053] The above object is further achieved by a method for producing a glass melting tank as described above, comprising the following steps:

[0054] • Provision of first palisade elements for the side wall of the glass melting tank and second palisade elements for the transition wall as well as floor slabs,

[0055] • Arrangement and fixing of the first and second palisade elements on or at the raised floor section of the glass melting tank and floor plates in the area of ​​the floor such that the hot space side of the lateral wall above a raised floor section essentially forms at least a 5-sided polygon, a circle or an ellipse in horizontal cross-section, wherein the floor has the raised floor section running around at least 70% of the circumference of the tank interior and a central homogenization floor section surrounded by the raised floor section and located lower relative to the raised floor section, wherein the raised floor section extends laterally from the hot space side of the lateral wall in the direction of the tank interior and has a width that is greater than or equal to 0.25 x D, where D is the average diameter of the tank interior above the raised floor section,wherein in the transition from the raised base section to the homogenization base section, a transition wall is formed which runs vertically or almost vertically with respect to the surface of the glass melt, and,

[0056] • Arrangement of the plurality of electrodes which heats the glass melt in the production operating state, wherein in the production operating state the surface of the glass melt lies above the raised bottom section, such that a first group of the plurality of electrodes projects into the glass melt in an area adjacent to the lateral wall above the raised bottom section or from the raised bottom section, and a second group of the plurality of electrodes is arranged in an area adjacent to the transition wall in the raised bottom section and projects into the glass melt from the raised bottom section, so that a melting and refining space is formed for the glass melt in the interior of the tank above the level of the raised bottom section and a homogenization space is formed below this level, wherein the homogenization space is surrounded laterally by the transition wall and below by the homogenization bottom section.

[0057] Using the above method, the glass melting tank shown above can be constructed simply and cost-effectively. As already described above, the palisade elements can be arranged side by side and, if necessary, stacked on top of each other. The palisade elements are preferably secured using the external steel framework described above. The materials suitable for the palisade elements have also been specified above.

[0058] The glass melting tank described above is suitable, as corresponding simulations have shown, for glass throughputs in the range of 80 t / day to 450 t / day. The following parameters of the glass melting tank described above and the parameters of the following exemplary embodiments were also determined on the basis of simulations and various tests. Computerized Fluid Dynamics (CFD) was used in particular as the simulation method. With this method, for example, flow and temperature profiles can be calculated and quality indices of the resulting, simulated glass melt can be determined from these, which are known to those skilled in the art. The average diameter D of the glass melting tank in relation to the hot space side of the side wall above the raised floor section can be, for example, between 5 m and 16 m.The average diameter d with respect to the hot side of the homogenization chamber between opposite areas of the transition wall can, for example, be between 2.5 m and 8 m. As already stated above, the glass depth T down to the homogenization floor section can, for example, be 1.3 m to 3.2 m. Accordingly, the interior of the furnace has a greater height (in the vertical direction) H compared to the glass depth T. The melting surface (surface of the glass melt in production operating condition) can, for example, be between 19.5 m. 2 and 200 m 2 be.

[0059] The novel glass melting tank described above can be used for soda-lime glasses, borosilicate glasses, fiberglass, or other types of glasses. The invention is explained below using exemplary embodiments and with reference to the figures. All described and / or illustrated features, individually or in any combination, constitute the subject matter of the invention, regardless of their summary in the claims or their references. They show schematically:

[0060] Fig. 1 shows a first embodiment of a glass melting tank and a glass melting plant in a perspective view from the side, partially cut away,

[0061] Fig. 2, 2a-4 the glass melting tank according to Fig. 1 in three vertical

[0062] Cross sections (Fig. 2, 2a, 2b, 2c), in a horizontal cross section with reference symbols (Fig. 3) and again without reference symbols (Fig. 4), where Fig. 2b and 2c show simulation data for the embodiment,

[0063] Fig. 5-6 the glass melting tank and feeding system according to Fig. 1 in a view from above (Fig. 5) and in a view from below (Fig. 6),

[0064] Fig. 7-8 a second embodiment of a glass melting tank in a vertical cross-section (Fig. 7) and in a horizontal cross-section (Fig. 8),

[0065] Fig. 9-10 a third embodiment of a glass melting tank in a vertical cross-section (Fig. 9) and in a horizontal cross-section (Fig. 10),

[0066] Fig. 11 a fourth embodiment of a glass melting tank with feed system in a perspective view from the side, partially cut away,

