Segmented Glass Melting Furnace

Abstract

The present invention relates to a furnace for melting vitrifiable materials, the furnace comprising: (i) at least one melting tank T1 having a crown and provided with electrical heating means; (ii) a fining tank T2 having a crown and provided with combustion heating means; (iii) at least one neck having a crown and separating the at least one melting tank and the fining tank; the furnace is defined by the following: W1 is at least 1.4×W3; W3 is at least 0.1×W2 and at most 0.6×W2, W1: width of tank T1; W2: width of tank T2; W3: width of the neck. This furnace, due to its high electricity input fraction (i.e. >20% or even 30%), has a low overall energy consumption and a low CO2 emission. 2 This is particularly advantageous since emissions are significantly reduced while the mechanical stability and life of the furnace are not adversely affected or are even improved.

Description

[Technical field]

[0001] The present invention relates to a glass melting furnace intended to continuously supply molten glass to a glass forming installation such as a float installation or a rolling installation, etc. In particular, the present invention relates to a glass melting furnace which offers a number of advantages, in particular with regard to energy consumption, CO2 emissions and process flexibility.

[0002] The invention particularly, but not exclusively, relates to melting furnaces for flat glass with high production capacities, ie up to 1000 tonnes / day and above, and power requirements of up to 60 MW. [Background technology]

[0003] In the prior art, vitrifiable materials or glass raw materials are: - a tank, covered by a crown, which contains the melt when the furnace is in use; - at least one inlet arranged upstream of the furnace for introducing the glass raw material to be heated; - heating means arranged in the tank; - at least one downstream outlet for the molten glass to reach a processing zone or working end; The glass is melted in a glass melting furnace, which generally contains

[0004] In such glass melting furnaces, the glass is generally melted by a flame obtained by combustion generated by burners placed above the glass surface and capable of heating the bath of molten glass / raw materials from above. Glass melting furnaces using oxy-fuel or air-fuel combustion are well known. The fuel can be, for example, fossil fuels, natural gas, biogas or hydrogen.

[0005] It is also known to combine combustion and electrical heating means in hybrid systems. In such a configuration, the melting furnace, in addition to the burners, comprises electrodes, which are forcedly immersed and are generally placed at the bottom of the tank, through which current / power can flow to heat the bath of molten glass from its bulk. It should be noted that glass melting furnaces, in which the heating capacity is entirely obtained by electricity, could be an option, but these are not adopted in flat glass technology when high quality glass is required. Indeed, firstly, the temperatures required for fining the glass melt must exceed >1400°C, preferably 1450°C, while the temperature at the bottom in the tank must be kept at a lower level (i.e. <1300°C) to limit the corrosion of the refractories, which is not possible to achieve with only bottom electrodes, and secondly, the production of high quality flat glass requires areas where the glass melt flow is layered and stratified with a free surface to allow the escape of gas bubbles from the glass melt. In the art, these two conditions are generally achieved by heating this free surface of the glass melt from above in order to reach a sufficiently high temperature while obtaining a stratified laminar glass flow. Moreover, the heat released at each electrode creates a large localized glass convection current, which completely hinders the required stratified laminar glass flow.

[0006] Global warming and the requirement to reduce CO2 emissions are putting increasing pressure on glass manufacturers, and increasing energy prices and CO2 taxes could pose a serious threat to the competitiveness of the glass business in the near future.

[0007] Electric melting could be part of the solution, as it helps to reduce CO2 emissions and also helps to reduce the total energy consumption of the melting furnace (fuel + electricity). However, conventional combustion glass melting furnaces can only be "boosted" with electrodes. Indeed, in such "electrically boosted combustion furnaces" the electricity input fraction is limited to a maximum of 10-15% of the total energy input.

[0008] The main limitations to the design of conventional electrically boosted fired furnaces as the electrical input fraction increases (i.e., above 15%) are: (i) the temperature of the bottom refractories in the melting zone where the electrodes are located increases significantly, thereby accelerating their corrosion; and (ii) The crown temperature in the fusion zone is significantly reduced, which increases the NaOH concentration in said zone, resulting in increased corrosion of the crown refractory.

[0009] These two combined corrosion phenomena (i)-(ii) have a significant negative impact on the mechanical stability and life span of highly electrically boosted furnaces, which is highly undesirable when investing in glass melting furnaces. Indeed, large glass melting furnaces, i.e. furnaces with a production capacity of several hundred tons per day, are constructed to operate uninterrupted for periods exceeding 10 years and their life span is determined primarily by the corrosion of the refractory material that forms their walls.

[0010] Therefore, these limitations on the maximum electrical input fraction of conventionally fired glass melting furnaces prevent the full benefit of the advantages of electric melting (reduced overall energy consumption and CO2 emissions).

[0011] However, there is currently a need to have a glass melting furnace design in which combustion burners and electrodes are used together as the heating means, which can significantly increase the fractional electrical input (compared to conventional electrically boosted combustion melting furnaces) while maintaining or even improving its mechanical stability and lifespan. Summary of the Invention [Problem to be solved by the invention]

[0012] One of the objectives of the present invention is to overcome the aforementioned shortcomings of the state of the art and to solve the technical problems, namely by providing a flat glass melting furnace in which combustion burners and electrodes are used in combination as heating means, which exhibits reduced overall energy consumption and reduced CO2 emissions compared to conventional electrically boosted combustion melting furnaces.

[0013] A further object of the present invention is to provide a glass melting furnace in which combustion burners and electrodes are used together as heating means without adversely affecting or even improving its service life.

