JPH0337093B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion device such as a burner, and in particular, when the combustion device is operated from a low load to a high load, the NOx value in exhaust gas and CO
The present invention relates to a combustion device that suppresses the combustion value to a certain value or less.

Nitrogen oxides (NOx) are responsible for photochemical oxidants, and in recent years there has been a demand for the development of combustion methods that suppress the amount of nitrogen oxides (NOx) generated. NOx generated in combustion devices can be roughly divided into two types: thermal NOx, which is generated at high temperatures and high oxygen concentrations, and fuel NOx, which is generated from nitrogen contained in fuel.

Conventional combustion methods to suppress the generation of NOx include (1) forming a primary combustion zone with less than the stoichiometric amount of air, and introducing the insufficient amount of air into the wake of this zone; A two-stage combustion method that creates a secondary combustion zone.

(2) An exhaust gas recirculation method that circulates the exhaust gas generated by combustion and supplies it again to the burner section.

It has been known.

All of these combustion methods suppress the generation of thermal NOx or reduce the conversion rate of nitrogen oxides to NOx in the fuel by lowering the combustion temperature and oxygen partial pressure. It is something.

On the other hand, in addition to the above-mentioned low NOx combustion method, a new combustion method that combines burners with different air-fuel ratios has been proposed as a method for further reducing NOx in exhaust gas. This method utilizes the fact that a flame with an air-fuel ratio of 1 or less has a reducing effect, and the air-fuel ratio is 1 or less in the wake of the main combustion zone generated by the main burner.
By colliding the flames generated by the following burners, a denitrification combustion zone is formed and NOx formed in the main combustion zone is reduced to harmless nitrogen (N ₂ ).

An example of a combustion device based on these combustion methods will be further explained with reference to the drawings.

FIG. 1 is a longitudinal sectional view of the combustion device, and FIG. 2 is a front view of FIG. 1.

As shown in Figures 1 and 2, the combustion device is
It is composed of a main burner 3 disposed within a burner throat 2 of a furnace wall 1 and a sub burner 4 having an air-fuel ratio of 1 or less.

Then, a part of the combustion air is given a swirling force by swirling vanes 6 disposed in the primary air passage 5 as shown by an arrow, and is sent to the burner throat 2 where a flame stabilizing impeller 7 is installed. The remaining combustion air is supplied into the furnace 10 through the after air port 8 or 9.

On the other hand, a main combustion zone 11 is formed by the primary fuel injected from the main burner 3, and this main combustion zone 11
A denitrification combustion zone 12 is formed around the main combustion zone 11 by secondary fuel ejected from the auxiliary burner 4, and NOx generated in the main combustion zone 11 is reduced to harmless _N2 . Furthermore, the insufficient amount of combustion air is supplied from after air ports 8 and 9, and the CO generated in the denitrification combustion zone 12 is completely combusted.

In this way, combustion air is dividedly supplied to the combustion device from the primary air passage 5 in the burner throat 2 and the after air port 8 or 9, and fuel is also supplied from the primary fuel from the main burner 3 and the secondary fuel from the auxiliary burner 4. This system is designed to reduce NOx in exhaust gas by dividing and supplying fuel and fuel.

However, in this type of combustion device, when starting up or under low load, the injection speed is slow because the fuel and air are supplied separately as described above, resulting in poor mixing of fuel and air in the main combustion zone 11. .

In addition, because the amount of fuel from the auxiliary burner 4 and the amount of air from the after air ports 8 and 9 are small, the penetration force into the furnace 10 becomes weak, causing unstable combustion and generating a large amount of CO and soot in the exhaust gas. I don't like it.

Furthermore, if only normal combustion is performed in the main burner 3 and the auxiliary burner 4, CO and soot and dust will decrease, but NOx will increase, which is not preferable.

