METHOD OF MELTING RAW MATERIALS SUCH AS GLASS BY A CROSS-FIRED MELTING FURNACE

Abstract

A cross-fired melting furnace and a method of melting raw materials by a cross-fired melting furnace are provided, where the furnace includes a melting tank, a melting chamber, N first ports associated N first burners, N second ports, an auxiliary fuel injector for introducing a fraction of fuel required for melting as auxiliary fuel in a direction of a flow of re-circulating combustion products without additional oxidiser, into the re-circulating combustion products in the direction of the flow of the re-circulating combustion products, and with a chosen velocity such that the fraction of fuel mixes with the re-circulating combustion products before being combusted by oxidiser entering the furnace.

Claims

1. A method of melting raw materials by a cross-fired melting furnace which has: a melting tank configured to receive the raw materials to be melted and to accommodate a melted materials bath; a melting chamber located above the melting tank and comprising a first side wall, a second side wall opposite the first side wall, a back wall located at an upstream area of the melting tank, a front wall located at a downstream area of the melting tank, and a roof; multiple first ports provided in the first side wall in horizontally spaced locations between the back wall and the front wall, each of the first ports associated with a corresponding first burner of a series of first burners; multiple second ports provided in the second side wall in horizontally spaced locations between the back wall and the front wall, each of the second ports located opposite a corresponding one of the first ports to define multiple couples of first and second ports; wherein re-circulating combustion products flow in a substantially vertical loop above a flame; the method comprising: introducing a first fraction X1 of fuel into the melting chamber via the first burners; and introducing a second fraction X2 of auxiliary fuel, with X2+X1 being equal to 1, using at least one auxiliary fuel injector, the at least one auxiliary fuel injector arranged in the cross-fired melting furnace in the roof or in the side wall not comprising burners so that the at least one auxiliary fuel injector introduces the second fraction X2 of auxiliary fuel: in a direction of the flow of the re-circulating combustion products; without additional oxidiser; into the re-circulating combustion products, the at least one auxiliary fuel injector located at a point where the second fraction X2 of auxiliary fuel will mix with the re-circulating combustion products before reaching incoming oxidiser; such that velocities of jets introducing the first fraction X1 of fuel and the second fraction X2 of auxiliary fuel are adapted so that a sum of their corresponding jet momenta is between 30% and +30% of a value corresponding to the jet momentum of the fuel when X2 equals zero; and such that energy provided by a quantity of a sum of the first fraction X1 of fuel and the second fraction X2 of auxiliary fuel is adapted to produce a given energy for melting the raw materials without over-fuelling the furnace.

2. The method of claim 1, wherein the at least one auxiliary fuel injector is located in the roof at a same distance from a specified one of the first ports and a specified one of the second ports opposite to the specified first port.

3. The method of claim 1, wherein: each of the second ports is associated with a corresponding second burner of a series of second burners; and the first ports and the second ports are alternately operable as inlet ports and as exhaust ports such that (i) the first ports are operable as inlet ports when the second ports are operable as exhaust ports and (ii) the first ports are operable as exhaust ports when the second ports are operable as inlet ports.

4. The method of claim 3, wherein: the at least one auxiliary fuel injector comprises multiple first auxiliary fuel injectors and multiple second auxiliary fuel injectors; couples of the first and second auxiliary fuel injectors are associated with the couples of oppositely-arranged first and second ports; the first and second auxiliary fuel injectors are located in the roof or in the first and second side walls respectively in a vicinity of the first and second ports of the associated couples of oppositely-arranged first and second ports so that the first and second auxiliary fuel injectors are alternately operable to inject the second fraction X2 of auxiliary fuel; and the first or second auxiliary fuel injectors are operable when the corresponding first or second ports located in the vicinity of the first or second auxiliary fuel injectors are exhaust ports.

5. The method of claim 1, wherein the burners and the at least one auxiliary fuel injector operate with a same fuel.

6. The method of claim 1, wherein the burners and the at least one auxiliary fuel injector operate with different fuels.

7. The method of claim 1, wherein the burners and the at least one auxiliary fuel injector each operate with a fuel selected from the group consisting of: natural gas, LPG, fuel oil, coke-oven gas, blast furnace gas, reforming gas, biofuel, methane, and hydrogen.

