CZ2018246A3 - Glass melting furnace - Google Patents

Abstract

The glass melting furnace is arranged in such a way that a heating auxiliary electrode (5) with reinforced ends (6), which can be provided with a thermocouple, is introduced from above into the floating charge (4). The auxiliary electrodes (5) are provided with their own power supply (8). A voltage gradient of greater than 2 V.cm and less than 30 V.cm is interposed between adjacent auxiliary electrodes (5). The auxiliary electrodes (5) are parallel to each other, have a plate-like shape and are made of a material which resists the action of gases leaving the charge (4) at temperatures of 100 to 1000 ° C. The stacker (7) situated above the charge (4) and the auxiliary electrodes (5) is equipped with a sensor (13) for sensing the surface temperature of the floating charge (4). The furnace (1) is equipped with an infrared camera for temperature sensing and movement control of the stacker (7). A thermocouple at each thickened end (6) of the auxiliary electrode (5) and / or a sensor (13) for sensing the surface temperature of the floating charge (4) is connected to a control computer to adjust the position of each auxiliary electrode (5). The auxiliary electrodes (5) are located on a sliding electrically insulated and / or non-conductive beam (11) which is connected to a lifting device (9) for reciprocating vertical displacement of the auxiliary electrodes (5). The hearth (2) has vertical refractory tubes (14) mounted on the refractory walls facing the glass (3) and the charge (4), the upper end of which is situated above the surface of the charge (4) and the lower end of the mouth into the charge (4). 600 to 1000 ° C for the evacuation of gaseous products through their open upper end. The refractory tube (14) may be provided with side openings for evacuating gaseous products, preferably internally electrically heated, to prevent sticking of the glass (4).

Description

Technical field

The invention relates to a glass melting furnace comprising a refractory hearth with a bottom and side walls. In the hearth is glass with a floating charge of glass raw materials and glass shards. The hearth is fitted with conventional molybdenum heating electrodes. The furnace is equipped with a stacker for transporting the cold charge to the surface of the floating charge in the furnace.

BACKGROUND OF THE INVENTION

Melting glass directly by passing electrical current through molten glass has been known for nearly 100 years. The glass melting furnace is characterized by a low temperature of the top surface of the glass batch. The spread of this method of all-electric melting occurred in the last 60 years, when molybdenum was used as a material for heating electrodes. This material allows the molybdenum electrodes to be loaded with a large current so that large and efficient furnaces could be built. However, molybdenum cannot be exposed to air at temperatures above 200 ° C because it oxidizes immediately. Therefore, molybdenum electrodes are inserted into the molten glass. The portion of the electrode that is not wetted by the glass is usually intensively cooled with water by means of a suitable holder.

In all-electric melting, Joule's heat is released in the already molten glass ("bath") and from there is transferred to the charge layer, which is a mixture of glass raw materials and shard lying on the surface of the bath. The electric current does not heat the glass batch directly, but the heat released in the already molten glass is transferred upwards into the batch layer by the heat transfer mechanisms, ie by conduction, radiation and convection. Because the glass charge is a poor heat conductor, the deep heat sink is slow and hits a certain limit value. For conduction and radiation heat transfer, it is only possible to increase the heat flow to the charge by increasing the bath temperature. This implies the durability of the refractory material of the bath wall. Therefore, when using conventional refractory materials, a temperature is encountered whose exceeding leads to rapid corrosion of the glass furnace.

To exceed the melting capacity limit of approx. 2.5 tons of glass per m ² per day, today it is possible only by using the last heat transfer mechanism, namely by glass flow. This requires a large furnace volume. Therefore, furnaces are built relatively deep. Of course, as the outer surface of the furnace increases, heat losses increase, which is noticeable when using relatively expensive electrical energy.

Another way of increasing the specific power is to use bubble - blowing air into the glass bath. This method has limited use, mainly for vitrification of waste, where the quality of the effluent does not matter.