The present invention attempts to eliminate such conventional drawbacks, and its purpose is to reduce the amount of NOx and CO in exhaust gas under stable combustion from low load to high load, including startup. The aim is to obtain a combustion device that can suppress the

In order to achieve the above-mentioned object, the present invention includes: a main burner forming a main combustion zone; a sub-burner forming a denitrification combustion zone; a fuel supply system for supplying fuel to the main burner and the sub-burner; and a combustion air supply system for supplying combustion air to the auxiliary burner, a fuel supply amount control means capable of controlling the amount of fuel supplied to the auxiliary burner is provided, and the normal combustion mode and the It is possible to switch between the main combustion zone and the denitrification combustion mode that forms the denitrification combustion zone, and the load zone of the combustion device is divided into a low load zone and a high load zone, and the normal combustion mode is used in the low load zone. The combustion apparatus is operated and switched to the denitrification combustion mode by shifting from a low load area to a high load area, and is controlled to increase the amount of fuel supplied to the auxiliary burner as the load on the combustion apparatus increases. It is characterized by:

Furthermore, in order to achieve the above-mentioned object, the present invention includes a main burner forming a main combustion zone, a sub-burner forming a denitrification combustion zone, and a combustion chamber for unburned matter on the downstream side of the main combustion zone in the flow direction of combustion gas. a fuel supply system that supplies fuel to the main burner and the auxiliary burner; and a combustion air supply system that supplies combustion air to the main burner, the auxiliary burner, and the after air port. The combustion apparatus is provided with a fuel supply amount control means that can control the amount of fuel supplied to the auxiliary burner, and an after air port air supply amount control means that can control the amount of combustion air supplied to the after air port, and usually Combustion mode, a two-stage combustion mode that supplies combustion air to the after air port, and a denitrification combustion mode that forms the main combustion zone and the denitrification combustion zone and supplies combustion air to the after air port can be switched. The load range of the combustion equipment is divided into a low load range, an intermediate load range, and a high load range, and the combustion equipment operates in the normal combustion mode in the low load range, and then shifts from the low load range to the intermediate load range. by switching to the two-stage combustion mode, and by shifting from the intermediate load region to the high load region, switching to the denitrification combustion mode; The amount of air supplied to the air port is controlled, and in the denitrification combustion mode, the amount of air supplied to the after air port is controlled according to the load by the after-air port air supply amount control means, and the amount of air supplied to the after-air port is controlled according to the load, and the amount of air supplied to the after-air port is controlled according to the load. The present invention is characterized in that the amount of fuel supplied to the sub-burner can be controlled according to the amount of fuel supplied to the sub-burner.

Embodiments of the present invention will be described below with reference to the drawings. 3 and 4 are schematic control system diagrams of the combustion apparatus according to the present invention.

In FIGS. 3 and 4, numerals 1 to 12 are the same as those in FIGS. 1 and 2.

13 is a fuel supply system that supplies fuel to the main burner 3 and auxiliary burner 4; 14 is an air supply system that supplies secondary air to the primary air passage 5 and after air ports 8 and 9; 15 is the amount of fuel in the fuel supply system 13; , or detection means for detecting the NOx amount and CO amount at the outlet of the furnace 10, 16 is a detected value, 17 is a set value,
18 is a calculator that calculates the deviation between the detected value 16 and the set value 17; 19 is a fuel valve that controls the amount of secondary fuel to the auxiliary burner 4; and 20 is a damper that controls the amount of secondary air in the after air ports 8 and 9. , 21 are control values.

In such a structure, in the combustion apparatus shown in FIGS. 1 to 4, normal combustion is performed using primary fuel from the main burner 3 and primary air from the primary air passage 5, and an after air port is used for this normal combustion. It is possible to perform two-stage combustion by adding secondary air from 8 and 9, and to perform denitrification combustion by adding secondary fuel from the auxiliary burner 4 to this two-stage combustion.

In the schematic control system diagram shown in Figure 3,
The fuel flow rate of the fuel supply system 13 is detected as a detection value 16 by the detection means 15, and the burner load is calculated based on this detection value 16. 4 by opening and closing the fuel valve 19, and opening and closing the damper 20 of the air supply system 14 to control the amount of secondary air from the after air port 8 or 9, thereby controlling the amount of secondary air flowing to the burner. The combustion state changes depending on the load on the fuel.

4, the NOx amount and CO amount are detected as detected values 16 by the detection means 15 at the outlet of the furnace 10, and the deviation from the set value 17 is determined by the calculator 18 and determined by the control value 21. It opens and closes the fuel valve 19 and damper 20.

The control of the amount of secondary air and the amount of secondary fuel will be explained below, but before that we will introduce the experimental data conducted by the inventors using the combustion apparatus shown in FIGS. 1 and 2.

Fig. 5 is a characteristic curve diagram in which the vertical axis shows the NOx amount and CO amount, and the horizontal axis shows the burner load. Fig. 6 shows the sub-burner fuel quantity ratio and after-airport air quantity ratio in the vertical axis, and the horizontal axis shows the burner load. FIG. 3 is a characteristic diagram showing the operating range of the combustion device with the burner load shown in FIG.

