Combustor and method of forming flame in furnace by means of combustor

Abstract

The invention provides a combustor. The combustor comprises a combustor frame and a combustion head, a primary gas tube for supplying gaseous fuel to the furnace, which extends inside the combustion head in the longitudinal direction of the combustion head, the orifices of which open into or close to the furnace, a primary air supply tube also extending inside the combustion head and surrounding the primary gas tube; a flow duct for main combustion air extends inside the combustion head and surrounds the primary air supply pipe at least inside the end portion; and a set of main gas rods for supplying fuel to the furnace, arranged at least partially outside the cylindrical body of the combustion head, extending near the junction between the cylindrical body and the end portion such that they surround the body at equal intervals about the circumference thereof; a number of injector conduits associated with the primary gas rod are provided at an end portion of the combustion head for recirculating flue gas from the furnace into the gaseous fuel from the primary gas rod and further delivering the resulting flue gas-fuel mixture to the furnace.

Description

Technical Field

[0001] The invention relates to a burner for forming a flame in a furnace by means of a gaseous fuel and combustion air and for simultaneously recirculating flue gases in the furnace according to the preamble of claim 1.

[0002] The invention also relates to a method for forming a flame in a furnace by means of a burner according to claim 1 according to the preamble of claim 21 .

[0003] The invention also relates to a burner-boiler assembly, in which a burner frame of a burner as defined in claim 1 is installed in a boiler.

[0004] The present invention relates to a burner whose operation is based on internal recirculation of flue gases. Internal recirculation of flue gases is the process of recirculating the flue gases produced by combustion back to the bottom of the flame. The purpose of internal recirculation of flue gases in the furnace is to reduce the nitrogen oxides produced by combustion and to enhance the cooling of the combustion head. Background Art

[0005] The applicant's own published application FI 20215192 discloses a burner in which internal recirculation of flue gases in the furnace is used to reduce the nitrogen oxides produced by combustion. However, this burner has some disadvantages. For example, the distribution of the staged primary combustion air for combustion is achieved by means of a guide plate, which may interfere with the formation of the flame. Summary of the invention

[0006] The object of the present invention is to reduce or at least alleviate the problems existing in the prior art and to further reduce the amount of nitrogen oxides generated by the use of burners by more effective internal recirculation of the flue gases.

[0007] The above objects are achieved by a burner for forming a flame in a furnace by means of gaseous fuel and combustion air with simultaneous recirculation of flue gases according to claim 1 and by a corresponding method for forming a flame in a furnace by means of a burner as defined in claim 1.

[0008] More precisely, the invention relates to a burner for forming a flame in a furnace by means of gaseous fuel and combustion air and for simultaneously recirculating flue gases in the furnace according to claim 1. The burner comprises:

[0009] - a burner frame and a burner head, which is connected to the burner frame by its cylindrical body, wherein a first end of an end portion of the burner head facing the furnace extends into the furnace and a second end of the end portion is connected to said cylindrical body;

[0010] a primary gas pipe for supplying gaseous fuel to the furnace, which extends inside the burner head in its longitudinal direction, in particular inside the end portion of the burner head, and whose orifice opens into the furnace or into the vicinity of the furnace, and a primary air supply pipe also extends inside the burner head, around said primary gas pipe, and whose orifice opens into the furnace or into the orifice of the end portion of the burner head;

[0011] - For main combustion air (I 主 ) which extends inside the burner head and surrounds the primary air supply pipe at least inside the end portion; and

[0012] - a set of primary gas rods, comprising a set of elongated primary gas rods extending in the longitudinal direction of the burner head, for supplying fuel to the furnace, wherein the primary gas rods are at least partially arranged outside the cylindrical body of the burner head, extending close to the junction between the cylindrical body and the end portion, so that they surround the body at regular intervals around the circumference of the body.

[0013] Furthermore, a plurality of injector ducts associated with the primary gas sticks are provided in the end portion of the burner head for recirculating flue gases from the furnace to the gas fuel from the main gas sticks and for conveying the resulting mixture of flue gases and fuel further to the furnace.

[0014] The end portion of the burner head is truncated conical and comprises injector pipes and air pipes alternately arranged in the circumferential direction of the end portion, the free ends of these pipes are open in the direction of the furnace, and the top end of the pipe groove of each injector pipe is also open in the direction of the furnace, and the lower end of the pipe groove of each air pipe is also open in the direction of the central axis of the burner head, wherein the truncated conical end portion expands at an angle of 3 to 30 degrees from the direction of the joint between the cylindrical body of the burner head and the end portion of the burner head.

[0015] In the method according to the invention, a flame is formed in a furnace by means of a burner as defined in claim 1 with gaseous fuel and combustion air, while simultaneously recirculating the flue gases.

[0016] - to form the primary flame, primary gas is supplied to the primary gas pipe via its portion on the burner frame side, and primary air is also supplied through a primary air supply pipe extending inside the burner head and leading to the furnace; and

[0017] - To form the main flame, a main combustion air flow is conveyed from the interior of the burner head to the furnace, and a main gas flow is conveyed via the main gas sticks, wherein the main gas is conveyed into each main gas stick via the part of the main gas stick on the burner frame side, wherein the flue gas from the furnace is mixed into the main gas flow via the injector duct at the orifice of the end part of the burner head. The flame generated in the furnace, which is formed by the primary flame and the main flame, and the distribution of the fuel, the combustion air and the internally recirculated flue gas at the orifice of the burner head, which is achieved by the shape of the burner head, result in an inert return flow of flue gas with a low content of oxygen and unburned fuel components.

[0018] If natural gas is used as fuel, the carbon monoxide content in the inert return flow to the area of ​​the burner head is less than 5000 ppm and the methane content is less than 5000 ppm. The oxygen content in the return flow depends on the overall air coefficient. The oxygen content is on average less than 5 wt% (weight percentage) and the overall air coefficient λ is 1.15.

