JP7583598B2 - Fuel Combustion System - Google Patents

Description

The present invention relates to a fuel combustion system equipped with a combustion furnace that burns a primary fuel such as petroleum residue.

In recent years, with the demand for more efficient use of fossil fuels, advances in petroleum resource development technology have led to increasingly heavy residues from mined crude oil. As a result, technology has been proposed to effectively use the petroleum residues remaining after the extraction of light oil from crude oil as fuel for power generation and thermal energy recovery.

In addition to the efficient use of fossil fuels, it is becoming increasingly important to reduce carbon dioxide emissions from combustion in order to promote environmental protection. In recent years, ammonia gas has been attracting attention as a carbon dioxide-free fuel. Ammonia gas is a relatively easy-to-handle fuel, and Patent Document 1, for example, discloses a boiler in which ammonia gas is injected into a combustion furnace using a burner. In the boiler in the above document, carbon fuel is also injected into the combustion furnace along with ammonia gas and combusted, which makes it possible to suppress the generation of thermal NOx (nitrogen oxides).

JP 2018-200144 A

When using ammonia gas as fuel, as in the boiler of Patent Document 1, it is important to further suppress the generation of thermal NOx, and it is also important from the standpoint of improving combustion efficiency to suppress the discharge of ammonia gas without being burned, which is caused by the relatively slow combustion speed of ammonia gas. However, with the boiler configuration of the above document, it is difficult to further suppress thermal NOx and suppress insufficient combustion of ammonia gas.

The present invention aims to provide a fuel combustion system that can suppress insufficient combustion of fuel gas and suppress thermal NOx.

The fuel combustion system of the present invention comprises a combustion furnace for burning a main fuel, a refractory material arranged to cover at least a portion of the inside of the combustion furnace, a burner for injecting the main fuel into the combustion furnace and burning it, and a fuel gas injection nozzle arranged separately from the burner for injecting fuel gas into the combustion furnace.

Fuel gas is generally introduced into the combustion furnace by being injected from a burner in the same manner as the main fuel. In this regard, when the amount of fuel gas injected is small, the effect of reducing thermal NOx and fuel NOx is expected due to the denitrification reaction in the high-temperature reduction region formed in front of the burner. However, as the amount of fuel gas injected is increased, the proportion of fuel gas that is not completely burned in the high-temperature reduction region in front of the burner increases. Therefore, there is a risk of locally lowering the temperature in front of the burner. As a result, there is a risk that the reduction reaction will be suppressed or that this will lead to a decrease in combustion efficiency. This tendency is more pronounced for fuel gases with slower combustion speeds, such as ammonia gas. In contrast, by providing a fuel gas injection nozzle separately from the burner as in the present invention (hereinafter referred to as this configuration), the fuel gas can be supplied to the high-temperature, oxygen-lean region (high-temperature reduction region) in the combustion furnace without being diluted by the air injected from the burner (air carrying the main fuel). This suppresses the generation of thermal NOx. In addition, this configuration can lengthen the residence time of the fuel gas in the combustion furnace (the time until combustion), and allow most of the fuel gas to pass through an oxygen-lean atmosphere. This can prevent the fuel gas from being incompletely burned, which can prevent the temperature in the reduction area from dropping, and therefore the denitrification reaction can be maintained. Furthermore, this configuration can prevent the fuel gas injected from the fuel gas injection nozzle from being excessively concentrated in front of the burner. This can further prevent the fuel gas from being incompletely burned, which can further prevent the temperature in the reduction area from dropping, and therefore the denitrification reaction can be maintained. As described above, according to the present invention, it is possible to suppress insufficient combustion of the fuel gas and suppress thermal NOx.

The present invention provides a fuel combustion system that can suppress insufficient combustion of fuel gas and suppress thermal NOx.

1 is a diagram showing a schematic configuration of a boiler according to an embodiment of the present invention; FIG. 2 is a perspective view showing an example of an arrangement of burners and fuel gas injection nozzles in a lower combustion chamber formed in a lower portion of a combustion furnace. FIG. 11 is a perspective view showing a modified example of the arrangement of the burners and the fuel gas injection nozzles in the lower combustion chamber.

