Combustion furnace and fuel combustion method

Abstract

A combustion furnace according to the present invention comprises: a furnace body that has a combustion chamber in which a vertical gas flow occurs; a burner that is disposed on a furnace side wall of the furnace body and that ejects a nitrogen-containing fuel and combustion air toward the combustion chamber; an additional combustion air port that is disposed on the furnace side wall and that supplies additional combustion air downstream in the gas flow relative to a combustion region where fuel is combusted by the combustion air ejected from the burner; and at least one ammonia nozzle that is disposed on the furnace side wall and that ejects ammonia gas upstream in the gas flow relative to the combustion region such that a circulating vortex of the ammonia gas is generated upstream in the gas flow relative to the combustion region.

Description

Combustion furnace and fuel combustion method

[0001] This disclosure relates to NO production by combustion. Ｘ The present invention relates to a combustion furnace for fuels that generate [unspecified] and a method for burning said fuel.

[0002] In recent years, amidst the growing efforts toward carbon neutrality, the use of ammonia as a fuel, a "carbon-free" substance that does not emit carbon dioxide when burned, is attracting attention as an effective means of reducing carbon dioxide emissions. On the other hand, ammonia, which contains nitrogen, undergoes an oxidation reaction during combustion that produces NO Ｘ (Nitrogen oxides) are produced, so NO is present in the exhaust gas from combustion when ammonia is used as fuel. Ｘ An increase in concentration is a concern. Therefore, in combustion furnaces that use ammonia as fuel (for example, boiler furnaces), NO in the combustion exhaust gas Ｘ Techniques to suppress the concentration have been proposed.

[0003] For example, the boiler disclosed in Patent Document 1 is equipped with a furnace employing a two-stage combustion method. This furnace has a plurality of vertically arranged burners for pulverized coal only or mixed combustion positioned on the side wall of the furnace, an additional air supply unit positioned downstream of the furnace gas flow relative to the plurality of burners, and an ammonia fuel supply unit that supplies ammonia to an ammonia supply position defined upstream of the furnace gas flow relative to the additional air supply unit. The ammonia fuel supply unit injects ammonia fuel toward the ammonia supply position via the burner positioned furthest upstream of the furnace gas flow among the plurality of burners. In this furnace, the pulverized coal fuel and some of the ammonia fuel injected into the furnace undergo low-oxygen combustion, and these fuels move downstream in an incompletely combusted state, so a reducing atmosphere region is formed downstream of the low-oxygen combustion region and upstream of the re-combustion region by the additional air. Nitrogen contained in the ammonia fuel and NO produced by the combustion of the fuel Ｘ It is reduced to nitrogen in a reducing atmosphere, and NO is present in the combustion exhaust gas. Ｘ The concentration is suppressed.

[0004] Japanese Patent Publication No. 2018-76985

[0005] Ammonia is NO Ｘ It has the property of reducing NO in the exhaust gas of a combustion furnace.Ｘ In order to efficiently suppress the concentration, it is effective to increase the residence time of ammonia in the furnace and increase the contact time between NO in the combustion gas and ammonia. Ｘ

[0006] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a technique for efficiently suppressing the NO concentration in the combustion exhaust gas of a combustion furnace by supplying ammonia in a combustion furnace for a fuel that generates NO by combustion. Ｘ Ｘ

[0007] In order to solve the above problems, a combustion furnace according to an aspect of the present disclosure includes a furnace body having a combustion chamber in which a gas flow in the vertical direction occurs, a burner disposed on a furnace side wall of the furnace body and ejecting a fuel containing a nitrogen component and combustion air toward the combustion chamber, an additional combustion air port disposed on the furnace side wall and supplying additional combustion air downstream of the gas flow from a combustion region where the fuel burns by the combustion air ejected from the burner, and at least one ammonia nozzle disposed on the furnace side wall and ejecting the ammonia gas upstream of the gas flow from the combustion region so that a circulation vortex of the ammonia gas occurs upstream of the combustion region.

[0008] Further, a method for burning a fuel according to an aspect of the present disclosure is a method for burning a fuel containing a nitrogen component in a combustion furnace having a combustion chamber in which a gas flow in the vertical direction occurs, including ejecting the fuel and combustion air from a burner toward the combustion chamber, supplying additional combustion air downstream of the gas flow from a combustion region where the fuel burns by the combustion air ejected from the burner, and ejecting the ammonia gas upstream of the gas flow from the combustion region so that a circulation vortex of the ammonia gas occurs upstream of the combustion region.

