TWI838836B - Boiler, boiler control method, and boiler transformation method - Google Patents

Abstract

The burner arrangement of the boiler is such that the ammonia burner and the pulverized coal burner are arranged separately. Specifically, the boiler of several embodiments of the present invention comprises: a furnace including a furnace wall, an ammonia burner disposed on the furnace wall and burning ammonia fuel, and a pulverized coal burner disposed at a position of the furnace wall different from the ammonia burner and burning pulverized coal.

Description

Boiler, boiler control method, and boiler transformation method

The present invention relates to a boiler for burning ammonia and pulverized coal, a boiler control method, and a boiler modification method. This case claims priority based on Special Application No. 2021-146609 filed on September 9, 2021 at the Japan Patent Office and Special Application No. 2021-200928 filed on December 10, 2021 at the Japan Patent Office, and the contents thereof are hereby cited.

In the past, there is a known boiler that supplies ammonia as fuel to the furnace. When ammonia is used as fuel, it is necessary to suppress the emission of nitrogen oxides (NOx). For example, in the burner disclosed in Patent Document 1 (shown in FIG. 2 ), a nozzle that rotates around the nozzle that feeds ammonia is provided (it is stated that it may not rotate) to mix ammonia with the rotating coal powder flame. In addition, the following is disclosed. That is, the combustion device 4A installed in the furnace and capable of burning ammonia as fuel comprises: an inner tube nozzle 41 which is arranged at the center when viewed from the fuel injection direction and injects ammonia; and an outer tube nozzle 42 which is arranged to surround the inner tube nozzle 41 from the radial outer side when viewed from the fuel injection direction and injects ammonia around the inner tube nozzle 41. The vortexer 45 is arranged inside the outer tube nozzle 42 and causes the flow of ammonia injected around the inner tube nozzle 41 to swirl. According to Patent Document 1, ammonia sprayed from the inner cylinder nozzle 41 forms a reduction zone with a high ammonia concentration and a low oxygen concentration in the center of the flame when viewed from the injection direction of the fuel. On the other hand, nitrogen oxides generated by the combustion of ammonia sprayed from the outer cylinder nozzle to the periphery of the inner cylinder nozzle and mixed with oxygen are supplied to the reduction zone along the circulation flow by flowing back from the outer edge of the flame toward the center. As a result, nitrogen oxides generated at the outer edge of the flame are reduced to nitrogen (N2) in the reduction zone formed by ammonia sprayed from the inner cylinder nozzle. Therefore, according to Patent Document 1, the increase of nitrogen oxides can be suppressed in a boiler that can burn ammonia as fuel. [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Application Publication No. 2020-41748

[The problem the invention is trying to solve]

From the inventors' point of view, in order to suppress the emission of nitrogen oxides, it is better to use other fuels to make the combustion environment in the boiler into a reducing zone and correctly control the air ratio near the ignition point. However, Patent Document 1 does not specifically reveal such a structure. Moreover, when the burner shown in Patent Document 1 is used to make ammonia mixed combustion, if the mixed combustion (mixed combustion) rate of ammonia is increased, the air ratio of the coal nozzle will increase. In order to prevent the coal in the coal nozzle from settling, a certain amount of transport air must be maintained. If the ammonia mixed combustion rate is increased, the coal supply will decrease, so the transport air volume will increase relative to the coal flow rate. Therefore, when the ammonia co-combustion rate is high, the air ratio around the ammonia nozzle will become higher, and ammonia oxidation will cause a rapid increase in nitrogen oxides.

Therefore, the purpose of the present invention is to provide a boiler, a boiler control method, and a boiler modification method, which can burn ammonia fuel under conditions that can suppress the generation of nitrogen oxides. [Technical means for solving the problem]

The burner configuration of the boiler of at least one embodiment of the present invention is to configure the ammonia and pulverized coal burners separately. That is, the boiler of at least one embodiment of the present invention comprises: a furnace including a furnace wall, an ammonia burner disposed on the aforementioned furnace wall and burning ammonia fuel, and a pulverized coal burner disposed at a position of the aforementioned furnace wall different from the aforementioned ammonia burner and burning pulverized coal.