[0067] Fig. 12-13 the glass melting tank according to Fig. 11 in a vertical cross-section (Fig. 12) and in a horizontal cross-section (Fig. 13),

[0068] Fig. 14 the glass melting tank according to Fig. 11 in a view from below,

[0069] Fig. 15-16 a fifth embodiment of a glass melting tank in a vertical cross-section (Fig. 15) and in a horizontal cross-section (Fig. 16),

[0070] Fig. 17 a sixth embodiment of a glass melting tank with a feed system in a perspective view from the side, partially cut away,

[0071] Fig. 18-19 the glass melting tank according to Fig. 17 in a vertical cross-section (Fig. 18) and in a horizontal cross-section (Fig. 19),

[0072] Fig. 20-21 the glass melting tank according to Fig. 17 in a view from above (Fig. 20) and in a view from below (Fig. 21),

[0073] Fig. 22 shows a seventh embodiment of a glass melting tank with a feed system in a perspective view from the side, partially cut away,

[0074] Fig. 23-24 the glass melting tank according to Fig. 22 in a vertical cross-section (Fig. 23) and in a horizontal cross-section (Fig. 24),

[0075] Fig. 25-26 the glass melting tank according to Fig. 22 in a view from above (Fig. 25) and in a view from below (Fig. 26),

[0076] Fig. 27 an eighth embodiment of a glass melting tank with a feed system in a perspective view from the side, partially cut away,

[0077] Fig. 28-30 a section of the side wall of the embodiment according to Fig. 1 with top electrode and electrode holder in a perspective view from the side with the electrode in the production operating state (Fig. 28) and in the partially or completely swung out state (Figs. 29 and 30),

[0078] Fig. 31-32 a region of the raised bottom section of the embodiment according to Fig. 1 with bottom electrode and electrode holder in a perspective view from the side with countersunk electrode (Fig. 31) and electrode in the production operating state (Fig. 32),

[0079] Fig. 33 is a vertical cross-section through an upper region of a side wall and through a rotating cover of a ninth embodiment of one of the glass melting tanks, and

[0080] Fig. 34 shows a horizontal cross-section of the glass melting tank according to Fig. 1, illustrating the connection of the electrodes in this exemplary embodiment. The exemplary embodiments of a glass melting tank or a glass melting system described below contain top electrodes as electrodes of the first group, which are arranged in an area adjacent to the lateral wall. The exemplary embodiments can also be implemented analogously with bottom electrodes that protrude from the raised bottom section into the molten glass or with side electrodes that protrude from the lateral wall in a horizontal direction into the molten glass. The bottom electrodes, like the top electrodes, have a predetermined distance from the hot space side of the lateral wall.

[0081] The first embodiment of a glass melting plant with a glass melting tank 10 shown in Figs. 1 to 6, 28 to 32 and 34 is shown partially cut away in Fig. 1, so that the tank interior 11 is visible. As Figs. 1 to 4 show, the tank interior 11, in which the glass melt 12 is arranged, is laterally delimited by a lateral wall 13. Furthermore, a raised floor section 14 and a homogenization floor section 15 are provided, which together delimit the tank interior 11 from below. The raised floor section 14 and the homogenization floor section 15 are connected to one another by a transition wall 16 running vertically (perpendicular to the surface of the glass melt 12), so that a step is formed in the glass melting tank 10. The glass melting tank 10 operates according to the cold top principle and therefore has a covering 12a (see Fig.2) the glass melt 12 consists of unmelted raw material mixture and / or cullet, which covers the majority of the surface of the glass melt 12. The raw material mixture and / or the cullet are, as described in more detail below, fed from above to the glass melt 12 through the dust-free, sealed cover of the tank interior 11, which is designed as a suspended rotating ceiling 19. The tank interior 11 is composed, as shown in Figs. 2a, 2b and 2c, of the cylindrical melting and refining chamber 11a arranged above the raised floor section 14 and of the cylindrically shaped homogenization chamber 11b adjoining it and arranged concentrically with the melting and refining chamber 11a, wherein the homogenization chamber 11b is bounded laterally by the transition wall 16 and below by the homogenization floor section 15.The common, vertically extending axis 11e formed by the melting and refining chamber 11a and the homogenization chamber 11b is shown in Fig. 2. In Fig. 2a, which corresponds to the cross-section shown in Fig. 2, the two subchambers 11a, 11b of the tank interior 11 are illustrated by different hatching. The position of the cross-sections according to Figs. 2 and 2a is illustrated in Fig. 4 by a dashed line S1, and the position of the cross-section according to Figs. 2b and 2c is illustrated in Fig. 4 by a dash-dotted line S2.