[0014] A further object of the present invention is to provide a glass melting furnace having a high degree of freedom in which a combustion burner and an electrode are used in combination as a heating means. [Means for solving the problem]

[0015] The present invention relates to a furnace for melting a vitrifiable material, comprising: (i) at least one melting tank T1i covered by a melting crown C1i and provided with electrical heating means; (ii) a fining tank T2 covered by a fining crown C2 and provided with combustion heating means; (iii) at least one neck Ni covered by a crown C3i and separating at least one melting tank T1i and a fining tank T2; (iv) at least one inlet means Li arranged in the at least one melting tank for introducing the vitrifiable material to be heated; (v) at least one outlet means Oi located downstream of the fining tank for allowing the molten glass to flow to the working zone; This relates to a furnace including

[0016] According to the invention, the furnace comprises: 0.1*W2≦W3i≦0.6*W2; W1i≧1.4*W3i As prescribed by; W1i is the width of tank T1i; W2 is the width of tank T2; W3i is the width of the neck Ni. The present invention is therefore based on a new and inventive method. In particular, the inventors have found that by separating one or more electrically heated melting zones and the combustion fining zones by one or more necks of special design (as many as the number of melting zones), the overall energy consumption and CO2 emissions of the furnace can be significantly reduced through a high electricity input fraction (i.e. >20% or even 30-50%), while at the same time the mechanical stability and life of the furnace is not adversely affected or even improved. By "electricity input fraction" is meant the part of electricity in the total energy input of the furnace for melting / fining, i.e. electricity / (fuel+electricity), the total energy input being the energy input of the furnace in standard / normal production regime, i.e. in its standard draw range (periods of start-up, maintenance, hot repairs, culleting, ... are excluded).

[0017] The neck width in the present invention has been specifically designed by the inventors to find a good compromise between two opposing requirements: from one side, the neck between the melting and fining zones should ideally be as narrow as possible, (1) to reduce the opening between the melting and fining superstructures / crowns, and (2) to form an obstacle to the overall glass melt convection strength in the melting tank, and from the other side, the neck should ideally be as wide as possible, to limit the glass velocity inside the neck so that wear / erosion of the neck refractory wall is limited.

[0018] The inventors have shown that a number of advantages can be obtained in favor of energy consumption / CO2 emissions and / or in favor of the mechanical stability / lifetime of the furnace. In particular, the furnace of the present invention, with its special segmented design: - The heat radiation from the flame in the fining tank towards the melting tank can be blocked in order to efficiently confine the combustion energy in the zone where high temperatures are required (fining zone); - possible separation of the atmospheres between the melting tank and the fining tank, thereby limiting the backflow of corrosive fumes from the fining tank to the melting tank; - restricting the overall molten glass flow, which advantageously reduces the intensity of the glass convection in the melting tank and the glass velocity, thereby reducing the wear and erosion of the bottom refractory; - Full separation of melting and fining tank dimensioning (length, width, and crown height) and refractory properties, allowing each tank to be optimized for energy efficiency, glass quality, and mechanical / structural / other constraints.

[0019] It is well understood by those skilled in the art that the terms "a", "an" or "the" as used herein in the specification and claims mean at least "one" and should not be limited to "only one" unless expressly stated to the contrary. Also, when a range is indicated, the end values ​​are included. Moreover, all integer and subdomain values ​​within the numerical range are expressly included as if expressly stated. Finally, the terms "upstream" and "downstream" refer to the glass flow direction and should be understood in their general sense, i.e. along the average direction of movement of the vitrifiable material / glass melt (defined herein as "glass stream") from the inlet means to the outlet means when operating the furnace according to the present invention, i.e., along the direction going from left to right in FIG. 2.

[0020] According to the present invention, as is commonly employed in the glass technology field, a "melting tank" means a tank defining a zone in which the vitrifiable material is introduced and melted by heating, and which, when the furnace is in process, contains the melt and a "blanket" of unmelted vitrifiable material which floats on the melt and melts gradually from the upstream to the downstream of the melting tank, as a result of which the amount decreases.

[0021] According to the present invention, as commonly adopted in the glass technology field, a "fining tank" means a tank defining a zone where there is no longer a "blanket" of unmolten vitrifiable material floating on the melt and where the glass melt is heated to a temperature higher than the melting tank temperature (generally above 1400° C. or even above 1450° C.) in order to fine the glass (by removing most of the gas bubbles). This fining tank is also commonly called a "fining tank" in the art.

[0022] For clarity, according to the present invention, as generally accepted in the art, it is meant that the "neck" Ni (i) has a smaller width and (crown) height than at least one of the melting tank T1i and the fining tank T2, and (ii) the opening of the neck Ni is only partially below the glass melt / batch blanket free surface, thereby leaving a free opening above the glass melt / batch blanket. Thus, as accepted in the art, this definition excludes "throats" that have an "opening" completely below the glass melt / blanket free surface (so that no free space is left above the glass melt / batch blanket).

[0023] "Width" in this invention, here and throughout this specification and claims, means the (average) dimension perpendicular to the glass stream, unless otherwise specified.

[0024] Other characteristics and advantages of the invention will become more apparent on reading the following description of preferred embodiments and of the drawings, given by way of simple, illustrative and non-limiting example. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic perspective view of an embodiment of the furnace according to the invention in a “one melting tank” configuration;

[0026] [Diagram 2]FIG. 2 is a schematic plan view (horizontal cross section) of the furnace of FIG.

