Mixing electrode and method for production thereof

Abstract

The invention relates to a mixing electrode and a method for production thereof. The mixing electrode according to the invention is intended for use in glass melting processes, serving to heat the glass batch and introduce gas under pressure into the batch at the same time to ensure optimal mixing of the molten glass batch in the furnace. The electrode according to the invention comprises a body (1) made of an electrically conductive material with an at least one through hole (8) extending along the longitudinal axis of the mixing electrode and an at least one fluid-transporting channel (7) to force movement of the molten glass by a stream of gas bubbles. In the at least one through hole (8), an at least one filling element (2) partially reducing the cross-section area of the through hole (8) is arranged, wherein the at least one fluid -transporting channel (7) is formed between the body (1) and the filling element (2) and / or between the at least two filling elements (2).

Description

[0001] MIXING ELECTRODE AND METHOD FOR PRODUCTION THEREOF

[0002] Field of invention

[0003] The invention relates to a mixing electrode and a method for production thereof. The mixing electrode according to the present invention (also referred to as the electrode-bubbler) is intended for use in glass melting processes serving to heat the glass and introduce a stream of gas bubbles under pressure into the glass at the same time, the gas bubbles being then directed towards the batch layer floating on the surface to ensure accelerated heating, melting the batch and homogenization thereof with the molten glass in the furnace.

[0004] Background art

[0005] US3305340 discloses the construction of a molybdenum electrode -bubbler of 3 inches (76.2 mm) in diameter, comprising a central bore of larger diameter (2 inches, i.e. 50.8 mm), from which channels of smaller diameter (1 / 32 to 1 / 8 inch, i.e. 0.8 to 3.2 mm) extend radially and diagonally downwards.

[0006] EP 3647280 Al discloses the construction of a two- or three-element electrode -bubbler, where gases are transported through a single channel or multiple channels co-axially arranged inside a ceramic rod. The diameter of the gas -transporting channels in the electrode -bubbler ceramic core is not greater than 1 mm, preferably less than 0.5 mm . These channels are formed at the stage of forming the ceramics.

[0007] EP 270518 A2 discloses the construction of a multi-segment bubbler with ceramic core provided with a system of directed pores or channels for gas flow, oriented parallel to the longitudinal axis of the bubbler. In order to increase the lifetime of the bubbler, a gap is left between the outer surface of the core with gas -transporting channels and the inner surface of its ceramic lining, into which a pressurized refrigerant is injected.

[0008] Nevertheless, there is a continuous need for improvements in the design of mixing electrodes, including in particular the need to ensure gas -transporting channels with the smallest possible diameter. Techniques of making holes used so far (drilling, hollowing or forming when the core is created) did not allow for obtaining gas-transporting channels with small diameters at relatively large (1.5 - 2.5 m) electrode lengths. As a consequence, there is also a need for an alternative method to produce mixing electrodes, which allows for production of mixing electrodes in a simple, inexpensive and reliable way, even in the case of small diameters of gas -transporting channels at long electrode lengths. Summary of the invention

[0009] Unexpectedly, the inventors of the present invention found that there is a simple and inexpensive method to produce a mixing electrode with fluid-transporting channels of relatively small diameters which cannot be made by traditional techniques, consisting in that at least one fdling element with transverse dimensions smaller than the transverse dimensions of the through hole is inserted into the through hole in the mixing electrode body, which the at least one fdling element reduces the cross - section area of the through hole and thus creates smaller fluid-transporting channels in the empty spaces between the fdling element (its outer surface) and the electrode body (the inner boundary surface of the through hole) or between the fdling elements themselves.

[0010] According to the first aspect of the present invention, a mixing electrode is provided for use in a glass melting process, in the form of a rod, wherein a body of the mixing electrode is made of an electrically conductive material, with an at least one through hole extending along a longitudinal axis of the mixing electrode and an at least one fluid-transporting channel to force movement of a melted glass by a stream of gas bubbles, wherein an at least one fdling element partially reducing the crosssection area of the at least one through hole is arranged in the at least one through hole, wherein the at least one fluid-transporting channel is formed: between the body and the fdling element, and / or between at least two fdling elements.

[0011] In one embodiment, a plurality of fdling elements are arranged in the through hole, which reduce the cross-section area of the through hole to form a plurality of fluid-transporting channels.

[0012] In another embodiment, at least two fdling elements are arranged one next to the other along essentially the entire length of the through hole.

[0013] In yet another embodiment, at least two fdling elements are arranged one above the other along essentially the entire length of the through hole.

[0014] In yet another embodiment, at least two fdling elements are arranged one in the other along essentially the entire length of the through hole.

[0015] The at least one fdling element may have a polygon-shaped or circular cross-section.

[0016] In one embodiment, an at least one longitudinal groove is arranged on at least one of an inner surface of the body and an outer surface of the at least one fdling element, which after inserting of the at least one filling element into the through hole of the body, forms the at least one fluidtransporting channel.

[0017] In yet another embodiment, the at least one groove runs parallel to the longitudinal axis of the mixing electrode.

[0018] In yet another embodiment, the at least one groove spirals around the longitudinal axis of the mixing electrode.

[0019] In yet another embodiment, the at least one groove has a cross-section selected from the semicircular, square, rectangular, triangular, elliptical and trapezoidal sections. Preferably, the cross-section of the at least one groove is from 0.05 to 64 mm2, and more preferably from 0.05 to 0.6 mm2.

