SEGMENTED GLASS MELTING FURNACE

Abstract

A furnace for melting vitrifiable materials, including at least one first melting tank covered by a first melting crown and provided with electrical heating, a fining tank covered by a fining crown and provided with combustion heating, at least one first neck covered by a first crown and separating the at least one first melting tank and the fining tank, at least one first inlet located at the at least one first melting tank, for charging the at least one first melting tank with the vitrifiable materials to be heated, and at least one outlet located downstream of the fining tank for a melted glass to flow to a working zone.

Claims

1: A furnace for melting vitrifiable materials, comprising: at least one first melting tank covered by a first melting crown and provided with electrical heating means; a fining tank covered by a fining crown and provided with combustion heating means; at least one first neck covered by a first crown and separating the at least one first melting tank and the fining tank; at least one first inlet means located at the at least one first melting tank, for charging the at least one first melting tank with the vitrifiable materials to be heated; and at least one outlet means located downstream of the fining tank for a melted glass to flow to a working zone; wherein the furnace is defined by the following: $0.1*W2?W3i?0.6*W2;W1i?1.4*W3i;$ W1i being a width of the at least one first melting tank; W2 being a width of the fining tank; W3i being a width of the at least one first neck.

2: The furnace according to claim 1, wherein the first melting crown has a height which is lower than a height of the fining crown.

3: The furnace according to claim 1, wherein the first crown has a height which is equal or lower than a height of the fining crown.

4: The furnace according to claim 1, wherein the first crown has a height which is equal or lower than a height of the first melting crown.

5: The furnace according to claim 1, wherein the furnace is defined by: W1i?1.5*W3i.

6: The furnace according to claim 1, wherein the furnace is defined by 0.2*W2?W3i?0.6*W2.

7: The furnace according to claim 1, wherein the at least one first inlet means is located upstream of the at least one first melting tank or located at a top of the at least one first melting tank.

8: The furnace according to claim 7, wherein the at least one first inlet means is located upstream of the at least one first melting tank.

9: The furnace according to claim 1, further comprising: a second melting tank covered by a second melting crown and provided with electrical heating means located at a bottom of said second melting tank; a second neck covered by a second crown and separating said second melting tank and the fining tank; at least one second inlet means located at the second melting tank, for charging it with the vitrifiable materials to be heated; wherein the furnace is further defined by the following: $0.1*W2?W3\mathrm{ii}?0.6*W2;W1\mathrm{ii}?1.4*W3\mathrm{ii};$ W1ii being a width of the second melting tank; W3ii being a width of the second neck.

10: The furnace according to claim 9, wherein the second melting crown has a height which is lower than a height of the fining crown.

11: The furnace according to claim 9, wherein the second crown has a height which is equal or lower than a height of the fining crown.

12: The furnace according to claim 9, wherein the second crown has a height which is equal or lower than a height of the second melting crown.

13: The furnace according to claim 9, wherein the furnace is defined by: W1ii?1.5*W3ii.

14: The furnace according to claim 9, wherein the furnace is defined by 0.2*W2?W3ii?0.6*W2.

15: The furnace according to claim 9, wherein the at least one second inlet means is located upstream of the at least one first melting tank or located at a top of the at least one first melting tank.

16: The furnace according to claim 15, wherein the at least one second inlet means is located upstream of the at least one first melting tank.

17: The furnace according to claim 9, further comprising: a third melting tank covered by a third melting crown provided with electrical heating means located at the bottom of said tanks; a third neck covered by a third crown and separating said third melting tank and the fining tank; at least one third inlet means located at the third melting tank, for charging the third melting tank with the vitrifiable materials to be heated; wherein the furnace is further defined by the following: $0.1*W2?W3\mathrm{iii}?0.6*W2;W1\mathrm{iii}?1.4*W3\mathrm{iii};$ W1iii being a width of the third melting tank; W3iii being a width of the third neck.

18: The furnace according to claim 17, wherein the third crown has a height which is lower than a height of the fining crown.

19: The furnace according to claim 17, wherein the third crown has a height which is equal or lower than a height of the fining crown.

20: The furnace according to claim 17, wherein the third crown has a height which is equal or lower than a height of the third melting crown.

21: The furnace according to claim 17, wherein the furnace is defined by: W1ii?1.5*W3iii.

22: The furnace according to claim 17, wherein the furnace is defined by 0.2*W2?W3iii?0.6*W2.

