Glass wool fiber stretch burner

Abstract

The invention relates to a burner (1) suitable for drawing glass fibres, comprising: a ring-shaped combustion chamber (2), bounded by a wall, preferentially made of refractory material, opening into an annular development slot (3), the direction of which is substantially parallel to the axis of the burner (1); and an injection system (4) with at least one injector (5), preferentially tubular, arranged to supply fuel and oxidizer in gaseous state to the combustion chamber (2), the burner (1) being characterised in that the injector (5) has at least one angular deflection element (51) suitable for generating a flow of oxidizer and / or fuel, which flow forms a swirl.

Description

[Technical field]

[0001] The present invention relates to a burner for use in a glass fiber forming process in which drawing of the fibers is accomplished by a high temperature, high velocity gas flow emitted by the burner alone or in combination with other means such as centrifugal means or die-type drawing means. [Background technology]

[0002] A fiber drawing method commonly used for the production of glass fibers is the method known as internal centrifugation. It consists in introducing a web of molten drawable material into a centrifuge, also called fiberizing spinner, which rotates at high speed. Such a fiberizing spinner may alternatively have a bottom, pierced at its periphery by a large number of orifices, through which the material is sprayed in the form of filaments under the action of centrifugal force. These filaments are then subjected by means of an annular-shaped burner to the action of a hot and high-velocity gas annular drawing flow (depending on the desired article, the temperature can reach 1000° C. and the speed is 250 m / s), which flows along the wall of the centrifuge, which attenuates the filaments and transforms them into fibers. For further details of fiber drawing methods using the internal centrifugation method, reference may be made to WO 99 / 065835 and WO 97 / 015532.

[0003] This method of fiber drawing of glass wool is distinguished from that commonly used for rock fibers, called external centrifugal fiber drawing method, in which the material to be fiber drawn is poured in the molten state onto the peripheral treads of rotating centrifuge wheels, accelerated by these wheels, leaves them and is partially converted into fibers under the effect of centrifugal forces, and a gas flow is released tangentially to the peripheral treads of the wheels, thereby picking up the fiber drawn material by separating it from the non-fiber drawn material and transporting it to a receiving member. For example, reference may be made to fiber drawing by external centrifugation in EP-A-0195725.

[0004] For glass wool fiber drawing, EP 0189354 discloses a glass fiber drawing burner having a ring-shaped combustion chamber bounded by a wall made of refractory material and opening into an annular deployment slot, the direction of which is substantially parallel to the axis of the burner.

[0005] It should be noted that burners of the type disclosed in EP 0189354, also shown in FIG. 1, have injectors opening in the bottom peripheral portion of the combustion chamber, thereby injecting a mixture of oxidizer and fuel gas. In the context of these burners, the fuel and oxidizer are therefore mixed before being introduced into the combustion chamber. This technical choice stems from the physical mechanisms involved in the stabilization of the burner flame. As shown in FIG. 2, FIG. 3 and FIG. 4, the stability of the flame mainly depends on two opposing velocities: on the one hand, the ejection velocity (uf) of the fuel / oxidizer mixed flow, and on the other hand, the flame displacement velocity (Sf). If these two velocities are balanced, as in FIG. 2, the flame is stable. In such a state, the flame can alternatively remain "hooked" to the injector or keep a certain distance from it. Conversely, if the flame speed (Sf) is greater than the fuel / oxidizer mixture speed (uf), as shown in Figure 3, the flame will move (Sd) towards the injector source and a risk of explosion, or at least injector damage, is inherent in such a situation. This is known as "flashback". In contrast, if the flame speed (Sf) is lower than the fuel / oxidizer mixture speed (uf), as shown in Figure 4, the flame will move away from the injector (Sd) and risk being extinguished, or in other words "blown out".

[0006] In this context, it has been observed that if the effective ratio of fuel mass to oxidizer mass is reduced by reducing the fuel concentration, the laminar burning velocity at the flame periphery also decreases. As a result, the combustion becomes unstable and thus the flame becomes more likely to become unstable. In other words, in the so-called "lean" combustion region, where the ratio of fuel mass to oxidizer mass is low compared to the known stoichiometric ratio, the flame becomes more susceptible to fluctuations.

[0007] However, there is a need to stabilize the burner flame, especially under lean conditions, thereby, inter alia, limiting fuel consumption / reducing greenhouse gas emissions.