[0020] In another embodiment, a plurality of grooves are arranged on the outer surface of the at least one filling element so that when the at least one filling element is inserted into the through hole of the body, they form a system of fluid-transporting channels.

[0021] In yet another embodiment, on at least one surface selected from:

[0022] - the inner surface of the body,

[0023] - an outer surface of an at least one intermediate cylindrical filling element,

[0024] - an inner surface of an at least one intermediate cylindrical filling element,

[0025] - the outer surface of the at least one filling element which is arranged inside the at least one intermediate filling element and has a solid cross-section, the at least one groove is arranged which, when the at least one filling element and the at least one intermediate filling element are inserted into the through hole of the body, constitutes a fluidtransporting channel.

[0026] According to the second aspect of the present invention, there is provided a method for producing a mixing electrode for use in a glass melting process, in the form of a rod, a body of which electrode is made of an electrically conductive material, with an at least one through hole extending along a longitudinal axis of the mixing electrode, wherein on at least one surface selected from:

[0027] - an inner surface of the body,

[0028] - an outer surface of a filling element, an at least one groove extending along the entire length of the body and / or the filling element is made, and then said filling element is inserted into the through hole of the body so that the at least one groove forms a fluid-transporting channel.

[0029] The mixing electrode of the invention is used to heat the molten medium, mainly glass, with the Joule heat, and at the same time to stir it with a stream of hot gas bubbles released at its tip. It allows for a very wide range of influences on the furnace batch during its conversion into a melt at all stages of the process.

[0030] In particular, the mixing electrode provided with fluid-transporting channels with a cross-section area of a single channel in the range of 0.05 to 64 mm2, and in particular in the range of 0.05 to 0.6 mm2, is a very useful tool for monitoring and controlling the melting process in furnaces using electricity as the sole source of energy, and in furnaces designed to use heat from the combustion of gas or oil above the batch surface as the sole or main source of energy, wherein significant part of the energy (even up to 60%) is / can be supplied by electrodes installed in the bottom of the furnace.

[0031] The mixing electrodes of the present invention can be made of any material used as material for standard electrodes without mixing functionality and installed in place of standard molybdenum electrodes, austenitic nickel -chromium superalloys (so-called inconel alloys), SNO2, graphite electrodes and electrodes made of any other material in all their design variants (also as twisted segments) and applications in melting furnaces, primarily glass furnaces.

[0032] Due to the concept of filling of the through hole with filling elements that reduce its cross -section area thus creating smaller fluid-transporting channels, the method for producing the mixing electrode allows for overcoming the technical limitations associated with drilling or hollowing holes or creating them in the forming process. In particular, the method according to the invention allows for obtaining electrodes equipped with a plurality of fluid-transporting channels of small diameter (less than 0.5 mm) in electrodes of large length (up to 3 m and more). This method is not only easier to implement and cheaper than previously used techniques of creating fluid -transporting channels, but also ensures the manufacturing of electrodes with channel parameters (small diameter, small distances between channels, channel run in a pattern other than rectilinear, e.g. in a spiral system) which were not possible to produce until now.

[0033] Brief description of the drawings

[0034] The object of the invention is illustrated in embodiments in the drawings in which:

[0035] Fig. 1 shows a mixing electrode in an embodiment according to the invention in side view;

[0036] Fig. 2 shows a mixing electrode in an embodiment according to the invention in longitudinal section;

[0037] Fig. 3 shows the detail B of Fig. 2;

[0038] Fig. 4 shows a variant of embodiment of a fdling element according to the invention with longitudinal grooves in partial side view;

[0039] Fig. 5 shows another variant of a fdling element according to the invention with spiral grooves in partial side view;

[0040] Fig. 6 shows another variant of a fdling element according to the invention with different crosssection shapes without grooves, in side view;

[0041] Figs. 7-12 show different variants of a mixing electrode according to the invention in cross-section in embodiments with differently shaped fdling elements;

[0042] Figs. 13-20 show different variants of a mixing electrode according to the invention in crosssection in embodiments with one fdling element in the through hole and grooves forming the pattern of fluid-transporting channels;

[0043] Figs. 21-28 show different variants of a mixing electrode according to the invention in crosssection in embodiments in which at least two fdling elements are arranged one in the other with grooves and without grooves;

[0044] Figs. 29-32 show vertical velocity and temperature distribution vectors in the melt in the neighbourhood of: a comparative standard electrode (Fig. 29) and the mixing electrode of the invention at a gas flow rate of 0.4 1 / min. (Fig. 30), 1.2 1 / min. (Fig. 31) and 2.0 1 / min. (Fig. 32); Fig. 33 shows the average rate of sand grains dissolution in the melting zone of the glass furnace in the neighbourhood of the electrode as a function of the rate of the gas flow through the mixing electrode of the invention (for the flow rate of 0 1 / min. this is the comparative standard electrode);

[0045] Fig. 34a, 35a and 36a show the distributions of batch concentrations in the melting zone of the glass furnace for standard electrodes, in a layer 1 cm below the surface of the glass, in a layer 10 cm below the surface of the glass, and in a layer at the level of electrode tips, respectively;

[0046] Fig. 34b, 35b and 36b show the distributions of batch concentrations in the melting zone of the glass furnace for mixing electrodes of the invention, in a layer 1 cm below the surface of the glass, in a layer 10 cm below the surface of the glass, and in a layer at the level of electrode tips, respectively;

[0047] Fig. 37-40 show vertical velocity and temperature distribution vectors in the barrier boosting plane in front of the glass furnace clarification zone in the neighbourhood of: a comparative standard electrode (Fig. 37) and a mixing electrode of the invention at a gas flow rate of 0.4 1 / min. (Fig. 38), 1.2 1 / min. (Fig. 39) and 2.0 1 / min. (Fig. 40);

[0048] Fig. 41 shows the averaged diameter of bubbles in the layer below the glass / combustion surface above the barrier boosting in front of the glass furnace clarification zone in the neighbourhood of the electrode as a function of the rate of gas flow through the mixing electrode of the invention (for the flow rate value of 0 1 / min. this is the comparative standard electrode).