[0019] The invention also relates to a burner-boiler assembly, wherein the frame of the burner as defined in claim 1 is mounted in the boiler so that the combustion head of the burner extends into the furnace. 2 ), that is, the fuel power (kW) of the burner relative to the cross-sectional area (m 2 ) not more than 10,000kW / m 2 .

[0020] The invention is based on the idea that the orifice of the burner head in the shape and structure of a truncated cone at the end portion of the burner provides secondary and tertiary flows of the main combustion air, and the alternation of the injector ducts and the air ducts at the orifice of the burner in the circumferential direction thereof. This in turn leads to an effective staging of the combustion and a main flame at which the main gas is burned in such a way that the return flow of the flue gases is as inert as possible and the amount of nitrogen oxides produced during the combustion of the main gas is also as small as possible. When the return flow of the flue gases is effectively mixed with the main gas via the injector ducts at the orifice of the burner head, the amount of nitrogen oxides during combustion can be effectively reduced and the temperature of the burner head can be lowered.

[0021] By the design of the burner head and by internal recirculation of the flue gases, in particular in the case of natural gas, nitrogen oxide emission levels of even below 2.5 ppm (per normal cubic meter, dry, meaning 3% residual oxygen) can be achieved without external recirculation of the flue gases.

[0022] Inert recirculation of flue gases refers to flue gas compositions whose fuel contents are so low that they cannot provide significant combustion power and whose oxygen content is as low as possible.

[0023] The backflow of flue gas refers to the flow of flue gas outside the diameter of an approximately cylindrical burner head, wherein the velocity component of the flue gas flow in the axial direction of the burner head extends in the opposite direction to the velocity component of the fluid flow (air flow + air flow) from the burner head in the axial direction of the burner head.

[0024] The frustoconical orifice of the burner head and the alternation of the injector duct and the air duct in the end portion of the burner head and in particular on the circumference of the orifice of the burner head lead to a distribution of the air for the primary gas combustion into the secondary and tertiary air flows. By staging the secondary and tertiary air flows, it is possible to optimize the temperature of the flame and provide the desired combustion rate in various conditions of use and furnaces.

[0025] The primary air and the primary gas are introduced into the furnace together through the primary nozzle, and in the dual fuel burner, the liquid fuel is supplied to the burner through the oil inlet. Through the primary air and the primary gas, a primary flame is generated to achieve stable combustion.

[0026] In one embodiment of the invention, the burner further comprises an air injector connected to the flow duct for the main combustion air and arranged to absorb the fumes from the furnace.

[0027] Preferably, the orifices of the flue gas ducts of the air injectors are arranged uniformly in the end portion of the burner head over the entire flow area (B) of the main combustion air, and the structure of each air injector is arranged so that the respective air injector is able to absorb at least 0.3% of the flue gas into the main combustion air (l 主 ), this is calculated based on the total amount of main combustion air passing through the injector in a given time period (wt-% / wt-%).

[0028] Flue gases can be conveyed from the furnace to the air injector via openings in a row of openings arranged in the region of the body of the burner head defined by the set of main gas sticks. These openings in the body of the burner head are at regular intervals around the body of the burner head and lead to the flue gas duct of the air injector.

[0029] With such an air injector a mixing ratio between flue gas and air is achieved which ensures that the maximum temperature of the air-flue gas mixture downstream of the air injector is below 500° C. In a preferred embodiment of the invention the maximum temperature of the air-flue gas mixture inside the burner head is below 300° C.

[0030] Air injectors of the above type connected to the main air duct further promote the recirculation of the flue gases, enabling further reduction of the nitrogen oxide level and good cooling of the combustion head. For a more detailed structure of the air injectors, reference is made to the prior art, such as the applicant's own published application FI 20215192. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Hereinafter, the present invention and the advantages achieved thereof will be described in more detail with reference to the accompanying drawings.

[0032] Figure 1 A schematic perspective view of a combustion head of a burner according to the invention is shown.

[0033] Figure 2A A schematic diagram showing a longitudinal section of a frame of a burner according to the invention and a burner head connected thereto is shown.

[0034] Figure 2B A schematic top view of a burner head according to an embodiment of the present invention is shown.

[0035] Figure 2C Shows Figure 2B Schematic diagram of the front view of the combustion head.

[0036] Figure 3 A schematic diagram showing a flame formed by gas fuel and combustion air discharged from the orifices of a burner head. DETAILED DESCRIPTION

[0037] In the following, we will first briefly discuss Figures 1 to 3 Some aspects of the invention are shown in each case as well as the structural and functional characteristics of the burner shown in the figures.

[0038] Figure 1 and Figure 2A A burner 1 according to the invention is shown for forming a flame F in a furnace 3 using a gaseous fuel G and combustion air (I). To form the flame, flue gases S which are as inert as possible are recirculated in the furnace 3 .

[0039] Figure 1 A burner head 2 of a burner is shown, comprising a body 20 of the burner head 2 to which a frustoconical end portion 21 of the burner head 2 is connected.

[0040] Figure 2A A furnace 3 is shown in which a burner 1 is mounted in an intermediate wall 31. The burner frame 1a is shown on the left side of the intermediate wall 31 and the body 20 of the burner head is shown on the right side of the intermediate wall 31.

[0041] Figure 2AA longitudinal section of a burner in a furnace 3 is shown, showing a burner frame 1a of the burner 1 and a burner head 2 connected thereto and extending into the furnace 3. The burner head 2 comprises a cylindrical body 20, to which an end portion 21 in the shape of a truncated cone is connected and extends into the furnace 3. The portion of the end portion 21 on the furnace 3 side constitutes an orifice 25 leading into the furnace 3. The conical end portion 21 is connected to the cylindrical body 20 at a joint L extending around the body 20.