[0009] According to the present disclosure, in a combustion furnace for a fuel that generates NO by combustion, the NO concentration in the combustion exhaust gas of the combustion furnace can be efficiently suppressed by supplying ammonia. Ｘ Ｘ

[0010] Figure 1 is a diagram illustrating the schematic configuration of a combustion furnace according to one embodiment of the present disclosure. Figure 2 is a diagram illustrating the gas flow in the first-stage combustion region and the ammonia supply region of the combustion furnace. Figure 3 is a cross-sectional view of the combustion furnace illustrating the arrangement of ammonia nozzles. Figure 4 is a cross-sectional view of the combustion furnace illustrating the distance between the centers of adjacent ammonia nozzles. Figure 5 is a diagram illustrating the gas flow in the first-stage combustion region and the ammonia supply region of a combustion furnace according to Modification 1.

[0011] Next, embodiments of the present disclosure will be described with reference to the drawings. Figure 1 is a diagram showing a schematic configuration of a combustion furnace 1 according to one aspect of the present disclosure. The combustion furnace 1 is, for example, a furnace that burns fuel such as a boiler furnace.

[0012] 《Configuration of Combustion Furnace 1》 The combustion furnace 1 shown in Figure 1 employs a two-stage combustion method. The combustion furnace 1 comprises a furnace body 11 having a combustion chamber 12 extending in the vertical direction inside. In the combustion furnace 1 according to this embodiment, a vertical gas flow X is generated in the combustion chamber 12 as a whole, moving from bottom to top. However, the combustion furnace 1 may be configured in an inverted type in which a gas flow X is generated in the combustion chamber 12 from top to bottom. Hereinafter, the upstream of the gas flow X when viewed from a certain position in the combustion chamber 12 will be simply referred to as "upstream," and the downstream of the gas flow X will be simply referred to as "downstream."

[0013] The combustion chamber 12 is configured with a first-stage combustion region 21, which is the main combustion region of the fuel; a reduction region 22 downstream of the first-stage combustion region 21; a second-stage combustion region 23 downstream of the reduction region 22; and an ammonia supply region 25 upstream of the first-stage combustion region 21. The first-stage combustion region 21 and the second-stage combustion region 23 are separated vertically, with the reduction region 22 positioned between them. The ammonia supply region 25 is located on the opposite side of the first-stage combustion region 21 from the reduction region 22 and the second-stage combustion region 23 in the vertical direction.

[0014] The furnace side wall 13 of the furnace body 11 is provided with a burner 15, an additional combustion air port 16, and an ammonia nozzle 18.

[0015] Multiple burners 15, arranged at approximately the same height, constitute a single burner stage, and multiple burner stages are provided vertically on the furnace side wall 13 of the furnace body 11. In Figure 1, only one burner 15 of the burner stage is shown, and the other burners are omitted.

[0016] The burner 15 injects the main fuel and combustion air toward the first-stage combustion region 21 of the combustion chamber 12. The main fuel is, for example, pulverized coal fuel. However, the main fuel is not limited to pulverized coal fuel, and may be oil fuel or gaseous fuel such as ammonia fuel. The burner 15 may be configured to inject a secondary fuel in addition to or instead of the main fuel. The secondary fuel is, for example, ammonia fuel.

[0017] The burner 15 supplies combustion air at a ratio less than the stoichiometric amount of fuel to the fuel so that the fuel undergoes low-oxygen combustion in the first-stage combustion region 21. Depending on the configuration of the burner 15, the combustion air ejected from the burner 15 may include primary and secondary combustion air, or primary to tertiary combustion air.

[0018] The additional combustion air port 16 supplies additional combustion air to the second-stage combustion region 23 of the combustion chamber 12. The amount of combustion air supplied from the additional combustion air port 16 is greater than or equal to the amount of air equivalent to the stoichiometric air-fuel ratio of fuel supplied to the combustion chamber 12 minus the amount of combustion air supplied from the burner 15, so that any oxygen insufficient for fuel combustion is compensated for by the additional combustion air supplied from the additional combustion air port 16. In Figure 1, one additional combustion air port 16 is shown, but multiple additional combustion air ports 16 may be arranged in the vertical direction, or multiple additional combustion air ports 16 may be arranged in each stage.