8. The method of claim 1, wherein the at least one auxiliary fuel injector is configured to put the injected auxiliary fuel into rotation to create a swirl effect.

9. The method of claim 1, wherein the at least one auxiliary fuel injector is configured to adjust or alter the jet momentum of the injected auxiliary fuel.

10. The method of claim 1, wherein the second fraction X2 of auxiliary fuel represents between 10% and 100% of the sum of the first and second fractions X1 and X2 of fuel.

11. The method of claim 1, further comprising: introducing the second fraction X2 of auxiliary fuel so as to reinforce a mass flow of the re-circulating combustion products.

12. The method of claim 1, further comprising: adjusting or turning off some of the burners so as to reinforce a mass flow of the re-circulating combustion products.

13. The method of claim 1, wherein the velocity of the jet introducing the second fraction X2 of auxiliary fuel is between 10 m/s and 70 m/s.

14. The method of claim 4, wherein: the first auxiliary fuel injectors are located at a quarter of a width of the melting chamber from the side wall that is closest to the first auxiliary injectors; and the second auxiliary fuel injectors are located at a quarter of the width of the melting chamber from the side wall that is closest to the second auxiliary injectors.

15. A cross-fired melting furnace comprising: a melting tank configured to receive raw materials to be melted and to accommodate a melted materials bath; a melting chamber located above the melting tank and comprising a first side wall, a second side wall opposite the first side wall, a back wall located at an upstream area of the melting tank, a front wall located at a downstream area of the melting tank, and a roof; multiple first ports provided in the first side wall in horizontally spaced locations between the back wall and the front wall, each of the first ports associated with a corresponding first burner of a series of first burners, wherein the first burners are configured to introduce a first fraction X1 of fuel into the melting chamber, wherein the furnace is configured such that re-circulating combustion products flow in a substantially vertical loop above a flame; multiple second ports provided in the second side wall in horizontally spaced locations between the back wall and the front wall, each of the second ports located opposite a corresponding one of the first ports to define multiple couples of first and second ports; at least one auxiliary fuel injector arranged in the cross-fired melting furnace in the roof or in the side wall not comprising burners that introduce fuel, the at least one auxiliary fuel injector configured to introduce a second fraction X2 of auxiliary fuel: in a direction of the flow of the re-circulating combustion products; without additional oxidiser; into the re-circulating combustion products, the at least one auxiliary fuel injector located at a point where the second fraction X2 of auxiliary fuel will mix with the re-circulating combustion products before reaching incoming oxidiser; such that velocities of jets introducing the first fraction X1 of fuel and the second fraction X2 of auxiliary fuel are adapted so that a sum of their corresponding jet momenta is between 30% and +30% of a value corresponding to the jet momentum of the fuel when X2 equals zero; and such that energy provided by a quantity of a sum of the first fraction X1 of fuel and the second fraction X2 of auxiliary fuel is adapted to produce a given energy for melting the raw materials without over-fuelling the furnace.

16. The cross-fired melting furnace of claim 15, wherein the at least one auxiliary fuel injector is located in the roof at a same distance from a specified one of the first ports and a specified one of the second ports opposite to the specified first port.

17. The cross-fired melting furnace of claim 15, wherein: each of the second ports is associated with a corresponding second burner of a series of second burners; and the first ports and the second ports are alternately operable as inlet ports and as exhaust ports such that (i) the first ports are operable as inlet ports when the second ports are operable as exhaust ports and (ii) the first ports are operable as exhaust ports when the second ports are operable as inlet ports.

18. The cross-fired melting furnace of claim 17, wherein: the at least one auxiliary fuel injector comprises multiple first auxiliary fuel injectors and multiple second auxiliary fuel injectors; couples of the first and second auxiliary fuel injectors are associated with the couples of oppositely-arranged first and second ports; the first and second auxiliary fuel injectors are located in the roof or in the first and second side walls respectively in a vicinity of the first and second ports of the associated couples of oppositely-arranged first and second ports so that the first and second auxiliary fuel injectors are alternately operable to inject the second fraction X2 of auxiliary fuel; and the first or second auxiliary fuel injectors are operable when the corresponding first or second ports located in the vicinity of the first or second auxiliary fuel injectors are exhaust ports.