[0027] [Diagram 3] 1 is a schematic plan view (horizontal section) of one embodiment of a furnace according to the present invention;

[0028] [Figure 4] 1 is a schematic plan view (horizontal section) of one embodiment of a furnace according to the present invention;

[0029] [Diagram 5] FIG. 1 is a schematic plan view (horizontal section) of an embodiment of the furnace according to the invention in a “two melting tank” configuration. [Figure 6] The evolution of the bottom refractory temperature as a function of the distance (in meters) starting from the inlet means to the outlet means is shown for furnace 1, furnace 2 and furnace 3 with an unrealistic power of 16 MW (considering an equivalent power allows a fair comparison with the furnace of the invention). [Figure 7] 1 shows the temperature evolution of the crown refractory as a function of distance (in meters) starting from the inlet means to the outlet means for furnace 1 (comparative), furnace 2 and furnace 3 with 16 MW electric boost. [Figure 8] Illustrates the occurrence of circulation of molten glass according to the distance (in meters) starting from the inlet means to the outlet means for furnace 1 (for comparison), furnace 2 and furnace 3 with 16 MW electric boost. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Furnace 1 ("one melting tank" configuration) of Figures 1-3 includes one melting tank T1i, one neck Ni, and one fining tank T2. The assembly of T1i, Ni, and T2 is generally made of refractory materials that are resistant to temperature, corrosion of fumes, and aggressive action of molten materials. The liquid level of an exemplary bath in the tanks is indicated by a dashed line.

[0031] According to the invention, the furnace 1 is supplied with vitrifiable material in a melting tank T1i by means of at least one inlet means Li. Preferably, the at least one inlet means Li is either arranged upstream of the melting tank T1i or at the top of the melting tank T1i, as is known in the art.

[0032] In one embodiment, at least one inlet means Li is arranged upstream of the melt tank T1i (as shown in figures 1-2), either in the width of said tank or laterally in its length. In this embodiment, several inlet means, i.e. two inlet means, arranged upstream of the melt tank can advantageously be provided in order to improve the distribution over the surface of the tank T1i.

[0033] In another embodiment, at least one inlet means Li is placed at the top of the melting tank. This inlet means is known in the art as a "top batch injector". This particular embodiment is advantageous since it allows the injecting of raw materials directly at the top of the glass melt, in particular on the entire surface of the melting tank T1i, thereby obtaining a batch blanket covering the entire glass melt surface, as a result of which large temperature differences detrimental to the crown C1i (as well as the situation of varying blanket coverage during the melting process) can be avoided. It may advantageously be of the type of "rotary batch injector" or "linear XY-batch injector" placed above the glass melt and below the crown C1i. In FIG. 3, the inlet means Li is of the type of "linear XY batch injector" in the form of a distribution arm that is placed at the top of the melting tank T1i and that is movable in both directions XY, i.e. in the direction of the length and width of the melting tank. The "top batch injector" according to this embodiment may be of the type known as a "rotary crown batch injector", i.e. of the type proposed by Sorg®.

[0034] The furnace 1 includes a melting tank T1i provided with electrical heating means 2. The electrical heating means 2 according to the present invention is preferably arranged at the bottom of the tank T1i and is preferably composed of immersion electrodes. In order to facilitate the connection to the transformer and the current balance, the electrodes are advantageously arranged in a grid pattern (checkerboard) of 3 or a multiple of 2. For example, considering a maximum current density of 1.5 A / cm 2 at the electrode surface, the number of electrodes is planned so that the maximum output of each electrode is limited to 200 kW. Also, for example, the height of the immersion electrode is between 0.3 and 0.8 times the height of the glass melt.

[0035] According to one embodiment, the melting tank T1i does not include any combustion means, such as a burner.

[0036] The crown C1 according to the present invention may generally be arch-shaped or round ceiling-shaped, or may be flat. In particular, when the width W1i of the melting tank is narrower than that of a general glass melting furnace and narrower than the width W2 of the fining tank 2 (low-span crown), the crown C1i may be flat. When the crown C1i is arch-shaped / round ceiling-shaped, this may advantageously be composed of a refractory of the alumina or spinel type, which has better resistance to corrosion and thus a better service life (however, it has lower creep resistance, which can be compensated by a shorter span of the crown).

[0037] The crown C1i according to the present invention preferably has a height H1i lower than the height H2 of the crown C2 of the fining tank T2 (H1i < H2). In fact, the lower crown height H1i results in less horizontal radiative heat transfer, and subsequently, when the flue gas is withdrawn from the fining tank T2 towards the melting tank T1i, the heat transfer from the flue gas to the glass melt is better. In the present invention, the "height" of the crown means the average internal height from the inner surface of the above crown to the glass melt (excluding the batch blanket if it exists), that is, in the case of an arch-shaped / round ceiling-shaped crown.

[0038] According to the invention, the furnace comprises a fining tank T2 covered with a fining crown C2 and provided with combustion heating means 3.

[0039] The fining crown C2 according to the present invention is preferably arched or vaulted.

[0040] The combustion heating means 3 according to the invention consist in particular of burners arranged in the tank T2, usually arranged along the side walls on each side of said tank, in order to spread the flame over substantially the entire width of said tank. The burners are spaced apart from each other in order to distribute the energy supply over a portion of the fining tank T2 (i.e. about 50% of the length). They are also generally arranged in a row on either side of the tank.

[0041] The burner may be supplied with fuel and air, or fuel and oxygen, or fuel and an oxygen-rich gas. The fuel may be a fossil fuel, natural gas, biogas, hydrogen, ammonia, syngas, or mixtures thereof.

[0042] According to the invention, the furnace comprises at least one neck Ni, covered by a crown C3i, separating at least one melting tank T1i and a fining tank T2. The base of the neck Ni can be located essentially at the level of the floor / bottom of the melting tank T1i. Furthermore, the base of the neck Ni can be located essentially at the level of the floor / bottom of the fining tank T2, or higher than said level, or lower than said level.

[0043] According to one embodiment, the neck Ni does not include any heating means, for example electrical heating means and / or combustion means.