[0019] The ammonia nozzle 18 ejects ammonia gas, that is, a gas containing ammonia, into the ammonia supply area 25. The ammonia nozzle 18 is positioned at the same height as the burner 15 of the uppermost burner stage among the multiple burner stages provided in the furnace body 11, or upstream of the burner 15 of the uppermost burner stage.

[0020] Here, the ammonia nozzle 18 will be described in detail. Figure 2 is a diagram illustrating the gas flow in the first-stage combustion region 21 and the ammonia supply region 25 of the combustion furnace 1, and Figure 3 is a cross-sectional view of the combustion furnace 1 illustrating the arrangement of the ammonia nozzle 18. The ammonia nozzle 18 shown in Figure 2 is independent of the burner 15. However, the ammonia nozzle 18 may utilize the flow path of the burner 15. For example, the ammonia nozzle 18 may utilize the flow path of the burner 15 of the uppermost burner stage, which is shut down during low-load operation of the combustion furnace 1, and may be configured to inject ammonia gas through the flow path of the burner 15 while the burner 15 is shut down.

[0021] At least one pair of ammonia nozzles 18 are arranged opposite each other in the combustion chamber 12 so that the ammonia gas jets ejected from the ammonia nozzles 18 collide with each other. As shown in Figure 3, in the combustion furnace 1 according to this embodiment, ammonia nozzles 18 are arranged on each of a pair of opposing furnace side walls 13, and for each ammonia nozzle 18 located on one of the pair of furnace side walls 13, there is an opposing ammonia nozzle 18 located on the other furnace side wall 13. The space between the pair of opposing furnace side walls 13 is the combustion chamber 12, and the set of points (i.e., a surface) equidistant from each furnace side wall 13 in the combustion chamber 12 is defined as the approximate center C of the combustion chamber 12. It is preferable that the ammonia gas jets ejected from the opposing ammonia nozzles 18 collide at the approximate center C of the combustion chamber 12.

[0022] If the distance lm between the centers of adjacent ammonia nozzles 18 is too small, the number of ammonia nozzles 18 required to evenly diffuse ammonia gas within the combustion chamber 12 will increase, which is not economical. Conversely, if the distance lm between the centers of adjacent ammonia nozzles 18 is too large, it becomes difficult to evenly diffuse ammonia gas within the combustion chamber 12. Therefore, as shown in Figure 4, the horizontal diffusion angle θm of the ammonia gas jet from the outlet of the ammonia nozzle 18 is set to be between α1° and α2° (α1≦θm≦α2), and the distance from the outlet of the ammonia nozzle 18 to the approximate center C of the combustion chamber 12 in a plan view is denoted as W, so that the distance lm between the centers of adjacent ammonia nozzles 18 satisfies the following equation (Equation 1).

[0023]

[0024] By satisfying the condition that the center-to-center distance \(l_m\) between adjacent ammonia nozzles 18 satisfies the above (Equation 1), in the range from more than half of the distance \(W\) from the outlet of the ammonia nozzle 18 to the approximate center \(C\) of the combustion chamber 12 to the center \(C\), the ammonia gas jets from adjacent ammonia nozzles 18 are mixed. As a result, without an excessive number of ammonia nozzles 18, the ammonia gas can diffuse into the combustion chamber 12, and after the circulation vortex 33 is generated, the ammonia gas can be uniformly mixed with the combustion gas.

[0025] Returning to FIG. 2, the injection direction of the ammonia nozzle 18 is directed upstream of the gas flow \(X\) in the combustion chamber 12 with respect to the position of the ammonia nozzle 18. Here, the injection direction is the same as the extending direction of the nozzle axis in a general gas injection nozzle. In a side view, the angle formed between the injection direction of the ammonia nozzle 18 and the furnace side wall 13 of the furnace body 11 where the ammonia nozzle 18 is disposed is \(\theta1^{\circ}\). That is, the injection direction of the ammonia nozzle 18 is inclined by \(\theta1^{\circ}\) from the direction parallel to the furnace side wall 13, that is, from the vertical direction. In other words, the angle formed between the injection direction of the ammonia nozzle 18 and the horizontal direction is \((90 - \theta1)^{\circ}\). \(\theta1\) is preferably 60 or more and 80 or less, and is the angle at which the circulation vortex 33 is formed in the ammonia supply region 25 by the ammonia gas jet ejected from the ammonia nozzle 18. The ammonia injection amount of the ammonia nozzle 18 is the flow rate at which the ammonia gas jets ejected from the ammonia nozzles 18 disposed opposite each other at approximately the center in a plan view of the combustion chamber 12 can collide with each other.