[0049] Detailed description of preferred embodiments of the invention

[0050] A mixing electrode in a preferred embodiment of the invention is generally shown in Figs. 1-3. The mixing electrode has the form of a rod or a thick -walled cylinder with a through hole 8 made in a body 1. The body 1 of the mixing electrode is made of an electrically conductive material. The through hole 8 extends over the entire length of the body 1 , along its longitudinal axis . In the through hole 8, a fdling element 2 is arranged, which limits its cross-section area, thus creating an at least one fluid-transporting channel 7 with a smaller cross-section area and a smaller diameter as well. The fluid-transporting channels 7 generally extend also over the entire length of the body 1 and are used to introduce a stream of gas bubbles into the molten glass to force its movement.

[0051] As shown in Fig. 2 illustrating detail B of Fig. 2 in a longitudinal section, the end of the fdling element 2 is fitted with a stub pipe 4 fitted with a nut 6, by which the mixing electrode is connected to the gas supply system. The mixing electrode is connected to the AC power supply in a manner identical to the standard electrodes (the electrical connection system does not fall within the scope of the present invention). The main conductive component of the mixing electrode of the invention is the body 1.

[0052] The filling element 2 is shown - in three variants - in Figs. 4-6. More specifically, Fig. 4 shows the first variant of the filling element 2 in partial side view with grooves 3 running parallel to the longitudinal axis of the mixing electrode. Fig. 5 in turn shows the second variant of the filling element 2 in partial side view with grooves 3 spiralling around the longitudinal axis of the mixing electrode. Further, Fig. 6 shows in partial side view a variant of the filling element without grooves of differently shaped cross-section, the exemplary shapes of which are shown in Figs. 7-12.

[0053] The filling element 2 extends preferably over the entire length of the through hole 8. Preferably, a plurality of filling elements 2 may be disposed in the through hole 8 arranged in such a way that a plurality of longitudinal fluid-transporting channels 7 are formed between the filling elements 2 and / or between the filling elements 2 and the body 1 (an inner surface boundary of the through hole 8) . For example, the filling elements 2 of the same or different shapes and dimensions can be arranged parallel to each other, one above the other, or one in the other (e.g. concentrically). Preferably, the filling element 2 is longer than the body 1 and protrudes from one or both sides of the through hole 8 - this makes it easier to connect to the gas connection. For example, the filling element 2 can be at least 30 mm long and preferably at least 50 mm longer than the body 1 of the mixing electrode.

[0054] The filling element 2 can be made, for example, of the same materials as the electrode body, i.e. molybdenum, austenitic nickel -chromium superalloys (so-called inconel alloys), SnO2, graphite, platinum and others.

[0055] The transporting channels 7 are configured to transport gases and liquids. The fluid-transporting channels 7 are used to introduce a stream of gas bubbles into the melted glass to stimulate its movement, e.g. gas bubbles coming directly from the gas transported through the through holes 8 or from evaporation of the liquid transported through the through hole 8.

[0056] Figs. 7-12 show, in cross-section, various embodiments of the mixing electrode with differently shaped filling elements 2. The filling elements 2 may, for example, have a circular (circle-, oval-, ellipse-shaped or similar) or a polygonal (e.g. triangular, quadrangular, etc.) cross-section. And so, Fig. 7 shows the mixing electrode with one filling element 2 with circle-shaped cross-section, arranged in a coaxial position in the through hole 8, Fig. 8 shows the same filling element 2 as in Fig. 7, but arranged non-coaxially in the through hole 8 (its central axis is shifted laterally with respect to the longitudinal axis of the mixing electrode), Fig. 9 shows a filling element 2 with square cross-section, Fig. 10 in hexagonal shape, Fig. 11 shows the mixing electrode with a plurality of circle-shaped filling elements 2, and Fig. 12 - with a plurality of octagon-shaped filling elements.

[0057] Figs. 13-20 show various embodiments of the mixing electrode of the invention in cross-section with grooves 3 made on the outer surface of the filling element 2, which serve as fluid-transporting channels 7, wherein in Fig. 13 the cross-section of the grooves 3 made in the outer surface of the core 2 is semi-circular, in Fig. 14 - rectangular, in Fig. 15 and 16 - square, wherein Fig. 16 shows a variant with four through holes 8, in Fig. 17 - triangular, in Fig. 18 - elliptical, and in Fig. 19 - trapezoidal. In all these variants, the outlets of the fluid-transporting channels 7 form a single ring of outlet holes at the top of the mixing electrode. Further, Fig. 20 shows an embodiment, in which grooves 3 with rectangular cross-section are made not on the filling element 2 but on the inner surface of the body 1. The grooves 3 can preferably run longitudinally or spirally, as shown in Figs. 4 and 5. Another run of grooves is also possible.