[0042] The burner head 2 is provided with a set of main gas rods 6, including a plurality of slender main gas rods 6 1 , 6 2 …6 n , used to supply fuel to furnace 3.

[0043] exist Figure 2A , the portion of the main gas rod 6 supplied with the main gas G2 is marked as the portion 6a of the main gas rod 6 extending on the burner frame 1a side. Correspondingly, the portion of the main gas rod 6 protruding into the furnace 3 is marked as the portion 6b of the main gas rod 6 extending on the furnace 3 side. The main gas rod 6 extends in the longitudinal direction of the burner. Figure 1 The main gas rod 6 is shown 1 , 6 2 …6 n How to extend at least partially outside the body 20 of the burner head 2 and how to be connected to the cylindrical body 20 of the burner in such a way that they extend around said body 20 at regular mutual distances in the circumferential direction of the body 20 .

[0044] The group of main gas rods 6 extends into the furnace 3 through the intermediate wall 31 separating the furnace 3 from the burner body 20, and each main gas rod 6 1 , 6 2 …6 n The furnace 3 side portion 6b extends in the longitudinal direction of the body 20 of the burner head 2 (= in the direction of the center line P of the burner head 2) to a distance from the intermediate wall 31. Preferably, the main gas rod 6 extends close to the junction L between the cylindrical body 20 and the end portion 21.

[0045] A plurality of main gas rods 6 are provided in the end portion 21 of the burner head 2. 1 , 6 2 …6 n An associated ejector duct (8; 81) is used to recirculate the flue gas S from the furnace 3 to the gas fuel (G; G2) coming from the main gas stick 6 and to convey the resulting flue gas-fuel mixture (S+G2) further to the furnace 3.

[0046] The end portion 21 of the combustion head 2 of the burner 1 is in the shape of a truncated cone and comprises an injector duct 81 opening in the direction of the furnace 3 and an air duct 82 opening in the direction of the interior T of the end portion 2 of the burner head, the injector duct 81 and the air duct 82 alternating in the circumferential direction of said end portion 21 (see in particular Figure 1 ).

[0047] The end portion 21 of frustoconical shape expands at an angle of 3 to 30 degrees, seen from the junction L between the cylindrical body 20 of the burner head 2 and the end portion 21 of the burner head 2. This expansion of the end portion of the burner head is shown by the angle C, which is measured as the distance from the center line P of the burner head to the bottom of the air duct 82 in the axial direction of the end portion of the burner head. At the junction L, the distance from the center line P of the burner head to the bottom 82d of the groove of the air duct is 3% to 30% smaller than this distance between the center line of the burner head and the bottom of the groove measured at the orifice 25 of the end portion 21.

[0048] Each injector duct 81 also opens at the top of the duct groove 81f facing the furnace 3, and each air duct 82 also opens at the bottom of the duct groove 82f towards the central axis P of the burner head, ie towards the interior T of the end portion.

[0049] Preferably, one primary gas injector conduit 81 is provided for each primary gas stick 6 .

[0050] like Figure 2A As shown in the cross-sectional view of , the burner 1 also includes a primary gas pipe 10 for supplying gas fuel (G; G1) to the furnace 3. The primary gas pipe 10 extends inside the burner head 2 in its longitudinal direction, in particular inside T of the end portion 21 of the burner head 2. The orifice of the primary gas pipe 10 opens into the furnace 3 or close to the furnace 3, such as into the orifice 25 of the end portion. An inlet pipe 14 for primary air also extends around the primary gas pipe 10 inside the burner head 2. The orifice of the primary air inlet pipe 14 opens into the furnace 3 or into the orifice 25 of the end portion 21 of the burner head 2.

[0051] The main combustion air (I) used in the burner 2 主 ) extends inside the burner head 2 and surrounds the primary air inlet pipe 14 at least in the interior T of the end portion 21 .

[0052] In a preferred embodiment of the present invention, the primary flame F1 can be generated by supplying liquid fuel for the primary flame along a channel extending inside the primary tube 14. The supply of this liquid fuel is provided by a cross-sectional Figure 2A Indicated by the mark "Oil" in the figure.

[0053] The main gas G2 is supplied to the injector duct 81 along the main gas rod 6. Separate gas inlets and controls are provided for the primary gas GA and the main gas G2, respectively, so that the ratio between these gases can be optimized for each application to achieve good flame stability and the highest possible efficiency of the injector duct 81.

[0054] Figure 2A Also shown is a stabilizer 9, which is used to form the primary flame close to the combustion head and keep it burning under all operating conditions. This achieves a safe and stable combustion.

[0055] The primary gas nozzles 11 and the oil nozzles 12 may be positioned upstream and / or downstream of the stabilizer.

[0056] Figure 2B and Figure 2C A more detailed view of the structure in which the injector ducts 81 and the air ducts 82 alternate in the circumferential direction of the end portion 21 of the burner head 2 is shown.

[0057] Figure 2B An embodiment of the invention is shown, with the burner head 2 being depicted from above. Figure 2B Four main gas rods (6; 6 1 , 6 2 , 6 3 and 6 4 ) (As shown in FIG. 2 , a total of eight rods are provided in the burner head 2 ). These main gas rods (6; 6 1 , 6 2 , 6 3 and 6 4 ) extends from the intermediate wall 31 on the shell 20d of the body 20 in the direction of the center line 9 of the burner head to the joint L between the body 20 and the end portion 21. The injector pipe 81 of the end portion 21 extends from each main gas rod (6; 6 1 , 6 2 , 6 3 and 6 4 ) extends from the end of the ejector pipe 81, and the air duct 82 is arranged on both sides of the ejector pipe 81.

[0058] Figure 2C The burner head 2 is then shown directly from the front, ie from the direction of the orifice 25. FIG. 2 shows eight main gas rods (6; 6 1 ,6 2 ...6 8 These main gas rods (6; 6 1 , 6 2 …6 8 ) extends from the shell 20d of the body 20 of the burner head 2 to the joint L between the body 20 and the end portion 21, as shown in FIG. Figure 2Cshown.