In addition, the inventors described (a) a case in which fuel is supplied only to the main burner 3 and combustion air is supplied only to the primary air passage 5 of the burner throat 2 for combustion (normal combustion);

(b) When fuel is supplied only to the main burner 3, combustion air is supplied from the primary air passage 5 of the burner throat 2, and the remaining combustion air is supplied from the after air port 8 or 9 for combustion (two-stage combustion).

(c) The fuel is sent to the main burner 3 and the remaining fuel is sent to the auxiliary burner 4.
When the combustion air is supplied to the primary air passage 5 of the burner throat 2 and the remaining combustion air is supplied to the after air port 8 or 9 for combustion (denitrification combustion).

Burner load and furnace 10 during the combustion process of (a) to (c)
We actually measured the amount of NOx and CO at the outlet.
The combustion test conditions at this time were as follows.

Furnace dimensions: 2m x 2m x 2.5m (length, width, length) Furnace outlet oxygen concentration: 2% constant Fuel amount: LPG 150Nm ³ /H when burner load is 100%
So, when the burner load decreased, the fuel amount was also decreased according to the load ratio.

In addition, in the case of two-stage combustion, after air port 8,
The air amount ratio from 9 was set to 20%. Here, the after air port air amount ratio from the after air ports 8 and 9 is defined by the following equation.

After air port air amount ratio = after air port supply combustion air amount / total combustion air amount In addition, in the case of denitrification combustion, the after air port air amount ratio is 40%, and the fuel amount ratio from auxiliary burner 4 is
It was set at 20%. Here, the sub-burner fuel quantity ratio is defined by the following equation.

Sub-burner fuel quantity ratio = Sub-burner supplied fuel quantity/total fuel quantity In Fig. 5, the curve ~ indicates the NOx quantity,
The curve shows the normal combustion, the curve shows the two-stage combustion, and the curve shows the denitrification combustion.

The curve ~ shows the amount of CO, the curve shows that during denitrification combustion, the curve shows that during two-stage combustion, and the curve shows that during normal combustion.

Then, the curve for normal combustion and the burner load at 25% is point A, the curve for two-stage combustion is at point B when the burner load is 75%, the curve for denitrification combustion,
Point C is when the burner load is 100%, point D is when the burner load is 50% on the curve during two-stage combustion, point E is when the burner load is 75% on the curve during denitrification combustion, and
Points A to E in the figure correspond to points A to E in FIG. 5.

According to the experimental data shown in Figure 5, normal combustion,
In both cases of two-stage combustion and denitrification combustion,
As the burner load decreases, the NOx value tends to decrease as shown in the curve ~, and as the burner load decreases, the CO amount tends to increase as shown in the curve ~.

The amount of NOx decreases in the order of normal combustion, two-stage combustion, and denitrification combustion, as shown in the curve ~, regardless of the load, and conversely, the amount of CO decreases in the order of normal combustion, two-stage combustion, and denitrification combustion, as shown in the curve ~. It can be seen that the amount increases in the order of , denitrification and combustion.

Therefore, based on this experimental data, the present inventors changed the combustion state of the combustion device depending on the burner load, as explained below.

When the burner load is low, including during start-up, normal combustion is performed, which produces the least amount of CO, and when the load increases and the load increases from low to intermediate, the NOx amount exceeds the specified value, so the normal combustion changes to two-stage combustion. Then, adjust the after air port air amount ratio of after air port 8 or 9 so that not only the NOx amount but also the CO amount does not exceed the specified value.

Then, as the load increases further and the NOx amount exceeds the specified value from intermediate load to full load, the transition from two-stage combustion to denitrification combustion occurs, and not only the NOx amount but also the CO amount exceeds the specified value, so the after-sales service is completed. The airport air amount ratio and the auxiliary burner fuel amount ratio from the auxiliary burner 4 are adjusted.

An example of control of such a combustion device will be explained based on the combustion test results shown in FIG.

For example, when increasing the burner load assuming that the upper limit of NOx amount is 53 ppm and the upper limit of CO amount is 5 ppm, normal combustion is performed until the burner load reaches 25%. At this time, as shown by point A of the curve in Figure 5,
The amount of NOx was 53ppm and the amount of CO was 5ppm, both within the upper limits.

