WO2011151735A1

WO2011151735A1 - Burner and kiln comprising said burner

Info

Publication number: WO2011151735A1
Application number: PCT/IB2011/050849
Authority: WO
Inventors: Marco Braglia
Original assignee: F.I.R.E. S.R.L.
Priority date: 2010-06-04
Filing date: 2011-02-28
Publication date: 2011-12-08
Also published as: ITPR20100051A1; IT1400302B1

Abstract

A burner for a glass kiln comprising a supply conduit (2) for a liquid or gaseous fuel which defines a slot (21) downstream whereof a flame is generated; said slot (21) extending over a first fictitious surface for a first length (23) following a preponderant line (22) of extension. The ratio between the first length (23) and a first width of said slot (21) is greater than 60, said first width being equal to the ratio between the area of said slot (21) measured on the basis of said first surface and the value of said first length (23).

Description

BURNER AND KILN COMPRISING SAID BURNER

DESCRIPTION

The present invention relates to a burner for a glass kiln and a glass kiln comprising said burner.

Glass kilns are used to heat glass at a high temperature and are designed to withstand temperature peaks above 1500 °C-2500 °C . This enables the glass to undergo a series of internal physical and chemical transformations .

Glass kilns are known in which a mass of refractory material defines a treatment chamber, in the lower portion of which there is placed a glass mass which is heated at a high temperature.

Such kilns comprise a plurality of burners, each comprising one or more circular outlet sections. Said burners are in fluid communication with the treatment chamber via a passage formed on a refractory portion. The system for supplying combustion air comprises a plurality of slots that lead into said treatment chamber in proximity to said burners.

Being designed to reach the above-mentioned temperatures, glass kilns imply a considerable consumption of energy. The transfer of energy to the glass mass largely takes place by radiation and it is important that the flame generated by the burners have a temperature which is as uniform as possible. In fact, at every temperature electromagnetic radiation is radiated which has a corresponding wavelength. Glass, also based on its composition, is particularly sensitive to a predetermined interval of temperatures and it is thus important that it be radiated with a flame that generates a spectrum within the interval concerned. In this manner, despite limiting the maximum temperature reached by the flame (with a consequent lower consumption of fuel and reduction in the production of NOx) , it is possible to improve the energy transferred to the glass. A further drawback of glass kilns is the inevitable generation of harmful products which accompanies combustion.

In this context, the technical task at the basis of the present invention is to propose a burner enabling the energy transferred to the glass to be optimised.

In particular, it is an object of the present invention to provide a burner for a glass kiln that is capable of generating a flame having as uniform a temperature as possible .

A further object of the present invention is to reduce the generation of NOx during combustion.

Yet a further object of the present invention is to propose a glass kiln comprising said burner.

The defined technical task and the specified objects hereof are substantially achieved by a burner for a glass kiln and a kiln comprising said burner, comprising the technical characteristics described in one or more of the appended claims.

Further characteristics and advantages of the present invention will become more apparent from the following approximate, and hence non-limiting, description of a preferred, but not exclusive, embodiment of a burner for a glass kiln, as illustrated in the appended drawings , in which:

figure 1 shows a perspective view of a burner according to the present invention;

- figure 2 shows a burner according to the present invention from different points of view;

figure 2a shows an enlarged view of a detail of figure 2;

- figures 3 and 4 show two cross sections respectively along the lines D-D and E-E of figure 2;

figure 5 shows a perspective view of a device illustrati .ng the burner according to the present invention in combination with other elements to which it is connected;

- figures 6 and 7 show two orthogonal views of the device of figure 5;

- figures 8 and 9 show two cross sections along the lines B-B and C-C of figures 6 and 7;

- figures 10 and 11 show two views of a glass kiln according to the present invention;

figures 12 and 13 respectively indicate the distribution of temperature in a horizontal plane at the level of the burners in a known kiln and in the same kiln using the burners according to the present invention (the surrounding conditions being equal) .

figures 14 and 15 respectively indicate the distribution of the radiation incident upon the surface of the glass in a known kiln and in the same kiln using the burners according to the present invention (the surrounding conditions being equal) .