[0082] The lateral wall 13 has (relative to a horizontal cross-section) a circular shape above the raised floor section 14 and a vertical height H, so that the melting and refining chamber 11a is essentially cylindrical. The average diameter D above the raised floor section between opposite hot space sides of the lateral wall 13 is 14 m in this embodiment. The raised floor section 14 has a width B of 4.2 m, so that the diameter d of the homogenization chamber or the distance between opposite hot space sides of the transition wall 16 is approximately 5.6 m. The height difference h between the circular homogenization floor section 15 and the raised floor section 14 running around the homogenization floor section 15 is approximately 1.1 m (see Fig. 2).As can be seen from the table below, simulations have shown that a throughput of 350 t / day can be achieved with such a glass melting tank, with a volume of molten glass of 285.7 m. 3 and the surface of the glass melt is 153.9 m 2 . In the glass melting tank 10, at the lower end of the side wall

[0083] 13, an outlet opening 13a is provided through which the molten glass is drawn off, for subsequent processing, for example, into container glass. For this purpose, the lateral wall 13 extends in the region of the outlet opening 13a to the homogenization base section and is connected to the homogenization chamber 11b via a channel 11c extending along the radial direction. In the region of the channel 11c, the raised base section

[0084] 14. The lower end of the outlet opening 13a is located at the level of the homogenization base section 15, so that the channel 11c runs straight from the latter toward the outlet opening 13a. Adjoining the outlet opening 13a in the flow direction of the glass melt are the passage channel 21, the riser 22, and the working tank 23.

[0085] The glass melting tank 10 has two groups of electrodes. A first group of electrodes 17 (here: 24 electrodes) are arranged at a distance of approximately 250 mm to 550 mm next to the side wall 13 and are designed as top electrodes. They protrude from above into the glass melt 12. These electrodes are also referred to below as outer electrodes 17. Furthermore, a second group of electrodes 18 is provided, which are arranged on the raised floor section 14, at a distance of approximately 600 mm to 800 mm from the transition wall and are designed as bottom electrodes. They protrude from the raised floor section 14 vertically upwards or slightly inclined to the vertical into the glass melt 12. The electrodes of the second group are also referred to as inner electrodes 18. The two groups are spaced apart, for example, between 2.85 m and 3.35 m. The distance between opposite inner electrodes 18 is, for example, 6.8 m.

[0086] In one exemplary embodiment, each outer electrode 17, as shown in more detail in Fig. 28, projects through an opening 13d arranged above the lateral wall 13 into the tank interior 11 and from above into the glass melt 12. As shown in Figs. 29 to 30, each outer electrode 17 is designed to be pivotable between a first position shown in Fig. 28 and a second position sketched in Fig. 30. In the first position, the electrode 17 is in the working state in which the electrode supplies the glass melt 12 in production operation due to the Joule effect. In the second position of the electrode 17, it is completely moved out of the tank interior 11 and can, for example, be serviced. The position shown in Fig. 29 symbolizes the movement of the electrode 17 out of the tank interior 11.For moving the electrode in and out and securely positioning it in the tank interior, each outer electrode has a holder 17a with which the electrode can be pivoted and which fastens the electrode to an external steel frame 36 arranged on the outside of the lateral wall 13. In the production operating state, each electrode is arranged at a slight incline (e.g., at an angle of 5° to 20°) to the vertical direction (see Fig. 28), which facilitates pivoting the electrode in and out. In one embodiment, each opening 13d is sealed dust-tight in the production operating state. Specifically, this embodiment has twelve inner electrodes 18 and twenty-four outer electrodes 17, which are each arranged in pairs and otherwise evenly distributed along / next to the lateral wall 13 or the transition wall 16.Alternatively, the outer electrodes can also be arranged in groups of three pairs, each of which has a smaller distance from the adjacent pair than if the pairs were evenly distributed over the entire circumference. No electrodes are provided in the area of ​​channel 11c.