SUMMARY OF THE INVENTION

The all-electric glass melting furnace of the present invention comprises a refractory crucible with a bottom and side walls and a stacker for conveying a cold glass batch to the surface of a floating glass batch. At the hearth there is glass with a floating charge. The furnace is fitted with conventional molybdenum heating electrodes. It is an object of the present invention to introduce heating auxiliary electrodes from above into the floating charge, the thickened ends of which are located at the bottom of the floating charge and do not interfere with the molten glass. The auxiliary electrodes have their own power supply. A voltage gradient of greater than 2 V.cm ¹ and less than 30 V.cm ¹ is interposed between adjacent auxiliary electrodes. The main advantage of the present invention is to obtain a high melting power, up to 1 Ox compared to the current state without auxiliary electrodes. Defined

A3 voltage gradient ensures sufficient electrical power to be enforced.

Preferably, the auxiliary electrodes are parallel to each other, having a plate-like shape to achieve a large surface area and thus a low electrical specific load. The auxiliary electrodes are made of a material that resists the effects of gases leaving the charge at temperatures of 100 to 1000 ° C to resist corrosion. According to the manufacturer, corrosion data indicate a service life of more than 2 to 3 years.

It is further preferred that the auxiliary electrodes have a lower end reinforced and made of a more heat-resistant material than the upper part of the electrode. The thickened lower end of the auxiliary electrodes ensures low electrical resistance and longer life.

The thickened end of each auxiliary electrode may be provided with at least one thermocouple to control the temperature of the auxiliary electrode.

In a preferred embodiment, the auxiliary electrodes and their thickened ends are made of a material selected from the group consisting of chromium-nickel steel, Kanthal-type alloys, metal aluminides, conductive ceramics. The auxiliary electrodes and / or their thickened ends are provided with a coating which resists gaseous fumes from the molten glass, selected from the group of platinum based nickel, chromium or zirconium.

The stacker situated above the charge and the auxiliary electrodes is preferably provided with a sensor for sensing the surface temperature of the floating charge.

The glass melting all-electric furnace is equipped in the vault with an infrared camera for sensing and controlling the movement of the stacker.

The thermocouple at each thickened end of the auxiliary electrode and / or the sensor for sensing the surface temperature of the floating charge are preferably connected to a control computer to adjust the position of each auxiliary electrode.

The auxiliary electrodes are preferably located on a sliding electrically insulated and / or non-conductive beam. The electrically insulated and / or non-conductive beam can advantageously be connected to a lifting device for reciprocating vertical displacement of the auxiliary electrodes.

Preferably, the hearth on the refractory walls facing the glass and the charge has vertical refractory tubes, the upper end of which is situated above the surface of the charge and the lower end of the discharge into the charge at temperatures of 600 to 1000 ° C for evacuating exhaust gases through their open top. The refractory tube may be provided with side vents for evacuating gaseous gases internally electrically heated to prevent sticking of the glass.

For an all-electric glass melting furnace, a furnace of substantially any shape may be used, for example a rectangular or square or multi-angle or round plan view.

Clarification of drawings

The invention is described in detail below and is explained in more detail in the accompanying schematic drawings. The same reference numbers correspond to equally functioning components.

Giant. 1 depicts the dependence of the measurement of the rate of rise of the temperature provided by Joule heat between two measuring electrodes and the resistance between these electrodes decreasing with the charge being charged.

Giant. 2 schematically shows a section through the longitudinal axis of the glass melting furnace on which they are

-2GB 2018 - 246 A3 Auxiliary electrodes are used in the charge.