[0058] Figs. 21-28 show yet other embodiments of the mixing electrode, where at least two fdling elements 2 are arranged one in the other, i.e. concentrically or essentially concentrically. In these embodiments, at least one fdling element 2, identified for simplicity by the numerical reference 5, is referred to as intermediate filling element and is in the form of a cylinder or pipe.

[0059] Figs. 21-27 show various variants of the electrode of the invention in cross-section, with grooves 3 made in the filling element 2 and the intermediate filling element 5, wherein in Fig. 21 the cross - section of the grooves 3 made in the outer surface of the filling element 2 and the outer surface of the intermediate filling element 5 has a semicircular shape, in Fig. 22 - rectangular (in this example the through hole made is not-coaxial with respect to the central axis of the body 1), in Fig. 23 and 24 - square, in Fig. 25 - triangular, in Fig. 26 - elliptical, and in Fig. 27 - trapezoidal. In all these variants, the outlets of the fluid-transporting channels 7 form two concentric rings of the outlet holes at the tip of the mixing electrode.

[0060] The grooves 3 in the outer surfaces of the filling element 2 and the intermediate filling element 5 according to the embodiment from Figs. 21-27 can be made in a similar way as shown in Figs. 4 and 5, i.e. they can run parallel to the longitudinal axis of the mixing electrode or spiral around the longitudinal axis of the mixing electrode.

[0061] Fig. 28 presents another embodiment without grooves 3, wherein two filling elements 2 and 5 are arranged coaxially one in the other, so that the fluid -transporting channels 7 are formed in the gaps between the intermediate filling element 5 and the body 1, and between the filling element 2 and the intermediate filling element 5.

[0062] The outer diameter of the mixing electrode of the invention may be of any value, but preferably it assumes the same values as for the diameters of standard electrodes, e.g. molybdenum ones, i.e. 1.5 inches (3.81 cm), 2 inches (5.08 cm), 2.5 inches (6.35 cm), 3 inches (7.62 cm). In this embodiment variant, the mixing electrodes of the invention are compatible with commercially available electrode holders (coolers) (the design solution of the holder - cooler does not fall within the scope of the present invention) and can be installed in existing furnaces.

[0063] The grooves 3 can be obtained by any surface treatment technique, including machining (including milling, turning and boring), laser beam cutting or high-pressure liquid jet cutting, optionally with the addition of abrasive. The grooves 3 can also be shaped when forming the body 1, the fdling elements 2 and the intermediate fdling elements 5, for example by using suitable mouthpieces in extrusion.

[0064] Using the milling technique, grooves 3 can be obtained, which, after assembling the components of the mixing electrode of the invention, form fluid -transporting channels with a cross- section area of less than 0.1 mm2(which corresponds to a rectangular section of 0.2 x 0.5 mm) and even less than 0.05 mm2(which corresponds to a semicircular section of 0.25 mm in diameter). The upper limit of the cross-section area of a single channel is not determined by technical possibilities of shaping grooves 3, but by the requirement that the mixing electrode is invulnerable to plugging with the melt when the gas stops to flow.

[0065] The maximum safe cross-section size of the fluid-transporting channel 7 (the diameter and the surface area) depends on the wetting angle of a specific electrode material with a specific melt at the electrode’s operating temperatures and the distance from the tip of the electrode to its cooler. For silicate sodium-calcium glasses and molybdenum electrodes exposed to glass at a height of 500 - 800 mm, operating at temperatures of 1200 - 1500°C, the safe cross-section area of a single gas outlet (the cross-section of the fluid-transporting channel directly at the gas outlet, i.e. at the tip of the mixing electrode), that is a such one which protects the mixing electrode against irreversible plugging in the case the gas flow stops for 1 hour is about 0.4 - 0.6 mm2, which corresponds to a diameter of a circular opening of about 0.7 mm.

[0066] The outer diameter range of the filling elements 2 (and the intermediate filling elements 5) matches the outer diameter of the body 1, i.e. the outer diameter of the mixing electrode. As a rule, it is to be assumed that a larger diameter of a single ring or several rings formed by the outlet holes of the fluid-transporting channels at the electrode tip resulting from a larger number of grooves 3 (forming the fluid-transporting channels 7 after assembling the components of the mixing electrode) with small cross-section, provides a wider spectrum of possible influences on the melted batch and gives more control options over individual stages of conversion of the batch of raw materials into the melt.

[0067] In a particular embodiment, although the mixing electrode can be provided with only one fluidtransporting channel 7, the recommended number of fluid-transporting channels 7 in a single mixing electrode of the invention is at least three, and preferably between ten and twenty.

[0068] The recommended distance between the outer edges of the outlet openings of adjacent fluidtransporting channels 7 should be approximately 1 mm, although both a smaller and a larger distance are applicable and do not prevent or restrict the possibility of producing the mixing electrode using the methods described in the present application.

[0069] The mixing electrodes of the invention, provided with fluid-transporting channels 7 with a crosssection area of a single groove 3 of 0.05 to 0.64 mm2, and preferably 0.05 to 0.6 mm2, can operate at gas flow rates from 0.1 1 / min. to up to 5 1 / min., although the recommended preferred flow rate range used in the glass melting furnaces, necessary to accelerate the process of mixing the cold batch with glass, or accelerate the sand dissolution or accelerate the growth process of bubbles during clarification, is in the range from about 0.2 to about 2.0 1 / min.