23: The furnace according to claim 17, wherein the at least one third inlet means is located upstream of the at least one first melting tank or located at a top of the at least one first melting tank.

24: The furnace according to claim 23, wherein the at least one third inlet means is located upstream of the at least one first melting tank.

Description

[0043] Other features and advantages of the invention will be made clearer from reading the following description of preferred embodiments and figures, given by way of simple illustrative and non-restrictive examples.

[0044] FIG. 1 is a schematic perspective view of an embodiment of a furnace according to the invention, in a one melting tank configuration.

[0045] FIG. 2 is a schematic plan view (horizontal cross-section) of the furnace of FIG. 1.

[0046] FIG. 3 is a schematic plan view (horizontal cross-section) of an embodiment of a furnace according to the invention.

[0047] FIG. 4 is a schematic plan view (horizontal cross-section) of an embodiment of a furnace according to the invention.

[0048] FIG. 5 is a schematic plan view (horizontal cross-section) of an embodiment of a furnace according to the invention, in a two melting tanks configuration.

[0049] The furnace 1 of FIGS. 1-3 (one melting tank configuration) comprises one melting tank T1i, one neck Ni and one fining tank T2. The assemblies of T1i, Ni and T2 is commonly made from refractory materials resistant to temperatures, corrosion of the fumes and aggressive action of the molten materials. The illustrative bath level in the tank is shown by a broken line.

[0050] According to the invention, the furnace 1 is supplied with vitrifiable materials at the melting tank T1i, thanks to at least one inlet mean Li. Preferably, and as known in the art, the at least one inlet mean Li is either located upstream of the melting tank T1i or located at the top of the melting tank T1i.

[0051] In an embodiment, the at least one inlet mean Li is located upstream of the melting tank T1i, either in the width of said tank (as illustrated in FIGS. 1-2) or laterally in its length. In this embodiment, to improve distribution over the surface of the tank T1i, several inlet means located upstream of the melting tank may be advantageously provided, i.e. two inlet means.

[0052] In an alternative embodiment, the at least one inlet mean Li is a located at the top of the melting tank. This inlet mean is known in the art as top batch charger. This particular embodiment is advantageous as it allows to charge the raw materials directly on the top of glass melt, especially over the entire surface of the melting tank T1i thereby allowing to obtain a batch blanket covering the whole glass melt surface and consequently avoiding high temperature differences detrimental to crown C1i (like in a situation where the blanket coverage varies during melting process). It may advantageously be of the type rotating batch charger or linear X-Y-batch charger, located above the glass melt and below the crown C1i. In FIG. 3, the inlet mean Li is located at the top of the melting tank T1i and is of the type linear X-Y batch charger in the form of a distributor arm that can move in both directions X-Y, namely in the length and width of the melting tank. The top batch charger according to this embodiment may also be of the type known as rotating crown batch charger, i.e. as that proposed by Sorg?.

[0053] The furnace 1 includes a melting tank T1i provided with electrical heating means 2. Electrical heating means 2 according to the invention are preferably located at the bottom of the tank T1i and preferably, also, composed of immersed electrodes. The electrodes are advantageously arranged in grid pattern (checkerboard) multiple of 3 or 2, in order to facilitate connection to transformers and electric current balance. For example, the number of electrodes is designed in order to limit maximum power for each electrode to 200 kW, by respecting a maximum current density of 1.5 A/cm.sup.2 at the electrode surface. For example also, immersed electrodes height is between 0.3 and 0.8 times glass melt height.

[0054] According to an embodiment, the melting tank T1i does not comprise any combustion means, e.g. any burner.

[0055] The crown C1i according to the invention may be commonly arched or vaulted, or alternatively, it may be flat. The crown C1i may be flat especially if the width W1i of the melting tank is lowered compared to common glass melting furnace and compared to width W2 of fining tank 2 (low span crown). When the crown C1i is arched/vaulted, it may be advantageously composed of refractories of the type alumina or spinel, which have a better resistance to corrosion and therefore a better lifetime (but lower creep resistance, that can be compensated by a lower crown span).

[0056] The crown C1i according to the invention has preferably a height H1i which is lower than the height H2 of the crown C2 of the fining tank T2 (H1i<H2). Indeed, a lower crown height H1i will lead to lower horizontal radiation heat transfer, and subsequently to better heat transfer from flue gases to the glass melt in case flue gases are extracted from the fining tank T2 towards the melting tank T1i.