[0087] The inner electrodes 18 are designed as bottom electrodes which, during production operation, protrude vertically upwards from the raised bottom section 14 into the glass melt 12, as shown in more detail in Fig. 32. Each electrode 18 is designed to be movable, as shown in Figs. 31 and 32, so that it can be replaced or adjusted when worn. The electrode is inserted into the tank interior 11 through a bore 14a in the bottom section 14, which is closed by an electrode block 12b made of particularly high-strength refractory material (e.g., AZS with a high zirconium content of at least 41%). Furthermore, the electrode 18 has a hollow-cylindrical insulation and cooling unit 18a, which is cooled, for example, with water. A holder 18b is also provided, with which the electrode 18 is fastened to the cold space side of the raised bottom section 14.The holder 18b is further designed to allow manual displacement of the electrode 18 in the vertical direction along a guide rail running parallel to the electrode. This allows for a defined tracking of the electrode 18. Fig. 31 shows the electrode 18 in a state in which the electrode 18 is retracted.

[0088] As already explained above, the arrangement of the electrodes and the dimensioning of the raised base section 14, the transition wall 16 and the homogenization base section 15 cause convection bands KB1 to KB6 to form in the melting and refining chamber 11a between opposing electrodes, so that good melting of the starting materials and good refining are achieved. The convection bands located between two electrodes and rotating in opposite directions are convection bands KB1 and KB2, KB3 and KB4 and KB5 and KB6. Two further convection bands KB7 and KB8 are formed between the electrodes 17 and the side wall 13. The convection bands KB1 to KB8 are illustrated in the simulation shown in Fig. 2b and, because the arrows in the simulation are very small, are shown schematically in Fig. 2c. The glass melting tank 10' used for the simulation does not exactly correspond to the one shown in Fig.1, 2, 2a, 3 and 4, because in the variant of Figs. 2b and 2c the outlet opening 13a' is set somewhat lower and the outer electrodes 17' are arranged directly opposite the respective inner electrodes 18 of the variant of Figs. 1, 2, 2a, 3 and 4. Furthermore, it should be noted with regard to the convection bands KB3, KB4 and KB5 that these partially extend into the plane of the drawing and are therefore not so clearly visible in the simulation data shown in Fig. 2b.

[0089] In the simulation in Fig. 2b, the direction of the arrows represents the flow direction of the molten glass and the length of the arrows represents the velocity at each location in the molten glass. The convection in the form of the convection bands KB1 to KB8 is very strong in the melting and refining area 11a. The simulation shown in Fig. 2b also shows that, in contrast, a low flow can be observed in the homogenization chamber 11b (or in its main section located below a transition section). The vertical component of the flow velocity of the molten glass towards the outlet opening 13a is smaller than or on the order of magnitude of the buoyancy-related velocity of the gas bubbles enclosed in the molten glass. This is also evident from the following table, which contains measured values ​​determined by means of the simulation. The measured values ​​were recorded for a total of 11 different measuring points M1 to M11 in the chamber shown in Fig.2c, the measuring points M1 to M1 1 being shown in Fig. 2c.

[0090]

[0091] The CFD simulation is based on the following dimensions of the glass melting tank 10': D = 14 m; d = 5.6 m; h = 1.1 m; H = 1.8 m. The electrodes 17 of the first group are arranged at a distance of 0.75 m from the hot chamber side of the side wall 13, and the electrodes 18 of the second group are arranged at a distance of 0.6 m from the transition wall 16. The glass type used for the simulation was soda-lime glass with a glass density (under production conditions) of 2.4 t / m 3used. The circular disk-shaped rotating ceiling 19, shown in particular in Figs. 1, 5 and 6, which seals off the interior 11 of the tank from above with regard to heat loss, dust and exhaust gases, with dust and exhaust gases being sucked off into a filter system, has nine dust-tight openings 19a, of which four or five are located next to one another in the radial direction. A negative pressure is created by means of the suction system. Raw material mixture and / or cullet is fed through the openings 19a to the interior 11 of the tank, in particular to the surface of the molten glass 12. The rotating ceiling 19 is designed as a suspended rotating ceiling and is rotatably fastened by its upper side to a steel frame which extends over the upper side of the glass melting tank 10 and which is not shown in Figs. 1, 5 and 6.