The boiler is provided with a control device for controlling the supply amounts of the ammonia fuel, the pulverized coal and the combustion air, the control device comprising: a first calculation unit, which calculates the ratio of the amount of air for ammonia combustion supplied to the ammonia fuel to the theoretical amount of air required for burning the ammonia fuel, i.e., the ammonia-air ratio; a second calculation unit, which calculates the ratio of the amount of air for pulverized coal combustion supplied to the pulverized coal to the theoretical amount of air required for burning the pulverized coal, i.e., the pulverized coal-air ratio; and a control unit, which controls the supply amounts so that the ammonia-air ratio satisfies a first standard range and the pulverized coal-air ratio satisfies a second standard range.

The first calculation unit calculates the ammonia-air ratio for each of the plurality of ammonia burners, and the control unit controls the supply amount so that each ammonia-air ratio satisfies the first reference range.

The furnace wall is provided with an air nozzle disposed adjacent to the ammonia burner. The first calculation unit calculates the ammonia-air ratio using the amount of air for ammonia combustion including the amount of air supplied to the ammonia fuel, among the amount of air ejected from the air nozzle.

The upper limit value of the first reference range is lower than the upper limit value of the second reference range.

The first reference range is below 0.8.

The first reference range is below 0.7.

The first reference range is set based on the value of nitrogen oxides in the combustion gas exhausted from the furnace.

The boiler has an auxiliary air nozzle adjacent to the ammonia burner for supplying auxiliary air. The auxiliary air nozzle has a damper capable of adjusting the amount of auxiliary air. The auxiliary air can be supplied in the direction of the ammonia burner.

The aforementioned ammonia burner comprises: an ammonia nozzle for injecting the aforementioned ammonia fuel, a starting fuel nozzle for injecting starting fuel.

The aforementioned ammonia burner is arranged adjacent to the aforementioned pulverized coal burner.

The aforementioned ammonia burner is arranged adjacent to the aforementioned pulverized coal burner.

The aforementioned furnace wall includes: a burner configuration area, which is provided with the aforementioned ammonia burner and the aforementioned pulverized coal burner; and an additional air supply area, which is provided with an additional air supply section that supplies additional air at a location downstream of the aforementioned burner configuration area, and the aforementioned ammonia burner is located at the uppermost section of the aforementioned burner configuration area.

The aforementioned ammonia burner is a diffusion burner or a partially premixed burner.

The aforementioned diffusion burner or the aforementioned partial premixing burner is any one of a partially premixing joint type, a diffusion type and a swirler type or a diffuser type with a different structure of the flame protector.

At least one embodiment of the present invention is a boiler control method for controlling the supply of ammonia fuel, pulverized coal and combustion air in a boiler, wherein the boiler comprises: a furnace comprising a furnace wall, an ammonia burner disposed on the furnace wall and burning the ammonia fuel, and a pulverized coal burner disposed at a position of the furnace wall different from the ammonia burner and burning the pulverized coal, and wherein the boiler comprises: a first calculation step for calculating the supply of the ammonia fuel a first calculation step of calculating the ratio of the amount of air for combustion of ammonia supplied to the aforementioned pulverized coal to the theoretical amount of air required for combustion of the aforementioned pulverized coal, i.e. the pulverized coal-air ratio; and a control step of controlling the aforementioned supply amount so that the aforementioned ammonia-air ratio satisfies a first standard range and the aforementioned pulverized coal-air ratio satisfies a second standard range.