[0044] The crown C3i according to the present invention may be of an arch type or a round ceiling type, or may be flat. The crown C3i of the neck Ni can preferably have a height H3i that is less than or equal to the height H2 of the crown C2 of the clarification tank T2 (H3i ≤ H2). Also preferably, the neck Ni can have a height H3i that is less than or equal to the height H1i of the crown C1i of the melting tank T1i (H3i ≤ H1i). More preferably, H3i ≤ H2 and H3i ≤ H1i.

[0045] According to an advantageous embodiment, the furnace is defined by W1i ≤ W2. More preferably, the furnace of the present invention is defined by W1i < W2, or even better by W1i < 0.8 * W2. Thereby, the stress inside the melting crown C1i can be further reduced by reducing its span. In fact, corrosion and temperature variations are known to be most important in the melting zone. By reducing the stress level inside the melting crown, it becomes possible to use refractory materials that are more resistant to corrosion and less resistant to creep.

[0046] According to the present invention, the furnace 1 is defined by 0.1 * W2 ≤ W3i ≤ 0.6 * W2. Preferably, the furnace of the present invention is defined by 0.2 * W2 ≤ W3i ≤ 0.6 * W2. More preferably, the furnace of the present invention is defined by 0.3 * W2 ≤ W3i ≤ 0.5 * W2. Thereby, it is possible to reach a better compromise as described in paragraph

[0017] .

[0047] According to the present invention, the furnace 1 is defined by W1i ≥ 1.4 * W3i. Preferably, the furnace of the present invention is defined by W1i ≥ 1.5 * W3i, or even further by W1i ≥ 1.8 * W3i. More preferably, the furnace of the present invention is defined by W1i ≥ 2 * W3i. Thereby, it is possible to reach a greater width limitation at the neck Ni and improve the aforementioned advantages of the furnace of the present invention (blocking of heat radiation, possible separation of the atmosphere, generation of restriction of the molten glass flow).

[0048] According to an advantageous embodiment of the invention, the furnace further comprises means for extraction 4 of flue gases (generated in the fining tank T2) from upstream of the at least one melting tank T1i, preferably near the inlet means Li, in order to recover and transfer heat from the flue gases to the glass melt in the melting tank and / or to the unmolten vitrifiable material. Additionally or alternatively, the furnace may comprise means for extraction of flue gases (generated in the fining tank T2) arranged downstream of the at least one melting tank T1i. Also additionally or alternatively, the furnace may further comprise means for extraction of flue gases from the upstream part of the fining tank T2.

[0049] According to yet another advantageous embodiment of the invention, the furnace may comprise a removable wall (e.g., a skimbar from the side wall of the neck) arranged in at least one neck Ni in order (i) to possibly stop unmolten vitrifiable material that may reach the end of the melting tank, thereby avoiding it passing through the neck towards the fining tank, and (ii) to control the intensity or even eliminate the backflow of glass melt from the fining tank towards the melting tank.

[0050] According to the invention, the furnace 1 comprises at least one outlet means Oi arranged downstream of the fining tank T2 for the molten glass to reach the working zone. According to one embodiment, the outlet means Oi is usually constituted by a neck to guide the melt to a working zone, generally called the "working end", also called the "braise", also called the "conditioning zone". Alternatively, the outlet means Oi is constituted by a throat to guide the melt to a working zone, such as a forehearth. The working zone according to the invention can comprise, for example, a conditioning zone, in which the glass melt is thermally conditioned by controlled cooling before it leaves said zone through an outlet to reach the forming zone. Such a forming zone can comprise, for example, a float installation and / or a rolling installation.

[0051] In one embodiment of the present invention, as shown in Figure 4, a furnace for melting vitrifiable material comprises a melting tank T1i, laterally expanded and fitted with inlet means Li and Lii arranged on each side, so that the melting tank comprises two upstream zones with two opposite glass streams that join through a central downstream zone (when the furnace is operated). In such a configuration, the width W1i of the melting tank T1i is defined as the (average) dimension taken perpendicular to the glass streams in the neck Ni.

[0052] In a highly preferred embodiment of the invention, the furnace for melting vitrifiable material is configured with two melting tanks T1i, T1ii; two necks Ni, Nii; and at least two inlet means Li, Lii. According to this advantageous embodiment, the furnace of the invention comprises: - a melting tank T1ii covered with a melting crown C1ii and provided with electrical heating means arranged at the bottom of said tank; - a neck Nii covered by a crown C3ii and separating the melting tank T1ii from the fining tank T2; - at least one inlet means Lii arranged in the melting tank T1ii for introducing the vitrifiable material to be heated; further comprising; The furnace is 0.1*W2≦W3ii≦0.6*W2; W1ii≧1.4*W3ii as further defined by; W1ii is the width of the tank T1ii; W3ii is the width of the neck Nii.

[0053] Thus, in this "two melting tank" configuration, the furnace for melting the vitrifiable material is: (i) two melting tanks T1i, T1ii, each covered with a melting crown C1i, C1ii, respectively, and provided with electric heating means arranged at the bottom of said tanks; (ii) a fining tank T2 covered with a fining crown C2 and provided with combustion heating means; (iii) a neck Ni covered by a crown C3i and separating said melting tank T1i from the fining tank T2; (iv) a neck Nii covered by a crown C3ii and separating said melting tank T1ii from the fining tank T2; (v) at least one inlet means Li arranged in the melting tank T1i for introducing the vitrifiable material to be heated; (vi) at least one inlet means Lii arranged in the melting tank T1ii for introducing the vitrifiable material to be heated; (vii) at least one outlet means Oi located downstream of the fining tank for allowing the molten glass to flow to the working zone; Includes; The furnace is 0.1*W2≦W3i≦0.6*W2; 0.1*W2≦W3ii≦0.6*W2; W1i ≥ 1.4*W3i; W1ii≧1.4*W3ii as further defined by; W1i is the width of tank T1i; W1ii is the width of the tank T1ii; W2 is the width of tank T2; W3i is the width of neck Ni; W3ii is the width of the neck Nii.