The subject matter of the present invention is a burner for a glass kiln. Glass kilns are high-temperature ovens. They must withstand temperatures higher than at least 1500°C (the temperature of the flame can even exceed 2000°C or more in certain points).

The burner comprises a supply conduit 2 for a fuel. The supply conduit 2 in turn defines a slot 21 downstream of which a flame is generated. Said fuel is liquid or preferably gaseous (typically natural gas). Advantageously, the supply conduit 2 comprises a nozzle 8 supplementing said slot 21 (see for example figure 8). Conveniently, the nozzle 8 is removably connectable to remaining parts of the fuel supply conduit 2 so as to facilitate interchangeability with nozzles 8 having slots 21 of different dimensions. Advantageously, the nozzle 8 removably connected to the remaining parts of the conduit 2 by threaded connection means. Advantageously, the nozzle 8 is at one end of said fuel supply conduit 2 (and in particular of the burner 1) . Conveniently, but not necessarily, the nozzle 8 along a fuel flow line 250 has firstly a section in which two opposite surfaces 265 thereof (which contribute to defining a passage section for the fuel) converge and then diverge until leading into said slot 21. Said slot 21 is situated at one end of the nozzle 8.

The removable nozzle 8 could also not be present and in such a case the slot 21 can be indicated by way of example as in figures 2, 2a, 3, 4.

The slot 21 is elongated and extends over a first fictitious surface for a first length 23 following a preponderant line 22 of extension. Said first length 23 is measured along the line 22 of extension between two ends between which said slot 21 extends. Preferably, said line 22 of extension is a straight line. Conveniently, the first surface is flat. The first surface is substantially orthogonal to the direction of flow of the fuel at said slot 21. In particular, said first surface is substantially orthogonal to the tangent, measured at said slot 21, to the ideal fuel flow line 250.

The ratio between the first length 23 and a first width of said slot 21 is greater than 60 (the unit of measurement of the first length 23 and of the first width of said slot 21 is the same) . The first width is equal to the ratio between the area of said slot 21 measured on the basis of said first surface and said first length 23 (the unit of measurement of the area of said slot 21 is equal to the square of the unit of measurement of said first length 23 or of said first width) . The first length 23 thus provides an indication of the average width of the slot 21 along the preponderant line 22 of extension.

The Applicant has verified that, in order to obtain a greater reduction in NOx and render the temperature of the generated flame uniform, advantageously the ratio between the first length 23 and the first width of said slot 21 should be greater than 65 or 70, preferably greater than 80.

Normally the fuel comes out of said slot at high speeds (usually greater than at least 80 km/h) . In the preferred solution, the slot 21 has a width 24 which varies along the preponderant line 22 of extension, said width 24 being measured orthogonally to the preponderant line 22 of extension. This serves to modify the load losses in such a way as to ensure an even distribution in the flow rate of fuel. Advantageously, the width 24 of said slot 21 is narrower in a first central section 27 than in a second and in a third section 28, 29, between which said first central section 27 is interposed to facilitate a uniform distribution of the flow rate of fuel along the slot 21. The supply conduit 2 comprises a connector 25. Conveniently, the connector 25 connects said slot 22 and a section of said conduit 2 having a circular or approximately circular cross section. The connector 25 in turn comprises a first and second opposite walls 261, 262 which define a divergence 26. Advantageously, said nozzle 8 is situated at the end of the divergence 26. The slot 21 is situated in proximity to the end of the divergence 26. Advantageously, said slot 21 is symmetrical in relation to at « least two mutually orthogonal planes. A plane parallel to the first plane and passing through said connector 25 identifies a cross section extending along a line of extension parallel to that of the slot 21. Said slot 21 faces a body (situated downstream, along the fuel flow line 250) against which it simply rests. It may thus be understood that said slot 21 is situated at one end of the burner 1. The fact that the width 24 of the slot 21 is narrower in said first central section 27 of the slot 21 is particularly convenient in the case where said divergence 26 is upstream of the slot 21 and in proximity thereto (relative to the direction of flow of the fuel) . In this manner, in fact, the narrower thickness in said first central section 27 serves to increase the load losses in said first central section 27, thus favouring a shift in the flow rate of the fuel onto the second and third sections 28, 29. Otherwise, the flow rate of fuel would tend to be concentrated in the first section 27 and not follow with precision the broadening imposed by the divergence 26. In the preferred solution said slot 21 (along the preponderant line 22 of extension) is defined by making a plurality of sections adjacent, on the inside of each of which the width 24 is constant.

