Burner, apparatus and method for firing ceramic articles

Abstract

Burner (1) for firing ceramic articles (T) comprising: a mixing body (5) comprising, in turn, at least one duct (6) for supplying a fuel (FL) and at least one duct (7) for supplying an oxidizer (OX); a spark device (8) for starting a combustion; a flame detection device (9); a first tubular discharge element (11), which is configured to be flown through by a fluid (F) flowing out of the mixing body (5) and is provided with a first end (12), in which at least part of the mixing body (5) is inserted, and a second end (14), which is opposite the first end (12) and is provided with a first open channel (60); and an introduction element, which is configured to inject fuel (FL) downstream of the first tubular discharge element (11), in the area of the second end (14) or projecting from the second end (14); wherein the first tubular discharge element (11) comprises a second open channel (61), different from the first open channel (60), in which the introduction element (18) is at least partly inserted.

Description

[0001] " BURNER, APPARATUS AND METHOD FOR FIRING CERAMIC ARTICLES"

[0002] Cross-Reference to Related Applications This Patent Application claims priority from Italian Patent Application No. 102025000001134 filed on January 23, 2025, the entire disclosure of which is incorporated herein by reference.

[0003] Technical Field

[0004] The invention relates to a burner and an apparatus for firing of ceramic articles.

[0005] In particular, the invention advantageously, though not exclusively applies to the firing of ceramic articles to obtain tiles, to which explicit reference will be made in the description below without because of this lacking generality

[0006] Background of the Invention

[0007] The firing of ceramic articles to obtain tiles generally takes place in tunnel kilns, which are delimited by two opposite walls and by a roof. These kilns are usually heated by two series of burners, each located on one side of the tunnel.

[0008] The burners, which operate with natural gas ( for example, methane), are typically placed on the side walls of the tunnel on different levels and face the opposite wall.

[0009] The ceramic article firing cycle is designed with great precision and entails: heating the ceramic articles starting from the input of the kiln, having them remain inside the firing chamber at a predefined temperature, and cooling them in a controlled manner before they reach the output of the kiln.

[0010] The ceramic articles are usually transported on a large-sized conveyor consisting of a series of ceramic rollers. As a consequence, it is important to make sure that the temperature inside the firing chamber is even along the entire width of the kiln.

[0011] To this aim, different types of industrial burners were developed, as well as different arrangements of the burners inside complex apparatuses, so as to obtain a more and more constant temperature inside the firing chamber. In particular, especially in very large tunnel kilns, there generally is a non-homogeneous distribution of the temperature in the different cross sections, which leads to local temperature peaks determined based on the position of the burners.

[0012] To overcome the problems mentioned above, different types of so-called "high-speed" burners have been produced, which introduce combustion fumes (and flame) deep into the firing chamber, so as to improve the heat exchange inside it.

[0013] However, as mentioned above, known ceramic burners are substantially powered by fossil fuels (methane, LPG), which determine an anti-ecological exploitation of non-renewable resources. For this reason, several "environmentally friendly" solutions are under consideration, such as, for example, the use of fuels other than fossils, including hydrogen.

[0014] Nowadays, however, the use of hydrogen is hindered by several factors. First of all, this fuel causes high temperature peaks, which generate an increase in the production of NOx even compared to fossil fuels. In addition, hydrogen usually generates a highly unstable flame, which determines an extremely greater backfire than methane (orLPG), consequently generating a flame front positioned much further back (near the fuel supplying duct), which causes an overheating of the burner and risks being the cause of uncontrolled explosions with possible damage to the burners themselves and to the firing apparatuses.

[0015] In order to try to overcome these problems, the Applicant filed Italian patent application 102022000015384 relating to a burner provided with a fuel introduction element. This burner, however, does not feature sufficient flexibility to enable the prolonged use both of a flameless firing mode and of a flame firing mode, since, especially by using the flame mode, after a certain amount of time, the introduction element deteriorates, in particular with a scaling of the distal portion that may lead - over time - to a perforation of said portion, thus generating the need to frequently replace the introduction element. As a result, there is an increase in waste, energy expenditure and emissions for the production and disposal of these elements.

[0016] Therefore, this determines a poor flexibility of the structure of the burner, which, according to the customer' s requests or the specifications and costs in the respective countries, could be intended to operate both in flame mode and in flameless mode.

[0017] The obj ect of the invention is to provide an apparatus, a burner and a method, which are designed to at least partially overcome the drawbacks of the prior art and, at the same time, are cheap and easy to be manufactured and implemented.

[0018] Summary

[0019] According to the invention, there are provided a burner, an apparatus and a method for firing ceramic articlesaccording to the independent claims attached hereto and, preferably, according to any one of the dependent claims directly or indirectly depending on the independent claims.

[0020] The appended claims describe preferred embodiments of the invention and form an integral part of the description.

[0021] Brief Description of the Drawings

[0022] The invention will now be described with reference to the accompanying drawings, which show some non-limiting embodiments thereof, wherein:

[0023] figure 1 is a sectional front view of a first embodiment of an apparatus according to the invention;

[0024] - figure 2 is a schematic plan view of a segment of a second embodiment of an apparatus according to the invention;

[0025] - figure 3 is a schematic perspective view of part of the apparatus of figure 1 comprising a burner according to the invention;

[0026] - figure 4 is a sectional front view of the part of figure 3;

[0027] - figure 5 is a sectional plan view of the part of figure 3;

[0028] - figure 6 is a schematic perspective view of part of the burner of figure 3;

[0029] - figure 7 is a longitudinal sectional view, in detail, of the burner of figure 6;

[0030] - figure 8 is sectional front view of a combustion head of the burner of figure 3;

[0031] - figure 9 is a schematic perspective view of a distal portion of the burner of figure 3;

[0032] - figure 10 illustrates a diagram showing a comparison of the production of NOx (chamber temperature at 900°C) as a function of the capacities of a burner operating indifferent modes, with different fuels and with different geometries for the introduction elements.

[0033] Detailed Description

[0034] In figure 1, number 1 indicates, as a whole, a burner for the firing of ceramic articles T according to a first aspect of the invention.

[0035] The burner 1 can be preferably, though not necessarily installed in an industrial kiln 2, in particular a tunnel kiln, comprising a firing chamber 3.

[0036] In particular, according to figures 1 and 2, the ceramic articles T are conveyed by a transport system 4 along a conveying path P.

[0037] More precisely, the ceramic articles T are any type of ceramic articles needing at least a kiln firing.

[0038] In the non-limiting embodiment shown in figures 1 and 2, the transport system 4 comprises a conveyor belt, on which the raw ceramic articles T to be fired are placed, preferably in an orderly fashion.

[0039] According to some non-limiting embodiments which are not shown herein, the transport system 4 comprises a plurality of ceramic rollers (if necessary, moved at different speeds in order to differentiate the firing of the articles ).