19. The cross-fired melting furnace of claim 15, wherein the second fraction X2 of auxiliary fuel represents between 10% and 100% of the sum of the first and second fractions X1 and X2 of fuel.

20. A cross-fired melting furnace comprising: a melting tank configured to receive one or more raw materials; a melting chamber located above the melting tank; multiple first burners configured to introduce a first fraction of fuel into the melting chamber, wherein the furnace is configured such that re-circulating combustion products flow in a substantially vertical loop above a flame; multiple first ports each associated with a corresponding one of the first burners; multiple second ports located in the furnace opposite corresponding ones of the first ports to define multiple couples of first and second ports; and at least one auxiliary fuel injector configured to introduce a second fraction of fuel in a direction of the flow of the re-circulating combustion products in the furnace, wherein the at least one auxiliary fuel injector is configured to introduce the second fraction of fuel: without additional oxidiser; into the re-circulating combustion products before reaching incoming oxidiser; such that velocities of jets introducing the first fraction of fuel and the second fraction of fuel are adapted so that a sum of their corresponding jet momenta is between 30% and +30% of a value corresponding to the jet momentum of the first fraction of fuel when the second fraction equals zero; and such that the first fraction of fuel and the second fraction of fuel provide a given energy for melting the one or more raw materials without over-fuelling the furnace.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0090] FIG. 1 is a longitudinal horizontal sectional view of a cross-fired melting furnace according to the invention;

[0091] FIG. 2 is a perspective view of a cross-fired melting furnace according to the invention, a portion of the furnace casing being removed;

[0092] FIG. 3 is a longitudinal horizontal sectional view which is analogous to FIG. 1, but relates to a variant embodiment of the cross-fired melting furnace of FIG. 2; and

[0093] FIG. 4 is a transversal vertical sectional view along line IV-IV of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0094] The present invention will be described in connection with preferred embodiments which are given by way of examples. In the following examples, glass is the material to be melted by the furnace. However, the invention is also directed to the melting of other types of materials. The features of the different embodiments may be combined unless otherwise stated.

[0095] A typical arrangement of an embodiment of the invention is illustrated in FIG. 2, which schematically shows a melting furnace 10, of the type known as cross-fired melting furnace, for melting glass. The present invention is however not limited to the melting of glass and can be adapted on furnaces for melting other types of raw materials.

[0096] As shown in FIG. 2, the cross-fired melting furnace 10 comprises a melting tank 7 receiving through inlets (not shown), which are located in an upstream area of the melting tank 7, glass to be melted. The melting tank 7 having a bottom 5 accommodates a melted glass bath 110 and outputs the melted glass bath 110 through an outlet 17, which is located in a downstream area of the melting tank 7 in a front wall thereof.

[0097] A melting chamber 8 is located above the melting tank 7 and comprises a first side wall 2, a second side wall 1, a back wall 3 located at the upstream area of the melting tank 7, a front wall 4 located at the downstream area of the melting tank 7, and a roof 6.

[0098] A first set of horizontally aligned N first ports 31 to 36 are provided in the side wall 2 of the melting chamber 8 whereas a second set of horizontally aligned N second ports 41 to 46 are provided in the side wall 1 of the melting chamber 8. The second ports 41 to 46 are transversely aligned with the first ports 31 to 36, thus defining a set of N couples of first and second ports 31, 41, . . . , 36, 46.

[0099] N is an integer which may be preferably comprised between 1 and 8. In the examples shown in the drawings, N=6.

[0100] The first and second ports 31 to 36 and 41 to 46 are associated with first and second burners 11 to 16 and 21 to 26 respectively for injecting a first fuel into the melting chamber 8. The first and second ports 31 to 36 and 41 to 46 are alternately operable as inlet ports for introducing oxidiser (for example air) in the chamber and as exhaust ports for combustion products. The first ports 31 to 36 are inlet ports when the second ports 41 to 46 are exhaust ports and the first ports 31 to 36 are exhaust ports when the second ports 41 to 46 are inlet ports.

[0101] As schematically shown in FIG. 4, a heating burner flame 103, created when the first ports 31 to 36 are operated as inlet ports introducing oxidiser (for example air) and a first fuel is ejected through the first burners 11 to 16, has an elongated shape over the melting bath 110 and produces combustion products 102 which exit the chamber through second ports 41 to 46. A portion of the combustion products re-circulate in a substantially vertical loop of re-circulating combustion products 104 shown on FIG. 4.