Below, a fuel combustion system according to one embodiment of the present invention will be described with reference to the drawings. The fuel combustion system described below is merely one embodiment of the present invention. Therefore, the present invention is not limited to the following embodiment, and additions, deletions, and modifications are possible without departing from the spirit of the present invention.

Figure 1 is a schematic diagram showing the configuration of a boiler 10, which is an example of a fuel combustion system according to this embodiment. As shown in Figure 1, the boiler 10 of this embodiment includes a combustion furnace 2 that burns fuel, and a boiler body 40 and a superheater 42 that generate steam using the combustion heat. The boiler 10 is a thermal boiler that uses at least one of petroleum residues such as pitch coke, heavy oils such as asphalt, heavy oil, and pulverized coal as its main fuel.

A vertical combustion chamber 20 is formed inside the combustion furnace 2. In this combustion furnace 2, a high-temperature reduction zone 21 is formed in the lower part of the combustion chamber 20, a low-temperature oxidation zone 22 is formed in the upper part of the combustion chamber 20, and a constriction section 23 is formed between the high-temperature reduction zone 21 and the low-temperature oxidation zone 22. However, the combustion furnace 2 may be configured such that the high-temperature reduction zone 21 is formed in the upper part of the combustion chamber 20, and the low-temperature oxidation zone 22 is formed in the lower part of the combustion chamber 20.

The lower combustion chamber 70, which is one of the inner walls of the combustion furnace 2 and forms the high-temperature reduction zone 21, is covered with a refractory material 25. The refractory material 25 may cover the entire lower combustion chamber 70, or may cover only a portion of it. The refractory material 25 can withstand a high temperature of approximately 2000°C. The furnace wall of the lower combustion chamber 70 is provided with a plurality of burners 5 that blow fuel and air for the first stage combustion into the high-temperature reduction zone 21. Fuel and air are blown from each burner 5 into the lower combustion chamber 70. The fuel includes the main fuel described above and auxiliary fuel containing ammonia gas. The blown fuel is mixed with air and combusted, generating a flame.

The burners 5 are provided on each of a pair of opposing furnace walls. Each furnace wall is provided with at least one burner stage in the vertical direction, and each burner stage is formed by a plurality of burners 5 arranged in the horizontal direction. The burners 5 thus arranged opposite each other are staggered so that the burner axes of each burner 5 do not intersect.

The outlet of the high-temperature reduction zone 21 (i.e., the upper part of the high-temperature reduction zone 21) is connected to the inlet of the low-temperature oxidation zone 22 (i.e., the lower part of the low-temperature oxidation zone 22) via the constriction section 23. The smallest horizontal cross-sectional area of the constriction section 23 is approximately 20 to 50% of the horizontal cross-sectional area of the high-temperature reduction zone 21.

Multiple air nozzles 26 are provided on the upper furnace wall of the combustion furnace 2. Air for secondary combustion is blown out from each air nozzle 26 into the low-temperature oxidation zone 22. In this embodiment, multiple air nozzle stages are provided in the vertical direction, and each air nozzle stage is formed by multiple air nozzles 26 lined up in the horizontal direction.

The area between the constriction section 23 and the multiple air nozzles 26 in the low-temperature oxidation zone 22 above and below forms the cooling section 24. The furnace wall of the cooling section 24 is a water-cooled wall with water pipes (not shown) of the boiler body 40 running throughout it.

The outlet of the low-temperature oxidation zone 22 (i.e., the upper part of the low-temperature oxidation zone 22) is connected to the inlet of the flue 28 provided at the top of the combustion furnace 2. A superheater tube 43 of a superheater 42 is provided in the upstream part of the flue 28. In addition, water pipes 41 of the boiler body 40 are laid around the wall of the flue 28. The exhaust gas treatment system 30 is connected to the outlet of the flue 28. The exhaust gas treatment system 30 is provided with an economizer 31 that uses the residual heat of the combustion exhaust gas to preheat the air sent to the burner 5, a denitrification device 32 that denitrifies the combustion exhaust gas, and the like.