[0040] Advantageously, though not in a limiting manner, the burner 1 is configured for firing the ceramic articles T both in flameless mode and in flame mode. In other words, the burner 1 is versatile and can fire the ceramic articles T in a predefined manner that can be configured to be either one of the two discussed above. Therefore, the burner 1 does not only use the flame to heat the kiln 2 in order to initiate flameless mode, but is also capable of completely operatingin flame mode in an effective manner and for a long time. According to figures 1 to 6, the burner 1 comprises a mixing body 5, which, in turn, comprises a duct 6 for supplying a fuel FL provided with a given percentage of hydrogen (in particular greater than 50%, more precisely greater than 70%, preferably entirely hydrogen), a duct 7 for supplying the oxidizer, a spark device 8 for starting a combustion and a flame detection device 9. In other words, the mixing body 5 is the part of the burner that is needed to generate the air-gas mixture which ( following an ignition in order to obtain a flame) heats the firing chamber 3.

[0041] In particular, the fuel FL introduced through the fuel supplying duct 6 is gaseous, more in particular mainly hydrogen (if necessary, mixed with natural gas such as methane or LPG), whereas the oxidizer introduced through the oxidizer supplying duct 7 substantially is ambient air ( for example, with approximately 21% of oxygen). Preferably, though not in a limiting manner, the oxidizer OX is preheated, in particular to a temperature higher than 100°C, in particular between 130°C and 300°C, more in particular between 150°C and 250°C.

[0042] The burner 1 further comprises a tubular discharge element 11, which is designed (configured) to be flown through by a fluid F flowing out of the mixing body 5 (consisting of the mixture of fuel FL and oxidizer OX and / or a possible combustion thereof ) and is provided with an end 12 having an opening 13, in which at least part of the mixing body 5 is inserted, and an end 14, which is opposite the end 12 and has an opening 15. In other words, the end 14 faces the firing chamber 3.

[0043] According to some non-limiting embodiments, the mixingbody 5 is coupled to the tubular discharge element 11 through fixing elements. Advantageously, though not necessarily, like in the embodiment shown in figures 4 and 5, the fixing elements are bolts 16.

[0044] In the non-limiting embodiment shown in figures 3, 4 and 5, the mixing body 5 is partly inserted in the discharge element 11 and partly located on the outside of the kiln 2. In particular, in the embodiment of figures 4 and 5, the discharge element 11 is inserted inside a side wall 17 of the tunnel kiln 2. More precisely, the discharge element 11 completely extends inside the side wall 17. On the contrary, in other non-limiting embodiments, the discharge element 11 extends along the entire length of the side wall 17, also partly entering the firing chamber 3 of the kiln 2.

[0045] Advantageously, the burner 1 comprises an introduction element 18, which is configured to inj ect fuel FL downstream of the tubular discharge element 11.

[0046] According to some preferred non-limiting embodiments, as shown in figures 4 and 5, the introduction element 18 is configured to inj ect fuel FL at the second end 14, in particular close to the second opening 15, namely at a distance of less than 10 cm from the second opening 15.

[0047] In particular, the first tubular discharge element 11 comprises, at the second end 14, a first open channel 60 to let the fluid F out of the first tubular discharge element 11. In detail, the first open channel 60 fluidly connects the inside and the outside of the first tubular discharge element 11.

[0048] Advantageously, the first tubular discharge element 11 comprises a second open channel 61, different from the first open channel 60 (and from the first opening 13), in whichthe introduction element 18 is at least partly inserted. In particular, therefore, the second open channel 61 is located at the second end 14 or proj ects from the second end 14, namely facing the firing chamber 3.

[0049] Preferably, as shown in the non-limiting embodiments of the accompanying figures, the introduction element 18 proj ects from the second end 14 into the firing chamber 3.

[0050] In particular, the introduction element 18 is fluidly separate from the inside of the tubular discharge element 11. In other words, the fuel FL introduced into the firing chamber 3 through the introduction element 18 does not come into contact with the oxidizer OX inside the tubular discharge element 11, but only outside it, namely already in the firing chamber 3.

[0051] In the non-limiting embodiments of figures 3 to 7, the introduction element 18 comprises a tubular duct 19, which extends at least from the end ( 12 ) to the end 14, in particular which goes through the first tubular discharge element 11 from side to side. In detail, the introduction element 18 is configured to directly introduce fuel FL into the firing chamber 3, downstream of the tubular discharge element 11, namely the outflow of fuel FL from the introduction element 18, in particular from the tubular duct 19, takes place to more inside the firing chamber 3, namely farther from the mixing body 5 than from the opening 15.

[0052] Preferably, though not in a limiting manner, the second open channel 61 is completely crossed by the introduction element 18, in particular by the tubular duct 19.

[0053] According to some preferred, though non-limiting embodiments, the tubular element 18 longitudinally goes through the tubular discharge element 11 from side to side.In some non-limiting cases, the burner 1 comprises one single introduction element 18.

[0054] In other non-limiting cases, the burner 1 comprises a plurality of introduction elements 18.

[0055] Preferably, as shown in the non-limiting embodiments of figures 4 to 6, furthermore, the introduction element 18 substantially extends inside the tubular discharge element 11. In this way, it is possible to replace a standard burner with the burner 1 without making significant changes to the kiln 2.

[0056] In some non-limiting cases, the burner 1 is configured to initially operate in flame mode, namely a mode in which a flame front is present (which conventionally is the case with ceramic plants) and, once a predefined temperature is reached, namely a temperature equal to or higher than the autoignition temperature of the fuel-oxidizer mixture to be introduced into the kiln, it is configured to operate in flameless mode, in which the combustion of fuel takes place without the formation of a traditional flame, thanks to a high dilution of the reagents and to a strong pre-heating of the oxidizing air. The flameless mode is a combustion condition in which the chemical reaction takes place in a distributed manner within the volume of the kiln, without a localized flame front, producing more even temperatures, lower thermal peaks and smaller Nox emissions.

[0057] In addition, the burner 1 is also configured to entirely operate in flame mode, without this generating a rapid deterioration of the tubular duct 19.

[0058] Advantageously, but not in a limiting manner, the introduction element 18 is configured to introduce fuel FL into the firing chamber 3 alternatively to the supplyingduct 6 for the fuel FL. In other words, the introduction element 18 is configured to alternatively introduce fuel FL into the firing chamber 3 when the burner 1 operates in flameless mode, namely without determining the generation of a flame front (namely, that limited region, usually less than one millimetre, where the combustion reactions take place in flame mode).

[0059] In some preferred non-limiting cases, like the ones shown in figures 4 to 7, in detail, as visible from figure 5, the tubular duct 19 extends asymmetrically relative to a longitudinal symmetry axis AA of the burner 1. In particular, the tubular duct 19 at least partly extends parallel to an inner wall 20 of the tubular discharge element 11.