If normal combustion continues even when the burner load exceeds 25%, the NOx amount will exceed the upper limit, as shown by the curve in Figure 5, and the burner load will exceed 25%.75
%, in order to move from point A of the curve to point B of the curve in FIG. is also gradually increased from point A to point B in FIG.

When the burner load exceeds 75% and reaches 100%, if the two-stage combustion continues, the amount of NOx will exceed the upper limit as shown by the curve in Figure 3, so the two-stage combustion is further shifted to denitrification combustion.

At this time, the fuel to the auxiliary burner 4 is gradually opened by gradually opening the fuel valve 19 according to the control value 21, and the auxiliary burner fuel amount ratio is gradually increased from point B to point C in FIG. Since the amount of air becomes insufficient as the amount of fuel increases, the after air port air amount ratio from after air port 8 or 9 is also controlled to increase from point B to point C in FIG. 6.

In this way, the amount of NOx associated with an increase in burner load is
By shifting the combustion from point A of the curve in FIG. 5 to point B of the curve, and further from point B of the curve to point C of the curve, the amount of NOx can be suppressed.

Next, in order to suppress the amount of NOx as much as possible and control the combustion equipment so that the amount of CO does not exceed the upper limit, both the after-air port air amount ratio and the sub-burner fuel amount ratio must be adjusted from point A in Figure 6. Control is performed so that it is expressed by a line passing through D and E and ending at point C.

In other words, when the burner load exceeds 25% and reaches 50%, normal combustion is shifted from point A to point D of the curve in Figure 5 to prevent the CO amount from exceeding the upper limit. Then, the after-air port air amount ratio is gradually increased from point A to point D in FIG.

When the burner load exceeds 50% and reaches 100%, the transition is made from two-stage combustion to denitrification combustion as shown from point D on the curve in Figure 5 to point E and C on the curve, so that the amount of CO exceeds the upper limit. To prevent this, the sub-burner nozzle fuel ratio is gradually increased from point D to point E in Fig. 6. At this time, as the amount of fuel from the sub-burner 4 increases, the amount of air becomes insufficient, so from the after air port 8 or 9. The after-air air amount ratio is also controlled to increase from point D to point E to point C in FIG.

That is, in FIGS. 3 and 4, when increasing the burner load, the amount of fuel in the fuel supply system 13 is detected by the detection means 15, or the amount of NOx and CO in the exhaust gas at the outlet of the furnace 10 is detected by the detection means 15. The deviation of this detected value 16 from the set value 17 is determined by the calculator 18, and the control value 21 is used to control the fuel valve 19 from point A as shown in the auxiliary burner fuel amount ratio in FIG. Points D, E, and C, or points B and C gradually open to increase the amount of secondary fuel.

On the other hand, the dampers 20 of the after air ports 8 and 9 are also as shown in the after air port air amount ratio in FIG.
The secondary air volume is increased by gradually opening from point A to points D, E, and C or points B and C.

When controlled in this way, the amount of NOx can also be controlled at point A, point D, point E, and C of the curve in Figure 5.
It can be a low value that connects the points.

As mentioned above, for example, the upper limit of NOx value
53ppm, and in order to operate without exceeding the CO amount upper limit of 5ppm, the combustion state of the combustion device must be shifted to points A, B, and C in Figure 3, or the combustion state of the combustion equipment must be shifted to point A,
By moving to point D, point E, and point C,
In other words, the operation should be shifted within the shaded area in Fig. 5. For this purpose, the after-air port air amount ratio and sub-burner fuel quantity ratio may also be set arbitrarily within the shaded area in Fig. 6, and the low The amount of NOx and CO in the exhaust gas can be suppressed from load to high load, and combustion can be performed stably.

7 and 8 show other embodiments of the combustion apparatus shown in FIGS. 1 and 2. In FIGS.

FIG. 7 is a longitudinal cross-sectional view of the combustion device, and FIG. 8 is an enlarged view of the main burner 3 and auxiliary burner 4 shown in FIG.

The difference from the combustion apparatus shown in FIGS. 1 and 2 is that in the combustion apparatus shown in FIGS. However, in the combustion devices shown in Figures 7 and 8, the burner throat 2
A main burner 3 and a sub-burner 4 are arranged inside.

In Figures 7 and 8, 22, 23
are the fuel injection holes of the main burner 3 and the auxiliary burner 4.