[0092] A feed device comprises a stationary storage container (not shown) with a dosing device. Furthermore, a storage container 24 rotating with the rotating ceiling 19 is provided on each side. From each storage container 24 rotating with the rotating ceiling 19, the raw material mixture and / or cullet enters a screw or vibrating chute 27 and is transported by this via further rotating storage containers 28 through a continuous opening 19a, each by means of small vibrating chutes, into the interior 11 of the tank and onto the surface of the molten glass 12. Due to the rotating movement of the rotating cover 19 about a rotation axis running approximately in the region of the vertical axis 11e of the melting and refining chamber 11a or the homogenization chamber 11b, a large part of the surface of the glass melt 12 located in the interior 11 of the tank is successively provided with a (cold) covering 12a of raw material mixture and / or cullet.Through each opening 19a, an approximately ring-shaped carpet of raw material mixture and / or cullet is formed. In the illustrated embodiment, each opening 19a of the first group, connected via a screw or vibrating chute 27, is arranged radially offset from the openings 19a of the second group, which is connected via a further screw or vibrating chute 27, in order to ensure a uniform distribution of the raw material mixture or cullet on the surface of the molten glass 12. Each storage container 24 receives additional raw materials / cullet from the stationary storage container (not shown) when it is guided past the stationary container during the continuous rotation of the rotating ceiling through 360° and is arranged below it for a predetermined time.Furthermore, the dosing, in particular of the screw or vibrating chute 27, can be designed such that the further, co-rotating storage containers 28 located further inside receive a smaller amount of starting materials than the co-rotating storage containers 28 located further out.

[0093] The lateral wall 13 and the transition wall 16 are composed of palisade elements arranged one above the other and next to the other. This can be seen in the cutaway view in Fig. 1 at the respective ends of the lateral wall 13 and the transition wall 16. Above the lateral wall 13, in the area where the openings 13d for the outer electrodes 17 are located, there is a small shoulder 13e formed by horizontally extending palisade elements. During the manufacture of the glass melting tank 10, these palisade elements are arranged next to or above one another as shown, attached to or next to the raised floor section 14 or to or next to the homogenization floor section 15, and held by a steel frame 36 and steel supports 38, as described above.

[0094] The wiring of the outer electrodes 17 and the inner electrodes 18 will be explained below with reference to Fig. 34. As already explained above, twelve pairs of top electrodes 17 are arranged in the tank interior 11 in the area adjacent to the side wall 13, and six pairs of bottom electrodes 18 are arranged in the area adjacent to the transition wall 16. In this exemplary embodiment, a power supply device 20, sketched in Fig. 1, is provided, which has three transformers that supply the total of thirty-six electrodes 17, 18. The thirty-six electrodes are divided into three groups of six electrode pairs each, and each group is assigned to a transformer, whereby the open three-phase system is used. Two transformers are connected in a delta connection on the primary side (offset by 60°, the first delta connection is indicated in Fig.14 by dotted lines and a second delta connection by dashed lines), whereby the delta connections each include opposite inner electrode(s) 18 and outer electrode(s) 17. Furthermore, a transformer is designed in a star connection (see connection indicated by dash-dot lines), whereby the star connection only includes outer electrode(s). Since the geometric / mechanical arrangement of the electrodes in the glass melting tank follows the position of the pointers in the electrical pointer diagram, a uniform current load is achieved for all electrodes. Furthermore, since the distances between associated electrodes / "heating partners" are not too long, manageable values ​​for the operating voltage / secondary voltage are obtained.

[0095] In the above embodiment (and in all other embodiments explained below), in order not to exceed the above-mentioned limits of electrode current density and electrode current per bottom or top electrode, an installation of two top or bottom electrodes arranged closely next to one another and connected electrically in parallel was used. This achieves a high number of electrodes. The top electrodes arranged closely next to one another and connected in parallel electrically form, in a sense, a coherent "virtual electrode." Alternatively, a single electrode can be used for each electrode pair. Further embodiments and design variants are explained below. Particular reference is made to the differences from the first embodiment and other embodiments.Since the glass melting tanks basically have the same structure, not all elements are described for each exemplary embodiment. Identical elements have the same reference numerals in the tens and ones positions of the respective reference number, with the reference numerals of different exemplary embodiments differing by whole hundreds. For example, the outer electrodes have the reference numeral 18 in the first exemplary embodiment, 118 in the second, and 218 in the third exemplary embodiment, etc. For explanations of the individual elements, reference is made to the first exemplary embodiment described above.

[0096] The second embodiment of a glass melting tank 110 shown in Figs. 7 and 8 has an average diameter D above the raised floor section 114 of 11 m. Accordingly, the average diameter d in the region of the homogenization chamber is approximately 5.4 m. The channel 111c, which connects the homogenization chamber to the outlet opening 113a in the region of the lateral wall 113, has a channel-shaped recess 111d, which causes the outlet opening 113a to lie with its lower end below the homogenization floor section 115. The recess 111d extends into the homogenization floor section 115. This promotes the withdrawal of well-homogenized glass melt. The width of the recess 111d in the horizontal direction is, for example, 400 mm.