[0057] By height for a crown in the invention, it is meant the average inner height (i.e. in case of an arched/vaulted crown), from the inner surface of said crown to the glass melt (excluding batch blanket if present).

[0058] According to the invention, the furnace comprises a fining tank T2 covered by a fining crown C2 and provided with combustion heating means 3.

[0059] The fining crown C2 according to the invention is preferably arched or vaulted.

[0060] Combustion heating means 3 according to the invention are especially composed of burners located in the tank T2 and are usually arranged along the side walls of said tank on each side thereof to spread the flames over practically the entire width of the tank. The burners are spaced from one another in order to distribute the energy supply over a portion (i.e. .sup.?50% of the length) of the fining tank T2. They are also commonly arranged in rows on either side of the tank.

[0061] The burners may be supplied with fuel and air, or fuel and oxygen, or fuel and a gas that is enriched in oxygen. Fuel may be fossil fuel, natural gas, biogas, hydrogen, ammonia, synthetic gas or mixture thereof.

[0062] According to the invention, the furnace comprises at least one neck Ni covered by a crown C3i and separating the at least one melting tank T1i and the fining tank T2. The base of the neck Ni may be located essentially at the level of the floor/bottom of the melting tank T1i. Moreover, the base of the neck Ni may be located essentially at the level of the floor/bottom of the fining tank T2 or above said level or below said level.

[0063] According to an embodiment, the neck Ni does not comprise any heating means, e.g. any electrical heating means and/or combustion means.

[0064] The crown C3i according to the invention may be arched or vaulted, or alternatively, it may be flat. The crown C3i of the neck Ni may preferably have a height H3i which is equal or lower than the height H2 of the crown C2 of the fining tank T2 (H3i?H2). Preferably also, the neck Ni may have a height H3i which is equal or lower than the height H1i of the crown C1i of the melting tank T1i (H3i?H1i). More preferably, H3i?H2 and H3i?H1i.

[0065] According to an advantageous embodiment, the furnace is defined by W1i W2. More preferably, the furnace of the invention is defined by W1i<W2 or better W1i<0.8*W2. This allows to reduce further the stress inside the melting crown C1i by reducing its span. Indeed, it is known that the corrosion and temperature variations are the most critical in the melting zone. By reducing stress level inside the melting crown, it will then make possible the use of refractory materials that are more resistant to corrosion and less resistant to creep.

[0066] According to the invention, the furnace 1 is defined by 0.1*W2?W3i?0.6*W2. Preferably, the furnace of the invention is defined by 0.2*W2?W3i?0.6*W2. More preferably, the furnace of the invention is defined by 0.3*W2?W3i?0.5*W2. This allow to reach a better compromise as exposed above at paragraph [0017].

[0067] According to the invention, the furnace 1 is defined by W1i?1.4*W3i. Preferably, the furnace of the invention is defined by W1i?1.5*W3i, or even W1i?1.8*W3i. More preferably, the furnace of the invention is defined by W1i?2*W3i. This allows to reach a higher width restriction at the neck Ni and to enhance the above-cited advantages of the furnace of the invention (to cut off heat radiation, to optionally separate atmospheres, to generate a restriction of the molten glass flow).

[0068] According to an advantageous embodiment of the invention, the furnace comprises further an extraction mean 4 of flue gas (generated in the fining tank T2) from upstream of the at least one melting tank T1i, preferably close to inlet mean(s) Li, in order to recover and transfer heat from flue gas to the glass melt and/or unmelted vitrifiable materials in the melting tank. Additionally or alternatively, the furnace may comprise an extraction mean of flue gas (generated in the fining tank T2) located downstream of the at least one melting tank T1i. Additionally or alternatively also, the furnace may comprise further an extraction mean of flue gas from upstream part of the fining tank T2.

[0069] According to still another advantageous embodiment of the invention, the furnace may comprise a removable wall located at the at least one neck Ni (e.g. a skimbar coming from the side wall of the neck), in order to (i) possibly stop unmelted vitrifiable materials that could arrive at the end of the melting tank and thereby avoid their passing through the neck towards the fining tank and (ii) control the intensity of or annihilate the backward flow of the glass melt from the fining towards the melting tank.