[0059] The ejector conduit 81 of the end portion 21 extends from each main gas rod (6; 6 1 , 6 2 , 6 3 and 6 8 ) extends from the end of the end portion 21, while the air duct 82 is arranged on both sides and is open in the direction of the center line P of the combustion head, that is, leading to the interior T of the end portion 21.

[0060] like Figure 2B to Figure 2C As shown, and partly as Figure 1 As shown, each injector pipe 81 at the end portion 21 of the burner head 2 comprises a groove bottom 81d in the longitudinal direction of the burner head 2, wherein groove walls 81b or 81c extend upwardly from the groove bottom 81d on both sides, i.e. away from the longitudinal center axis P of the burner head 2. The pipe groove 81f of the injector pipe 81 left between these groove walls 81b, 81c is open at its top facing the furnace 3.

[0061] Figure 1 It is shown how each injector pipe 81 extends substantially parallel to the main gas rod 6, which terminates at the upstream end of the corresponding injector pipe, i.e., at the intermediate wall side. However, when the groove bottom 81d is viewed from the junction L between the cylindrical body 20 of the burner head and the end portion 21 of the burner head 2, the groove bottom 81d of the injector pipe 81 at the end portion 21 of the burner head 2 is inclined downwardly, i.e., in the direction of the longitudinal center axis P of the burner head 2, at an angle X of about 3 to 20 degrees, extending around the burner head 2. The main gas jet from the main gas rod 6 is directed to the injector pipe 81 at an angle D that is the same as or different from the inclination angle X of the groove bottom 81d.

[0062] When the injector pipe 81 is viewed from the joint L1 between the injector pipe 81 and the body 20 toward the free end 81d1 of the groove bottom 81d of the injector pipe 81 facing the furnace 3, the groove bottom 81d of the injector pipe 82 at the end portion 21 of the burner head 2 tapers or has a constant width.

[0063] In addition, when the injector pipe 81 is viewed from the joint L1 between the cylindrical body 20 of the burner head 2 and the injector pipe, the groove bottom 81d of the injector pipe 81 at the end portion 21 of the burner head 2 is flush with the shell 20d of the cylindrical body 20 at the joint L1 between the injector pipe 81 and the cylindrical body 20 of the burner head 2.

[0064] The groove walls 81b, 81c of the injector pipe 81 at the end portion 21 of the burner head 2 extend obliquely upwards from the groove bottom 81d of the injector pipe 81, i.e. away from the center line of the burner head, towards the furnace 3. The planes extending through the groove walls 81b, 81c of the injector pipe 81 are arranged at an angle A of 1 to 30 degrees to each other.

[0065] The width of the pipe groove 81f of the injector pipe 81 at the end portion 21 of the burner head 2, measured at the joint L1 between the groove bottom 81d of the injector pipe 81d and the cylindrical body 20, is 0.2 to 1 times the length of the circumference of the shell 20d of the cylindrical body 20 divided by the number n of the injector pipes 81 at the end portion 21 of the burner head 2.

[0066] When the width of the pipe groove 81f is measured at the joint L1 between the groove bottom 81d of the injector pipe 81 and the cylindrical body 20, the length of the pipe groove 81f of each injector pipe 81 is 3 to 15 times the width of the same pipe groove 81f of the injector pipe 81.

[0067] In the above, the injector ducts 81 at the end portion of the burner head 2 have been discussed. The air ducts 82 are provided on both sides of each injector duct 81. The groove walls 81b, 81c of each injector duct 81 at the end portion 21 of the burner head 2 simultaneously constitute the groove walls 82b, 82c of two adjacent air ducts 82. In the following, particular reference will be made to Figure 1 , Figure 2B and Figure 2C The structure and function of these air ducts are discussed in more detail.

[0068] Each air duct 82 at the end portion 21 of the burner head 2 includes a groove bottom 82d in the longitudinal direction of the burner head 2, wherein groove walls 82b, 82c extend downward from the groove bottom 82d on both sides. The duct groove 82f of the air duct 82 formed between the groove walls 82b, 82c is open toward the interior T of the end portion 21 of the burner head 2, surrounding the central axis P of the burner head 2 at the end portion 21.

[0069] When the air duct 82 is viewed from the junction L between the cylindrical body 20 and the end portion 21, the groove bottom 82d of each air duct 82 at the end portion 21 of the burner head 2 extends upward, i.e., away from the longitudinal center axis P of the burner head, at an angle of 3 to 30 degrees, and surrounds the burner head 2. The inner portion T of the end portion 21 around the longitudinal center line (P; P2) of the burner head 2 is expanded so that the distance S between the groove bottom 82d of each air duct 82 at the end portion 21 of the burner head 2 and the longitudinal center line P of the burner head 2 is 3% to 30% larger at the end of the groove bottom 82 of the air duct 82 on the furnace side than at the junction L1 between the groove bottom 82d of the same air duct 82 and the cylindrical body 20 of the burner head 2.

[0070] The burner 1 may further include an air injector 9, which is connected to the body 20 of the burner head 2 to inject the main combustion air. 主 The burner head 2 is associated with a flow duct which is provided for taking in flue gases from the furnace 3. The air injectors 9 at the body 20 of the burner head 2 and the injector duct 82 at the end portion 21 of the burner head 2 are arranged relative to each other in such a way that, seen in the direction of the orifice 25 of the end portion 21 of the burner head 2, the position for feeding the flue gases S into the injector duct 82 is upstream of the opening for the air injectors 9 in the body 20.