[0097] The third embodiment of a glass melting tank 210 corresponds to the second embodiment, with the raised floor section 214 being wider in the horizontal direction than in the second embodiment. The diameter d in the region of the homogenization chamber is approximately 3.6 m, so the width has been increased from 2.8 m (width of the raised floor section 114 of the second embodiment) to 3.7 m. This brings the inner electrodes 18 closer together and evens out the flow in the melting and refining chamber, which has a positive effect on the glass quality.

[0098] The fourth exemplary embodiment of a glass melting tank 310 shown in FIGS. 11 to 14 differs from the first exemplary embodiment in that the homogenization chamber has the shape of a 6-sided prism due to the corresponding design of the transition wall 316 and the raised floor section 314 of the homogenization chamber. The width B of the melting and refining chamber above the raised floor section 314 is, for example, 14 m and the average diameter d of the homogenization chamber is, for example, 7 m. Furthermore, the height difference h = 1.8 m and is thus greater than in the first exemplary embodiment. This also results in better homogenization of the glass melt 12. In this exemplary embodiment, the outlet opening 313a is arranged at the lower end of the transition wall 316. The raised floor section 314 extends, as shown in FIG. 13, completely around the homogenization chamber, i.e. without interruption by a channel.In addition, the rotating storage container for the raw material mixture and / or the cullet is arranged centrally relative to the glass melting tank 310 above the screw or vibrating chutes 327. The stationary storage container is also located centrally above the glass melting tank 310.

[0099] The fifth embodiment of a glass melting tank 410 shown in Figs. 15 and 17 differs from the fourth embodiment in that the diameter d of the homogenization chamber is smaller (here: 4.7 m) and thus the width of the raised floor section 414 is larger (b = 4.7 m). The dynamics in the melting and refining chamber can be evened out by the more uniform arrangement of the electrodes, which is caused by the widening of the raised floor section 414. Figs. 17 to 21 show the sixth embodiment of a glass melting tank 510. This differs from the third embodiment in the shape of the channel 511c, which runs from the homogenization chamber to the outlet opening 513a and serves to discharge the homogenized glass melt. In this embodiment, the width of the channel 511 c in the horizontal direction corresponds to the mean diameter d (d = 3.6 m) of the homogenization space.This reduces wear on the refractory material in the area of ​​channel 511c and is easy to implement. However, this reduces the area of ​​the raised floor section 514, which is penetrated by channel 511c. As a result, the inner electrodes 518 arranged next to channel 511c must be slightly displaced, since the electrodes 518 should be arranged at some distance in the horizontal direction from channel 511c. The glass melting tank 510 also has a feed device for feeding the raw material mixture and / or the glass cullet, analogous to the fourth embodiment.

[0100] The seventh embodiment of a glass melting tank shown in Figs. 22 to 26 is very similar to the first embodiment. Unlike the first, it has two outlet openings 613a arranged opposite one another along the circumferential direction at the bottom of the lateral wall 613. This ensures a uniform discharge of the homogenized glass melt. Accordingly, two channels 611c are provided opposite one another, which guide the glass melt to the respective outlet opening 613a.

[0101] For demanding glass qualities, a collar 716a can be provided on the transition wall 716, as in the eighth embodiment of a glass melting tank shown in Fig. 27. This collar, for example, has a vertical height of approximately 100 mm measured from the raised floor section 714 and a horizontal width of 150 mm. The collar is integrated into the raised floor section in the area of ​​the inner edge and merely forms a raised portion on this floor section. The collar 716a prevents bubbles from flowing directly toward the outlet opening 713a.

[0102] Finally, the structure of the glass melting tank 810 with regard to the steel frame will be explained in more detail below using a ninth exemplary embodiment of a glass melting tank 810 shown in Fig. 33. In the exemplary embodiment shown in Fig. 33, three through openings 819a are arranged in the rotating ceiling 819, which serve to supply raw material mixture and / or cullet. Otherwise, the glass melting tank 810 has the structure of the first exemplary embodiment.