In a boiler 10 having such a configuration, the air ratio between the fuel supplied to the high-temperature reduction zone 21 and the air for the first stage combustion is maintained at less than 1 (for example, about 0.7). Furthermore, the high-temperature reduction zone 21 covered with refractory material 25 is less susceptible to a drop in temperature inside the furnace compared to other parts of the furnace. As a result, the high-temperature reduction zone 21 is a high-temperature reducing atmosphere with an average temperature of about 1500°C, and gasification of the fuel is promoted in the high-temperature reduction zone 21.

In the high-temperature reduction zone 21, the fuel is gasified to generate combustion gas. This combustion gas flows into the low-temperature oxidation zone 22 through the constriction 23. The air ratio of the low-temperature oxidation zone 22 is maintained at 1 or more (for example, about 1.1) by the air for second-stage combustion supplied to the low-temperature oxidation zone 22 from the air nozzle 26. This creates an oxidizing atmosphere in the low-temperature oxidation zone 22, promoting the combustion of the combustion gas in the low-temperature oxidation zone 22.

In the low-temperature oxidation zone 22, the combustion of the unburned fuel in the combustion gas is completed (i.e., complete combustion occurs). The combustion exhaust gas from the low-temperature oxidation zone 22 flows out to the exhaust gas treatment system 30 through the flue 28. The heat of the combustion exhaust gas is recovered by the water pipe 41 installed in the flue 28, and steam is generated in the boiler body 40. In addition, the heat of the combustion exhaust gas is recovered by the superheater pipe 43 installed in the flue 28, and superheated steam is generated in the superheater 42. The generated superheated steam is used, for example, in a steam turbine (not shown) of a power generation facility.

Next, the arrangement of the burner 5 and fuel gas injection nozzle 50 in the boiler 10 of this embodiment will be described. First, the technical aspects of the present invention that form the basis of the configuration that realizes optimal in-furnace denitrification in the boiler 10 of this embodiment will be described.

Conventionally, fuel gas has generally been injected from the burner in the same way as the main fuel. In this regard, when the amount of fuel gas injected is small, it is expected that the effect of reducing thermal NOx will be achieved by the denitrification reaction in the high-temperature reduction area formed in front of the burner. However, as the amount of fuel gas injected is increased, the proportion of fuel gas that does not completely burn in the high-temperature reduction area in front of the burner increases. This can cause a localized drop in the temperature in front of the burner, which may lead to a decrease in combustion efficiency. This tendency is more pronounced for fuel gases with slower combustion speeds, such as ammonia gas.

Therefore, in order to achieve optimal in-furnace denitrification, the following method is adopted in the boiler 10 of this embodiment.

(1) Injection of fuel gas into high-temperature reduction region In this embodiment, fuel gas that is not diluted with air is introduced into a high-temperature, oxygen-lean region (high-temperature reduction region) in the combustion furnace 2. This is based on the viewpoint that injecting fuel gas into a high-temperature, oxygen-rich atmosphere may promote the generation of thermal NOx, and therefore it is not preferable to mix the fuel gas with air.

(2) Ensuring the residence time of the fuel gas in the high-temperature reduction region In the present embodiment, the residence time of the fuel gas in the combustion furnace 2 is lengthened so that most of the flow lines of the fuel gas pass through an oxygen-lean atmosphere. This is based on the viewpoint of preventing insufficient residence time of the fuel gas due to a short pass of the fuel gas in the combustion furnace 2, etc., when co-firing a fuel gas having a slow combustion speed such as ammonia gas, the fuel gas that is not completely burned is discharged as exhaust gas.

(3) Suppression of temperature drop in front of burner Furthermore, in this embodiment, fuel gas is injected so as not to be excessively concentrated in front of the burner. The position in the combustion furnace 2 where high-temperature reduction is most pronounced is the region in front of the burner, and it is expected that a strong denitration reaction will occur by injecting fuel gas into that region. On the other hand, if a large amount of fuel gas is injected from the burner 5 and the fuel gas is concentrated too much in front of the burner, some of the fuel gas will not burn completely. Therefore, there is a risk that the temperature in the reduction region will drop and the gasification reaction and denitration reaction will be suppressed, and this is based on the viewpoint of preventing this.