[0008] Faced with this problem, those skilled in the art were prompted to develop an already known technical solution, known as the "bluff body", which is notably disclosed in EP 1474636. According to this concept, the combustion chamber is provided with at least one flame stabilisation element arranged close to the inner wall of the combustion chamber and to the expansion orifice, which flame stabilisation element constitutes a recirculation zone in which at least a part of the combustion between one or more oxidants and one or more fuels may be maintained, thereby stabilising the burner flame therein.

[0009] However, recent in-house observations by the inventors have highlighted the limitations of such "bluff body" solutions. As a result, certain flame instabilities remain, in particular linked to very high velocities of the fluid leaving the stabilizing element, which tend to blow out the flame, despite the compensation provided by the recirculation area located downstream of the stabilizing element. Furthermore, the stabilizing element needs to be formed inside the combustion chamber, which necessarily means additional technical production constraints. Finally, these stabilizing elements are subject to high thermal stresses and therefore have limited durability. Their replacement is furthermore technically complex and costly. Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, there is a need to further improve burner durability and flame stability. [Means for solving the problem]

[0011] The present invention meets this need and relates to a burner for drawing glass fibers, comprising: - a ring-shaped combustion chamber, bounded by a wall preferentially made of refractory material and opening into an annular expansion slot, the direction of which is substantially parallel to the axis of the burner; and - an injection system having at least one injector, preferentially tubular, arranged to supply fuel and oxidizer in gaseous state to the combustion chamber; The burner is characterized in that the injector has at least one angular deflection element suitable for generating a flow of oxidizer and / or fuel, which flow forms a swirl.

[0012] In this specification, "tubular" refers to an injector made of one or a series of coaxial hollow cylinders, the central cavity of which is the injection chamber opening onto the combustion chamber. Angular deflection refers to the injector modifying the trajectory of the oxidizer and / or fuel flow to make it form a swirl. The fuel can be liquid or gas. The oxidizer is selected from a non-limiting list, including air. A "swirl" flow is a helical flow with a non-negligible tangential (or azimuthal) component, which creates a pressure drop along the injector axis and creates an internal recirculation zone. As shown in FIG. 7, this internal recirculation zone allows the flame to remain near the injector exit. In fact, such a zone is characterized by a high level of negative axial velocity. Flame retention is further enhanced by the presence of a donut-shaped recirculation zone, which returns a portion of the burnt gases to the bottom of the combustion chamber, thus significantly preheating the fresh gases.

[0013] The flame is relatively stable and thus it is possible to reduce the amount of fuel (gas) injected into the combustion chamber without the risk of the flame blowing out. The burner according to the invention therefore allows a significant improvement in the combustion efficiency, especially in lean operation where the ratio of the amount of fuel (gas) to the amount of oxidant (air) is low. For the same heating capacity, the fuel consumption and the associated CO2 emissions are therefore reduced. Furthermore, the extended operating range of the burner provides a relatively high flexibility in the operating conditions for fiber drawing. This makes it possible to vary the diameter and / or length of the glass fibers.

[0014] Finally, since the improved flame stability is due solely to the aerodynamic recirculation motion occurring in the vicinity of the injector, the burner according to the invention has improved durability over time compared to "bluff body" type burners, and furthermore, unlike "bluff body" type burners, is compatible with the injection of a premix of fuel and oxidizer.

[0015] According to a particular embodiment, said angular deflection element has a swirl number S that satisfies the equation S=2 / 3tanΦ, Φ being the angle of angular deflection of the oxidizer and / or fuel flow after passing through the injector, said swirl number S being between 0.10 and 2.00, preferentially between 0.25 and 1.70, even more preferentially between 0.35 and 1.40, even more preferentially between 0.45 and 1.10, even more preferentially between 0.55 and 0.90, even more preferentially between 0.65 and 0.70.

[0016] The strength of the rotational motion of the flow is characterized by the value of the swirl number S at the injector exit. The swirl number S is a common expression for the ratio of the tangential momentum flow to the axial momentum flow and is defined as:

[0017]

number

[0018] where U and W are the axial and tangential components of the mean flow velocity, respectively, and Re is the radius.

[0019] In the context of the present invention, this swirl number S is approximated by the formula S=2 / 3 tan Φ, where Φ is the angle of angular deflection of the oxidizer and / or fuel streams after passing through the injector.

[0020] Increasing the value of the swirl number S reduces the flame height but tends to increase the flame opening. Advantageously, a wide flame opening can be employed to limit the number of injectors positioned around the periphery of the combustion chamber while still ensuring homogeneous heating of the combustion chamber.