[0103] The lateral wall 813 has an outer steel frame 36, which holds and secures the palisade elements of the lateral wall 813. A circular guide rail 36a is provided on the upper end face of the outer steel frame 36, on which rollers 819c are guided such that the rotating ceiling can rotate 360° in a first direction of rotation and in the opposite direction of rotation. The rollers 819c are connected to the steel frame 38 of the rotating ceiling 819. Furthermore, the steel frame 38 of the rotating ceiling 819 has an annular sealing apron 819d with a sealing edge, wherein each sealing apron 819d is guided in a circular sealing groove 36b filled with sand to seal it. The sealing groove 36b is arranged on the upper end face of the lateral wall 813.

[0104] The glass melting tank design examples described above, along with other variants, are summarized in a table below. There are 12 examples in total. The designs of these glass melting tanks were determined based on simulations, with the dimensions always measured relative to the respective hot chamber side. pen (DEG2) / (DEG1)

[0105]

[0106] Here, D is the diameter above the raised bottom section, the area A1 is the size of the melt surface, H is the height of the side wall above the raised bottom section (see Fig. 2 and 3), DEG1 is the diameter of a horizontal circle / line on which the first group of electrodes is arranged (if these are top or bottom electrodes), d is the diameter of the homogenization space, A2 is the cross-sectional area of ​​the homogenization space, h is the height of the homogenization space orthe height difference between the raised floor section and the homogenization floor section, DEG2 is the diameter of a horizontal circle / line on which the second group of electrodes is arranged, DEG2 / DEG1 is the ratio of the diameters DEG2 and DEG1, the ratio of the width of the raised floor section to the radius of the melting and refining chamber, V is the volume of the glass melt arranged in the respective glass melting tank, B is the width of the raised floor section, the throughput related to the surface of the glass melt and one day, T is the throughput per day and spVP is the specific volume load as throughput related to the melt volume and one day.

[0107] With regard to the above-described new design of a glass melting tank with a surrounding raised floor section and a homogenization floor section, as well as the described arrangement of the electrodes, simulations have shown that a medium throughput (80 to 450 t / day, in particular 220 to 350 t / day) can be achieved, which represents a significant increase in throughput compared to conventional all-electric glass melting tanks. The model predicts good glass quality with significantly fewer than 10 bubbles per 100 g. The compactness of the system is also advantageous for its use. The implementation of a wide raised floor section and a deep homogenization chamber appears particularly positive with regard to high glass quality. The present invention thus opens up a throughput range that was previously closed to all-electric heating.The realization of such a glass melting tank is not significantly more complex than conventional glass melting tanks.

Claims

Patent claims:

1. A glass melting tank for fully electric heating, in production mode, of a glass melt arranged in a tank interior, having a stepped bottom and a side wall, wherein the bottom defines the bottom of the tank interior and the side wall laterally encloses the tank interior, wherein in production mode, the glass melt is arranged in the tank interior, wherein the hot space side of the side wall, above a raised bottom section, essentially forms at least a 5-sided polygon, a circle, or an ellipse in horizontal cross-section, wherein the bottom has the raised bottom section running around at least 70% of the circumference of the tank interior and a central homogenization bottom section surrounded by the raised bottom section and located lower relative to the raised bottom section,wherein the raised bottom section extends laterally from the hot space side of the lateral wall towards the interior of the tank and has a width (B) which is greater than or equal to 0.25 x D, where D is the average diameter of the interior of the tank above the raised bottom section, wherein a transition wall is formed in the transition from the raised bottom section to the homogenization bottom section, which is perpendicular or almost perpendicular to the surface of the glass melt, wherein the glass melting tank has a plurality of electrodes which heat the glass melt arranged in the melting and refining space in the production operating state,wherein in the production operating state, the surface of the glass melt lies above the raised bottom section and a first group of the plurality of electrodes projects into the glass melt in a region adjacent to the lateral wall above the raised bottom section or from the raised bottom section and a second group of the plurality of electrodes is arranged in a region adjacent to the transition wall in the raised bottom section and from the raised bottom section into the, Glass melt protrudes, so that a melting and refining chamber is formed for the glass melt in the interior of the tank above the level of the raised floor section and a homogenization chamber is formed below this level, wherein the homogenization chamber is surrounded laterally by the transition wall and below by the homogenization floor section.

2. Glass melting tank according to claim 1, characterized in that the tank interior is covered at the top by a ceiling which seals the tank interior almost completely dust-tight.