To achieve the above (1) to (3), the boiler 10 of this embodiment is configured as follows. The following description will be given with reference to the drawings.

Figure 2 is a perspective view of the lower combustion chamber 70 formed in the lower part of the combustion furnace 2. Note that since Figure 2 shows only the lower combustion chamber 70 of the combustion furnace 2, the upper part of the lower combustion chamber 70 is open. As shown in Figure 2, the lower combustion chamber 70 has four furnace walls 70a, 70b, 70c, and 70d that form, for example, a square or rectangle in a plan view. The furnace wall (first furnace wall) 70a and the furnace wall (third furnace wall) 70c are arranged to face each other, and the furnace wall (second furnace wall) 70b and the furnace wall (fourth furnace wall) 70d are arranged to face each other. As described above, the four furnace walls 70a, 70b, 70c, and 70d are covered with refractory material 25 (Figure 1).

In the boiler 10 of this embodiment, the fuel gas injection nozzle 50 is provided separately from the burner 5. The fuel gas injection nozzle 50 injects fuel gas into the lower combustion chamber 70. For example, the arrangement of the two burners 5 and the two fuel gas injection nozzles 50 provided in the lower combustion chamber 70 will be described. In FIG. 2, the burner port of one burner 5A is provided in the furnace wall 70a, and the burner port of the other burner 5B is provided in the furnace wall 70c. The burner port of burner 5B is arranged at a predetermined distance from the burner port of burner 5A in the extension direction d1 of the furnace walls 70a and 70c. In the following, the direction perpendicular to the above-mentioned extension direction d1 is referred to as the injection direction d2.

The nozzle mouth of one fuel gas injection nozzle 50A is provided in the furnace wall 70a, and the nozzle mouth of the other fuel gas injection nozzle 50B is provided in the furnace wall 70c. The nozzle mouth of the fuel gas injection nozzle 50A is arranged at a predetermined distance in the extension direction d1 with respect to the burner 5A. The nozzle mouth of the fuel gas injection nozzle 50A is arranged opposite the burner mouth of the burner 5B in the injection direction d2. On the other hand, the nozzle mouth of the fuel gas injection nozzle 50B is arranged at a predetermined distance in the extension direction d1 with respect to the burner 5B. The nozzle mouth of the fuel gas injection nozzle 50B is arranged opposite the burner mouth of the burner 5A in the injection direction d2. That is, in a plan view, the burner 5A, the burner 5B, the fuel gas injection nozzle 50A, and the fuel gas injection nozzle 50B are arranged in a staggered manner.

The fuel gas injection nozzles 50A, 50B are provided with a flow rate control device 60 that controls the injection flow rate of the fuel gas. This flow rate control device 60 has, for example, a CPU, ROM, RAM, and a hard disk, and controls the opening area of the fuel gas injection nozzles 50A, 50B by executing a predetermined program stored in the ROM. By controlling the injection flow rate of the fuel gas with the flow rate control device 60, excessive concentration of the fuel gas in front of the burner is prevented. This prevents insufficient combustion of the fuel gas.

In the above configuration, fuel gas is injected from each fuel gas injection nozzle 50 toward each burner 5. As a result, the fuel gas injected from each fuel gas injection nozzle 50 passes through an area with a low oxygen concentration in the lower combustion chamber 70, and then reaches the front of the burner. In this case, in a conventional boiler, it is difficult to realize such a fuel gas injection method because the temperature is low at points far from the burner and near the furnace wall, but this can be realized because the lower combustion chamber 70 of this embodiment is covered with refractory material 25.

A recirculation vortex R is formed in front of each burner by the swirling tertiary air. The recirculation vortex R is a region where exhaust gas, fuel gas, and intermediate products of the combustion process coexist, and is a reduction region with low oxygen concentration and high temperature (a particularly high-temperature reduction region in the lower combustion chamber 70). When fuel gas reaches the region of this recirculation vortex R, the fuel gas is taken in by the recirculation vortex R, and combustion proceeds in a high-temperature reduction atmosphere. This configuration suppresses the generation of thermal NOx. In addition, compared to the conventional mode in which fuel gas is injected from the burner 5, it is possible to ensure a long combustion time from when the fuel gas is injected until it reaches the recirculation vortex R. Therefore, even if a fuel gas such as ammonia gas, which has a slow combustion speed, is injected into the lower combustion chamber 70, the temperature in front of the burner is unlikely to be lowered, and therefore the denitrification effect due to the high-temperature reduction region is easily maintained even if a large amount of fuel gas is injected.