Giant. 3 schematically shows a cross-section of a glass melting furnace with auxiliary electrodes into a charge.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

FIG. 2 shows an exemplary glass melting furnace 1 consisting of hearths 2 of a refractory material in which the molten glass 3 is represented by ripples. A glass batch 4 floats on the surface of the glass 3, shown by horizontal hatching. Auxiliary electrodes 5, indicated by oblique hatching, are introduced from above into the charge 4. Each auxiliary electrode 5 is provided with a thickened end 6. The charge 4 is conveyed to the furnace 1 by a moving stacker 7 located above the auxiliary electrodes 5. Electrical current is applied to the auxiliary electrodes 5 by means of a power supply 8. The auxiliary electrodes 5 are attached to an insulated support beam 11 which is supported by the lifting device 9. In addition, the furnace 7 is fitted with conventional molybdenum electrodes 10, which can be plate and rod electrodes and located from the bottom and side walls of the furnace 1. Charger 4 runs from above the charger 7 in a vertical direction, indicated by an arrow 12, around the auxiliary electrodes 5. The charger 7 is equipped with a temperature sensor 13. In Fig. 3 a tube 14 is inserted near the refractory wall of the furnace 1. The tube 14 may have side openings (not shown) for gas evacuation, and the openings may be electrically heated to prevent glazing. The upper end of the tube 14 can be connected to the exhaust of gases from the molten glass 3. The distribution of the temperature field on the surface of the charge 4 can be monitored by an infrared camera (not shown) located in the furnace vault 1. At least one thermocouple and The current drop through each auxiliary electrode 5 is sensed, and the current passing through the auxiliary electrodes 5 is measured at each phase. The voltage drop, current, and measured temperature are fed to a control computer which evaluates these values and signals the hoisting device 9 and electrodes 5.

The principle of the invention is to introduce electrical current directly into the charge layer 4. This has not yet been tried, since the charge is not only a bad heat conductor but also a bad electric conductor. Therefore, even when using level electrodes ("TOP" electrodes) passing from above through the layer of charge 4 to the molten glass bath 3 as described, eg US 6125658, it was not observed that the charge was heated more because almost all the heat was released in the bath. This was caused by a low voltage between the electrodes, which was sufficient to pass the current through the molten glass bath 3 but not to the feed passes.

4. The point source represented by the rod electrode also does not allow significant heating of the charge 4.

Surprisingly, by measuring the thermal and electric field in charge 4 in Figure 1 of the present invention, it has been found that, surprisingly, there are temperature regions where the charge 4 heats up more rapidly and thus has less electrical resistance. For example, for SIMAX glass it is about 400 to 800 ° C by introducing a stronger electric field. Thus, by increasing the voltage gradient within a defined range between adjacent auxiliary electrodes 5, where a voltage gradient of greater than 2 V.cm < ^-1 & gt ^; and less than 30 V.cm &^lt; -1 ^>, preferably about 20 V.cm &^lt; -1 ^> Of course, the auxiliary electrodes 5 must not pass into the molten glass bath 3, since then heat would be released predominantly in the plane of lowest resistance.

These auxiliary electrodes 5 immersed in the charge 4 must resist oxidation up to 1000 ° C, ie molybdenum cannot be used. Conventional high-temperature alloys and combinations thereof can be used, for example a low-temperature, cheaper material can be used for the upper supply part, and the actual heating part of 2-10 cm height can be made of more durable steel or possibly of greater thickness. It is possible to use chrome-nickel steel,

-3 EN 2018-246 A3

Kanthal, metal aluminides, conductive ceramics or the surface of the auxiliary electrodes 5 can be coated with a platinum or nickel or chromium or zirconium protective coating.

However, it is possible to add to the batch 4 a substance which releases an inert gas between 100 and 800 ° C, which expels air from the batch 4 and thus protects the auxiliary electrodes 5. These substances include, for example, water free from moisture, water bound in the batch compounds such as borax decahydrate and pentahydrate, boric acid, water glass, aluminum hydrate, carbonates, some chlorides. The water also dissolves the soluble components of batch 4 to form conductive liquid bridges and the resulting solutions have a higher boiling point than pure water. Therefore, it is advantageous to analyze the off gases from batch 4 by mass spectrometer under heating to determine at which temperature the water still leaves , or oxygen or carbon dioxide or sulfur dioxide and other gases, and select auxiliary electrode material 5 accordingly.