3. Glass melting tank according to one of the preceding claims, characterized in that the ceiling is designed as a rotating ceiling which has substantially the shape of a disc and which is preferably designed as a suspended rotating ceiling.

4. Glass melting tank according to one of the preceding claims, characterized in that the glass melting tank is designed such that it can be operated according to the cold-top principle.

5. Glass melting tank according to one of the preceding claims, characterized in that the supply of raw material mixture and / or cullet into the glass melting tank from above through at least one corresponding, dust-tight sealed opening in the roof such that the raw material mixture and / or cullet is continuously applied over a large area to the surface of the glass melt, for example in the form of one or more annular strips.

6. Glass melting tank according to one of the preceding claims, characterized in that the height difference h between the raised floor section and the homogenization floor section, that is to say the vertical Height of the homogenisation chamber is at least 0.5 m and / or that the mean diameter D of the melting and refining chamber is at least 5 m.

7. Glass melting tank according to one of the preceding claims, characterized in that a collar is arranged on the transition wall in the region of the raised bottom section, which collar is at least 50 mm high and / or at least 50 mm wide.

8. Glass melting tank according to one of the preceding claims, characterized in that it has at least one outlet opening which is arranged in the region of the homogenization bottom section, the lower end of the transition wall and / or the lower end of the lateral wall.

9. Glass melting tank according to one of claims 3 to 8, characterized in that a feeding device and the rotating ceiling are designed such that the feeding of raw material mixture and / or cullet into the glass melting tank takes place through a plurality of dust-tight sealed openings in the rotating ceiling.

10. Glass melting tank according to one of the preceding claims, characterized in that each electrode of the first group is designed such that, in the production operating state, it projects vertically with respect to the surface of the glass melt or at a small angle to this vertical direction obliquely from above into the glass melt and / or that each electrode of the second group is designed such that, in the production operating state, it projects vertically with respect to the surface of the glass melt or at a small angle to this vertical direction obliquely from the raised bottom section into the glass melt.

11. Glass melting tank according to one of the preceding claims, characterized in that each electrode of the first group is designed to be pivotable into and out of the tank interior and / or that each electrode of the second group is designed to be pushable into the tank interior.

12. Glass melting tank according to one of the preceding claims, characterized in that the energy supply and the diameter of the plurality of electrodes are determined on the basis of the melting and refining energy required for a given glass throughput.

13. A glass melting plant comprising a glass melting tank according to any one of claims 1 to 12, wherein the glass melting plant further comprises a supply system for supplying raw material mixture and / or glass cullet and a power supply device for the plurality of electrodes, the power supply device being connected to each electrode.

14. A method for producing a glass melting tank according to any one of claims 1 to 12, comprising the following steps: • Provision of first palisade elements for the side wall of the glass melting tank and second palisade elements for the transition wall as well as floor slabs, • Arrangement and fixing of the first and second palisade elements on or at the raised floor section of the glass melting tank and floor plates in the area of ​​the floor such that the hot space side of the lateral wall above a raised floor section in horizontal cross-section essentially forms at least a 5-sided polygon, a circle or an ellipse, wherein the floor comprises the raised floor section running around at least 70% of the circumference of the tank interior and a central floor section surrounded by the raised floor section and lying lower in relation to the raised floor section. Homogenization bottom section, wherein the raised bottom section extends laterally from the hot space side of the lateral wall in the direction of the tank interior and has a width (B) which is greater than or equal to 0.25 x D, where D is the mean diameter of the tank interior above the raised bottom section, wherein in the transition from the raised bottom section to the homogenization bottom section a transition wall is formed which runs perpendicularly or almost perpendicularly with respect to the surface of the glass melt, and • Arrangement of the plurality of electrodes which heats the glass melt in the production operating state, wherein in the production operating state the surface of the glass melt lies above the raised bottom section, such that a first group of the plurality of electrodes projects into the glass melt in an area adjacent to the lateral wall above the raised bottom section or from the raised bottom section, and a second group of the plurality of electrodes is arranged in an area adjacent to the transition wall in the raised bottom section and projects into the glass melt from the raised bottom section, so that a melting and refining space is formed for the glass melt in the interior of the tank above the level of the raised bottom section and a homogenization space is formed below this level, wherein the homogenization space is surrounded laterally by the transition wall and below by the homogenization bottom section.

15. The method according to claim 14, characterized in that a ceiling is arranged above the interior of the tub in such a way that the interior is covered at the top by the ceiling, so that the interior of the tub is almost completely sealed off from dust.

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