[0070] According to the invention, the furnace 1 comprises at least one outlet mean Oi located downstream of the fining tank T2 for the melted glass to reach a working zone. According to an embodiment, the outlet mean Oi is composed usually of a neck, in order to lead the melt towards a working zone commonly called working end or also braise or also conditioning zone.

[0071] Alternatively, the outlet mean Oi is composed of a throat, in order to lead the melt towards a working zone including, for example, fore heart(s). The working zone according to the invention may comprise, for example, a conditioning zone in which thermal conditioning by controlled cooling is carried out prior to glass melt leaving said zone through an outlet to a forming zone. Such a forming zone may comprise, for example, a float installation and/or a rolling installation.

[0072] In an embodiment of the invention, illustrated at FIG. 4, the furnace for melting vitrifiable materials comprises a melting tank T1i enlarged laterally and equipped with inlet mean(s) Li and Lii located at each lateral side, so that the melting tank comprises two upstream zones with two opposed glass streams (when the furnace is operating) converging through a central downstream zone. In such a configuration, the width W1i of the melting tank T1i is defined as the dimension (in average) taken perpendicularly to the glass stream in the neck Ni.

[0073] In a very preferred embodiment of the invention, the furnace for melting vitrifiable materials is in a configuration 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 additionally comprises: [0074] a melting tank T1ii covered by a melting crown C1ii and provided with electrical heating means located at the bottom of said tank; [0075] a neck Nii covered by a crown C3ii and separating said melting tank T1ii and the fining tank T2; [0076] at least one inlet mean Lii located at the melting tank T1ii, for charging it with vitrifiable materials to be heated;
the furnace being further defined by the following:

[00002]$0.1*W2?W3\mathrm{ii}?0.6*W2;W1\mathrm{ii}?1.4*W3\mathrm{ii};$ [0077] W1ii being the width of tank T1ii; [0078] W3ii being the width of neck Nii.

[0079] In this two-melting tanks configuration, the furnace for melting vitrifiable materials therefore comprises: [0080] (i) two melting tanks T1i, T1ii; each covered by a melting crown C1i, C1ii, respectively and provided with electrical heating means located at the bottom of said tanks; [0081] (ii) a fining tank T2 covered by a fining crown C2 and provided with combustion heating means; [0082] (iii) a neck Ni covered by a crown C3i and separating said melting tank T1i and the fining tank T2; [0083] (iv) a neck Nii covered by a crown C3ii and separating said melting tank T1ii and the fining tank T2; [0084] (v) at least one inlet mean Li located at the melting tank T1i, for charging it with vitrifiable materials to be heated; [0085] (vi) at least one inlet mean Lii located at the melting tank T1ii, for charging it with vitrifiable materials to be heated; [0086] (vii) at least one outlet Oi mean located downstream of fining tank for the melted glass to flow to a working zone; [0087] the furnace being defined by the following:

[00003]$0.1*W2?W3i?0.6*W2;0.1*W2?W3\mathrm{ii}?0.6*W2;W1i?1.4*W3i;W1\mathrm{ii}?1.4*W3\mathrm{ii};$ [0088] W1i being the width of tank T1i; [0089] W1ii being the width of tank T1ii; [0090] W2 being the width of tank T2; [0091] W3i being the width of neck Ni; [0092] W3ii being the width of neck Nii.

[0093] This particular embodiment is illustrated in FIG. 5, with inlet means Li and Lii located upstream of the melting tank T1i and T1ii, respectively.

[0094] This embodiment is particularly advantageous compared to the configuration with one melting tank (FIGS. 1-3) as it allows: [0095] to reduce the crown span of each melting tank for a same global melting tank area and furnace length (the length is generally more a constraint than the width). The reduction of crown span allows [0096] (i) to reduce stress inside the crown materials, and then reduce risk regarding material creep and crown sagging. It will then make possible the use of refractory materials that are more resistant to corrosion and less resistant to creep, such as alumina or spinel, and thereby increase furnace lifetime; [0097] (ii) to reduce crown average height in case of arched shaped neck crown C3, leading to lower horizontal radiation transfer, and subsequently to better heat transfer from flue gas to the glass melt in case flue gas is extracted from melting tanks; [0098] for a same total neck width (W3i+W3ii) and in case of arched shaped neck crown C3, to reduce the opening surface between the melting and fining tanks; [0099] for a same total neck width (W3i+W3ii), to reduce the strength of glass convection in the melting tank; [0100] to render easier furnace maintenance in the melting zone. Indeed, with 2 melting tanks, it is possible to isolate one melting tank from the rest of the furnace and cooling it down, while pursuing production with the other melting tank. It is then possible to increase the total furnace lifetime, by replacing worn refractory materials in the melting areas which is the most critical area regarding wear/corrosion.