Therefore, the fuel injected from the fuel injection hole 22 of the main burner 3 forms a main combustion zone 11 near the flame-holding impeller 7 as shown in FIG.
A denitrification combustion zone 12 is formed in the wake of the combustion chamber 1 by fuel from the fuel injection hole 23 of the auxiliary burner 4, and NOx generated in the main combustion zone 11 is reduced to harmless _N2 .

In this way, in the combustion devices shown in FIGS. 7 and 8, normal combustion from the main burner 3 and main burner 3
and denitrification combustion using the auxiliary burner 4.

In the schematic control system diagrams of FIGS. 9 and 10, the amount of fuel in the fuel supply system 13, or the amount of NOx or CO at the outlet of the furnace 10 is detected by the detection means 15 as a detected value 16, Based on this detected value 16, the burner load is calculated and the detected value is 16.
The deviation between the value and the set value 17 is determined by the calculator 18, and the fuel valve 19 of the auxiliary burner 4 is opened and closed according to the control value 21 to increase or decrease the amount.

The control of the secondary fuel amount will be explained below.
We will introduce experimental data that the inventors conducted before that. The combustion test conditions are shown in Figures 1 and 2.
It is the same as the one shown in the figure.

In Fig. 11, the curve indicates the amount of NOx,
The curve shows that during normal combustion, and the curve shows that during denitrification combustion.

The curve indicates the amount of CO, the curve indicates that during denitrification combustion, and the curve indicates that during normal combustion.

And the burner load of the curve during normal combustion
Point F is at 25%, point G is at 50% burner load, point J is at 75% burner load, point H is at 75% burner load, and point I is at 100% burner load.
Points F to I in Figure 12 are F to I in Figure 11.
This point corresponds to the point.

According to the experimental data shown in Figure 11, in both normal combustion and denitrification combustion, as the burner load decreases, the NOx value tends to decrease as shown in the curve, and the CO amount decreases as the burner load decreases. The curve tends to increase as shown in the figure.

Therefore, based on this experimental data, the inventors changed the combustion state depending on the burner load as explained below.

When the burner load is up to 75%, normal combustion with a small amount of CO is performed, and when the load exceeds 75%, the NOx amount exceeds the specified value, so denitrification combustion is performed, or when the burner load is up to 50%, normal combustion is performed. ,
When the load exceeds 50%, denitrification combustion is performed.

For example, when increasing the burner load assuming that the upper limit of the NOx amount is 60 ppm and the upper limit of the CO amount is 10 ppm, normal combustion is performed by the main burner 3 until the burner load reaches 75%. At this time, the curve in Figure 11,
As shown at point J, the amount of NOx is 60ppm, and the amount of CO is
It is within the upper limit at 10ppm.

If normal combustion continues even when the burner load exceeds 75%, the NOx amount will exceed the upper limit, as shown by the curve in Figure 11, and the burner load will exceed 75%.
Up to 100%, in order to move from point J on the curve in Figure 11 to point I on the curve,
The number of fuel valves 19 in Fig. 0 is gradually increased from point J to point I in Fig. 12.

At this time, the detection means 15 shown in FIG. 9 compares the detected value 16 of the NOx amount and CO amount at the outlet of the furnace 10 with the set value 17, or the detection means 1 shown in FIG.
5, the fuel valve 19 to the auxiliary burner 4 is gradually opened by comparing the detected value 16 of the fuel amount in the fuel supply system 13 with the set value 17, and the fuel amount to the auxiliary burner 4 is adjusted to J in FIG. It increases from point to point I.

On the other hand, normal combustion is performed when the burner load reaches 50%, and denitrification combustion is performed when the burner load exceeds 50%.

If this is explained in Figure 11, the burner load will be 50%.
Until then, normal combustion is performed up to point G on the curve, and when the burner load reaches 50% or more, the combustion moves from point G to point H and I on the curve in FIG. 11, where denitration combustion is performed.

In this way, when changing the combustion state depending on the burner load, the fuel valve 19 shown in FIGS.
is gradually opened to increase the amount of fuel in the auxiliary burner 4 from point G to point H in FIG.

As mentioned above, in the combustion devices shown in Figures 7 and 8, in order to reduce the NOx value to 60 ppm and the CO amount to 10 ppm or less, for example, move from point F to points G, J, and I in Figure 11. By shifting the combustion state or shifting from point F to points G, H, and I, the amount of fuel to the sub-burner 4 can also be changed from point F to G, H, and I.
By changing from point J, I or point G to point H, I, that is, FIG.
If the combustion conditions are changed in the shaded area in Figure 2, the amount of NOx in the exhaust gas will change from low load to high load.
The amount of CO can be suppressed and stabilized regardless of burner load.