[0026] 《Operating Method of Combustion Furnace 1》 The operating method of the combustion furnace 1 having the above configuration will be described. In the combustion furnace 1 during operation, fuel and combustion air are ejected from the burner 15, additional combustion air is ejected from the additional combustion air port 16, and ammonia gas is ejected from the ammonia nozzle 18.

[0027] In the first-stage combustion region 21 of the combustion chamber 12, low-oxygen combustion of the fuel by combustion air and thermal decomposition of the fuel occur. The combustion gas generated in the first-stage combustion region 21 contains CO, CO ２ 、NOＸ In addition to oxides of fuels such as those mentioned above, intermediate products generated by thermal decomposition and unburned components are included. The reduction region 22 is in a reducing atmosphere due to the combustion gas that has moved downstream from the first-stage combustion region 21. The combustion gas passes through the reduction region 22 and moves to the second-stage combustion region 23. In the second-stage combustion region 23, the unburned components in the combustion gas are completely burned by additional combustion air.

[0028] In the ammonia supply region 25, ammonia gas jets 30 emerging from the oppositely arranged ammonia nozzles 18 collide with each other. A part of the ammonia gas jets 30 changes direction upward to become an upward ammonia gas flow 31, and another part of the ammonia gas jets 30 changes direction downward to become a downward ammonia gas flow 32.

[0029] The upward ammonia gas flow 31 flows downstream in the central part of the combustion chamber 12 in plan view. Since the burner 15 is arranged on the furnace side wall 13, the oxygen concentration in the central part of the combustion chamber 12 in plan view is lower compared to the vicinity of the furnace side wall 13. The upward ammonia gas flow 31 passes through the first-stage combustion region 21 and the reduction region 22, and NO Ｘ generated in the first-stage combustion region 21 during the passage. Ｘ contacts and reduces NO Ｘ to nitrogen. Also, NO Ｘ generated by the oxidation of ammonia and the nitrogen content contained in ammonia are reduced to nitrogen during the passage through the first-stage combustion region 21 and the reduction region 22. Thus, NO Ｘ generated in the combustion chamber 12 is reduced to nitrogen, and the NO Ｘ concentration of the combustion gas after re-combustion in the second-stage combustion region 23, that is, the combustion exhaust gas discharged from the combustion chamber 12, can be suppressed.

[0030] The downward ammonia gas flow 32 forms a circulation vortex 33 in the ammonia supply region 25. In other words, a circulation vortex 33 of ammonia gas is formed between the ammonia gas jet 30 coming out of the ammonia nozzle 18 and the bottom of the furnace body 11. The circulation vortex 33 entrains a portion of the combustion gas generated in the first-stage combustion region 21, promoting the diffusion of ammonia gas within the combustion chamber 12 and the mixing of ammonia gas and combustion gas. In addition, a portion of the ammonia gas flow forming the circulation vortex 33 is drawn into the combustion gas flow and the upward ammonia gas flow 31. The circulation vortex 33 increases the residence time of ammonia gas in the furnace, and NO generated by the combustion of fuel is reduced. Ｘ The opportunity for contact with ammonia gas increases, and NO from the combustion exhaust gas from the combustion chamber 12 Ｘ The concentration can be effectively reduced.

[0031] [Modification 1] Next, a modification of the above embodiment will be described. In the above embodiment, a circulation vortex 33 is generated by the collision of ammonia gas jets 30, but the ammonia gas circulation vortex 33 may be generated in the ammonia supply region 25 of the combustion chamber 12 by other means.

[0032] Figure 5 is a diagram illustrating the gas flow in the first-stage combustion region 21 and the ammonia supply region 25 of the combustion furnace 1 according to Modification 1. In this description of Modification 1, the same or similar components as those in the previously described embodiment are denoted by the same reference numerals in the drawings, and their descriptions are omitted. The combustion furnace 1 according to Modification 1 has substantially the same configuration as the combustion furnace 1 according to the previously described embodiment, except for the ammonia gas ejection direction of the ammonia nozzle 18.