In order not to overheat the auxiliary electrodes 5, the temperature of each electrode is monitored by at least one, preferably three, thermocouples. In addition, the average temperature of each auxiliary electrode 5 can be monitored by measuring the voltage drop at the beginning and at the end of the auxiliary electrode 5, from which the instantaneous resistance of the auxiliary electrode 5, proportional to the temperature, can be calculated. The total power input can be controlled by the interfacial voltage. The signal for the control computer can be obtained by calculating the resistance between the auxiliary electrodes 5.

The flat auxiliary electrodes 5 having a height of 10 to 50 cm, depending on the local conditions and the height of the charge layer 4, almost as long as the hearth 2, are suspended on a supporting non-conductive beam 11 resting on a withdrawable holder. The actual power supply 8 is provided by an insulated cable directly to the auxiliary electrode 5. The withdrawable holder is located on the outer circumference of the hearth 2 of the furnace 6 in an insulated manner. The withdrawable holders are controlled by the temperature or resistance signal on the auxiliary electrodes 5. When the permitted temperature is exceeded, the auxiliary electrodes 5 automatically extend slightly to increase the resistance and decrease the temperature. In addition, the holders must allow the auxiliary electrodes 5 to extend above the charge 4 in the event of a break in operation.

In addition to introducing the current into the batch 4, the glass 3 is heated in the conventional manner by means of molybdenum electrodes 10. This achieves the necessary temperature for melting the glass 3 and completing all the glass-forming processes as in a conventional furnace. Auxiliary electrodes 5 introduce, for example, 1/3 to 2/3 of the total energy supplied to the furnace. By feeding into the molten glass 3, for example with only 1/3 of the molybdenum electrodes 10, the problems of overheating during melting of the opaque glasses are greatly reduced.

The charging of the charge 4 is carried out in the same way as on today's baths, i.e. by inserting a belt or roller shutter 7, which sprinkles the charge at every point in the furnace melting surface. Therefore, the metering of the energy is strictly maintained according to the instantaneous melting power, while the constant temperatures in the individual horizontal planes remain the same as without the use of the auxiliary electrodes 5. The auxiliary electrodes 5 can also be applied to existing furnaces, windows in the upper structure of the furnace 6.

If it is desired to create a free space, for example at the refractory wall of the furnace 6, the auxiliary flat electrode can serve to protect the refractory material from feeding the corrosive charge.

The supplementary heating by the auxiliary electrodes 5 into the charge 4 can be immediately interrupted by removing them from the charge 4 or removing them completely from the furnace 6. This is advantageous if the furnace 6 is heated by electricity from a photovoltaic or wind power plant and the power supply suddenly decreases.

Example 2

The principle of using the auxiliary electrodes 5 in the batch 4 can be well described by way of example of a glass melting furnace 6, for example having a melting area of 1x2 m ² . with a hearth of 2 and a depth of 1 m. Its melting capacity is, for example, 100 kg m ^-2 . a total of 4.8 tons per day. The refractory lining forms the hearth of 2 furnaces 4, h