[0060] In other words, the tubular duct 19 does not extend along the longitudinal symmetry axis AA. The asymmetry in the arrangement of the tubular duct 19, in detail its offset arrangement towards the wall 20, allows thermal stress to be reduced, therefore preserving it, during operations in flame mode. In this way, indeed, the tubular duct 19 is immersed in the flame to a smaller extent.

[0061] Advantageously, though not in a limiting manner, the tubular duct 19 follows the shape of the inner wall 20, which, though, has a narrowing 21 in the area of the opening 15.

[0062] In the non-limiting embodiments of the accompanying figures, the second open channel 61 is obtained in the area of the narrowing 21, in particular goes through it.

[0063] Preferably, though not in a limiting manner, the tubular duct 19 extends along a respective longitudinal (symmetry) axis BB, which is parallel to the axis AA.

[0064] In particular, the tubular duct 19 comprises at leasta first portion 22 on the inside of the first tubular discharge element 11 and a second portion 23, downstream of the first portion 22 towards the second end 15, inserted in the second open channel 61. In particular, the first tubular duct 19 also comprises a third portion 24 projecting, on the outside of the first tubular discharge element 11, from the second open channel 61. In detail, the first portion 22 is radially arranged at a distance from the longitudinal symmetry axis AA that is the same as the one of the second portion 23 and the fourth portion 24. In this way, the tubular duct 19 undergoes less stress compared to the solutions of the prior art.

[0065] Advantageously, though not necessarily, in order to permit a deep introduction of the fuel FL into the firing chamber 3 during the flameless mode, the tubular duct 19 has an inner diameter ID, namely an inner opening, equal to or smaller than 10 mm, in particular equal to or smaller than 7 mm, more in particular equal to or smaller than 5 mm.

[0066] Advantageously, though not in a limiting manner, the first tubular duct 19 is substantially entirely straight and extends along the axis BB. In this way, its manufacturing is simplified and its structure is preserved, as it is substantially less immersed in the flame during the flame mode.

[0067] Advantageously, though not in a limiting manner, and as shown in the embodiments of figures 5, 6 and 9, the second open channel 61 substantially is a special perforated appendage (or, if necessary, it could even be just a hole) manufactured as one single piece together with the rest of the tubular discharge element 11, namely preferably made of silicon carbide.In particular, the second open channel 61 is connected to the first open channel 60 by means of a rib 62, which preferably extends along the plane joining the axes AA and BB.

[0068] Advantageously, though not in a limiting manner, the diameter of the first open channel 60, namely of the opening 15, is greater than the diameter of the second open channel 61, which is sufficiently wide to be crossed by the tubular duct 19. In particular, the space interposed between the tubular duct 19 and the second open channel 61 preferably is smaller than 2 mm, in particular 1 mm. In this way, given the fact that the second open channel 61 extends along several centimetres lengthwise, the oxidizing air that manages to flow through said space is negligible as the load necessary to flow through it makes it preferable, for the oxidizer OX or for the fluid F in general, to flow through the first open channel 60.

[0069] According to other non-limiting embodiments which are not shown herein, the second open channel 61 is obtained on the side wall 20 of the tubular discharge element 11.

[0070] Therefore, the second open channel 61 can be obtained on the side wall 20 of the tubular discharge element 11 or it can be located at the second end 14 (in particular at a distance from the second end equal to or less than 30 cm, preferably at 20 cm, more in particular at 10 cm, in particular at 5 cm) or project from the second end 14, namely facing the firing chamber 3.

[0071] In the non-limiting embodiments of figures 4 to 6, the introduction element 18 comprises an end 25 projecting from the opening 15 for a distance of 5 mm or more, in particular 10 mm or more, preferably ranging from 10 to 20 mm. In thisway, it is possible to introduce the fuel FL into the firing chamber 3 (during the flameless combustion) by further reducing the risk that the combustion propagates again inside the tubular discharge element 11 (recreating the flame front and, especially in the case of hydrogen as fuel FL, generating dangerous detonations inside the burner 1 ).

[0072] In some non-limiting cases, and as shown in the embodiment of figure 5, the burner 1 comprises a supply system 26 for the fuel FL connected to the duct 6 for supplying the fuel FL and a supply system 27 for the fuel FL, separate from the supply system 26 for the fuel FL, connected to the introduction element 18. In particular, the supply system 26 for the fuel FL and the supply system 27 for the fuel FL can be operated selectively and / or independently, for example by means of special solenoid valves 28 (preferably redundant for safety reasons).

[0073] Advantageously, though not necessarily, as visible in figure 5, the supply system 26 for the fuel FL and the supply system 27 for the fuel FL are both connected to different ducts 6, 6' obtained on a breech 29 of the mixing body 5.

[0074] In other non-limiting cases which are not shown herein, the supply system 26 for the fuel FL and the supply system 27 for the fuel FL are connected to the same duct 6 on the breech 29, which is provided with a deflecting valve, which introduces the fuel FL into the mixing body 5 or into the introduction element 18 as a function of the operating mode, flame or flameless mode, respectively, of the burner 1.

[0075] Provided below are some advantageous, though nonlimiting features of burner 1 during the flame operating mode. These features combine themselves with the rest of the disclosure to allow for the use of a 100% hydrogen fuel or,in any case, a fuel with a high percentage of hydrogen. Advantageously, though not in a limiting manner, and as shown in the non-limiting embodiment of figures 4 to 8, the mixing body 5 comprises both a partitioning system FPS for the fuel FL, which is configured to divide the fuel FL into a plurality of portions FL', FL' ’, FL' ’ ’, and a partitioning system OPS for the oxidizer OX, which is configured to divide the oxidizer OX into a plurality of portions OX', OX' ’, OX' ’ ’ (see, for example, figure 8 ). The burner 1 is configured so that the plurality of portions FL', FL' ’, FL' ’ ’ and the plurality of portions OX', OX' ’, OX' ’ ’ are conveyed so as to be mixed with one another in at least two (in particular, three or more) stages ( forming respective mixtures M', M' ’, M' ’ ’ ). In this way, the generation of the flame is contained and controlled when the fuel FL is mainly or totally hydrogen.

[0076] Advantageously, though not necessarily, the oxidizer partitioning system OPS comprises a combustion head 10, which is (at least partially) located inside the first tubular discharge element 11 (through the opening 13) and comprises one or more combustion chambers 30, 31, configured to each contain a different stage (or mixture Ml, M2 ) of the combustion of the flame.

[0077] Advantageously, though not necessarily, the partitioning system FPS for the fuel FL comprises an injection element 32, which is configured to inject, during combustion with flame, at least the majority FL' ’ ’ ’ of the fuel FL downstream of the combustion head 10 (into the tubular discharge element 11 ) towards the end 14, namely towards the firing chamber 3. In this way, the majority of the flame develops away from the end 12 of the burner 1,allowing at the same time the flame front to be brought closer to the firing chamber, thus reducing the overheating of the mixing body and of the discharge element 11.

[0078] In particular, the tubular discharge element 11 is configured to contain a primary stage F' of the combustion of the flame.