At least one embodiment of the present invention provides a boiler modification method, wherein the boiler comprises: a furnace including a furnace wall, a pulverized coal burner disposed on the furnace wall and burning pulverized coal, a plurality of injection units disposed at positions of the furnace wall different from the pulverized coal burner and injecting pulverized coal or starting fuel or auxiliary air, and a control device. The boiler modification method comprises a replacement step of replacing at least one of the plurality of injection units with an ammonia burner that burns ammonia fuel, controlling the supply of the ammonia fuel, the pulverized coal, and the combustion air. The control device for controlling the supply amount comprises: a first calculation unit, which calculates the ratio of the amount of air for ammonia combustion supplied to the ammonia fuel to the theoretical amount of air required for the combustion of the ammonia fuel, i.e., the ammonia-air ratio; a second calculation unit, which calculates the ratio of the amount of air for pulverized coal combustion supplied to the pulverized coal to the theoretical amount of air required for the combustion of the pulverized coal, i.e., the pulverized coal-air ratio; and a control unit, which controls the supply amount so that the ammonia-air ratio satisfies the first standard range and the pulverized coal-air ratio satisfies the second standard range. [Effect of the invention]

According to the present invention, a boiler, a boiler control method and a boiler modification method can be provided, which can burn ammonia fuel under the condition that the generation of NOx can be suppressed.

Hereinafter, several embodiments of the present invention will be described with reference to the attached drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described or shown in the drawings as embodiments are not intended to limit the scope of the present invention to these embodiments, but are merely illustrative examples.

FIG1 is a conceptual diagram of a boiler operation system 1 in an implementation form. The boiler operation system 1, for example, comprises: a boiler 2 assembled in a thermal power plant not shown in the figure, a supply system 15 for supplying air and fuel to the boiler 2, and a measuring system 9 for measuring parameters related to the operation of the boiler 2. The fuel supplied to the boiler 2 from the supply system 15 contains ammonia fuel. The ammonia fuel may be either liquid ammonia or ammonia gas. Below, an implementation form in which the ammonia fuel is liquid ammonia is given. In one implementation form, liquid ammonia is supplied to the boiler 2 in liquid form. Although liquid ammonia does not contain gases such as hydrogen, it may contain impurities (such as urea) to the extent that they do not affect the combustion of boiler 2. Liquid ammonia is vaporized into ammonia gas in boiler 2. Moreover, the fuel supplied to boiler 2 from supply system 15 contains other fuels besides ammonia fuel. For example, in boiler 2, after combustion using other fuels, mixed combustion (mixed combustion) of ammonia and other fuels or dedicated combustion (dedicated combustion) of ammonia is performed. An example of other fuels besides ammonia is also a carbon-containing fuel, such as biomass fuel or fossil fuel. Fossil fuels are oils such as liquefied natural gas, heavy oil or light oil, or coal such as pulverized coal. The following is an example of an implementation form in which the carbon-containing fuel is oil and pulverized coal.

A boiler 2 in an embodiment includes a furnace 20 including a furnace wall 19. The furnace wall 19 includes a burner arrangement area 21 provided with at least one burner unit 30, and an additional air supply area 22 provided with an additional air supply portion 4 for supplying additional air (extra air). The additional air supply area 22 is located downstream of the burner arrangement area 21. The furnace 20 is a cylindrical hollow body for reacting the fuel sprayed by the burner unit 30 with the combustion air and burning, and can be various shapes such as a cylindrical shape or a quadrangular prism shape. Furthermore, the furnace 20 in an embodiment includes a nose 11 protruding toward the furnace 20. The nose 11 allows the gas (e.g., combustion gas and unburned gas) generated in the combustion space 7 of the furnace 20 to flow appropriately in the flow path downstream of the furnace 20. The flow path downstream of the furnace 20 is, for example, the flue 8. At least one burner unit 30 allows the fuel to burn in the combustion space 7 of the furnace 20. In the embodiment shown in FIG. 1 , the burner unit 30 is divided into three sections and arranged along the direction of flow of the gas generated in the combustion space 7 (arrow A in FIG. 1 ). Hereinafter, the burner units 30 of each stage are sometimes referred to as the first burner unit 31, the second burner unit 32, and the third burner unit 33 in order from the downstream side of the gas flow direction, and there are also cases where the three burners are collectively referred to as the burner unit 30. In addition, the burner unit 30 may be arranged in two stages or four stages. The boiler 2 of one embodiment is a cyclonic combustion boiler, and the burner units 30 provided in each stage are arranged in multiple numbers at equal intervals along the circumferential direction of the furnace 20. The number of the burner units 30 of each stage is four as an example, but only one burner unit 30 of each stage is illustrated in FIG1. Furthermore, the number of the burner units 30 in each stage may be three or five or more. The boiler 2 in another embodiment is a facing combustion type boiler. In this case, at least one pair of the burner units 30 in each stage are provided at positions facing each other.