[0054] This particular embodiment is shown in FIG. 5 and has inlet means Li and Lii arranged upstream of melter tanks T1i and T1ii, respectively.

[0055] This embodiment is particularly advantageous over the configuration with one melting tank (FIGS. 1-3), since it allows: - For the same overall melt tank area and furnace length (length is generally a greater constraint than width), the crown span of each melt tank can be reduced. By reducing the crown span, (i) the internal stresses in the crown material can be reduced, which in turn reduces the risks associated with creep of the material and deflection of the crown; it allows the use of refractory materials that are more resistant to corrosion and less resistant to creep, such as alumina or spinel, thereby increasing the life of the furnace; (ii) the average crown height can be reduced in the case of the arched neck crown C3, which results in less horizontal radiation transfer and subsequently better heat transfer from the flue gases to the glass melt when the flue gases are extracted from the melting tank; - for the same total neck width (W3i+W3ii), the open surface between the melting tank and the fining tank can be reduced in the case of an arched neck crown C3; - for the same total neck width (W3i+W3ii), the intensity of glass convection in the melting tank can be reduced; - Maintenance of the furnace in the melting zone can be made easier. Indeed, when having two melting tanks, one melting tank can be isolated from the rest of the furnace and cooled while production continues in the other melting tank. The life of the entire furnace can then be increased by replacing worn refractory material in the melting area, which is the most critical in terms of wear / corrosion.

[0056] In this advantageous embodiment, in which the furnace has two necks, two melting tanks and at least two inlet means (a "two melting tank" furnace as shown in FIG. 5), each neck, each melting tank and each inlet means can be designed independently of each other neck, melting tank and inlet means, according to the above description.

[0057] The specific advantageous features described in connection with the furnace of the foregoing "one melting tank" configuration, i.e., in connection with T1i, C1i, Li, are also applicable to the "two melting tanks" configuration and have the same advantages. Therefore, for clarity, the features described above with respect to T1i are also applicable to T1ii, the features described above with respect to C1i are also applicable to C1ii, and the features described above with respect to Li are also applicable to Lii.

[0058] In particular, the crown C3ii of the neck Nii can preferably have a height H3ii that is less than or equal to the height H2 of the crown C2 of the clarification tank T2 (H3ii ≤ H2). Also preferably, the neck Nii can have a height H3ii that is less than or equal to the height H1ii of the crown C1ii of the melting tank T1ii (H3ii ≤ H1ii).

[0059] Preferably, the "two melting tanks" furnace is defined by 0.2*W2 ≤ W3ii ≤ 0.6*W2. More preferably, this is defined by 0.3*W2 ≤ W3ii ≤ 0.5*W2.

[0060] According to an advantageous embodiment, the "two melting tanks" furnace is defined by W1ii ≤ W2. More preferably, the furnace of the present invention is defined by W1ii < W2, or even better by W1ii < 0.8*W2. By reducing the span of the melting crown C1i in this way, the stress inside it can be further reduced. In fact, it is known that corrosion and temperature variations are most important in the melting zone.

[0061] Also preferably, the "two melting tanks" furnace is defined by W1ii ≥ 1.5*W3ii, or even more preferably by W1ii ≥ 1.8*W3ii. More preferably, the "two melting tanks" furnace is defined by W1ii ≥ 2*W3i.

[0062] In a "two melting tank" furnace according to the invention, the two melting tanks T1i, T1ii are preferably connected to the refining tank by necks Ni, Nii arranged within the width W2 of said refining tank (as shown in FIG. 5). Alternatively, in a "two melting tank" furnace according to the invention, one melting tank is connected to the refining tank by a neck arranged within the width W2 of the refining tank and the other melting tank is connected to the refining tank by a neck arranged within the length (right or left) of the refining tank, near the upstream of the refining tank (i.e. in the first third of its length). This last configuration can be advantageous, for example, if the space present in the plant housing the furnace is insufficient to arrange two melting tanks side by side.

[0063] In a "two melting tank" furnace according to the invention, when the two melting tanks T1i, T1ii are connected to the fining tank by necks Ni, Nii arranged within the width W2 of said fining tank, the distance D between the two melting tanks T1i and T1ii is preferably at least 1 m, more preferably at least 2 m, better still at least 3 m. This is advantageous in case of maintenance work and repainting of the tank walls, as this zone can be reached.

[0064] In another embodiment of the invention, the furnace for melting vitrifiable material is configured with three melting tanks T1i, T1ii, T1iii; three necks Ni, Nii, Niii and three inlet means Li, Lii, Liii. According to this advantageous embodiment, the furnace of the invention comprises: - a melting tank T1iii provided with electrical heating means covered with a melting crown C1iii and arranged at the bottom of said tank; - a neck Niii covered with a crown C3iii and separating the melting tank T1iii from the fining tank T2; - at least one inlet means Liii arranged in the melting tank T1iii for introducing the vitrifiable material to be heated further comprising; The furnace is 0.1*W2≦W3iii≦0.6*W2; W1iii≧1.4*W3iii as further defined by; W1iii is the width of the tank T1iii; W3iii is the width of the neck Niii.