[0102] By way of example, the incoming oxidiser exiting port 32 on FIG. 4 may have a quantity of oxygen of 21%, while the combustion products 102 and the re-circulating combustion products have a quantity of oxygen of 2%.

[0103] Similarly during alternate periods of time, the cycle is reversed: the first fuel is injected through burners 21 to 26 instead of burners 11 to 16, the oxidiser enters through the second ports 41 to 46 and the combustion products are finally exhausted through the first ports 31 to 36, the burners 11 to 16 being inactive. Re-circulated combustion products also recirculate in a substantially vertical loop above the flame having a reversed orientation.

[0104] The first and second ports 31 to 36 and 41 to 46 and the associated first and second burners 11 to 16 and 21 to 26 are thus alternately and repeatedly used as burners to mix first fuel with an oxidiser (usually air or oxygen). The changeover between the first and second sets of N first and second ports 31 to 36 and 41 to 46 and correspondingly the first and second sets of N first and second burners 11 to 16 and 21 to 26 occurs cyclically, with a cycle time being e.g. between 10 and 30 minutes, more specifically between 20 and 30 minutes. A first fraction X1 of fuel is injected into the melting chamber 8 via the alternately operated first and second burners 11 to 16 and 21 to 26. On a melting furnace not equipped with auxiliary fuel injectors of the present invention, X1 equals 1.

[0105] Advantageously, first and second regenerative heat exchangers (not shown) are operatively associated with the first and second ports 31 to 36 and 41 to 46. The ambient combustion air is pre-heated in a first regenerative heat exchanger re-heated by hot combustion products of a preceding cycle. The pre-heated oxidiser (air) is then directed towards the first ports 31 to 36 of the first burners 11 to 16. The resulting combustion products are then directed towards a second regenerative heat exchanger (not shown) in order to re-heat it and pre-heat oxidiser to be applied through the second ports 41 to 46 of the second burners 21 to 26 during the next cycle.

[0106] During a cycle in which the first burners are operated to introduce fuel, the first burners introduce a first fraction X1 of fuel into the melting chamber. The jets J1 of the introduction of fuel is represented on FIGS. 1, 3 and 4. A module may control the jet J1.

[0107] According to an embodiment, auxiliary fuel injectors 51 to 56 are arranged in the cross-fired melting furnace 10, in the roof 6, for each couple of oppositely arranged first and second ports 31, 41; . . . ; 36, 46.

[0108] The auxiliary fuel injectors may be arranged along a centre line of a couple of ports.

[0109] The auxiliary fuel injectors 51 to 56 are arranged so that they inject, or introduce, in the combustion chamber 8, a second fraction X2 of auxiliary fuel, with X2+X1 being equal to 1:

[0110] in the direction of the flow of said re-circulating combustion products 104,

[0111] without additional oxidiser,

[0112] into said re-circulating combustion products, the auxiliary fuel injector being located at a point where said second fraction X2 of auxiliary fuel will mix with the recirculating combustion products, before reaching incoming oxidiser introduced by a port,

[0113] the velocities of the jets introducing the fraction X1 of fuel and the fraction X2 of auxiliary fuel being adapted so that the sum of their corresponding jet momenta is comprised between 30% or +30% of a value corresponding to the jet momentum of the fuel when X2 equals zero (and X1 equals 1), and

[0114] the energy provided by the quantity of the sum of the first fraction of fuel X1 and the second fraction of fuel X2 being adapted to produce a given required energy for melting said materials without over-fuelling the furnace.

[0115] The jets J2 of the introduction of auxiliary fuel is represented on FIGS. 1, 3 and 4. As can be seen on FIG. 4, the jet J2 is directed towards the corresponding port introducing oxidiser in the chamber. A module may control the jet J2.

[0116] Among 100% of the first and second fuels (quantity X) injected into the melting chamber 8 through the first and second burners 11 to 16, 21 to 26 and the additional fuel injectors, the fraction X2 of fuel jet emitted by the additional fuel injectors is preferably from 10% to 100% of the sum X.