-4GB 2018-246 A3 where the molten glass bath 3 is floated, on which a layer of lighter charge 4, consisting of a mixture of raw materials and shard, floats to the furnace 1. is transported by the stacker 7. The molten glass 3 is discharged (not shown). The energy supply to the molten glass is molybdenum electrodes 10 in a conventional manner, i.e. the electrodes can be plate or bar electrodes located in the side walls or in the bottom of the furnace 1, exceptionally passing through the molten glass level 3. Auxiliary plate electrodes 5 of refractory steel 20 x 190 cm, having a bottom end 6 resistant to 1000 ° C. These auxiliary electrodes 5 are suspended in an insulated manner on a non-conductive beam 11 resting on the lifting device 9. The power supply 8 to the auxiliary electrodes 5 is carried out by a flexible cable 8 long enough to allow all auxiliary electrodes 5 to extend above the hearth. a 5 cm wide strip of charge 4 is formed, from which gases from charge 4 can escape. This space can be left free, i.e. not laid, or can only be sharded, or vice versa, will be laid more or wet in order to cool the refractory wall This space will be heated by the passage of current between the auxiliary electrode 5 and the molybdenum electrode 10. In some places at the lower edge of the auxiliary electrode 5, thermocouples of type "K" are placed and their signal is routed in isolation to the control computer. Each current supply through the cable 8 is provided with a measurement of the leakage voltage at the auxiliary electrode 5. This data, together with the total phase current, serves to calculate the instantaneous resistance at the auxiliary electrode 5 and deviates from the specified value and taking into account the thermocouple data to change the position. An alternating current from two phases is applied to each electrode, as in Figure 3, using the phases supplying the lower molybdenum electrodes 10 (often using one transformer). However, it is possible to use all 3 phases and ensure that the lower molybdenum electrodes 10 heat with the upper auxiliary electrodes 5. A voltage is applied to the auxiliary electrodes 5 so as to generate a voltage drop between adjacent electrodes 5 of at least 2 V.cm ¹ V.cm ¹ . The exact value depends on the resistance of the charge, ie mostly on the content of alkaline raw materials, the content of bound water in them, the charge moisture (causes a decrease in resistance at temperatures of 100 to 400 ° C), shard content, electrical conductivity of used auxiliary electrodes. The heat released in the volume unit depends on the intensity of the electric field, which is negligible in the horizontal direction in charge 4, and the energy is released only due to the vertical gradient of voltage in some planes where it changes resistance or permittivity. When a higher voltage is applied in the horizontal direction, the vector sum of both gradients is already significant, and even a small change in the voltage gradient will significantly increase the input power to charge 4.

Volume input P (W / cm ³⁾ can be expressed

P = E ² / p = w.Cp.h ΔΤ / Ay (1) where w is the descending rate of charge 4 (cm.sec ^_1 );

C _p specific heat of charge 4 (Jg kK ¹ );

h specific volume of charge 4 (g.cm ^-3) ;

Ay / Ay vertical temperature gradient K / cm, measured up to 500 Kcm ¹ ;

p resistivity (Ω.αη)

E (x, y) electric field intensity (V.cm- ¹ ).

Therefore, even a small change in the voltage drop will greatly increase the power input to the batch 4. A voltage drop above 30 V / cm already threatens that a small change in local temperature will cause a stepwise and continuous increase in power input that would require a significant flow of batch 4.

-5 CZ 2018-246 A3

Example 3

A glass having a low alkali content of 3.5% and a 50% cullet content in the batch is melted on the glass melting furnace 1 according to the previous example 2. This batch 4 has a specific electrical resistance of 0.1 to 1.0 ohm.cm at temperatures of 400 to 800 ° C, and a specific electrical resistance of 1 to 6 ohms at temperatures of 800 to 1000 ° C. cm, an average electrical resistance of 1.7 Ω.οηι at 400 to 1000 ° C (see Figure 1). For this charge, it would be sufficient to feed current only to 800 ° C, which would save the auxiliary electrodes 5. Taking the highest resistivity value of 6 c-cni, measured at temperatures of 400 to 1000 ° C, yields ten times the current input to the charge 4, ie 400 kW.m ^-2 voltage drop 15 V.cm ¹ , ie 465 V phase voltage. If the transformer is dimensioned to 600 V, ie we create a 20 V / cm gradient, the same power is possible even if the resistance increases to 10 Ω.οηι. If not, the auxiliary electrodes 5 can be brought close together and possibly inserted another row of auxiliary electrodes 5 At ten times today's melting capacity of 24 tm ^-2 per day, the mean residence time of the glass 3 in the bathtub is 2.3 hours, which is close to This time guarantees good quality of glass 3. In this furnace 1 it is possible to achieve almost piston flow, ie 100% utilization of furnace volume T

Example 4

In the same furnace 1 as in Example 2 and with the same electrode arrangement 5, 10, we want to melt very soft glass whose melting charge 4 has a resistivity of 0.1 ohm.cm. A 60 V voltage is applied between the auxiliary electrodes 5, creating a voltage drop 2 V.cm ¹ . The equation (1) results in a power input of 40W.cm ^-3 , ie 400 kW.m ^-2 . This would mean a 10x higher melting capacity than today. Any doubling of the resistance would be corrected by increasing the voltage to 85 V.