Advantageously, the width 24 in said first section 27 is equal to about three millimetres, whereas at the two ends of the slot 21 the width 24 is equal to about 4 millimetres. Preferably, said first length 23 is comprised between 260 and 300 millimetres. Advantageously the nozzle 8 is made of stainless steel, preferably AISI 310. Conveniently, the burner 1 does not have a combustion agent supply conduit incorporated inside it, nor is it intended to be immediately adjacent thereto.

Conveniently, the burner 1 comprises baffle means 3 which can be adjusted so as to render uniform the distribution of fuel along the preponderant line 22 of extension of said slot 21. The action of the baffle means 3, possibly in addition to the variation in the width 24 of the slot 21 along the preponderant line 22 of extension, permits a distribution of the flow of fuel along the slot 21 which is as uniform as possible. The baffle means 3 are situated inside the fuel supply conduit 2 upstream of said slot 21. The connector 25 comprises a third and a fourth opposing walls 263, 264 which define a convergence 260. The first and second walls 261, 262 are interposed (and normally adjacent) between the third and fourth walls 263, 264. The adjustable baffle means 3 comprise a shutter 30 which is movable between a first and a second position. In the second position the shutter 30 is closer than in the first position to the third and fourth walls 263, 264 in order to divert the flow toward the first and second walls 261, 262 and facilitate a uniform distribution of fuel along the preponderant line 22 of extension of the slot 21. By way of example, but not necessarily, in the second position the shutter 30 is in contact with the third and fourth walls 263, 264. In the preferred solution, the shutter 30 never obstructs the entire fuel supply conduit 2.

The shutter 30 advantageously has an aerodynamic shape. In particular, the shutter 30 has a drop-like shape in order to offer low resistance to the advancing of the fuel. Upstream (relative to the direction of flow of the fuel) of said connector 25, the supply conduit 2 has a portion having a section orthogonal to the advancing direction of the fuel and whose outer dimension is substantially constant. Conveniently, in the first position the shutter 30 is situated at least in part in said portion having a substantially constant outer dimension and the fuel flows around the drop on all sides; in the second position the shutter 30 is situated at least in part in said connector 25 and diverts the flow rate of fuel principally along the divergent walls 261, 262 of the connector 25. Advantageously, said shutter 30 is connected to a rod 31 which protrudes outside the fuel supply conduit 2 and can be manually operated. Advantageously, the fuel supply conduit 2 has a bend 80 linking two sections of the conduit 2 which extend along two incident lines. Advantageously, said rod 31 extends along one of said two incident lines. Advantageously, said rod 31 extending along one of said two incident lines protrudes outside the supply conduit 2 in proximity to said bend 80.

The subject matter of the present invention is also a glass kiln 10 comprising:

-a burner 1 having one or more of the previously described technical characteristics;

-a material treatment chamber 4 designed to withstand temperatures higher than at least 1500 °C, preferably higher than at least 2500°C. In the preferred solution said chamber 4 is a glass treatment chamber 4. The burner 1 is in thermal and fluid communication with said glass treatment chamber 4.

The kiln 10 comprises a body 51 made of refractory material which contributes to defining said chamber 4 and comprises a passage 510 which allows fluid communication between said burner 1 and said treatment chamber 4. Orthogonally to the direction of flow of the fuel (or of propagation of the flame) such passage has an elongated outlet slit 210. The passage 510 has a flared shaped in order to connect said slit 210 with said slot 21. The kiln 1 further comprises a cooling plate 50 interposed between said body 51 of refractory material and said burner 1. The cooling plate 50 has a hole serving to place the passage 510 in fluid communication with the slot 21. Given the high temperatures involved, advantageously the plate 50 is made of cast iron. It is also provided with fins to facilitate the cooling thereof. Conveniently, the plate 50 is removably connected with the body 51, preferably by threaded means. The nozzle 8 conveniently rests upon the cooling plate 50. Normally the flame can develop inside said passage 510 or directly in the treatment chamber 4 (mainly depending on the speed at which the fuel comes out of the nozzle 8) . In the case of very low speeds the flame might at worst develop at said nozzle 8. In fact, the combustion air present in the chamber 4 is at very high temperatures and as soon as it comes into contact with the fuel coming out of the nozzle 8 it will cause the fuel to self-ignite.