Each burner unit 30 includes at least one burner. Moreover, in at least one burner unit 30, the burner is an ammonia burner 306 that sprays liquid ammonia in liquid form into the interior of the furnace 20. The ammonia burner 306 may spray only liquid ammonia. Alternatively, the ammonia burner 306 may spray liquid ammonia together with the carbon-containing fuel (or instead of the carbon-containing fuel) after spraying the carbon-containing fuel. In one embodiment, the first burner unit 31 includes the ammonia burner 306. The second burner unit 32 and the third burner unit 33 may or may not include the ammonia burner 306. In other embodiments, the ammonia burner 306 may include only the second burner unit 32 or the third burner unit 33. In addition, any burner unit 30 may include a coal burner 302, 304 (coal burners 302, 304 shown in FIG. 3A) for injecting pulverized coal as an example of carbon-containing fuel into the furnace 20, a start-up fuel burner 307 (see FIG. 3A) for injecting oil as an example of start-up fuel into the furnace 20, or an auxiliary air nozzle (air nozzle) 301, 305 (see FIG. 3A) for injecting auxiliary air. Details will be described later.

In one embodiment, the supply system 15 supplies primary air and fuel to the burner unit 30. The fuel (in this example, liquid ammonia and carbon-containing fuel) supplied to the burner unit 30 can be switched. For example, liquid ammonia may be supplied to the burner unit 30 of any stage after the carbon-containing fuel (such as oil) has been supplied.

A measurement system 9 in one embodiment includes: a plurality of flow meters for measuring the flow rate of air or fuel supplied from a supply system 15; and a furnace thermometer 6 for measuring a representative temperature in a furnace 20. The representative temperature in the furnace 20 is the temperature of the gas in the combustion space 7 of the furnace 20, that is, a temperature related to the gas temperature. As an example, the representative temperature in the furnace 20 is the temperature of the inner wall surface of the nose 11 (hereinafter referred to as the nose temperature). The nose temperature is measured by the furnace thermometer 6. In addition, the representative temperature in the furnace 20 may be, for example, the gas temperature.

The boiler operation system 1 may be operated by the operation of an operator, by the control of a control device 5 (see FIG. 9 ) described later, or by a combination of these. In the furnace 20 of one embodiment, the supply of ammonia fuel is started after the combustion of a fuel other than ammonia fuel (in this case, a carbon-containing fuel), and a mixed combustion of ammonia fuel and other fuels may be performed.