PATENT CLAIMS

Claims (14)

A glass melting all-electric furnace (1) with a cold glass level (1), comprising a refractory hearth (2) with a bottom and side walls, in the hearth (2) there is glass (3) with a floating batch (4) of glass raw materials and glass cullet is equipped with conventional molybdenum heating electrodes (10), the furnace (1) is equipped with a stacker (7) for transporting the cold charge (4) to the surface of the floating charge (4) in the furnace (1), characterized in that (4) are introduced from above the heating auxiliary electrodes (5), whose thickened ends (6) are located at the bottom of the floating charge (4) and do not interfere with the molten glass (3), the auxiliary electrodes (5) are provided with A voltage gradient of greater than 2 V.cm < ^-1 & gt ^; and less than 30 V cm &^lt; -1 ^> is interposed between adjacent auxiliary electrodes (5). Glass melting furnace according to claim 1, characterized in that the auxiliary electrodes (5) are parallel to each other, have a plate shape and are made of a material which resists the action of the gas leaving the charge (4) at temperatures of 100 to 1000 ° C. . Glass melting furnace according to claim 2, characterized in that the auxiliary electrodes (5) have a lower end (6) reinforced and made of a more heat-resistant material than the upper part of the electrode (5). A glass melting furnace according to claim 3, characterized in that the thickened end (6) of each auxiliary electrode (5) is provided with at least one thermocouple. -6GB 2018 - 246 A3 A glass melting furnace according to any one of claims 1 to 4, characterized in that the auxiliary electrodes (5) and their thickened ends (6) are made of a material selected from the group consisting of chromium-nickel steel, Kanthal-type alloys, metal aluminides, conductive ceramics. . A glass melting furnace according to claim 4, characterized in that the auxiliary electrodes (5) and / or their thickened ends (6) are provided with a coating resistant to the gaseous products of the molten glass (3) selected from platinum-based coating. nickel, chromium or zirconium. A glass melting furnace according to claim 1, characterized in that a stacker (7) situated above the charge (4) and the auxiliary electrodes (5) is provided with a sensor (13) for sensing the surface temperature of the floating charge (4). The glass melting furnace according to claim 1, characterized in that the furnace (1) is provided in the arch with an infrared camera for sensing the temperature and controlling the movement of the stacker (7). Glass melting furnace according to claim 4 and / or 7, characterized in that the thermocouple at each reinforced end (6) of the auxiliary electrode (5) and / or the sensor for sensing the surface temperature of the floating charge (4) is connected a control computer for adjusting the position of each auxiliary electrode (5). Glass melting furnace according to claim 1, characterized in that the auxiliary electrodes (5) are arranged on a sliding electrically insulated and / or non-conductive beam (11). The glass melting furnace according to claim 10, characterized in that the electrically insulated and / or non-conductive beam (11) is connected to a lifting device (9) for reciprocating vertical displacement of the auxiliary electrodes (5). Glass melting furnace according to claim 1, characterized in that the crucible (2) has vertical refractory tubes (14) mounted on the refractory walls facing the glass (3) and the batch (4), the upper end of which is situated above the batch surface. (4) and the lower end opens into the batch (4) at temperatures of 600 to 1000 ° C to evacuate the exhaust gases through their open upper end. A glass melting furnace according to claim 12, characterized in that the refractory tube (14) is provided with side openings for evacuating gaseous fumes, preferably electrically heated internally, to prevent clogging of the glass (4). A glass melting furnace according to any of the preceding claims, characterized in that the furnace (1) has a rectangular or square or polygonal or round plan view.