[0033] The combustion furnace 1 according to the modified example 1 shown in Figure 5 is equipped with an ammonia nozzle 18 positioned on the furnace side wall 13 of the furnace body 11 and ejecting ammonia gas toward the ammonia supply area 25 of the combustion chamber 12. The ammonia gas jet 30 emitted from the ammonia nozzle 18 flows upstream relative to the overall gas flow X of the combustion chamber 12 along the furnace side wall 13 surrounding the ammonia supply area 25 due to the Coanda effect, and adheres to the furnace side wall 13 or the furnace bottom. In other words, the ammonia gas jet 30 is an adhering jet. A low-pressure vortex region (also called a separation vortex region) is generated between the ammonia gas jet 30 and the furnace side wall 13 along which the jet 30 flows, and a circulating vortex 33 of ammonia gas is formed in this low-pressure vortex region.

[0034] The injection direction of the ammonia nozzle 18 is directed upstream of the gas flow X in the combustion chamber 12 from the position of the ammonia nozzle 18. In a side view, the angle between the injection direction of the ammonia nozzle 18 and the furnace side wall 13a of the furnace body 11 where the ammonia nozzle 18 is located is θ2°. In other words, the injection direction of the ammonia nozzle 18 is inclined at θ2° from the direction parallel to the furnace side wall 13, i.e., from the vertical direction. To put it another way, the angle between the injection direction of the ammonia nozzle 18 and the horizontal direction is (90 - θ2)°. Also, in a side view, the angle between the downward extension of the furnace side wall 13a of the furnace body 11 where the ammonia nozzle 18 is located and the furnace side wall 13b along which the ammonia gas jet 30 flows is θ3°, and θ3 is between 0 and 35 degrees. In the example shown in Figure 5, θ3 is 0. In order for the flow separated from the ammonia gas jet 30 to form a circulating vortex 33, the relationship 20 ≤ θ2 ≤ (60 - θ3) preferably holds. When θ2 is less than 20, and when θ2 is greater than (60 - θ3), it is difficult for the circulating vortex 33 to form.

[0035] In the combustion furnace 1 according to Modification 1, a circulating vortex 33 is formed in the ammonia supply region 25 between the ammonia gas jet 30 and the furnace side wall 13b by the ammonia gas jet 30 emitted from the ammonia nozzle 18 during operation. The ammonia gas circulating vortex 33 promotes the uniform diffusion of ammonia gas in the combustion chamber 12 by drawing in the surrounding combustion gas. Furthermore, the ammonia gas circulating vortex 33 can increase the residence time of ammonia gas in the combustion chamber 12. As a result, NO in the combustion chamber 12 Ｘ The increased contact opportunities with ammonia gas and the NO in combustion exhaust gas Ｘ This can contribute to reducing the concentration.

[0036] Furthermore, the remaining portion of the ammonia gas jet 30 merges with the gas flow X in the combustion chamber 12 and becomes an ammonia gas flow 35 that moves downstream. The ammonia gas flow 35 moves sequentially from the ammonia supply region 25 through the first-stage combustion region 21, the reduction region 22, and the second-stage combustion region 23 (see Figure 1). As the ammonia gas passes through the first-stage combustion region 21 and the reduction region 22, it produces NO generated by the combustion of the fuel. Ｘ In contact with, NO Ｘ It reduces to nitrogen. Also, NO is produced by the oxidation of ammonia. Ｘ The nitrogen contained in the ammonia is reduced to nitrogen as it passes through the first-stage combustion region 21 and the reduction region 22. NO produced in the combustion chamber 12 in this way. Ｘ Since it is reduced to nitrogen, the combustion gas after re-combustion in the second-stage combustion region 23, i.e., the combustion exhaust gas from the combustion chamber 12, is NO Ｘ The concentration can be reduced.

[0037] [Summary] The combustion furnace 1 according to the first item of this disclosure comprises: a furnace body 11 having a combustion chamber 12 in which a vertical gas flow X occurs; a burner 15 arranged on the furnace side wall 13 of the furnace body 11 and ejecting a fuel containing nitrogen and combustion air toward the combustion chamber 12; an additional combustion air port 16 arranged on the furnace side wall 13 and supplying additional combustion air downstream of the gas flow X beyond the combustion region 21 in which the fuel is burned by the combustion air ejected from the burner 15; and at least one ammonia nozzle 18 arranged on the furnace side wall 13 and ejecting ammonia gas upstream of the gas flow X beyond the combustion region 21 in such a way that a circulation vortex 33 of ammonia gas is generated upstream of the gas flow X beyond the combustion region 21.