[0101] In this advantageous embodiment where the furnace has two necks, two melting tanks and at least two inlet means (two melting tanks furnace, as illustrated in FIG. 5), each neck, each melting tank and each inlet mean may be designed independently of the other neck, melting tank and inlet mean respectively, according to the description above.

[0102] Specific advantageous features described in relation with the furnace with one melting tank configuration above, i.e. those linked to T1i, C1i, Li are applicable to the two melting tanks configuration, with the same advantages. Hence, for sake of clarity, features described above in relation with T1i are applicable to T1ii, features described above in relation with C1i are applicable to C1ii, and features described above in relation with Li are applicable to Lii.

[0103] In particular, the crown C3ii of the neck Nii may preferably have a height H3ii which is equal or lower than the height H2 of the crown C2 of the fining tank T2 (H3ii?H2). Preferably also, the neck Nii may have a height H3ii which is equal or lower than the height H1ii of the crown C1ii of the melting tank T1ii (H3ii?H1ii).

[0104] Preferably, the two melting tanks furnace is defined by 0.2*W2?W3ii?0.6*W2. More preferably, it is defined by 0.3*W2?W3ii?0.5*W2.

[0105] According to an advantageous embodiment, the two melting tanks furnace is defined by W1ii?W2. More preferably, the furnace of the invention is defined by W1ii<W2 or better W1ii<0.8*W2. This allows to reduce further the stress inside the melting crown C1i by reducing its span.

[0106] Indeed, it is known that the corrosion and temperature variations are the most critical in the melting zone.

[0107] Preferably also, the two melting tanks furnace is defined by W1ii?1.5*W3ii, or even W1ii?1.8*W3ii. More preferably, the two melting tanks furnace is defined by W1ii?2*W3i.

[0108] In the two melting tanks furnace according to the invention, the two melting tanks T1i, T1ii are preferably connected to the fining tank by the necks Ni, Nii located in the width W2 of said fining tank (as illustrated in FIG. 5). Alternatively, in the two melting tanks furnace of the invention, one melting tank is connected to the fining tank by a neck located in the width W2 of the fining tank and the other melting tank is connected to the fining tank by a neck located in the length of the fining tank (right or left side) and close to upstream of the fining tank (i.e. in the first third of its length). This last configuration may be advantageous, for example, when the space existing in the plant housing the furnace is not sufficient to place two melting tanks side by side.

[0109] In the two melting tanks furnace according to the invention, in the case where the two melting tanks T1i, T1ii are connected to the fining tank by the necks Ni, Nii located in the width W2 of said fining tank, the distance D between the two melting tanks T1i and T1ii is preferably at least 1 m, and more preferably, at least 2 m, or better at least 3 m. This is advantageous as it allows access to the zone for maintenance operations and tank wall overcoating.

[0110] In an alternative embodiment of the invention, the furnace for melting vitrifiable materials is in a configuration 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 additionally comprises: [0111] a melting tank T1iii covered by a melting crown C1iii provided with electrical heating means located at the bottom of said tanks; [0112] a neck Niii covered by a crown C3iii and separating said melting tank T1iii and the fining tank T2; [0113] at least one inlet mean Liii located at the melting tank T1iii, for charging it with vitrifiable materials to be heated;
the furnace being further defined by the following

[00004]$0.1*W2?W3\mathrm{iii}?0.6*W2;W1\mathrm{iii}?1.4*W3\mathrm{iii};$ [0114] W1iii being the width of tank T1iii; [0115] W3iii being the width of neck Niii.