[0079] According to a preferred, though non-limiting embodiment shown in figures 4 to 8, the injection element comprises a tubular duct 33, in particular an axial duct (namely, located in the area of the longitudinal axis AA of the burner 1 ), which goes through said one or more combustion chambers 30, 31 from side to side and so as to convey the portion FL' ’ ’ of fuel FL (greater than 50%, preferably ranging from 70% to 80%) downstream of the combustion head 10, shifting the majority of the flame towards the firing chamber 3.

[0080] In the non limiting embodiments of figures 4 to 8, the tubular duct 33 has a substantially constant, preferably circular cross section. In particular, the tubular duct has a first cross section having an inner diameter ranging from 2 mm to 12 mm, in particular from 4 mm to 10 mm. In this way, it is possible to guarantee a high speed that facilitates a reduction / control of the backfire that usually is problematic in case of hydrogen, in addition, it helps the rest of the burner reach the speed necessary to introduce the fumes F deep into the firing chamber 3.

[0081] In some non-limiting cases, like the one shown in figures 4 to 8, the tubular duct 33 comprises an end 34 connected to the duct 6 for the supply of the fuel FL and an end 34' inside the tubular discharge element 11 towards the end 14. More in particular, the tubular duct 33 has a lengthranging from 40 mm to 150 mm, preferably from 60 mm to 110 mm.

[0082] Advantageously, though not necessarily, as shown in the non-limiting embodiments of figure 7, the tubular duct 33 has one or more distribution openings 35 for the fuel FL in the area of each combustion chamber 30, 31 so as to inj ect at least one of the portions FL', FL' ’ into each one of them. In particular, said one or more distribution openings 35 are through holes 36, which connect an inner area of the tubular duct 33 to a combustion chamber 30, 31.

[0083] Advantageously, though not necessarily, the through holes 36 are radial, preferably ring-shaped, holes, for example extending radially from the axis AA. Preferably, the holes 36 have a diameter of less than 5 mm, in particular ranging from 1 mm to 3 mm.

[0084] Advantageously, though not necessarily, the supplying duct 6 for the fuel FL comprises at least one narrow portion 37 of the type described in Italian patent application 102021000013535 of the Applicant.

[0085] Advantageously, though not necessarily, the burner 1 (the mixing body 5) comprises the breech 29 (in particular made of aluminium or cast iron and provided with the final part of the supplying channels 6 and 7 for the oxidizer and the fuel), which closes the burner 1 on the side opposite the firing chamber 3. In particular, the breech 29 is of the type described in Italian patent application 102021000013535 of the Applicant, except for the fuel supply system 27 and, therefore, for the duct 6' to which the fuel introduction element 18 is connected in the flameless mode.

[0086] Advantageously, though not necessarily, and as shown in the non-limiting embodiments of figures 1 to 4, the burner1 comprises a tubular discharge element 38 (shown, for example, in dashed outline in figure 4 ), which extends from the end 14 of the element 11 in the opposite direction with respect to the end 12, namely towards the (more precisely, the inside of the) firing chamber 3.

[0087] In some non-limiting cases, the burner 1 comprises a suction element 39, which is designed to (configured to) lead at least part of the gases G present on the outside of the burner 1 into the second tubular discharge element 38.

[0088] Preferably, the discharge element 38 and the suction element 39 are of the type described in Italian patent application 102021000013535 of the Applicant. In particular, together with the discharge element 11, the discharge element 38 and the suction element 39 form a combustion block of the type described in Italian patent application 102021000013535 of the Applicant

[0089] Advantageously, though not in a limiting manner, the combustion head 10 is a multi-stage combustion head, namely designed to (configured to) divide the formation of the flame into several stages. In this way, the so-called "air staging" technique can be used.

[0090] Advantageously, though not in a limiting manner, the duct 33, together with the openings 35, helps the combustion head 10 divide the flame into several stages, in particular by dividing the fuel FL. In this way, the so-called "fuel staging" technique can be used.

[0091] From the combination of the aforementioned techniques, it is possible to use the FL fuel with a substantial percentage of hydrogen and at the same time increase the flame speed up to over 160 m / s, in particular up to over 180 m / s, more precisely up to about 200 m / s. As a matter of fact,the term "high speed" means, specifically in the field of burners, a flame speed greater than or equal to 150 m / s.

[0092] Advantageously, though not necessarily, the combustion head 10 (with the tubular duct 33 on the inside) is at least partially mounted inside the tubular discharge element 11 so as to be coaxial thereto along the longitudinal symmetry axis AA of the burner 1.

[0093] As shown in the non-limiting embodiments of figures 4 to 8, advantageously, the multi-stage combustion head 10 comprises (at least) a combustion chamber 30, which is designed to (configured to) generate a first flame combustion phase (in particular to generate the so-called "base" of the flame) given by the combination of the portions FL' and OX', and (at least) a combustion chamber 31, communicating with the combustion chamber 30 and designed to (configured to) generate a second flame combustion phase (given by the combination of the portions FL' ’ and OX' ’ ) out of the combustion chamber 30. In particular, the combustion chambers 30 and 31 are configured to convey a secondary portion F' ’ (or secondary stage) of the flame into the tubular discharge element 11 towards the end 14 and, in particular, through the suction element 39 towards the tubular discharge element 38.

[0094] In the non-limiting embodiment of figures 6 to 8, the combustion head 10 comprises a crown 47 configured to adjust the flow of oxidizer OX into the tubular discharge element 11, which does not go through the combustion chambers 30 and 31. In particular, the crown 47 extends from the edge of the outlet opening 46 towards (up to) the inner wall of the tubular discharge element 11.

[0095] Advantageously, though not necessarily, the crown 47comprises slots 48 (or any other type of opening) configured to convey part OX'" of the oxidizer into the tubular discharge element 11 downstream of the combustion chambers 30 and 31. In this way, together with the oxidizer-fuel mixture M' ’ and the main fuel portion FL' ’ ’, a mixture M' ’ ’ is generated out of the tubular discharge element 11, possibly through the suction element 39 towards the tubular discharge element 38. In particular, the primary flame F' of the burner 1 is generated.

[0096] Preferably, though not in a limiting manner, the tubular duct 19 goes through the crown 47, in particular through one of the slots 48.

[0097] Advantageously, though not necessarily, the diameter of the narrowing 21 is smaller than 30 mm, in particular equal to or smaller than 25 mm. In detail, the diameter of the narrowing 21 ranges from 5 mm (in particular, from 10 mm; more in particular, from 20 mm) to 60 mm (in particular, to 40 mm; more in particular, to 30 mm). This feature also makes it possible to accelerate the fluid F flowing out of the burner 1, counteract backfire and, therefore, better manage the combustion with fuel FL mixtures that are very rich in hydrogen.

[0098] According to a preferred, though non-limiting embodiment, as shown in figures 4-8, the flame detection device 9 comprises a UV detection probe 49. In particular, the UV probe 49 is located along the longitudinal axis AA of the burner on board the breech 29, namely on board the mixing body 5.