[0117] The fuel injected through the first and second burners 11 to 16, 21 to 26 and the auxiliary fuel injectors may be selected from the group consisting of natural gas, LPG, fuel oil, coke-oven gas, blast furnace gas, reforming gas, biofuel, methane, and hydrogen.

[0118] The above mentioned recirculation of combustion products extends in a substantially vertical loop above the flame on a length (measured from the side wall being on the firing side) which has to be known so as to find the optimum location for the auxiliary fuel injectors. Also, the parameters of the injection and the fraction X2 of auxiliary fuel have to be determined in a manner such that the recirculation of combustion products is maintained. The size and strength of the recirculation can be calculated for example using the following equations derived by Thring (mentioned above), Craya (Craya A and Curtet R, On the spreading of a confined jet, Comptes-rendus de l'Academie des Sciences, Paris, 241, 1955) and others:

[00001]$\begin{array}{cc}x=4,5h& \left(1\right)\\ \frac{\mathrm{qr}}{Q}=0,43.Math.\left(\sqrt{m}-1,65\right)& \left(2\right)\\ m=\frac{G.Math..Math.0}{\mathrm{Ginf}}+\frac{\mathrm{Ga}}{2.Math.\mathrm{Ginf}}-0,5& \left(3\right)\end{array}$

in which:
x is the distance from the side wall (firing side) to the point where there is no longer recirculation in the furnace,
h is the hydraulic height of the space between the glass surface, the furnace front and back walls and the furnace roof,
qr is the mass of combustion products recirculating per unit time and per port,
Q is the total mass of fuel and oxidiser entering the furnace per unit time and per port,
G0 is the momentum of the incoming fuel jet(s) (mass flow rate multiplied by velocity), per port,
Ga is the momentum of the incoming oxidiser (mass flow rate multiplied by velocity), per port,
Ginf is the momentum of the outgoing hot exhaust gases (their mass flow rate multiplied by their mean velocity when they fill the furnace chamber), per port, and
m is a dimensionless number (Craya Curtet number) that relates to the relative jet momenta of the incoming fuel and oxidiser flows, and the outgoing combustion products.

[0119] The height of the furnace is generally determined to be sufficient to allow significant recirculation of combustion products. As far as the mass flow rate of recirculating combustion products is concerned, typical values for natural gas as fuel and for air as oxidiser together with typical air and gas velocities, when applied to equation (2), suggest that the mass of exhaust gases recirculating in a substantially vertical loop below the roof and above the flame is approximately equal to the incoming mass flow of fuel and oxidiser. This confirms that there is sufficient recirculation to carry up to 100% of the fuel flow entering the furnace (about 1/20th of the total mass flow entering the furnace) without affecting the furnace flow pattern and furnace operation.

[0120] However, as fuel is removed from the burners to supply the Auxiliary fuel injectors (for example because the second fraction X2 is introduced, the first fraction X1 has to be reduced), equation (2) indicates that the recirculation rate will eventually fall to values that are too low to carry the auxiliary fuel and maintain the furnace flow patterns, if the injectors are not in the above defined direction and if they do not inject with the above mentioned velocity.

[0121] According to a first embodiment which is illustrated in FIGS. 1 and 2 and also in dotted lines in FIG. 4, an auxiliary fuel injectors 51 to 56 associated with a couple of oppositely arranged first and second ports 31, 41; . . . ; 36, 46 comprises a single fuel injector located in the roof 6 substantially at the same distance from the first and second ports of the associated couple of oppositely arranged first and second ports 31, 41; . . . ; 36, 46.

[0122] The auxiliary fuel injectors 51 to 56 may comprise a swirl chamber to spread the fuel in the re-circulation loop of combustion products.

[0123] For improved effectiveness, for example in multi-port cross-fired furnaces and hence to improve the stability of the re-circulating flows, the auxiliary fuel injectors may direct a higher momentum jet of auxiliary fuel in the direction of the recirculated combustion products 104 to maintain and enhance their recirculation and mass flow. This will also allow the use of auxiliary injectors in cross-fired melting furnaces suffering from exhaust port blockages as the years of operation accumulate.