[0116] In this three melting tanks configuration, the furnace for melting vitrifiable materials therefore comprises: [0117] (i) three melting tanks T1i, T1ii, T1iii; each covered by a melting crown C1i, C1ii, C1iii respectively and provided with electrical heating means located at the bottom of said tanks; [0118] (ii) a fining tank T2 covered by a fining crown C2 and provided with combustion heating means; [0119] (iii) a neck Ni covered by a crown C3i and separating said melting tank T1i and the fining tank T2; [0120] (iv) a neck Nii covered by a crown C3ii and separating said melting tank T1ii and the fining tank T2; [0121] (v) a neck Niii covered by a crown C3iii and separating said melting tank T1iii and the fining tank T2; [0122] (vi) at least one inlet mean Li located at the melting tank T1i, for charging it with vitrifiable materials to be heated; [0123] (vii) at least one inlet mean Lii located at the melting tank T1ii, for charging it with vitrifiable materials to be heated; [0124] (viii) at least one inlet mean Liii located at the melting tank T1iii, for charging it with vitrifiable materials to be heated; [0125] (ix) at least one outlet mean Oi located downstream of fining tank for the melted glass to flow to a working zone; [0126] the furnace being defined by the following

[00005]$0.1*W2?W3i?0.6*W2;0.1*W2?W3\mathrm{ii}?0.6*W2;0.1*W2?W3\mathrm{iii}?0.6*W2;W1i?1.4*W3i;W1\mathrm{ii}?1.4*W3\mathrm{ii};W1\mathrm{iii}?1.4*W3\mathrm{iii};$ [0127] W1i being the width of tank T1i; [0128] W1ii being the width of tank T1ii; [0129] W1iii being the width of tank T1iii; [0130] W2 being the width of tank T2; [0131] W3i being the width of neck Ni; [0132] W3ii being the width of neck Nii; [0133] W3iii being the width of neck Niii.

[0134] This embodiment is particularly advantageous compared to the configuration with one melting tank in the same way as for the two melting tanks configuration.

[0135] In this three melting tanks, each neck, each melting tank and each inlet mean may be designed independently of the other necks, melting tanks and inlet means respectively, according to the description above.

[0136] Specific advantageous features described in relation with the furnace with one melting tank and with two melting tanks configurations above i.e. those linked to T1i, T1ii, C1i, C1ii, Li, Lii, are applicable to the three melting tanks configuration, with the same advantages. Hence, for sake of clarity, features described above in relation with T1i, T1ii are applicable to T1iii, features described above in relation with C1i, C1ii are applicable to C1iii, and features described above in relation with Li, Lii are applicable to Liii.

[0137] In particular, the crown C3iii of the neck Niii may preferably have a height H3iii which is equal or lower than the height H2 of the crown C2 of the fining tank T2 (H3iii?H2). Preferably also, the neck Niii may have a height H3iii which is equal or lower than the height H1iii of the crown C1iii of the melting tank T1iii (H3iii?H1iii).

[0138] Preferably, the three melting tanks furnace is defined by 0.2*W2?W3iii?0.6*W2. More preferably, it is defined by 0.3*W2?W3iii?0.5*W2.

[0139] Preferably, the three melting tanks furnace is defined by W1iii<W2. More preferably, it is defined by W1iii<0.8*W2. This allows to reduce further the stress inside the melting crown C1i by reducing its span. Indeed, it is known that the corrosion and temperature variations are the most critical in the melting zone.

[0140] Preferably also, the three melting tanks furnace is defined by W1iii?1.5*W3iii, or even W1iii?1.8*W3iii. More preferably, the three melting tanks furnace is defined by W1iii?2*W3ii.

[0141] In the three melting tanks furnace according to the invention, the three melting tanks T1i, T1ii, T1iii may be connected to the fining tank by the necks Ni, Nii, Niii located in the width W2 of said fining tank. Alternatively, in the three melting tanks furnace of the invention, one melting tank may be connected to the fining tank by a neck located in the width W2 of the fining tank and the two other melting tanks may be connected to the fining tank by a neck located in the length of the fining tank and close to upstream of the fining tank (i.e. in the first third of its length), the first one being on the right side and the second one being on the left side of the fining tank. This last configuration may be advantageous, for example, when the space existing in the plant housing the furnace is not sufficient to place three melting tanks side by side and/or when the designed dimensions for the melting tanks and the necks (especially W1i, W1ii, W1iii and W3i, W3ii, W3iii and) cannot be realized in the width W2 of the fining tank.