[0099] Advantageously, though not necessarily, the flame detection device 9 (more precisely, the UV detection probe 49) is configured so as to receive a UV beam (ultravioletradiation) coming from the flame going through the tubular discharge element 11. In use, the detection UV probe 49 provides data relating to the state of the flame generated by the burner, through which it is possible to properly adjust the flow rate of the fuel FL and / or of the oxidizer OX. Furthermore, once the flameless mode is activated as described below, the UV probe 49 is disabled because it is no longer able to detect any flame, since the flame front is diluted inside the firing chamber 3 of the kiln.

[0100] According to a second aspect of the invention, there is also provided an industrial plant 50 for firing of ceramic articles T, in particular as disclosed above.

[0101] According to some non-limiting embodiments, the ceramic articles T are, after having been fired, tiles. In particular, the ceramic articles T are raw when they enter the apparatus 50 and fired when they come out.

[0102] The industrial apparatus 50 comprises the kiln 2 (described above), in particular a tunnel kiln, provided with at least one side wall 17, which delimits the firing chamber 3 and has an inner surface 51 on the inside of the firing chamber 3 and an outer surface 52 on the outside of the firing chamber 3.

[0103] The industrial apparatus 50 further comprises the transport system 4 described above, in particular a horizontal transport system, which is configured to move the plurality of ceramic articles T along the conveying path P inside the firing chamber 3 ( from the input to the output of the firing chamber 3).

[0104] Advantageously, though not in a limiting manner, the apparatus 50 comprises a (hydrogen) burner 1 according to the description above.Advantageously, the apparatus 50 comprises a hydrogen supplying system S configured to inject hydrogen or a mixture comprising hydrogen into the supply systems 26 and 27 for the fuel FL. In particular, the hydrogen supplying system S is configured to selectively inject hydrogen or a mixture comprising hydrogen (namely, in a mutually exclusive manner) into the fuel supplying duct 6 or into the introduction element 18.

[0105] In particular, during the flameless operating mode, all the fuel FL flows through the introduction system 18, whereas all the oxidizer OX preferably flows through the discharge element 11 before being mixed into a mixture M* directly inside the firing chamber 3, without the generation of a localized flame front, hence flameless.

[0106] In the non-limiting embodiments of figures 1 to 4, the burner 1 is coupled, by means of the fixing elements 16, to the wall 17 of the kiln 2. In particular, the discharge element 11 is inserted inside the side wall 17. In this way, since the burner according to the invention substantially maintains the dimensions of a ceramic kiln burner, the replacement thereof is facilitated.

[0107] In the non-limiting embodiment of figure 1, the burners 1 are oriented in a direction DP, which is transverse (in particular, perpendicular) to the direction DD (and, hence, to the conveying path P).

[0108] Advantageously, though not necessarily, the tubular element 11 of the burner 1 is installed so as to at least partially (in particular, totally and transversely) go through one of the side walls 17 of the kiln 2. In this way, the flame produced by the burner 1 will directly reach the inside of the firing chamber 3 of the kiln 2.In particular, the axis AA (and, therefore, the axis BB) is perpendicular to the conveying path P. More in particular, the axis AA is also perpendicular to the side wall 17 of the industrial tunnel kiln 2.

[0109] According to some non-limiting embodiments which are not shown herein, the discharge element 11 of the burner 1 is installed so as to partially project into the firing chamber 3.

[0110] Advantageously, though not necessarily, the apparatus 50 (or each burner 1 ) comprises at least one electronic control unit 53, which is configured to control the burner 1 so as to switch from the flameless mode, whose configuration involves heating the firing chamber 3 with a flame and then switching to the flameless firing, to the flame mode, whose configuration involves both heating and firing, which are traditionally carried out with a flame.

[0111] In particular, the electronic control unit 53 is configured to control the burner 1 so as to switch from the flame mode to the flameless mode upon reaching a predefined temperature TV. More precisely, the predefined temperature TV is higher than the autoignition temperature of the fuel mixture M* ( for example, higher than 800°C). In this way, the mixture M* generated inside the firing chamber 3 will be devoid of a flame front, with all the advantages that this entails, which are described below.

[0112] Through this control of the supply of oxidizer OX and fuel FL to the burner 1, together with the presence of the introduction element 18, which directly injects the fuel into the firing chamber 3, it is possible to carry out a flameless combustion also with fuels such as hydrogen, which tend to reform the flame front in a sudden and unwanted wayinside the burner, in the event that the flameless mode continues over time even at low capacities (where the impulse of the flame, reducing its intensity, determines the establishment of conditions suitable for the formation of the flame front).

[0113] In particular, the electronic control unit 53 is configured, once the predefined temperature TV has been reached in the firing chamber 3, to put out the flame by decreasing or stopping the supply of fuel FL and, if necessary (but not in a limiting manner), of oxidizer OX into the fuel supplying duct 6 or into the oxidizer supplying duct 7, respectively. Once the flame has been put out, the control unit 53 is configured to introduce fuel FL into the introduction element 18 (and to restore the supply of oxidizer OX, in case it was interrupted), thus allowing the burner 1 to generate the mixture M* directly inside the firing chamber 3 and to fire the ceramic articles T in flameless mode.

[0114] Preferably, though not in a limiting manner, the control unit 53 is further configured to selectively inhibit the flame control (through the detection device 9) during the flameless operating mode.

[0115] By using a flameless combustion, namely a combustion that takes advantage of the fact that inside the kiln there is a temperature higher than the autoignition temperature of the fuel, it is in fact possible to drastically reduce the NOx emissions that are normally generated by the combustion of mixtures rich in hydrogen (and, in general, by combustions with high flame peaks), thus allowing for the use of an environmentally friendly fuel with low emissions. In particular, the alternating combination of flame and flameless modes compensates for the extreme ability to igniteand propagation (backfire) of hydrogen.

[0116] In particular, though not in a limiting manner, the electronic control unit 53 is configured to control the apparatus 50 so as to fire the tiles T only in the flameless configuration.

[0117] Advantageously, though not necessarily and according to the non-limiting embodiment of figure 1, the apparatus 50 comprises at least two temperature control devices 54, in particular at least two double-wire thermocouples 55, located in at least two different "significant" points of the kiln 2. These two points are such as to ensure that, in each point of the firing chamber, the temperature is sufficiently higher than the autoignition temperature of the fuel mixture (so as to enable, therefore, a reliable flameless firing).

[0118] Advantageously, though not necessarily, if the temperature detected by the two thermocouples 55 drops below the autoignition temperature, the flame is triggered and ignited again, namely the electronic control unit 53 immediately restores the flame operating mode of the burner 1.

[0119] According to a further aspect of the invention, there is provided a method for the firing of ceramic articles conveyed inside a tunnel kiln.