[0021] According to a particular embodiment, said angular deflection element is a ring coaxial with respect to the injector, preferentially removable, and has at least one lateral duct adapted to allow the introduction of a swirling flow of oxidizer and / or fuel into the injection chamber of the injector with said angular deflection angle Φ, the value of which is preferably between 10° and 80°, even more preferentially between 20° and 70°, even more preferentially between 30° and 60°, even more preferentially between 40° and 50°.

[0022] According to this particular embodiment, the angle formed by the side ducts with respect to the normal to the circular cross section of the ring corresponds to the angular deflection angle Φ of the oxidizer and / or fuel streams used to calculate the swirl number S.

[0023] When this angle Φ tends towards values ​​of 0° and 90°, the swirl effect disappears and the flow velocity tends to be exclusively axial, thus influencing the swirl number S and therefore the flame structure. In contrast, when the value of this angle Φ tends towards 45°, the swirl effect increases, allowing optimal mixing of the fuel and the oxidizer. For the same amount of fuel to be burned, it is possible to reduce the amount of fuel injected.

[0024] The removable nature of the angle deflection ring means that it can be replaced relatively simply and at relatively low cost for maintenance purposes, thereby adapting the injector to new operating ranges.

[0025] According to an alternative embodiment, the angular deflection element may be a set of deflectors disposed within the injection chamber to rotate the oxidizer and / or fuel flow.

[0026] According to a particular embodiment, the injection system is adapted to supply said injectors separately with fuel, on the one hand, and with oxidizer, on the other hand.

[0027] The risk of flame instability disclosed above tends to make those skilled in the art hesitate to implement separate supply of fuel and oxidizer to current injectors. In the context of current injectors, mixing of fuel and oxidizer only in the injection chamber is only partial and does not guarantee satisfactory combustion efficiency and flame stability. However, it has been determined that the injector according to the invention allows a relatively fast and relatively efficient mixing of fuel and oxidizer by a high level of turbulence compared to conventional injectors. Since the proportion of fuel required for ignition and combustion is reduced, it is possible to further reduce the concentration of the fuel (gas) and inject it separately from the oxidizer (air).

[0028] This type of separate injection protects against the risk of flashback in the absence of an oxidizer / fuel mixture upstream of the injector and allows the oxidizer (air) to be preheated before injection, thereby improving the combustion efficiency and lowering the flammability (ignition) limit of the mixture. It therefore allows a further reduction in fuel consumption, which in turn reduces the emissions of combustion gases (carbon dioxide). It should be noted that such preheating is prohibited in the context of premixing of fuel and oxidizer, due to the risk of explosion.

[0029] According to a particular embodiment, the injector has a central duct adapted to inject a flow of fuel along the injector axis, and an oxidizer flow is intended to flow through the deflection element.

[0030] The central fuel injection ensures optimal mixing of the oxidizer (air) and fuel (gas) flows. According to a particular embodiment, such a central duct extends at least partially into the injection chamber of the injector.

[0031] According to a particular embodiment, the outer surface of the upstream portion of said central duct is frustum-shaped, the diameter of said outer surface decreasing along the jet direction over this portion.

[0032] This frustum shape prevents the boundary layer from breaking away from the swirling flow, thereby reducing the risk of undesirable turbulence.

[0033] In a particular embodiment, the injector outlet is located within the injection chamber at a distance of 0-45 mm from the point of entry of the oxidizer and fuel injection streams into the combustion chamber.

[0034] Beyond this range of values, the flow losses become too great due to the strength of the oxidizer swirling flow. Conversely, as this distance approaches zero, in other words as the injector outlet approaches the combustion chamber, the central duct undergoes excessive wear due to its proximity to the inside of the combustion chamber of the burner and the heat it generates. Thus, preferentially, the distance between the injector outlet and the entry point into the combustion chamber of the oxidizer and fuel injection flows is greater than 5 mm, even more preferentially greater than 10 mm, even more preferentially greater than 15 mm and even more preferentially greater than 20 mm.

[0035] According to a particular embodiment, the cross section of the injector outlet is perpendicular to the injector axis.

[0036] The inventors have found that cutting the injector at an angle at the gas outlet, as is done in the art, tends to oppose the swirling circulation of the oxidizer / fuel mixture, thus reducing the beneficial technical effects associated therewith. In contrast, cutting the injector tip to have a cross section perpendicular to the burner axis produces a relatively stable flame that takes full advantage of the benefits of swirling injection.