The kiln 10 further comprises at least an intake conduit 6 for the combustion air. Advantageously, the ratio between the volume flow rate of the fuel (typically natural gas) and combustion air is equal to 1/10. The intake conduit 6 leads into said treatment chamber 4 at a distance from said passage 510 (which allows fluid communication between said burner 1 and said treatment chamber 4). Advantageously, along said intake conduit 6 the combustion air is heated before being introduced into the chamber 4. For example, it could flow over tube exchangers in which a hot fluid has previously been made to circulate (typically said hot fluid consists of the fumes generated by the combustion that takes place in the treatment chamber 4) .

Advantageously the kiln 10 comprises at least one outlet conduit 7 for the fumes generated by combustion. These fumes are at a high temperature and may consequently heat means (a heat exchange device) endowed with high thermal inertia. Accordingly, the kiln 10 can comprise means (not illustrated) for varying the flow path of the combustion air and of the fumes generated by combustion. In particular, said varying means permit the fumes produced by combustion to exit through one or more conduits which in a previous configuration of the kiln 1 were used to supply combustion air into the chamber 4, while permitting the combustion air to be introduced into the chamber 4 through one or more conduits which in said previous configuration were used for the outlet of the combustion fumes. In this manner, the heat provided by the combustion fumes . along said at least one fume outlet conduit 7 causes heating of a thermal inertia that in a subsequent configuration is used for preheating the combustion air flowing through the same conduit in the opposite direction. The above-mentioned varying means comprise a system of valves and ducts that serve to modify the flow path of the fumes and of the combustion air.

The intake conduit 6 and said passage 510 (defined by said body 51 of refractory material) are on a same wall 40 of the burner 1 and are along the same vertical line (see figure 10). In particular, the combustion agent intake conduit 6 is above said burner 1.

In virtue of the action of the above-mentioned varying means, there are present additional burners 1 by said at least one outlet conduit 7. Consequently, when said at least one outlet conduit 7 becomes (as a result of the action of the varying means) an intake conduit, the burners situated by the latter conduits (which otherwise are not active) are activated.

Advantageously, said kiln 10 comprises a plurality of burners 1. Each of said burners 1 leads into said treatment chamber 4 through a corresponding passage 510 formed in a corresponding body 51 of refractory material which defines said chamber 4. Advantageously, said burners 1 are placed side by side horizontally. Similarly, the corresponding passages 510 corresponding to the various burners 1 are placed side by side horizontally .

Advantageously, the kiln 10 comprises a first and a second slab of refractory material placed one on top of the other; between the first and the second slab the kiln 10 includes a strip in which there are positioned the bodies 51 of refractory material which contribute to defining said chamber 4, each comprising a passage 510 that permits fluid communication between a corresponding burner 1 and said treatment chamber 4. Additional refractory infill material is advantageously interposed between said bodies 51. These bodies 51 can be replaced simply by distancing the first and second slabs from each other, removing the body 51 and setting a new body 51 into place.

The invention achieves important advantages.

First of all it permits a more uniform, less uneven flame temperature, thus facilitating the radiative heat transfer to the glass mass. In particular, by carrying out simulations with computational fluid dynamics software the Applicant verified that by simply replacing the circular nozzle burners of the prior art with the burners of the present invention it was possible to obtain an increase of about 0.2% in the radiative heat transfer to the glass mass, notwithstanding a reduction of about 1% in the maximum flame temperature. If it is considered that the percentage values are calculated for very large numerical values, the considerable advantage provided by the present invention can be better appreciated. The solution described is particularly optimised to generate a flame that emits waves at the average infrared wavelengths to which glass is particularly sensitive.