As described above, the boiler 10 of this embodiment has the following effects. Fuel gas is generally introduced into the combustion furnace 2 by being injected from the burner in the same manner as the main fuel. In this regard, when the amount of fuel gas injected is small, the effect of reducing thermal NOx is expected due to the denitrification reaction in the high-temperature reduction region formed in front of the burner. However, as the amount of fuel gas injected is increased, the proportion of fuel gas that is not completely burned in the high-temperature reduction region in front of the burner increases. Therefore, there is a possibility that the temperature in front of the burner is locally lowered. As a result, there is a risk that the reduction reaction will be suppressed or that the combustion efficiency will be reduced. This tendency is more noticeable for fuel gases with a slow combustion speed, such as ammonia gas. In contrast, by providing the fuel gas injection nozzle 50 separately from the burner 5 as in this embodiment, the fuel gas can be supplied to the high-temperature and oxygen-lean region (high-temperature reduction region) in the combustion furnace 2 without being diluted by the air injected from the burner 5 (air carrying the main fuel). This suppresses the generation of thermal NOx. In addition, as described above, the fuel gas injection nozzle 50 is provided separately from the burner 5, thereby lengthening the residence time of the fuel gas in the combustion furnace 2. Increasing the residence time of the fuel gas in the combustion furnace 2 in this way makes it easier for the fuel gas to burn. This makes it possible to suppress a drop in the temperature of the reduction region, and therefore the denitrification reaction can be maintained. Furthermore, it is possible to prevent the fuel gas injected from the fuel gas injection nozzle 50 from concentrating excessively in front of the burner. This makes it possible to further suppress the fuel gas from being incompletely burned, which makes it possible to further suppress a drop in the temperature of the reduction region, and therefore the denitrification reaction can be maintained. As a result, it is possible to suppress thermal NOx while suppressing insufficient combustion of the fuel gas.

In addition, by covering the lower combustion chamber 70 with the refractory material 25, it becomes easier to form a high-temperature reduction region in the lower combustion chamber 70. This promotes gasification of the fuel in the lower combustion chamber 70, and even when using a flame-retardant main fuel such as petroleum residue, it is possible to achieve both improved combustion efficiency and low thermal NOx. In addition, even if ammonia gas is mixed with the main fuel, the combustion efficiency is less likely to decrease. In the case of conventional boilers, when the main fuel is mixed with a fuel gas, the high combustion speed of the fuel gas generally takes away oxygen for the main fuel combustion, resulting in a decrease in the combustion efficiency of the main fuel. In contrast, in the boiler 10, the refractory material 25 makes it difficult for the temperature in the lower combustion chamber 70 to decrease, thereby maintaining gasification in the lower combustion chamber 70 and making it difficult for the combustion efficiency to decrease.

In addition, in this embodiment, the fuel gas injection nozzle 50 injects fuel gas into the front of the burner, which is the hottest and most reducing area in the combustion furnace 2, thereby maintaining the denitrification reaction.

In addition, in this embodiment, the fuel gas injection nozzle 50 is provided on the furnace walls 70c, 70a that face the furnace walls 70a, 70c on which the burner 5 is provided, and is positioned opposite the burner 5, so that the fuel gas can be injected with high precision in front of the burner, which is the hottest and most reducing area in the combustion furnace 2. This improves the sustainability of the denitrification reaction.

Furthermore, in this embodiment, the injection flow rate of the fuel gas injection nozzle 50 is controlled by the flow rate control device 60, making it easier for the fuel gas to reach the front of the burner.

(Modification)
In addition to the above-described embodiment, the present invention can be modified in various ways without departing from the spirit and scope of the present invention.