[0037] According to certain embodiments, the entry point of the oxidizer and fuel jets into the combustion chamber is located proximate to the center of the combustion chamber wall furthest from the burner axis.

[0038] The wall furthest from the burner axis corresponds to the peripheral wall of the combustion chamber. Taking into account the usual shape of an annular combustion chamber, the inlets thus arranged in the combustion chamber for said jet flows of oxidizer and / or fuel are substantially equidistant from the upper and lower walls of the combustion chamber, which makes it possible to obtain a relatively homogeneous and stable flame, especially taking into account the gas flows circulating in said combustion chamber.

[0039] According to a particular embodiment, the entry point of the injection streams of oxidizer and fuel into the combustion chamber has a cross-sectional diameter adapted based on a desired flame stabilization distance.

[0040] The diameter of the outlet section affects the flow velocity. The smaller the cross-sectional area, the higher the velocity and the greater the flame stabilization distance. The flame is then called "lift". Above a certain velocity, the flame is "blown out". Conversely, the larger the cross-sectional area, the smaller the velocity of the ejection. Below a certain velocity, there is a risk of the flame stabilizing inside the fireproof wall, which should be avoided.

[0041] According to a particular embodiment, the injection system has a crown for distributing a flow of oxidizer and / or fuel to the at least one injector, the crown being preferentially fed via a number of inlets uniformly distributed around the circumference of the crown, the number of inlets being even more preferentially equal to the number of injectors.

[0042] The use of such a distribution crown ensures even distribution of the gas flow within the injector. The increased number of inlets around the circumference of the crown helps to promote this even distribution.

[0043] The invention also relates to a method for producing glass fibres, characterized in that it uses at least one burner as disclosed above.

[0044] According to a particular embodiment, the manufacturing method implements at least one burner, the injection system being adapted to supply separately to said injector a fuel on the one hand and an oxidizer on the other hand, said manufacturing method comprising a step of supplying separately to the injector a fuel on the one hand and an oxidizer on the other hand, and a preceding step of preheating said fuel, preferentially at least partially by gases resulting from the combustion.

[0045] Preheating the fuel increases the combustion efficiency and reduces the flammability (ignition) limits of the fuel / oxidizer mixture. Using gases for this purpose that are at least partially derived from combustion and thus already heated reduces the overall energy consumption of the melting and fiber drawing process. Since fuel consumption is reduced in relative terms, such preheating also reduces pollutant emissions.

[0046] The invention also relates to the glass fibres obtainable by carrying out such a manufacturing process.

[0047] The present invention also relates to a method of controlling a burner as disclosed above, said method comprising a step of controlling the flow of oxidizer and / or fuel based on measured / estimated temperature and / or pressure values, preferentially collected inside the combustion chamber.

[0048] The burner according to the invention makes it possible to vary the temperature and / or pressure parameters over a wider range than known burners.

[0049] The present invention also relates to a computer program downloadable from a communications network and / or recorded on a recording medium suitable for being read by a computer and / or executed by a processor, the computer program comprising instruction codes for implementing such a control method.

[0050] The program may be in any programming language and may be in the form of source code, object code, or a code intermediate between source code and object code, such as a partially compiled form.

[0051] The invention also covers a computer recording medium on which such a computer program is recorded. The recording medium may be any object or device capable of storing a program. For example, the medium may comprise a storage means, such as a read-only memory, a rewritable non-volatile memory, such as a USB stick, an SD card, an EEPROM, or even a magnetic recording means, such as a hard disk. The recording medium may also be an integrated circuit in which the program is embedded, this circuit being designed to perform or to be used to perform the method. The recording medium may be a transmissible medium, such as an electrical or optical signal, which may be transmitted by electrical or optical cable, by radio or by other means. The program according to the invention may be downloaded, in particular via an Internet-type network.

[0052] The present invention also relates to a fiber drawing installation comprising one or more burners as disclosed above.

[0053] Further features and advantages of the invention will become apparent from the following description of particular embodiments, given purely as illustrative and non-limiting examples, and from the accompanying drawings, in which: [Brief description of the drawings]

[0054] [Figure 1] FIG. 1 is a schematic cross-sectional view of a burner known from the state of the art;

[0055] [Diagram 2] FIG. 2 is a schematic diagram of the ejection velocity (uf) of the flow of the fuel / oxidizer mixture in the duct on the one hand and the flame displacement velocity (Sf) on the other hand. [Diagram 3] FIG. 3 is a schematic illustration of the ejection velocity (uf) of the flow of the fuel / oxidizer mixture in the duct on the one hand and the flame displacement velocity (Sf) on the other hand. [Figure 4] FIG. 4 is a schematic illustration of the ejection velocity (uf) of the flow of the fuel / oxidizer mixture in the duct on the one hand and the flame displacement velocity (Sf) on the other hand.