[0120] The method comprises at least one step of supplying a burner 1 as disclosed above with a fuel FL comprising at least a percentage of hydrogen exceeding 20%, in particular exceeding 50%, more in particular exceeding 70%, preferably entirely hydrogen. These fuel mixtures can be used in a flame operating mode thanks to the particular geometry of the burner described above, in particular thanks to the multi-stage combustion head 10 in combination with the injection element 32. Furthermore, the additional geometries described above synergistically achieve the significant technical effect of reducing environmental impact, respectively allowing for the use of a hydrogen-rich mixture as fuel and the reduction of NOx emissions.

[0121] In some non-limiting cases, the fuel FL comprises a percentage of hydrogen greater than 90%. In particular, the fuel is 100% hydrogen.

[0122] The method further comprises the step of simultaneously supplying the burner 1 with the oxidizer OX and igniting (lighting) the flame (through the spark device 8 ), which at least partially extends inside the burner 1 and the firing chamber 3 of the kiln 2.

[0123] Once the ignition of the flame is completed, the method entails controlling the flame through feedback thanks to the detection device 9, in detail until the predefined temperature TV is reached inside the firing chamber 3.

[0124] Advantageously, though not necessarily, the method comprises the further steps, once the firing chamber 3 of the kiln 2 has reached the predefined temperature TV (in particular higher than the autoignition temperature of the fuel FL), of putting out the flame by reducing (or interrupting) the supply of fuel FL and, if necessary, of oxidizer OX; preferably disabling the aforesaid flame feedback control; and introducing fuel FL into the introduction element 18 (namely, of the tubular duct 19, if necessary restoring the supply of oxidizer OX), thus directly generating, inside the firing chamber 3, the mixture M* determining the flameless combustion that fires the ceramic articles T.In particular, therefore, the fuel FL is introduced along the axis BB, which is parallel to and does not coincide with the axis AA. In this way, the fuel FL is directly introduced into the firing chamber 3 in an offset manner with respect to the oxidizer OX, allowing for a combustion with fumes having lower percentages of oxygen compared to ambient air, thus further reducing the formation of NOx.

[0125] In particular, the method involves switching from the flame mode to the flameless mode upon reaching the predefined temperature TV. More precisely, the predefined temperature TV is higher than the autoignition temperature of the fuel mixture.

[0126] Advantageously, though not necessarily, the method entails firing the tiles T only after having reached the flameless configuration. In other words, the burner 1 is supplied with oxidizer OX (through the discharge element 11 ) and fuel FL (through the introduction element 18 ), all without igniting the flame, by de-energizing and energizing (closing and opening) a solenoid valve 28 (in particular, two solenoid valves 28 in series, according to current regulations) of the supply system 27. At the same time, an air solenoid valve (not shown) is also momentarily closed.

[0127] In particular, the step of energizing the solenoid valves 28 (namely, the steps of supply and interruption of the oxidizer) are preferably carried out after the electronic control unit 53 has put out the flame in the burner 1 and inhibited the spark electrode 8 and the flame UV detection probe 49 (since the flame front is no longer located in the burner 1, but is diluted in the chamber 3 of the kiln). More in particular, through the aforementioned solenoid valves, the supply of oxidizer OX and fuel FL is digitally controlled(ON / OFF), namely shifting from the maximum flow rate to zero and vice versa. In this way, it is possible to avoid the formation of a stable flame front anchored inside the burner 1. In detail, this effect is due to the fact that a very high impulse is given to the flame supply, such as not to allow for the formation of the flame front in the burner, said flame front being then directly diluted in the firing chamber 3.

[0128] In other non-limiting cases, in accordance with the same principle explained above, the method entails, by means of the control unit 53, maintaining the supply of oxidizer OX and interrupting and subsequently supplying the duct 6 and the duct 19, respectively. In this way, it is possible to maintain a constant pressure state inside the chamber 3 of the kiln 2, without causing the flue draft to fluctuate. A possible re-ignition of the flame front inside the burner 1 is also precluded to a greater extent.

[0129] In the flameless step, la flame substantially is directly diluted in the chamber 3 of the kiln 2 with the combustion products already present in the chamber 3 with an oxygen content lower than the one of the oxidizing air OX ( for example, up to 14%, or even up to 4%, or even up to 2%, to further inertize the flame front). In other words, in this way, the oxidizer OX and the fuel FL separately flowing out of the burner 1 towards the firing chamber 3 form the mixture M*, which is oxidized inside the chamber 3.

[0130] By so doing, it is possible to avoid the presence of temperature peaks (which are among the main causes of production of NOx) compared to traditional flame-only solutions. This results, in turn, in a lower thermal load on the components of the burner 1 ( for example, on thecombustion head 10, on the tubular ducts 19 and / or 33, on the mixing body 5, on the combustion block, on the fuel and oxidizer pipes, etc. ). At the same time, therefore, a strong reduction in the thermal dissipations caused by the burner is obtained, thus improving the efficiency of the kiln 2. In the absence of flame, moreover, the burner 1 operates more quietly, thereby also reducing the noise pollution it produces.

[0131] Advantageously, though not necessarily, the power of the burner is smaller than 100 KW, in particular smaller than 70 KW, preferably smaller than 50 KW.

[0132] In use, the spark device 8 (in particular, the spark electrode) generates a spark that, together with the fuel FL entering from the duct 6 and the oxidizer OX entering from the duct 7, determines the generation of the flame. In particular, the oxidizer part OX' and the fuel part FL' generate the mixture M' inside the combustion chamber 30, which defines a first stage of the flame and continues towards the combustion chamber 31, inside which the mixture M', the fuel portion FL' ’ and the oxidizer part OX' ’ form the mixture M' ’, which defines a second stage of the flame. Inside the tubular discharge element 11, the mixture M' ’, by being mixed with the part OX'''of the oxidizer OX and with the portion FL' ’ ’ of the fuel FL flowing out of the end 34', forms the fluid F (and the primary flame F' ). Therefore, the mixing body 5 generates an at least partially combusted mixture, namely a flame, whose fluids F flow through the tubular discharge element 11, which introduces the flame into the combustion chamber 3.

[0133] The products of the combustion emitted by the burner 1 are not totally combusted when they go through the dischargeelement 11 for the first time, but the combustion is increased (completed) thanks to the continuous recirculation of the gases G (present inside the firing chamber 3 ) through high speed of the fluid and, if necessary, the presence of the suction element 39. In other words, the burner 1 generates, through the spark device 8, a primary combustion of the gases introduced by the ducts 6 and 7 ( fuel and oxidizer) and a secondary combustion thereof, using the gases G recirculated from the inside of the firing chamber 3, as they were not completely combusted (and, therefore, have residual oxygen), which are sucked by the speed of the fluid F and by the suction element 39. In particular, the primary combustion takes place inside the discharge element 11 and the secondary combustion takes place inside the firing chamber 3.