In the above embodiment, the fuel gas injection nozzle 50A is arranged on the furnace wall 70a on which the burner 5A is provided, and the fuel gas injection nozzle 50B is arranged on the furnace wall 70c on which the burner 5B is provided, but the arrangement of the fuel gas injection nozzles 50A and 50B is not limited to this. As shown in FIG. 3, the fuel gas injection nozzle 50B may be arranged on the furnace wall 70b perpendicular to the furnace wall 70a on which the burner 5A is provided, and the fuel gas injection nozzle 50A may be arranged on the furnace wall 70d perpendicular to the furnace wall 70c on which the burner 5B is provided. Even in this case, the injection direction of the fuel gas injection nozzle 50B is set to be mainly directed toward the recirculation vortex R in front of the burner 5A, and the injection direction of the fuel gas injection nozzle 50A is set to be mainly directed toward the recirculation vortex R in front of the burner 5B. In other words, as long as the injection direction of each fuel gas injection nozzle is set to be directed toward the area in front of the burner (i.e., the area where the recirculation vortex R exists), the arrangement of the fuel gas injection nozzles is not particularly limited.

In addition, in the above embodiment, the combustion ash is discharged from the top of the combustion furnace 2 and the burners 5A and 5B are arranged in the lower part of the combustion furnace 2 (lower combustion chamber 70), but this is not limited to the above, and the combustion ash may be discharged from the lower part of the combustion furnace 2 and the burners 5A and 5B may be arranged in the upper part of the combustion furnace 2.

In addition, in the above embodiment, the shape of the lower combustion chamber 70 is formed to be square or rectangular in plan view, but this is not limited thereto, and it is also possible to form it to be other shapes (polygonal shapes), such as a hexagon in plan view.

Furthermore, in the above embodiment, the fuel gas injection nozzle 50 may be provided only for the burner 5 arranged upstream of the combustion furnace 2. With this configuration, it is possible to ensure a long residence time of the fuel gas in the combustion furnace 2. This makes it possible to prevent the fuel gas from being incompletely burned, and therefore to prevent the temperature in the reduction region from decreasing, thereby maintaining the denitrification reaction.

(Reclaim)
The fuel combustion system of the present invention comprises a combustion furnace for burning a main fuel, a refractory material arranged to cover at least a portion of the inside of the combustion furnace, a burner for injecting the main fuel into the combustion furnace and burning it, and a fuel gas injection nozzle arranged separately from the burner for injecting fuel gas into the combustion furnace.

Fuel gas is generally introduced into the combustion furnace by being injected from a burner in the same manner as the main fuel. In this regard, when the amount of fuel gas injected is small, the effect of reducing thermal NOx and fuel NOx is expected due to the denitrification reaction in the high-temperature reduction region formed in front of the burner. However, as the amount of fuel gas injected is increased, the proportion of fuel gas that is not completely burned in the high-temperature reduction region in front of the burner increases. This may cause a local decrease in the temperature in front of the burner. As a result, the reduction reaction may be suppressed or the combustion efficiency may decrease. This tendency is more pronounced for fuel gases with slower combustion speeds, such as ammonia gas. In contrast, by providing a fuel gas injection nozzle separately from the burner as in the present invention (hereinafter referred to as this configuration), the fuel gas can be supplied to the high-temperature, oxygen-lean region (high-temperature reduction region) in the combustion furnace without being diluted by the air injected from the burner (air carrying the main fuel). This suppresses the generation of thermal NOx. In addition, this configuration lengthens the residence time of the fuel gas in the combustion furnace, so that most of the fuel gas passes through an oxygen-lean atmosphere. This makes it possible to prevent the fuel gas from being incompletely burned, which in turn makes it possible to prevent the temperature in the reduction region from dropping, thereby maintaining the denitration reaction. Furthermore, this configuration makes it possible to prevent the fuel gas injected from the fuel gas injection nozzle from concentrating excessively in front of the burner. This makes it possible to further prevent the fuel gas from being incompletely burned, which in turn makes it possible to further prevent the temperature in the reduction region from dropping, thereby maintaining the denitration reaction. As described above, according to the present invention, it is possible to suppress insufficient combustion of the fuel gas and suppress thermal NOx.