[0038] In the combustion furnace 1 with the above configuration, the ammonia gas circulation vortex 33 generated upstream of the gas flow X from the combustion region 21 entrains a portion of the combustion gas generated in the combustion region 21, promoting the mixing of ammonia gas and combustion gas, and the diffusion of ammonia gas within the combustion chamber 12. This allows ammonia gas to spread throughout the combustion chamber 12. Furthermore, the ammonia gas circulation vortex 33 can increase the residence time of ammonia gas within the combustion chamber 12. The increased residence time allows NO generated by the combustion of ammonia gas and fuel to be dispersed. Ｘ Increased opportunities for contact with NO in combustion exhaust gases Ｘ The concentration can be reduced.

[0039] The combustion furnace 1 according to the second item of this disclosure, in the combustion furnace 1 according to the first item, includes a pair of ammonia nozzles 18 arranged on opposing furnace side walls 13 of the combustion chamber 12, and the pair of ammonia nozzles 18 eject ammonia gas such that the ammonia gas jets 30 collide with each other.

[0040] The combustion furnace 1 according to the third item of this disclosure is a combustion furnace 1 according to the first or second item, wherein the injection direction of the ammonia nozzle 18 is directed upstream of the gas flow X, and the angle between the injection direction of the ammonia nozzle 18 and the vertical direction is 60° or more and 80° or less.

[0041] According to the combustion furnace 1 relating to the second and third items, the flow whose direction is changed to an upstream direction by the collision of ammonia gas jets 30, that is, the downward ammonia gas flow 32 mentioned above, can form an ammonia gas circulation vortex 33 between the ammonia gas jets 30 and the furnace side wall 13 (or furnace bottom).

[0042] The combustion furnace 1 according to the fourth item of this disclosure is the same as the combustion furnace 1 according to the first item, wherein the injection direction of the ammonia nozzle 18 is directed upstream of the gas flow X, and the ammonia gas jet 30 emitted from the ammonia nozzle 18 is an adhering jet that adheres to the furnace side wall 13 or furnace bottom, and a circulation vortex 33 is generated between the ammonia gas jet 30 and the furnace side wall 13 or furnace bottom.

[0043] The combustion furnace 1 relating to item 5 of this disclosure is the combustion furnace 1 relating to item 4, wherein the angle between the injection direction of the ammonia nozzle 18 and the vertical direction is 20° or more and 60° or less.

[0044] According to the combustion furnace 1 relating to items 4 and 5, a circulating vortex 33 can be formed between the ammonia gas jet 30 and the furnace side wall 13 (or furnace bottom).

[0045] The combustion furnace 1 according to item 6 of this disclosure is a combustion furnace 1 according to item 2, wherein at least one ammonia nozzle 18 includes horizontally adjacent ammonia nozzles 18 on the furnace side wall 13, the horizontal diffusion angle θm of the ammonia gas jet 30 coming out of adjacent ammonia nozzles 18 is α1° or more and α2° or less, and when the distance from the outlet of adjacent ammonia nozzles 18 to the center C of the combustion chamber is W, the distance lm between the centers of adjacent ammonia nozzles satisfies the above-mentioned formula 1.

[0046] According to the combustion furnace 1 described in item 6, the ammonia gas jets 30 emitted from horizontally adjacent ammonia nozzles 18 mix in the area from halfway to the approximate center C of the combustion chamber 12 up to the center C. This makes it possible to evenly diffuse the ammonia gas throughout the combustion chamber 12 without having an excessive number of ammonia nozzles 18.

[0047] The combustion furnace 1 relating to item 7 of this disclosure is a combustion furnace 1 relating to any of items 1 to 6, wherein the fuel includes ammonia fuel.

[0048] Ammonia fuel is produced by NO combustion. Ｘ However, according to the combustion furnace 1 related to item 7, NO is produced by ammonia present in the combustion chamber 12. Ｘ NO is reduced, and the NO in the combustion exhaust gas is reduced. Ｘ The concentration can be suppressed.

[0049] The eighth item of this disclosure relates to a method for burning a fuel containing nitrogen in a combustion furnace 1 having a combustion chamber 12 in which a vertical gas flow X occurs, and includes: injecting fuel and combustion air from a burner 15 toward the combustion chamber 12; supplying additional combustion air downstream of the gas flow X beyond the combustion region 21 in which the fuel is burned by the combustion air injected from the burner 15; and injecting ammonia gas upstream of the gas flow X beyond the combustion region 21 in such a way that a circulation vortex 33 of ammonia gas is generated upstream of the gas flow X beyond the combustion region 21.