[0065] Thus, in this "three melting tank" configuration, the furnace for melting the vitrifiable material is: (i) three melting tanks T1i, T1ii, T1iii; each covered with a melting crown C1i, C1ii, C1iii respectively and provided with electric heating means arranged at the bottom of said tanks; (ii) a fining tank T2 covered with a fining crown C2 and provided with combustion heating means; (iii) a neck Ni covered by a crown C3i and separating said melting tank T1i from the fining tank T2; (iv) a neck Nii covered by a crown C3ii and separating said melting tank T1ii from the fining tank T2; (v) a neck Niii covered by a crown C3iii and separating said melting tank T1iii from said fining tank T2; (vi) at least one inlet means Li arranged in the melting tank T1i for introducing the vitrifiable material to be heated; (vii) at least one inlet means Lii arranged in the melting tank T1ii for introducing the vitrifiable material to be heated; (viii) at least one inlet means Liii arranged in the melting tank T1iii for introducing the vitrifiable material to be heated; (ix) at least one outlet means Oi located downstream of the fining tank for allowing the molten glass to flow into the working zone; Includes; The furnace is 0.1*W2≦W3i≦0.6*W2; 0.1*W2≦W3ii≦0.6*W2; 0.1*W2≦W3iii≦0.6*W2; W1i ≥ 1.4*W3i; W1ii ≥ 1.4*W3ii; W1iii≧1.4*W3iii As prescribed by; W1i is the width of tank T1i; W1ii is the width of the tank T1ii; W1iii is the width of the tank T1iii; W2 is the width of tank T2; W3i is the width of neck Ni; W3ii is the width of the neck Nii; W3iii Neck width is Niii.

[0066] This embodiment is particularly advantageous compared to an arrangement having one melting tank, as is the case with a "two melting tank" arrangement.

[0067] In this "three melt tank" each neck, each melt tank, and each inlet means can be designed independently of each other neck, melt tank, and inlet means, in accordance with the above description.

[0068] Certain advantageous features described in connection with the furnaces of the above "one melt tank" and "two melt tank" configurations, i.e. T1i, T1ii, C1i, C1ii, Li, Lii, are also applicable to the "three melt tank" configuration with the same advantages. Thus, for the sake of clarity, the features described above with respect to T1i, T1ii are also applicable to T1iii, the features described above with respect to C1i, C1ii are also applicable to C1iii, and the features described above with respect to Li, Lii are also applicable to Liii.

[0069] In particular, the crown C3iii of the neck Niii may preferably have a height H3iii that is equal to or less than the height H2 of the crown C2 of the fining tank T2 (H3iii≦H2). Also preferably, the neck Niii may have a height H3iii that is equal to or less than the height H1iii of the crown C1iii of the melting tank T1iii (H3iii≦H1iii).

[0070] Preferably, the "three - melting tank" furnace is defined by 0.2*W2 ≦ W3iii ≦ 0.6*W2. More preferably, this is defined by 0.3*W2 ≦ W3iii ≦ 0.5*W2.

[0071] Preferably, the "three - melting tank" furnace is defined by W1iii < W2. More preferably, this is defined by W1iii < 0.8*W2. By this, the span of the molten crown C1i is decreased, and the internal stress can be further reduced. In fact, corrosion and temperature variations are known to be most important in the melting zone.

[0072] Also preferably, the "three - melting tank" furnace is defined by W1iii ≧ 1.5*W3iii, or even more preferably by W1iii ≧ 1.8*W3iii. More preferably, the "three - melting tank" furnace is defined by W1iii ≧ 2*W3ii.

[0073] In the "three - melting tank" furnace according to the present invention, the three melting tanks T1i, T1ii, T1iii can be connected to the clarification tank by necks Ni, Nii, Niii arranged within the width W2 of the clarification tank. Alternatively, in the "three - melting tank" furnace of the present invention, one melting tank can be connected to the clarification tank by a neck arranged within the width W2 of the clarification tank, and the other two melting tanks can be connected to the clarification tank by necks arranged near the upstream (i.e., the first one - third of its length) of the clarification tank within the length of the clarification tank. The first one is on the right side of the clarification tank, and the second one is on the left side of the clarification tank. This last configuration can be advantageous, for example, when the space existing in the plant housing the furnace is insufficient to arrange the three melting tanks side - by - side, and / or when the designed dimensions of the melting tanks and necks (especially W1i, W1ii, W1iii and W3i, W3ii, W3iii) cannot be realized within the width W2 of the clarification tank.

[0074] In a "three-melt-tank" furnace according to the invention, when at least two melting tanks are connected to the refining tank by necks located within the width W2 of said refining tank, the distance D between the two melting tanks is preferably at least 1 m, more preferably at least 2 m, better still at least 3 m. Independently of this, in a "three-melt-tank" furnace according to the invention, when three melting tanks are connected to the refining tank by necks located within the width W2 of said refining tank, the distance D between the two melting tanks T1i and T1ii is preferably at least 1 m, more preferably at least 2 m; the distance D' between the two melting tanks T1ii and T1iii is also preferably at least 1 m, more preferably at least 2 m.

[0075] In all furnace configurations according to the invention, i.e. the "one melting tank", "two melting tank" and "three melting tank" configurations, more than one inlet means may be provided for each melting tank to facilitate dispersion of the incoming vitrifiable material, i.e. two inlet means per melting tank.

[0076] In all furnace configurations according to the invention, the total surface area of ​​the melting tank is preferably between 25 and 400 m 2 Also preferably, according to the present invention, the surface area of ​​the clarifier tank is in the range of 25 to 400 m 2 The range is.

[0077] Those skilled in the art will recognize that the present invention is in no way limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. It is further noted that the present invention relates to all possible combinations of the features and preferred features described herein and recited in the claims.

[0078] The following examples are provided for illustrative purposes and are not intended to limit the scope of the present invention. EXAMPLES

[0079] Calculations were carried out for an example of a furnace according to the invention and for a comparative example of a conventionally fired furnace (possibly electrically boosted).