In the above invention, the fuel gas injection nozzle may inject the fuel gas toward the front of the burner.

According to the above configuration, the denitrification reaction can be maintained by injecting fuel gas in front of the burner, which is the hottest and most reducing area in the combustion furnace.

In the above invention, the combustion furnace is provided with a lower combustion chamber formed at its lower part, having at least four first to fourth furnace walls forming a polygon in a plan view, and covered with the refractory material, the first furnace wall and the third furnace wall are arranged opposite each other, the second furnace wall and the fourth furnace wall are arranged opposite each other, the burners include a plurality of burners provided on the first furnace wall and the third furnace wall, and the fuel gas injection nozzles may include a plurality of fuel gas injection nozzles provided on the first furnace wall and the third furnace wall, or on the second furnace wall and the fourth furnace wall, corresponding to the burners.

According to the above configuration, fuel gas can be injected with high precision in front of the burner, which is the hottest and most reducing area in the combustion furnace. This makes it possible to maintain the denitrification reaction.

In the above invention, one of the fuel gas injection nozzles may be provided on the third furnace wall so as to face the burner provided on the first furnace wall, and the other of the fuel gas injection nozzles may be provided on the first furnace wall so as to face the burner provided on the third furnace wall.

According to the above configuration, the fuel gas can be directly injected in front of the burner, which is the hottest and most reducing area in the combustion furnace. This makes it possible to maintain the denitrification reaction.

In the above invention, the burners may include a burner arranged upstream of the combustion furnace and a burner arranged downstream of the combustion furnace, and the fuel gas injection nozzle may be provided corresponding to the burner arranged upstream of the combustion furnace.

According to the above configuration, the residence time of the fuel gas in the combustion furnace can be extended. This prevents the fuel gas from being completely burned, and prevents the temperature in the reduction region from dropping, thereby maintaining the denitrification reaction.

In the above invention, the fuel combustion system may further include a flow rate control device that controls the injection flow rate of the fuel gas injection nozzle.

According to the above configuration, the injection flow rate of the fuel gas injection nozzle is controlled by the flow rate control device, making it easier for the fuel gas to reach the front of the burner.

2 Combustion furnace 5, 5A, 5B Burner 10 Boiler (an example of a fuel combustion system)
20 Combustion chamber 25 Refractory material 28 Flue 50, 50A, 50B Fuel gas injection nozzle 60 Flow rate control device 70 Lower combustion chamber 70a Furnace wall (first furnace wall)
70b Furnace wall (second furnace wall)
70c Furnace wall (third furnace wall)
70d Furnace wall (4th furnace wall)
d1 Extension direction d2 Injection direction R Recirculation vortex

Claims (3)

A combustion furnace that burns a main fuel;
A refractory material provided so as to cover at least a portion of the inside of the combustion furnace;
a burner for injecting the main fuel into the combustion furnace and burning the fuel;
a fuel gas injection nozzle provided separately from the burner and configured to inject fuel gas into the combustion furnace;
The combustion furnace includes a lower combustion chamber formed in a lower portion thereof, the lower combustion chamber having at least four first to fourth furnace walls that form a polygon in a plan view and that are covered with the refractory material,
The first furnace wall and the third furnace wall are disposed opposite to each other, and the second furnace wall and the fourth furnace wall are disposed opposite to each other,
The burner includes a plurality of burners provided on the first furnace wall and the third furnace wall,
The fuel gas injection nozzle includes a plurality of fuel gas injection nozzles provided on the second furnace wall and the fourth furnace wall corresponding to the burners,
The fuel combustion system, wherein the fuel gas injection nozzles inject the fuel gas into a recirculation vortex in front of the burner . The burners include a burner disposed upstream of the combustion furnace and a burner disposed downstream of the combustion furnace,
The fuel combustion system according to claim 1 , wherein the fuel gas injection nozzle is provided corresponding to the burner disposed upstream of the combustion furnace. The fuel combustion system according to claim 1 , further comprising a flow rate control device for controlling an injection flow rate of the fuel gas injection nozzle.

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