[0071] The flue gas S can be delivered to the air injectors 9 via a flue gas duct from a longitudinal region B of the body 20 of the burner head 2, where the main gas stick 6 extends to the outside of the body 20 of the burner head 2 in the furnace 3. Each air injector 9 is arranged to absorb at least 1% of the flue gas into the main combustion air (I 主 ), which is calculated based on the total content of the main combustion air (wt-% / wt-%).

[0072] Furthermore, the amount of flue gas absorbed into the main combustion air by the air injector 9 is adjusted so that the maximum temperature of the air-flue gas mixture in the flow direction of the air-flue gas mixture (I+S) downstream of the air injector 9 is below 500°C, preferably below 300°C.

[0073] At least one opening is provided for each air injector 9 in the frame, and the openings for the air injectors 9 in the air injector group arranged in the frame and connected to the flue gas duct constitute a row of 6 to 60 openings, which surround the burner head 2 at the same distance from a vertical plane extending through the orifice 25 of the burner head 2.

[0074] Each air injector 9 comprises one or more partially hollow blades including an inlet-side blade arranged to steadily accelerate the flow of combustion air I thereon.

[0075] In the following, we will discuss Figure 2A and Figure 3 , to illustrate the operation of the burner and the formation of flame F and backflow.

[0076] Figure 3 The formation of the flame produced by the burner according to the invention and the recirculation of the flue gases are shown. In the method according to the invention, the burner 1 according to the invention is used to form a primary flame F1 and a main flame F2 by means of a gas fuel (G) and combustion air (I), thereby recirculating the flue gases S simultaneously.

[0077] By adjusting the ratio between secondary air Is and tertiary air It and the ratio between primary gas and main gas appropriately, a uniform flame can be formed. Figure 3 shown. Figure 3 It is shown how the main flame F2 and the primary flame F1 merge to form the flame F and during the combustion a return flow P is formed which is an inert return flow PI at the combustion head.

[0078] Via the set of main gas rods 6, a first amount of gas fuel can be supplied to the furnace 3 for forming the main flame F2 through the secondary air Is and the tertiary air It; via the primary gas pipes 10, a second amount of gas fuel can be supplied to the furnace 3 for forming the primary flame F1. The amount of primary gas supplied to form the primary flame F1 and the amount of main gas supplied to form the main flame are mutually adjusted so that the main flame F2 and the primary flame F1 will merge.

[0079] This provides an effective combustion staging and a main flame F2, in which the main gas is burned so that the return flow P of the flue gas is a return flow PI that is as inert as possible. In addition, during the combustion of the main gas itself, the formation of nitrogen oxides is minimized as much as possible. Through the design of the burner head and the internal recirculation of the flue gas, it is possible to achieve nitrogen oxide emission levels even below 2.5 ppm (per standard cubic meter, dry, referring to 3% residual oxygen) without external recirculation of the flue gas, especially in the case of natural gas.

[0080] In order to form the primary flame F1, the primary gas G1 is supplied to the primary gas pipe 10 via the portion 10a of the primary gas pipe 10 on the burner frame 1a side. In addition, the primary air Ip is also supplied via the primary air inlet pipe 14, which extends inside the burner head 2 and leads to the furnace 3. The primary flame F1 can also be generated by supplying liquid fuel.

[0081] In order to form the main flame F2, the main combustion air flow (I 主 ) is delivered from the interior of the burner head 2 to the furnace 3, and the primary gas flow G2 is delivered via the primary gas rod 6 1 , 6 2 …6 n The main combustion air (I 主 ) flows inside the body 20 and the end 21 of the burner head 2, but flows outside the primary air inlet pipe 14.

[0082] The main gas G2 is introduced into each main gas rod 6 via a portion 6a of the main gas rod on the burner frame 1a side. 1 , 6 2 …6 n In this case, the flue gas S is mixed with the main gas G2 flow by the main gas injector 8. The flame (F; F1+F2) formed by the primary flame F1 and the main flame F2 in the furnace causes a flue gas recirculation PI (S) which is as inert as possible. 惰性 ). In the case of natural gas combustion, when the flue gas reflux PI (S 惰性 ) enters the combustion head area, its carbon monoxide content is less than 5000 ppm and its methane content is less than 5000 ppm. The oxygen content of the reflux depends on the total air coefficient. When the total air coefficient λ is 1.15, the average oxygen content is less than 5 wt-%.

[0083] As described above, the main gas G2 flow can be passed through the main gas rod 6 1 , 6 2 …6 n The flue gas S is thus delivered from the furnace 3 to each of the main gas sticks 6 in the group of main gas sticks 6 by means of the main gas injectors 8. 1 , 6 2 In the main gas G2 flowing in ..., each main gas rod 6 1 , 6 2 ... an ejector duct 81 is provided. The flue gas S is delivered to each main gas stick 6 through an ejector duct 81 arranged in association with (downstream of) each main gas stick. 1 , 6 2 …into the main gas G2 flowing in the main gas stick portion 61 on the burner frame 1 a side. The flue gas S from the furnace 3 and the main gas G2 flowing in the main gas stick 62 enter each injector pipe 81 .

[0084] The main combustion air (I 主 ) includes the area formed between the primary air inlet pipe 14 and the body 20 of the combustion head 2.

[0085] By the structure and dimensions of the injector duct 81 and the air duct 82 at the end portion 21 and by the conical shape of the end portion 21, the main combustion air flow (I 主 ) is divided into a secondary air flow Is and a tertiary air flow It at the end portion 21 of the burner head 2 (see Figure 2A ).

[0086] In the furnace 3 , the flue gases S flow to the root of the flame F, from where they are delivered via the injector duct 81 to the gas fuel (G; G2 ) flowing in the second portion 6 b of the main gas stick 6 .

[0087] like Figure 2A As shown, the main combustion air I 主 At the end portion of the combustion head, it is divided into tertiary air It and secondary air Is. The tertiary air constitutes the main combustion air I supplied to the furnace 3. 主 5 vol-% (volume percentage) to 50 vol-%, preferably 5 vol-% to 40 vol-%, and the secondary air I S The main combustion air (I 主 ), preferably 60 vol-% to 95 vol-%.