[0134] Once the predefined temperature TV has been reached, the control unit 53 puts out the flame and assigns the supply of fuel FL to the introduction element 18, which introduces fuel into the firing chamber 3 to generate the aforementioned mixture M*. In general, in order to obtain a good flameless combustion it is convenient to dilute the mixture M* as much as possible. In particular, the burner 1 is configured to keep the ratio between the quantity of recirculated fumes and the sum of the quantities of oxidizer OX and fuel FL greater than 3. In these conditions, it is possible to successfully avoid the reformation of the flame front, therefore continuing with the full flameless mode.

[0135] Therefore, it is evident that, by using an apparatus 50 or a set of burners 1 according to the invention, a greater uniformity of the temperature along the width of the firing chamber 3 of the kiln 2 can be obtained. In particular, thetemperature close to the wall 3 significantly increases thanks to the turbulences generated by the suction element 39 (thanks to the further speed enabled by the multi-stage combustion head 10) and to the contribution of the irradiation provided by the introduction element 18 close to said wall 3. In addition, the temperature at the centre of the kiln is increased compared to the traditional case because of the use of the introduction element 18, which allows the combustion block 38 to reach great depths inside the kiln 2. Therefore, the flame coming out of said discharge element 14 is emitted at a greater depth compared to traditional solutions.

[0136] It should be pointed out that the temperature peak close to the discharge of the burner 1 is (at least partially) flattened.

[0137] Even though the invention described above particularly relates to a precise example, it is not limited to said example, since its scope of protection extends to all those variants, changes or simplifications covered by the appended claims, such as for example a different geometry of the combustion head 10, of the introduction element 18, of the injection element 33, of the chambers 30 and 31, of the combustion block 38 and, in particular, of the suction element 39, a different method for sucking the gases G close to the inner surface 51 of the side wall 17, a different arrangement of the burners 1 inside the apparatus 50 (both in terms of position and in terms of alignment), a different transport system 4, etc.

[0138] The apparatus and the burner described above have many advantages.

[0139] First of all, the way in which the burner 1 ismanufactured and assembled is simpler compared to prior art solutions comprising more components, which, therefore, besides being more complicated to assemble, are also heavier and more large-sized. In addition, the burner 1, given the geometry and the penetration in the firing chamber 3, can easily be installed as a replacement (improvement) of a standard architecture.

[0140] The straight geometry of the introduction element 18 avoids an acceleration in the deterioration, with relative scaling of the material, of the tubular duct 19 in the portion most exposed to the flame. For this reason, it is also possible to use a same burner of the type described above both for firing in flameless mode (with the use of a flame inside the burner exclusively during the kiln starting / heating phase) and for firing in flame mode, since the introduction element 18 does not appear to be completely immersed in the centre of the flame in any point.

[0141] In particular, the straight shape of the introduction element 18 avoids the narrowing 21 of the burner 1, thus making it possible to avoid being immersed inside the flame.

[0142] The use of a multi-stage combustion head 10, in combination with the fuel introduction element 18, allows the burner (also operating with pure hydrogen, namely with a 100% hydrogen fuel, in flameless mode) to reduce its NOx emissions below those produced by a common high-speed burner operating with methane gas. To this regard, the diagram of figure 10, which was obtained experimentally, shows the NOx emissions produced by the burner 1 operating with hydrogen I or with methane M, both in flameless mode and in flame mode, both with a curved introduction element 18 and with a straight introduction element 18.In particular, the NOx emissions are expressed in ppm on the ordinate axis and the capacity P of the burner is expressed in KW on the abscissa axis. Therefore, figure 10 evidently shows the development of the NOx emissions as a function of the variation of the capacity P.

[0143] In particular, it should be pointed out that, for the production of NOx, on average, hydrogen is largely worsening compared to methane, in fact the profile IF, indicating the use of hydrogen with flame firing mode, is the one that produces most NOx.

[0144] The profile MF, on the other hand, indicates the use of methane with flame firing mode and confirms that this firing mode emits more NOx pollutants compared to the flameless mode, although less than the corresponding mode using hydrogen as fuel (which, however, has the great advantage of not being a fossil fuel).

[0145] As shown by the profiles IFC and IFR, relating to flameless firing modes with hydrogen as fuel, namely IFC for the curved geometry and IFR for the straight geometry of the introduction element 18, respectively, the second one surprisingly generates a more than significant decrease in the production of NOx compared to the first one, making the subj ect-matter of this disclosure even more convenient compared to the prior art.

[0146] The same trend can also be observed when using methane with the profiles MFC and MFR, relating to the curved geometry according to the prior art and to the straight geometry of the introduction element 18, respectively.

[0147] Such an important decrease could be explained by the fact that, when using the curved geometry, namely with the introduction element 18 going through the opening 15, thefuel FL flowing out of the introduction element 18 during the flameless mode is immersed in the j et of oxidizer OX (ambient air) flowing out of the opening 15 of the tubular discharge element 11. In this way, the fuel FL easily combines with the oxidizer OX just introduced into the firing chamber 3, especially in the case of hydrogen as fuel, given its wide flammability range.

[0148] On the contrary, with the straight introduction element solution out of the the opening 15 from which the oxidizer flows out in flameless mode, the reduction in the production of NOx is further improved, probably due to the fact that the fuel also mixes with combustion fumes G that are already present in the firing chamber, which have, for example, 8-12% oxygen (and not 21% as the ambient air). Therefore, the combination with oxidizers with a lower percentage of oxygen presumably is the cause of such a significant improvement in the reduction of NOx.

[0149] In addition, it has been noted that the increase in the diameter of the narrowing 21 and / or the increase in the diameter of the fuel introduction element 18 lead a smaller impulse of the flame in the kiln chamber with a consequent smaller dilution of the flame with the fumes present. As a result, there is a significant increase in the formation of NOx. However, the NOx emissions, even in this case, remain much lower compared the architectures of common high-speed burners operating in flame mode with methane gas as fuel.

[0150] In addition, the synergistic effect of the multi-stage combustion head 10, the injection element 32 and the introduction element 18 permits to reach a flame speed of about 200 m / s and to evenly dilute the combustion in the flameless mode.Furthermore, the flameless combustion dilutes the temperatures (namely, it decreases the peaks, thus increasing the median) and increases the coefficient of convective exchange with the ceramic articles T. For this reason, compared to a traditional architecture and given the same power, this invention makes its possible to heat the material to a greater extent without “attacking” it with temperature peaks in the area of the flames and oxidizing the organic substances contained in the ceramic products in a more even manner, thus avoiding the appearance of a darker colouration in the inner portion of a sectioned article. In this way, the risk of bursting of the ceramic articles T in a pre-heating area of the kiln 2 is also partially inhibited, for example when articles with an excessive moisture content are fired.

[0151] Finally, thanks to the special conformation of the introduction element, the mixture M* without the flame front is generated downstream of the discharge element 11, thus reducing the problems related to the backfire of hydrogen and to detonations in case of flame front reformation.