[0080] Without mathematical modeling, the optimization and design of melting furnaces is difficult, dangerous and very time-consuming. In fact, furnaces are very expensive, their life span exceeds 15 years, even up to 20 years. And there is only a small machine to carry out research and design modifications, and there is a high pressure to mitigate the risks associated with these modifications. Therefore, mathematical modeling of the melting process in operating glass furnaces is well developed in the glass technology field and is well known among glass manufacturers. By using mathematical models, detailed temperature and velocity fields of the glass melt in the tank and of the gases in the combustion / fining space are determined. The results of these existing mathematical modelings have been confirmed in many operating furnaces by comparison with measurements (thermocouples and infrared cameras).

[0081] For the present calculations the following furnaces with the same glass drawer were considered: - Furnace 1 (for comparison): conventional fired glass melting furnace: one tank containing a melting zone and a fining zone, fitted with air-gas fed burners and possibly with electrodes for electrical boosting. Furnace 2: a furnace according to the invention in the "one melting tank" configuration: - Melt tank T1i with tank width W1i = 13.0 m and average crown height H1i = 1.35 m - inlet means Li arranged upstream of the melting tank; - Electrodes in the melting tank, reaching a total installed power of 16.0MW - Neck Ni with width W3i=4.5m=0.35W1i and average crown height H3i=0.35m - Clarification tank T2 with tank width W2=13.0m and average crown height H2=3.5m - an oxyburner in the clarifier tank, supplied with pure oxygen and natural gas, with a total installed power of 16.0 MW; - Exit means O - extraction means for extracting flue gases, which are arranged in the upstream part of the melting tank, near the inlet through which the vitrifiable material is introduced; is attached; - Furnace 3: a furnace according to the invention in a "two melting tank" configuration. In the considered calculation, both melting tanks have identical dimensions and are arranged symmetrically (see FIG. 3). The distance between both melting tanks is 4.8 m. Furnace 3 has: - Melt tank T1i with tank width W1i = 8.4 m and average crown height H1i = 0.95 m - Melting tank T1ii for W1ii=W1i and H1ii=H1i - an inlet means Li arranged upstream of the melting tank T1i, - inlet means Lii arranged upstream of the melting tank T1i, - electrodes in the melting tank, with the installed power distributed equally between both tanks; - a neck Ni with a width W3i = 3.6 m and an average crown height H3i = 0.54 m; - a neck Nii with width W3ii=W3i and H3ii=H3i, - clarification tank T2 with the same tank dimensions as furnace 2, - a burner in the clarifier tank, supplied with air-gas, having the same characteristics as furnace 2; - exit means O, - Extraction means for extracting flue gases from the melting tank is attached.

[0082] The energy consumption (gas / electricity), bottom temperature, crown temperature, and glass circulation of these furnaces 1-3 were evaluated.

[0083] Energy consumption Table 1 shows the calculated gas consumption, power consumption, and total energy consumption of furnaces 1-3, as well as the electrical input fraction.

[0084] For conventional furnace 1, two situations were considered: an all-fired (100% gas energy) situation, and a situation at maximum feasible electric boost for this furnace (exceeding this maximum bottom and crown temperature would result in severe refractory corrosion and serious furnace damage). TIFF2024529770000002.tif83170

[0085] Table 1 very well shows that, compared to conventional electrically boosted combustion melting furnaces, the furnace according to the invention allows increasing the electrical input fraction (reaching values ​​of up to 50%) while reducing the total energy consumption (by about 30%), thereby significantly reducing CO2 emissions.

[0086] bottom temperature FIG. 6 shows the evolution of the bottom refractory temperature as a function of the distance (in meters) starting from the inlet means to the outlet means for furnaces 1, 2 and 3 with an unrealistic power of 16 MW (considering an equivalent power allows a fair comparison with the furnace of the invention). The y-axis shows the values ​​in degrees Celsius (T bottom -T ref ), and T bottom is the temperature at the bottom of the electrically boosted furnace 1, furnace 2, and furnace 3, and T ref is the maximum temperature at the bottom of furnace 1 (all-fuel conventional furnace) without electric boost. Furnaces 1 to 3 according to the invention are diagrammed at the top of the figure to show and allow comparison of the positions of the relevant zones of each configuration.

[0087] This figure shows that in conventional furnaces there is a large bottom temperature increase with increasing power input, while the furnace of the invention remains at a lower value for the same electrical input, which is favorable for avoiding corrosion and therefore increasing the lifespan of the furnace.

[0088] Crown Temperature FIG. 7 shows the temperature evolution of the crown refractory as a function of distance (in meters) starting from the inlet means to the outlet means for furnace 1 (comparative), furnace 2 and furnace 3 with 16 MW electric boost. The y-axis shows the value in degrees Celsius (Tcrown -T ref ), and T crown are the crown temperatures of electrically boosted furnaces 1, 2, and 3, and T ref is the maximum crown temperature for furnace 1 without electric boost (all-fuel conventional furnace). The conventional electric boost furnace 1 and furnaces 2-3 according to the invention are diagrammed at the top of the figure to show and allow comparison of the positions of the relevant zones for each configuration.

[0089] The figure shows that conventional furnace 1 and furnaces 2-3 according to the invention show a reduction in the crown temperature of the melting zone when compared to a conventional furnace without electric boost (ref). In an electrically boosted furnace this is a major drawback since serious corrosion phenomena occur at the crown (mainly due to the concentration of NaOH caused by fining). In a furnace according to the invention this reduction in crown temperature is more easily manageable because (i) when flue gases are extracted from the fining tank, the atmosphere from the fining zone and the melting zone is separated by at least one neck, which allows limiting or avoiding the backflow of corrosive fumes (NaOH) from the fining tank to the melting tank, and (ii) when flue gases are extracted from the melting tank, the crown span can be limited (especially in the case of multiple melting tanks), making the use of alumina refractories a viable option (known alumina is more resistant to corrosion but is not recommended for large crown spans).