[0088] The burner may include an air injector 9, such as Figure 2A As shown. A group of air injectors includes a plurality of elongated air injectors 9. The main combustion air (I 主 ) is forced through the set of air injectors. Each air injector 9 comprises a flue gas duct having two orifices leading from the body 20 of the burner head 2 to the flue gas duct of the furnace 3, these orifices of the flue gas duct being oriented in opposite directions as seen from the inside of the flue gas duct.

[0089] Each air injector 9 comprises one or more partially hollow blades. The air injector 9, which is composed of one or more blades, comprises an inlet side blade, which is arranged to steadily accelerate the main combustion air (I 主 The inlet-side blade extends into the flue gas duct and downstream of the flue gas duct, the same or different blade extends as an outlet-side blade, which is arranged to steadily decelerate the flow of the air-smoke mixture (S, I) on the outlet-side blade.

[0090] When the main combustion air (I 主) as it flows along the inlet-side blades towards the flue gas duct. The static pressure of the combustion air-smoke mixture (I+S) increases as the mixture flows along the outlet-side blades away from the flue gas duct. In the area B of the body 20, at least one opening, preferably two openings, is provided for each air injector 9 of the group of air injectors. The openings of the flue gas ducts of the air injectors 9 arranged in the frame and connected to the group of air injectors form a row of 6 to 60 openings, which surround the burner head 2 at the same distance from the vertical plane extending through the orifice 25 of the burner head 2.

[0091] Therefore, the main combustion air at the end portion 21 is divided into the tertiary air I t and secondary air I s Previously, the flue gas S (combustion gas) from the furnace 3 could be mixed with the main combustion air (I 主 ). Thus, the flue gases S can be conveyed from the furnace 3 to each air injector 9 of the group of air injectors through an opening in a row of openings in a region B of the body 20 of the burner head 2 at least partially defined by the group of main gas sticks 6, the openings of the body leading to the flue gas duct of the air injector 9, thereby mixing the main combustion air (I 主 ) in the entire flow area B to stably deliver the flue gas S to the main combustion air (I 主 ).

[0092] The air injector 9 has the following characteristics: it is able to absorb at least 0.3% of the flue gas into the main combustion air for each mbar static pressure loss produced by the injector, calculated on the basis of the total content of the main combustion air (wt-% / wt-%). 主 ). Preferably, the air injectors 9 are arranged to absorb at least 0.3%, preferably at least 1%, of the flue gas into the main combustion air for each mbar static pressure loss produced by the injectors 9, calculated on the basis of the total content of the main combustion air passing through the entire set of air injectors (wt-% / wt-%). 主 ). For a more detailed structure of these air injectors, reference may be made to the prior art, such as the applicant's own published application FI 20215192.

[0093] Reference numerals list

[0094] Burner 1

[0095] Burner frame 1a

[0096] Combustion head 2

[0097] Ontology 20

[0098] Housing 20d

[0099] End portion 21

[0100] Orifice 25 Furnace 3

[0101] Intermediate wall, furnace flange 31 Main gas inlet 4 Primary air inlet 5 Main gas stick set 6

[0102] Main gas stick 6 1 , 6 2 …6 n Main gas nozzle 7 Main gas injector 8

[0103] Injector pipe 8a

[0104] Free end 81a

[0105] Groove walls 81b, 81c Groove bottom 81d

[0106] Pipeline groove 81f Air pipe (for main gas) 82

[0107] Free end 82a

[0108] Groove walls 82b, 82c Groove bottom 82d

[0109] Pipeline groove 82f Air Injector 9

[0110] Primary gas pipe 10

[0111] Primary gas nozzle 11

[0112] Injector 12

[0113] Primary air supply pipe 14

[0114] Combustion head body area A

[0115] In the body of the burner,

[0116] Area B of the main combustion air flow in the air injector Once Flame F1

[0117] Main flame F2

[0118] Gas G

[0119] Primary gas G1

[0120] Main gas G2

[0121] Main gas + flue gas mixture G2 + S

[0122] Combustion air I

[0123] Primary air IP

[0124] Main combustion air I 主

[0125] Secondary AirIs

[0126] Three air It

[0127] Center axis P

[0128] Flue gas S

[0129] Internal T of the end section

Claims

1. A burner (1) for forming a flame (F) into a furnace (3) by means of a gaseous fuel (G) and combustion air (I) while recirculating flue gases (S) in the furnace (3), wherein: The burner (1) comprises: - a burner frame (1a) and a burner head (2), the burner head (2) being connected to the burner frame (1a) via its cylindrical body (20), wherein an end portion (21) of the burner head (2) facing the furnace (3) extends at its first end to the furnace (3) and a second end of the end portion (21) is connected to the cylindrical body (20), a primary gas pipe (10) for supplying gaseous fuel (G; G1) to the furnace (3), wherein the primary gas pipe (10) extends in the longitudinal direction of the burner head (2) inside the burner head, in particular inside (T) the end portion (21) of the burner head, and the orifice of the primary gas pipe (10) opens into or is close to the furnace (3), and a primary air supply pipe (14) also extends inside the burner head (2) and around the primary gas pipe (10), and the orifice of the supply pipe (14) opens into the furnace (3) or into the orifice (21) of the end portion (21) of the burner head (2), - flow duct for the main combustion air (I 主 ), and extending inside the burner head and surrounding the primary air supply pipe (14) at least inside (T) the end portion (21), and - a set of primary gas rods (6), comprising a set of elongated primary gas rods (6) extending in the longitudinal direction of the burner head 1 , 6 2 …6 n ), for supplying fuel to the furnace (3), wherein the main gas rod (6 1 , 6 2 …6 n ) are at least partially arranged outside the cylindrical body (20) of the burner head (2), extending close to the junction (L) between the cylindrical body (20) and the end portion (21), so that they surround the body (20) at equal intervals around the circumference of the body (20), And wherein, a plurality of gas rods (6) are provided at the end portion (21) of the burner head. 1 , 6 2 …6 n ) associated with an injector duct (8; 81) for recycling the flue gases (S) from the furnace (3) into the gas fuel (G; G2) from the main gas rod and for conveying the resulting flue gas-fuel mixture (S+G2) further to the furnace (3), Characterized in that the end portion (21) of the burner head (2) has a truncated cone shape and includes an injector pipe (81) and an air pipe (82), the injector pipe (81) and the air pipe (82) are alternately arranged in the circumferential direction of the end portion (21), the free ends (81a, 82a) of the pipes (81, 82) are open in the direction of the furnace (3), and the top end of the pipe groove (81f) of each injector pipe (81) is also open in the direction of the furnace (3), and the lower end of the pipe groove (82f) of each air pipe (82) is also open in the direction of the central axis (P) of the burner head (2), wherein, viewed from the direction of the joint (L) between the cylindrical body (20) of the burner head (2) and the end portion (21) of the burner head (2), the end portion (21) in the truncated cone shape expands at an angle of 3 to 30 degrees.