[0050] According to the combustion method described above, the ammonia gas circulation vortex 33 generated upstream of the gas flow X from the combustion region 21 entrains a portion of the combustion gas generated in the combustion region 21, promoting the mixing of ammonia gas and combustion gas, and the diffusion of ammonia gas within the combustion chamber 12. This allows ammonia gas to spread throughout the combustion chamber 12. Furthermore, the ammonia gas circulation vortex 33 can increase the residence time of ammonia gas within the combustion chamber 12. The increased residence time allows NO generated by the combustion of ammonia gas and fuel to be dispersed. Ｘ Increased opportunities for contact with NO in combustion exhaust gases Ｘ The concentration can be reduced.

[0051] The discussions of this disclosure described above are presented for illustrative and explanatory purposes only and are not intended to limit the disclosure to the forms disclosed herein. For example, in the detailed description above, various features of the disclosure are grouped into a single embodiment for the purpose of streamlining the disclosure, but some of the features may be combined. Furthermore, some of the features included in this disclosure may be combined into alternative embodiments, configurations, or aspects other than those discussed above.

[0052] 1: Combustion furnace 11: Furnace body 12: Combustion chamber 13, 13a, 13b: Furnace side walls 15: Burner 16: Additional combustion air port 18: Ammonia nozzle 21: First stage combustion zone 22: Reduction zone 23: Second stage combustion zone 25: Ammonia supply zone 30: Ammonia gas jet 33: Circulation vortex

Claims

1. A combustion furnace comprising: a furnace body having a combustion chamber in which a gas flow occurs in the vertical direction; a burner disposed on the furnace side wall of the furnace body and ejecting a fuel containing nitrogen and combustion air toward the combustion chamber; an additional combustion air port disposed on the furnace side wall and supplying additional combustion air downstream of the gas flow beyond the combustion region in which the fuel is burned by the combustion air ejected from the burner; and at least one ammonia nozzle disposed on the furnace side wall and ejecting the ammonia gas upstream of the gas flow beyond the combustion region so as to create a circulating vortex of ammonia gas upstream of the gas flow beyond the combustion region.

2. The combustion furnace according to claim 1, wherein the at least one ammonia nozzle includes a pair of ammonia nozzles arranged on opposing furnace side walls of the combustion chamber, and the pair of ammonia nozzles eject the ammonia gas such that the ammonia gas jets collide with each other.

3. The combustion furnace according to claim 1 or 2, wherein the injection direction of the ammonia nozzle is directed upstream of the gas flow, and the angle between the injection direction of the ammonia nozzle and the vertical direction is 60° or more and 80° or less.

4. The combustion furnace according to claim 1, wherein the injection direction of the ammonia nozzle is directed upstream of the gas flow, the ammonia gas jet discharged from the ammonia nozzle is an adhering jet that adheres to the furnace side wall or furnace bottom, and the circulation vortex is generated between the ammonia gas jet and the furnace side wall or furnace bottom.

5. The combustion furnace according to claim 4, wherein the angle between the injection direction of the ammonia nozzle and the vertical direction is 20° or more and 60° or less.

6. The combustion furnace according to claim 2, wherein the at least one ammonia nozzle includes an adjacent ammonia nozzle horizontally adjacent to the side wall of the furnace, the horizontal diffusion angle θm of the ammonia gas jet coming out of the adjacent ammonia nozzle is α1° or more and α2° or less, and when the distance from the outlet of the adjacent ammonia nozzle to the center of the combustion chamber is W, the distance lm between the centers of the adjacent ammonia nozzles satisfies the following formula 1.

7. The combustion furnace according to claim 1, wherein the fuel includes ammonia fuel.

8. A method for burning a nitrogen-containing fuel in a combustion furnace having a combustion chamber in which a vertical gas flow occurs, comprising: injecting the fuel and combustion air from a burner toward the combustion chamber; supplying additional combustion air downstream of the gas flow beyond the combustion region in which the fuel is burned by the combustion air injected from the burner; and injecting the ammonia gas upstream of the gas flow beyond the combustion region so as to create a circulating vortex of ammonia gas upstream of the gas flow beyond the combustion region.

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