[0124] According to a second embodiment which is illustrated in FIG. 3, and also in 4 (in solid lines), the auxiliary fuel injectors comprise first and second fuel injectors 61, 71; . . . ; 66, 76 which are associated with each couple of oppositely arranged first and second ports 31, 41; . . . ; 33, 43. The first and second auxiliary fuel injectors 61, 71; . . . ; 66, 76 are located in the roof 6.

[0125] The first and second auxiliary fuel injectors 61, 71; . . . ; 66, 76 are alternately operable to inject the second fraction X2 of auxiliary fuel in the direction of the flow of said re-circulating combustion products 104 and without additional oxidiser. Because the direction of the flow of the re-circulating combustion products will reverse when the firing direction reverses, the first and second auxiliary fuel injectors 61, 71; . . . ; 66, 76 are operable when the corresponding first or second ports (31, 41; . . . ; 36, 46) located in the vicinity of said first or second auxiliary fuel injectors (61, 71; . . . ; 66, 76) are exhaust ports.

[0126] It should be noted that in the various embodiments, the velocity of the jet for introducing the second fraction X2 of auxiliary fuel may be comprised between 10 and 70 m/s.

[0127] According to a variant embodiment, the auxiliary fuel injectors 51 to 56 or 61 to 66 and 71 to 76 each include a device putting into rotation the injected auxiliary fuel to create a swirl effect. This may increase the mixing of fuel with the re-circulating combustion products in the melting chamber 8.

[0128] According to another variant embodiment, the auxiliary fuel injectors 51 to 56 or 61 to 66 and 71 to 76 each include a device to adjust or alter the jet momentum or jet impulse or jet velocity of the injected auxiliary fuel.

[0129] In alternative embodiments (not shown), the auxiliary injectors may be located in the side walls. In such embodiments, the auxiliary injectors may only be used while the corresponding port on the opposite side wall introduces oxidiser.

[0130] Embodiments of the present invention may also relate to a method of melting raw materials by a cross-fired melting furnace 10 which has:

a melting tank 7 for receiving raw materials to be melted and for accommodating a melted materials bath;
a melting chamber 8 located above said melting tank and comprising a first side wall, a second side wall opposite said first side wall, a back wall located at an upstream area of said melting tank, a front wall located at a downstream area of said melting tank, and a roof;
N first ports 31, . . . , 36 being provided in the first side wall in horizontally spaced locations between said back wall and front wall, each of said at least one series of N first ports 31, . . . 36 being associated with a corresponding first burner of a series of N first burners 11, . . . , 16;
N second ports 41, . . . 46 being located in the second side wall in horizontally spaced locations between said back wall and front wall, each of said N second ports being located opposite a first port to define N couples of first and second ports 31, 41, . . . , 36, 46;
wherein re-circulating combustion products flow in a substantially vertical loop above a flame the method comprising:
introducing a first fraction X1 of fuel into said melting chamber via said first burners,
introducing a second fraction X2 of auxiliary fuel, with X2+X1 being equal to 1, using at least one auxiliary fuel injector 51, the at least one auxiliary fuel injector being arranged in the cross-fired melting furnace in said roof or in the side wall not comprising burners introducing fuel so that the at least one auxiliary fuel injector introduces the second fraction X2 of auxiliary fuel,

[0131] in the direction of the flow of said re-circulating combustion products 104,

[0132] without additional oxidiser,

[0133] into said re-circulating combustion products, the auxiliary fuel injector being located at a point where said second fraction X2 of auxiliary fuel will mix with the recirculating combustion products, before reaching incoming oxidiser introduced by a port,

[0134] the velocities of the jets introducing the fraction X1 of fuel and the fraction X2 of auxiliary fuel being adapted so that the sum of their corresponding jet momenta is comprised between 30% or +30% of a value corresponding to the jet momentum of the fuel when X2 equals zero (and X1 equals 1), and

the energy provided by the quantity of the sum of the first fraction of fuel X1 and the second fraction of fuel X2 being adapted to produce a given required energy for melting said materials without over-fuelling the furnace.

[0135] Generally speaking, the invention provides a simplification in the manufacturing process, increases performance and reduces cost.

[0136] Although preferred embodiments have been shown and described, it should be understood that any changes and modifications may be made therein without departing from the scope of the invention as defined in the appended claims. Thus the features of the different embodiments may be combined.