As described above, the present invention is capable of controlling the entire load range by switching between the normal combustion mode and the denitrification combustion mode, or by switching between the normal combustion mode, the two-stage combustion mode, and the denitrification combustion mode depending on the load range of the combustion device. It is possible to achieve stable combustion over a long period of time, and to effectively suppress the generation of NOx and CO.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view of the combustion device, Fig. 2 is a front view of Fig. 1, Figs. 3 and 4 are schematic control system diagrams of the combustion device of Figs. The vertical axis shows the NOx amount and CO amount, and the horizontal axis shows the burner load. Figure 6 shows the characteristic curve showing the operating range of the combustion equipment. , the horizontal axis shows the burner load, and a characteristic diagram showing changes in the fuel quantity ratio and air quantity ratio in the operating range of the combustion device, FIG. 7 is a longitudinal cross-sectional view of another combustion device, and FIG. 9 and 10 are schematic control system diagrams of the combustion apparatus shown in FIGS. 7 and 8,
Fig. 11 is a characteristic curve diagram showing the operating range of the combustion device with the vertical axis showing the NOx amount and CO amount and the horizontal axis showing the burner load, and Fig. 12 showing the sub-burner fuel quantity ratio on the vertical axis. FIG. 3 is a characteristic diagram showing the change in fuel quantity ratio in the operating range of the combustion device, with burner load plotted on the horizontal axis. 3...Main burner, 4...Sub-burner, 10...Furnace, 13...Fuel supply system, 14...Air supply system, 15...Detection means, 16...Detection value, 17...
...Set value, 18...Calculator, 19...Fuel valve, 2
0...Damper, 21...Control value.

Claims (1)

[Scope of Claims] 1. A main burner forming a main combustion zone, a sub-burner forming a denitrification combustion zone, a fuel supply system for supplying fuel to the main burner and the sub-burner, and a fuel supply system for supplying fuel to the main burner and the sub-burner. In a combustion apparatus equipped with a combustion air supply system that supplies combustion air, a fuel supply amount control means that can control the amount of fuel supplied to the auxiliary burner is provided, and the fuel supply amount control means is provided to control the amount of fuel supplied to the auxiliary burner, and the fuel supply amount control means is provided to control the amount of fuel supplied to the auxiliary burner. It is now possible to switch between the denitrification combustion mode that forms the denitrification combustion region, and the load region of the combustion device is divided into a low load region and a high load region, and in the low load region it operates in the normal combustion mode and in the low load region. The method is characterized in that the denitrification combustion mode is switched to when the load region shifts to a high load region, and the amount of fuel supplied to the auxiliary burner is increased as the load on the combustion device increases. A method for controlling a combustion device. 2 a main burner forming a main combustion zone; a sub-burner forming a denitrification combustion zone; an after-air port for supplying air for unburned combustion to the downstream side of the main combustion zone in the flow direction of combustion gas; A combustion apparatus comprising a fuel supply system that supplies fuel to a burner and a sub-burner, and a combustion air supply system that supplies combustion air to the main burner, sub-burner, and after-air port, wherein the fuel supply system supplies fuel to the sub-burner. A fuel supply amount control means capable of controlling the supply amount and an after air port air supply amount control means capable of controlling the supply amount of combustion air to the after air port are provided, and the fuel supply amount control means can control the supply amount of combustion air to the after air port. It is possible to switch between the two-stage combustion mode, which supplies combustion air, and the denitrification combustion mode, which forms the main combustion zone and denitrification combustion zone, and supplies combustion air to the after air port. The combustion equipment is divided into a load region, an intermediate load region, and a high load region, and in the low load region of the combustion device, the combustion device operates in the normal combustion mode, and when the low load region shifts to the intermediate load region, it switches to the two-stage combustion mode, and in the intermediate Switching to the denitrification combustion mode by shifting from the load region to the high load region, and in the two-stage combustion mode, the after air port air supply amount control means controls the amount of air supplied to the after air port according to the load, and the amount of air supplied to the after air port is controlled according to the load. In the denitrification combustion mode, the after-air port air supply amount control means controls the amount of air supplied to the after-air port according to the load, and the fuel supply amount control means controls the amount of fuel supplied to the sub-burner according to the load. 1. A method for controlling a combustion device, characterized in that the method is configured to control a combustion device.