[0142] In the three melting tanks furnace according to the invention, in the case where at least two melting tanks are connected to the fining tank by necks located in the width W2 of said fining tank, the distance D between the two melting tanks is preferably at least 1 m and more preferably, at least 2 m, or better at least 3 m. Independently, in the three melting tanks furnace according to the invention, in the case where the three melting tanks are connected to the fining tank by necks located in the width W2 of said fining tank, the distance D between the two melting tanks T1i and T1ii is preferably at least 1 m and more preferably, at least 2 m; and the distance D between the two melting tanks T1ii and T1iii T1ii is also preferably at least 1 m and more preferably, at least 2 m.

[0143] In all furnace configurations according to the invention, namely one melting tank, two melting tanks and three melting tanks configurations, to facilitate distribution of the vitrifiable materials to charge, more than one inlet mean may be provided for each melting tank, i.e. two inlet means by melting tank.

[0144] In all furnace configurations according to the invention, preferably, the total surface area of the melting tank(s) ranges from 25 to 400 m.sup.2. Preferably also, according to the invention, the surface area of the fining tank ranges from 25 to 400 m.sup.2.

[0145] The person skilled in the art realizes that the present invention is by no means 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 invention relates to all possible combinations of features, and preferred features, described herein and recited in the claims.

[0146] The following examples are provided for illustrative purposes, and are not intended to limit the scope of this invention.

Examples

[0147] Examples of furnaces according to the invention and a comparative example of a conventional combustion furnace (optionally electro-boosted) were computed.

[0148] The optimization and design of melting furnaces is difficult, risky and very slow without mathematical modelling. Indeed, furnaces are very expensive and their lifetime is more than 15 years, even up to 20 years. There are then only few occasions to perform study and design modifications, and there is a high pressure to reduce the risk related to these modifications. Therefore, mathematic modelling of the melting process in operated glass furnaces has been developed thoroughly in the glass art and is well known amongst glass manufacturers. Use of mathematical models provides detailed temperature and velocity fields of the glass melt in the tank(s), and of the gases in the combustion/fining space(s). The results of these existing mathematical modelling have been validated on many operating furnaces, by comparison with measurements (thermocouples and infrared cameras).

[0149] The following furnaces with same glass pull were considered for the present computations: [0150] Furnace 1 (comparative): conventional combustion glass melting furnace: one tank including melting and refining zones, equipped with burners fed with air-gas and with electrodes for optional electro-boosting. [0151] Furnace 2: furnace according to the invention, in a one melting tank configuration, equipped with: [0152] a melting tank T1i with a tank width W1i=13.0 m, and an average crown height H1i=1.35 m [0153] an inlet mean Li located upstream of the melting tank, [0154] electrodes in the melting tank reaching a total installed power equal to 16.0 MW [0155] a neck Ni with a width W3i=4.5 m=0.35 W1i, and an average crown height H3i=0.35 m [0156] a fining tank T2, with a tank width W2=13.0 m, and an average crown height H2=3.5 m [0157] oxy-burners fed with pure oxygen and natural gas in the fining tank, with a total installed power equal to 16.0 MW; [0158] an outlet mean O [0159] an extraction mean to extract flue gas located in the upstream part of the melting tank, close to the inlet where vitrifiable materials are charged; [0160] Furnace 3: furnace according to the invention, in a two melting tanks configuration. In this considered computation, both melting tanks have identical dimensions and are placed symmetrically (see FIG. 3). The distance between both melting tanks is equal to 4.8 m. Furnace 3 is equipped with: [0161] a melting tank T1i with a tank width W1i=8.4 m, and an average crown height H1i=0.95 m [0162] a melting tank T1ii with W1ii=W1i and H1ii=H1i [0163] an inlet mean Li located upstream of the melting tank T1i, [0164] an inlet mean Lii located upstream of the melting tank T1i, [0165] electrodes in the melting tanks with an installed power equally shared between both tanks, [0166] a neck Ni with a width W3i=3.6 m, and an average crown height H3i=0.54 m, [0167] a neck Nii with a width W3ii=W3i and H3ii=H3i, [0168] a fining tank T2 with tank dimensions equal to those of the Furnace 2, [0169] burners fed with air-gas in the fining tank with identical features as those of the Furnace 2, [0170] an outlet mean O, [0171] an extraction mean to extract flue gas from melting tank.

[0172] Energy consumption (gas/electricity), bottom temperatures, crown temperatures and glass circulation were evaluated for these furnaces 1-3.

Energy Consumption

[0173] Table 1 shows computed values for gas consumption, electricity consumption and total energy consumption, as well as the electrical input fraction for furnaces 1-3.