2. The burner (1) according to claim 1, characterized in that The injector pipe (81) at the end portion (21) of the burner head (2) includes a groove bottom (81d) along the longitudinal direction of the burner head (2), wherein groove walls (81b, 81c) extend upward from the groove bottom (81d) on both sides, and a pipe groove (81f) of the injector pipe (81) formed between the groove walls (81b, 81c) is open at its top facing the furnace (3).

3. The burner (1) according to claim 2, characterized in that When the groove bottom (81d) is viewed from the joint (L) between the cylindrical body (20) of the burner head and the end portion (21) of the burner head (2), the groove bottom (81d) of the injector pipe (81) at the end portion (21) of the burner head (2) extends downward at an angle of 3 to 20 degrees, that is, extends toward the longitudinal center axis (P) of the burner head (2), and surrounds the burner head (2).

4. The burner (1) according to claim 2 or 3, characterized in that The groove bottom of the injector pipe (81) at the end portion (21) of the burner head (2) tapers or has a constant width in a direction from the joint (L) between the cylindrical body (20) of the burner head (2) and the groove bottom (81d) of the injector pipe (81) at the end portion (20) of the burner head (2) toward the free end (81d1) of the groove bottom (81d) of the injector pipe (81) facing the furnace (3).

5. The burner (1) according to claim 3 or 4, characterized in that The groove bottom (81d) of the injector pipe (81) at the end portion (21) of the burner head (2) is flush with the shell (20d) of the cylindrical body (20) at the joint (L1) between the injector pipe (81) and the cylindrical body (20) of the burner head (2).

6. The burner (1) according to any one of claims 2 to 5, characterized in that The groove walls (81b, 81c) of the injector pipe (81) at the end portion (21) of the burner head (2) extend upwardly inclined from the groove bottom (81d) of the injector pipe (81), i.e. away from the center line of the burner head, toward the furnace (3), so that the planes extending through these groove walls (81b, 81c) are arranged at an angle A of 1 to 30 degrees to each other.

7. The burner (1) according to any one of claims 2 to 6, characterized in that The width of the pipe groove (81f) of the injector pipe (81) at the end portion (21) of the burner head (2), measured at the joint (L1) between the groove bottom (81d) of the injector pipe (81) and the cylindrical body (20), is 0.2 to 1 times the length of the circumference of the shell (20d) of the cylindrical body (20) divided by the number (n) of the injector pipes (81) at the end portion (21) of the burner head (2).

8. The burner (1) according to any one of claims 2 to 7, characterized in that The length of the pipe groove (81f) of each injector pipe (81) is 3 to 15 times the width of the same pipe groove (81f) of the injector pipe (81) measured at the joint (L1) between the groove bottom (81d) of the injector pipe (81) and the cylindrical body (20).

9. The burner (1) according to claim 1, characterized in that Each air duct (82) at the end portion (21) of the burner head (2) comprises a groove bottom (82d) along the longitudinal direction of the burner head (2), wherein groove walls (82b, 82c) extend downward from the groove bottom (82d) on both sides, i.e., extend in the direction of the center line (P) of the burner head, wherein the duct groove (82f) of the air duct (82) formed between the groove walls (82b, 82c) is open toward the interior (T) of the end portion (21) of the burner head (2), surrounding the center axis (P) of the burner head (2) at the end portion (21).

10. The burner (1) according to any one of claims 2 to 9, characterized in that The groove walls (81b, 81c) of each injector duct (81) at the end portion (21) of the burner head (2) simultaneously constitute the groove walls (82b, 82c) of two adjacent air ducts (82).

11. The burner (1) according to claim 9 or 10, characterized in that When the groove bottom (82d) of the air duct (82) is viewed from the joint (L) between the cylindrical body (20) and the body (21), the groove bottom (82) of each air duct (82b) at the end portion (21) of the burner head (2) extends upward at an angle of 3 to 30 degrees, that is, extends away from the longitudinal center axis (P) of the burner head, and surrounds the burner head (2).

12. The burner (1) according to any one of claims 9 to 11, characterized in that The interior (T) of the end portion (21) around the longitudinal center line (P) of the burner head (2) is expanded so that the distance (S) between the groove bottom (82d) of each air duct (82) at the end portion (21) of the burner head (2) and the longitudinal center line (P) of the burner head (2) is 3% to 30% larger at the end of the groove bottom (82d) of the air duct (82) on the furnace side than at the joint (L1) between the groove bottom (82d) of the same air duct (82) and the cylindrical body (20).