[0090] Glass Circulation FIG. 8 shows the occurrence of molten glass circulation as a function of distance (in meters) starting from the inlet means to the outlet means for furnace 1 (comparative), furnace 2 and furnace 3 with 16 MW electric boost. The y-axis shows the values ​​(m backward / m pull ), and m backward is the mass flow rate in the reverse direction, and m pull is the withdrawal mass flow rate. A conventional electrically boosted furnace 1 and furnaces 2-3 according to the invention are diagrammed in the upper part of the figure in order to show and compare the positions of the relevant zones of the respective configurations.

[0091] This figure shows that furnaces 2-3 according to the invention have significantly reduced overall molten glass circulation in the melting and fining zones, which advantageously reduces the molten glass velocity and thereby reduces bottom refractory corrosion.

Claims

1. A furnace for melting a vitrifiable material, the furnace comprising: (i) at least one melting tank T1i covered by a melting crown C1i and provided with electrical heating means; (ii) a fining tank T2 covered by a fining crown C2 and provided with combustion heating means; (iii) at least one neck Ni covered by a crown C3i and separating the at least one melting tank T1i from the fining tank T2; (iv) at least one inlet means Li disposed in the at least one melting tank for introducing the vitrifiable material to be heated; (v) at least one outlet means Oi disposed downstream of the fining tank for flowing the molten glass to a working zone and the furnace being 0.1 * W2 ≤ W3i ≤ 0.6 * W2; W1i ≥ 1.4 * W3i defined by; W1i is the width of the tank T1i; W2 is the width of the tank T2; W3i is the width of the neck Ni, the furnace.

2. The furnace according to claim 1, characterized in that the crown C1i has a height H1i lower than the height H2 of the crown C2.

3. The furnace according to claim 1 or 2, characterized in that the crown C3i has a height H3i less than or equal to the height H2 of the crown C2.

4. The furnace according to claim 1 or 2, characterized in that the crown C3i has a height H3i less than or equal to the height H1i of the crown C1i.

5. The furnace according to claim 1 or 2, characterized in that it is defined by W1i ≥ 1.5 * W3i.

6. The furnace according to claim 1 or 2, characterized in that it is defined by 0.2 * W2 ≤ W3i ≤ 0.6 * W2.

7. The furnace according to claim 1 or 2, characterized in that the at least one inlet means Li is disposed upstream of the melting tank T1i or at the upper part of the melting tank T1i.

8. The furnace according to claim 7, characterized in that the at least one inlet means Li is disposed upstream of the melting tank T1i.

9. - a melting tank T1ii covered by a melting crown C1ii and provided with electrical heating means disposed at the bottom of the tank; - a neck Nii covered by a crown C3ii and separating the melting tank T1ii from the fining tank T2; - At least one inlet means Lii arranged in the melting tank T1ii for introducing a vitrifiable material to be heated further comprising wherein the furnace 0.1 * W2 ≤ W3ii ≤ 0.6 * W2; W1ii ≥ 1.4 * W3ii is further defined by; W1ii is the width of the tank T1ii; W3ii is the width of the neck Nii The furnace according to claim 1 or 2, characterized in that.

10. The furnace according to claim 9, characterized in that the crown C1ii has a height H1ii lower than the height H2 of the crown C2.

11. The furnace according to claim 9, characterized in that the crown C3ii has a height H3ii less than or equal to the height H2 of the crown C2.

12. The furnace according to claim 9, characterized in that the crown C3ii has a height H3ii less than or equal to the height H1ii of the crown C1ii.

13. The furnace according to claim 9, characterized in that it is defined by W1ii ≥ 1.5 * W3ii.

14. The furnace according to claim 9, characterized in that it is defined by 0.2 * W2 ≤ W3ii ≤ 0.6 * W2.

15. The furnace according to claim 9, characterized in that the at least one inlet means Lii is arranged upstream of the melting tank T1ii or on the upper part of the melting tank T1ii.

16. The furnace according to claim 15, characterized in that the at least one inlet means Lii is arranged upstream of the melting tank T1ii.

17. - A melting tank T1iii covered by a melting crown C1iii and provided with electric heating means arranged at the bottom of the tank; - A neck Niii covered by a crown C3iii and separating the melting tank T1iii from the clarification tank T2; - At least one inlet means Liii arranged in the melting tank T1iii for introducing a vitrifiable material to be heated further comprising; wherein the furnace 0.1 * W2 ≤ W3iii ≤ 0.6 * W2; W1iii ≥ 1.4 * W3iii is further defined by; W1iii is the width of the tank T1iii; W3iii is the width of the neck Niii The furnace according to claim 9, characterized in that.

18. The furnace according to claim 17, characterized in that the crown C1iii has a height H1iii lower than the height H2 of the crown C2.

19. The furnace according to claim 17, characterized in that the crown C3iii has a height H3iii that is less than or equal to the height H2 of the crown C2.

20. The furnace according to claim 17, characterized in that the crown C3iii has a height H3iii that is less than or equal to the height H1iii of the crown C1iii.

21. The furnace according to claim 17, characterized in that it is defined by W1ii ≥ 1.5 * W3iii.

22. The furnace according to claim 17, characterized in that it is defined by 0.2 * W2 ≤ W3iii ≤ 0.6 * W2.

23. The furnace according to claim 17, characterized in that the at least one inlet means Liii is arranged upstream of the melting tank T1iii or on top of the melting tank T1iii.

24. The furnace according to claim 23, characterized in that the at least one inlet means Liii is arranged upstream of the melting tank T1iii.

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