[0070] The mixing electrodes of the invention are installed in the bottom of the furnace or on special shelves, vertically or at an angle. The mixing electrodes can operate independently in single pairs or in a coordinated manner in linear systems or other geometric configurations. The mixing electrodes of the invention can be used both in furnaces using electricity as the sole (exclusive) source of melting energy, and in furnaces using electricity in combination with other energy sources used to melt the batch, wherein the share of electricity use in the furnace can be in any ratio to the share of energy from other sources.

[0071] A special case for the use of mixing electrodes of the invention are glass melting furnaces with structures configured to use heat from gas or oil combustion above the surface of the batch as the sole or main source of energy, where depending on the chosen mode of operation, a significant part of energy (up to 60%) is supplied by electrodes installed in the bottom of the furnace tank, while the firing system provides a complementary part of 40 to 100% energy.

[0072] Due to a wider diameter range of the generated bubbles (mainly due to ability to generate small bubbles with a diameter of 1 - 5 mm) and a wider diameter range of the cone of influence of these bubbles on the glass (primarily the possibility of obtaining large diameters above 200 mm just below the glass surface), the mixing electrodes of the invention allow for such modification of convection currents in the molten glas that the furnaces equipped with them ensure that high quality product is obtained in a wide range of shares of electricity and fuel combustion. The heating power of systems based on the mixing electrodes of the invention ranges from a few kilowatts to several tens of megawatts, most often from several hundred kilowatts to about 20 megawatts.

[0073] The way the mixing electrodes of the invention affect the melted batch during glass melting:

[0074] In order to obtain the necessary heating power from the Joule heat (sometimes it is 10 MW or more), at the bottom of a typical furnace for melting packaging glass with a capacity of about 400 TPD (tons per day), instead of several to a dozen or so electrodes, several dozen of them are installed: 20, 30 and even 60 pieces. With such a large number of electrodes and installed power, it is difficult to obtain geometric separation of operation zones of the melting boosting and barrier boosting in the tank and (above all) a positive interaction of convection currents originating from various sources.

[0075] In a furnace with a high share of power from electric boosting, the rising convection currents generated by the heat released in the neighbourhood of electrodes are increasingly important. As a result, in the case of significant shares of boosting power (30-60%), two glass mass convection current patterns interacting with each other operate in the furnace. One pattern results from the presence of the so-called hot temperature spot (the area of the highest temperatures in the furnace) on the glass surface, arising from interaction of the firing system and barrier boosting. The second pattern originates in turn from a large amount of energy released by the system of electrodes installed in the bottom in the melting zone and, optionally, in the barrier boosting.

[0076] The first system is characterized by long-distance, horizontally oriented flows of molten glass mass streams: the surface current from the hot spot to the charging area and the bottom current in the opposite direction. The hot spot separates, or rather should separate, the glass circulating between it and the charging zone (melting zone) from the glass circulating between the hot spot and the passage (clarification and resorption zone). The separation of these zones is facilitated by the presence of a physical ceramic barrier in the furnace tank, the location of which roughly coincides with the hot spot.

[0077] A large amount of heat released in the neighbourhood of the electrodes, especially in the bottom glass layer with a height of about 700 mm, in the melting zone triggers vertically directed convection currents lifting this glass towards the surface covered by a much cooler batch. After transferring a part of the heat to the batch, the mixture of cooled glass mass with unmolten batch relics, mainly undissolved sand grains and gas bubbles from the decomposition of carbonates, settles towards the bottom.

[0078] Such a vertically directed current system is typical for the so-called cold top furnaces using 100% electricity. One of the most important technological problems associated with glass melting in the cold top furnaces is to maintain the vertical arrangement of zones corresponding to the stages of the melting process: heating the batch, dissolving sand relics, clarifying and cooling and homogenization (thermal and chemical), and to separate the sand dissolution and clarification zones.

[0079] In a furnace equipped with a classic firing system, where a significant part of energy (30-60%) is supplied by electrodes installed in the bottom of the furnace tank, the release of large amounts of heat in the bottom layers in the melting zone reduces the temperature gradient between the charging zone and the hot spot. A consequence of this reduction of the temperature gradient is the weakening of the return current of the glass mass from the hot spot to the charging zone and the bottom current in the opposite direction. However, the working current from the hot spot to the passage is not weakened, and it can even be strengthened if a high-power barrier boosting is used.

[0080] The co-occurrence of these two phenomena increases the risk of short cuts, i.e. the couplings of the return and working currents. The result of these couplings is that glass of poor quality is drawn from the bottom and / or surface layers from the melting zone directly into the passage, which contributes to the increase of production waste.

[0081] The above description shows that the operational flexibility of furnaces configured for alternate use of two energy sources is not only a design but also a technological challenge, which requires the use of new tools enabling the production of glass with high efficiency at variable extraction parameters regardless of the ratio of energy shares from these sources. The use of the mixing electrodes of the present invention equipped with fluid-transporting channels with small area outlet holes for implementation of boosting systems in such furnaces allows for effective monitoring and control of the course of all stages of the batch-to-glass conversion process.