[0174] For the conventional furnace 1, two situations were considered: the situation of full combustion (100% gas energy) and the situation with a maximum viable electro-boosting of this furnace (beyond this maximum, bottom and crown temperatures would lead to high refractory corrosion and serious furnace damage).

TABLE-US-00001 TABLE 1 Gas Electricity Total Electrical consumption consumption consumption input (in MW) (in MW) (in MW) fraction Furnace 1 47 0 47 0 (comparative) Furnace 1 with 37 5 43 12% viable maximum electro-boosting, 5 MW (comparative) Furnace 2 15 15 30 50% Furnace 3 15 16 31 52%

[0175] Table 1 shows very well that, compared to a classical electro-boosted combustion melting furnace, furnaces according to the invention allow to decrease total energy consumption (by ?30%) while increasing the electrical input fraction (reaching values up to 50%) and thereby decreasing significantly CO.sub.2 emissions.

Bottom Temperatures

[0176] FIG. 6 shows the evolution of bottom refractory temperatures according to the distance (in meters) starting from the inlet mean to outlet mean in furnace 1 with a non-realistic 16 MW electric power (by considering equivalent electric powers, fair comparison with furnaces of the invention may be achieved), furnace 2 and furnace 3. The y axis gives the value (T.sub.bottom?T.sub.ref) in degree celsius, T.sub.bottom being the temperature at the bottom of electro-boosted furnace 1, furnace 2 and furnace 3, and T.sub.ref being the maximum temperature at the bottom for furnace 1 without electro-boosting (full fuel conventional furnace). Furnaces 1-3 according to the invention are schematized at the top of the figure in order to locate the concerned zone in each configuration and to allow comparison.

[0177] This figure illustrates that there exists a significant bottom temperatures increase when increasing electrical power input in conventional furnace while the furnaces of the invention, for a same electrical input, allow to stay at lower value, which is advantageous for avoiding corrosion and thereby increasing furnace lifetime.

Crown Temperatures

[0178] FIG. 7 shows the evolution of crown refractory temperatures according to the distance (in meters) starting from the inlet mean to outlet mean in furnace 1 with 16 MW electro-boosting (comparative), furnace 2 and furnace 3. The y axis gives the value (T.sub.bottom?T.sub.ref) in degree celsius, T.sub.bottom being the temperature at the crown of electro-boosted furnace 1, furnace 2 and furnace 3, and T.sub.ref being the maximum temperature at the crown of furnace 1 without electro-boosting (full fuel conventional furnace). Conventional electro-boosted furnace 1 and furnaces 2-3 according to the invention are schematized at the top of the figure in order to locate the concerned zone in each configuration and to allow comparison.

[0179] This figure illustrates that conventional furnace 1 and furnaces 2-3 according to the invention show crown temperatures decrease in the melting zone compared to conventional furnace without electro-boosting (ref). In the electro-boosted furnace, this is a huge drawbacks, as this leads to serious corrosion phenomenon at the crown (due to condensation of NaOH coming mainly from fining). In furnaces according to the invention, this crown temperature decrease is more easily manageable as (i) if flue gas is extracted from the fining tank, atmospheres from fining zone and melting zone are separated by at least one neck, thereby giving the possibility to limit or avoid reflux of corrosive fumes (NaOH) from the fining tank to the melting tank(s) and (ii) if flue gas is extracted from the melting tank(s), as the crown span can be limited (in particular in the case of multiple melting tanks), it makes the use of alumina refractories a practicable option (knowing alumina is more resistant to corrosion but not recommended in the case of a large crown span).

Glass Circulation

[0180] FIG. 8 shows the evolution of the molten glass circulation according to the distance (in meters) starting from the inlet mean to outlet mean in furnace 1 with 16 MW electro-boosting (comparative), furnace 2 and furnace 3. The y axis gives the value (m.sub.backward/m.sub.pull), m.sub.backward being the backward mass flow and m.sub.pull being the pull mass flow. Conventional electro-boosted furnace 1 and furnaces 2-3 according to the invention are schematized at the top of the figure in order to locate the concerned zone in each configuration and to allow comparison.

[0181] This figure illustrates that the furnaces 2-3 according to the invention generate a significant decrease of the global molten glass circulation in the melting and fining zones that advantageously reduces the molten glass velocity, and thereby decreasing bottom refractory corrosion.