[0056] [Diagram 5] FIG. 5 is a schematic cross-sectional view of a burner according to the invention.

[0057] [Figure 6] FIG. 6 is a perspective view of an injector according to the present invention.

[0058] [Figure 7] FIG. 7 is a schematic cross-sectional view of an injector according to the present invention, with the oxidizer / fuel flows shown as thin dashed lines.

[0059] [Figure 8] FIG. 8 is a perspective view of three injection rings having angular deflection angles of 45°, 30°, and 20°, respectively.

[0060] [Figure 9] FIG. 9 is a perspective view of the combustion / fuel flow distribution crown.

[0061] [Figure 10] FIG. 10 is a graphical representation of fuel to oxidizer equivalence ratio values ​​based on changes in angular deflection angle and injector exit cross-sectional geometry.

[0062] [Figure 11] FIG. 11 is a pictorial representation of estimated fuel gain values ​​based on oxidizer preheat temperature.

[0063] [Figure 12] FIG. 12 is a graphical representation of estimated reduction in pollutant gas emissions based on oxidizer preheat temperature.

[0064] [Figure 13] FIG. 13 is a graphical representation of the variation of fuel flammability limits based on oxidizer preheat temperature. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] The various elements shown in the figures are not necessarily drawn to scale, with emphasis instead being placed on illustrating the general operation of the invention. In the various figures, unless otherwise indicated, the same reference numbers represent similar or identical elements.

[0066] Below are given some specific embodiments of the invention, it being understood that the invention is in no way limited to these specific embodiments, and other embodiments are entirely possible.

[0067] According to a particular embodiment, as illustrated by FIG. 5, a burner 1 according to the invention comprises: - a ring-shaped combustion chamber 2, bounded by a wall preferentially made of refractory material and opening into an annular expansion slot 3, the direction of which is substantially parallel to the axis of the burner 1; and an injection system 4 having at least one injector 5, preferentially tubular, arranged to supply fuel and oxidizer in gaseous state for the combustion 2;

[0068] In particular, such a burner 1 according to the invention has an injector 5 provided with at least one angular deflection element 51 adapted to generate a flow of oxidizer and / or fuel, which flow forms a swirl.

[0069] According to a particular embodiment, and as shown in more detail by Figures 6 and 7, said angular deflection element 51 is a ring coaxial with the injector 5 and has at least one lateral duct 511 adapted to enable the introduction of a swirling flow of oxidizer into the injection chamber 52 of the injector 5 at an angular deflection angle Φ, which is formed by the lateral duct relative to the normal to the circular cross section of the ring.

[0070] According to this particular embodiment, this angular deflection angle Φ is 45°. The corresponding swirl number S is 0.67, which optimizes the mixing of the fuel and the oxidizer and reduces the amount of fuel injected for the same amount of oxidizer.

[0071] In alternative embodiments, this angle may be other values. By way of example and not limitation, Figure 8 is a perspective view of three injection rings having angular deflection angles of 45°, 30°, and 20°, respectively.

[0072] According to another embodiment of the invention not shown, the angular deflection element may be a set of deflectors arranged within the injection chamber to rotate the oxidizer and / or fuel flow.

[0073] According to the particular embodiment shown in Figures 6 and 7, said injector 5 has a central duct 53, which extends partially into the injection chamber 52 of the injector and is adapted to inject a flow of fuel along the axis X of the injector 5, and an oxidizer flow is intended to flow through said deflection element 51.

[0074] According to the embodiment shown in Fig. 5, the injection system 4 of the burner 1 has, on the one hand, a supply of fuel gas, for example in the form of methane, which is injected via a central duct 53. On the other hand, it has a separate supply 42 of oxidizer, for example in the form of air, which is introduced into the injector via a lateral duct 511 of the injection ring 51 according to a swirl flow, i.e. a flow moving with a spiral motion with a non-negligible tangential component (also known as the azimuthal component). The entire mixture is generated in the injection chamber 52 before being discharged into the combustion chamber 2 of the burner 1. By way of example, in Fig. 7 the oxidizer / fuel flows are shown with thin dashed lines.