[0082] Warming up the batch components is the most energy-intensive and the dissolution of sand grains - the most time-consuming stage of the glass melting process. Clarification, i.e. removal of residual gas bubbles and chemical and thermal homogenization are the stages that determine the final quality of the glass mass at the outlet of the furnace. Due to wide available combinations of the boosting power used and the applied gas flow rate, the systems of the mixing electrodes of the invention allow for adjustment of parameters guaranteeing the most efficient use of the energy released in the neighbourhood of the electrodes to intensify each of these stages.

[0083] In the batch feeding zone of the furnace, the cold layer of the batch, due to the presence of occluded gas bubbles and polymorphic transformation of quartz into crystobalite, has a lower apparent density than the molten glass and floats on its surface.

[0084] In furnaces where energy is supplied only in the form of heat from fuel combustion above the glass and batch surface, due to very low values of the thermal conductivity coefficient of the batch at temperatures lower than 1000°C, the batch layer is heated primarily through its lower surface using the heat carried by the hot glass coming with the return current from the area of the highest temperatures in the furnace (hot spot). This process is slow, which is one of the reasons for a higher energy consumption for the melting process than it would follow from thermodynamics.

[0085] In furnaces equipped with bubbling systems in the melting zone, the hot glass can be lifted towards the batch layer by a forced convection current, the velocity of which depends on the gas flow rate and the bubbler geometry. Due to the lack of additional energy source, the bubblers are not the best tool for mixing glass and batch in areas close to the charging pockets, where the batch layer is relatively thick (10 - 20 cm) and its temperature is still low. Mixing large amounts of the cold batch with glass from the bottom layers not warmed up with additional heat from the electrode boosting leads to a significant local temperature decrease in this part of the tank, and thus to slowing down of all thermally activated reactions and processes occurring between the batch components and between the batch components and the glass.

[0086] In furnaces equipped with electric boosting in the melting zone, part of the energy used for heating the batch is released in the neighbourhood of the electrodes and further carried by a relatively weak (thermal) convection current towards the surface. In the case of standard electrodes, due to the low velocity of the glass in the rising convection current triggered by heating thereof in the neighbourhood of the electrode (0.2-0.5 mm / s), it is not able to interrupt the continuity of the batch layer. In this case, the hot glass is mixed with the batch only to a very limited extent and basically only exchanges heat with its lower surface. As a result, a large temperature gradient (in excess of 100°C) is maintained between the upper and the lower surfaces of the batch, and further timeconsuming heat transport through the entire batch layer takes place mainly by the conduction mechanism. An additional disadvantageous phenomenon accompanying the intensive heating of the batch layer without mixing with the hot glass is the formation of foam on the surface. This phenomenon additionally hinders the penetration of heat into the glass from the fire space and leads to unnecessary loss of a part of the clarifying agents already at this stage of melting.

[0087] When the standard electrodes in the melting boosting system are replaced with the mixing electrodes equipped with a plurality of fluid-transporting channels with a small cross-section area (less than 0.25 mm2, preferably 0.15 mm2), produced with the method of the present invention, and when low gas flow rates of 0.4 - 2 1 / min. (preferably less than 0.4 1 / min.) are used, a much stronger convection current than that obtained by operation of the standard electrodes is generated, forcing the hot glass to move with a high vertical velocity component. The continuity of the batch layer is interrupted, which allows for better heat penetration from the fire space. At a low gas flow rate through the mixing electrodes (not greater than 0.4 1 / min.), a preferred compromise is achieved: a controlled volumetric mixing of a portion of the batch with the glass (which accelerates heating and melting thereof), not leading, however, to a significant (dangerous) cooling of the resulting mixture.

[0088] A detailed comparison of the effects of convection currents generated by the standard electrodes and the mixing electrodes of the invention is shown in Figs. 29-32. Figs. 29-32 show the vertical velocity vectors and temperature maps in the melt in the neighbourhood of: a comparative standard electrode (Fig. 29) and a mixing electrode of the invention at a gas flow rate of 0.4 1 / min. (Fig. 30), 1.2 1 / min. (Fig. 31) and 2.0 1 / min. (Fig. 32). In the surface layer of the mixture of unmolten batch and glass containing still unmolten sand grains, at certain distance from the axis set by the axis of the mixing electrode of the invention (Figs. 30-32) preferred patterns of local convection currents are formed, triggering successive rotations of the glass mass, first counter-clockwise and then clockwise, which draw the mixture of unmolten batch and glass containing unmolten sand grains into the area of the Joule energy release near the surfaces of the electrodes. This mass, when heated by the energy released by the electrode, is reversed with the rising current, where a part of it re-enters the clockwise rotation movement. This cycle is further repeated many times, which promotes rapid dissolution of both individual sand grains and their aggregates.

[0089] Unlike the preferred pattern of convection currents created by the mixing electrodes, the standard electrodes (Fig. 29) produce local convection movements of the glass mass which poorly cooperate with each other. In the area of the Joule energy release, two glass rotations are visible, both clockwise. Due to the same direction of these rotations, only a part of the heated glass is lifted under the lower surface of the batch and glass mixture with relics of undissolved sand grains. Due to a too low kinetic energy of the glass, it does not pierce this layer, but spreads beneath its lower surface outwards from the axis set by the electrode, until it is hampered by viscous friction characteristic of liquids such as molten glass.

[0090] The hot glass in the zone of influence of the mixing electrode creates a cone that expands towards the glass surface covered with the batch layer. The cross-section area of this cone already at a distance of 1 cm above the upper surface of the mixing electrode of the invention is 4-5 times larger than for the standard electrode. The stream of this hot glass reaches the area of 1 cm below the upper surface of the batch at an average velocity of 4.3 (for a gas flow rate of 0.4 1 / min.) to 8.0 cm / s (for a gas flow rate of 2.0 1 / min.).