In particular, in figure 12 the reference number 101 indicates a zone in which the temperature is higher than 1750°C, while the reference number 102 indicates a zone in which the temperature is higher than 1850° and in which peaks above 2000°C are reached. In figure 13 the reference number 103 indicates a zone in which the maximum temperature is detected (higher than 1750°C), but in that zone there are no peaks above 2000 °C.

In figures 14 (kiln using prior art burners) and 15 (kiln according to the present invention) the reference numbers 104, 105, 106 indicate zones in which the radiation on the glass is respectively greater than 3340000, 2980000, 2800000 W/m2.

A further important advantage is tied to the reduction in the NOx (a pollutant particularly difficult to reduce) in combustion fumes. The reduction compared to identical kilns with circular nozzles of the known type is equal to about 8.7 ppm.

The invention thus conceived is susceptible of numerous modifications and variants, all falling within the scope of the inventive concept which characterises it. Moreover, all the details may be replaced with other technically equivalent ones. In practice, all of the materials used, as well as the dimensions, can be any whatsoever according to need.

Claims

1. A burner for a glass kiln comprising a supply conduit (2) for a liquid or gaseous fuel which defines a slot . (21) downstream whereof a flame is generated; said slot (21) extending over a first fictitious surface for a first length (23) following a preponderant line (22) of extension;

characterised in that the ratio between the first length (23) and a first width of said slot (21) is greater than 60, said first width being equal to the ratio between the area of said slot (21) measured on the basis of said first surface and the value of said first length (23) .

2. The burner according to claim 1, characterised in that the ratio between the first length (23) and the first width of said slot (21) is greater than 80.

3. The burner according to claim 1 or 2, characterised in that the slot (21) has a width (24) which varies along the second preponderant line (22) of extension, said width (24) being measured orthogonally to the second preponderant line (22) of extension; the width (24) of said slot (21) being narrower in a first central section (27) than in a second and in a third section (28, 29) between which said first central section (27) is interposed to facilitate a uniform distribution of the flow of fuel along said slot (21) .

4. The burner according to any of the preceding claims, characterised in that said supply conduit (2) comprises a connector (25) in turn comprising a first and second opposite walls (261, 262) which define a divergence (26) ; said slot (21) is located in proximity to the end of said divergence (26) .

5. The burner according to any of the preceding claims, characterised in that it comprises baffle means (3) which can be adjusted so as to render uniform the distribution of fuel along the preponderant line (22) of extension of said slot (21), said baffle means (3) being situated inside the fuel supply conduit (2) upstream of said slot (21) .

6. The burner according to claim 5 when it depends directly or indirectly on claim 4, characterised in that said connector (25) comprises a third and fourth opposing walls (263, 264) which define a convergence (260), said first and second walls (261, 262) being interposed between said third and fourth walls (263, 264); said adjustable baffle means (3) comprise a shutter (30) which is movable between a first and a second position; in said second position said shutter (30) being closer than in the first position to said third and fourth walls (263, 264) in order to divert the flow toward the first and second walls (261, 262) and facilitate a uniform distribution of fuel along the preponderant line (22) of extension of the slot (21).

7. The burner according to any of the preceding claims, characterised in that said fuel supply conduit (2) comprises a nozzle (8) supplementing said slot (21); said nozzle (8) being removably connectable to remaining parts of the fuel supply conduit (2) so as to facilitate interchangeability with nozzles (8) having slots (21) of different dimensions.

8. A glass kiln comprising:

-a burner (1) according to any of the claims_.1 to 7; -a glass treatment chamber (4), said burner (1) being in fluid communication with said glass treatment chamber ( 4 ) .

9. The kiln according to claim 8, characterised in that it comprises:

a body (51) made of refractory material which contributes to defining said chamber (4) and comprising a passage (510) which allows fluid communication between said burner (1) and said treatment chamber (4); - a cooling plate (50) interposed between said (51) body of refractory material and said burner (1) .

10. The kiln according to claim 8 or 9, characterised in that it comprises an intake conduit (6) for the combustion air, said intake conduit (6) leading into said treatment chamber (4) at a distance from said passage (510) which allows fluid communication between said burner (1) and said treatment chamber (4).

11. The kiln according to claim 8 or 9 or 10, characterised in that said intake conduit (6) and said passage (510) are on a same wall (40) of the burner (1) and are along the same vertical line.