[0075] This separate supply of fuel on the one hand and oxidizer on the other protects against the risk of flashback in the absence of an oxidizer / fuel mixture upstream of the injector and makes it possible to preheat the oxidizer (air) before injection, thereby improving combustion efficiency, reducing pollutants and lowering the flammability (ignition) limits of the mixture, as disclosed below in connection with Figures 11, 12 and 13.

[0076] In certain embodiments, the air is at least partially preheated by recovering heat from combustion gases produced by burners, glass melting furnaces (e.g., via a heat exchanger), and / or any other heat source generated during the glass wool production process.

[0077] It should be noted that the present invention is not limited to a particular selection of fuel and / or oxidant. Thus, the fuel may be in liquid or gas form, and the oxidant is selected from a non-limiting list including oxygen and air.

[0078] As shown in figure 5, said injection system 4 comprises a crown 41 for distributing the oxidizer and / or fuel flow to said at least one injector 5. This crown 41 is shown in more detail in figure 9 and is advantageously fed via a number of inlets 411, which are evenly distributed around the circumference of said crown 41, thereby allowing a homogeneous distribution of the fuel flow within the injectors.

[0079] According to an alternative embodiment of the invention, not shown, the injector does not have a central duct or the central duct is closed, the fuel / oxidizer mixture then being introduced upstream of the injector exclusively via the injection ring.

[0080] Once the fuel / oxidizer is mixed, this mixture is injected into the combustion chamber 2 of the burner 1 through a cross-sectional outlet. Considering the swirling nature of the flow injected into the combustion chamber 2, a pressure drop occurs along the injector axis, creating an internal recirculation zone. As shown in FIG. 7, this internal recirculation zone allows the flame to remain near the injector exit. In fact, such a zone is characterized by a high level of negative axial velocity. The flame retention is further enhanced by the presence of a toroidal recirculation zone, which returns a portion of the burned gases to the bottom of the combustion chamber, in this way the fresh gases are significantly preheated. As the flame is relatively stable, it is possible to reduce the amount of fuel (gas) injected into the combustion chamber without the risk of flame blowout, as disclosed below in connection with FIG. 10.

[0081] As shown in FIG. 5, the entry point 21 of the oxidizer and fuel jet into the combustion chamber 2 is located close to the center of the combustion chamber 2 wall furthest from the burner axis, i.e., the center of the perimeter wall of the combustion chamber 2. This results in a relatively homogeneous and stable flame, especially considering the gas flow circulating within the combustion chamber. The entry point 21 is also located close to the center of the combustion chamber 2 wall (approximately 1200 nm s) to help stabilize the flame at the entrance to the chamber 2. 3 / h fuel and oxidizer flow rates, and 15 mm cross-sectional diameter.

[0082] During combustion, sensors inside the chamber 2 collect pressure and temperature measurements to facilitate control of the burner 1, particularly by varying the injection rates of the oxidizer and / or fuel streams.

[0083] Conventionally, fumes resulting from the combustion of a fuel / oxidizer mixture are exhausted through a spreading slot 3 of the annular burner in a direction substantially parallel to the axis of the burner 1, thereby drawing and / or attenuating the glass fibers exiting the fiber drawing spinner.

[0084] In one embodiment, a portion of these fumes are used to preheat the oxidant (air) before it is introduced into the burner injector 1 .

[0085]

number

[0086] Qv: Volumetric flow rate

[0087] m_:mass flow rate

[0088] (m_fuel / m_oxidizer) theoretical value = 0.1

[0089] The tests are carried out at atmospheric pressure and temperature in a combustion laboratory on a test bench that reproduces the conditions of flame combustion in a ring burner. The objective of the test is to determine the stability limits of the injector. This is achieved by setting the gas (fuel) flow rate and gradually increasing the air (oxidizer) flow rate until an unstable flame is obtained. The ratio of fuel flow rate to oxidizer flow rate is then measured.

[0090] To evaluate the effect of the injector exit cross section geometry, a first series of tests is performed with an injector according to the invention, as shown in Figures 5 to 7, with a vertical exit cross section, and a second series of tests is performed with an injector according to the invention, but with an exit cross section oblique at an angle of 15° to the X-axis of the injector. For each of these series of tests, the injector is tested with three types of injector rings, with angular deflection angles of 20°, 30° and 45° respectively.