Claims

C L A I M S1. A burner ( 1 ) for firing ceramic articles ( T ), which can be installed in an industrial kiln ( 2 ) comprising a firing chamber ( 3 );the burner ( 1 ) comprising: a mixing body ( 5 ) comprising, in turn, at least one duct ( 6 ) for supplying a fuel ( FL ) and at least one duct ( 7 ) for supplying an oxidi zer ( OX ); a spark device ( 8 ) for starting a combustion; a flame detection device ( 9 ); a first tubular discharge element ( 11 ), which is configured to be flown through by a fluid ( F) flowing out of the mixing body ( 5 ) and is provided with a first end ( 12 ), in which at least part of the mixing body ( 5 ) is inserted, and a second end ( 14 ), which is opposite the first end ( 12 ); wherein the first tubular discharge element ( 11 ) comprises, at the second end ( 14 ), a first open channel ( 60 ) for letting the fluid ( F) out of the first tubular discharge element ( 11 ); the first open channel ( 60 ) fluidly connects the inside and the outside of the first tubular discharge element;the burner ( 1 ) further compri sing an introduction element, which is configured to inj ect fuel ( FL ) downstream of the first tubular discharge element ( 11 );the burner being characterized in that the first tubular discharge element ( 11 ) comprises a second open channel ( 61 ), di f ferent from the first open channel ( 60 ), in which the introduction element is at least partly inserted.

2. The burner ( 1 ) according to claim 1, wherein the second open channel ( 61 ) is completely crossed by the introduction element.

3. The burner ( 1 ) according to claim 1 or 2, wherein the second open channel ( 61 ) is located at the second end ( 14 ) or proj ects from the second end ( 14 ).

4. The burner ( 1 ) according to any one of the preceding claims, wherein the introduction element ( 18 ) comprises a first tubular duct ( 19 ), which extends at least from the first end ( 12 ) to the second end ( 14 ), in particular which goes through the first tubular discharge element ( 11 ) from side to side.

5. The burner ( 1 ) according to claim 4, wherein the first tubular duct ( 11 ) extends asymmetrically relative to a longitudinal symmetry axis (AA) of the burner ( 1 ), in particular wherein the first tubular duct ( 19 ) at least partly extends parallel to a wall ( 20 ), in particular an inner wall, of the first tubular discharge element ( 11 ).

6. The burner ( 1 ) according to any one of the claims 4 or 5, wherein the first tubular duct ( 19 ) comprises at least a first portion ( 22 ) on the inside of the first tubular discharge element ( 11 ) and a second portion ( 23 ), downstream of the first portion towards the second end, inserted in the second open channel ( 61 ); in particular, the first tubular duct ( 19 ) also comprises a third portion proj ecting, on the outside of the first tubular discharge element ( 11 ), from the second open channel ( 61 ).

7. The burner ( 1 ) according to claim 6, wherein the first tubular duct ( 19 ) substantially is entirely straight.

8. The burner ( 1 ) according to any one of the claims from 4 to 7, wherein the first tubular duct ( 19 ) has an inner diameter of 10 mm or less, in particular 7 mm or less.

9. The burner ( 1 ) according to any one of the preceding claims, wherein the introduction element ( 18 ) comprises an end ( 25 ) proj ecting out of the first tubular discharge duct ( 11 ) from the second open channel ( 61 ) for a distance of 5 mm or more, in particular 10 mm or more.

10. The burner ( 1 ) according to any one of the preceding claims and comprising a first supply system (26) for the fuel (FL) connected to the supplying duct ( 6) for the fuel (FL) and a second supply system (27 ) for the fuel (FL), which is separate from the first supply system (26) for the fuel (FL) and is connected to the introduction element ( 18 ); in particular, the first supply system (26) for the fuel (FL) and the second supply system (27 ) for the fuel (FL) being capable of being selectively and / or independently operated; in particular, the first supply system (26) for the fuel (FL) and the second supply system (27 ) for the fuel (FL) are both connected to the different ducts ( 6, 6' ) obtained on a breech (29) of the mixing body (5).

11. The burner ( 1 ) according to any one of the preceding claims, wherein the mixing body (5) comprises both a fuel partitioning system (FPS) for the fuel (FL), which is configured to divide the fuel (FL) into a plurality of first portions (FL', FL' ’, FL' ’ ’ ), and an oxidizer partitioning system (OPS) for the oxidizer (OX), which is configured to divide the oxidizer (OX) into a plurality of second portions (OX', OX' ’, OX' ’ ’ ), which are conveyed so as be mixed with the first portions in at least two different stages.

12. The burner ( 1 ) according to any one of the preceding claims and further comprising at least one second tubular discharge element (38 ), which extends from the second end ( 14 ) towards the opposite side relative to the first end ( 12 ); and a suction element (39), which is configured to lead at least part of the gases (G) present on the outside of the burner ( 1 ) into the second tubular discharge element13. An industrial apparatus (50) for the firing of ceramic articles (T) comprising: a tunnel kiln (2 ) provided with at least one side wall (27 ), which at least partially delimits a firing chamber (3) and has an inner surface (51 ) on the inside of the firing chamber (3) and an outer surface (52 ) on the outside of the firing chamber (3); a transport system (4 ), which is configured to convey a plurality of ceramic articles (T) along a conveying path (P) inside the firing chamber (3);the apparatus (50) being characterized in that it comprises at least one burner ( 1 ) according to any one of the claims from 1 to 12; the industrial apparatus (50) comprising at least one hydrogen supplying system (S), which is configured to selectively inject hydrogen or a mixture comprising hydrogen into the fuel supplying duct ( 6) or into the introduction element ( 18 ).

14. The apparatus (50) according to claim 13, comprising at least one electronic control unit (53 ), which is configured to control the burner ( 1 ) so that it can operate both with a flame and in a flameless mode.

15. A method for firing ceramic articles (T) conveyed inside a tunnel kiln (2 ) and comprising the steps of:- supplying a burner ( 1 ) in particular according to any one of the claims from 1 to 12 with a fuel (FL) comprising at least a percentage of hydrogen exceeding 20%, in particular exceeding 50%, more in particular exceeding 70%, more in particular entirely hydrogen;simultaneously supplying said burner ( 1 ) with an oxidizer (OX) and sparking a flame at least partially inside the burner ( 1 ) and inside a firing chamber (3) of the tunnel kiln (2 );controlling said flame through feedback until a predefined temperature is reached inside the firing chamber (3);the method being characterized in that it comprises, once the firing chamber (3) has reached the predefined temperature, the further steps of:- putting out the flame by decreasing or stopping the supply of fuel (FL) to the fuel supplying duct ( 6) and, in particular, of oxidizer (OX) to the oxidizer supplying duct ( 7 ); and- introducing fuel (FL) into the introduction element ( 18 ) and, in particular, restoring the supply of oxidizer (OX), thus directly generating, inside the firing chamber (3), a mixture (M* ) determining a flameless combustion, which fires the ceramic articles (T).

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