[0091] With the boosting power adjusted to the unit glass extraction capacity of the furnace, the velocities of the forced convection currents obtained at the flow rate of about 0.4 1 / min. allow for controlled mixing of the hot glass with the cold batch while maintaining the temperature of the resulting mixture above 1200°C, preferably above 1250°C, when the reactions of sand with the mixture of (mainly) silicates and sodium and calcium carbonates proceed at sufficient rate, and simultaneously there is no risk of escape of the melt with undissolved sand grains towards the clarification zone. The systems of mixing electrodes of the invention provide not only the Joule energy, but also, by faster batch-to- glass conversion, improve the efficiency of energy transfer from the fire space and the efficiency of the entire furnace. As a result, the average glass temperature in the furnace increases by up to several dozen °C at the same total energy consumption as in a furnace equipped with the standard electrode systems. In this way, the boosting systems constructed with the use of the mixing electrodes of the invention allow for intensification of the batch heating in conventional gas-fired furnaces, where the share of energy from electric boosting can reach up to 60%.

[0092] After melting and reacting of the carbonate batch components with sand, the process of dissolving the relict sand grains begins. The kinetics of sand dissolution are controlled by temperature (the [SiC ]4-diffusion coefficient in glass is temperature -dependent), as well as the factors affecting the thickness of the reaction layer on the surface of sand grains and the difference in Si O 2 concentrations between the reaction layer and the base glass in the furnace. The increase in average glass temperature in furnaces equipped with mixing electrode systems results in achieving high values of SiC>2 diffusion coefficients. Model studies show also a smaller volume (by about 25-30%) and batch surface area (by about 20-25%) in the melting tank and a larger share of sand grains dissolved in the melting zone equipped with the mixing electrodes as compared to the case where the standard electrodes are used (25 to 35%). To a significant extent, these effects result also from the effective removal of the reaction layer from their surfaces due to the double rotation of the glass mass shown in Figs. 29-32. As a result, the thickness of the layer through which [SiC>4]4" diffuses from a sand grain to glass is reduced much faster, and the difference of S i O2 concentrations is almost all the time maintained close to the maximum value. The effect of the flow rate of the gas used in the mixing electrodes on the sand dissolution process is illustrated in Fig. 33, where the average rate of sand grains dissolution in the melting zone in the neighbourhood of the electrode is presented as a function of the rate of gas flow through the mixing electrode of the invention.

[0093] Figs. 34a, 35a and 36a show distributions of batch concentrations for the standard electrodes - in a layer 1 cm below the surface of the glass, in a layer 10 cm below the surface of the glass, and in a layer at the level of electrode tips, respectively, and Figs. 34b, 35b and 36b - show corresponding distributions of batch concentrations at the same levels, i.e. in the same layers, but for the mixing electrodes of the invention. As shown in Figs. 34a-36b, the systems of mixing electrodes of the invention, with appropriately selected configuration and gas flow rate adjusted to the boosting power used, acting on the batch in the areas close to the charging pockets, increase the reaction rate of sand with soda and limestone at the early stage of melting, as evidenced by significantly lower batch concentrations in the layer 10 cm below the glass surface and in the layer set by the electrode tips. As a result, the primary melt flowing into further zones of the melting tank contains relics of sand grains of smaller average size, which also facilitates its faster complete melting in the further phases of the glass melting process in the furnace (reduction of the diameter of sand from 0.2 to 0.05 mm accelerates the process of dissolution by about 100%). In this way, the glass mass flowing into the clarification area is in many melting scenarios free of relics of unmolten sand, and in the case of high unit melting efficiencies exceeding 3 t / (m2-24h), these relics are smaller than 0.05 mm in size and are being completely dissolved on the way of the glass to the passage, which allows for obtaining glass containing less than 50 bubbles of 0.7 mm in diameter per 100 grams, preferably less than 30 bubbles of 0.7 mm in diameter per 100 grams.

[0094] The physical support of the clarification process is based on the co-operation of two factors: a temperature increase and a strong glass rising convection current. Figs. 37-40 show that the mixing electrodes of the invention, especially when using the gas flow rate in the range of 1.2 - 2.0 1 / min. (Figs. 39 and 40, respectively) ensure that these two conditions are met: at the electrode tips (500 mm above the bottom of the furnace), the glass reaches temperature above 1450°C, and the velocity of the rising convection current in the cylinder with the diameter of the electrode (approx. 65 - 76 mm) is 50 cm / s. The inverted cone lifting the glass to the surface reaches there a diameter of about 1 m and the glass reaches the edge of this circle at velocities of about 12 cm / s.

[0095] Moreover, unlike the standard electrodes, the mixing electrodes of the invention create a tight barrier by generating movement exactly across the glass flow stimulated by the working current. For the standard electrodes, the vertical velocity component created by the thermal convection current around them is too weak to break the dominance of the working current. This difference has a significant impact on the course of the clarification process.

[0096] In the case of a barrier made up of the mixing electrodes of the invention, where the gas flow rate is 1.2 1 / min., the averaged diameter of the bubbles in the 20 cm glass layer just below the surface is 1276 micrometers, their concentration is 72382 pieces / kg, which translates into a surface stream of gases released from the surface of 11.255 m3 / h - cf. Fig. 41.