[0091] These tests show that for an injector with a straight cross section, the fuel to oxidizer ratio is close to 3.00 at an angle of 20° and decreases as the deflection angle varies from 20° to 45°, reaching a minimum of 1.3 at 45°. The flame is most stable at this value, which makes it possible to reduce the amount of fuel (gas) injected into the combustion chamber without risk of flame blow-through or flashback. The burner according to the invention can therefore significantly improve the combustion efficiency, especially in lean operation, where the ratio of the amount of fuel (gas) to the amount of oxidizer (air) is low. For the same heating capacity, fuel consumption and therefore CO2 emissions are reduced.

[0092] For an injector with an oblique exit cross section, the fuel to oxidizer ratio is close to 1.80 at an angle of 20° and increases as the deflection angle varies from 20° to 45°, reaching a value of 3.50 at 45°.

[0093] It has been observed that for an angle value of 20°, the performance of the oblique injector is better than that of an injector with a vertical profile section. This is because at this angle value of 20°, the flow swirl effect, and therefore the mixing of the oxidizer and fuel, is low, which limits the performance of the vertical cross-section injector. The oblique shape generates a velocity gradient at its end, which appears to enhance the mixing of the oxidizer and fuel, resulting in relatively good performance at low angles.

[0094] However, this oblique profile has the negative effect of countering the swirl effect induced by the injector, which, when this swirl effect becomes relatively strong, adversely affects the performance of the oblique injector.

[0095] As a result, for angle values ​​of 30° and 40°, the injector with a vertical profile cross section performs better than the oblique injector, especially at 45°, where the performance of the oblique injector is significantly worse.

[0096] Thus, the first experimental protocol identifies that a vertical exit cross section injector with a 45° deflection angle provides the best performance in terms of flame stabilization.

[0097] According to the second experimental protocol, the results of which are shown in Figure 11, the value of the fuel gain (natural gas) is estimated based on the preheat temperature of the oxidizer (air).

[0098] According to this protocol, the burner is considered as a black box and the power balance is done by applying the first principle of thermodynamics (conservation of energy). In other words, the combustion is studied holistically from reactants to articles without considering the reaction mechanism.

[0099] According to the first principle of thermodynamics, the total energy stored by a control volume is the sum of the power it receives thermally, mechanically, and from the energy supplied by the molecules.

[0100] In the context of the present invention, the following assumptions are taken into account: - No energy is stored in the combustion chamber. - There are no moving mechanical parts to do work. - Kinetic and potential energy are ignored compared to the internal energy of the gas.

[0101] Heat losses through the walls are estimated to be 10% of the energy released during the reaction, or 10% of the gross calorific value (GCV).

[0102]

number

[0103] Here, h s m and h e m are the output and input molar enthalpies, respectively.

[0104] Enthalpy is a function of temperature only. Knowing the output enthalpy of the combustion gases, it is possible to infer the temperature of these gases.

[0105] The enthalpy of the products is calculated from this equation to determine the temperature at which the products of the reaction have the same enthalpy.

[0106] Once the final temperature is set, then the gain of combustion compared to preheating the reactants is determined.

[0107] The results obtained show that as the preheat temperature increases, the fuel to oxidizer ratio decreases, thus improving the energy efficiency of the burner.

[0108] According to the third experimental protocol, the results of which are shown in FIG. 12, the reduction in polluting gas emissions (carbon dioxide) is estimated based on the preheat temperature of the oxidant (air).

[0109] The chemical reaction equation for methane combustion with air can be written as follows for complete combustion: CH4 + 2O2 → 2H2O + CO2.

[0110] This means that for every cubic metre of methane burned, 1m 3 This means that carbon dioxide is released.

[0111] The results obtained show that as the preheating temperature increases, the emission of polluting gases (carbon dioxide) decreases.

[0112] FIG. 13 is a pictorial diagram showing the variation of the flammability limits of the fuel (natural gas) based on the preheat temperature of the oxidizer (air).

[0113] For a fire to spread, the layer next to the burning gas needs to be at a certain temperature so that it can burn faster. If the gas is heated to a high temperature, less heat is provided by the burning layer. The flammability limit is relatively low. Empirically, there is a linear relationship between the flammability limit and the initial temperature. The following empirical formula, used by the INRS (Institute of National Safety), defines the safe value of the flammability limit L at temperature t as a function of the limit L0 at a reference temperature T0:

number

[0114] The results show that the flammability limit becomes relatively lower as the preheat temperature increases.

[0115] The numerical values ​​disclosed herein are not to be understood as being strictly limited to the numerical value recited. Instead, unless otherwise specified, each numerical value specifies both the exact recited value and a range of functionally equivalent values ​​encompassing that value.