13. The burner (1) according to claim 1, characterized in that The main gas rod (6) extends into the furnace (3) through a flange (31) located between the furnace (3) and the burner frame, and extends along the longitudinal direction of the cylindrical body (20) of the burner head (2) to the joint (L1) between the body (20) of the burner head and the bottom (81d) of the injector pipe (81) at an end portion (21) of the burner head (2) at a certain distance from the flange (31).

14. The burner (1) according to claim 1, characterized in that The burner (1) further comprises an air injector (9) which is connected to the main combustion air (I) in the body (20) of the burner head (2). 主 ) is arranged in association with the flow channel of the furnace (3) and is arranged to absorb flue gases from the furnace (3).

15. The burner (1) according to claim 14, characterized in that The air injector (9) in the body (20) of the burner head (2) and the injector duct (81) at the end portion (21) of the burner head (2) are arranged relative to each other so that, seen from the direction of the orifice (25) of the end portion (21) of the burner head (2), the position for supplying flue gas (S) to the injector duct (82) is upstream of the opening to the air injector (9) in the body (20).

16. The burner (1) according to claim 15, characterized in that Flue gas (S) can be delivered to each air injector (9) via a flue gas duct of the air injector (9) from an area (B) in the longitudinal direction of the body (20) of the burner head (2), in which area (B) the main gas rod (6) extends in the furnace (3) outside the body (20) of the burner head (2).

17. The burner (1) according to claim 14, characterized in that Each air injector (9) is arranged to absorb at least 1% of the flue gas into the main combustion air (1) for each millibar static pressure loss produced by the injector 主 ), which is calculated based on the total content of the main combustion air (wt-% / wt%).

18. The burner (1) according to any one of claims 14 to 17, characterized in that The content of flue gas to be absorbed into the main combustion air by each air injector (9) is further adjusted so that, in the flow direction of the air-flue gas mixture (I+S), the maximum temperature of the air-flue gas mixture downstream of the air injector (30) is below 500°C, preferably below 300°C.

19. The burner (1) according to any one of claims 14 to 18, characterized in that At least one opening is provided for each air injector (9) in the body, and the openings provided for the air injectors in the air injector group in the body and connected to the flue gas duct form a row of 6 to 60 openings, which surround the body (20) of the burner head (2) at the same distance from a vertical plane extending through the orifice (25) of the burner head (2).

20. The burner (1) according to claim 14, characterized in that Each air injector (9) comprises one or more partially hollow blades, said blades comprising an inlet side blade, said inlet side blade being arranged to steadily accelerate the flow of combustion air (I) on said inlet side blade, wherein said inlet side blade extends into the flue gas duct of said air injector (9), and downstream of said flue gas duct, the same or a different blade extends as an outlet side blade, said outlet side blade being arranged to steadily decelerate the flow of an air-flue gas mixture (S, I) on said outlet side blade.

21. A method for forming a flame (F; F1, F2) into a furnace (3) by means of a burner (1) as defined in claim 1, with the aid of a gas fuel (G) and combustion air (I) and simultaneously recirculating the flue gases (S); wherein In order to form the primary flame (F1), primary gas is supplied into the primary gas pipe (10) via a portion (10a) of the primary gas pipe (10) on the burner frame (1a) side, and primary air (Ip) is also supplied by means of a primary air supply pipe (14) extending inside the burner head (2) and supplied into the furnace (3), and In order to form the main flame (F2), the main combustion air (I 主 Is+It) is transported from the inside of the burner head (2) to the furnace (3) and is fed through the main gas rod (6 1 , 6 2 ...6 n ) delivers the flow of the main gas (G2), thereby delivering the main gas (G2) to each main gas rod (6) via the portion (6a) of the main gas rod on the burner frame (1a) side. 1 , 6 2 ...6 n ), wherein the flue gases (S) from the furnace (3) are mixed into the flow of the main gas (G2) by means of an injector duct (81) at the orifice of the end portion of the burner head (2), characterised in that the flame (F; F1+F2) generated in the furnace and formed by the primary flame (F1) and the main flame (F2) and the distribution of the fuel, combustion air and internally recirculated flue gases at the opening of the burner head obtained by the shape of the burner head result in an inert recirculation (PI) of flue gases with a low oxygen content and unburned fuel components.

22. The method according to claim 21, wherein: The main gas (G2) is methane and wherein, when the total air factor λ is 1.15, the inert return (PI) of the flue gases returning to the region of the burner head (2) in the furnace contains less than 5000 ppm of carbon monoxide, less than 5000 ppm of methane and has an average oxygen content of less than 5 wt-%.

23. The method according to claim 21, characterized in that The inert flue gas (PI) is delivered to an injector duct (81) associated with the main gas stick (6).

24. The method according to claim 21, characterized in that When the injector pipe (81) is viewed from the joint between the cylindrical body (21a) and the orifice (21b), the main gas jet from the main gas rod (6) is directed from the main gas rod (6) to the injector pipe (81) at an angle (D) downward, i.e., at an angle toward the longitudinal axis of the burner head, and the angle (D) is in the same direction or in a different direction from the inclination angle (B) of the groove bottom (81d) of the injector pipe (81).

25. The method according to claim 21, characterized in that The main combustion air (I 主 Is + It) is directed to the primary air supply pipe (14) for the main combustion air (I 主 ) of the flow duct, and is divided into a tertiary air flow (It) flowing in the air duct (82) within the end portion (21) and a secondary air flow (Is) flowing outside the air duct.

26. The method according to claim 25, characterized in that The secondary air flow (Is) passes through the interior (T) of the end portion (21) of the burner head (2).

27. A burner-boiler assembly, wherein: The burner frame according to claim 1 is installed in a boiler so that the combustion head (2) of the burner extends into the furnace, characterized in that the power density of the burner is at most 10000 kW / m2 relative to the cross-sectional area of ​​the furnace. 2 .

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