[0097] In the case of a barrier made up of comparative standard electrodes (i.e. without mixing function), the averaged diameter ofbubbles in the 20 cm layer of glass just below the surface is 785 micrometers and their concentration is 125067 pieces / kg, which translates into a surface stream of gases released from the surface of 7.383 m3 / h. An increase in the average bubble size by 62.4%, a decrease in the bubble concentration in the surface layer by 42.1% and an increase in the surface stream of gases released from the surface by 52.4% show a very high efficiency of the mixing electrodes of the invention in intensifying the clarification process, especially in cases of high melting efficiencies.

[0098] The mixing electrodes of the invention significantly accelerate the clarification process due to thermal support of the diffusion of clarifying gases (usually SO2 and O2) into fine bubbles (mainly CO2) remaining in the glass mass after the melting process. In a cylinder with diameter about three times larger than the electrode, the velocity of glass is not less than 10 cm / s. For gas flow rates from the range of 1.2 - 2.0 1 / min., the glass is lifted rectilinearly with this current, without interference from the upper surface of the electrode, to the glass surface. Also, the glass from the layers lying below the electrode tip is drawn into this current as a result of the Joule heat release (cf. Figs. 38- 40).

[0099] The standard electrodes support the clarification process to a significantly smaller extent. The thermal convection currents generated by these electrodes are too weak to bring the glass with bubbles to the surface. About 250 - 300 mm from the surface, these currents are hampered, the glass mass changes the direction from vertical upwards to almost horizontal. As a result, in this area unclarified glass accumulates, which can be drawn with the working current to the passage.

Claims

Claims1. A mixing electrode for use in a glass melting process, in the form of a rod, having a body (1) made of an electrically conductive material, with an at least one through hole (8) extending along a longitudinal axis of the mixing electrode and an at least one fluid-transporting channel (7) to force movement of a melted glass by a stream of gas bubbles, characterized in that in the at least one through hole (8) an at least one fdling element (2) partially reducing the cross-section area of the at least one through hole (8) is arranged, wherein the at least one fluid -transporting channel (7) is formed between the body (1) and the fdling element (2) and / or between the at least two fdling elements (2).

2. The electrode according to claim 1, wherein a plurality of fdling elements (2) are arranged in the through hole (8), which reduce the cross-section area of the through hole (8) to form a plurality of the fluid-transporting channels (7).

3. The electrode according to either claim 1 or 2, wherein at least two fdling elements (2) are arranged one next to the other along essentially the entire length of the through hole (8).

4. The electrode according to claim 1 or 2, wherein at least two fdling elements (2) are arranged one above the other along essentially the entire length of the through hole (8).

5. The electrode according to claim 1 or 2, wherein at least two fdling elements (2) are arranged one in the other along essentially the entire length of the through hole (8).

6. The electrode according to any of the preceding claims 1 to 5, wherein the at least one fdling element (2) has a polygon-shaped cross-section.

7. The electrode according to any of the preceding claims 1 to 5, wherein the at least one fdling element (2) has a circular cross-section.

8. The electrode according to any of the preceding claims 1 to 7, wherein an at least one longitudinal groove (3) is arranged on at least one of an inner surface of the body (1) and an outer surface of the at least one fdling element (2), which after inserting of the at least one filling element (2) into the through hole (8) of the body (1) forms the at least one fluid- transporting channel (7).

9. The mixing electrode according to claim 8, wherein the at least one groove (3) runs parallel to the longitudinal axis of the mixing electrode.

10. The mixing electrode according to claim 8, wherein the at least one groove (3) spirals around the longitudinal axis of the mixing electrode.

11. The mixing electrode according to anyone of claims 8 to 10, wherein the at least one groove (3) has a cross-section selected from semicircular, square, rectangular, triangular, elliptical and trapezoidal sections.

12. The mixing electrode according to anyone of claims 8 to 11, wherein the cross-section of the at least one groove (3) is from 0.05 to 64 mm2, and more preferably from 0.05 to 0.6 mm2.

13. The mixing electrode according to anyone of claims 8 to 12, wherein a plurality of grooves (3) are arranged on the outer surface of the at least one filling element (2) so that when the at least one fillingelement (2) is inserted into the through hole (8) of the body (1), they form a system of fluidtransporting channels (7).

14. The mixing electrode according to anyone of claims 1 to 13, wherein on at least one surface selected from:- the inner surface of the body (1),- an outer surface of an at least one intermediate cylindrical filling element (5),- an inner surface of at an least one intermediate cylindrical filling element (5),- the outer surface of the at least one filling element (2), which is arranged inside the at least one intermediate filling element (5) and has a solid cross-section, the at least one groove (3) is arranged which, when the at least one filling element (2) and the at least one intermediate cylindrical filling element (5) are inserted into the through hole (8) of the body (1), constitutes the fluid-transporting channel (7).

15. A method for production of a mixing electrode for use in a glass melting process, the mixing electrode being in the form of a rod, having a body (1) made of an electrically conductive material, with an at least one through hole (8) extending along a longitudinal axis of the mixing electrode, characterized in that on at least one surface selected from:- an inner surface of the body (1),- an outer surface of a filling element (2), an at least one groove (3) extending along the entire length of the body (1) and / or the filling element (2) is made, and then said filling element (2) is inserted into the through hole (8) of the body (1) so that the at least one groove (3) forms a fluid-transporting channel (7).

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