[0116] Although particular embodiments of the present invention have been shown and described, it is apparent that various other changes and modifications can be made within the spirit and scope of the present invention. Accordingly, the present text intends to cover all such changes that fall within the scope of the present invention within the scope of protection defined by the appended claims.

Claims

1. A burner (1) suitable for stretching glass fibers, wherein the burner is as follows: - A ring-shaped combustion chamber (2), which is partitioned by walls, preferably made of fire-resistant material, and opens into an annular unfolding slot (3), in a direction substantially parallel to the axis of the burner (1); and, - An injection system (4) having at least one injector (5), which is preferably tubular and arranged to supply fuel and oxidizer in a gaseous state to the combustion chamber (2), It has, The burner (1) is characterized in that the injector (5) has at least one angular deflection element (51), the angular deflection element (51) is suitable for generating a flow of oxidizer and / or fuel, and the flow forms a swirl. Burner (1).

2. The burner (1) according to claim 1, wherein the angular deflection element (51) has a swirl number S that satisfies the formula S = 2 / 3 tanΦ, where Φ is the angular deflection angle of the flow of the oxidizer and / or fuel after passing through the injector, and the swirl number S is 0.10 to 2.00, preferably 0.25 to 1.70, more preferably 0.35 to 1.40, more preferably 0.45 to 1.10, more preferably 0.55 to 0.90, and more preferably 0.65 to 0.

70.

3. The burner (1) according to claim 2, wherein the angular deflection element (51) is a ring coaxial with respect to the injector (5), is preferably removable, and has at least one lateral duct (511) adapted to allow the introduction of a swirl flow of oxidizer and / or fuel into the injection chamber (52) of the injector (5) having the angular deflection angle Φ, wherein the value is preferably 10° to 80°, more preferably 20° to 70°, more preferably 30° to 60°, and more preferably 40° to 50°.

4. The burner (1) according to claim 1 or 2, wherein the injection system (4) is adapted to supply fuel to the injector (5) separately and an oxidizer to the other.

5. The burner (1) according to claim 4, wherein the injector (5) has a central duct (53) adapted to inject a flow of fuel along the axis (X) of the injector (5), and the flow of the oxidizer is intended to flow through the deflection element (51).

6. The burner (1) according to claim 5, wherein the outer surface of the upstream portion of the central duct (53) is frustum-shaped, and the diameter of the outer surface decreases along the injection direction in this portion.

7. The burner (1) according to claim 5, wherein the outlet of the injector (5) is located inside the injection chamber (52) at a distance of 0 to 45 mm from the entry point (21) of the injection flow of oxidizer and fuel into the combustion chamber (2).

8. The burner (1) according to claim 1 or 2, wherein the injector (5) has an outlet cross section perpendicular to the axis of the injector.

9. The burner (1) according to claim 1 or 2, wherein the entry point (21) of the injection flow of oxidizer and fuel into the combustion chamber (2) is located close to the center of the wall of the combustion chamber (2) that is furthest from the axis of the burner.

10. The burner (1) according to claim 1 or 2, wherein the entry point (21) of the oxidizer and fuel injection flow into the combustion chamber (2) has a cross-sectional diameter adapted based on a desired flame stabilization distance.

11. The burner (1) according to claim 1 or 2, wherein the injection system (4) has a crown (41) for distributing a flow of oxidizer and / or fuel to at least one injector (5), the crown being supplied via a plurality of inlets (411) which are preferably uniformly distributed around the circumference of the crown (41), and the number of inlets (411) is more preferably equal to the number of injectors (5).

12. A method for producing glass fibers, using at least one burner (1) as described in claim 1 or 2.

13. A method for manufacturing glass fibers, comprising the step of using at least one burner (1) as described in claim 4, and supplying fuel to the injector (5) separately on one side and an oxidizer on the other side, wherein the manufacturing method comprises a prior step of preheating the fuel, preferably using gases produced from at least partial combustion.

14. Glass fibers obtained by carrying out the manufacturing method described in claim 12.

15. A method for controlling a burner (1) according to claim 1 or 2, wherein the method includes the step of controlling the flow of an oxidizer and / or fuel based on measured / estimated temperature and / or pressure values, preferably collected inside the combustion chamber (2).

16. A computer program, which is downloadable from a communication network and / or recorded on a recording medium suitable for reading by a computer and / or for executing by a processor, comprising instruction code for carrying out the control method described in claim 12.

17. A fiber stretching apparatus comprising one or more burners as described in claim 1 or 2.

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