When nitrogen-containing fuels such as coal or ammonia are burned, the air ratio during combustion generally has a greater impact on the generation of nitrogen oxides. Here, the case where ammonia fuel is mixed with other fuels and burned is described below: as a comparative example, a case where the entire furnace is calculated to have a single air ratio, and as an implementation example, a case where the air ratios of ammonia fuel and carbon-containing fuel as other fuels are calculated. (Comparative example) The air ratio of the comparative example is the ratio of the air supply amount to the furnace 20 to the theoretical air amount required to burn the ammonia fuel and other fuels supplied to the furnace 20. The above-mentioned air supply amount to the furnace 20 does not include additional air (extra air). That is, in this example, the air ratio constituting the ammonia co-firing condition (details to be described later) is the value obtained by multiplying the supply ratio of air other than the additional air in all the air supplied to the furnace 20 by the total air ratio. Specifically, the air ratio constituting the ammonia co-firing condition (hereinafter sometimes referred to as the burner air ratio) is defined by the following formula (1). In the formula (1), _λb is the burner air ratio, λ is the total air ratio, and AA is the supply ratio of the additional air to the total air supply to the boiler 2. The total air ratio (λ) is defined by the formula (2), the formula (3), and the formula (4). In formula (2) to formula (4), Q _Air is the total air supply amount. And, Q _mf is the supply amount of ammonia fuel and other fuel (in this case, carbon-containing fuel) when the combustion performed in the furnace 20 is ammonia mixed combustion (mixing rate converted by weight: X%). _{Q x} is the air flow rate used to make the air ratio 1 during the mixed combustion. A _mf is the theoretical air amount of the fuel (in this case, ammonia fuel and carbon-containing fuel) when the above mixed combustion is performed, A _car is the theoretical air amount of the carbon-containing fuel, and A _NH3 is the theoretical air amount of the ammonia fuel. (Example) In the example, the ratio of the amount of air for ammonia combustion supplied to the ammonia fuel to the theoretical amount of air for ammonia fuel supplied to the furnace 20, i.e., the ammonia air ratio, and the ratio of the amount of air for combustion supplied to other fuels to the theoretical amount of air for other fuels, i.e., the air ratio for other fuels, are calculated respectively according to the fuel. The ammonia air ratio (hereinafter also referred to as the ammonia burner air ratio) is obtained by equation (5) and equation (6). Here, λ _NH3 in equation (5) is the ammonia air ratio, Q _{Air_NH3} is the air amount for ammonia combustion, and Q _{x_NH3} is the air flow rate for making the ammonia fuel air ratio 1. Also, Q _NH3 in equation (6) is the supply amount of ammonia fuel, and A _NH3 is the theoretical air amount of ammonia fuel. And, if carbon-containing fuel is taken as an example of other fuels, the air ratio of the carbon-containing fuel is obtained by equations (7) and (8). Here, λ _car of formula (7) is the air ratio of the carbon-containing fuel, Q _{Air_car} is the amount of air for combustion of the carbon-containing fuel, and Q _{x_car} is the air flow rate for making the air ratio of the carbon-containing fuel 1. Furthermore, Q _car of formula (8) is the supply amount of the carbon-containing fuel, and A _car is the theoretical air amount of the carbon-containing fuel. As in the present embodiment, the ammonia air ratio λ _NH3 and the air ratio λ _car of the carbon-containing fuel are calculated separately, thereby enabling individual adjustments. For example, in a boiler 2 using an ammonia burner 306 and a pulverized coal burner 302 (see FIG. 3B ), formulas (5) and (6) are applied to the air ratio of the ammonia burner 306, and formulas (7) and (8) are applied to the air ratio of the pulverized coal burner 302. In other words, the parameters of the carbon-containing fuel shown in equations (7) and (8) in this case all become parameters of the pulverized coal. Hereinafter, the air ratio refers to the one calculated in this embodiment.

In one embodiment, the coal burner 302 and the ammonia burner 306 are separately installed as shown in FIG. 3A to FIG. 3C as an example of a rotary combustion boiler (FIG. 3A shows the boiler before the modification before the ammonia burner 306 is installed). In this way, the air ratio can be adjusted individually, and even if the mixed combustion rate of ammonia is increased, the air ratio of ammonia can be reduced regardless of the use of the coal burner, thereby suppressing the rapid increase of NOx. In addition, the coal burner 302 of this embodiment is configured to burn coal (coal powder). In the following description, the coal burner 302 refers to the coal powder burner 302.

In one embodiment, the upper limit of the burner air ratio is 0.8 or less. If the ammonia fuel is supplied to the furnace 20 under the condition that the burner air ratio is 0.8 or less, the burner air ratio at the start of combustion of the ammonia fuel will also be below 0.8. This effectively reduces the NOx generated in the furnace 20. The upper limit of the burner air ratio may be 0.7 or less. In this case, the combustion of the ammonia fuel is started under the condition that the air ratio is 0.7 or less, and excessive generation of NOx is suppressed. In addition, in a general-sized boiler 2 used in a thermal power plant, it is not realistic to have a burner air ratio of less than 0.6. Therefore, the burner air ratio constituting the condition to be satisfied before the supply of ammonia fuel begins, i.e., the ammonia co-combustion condition, is preferably greater than 0.6 and less than 0.8, and more preferably greater than 0.6 and less than 0.7. Furthermore, in the case where a plurality of ammonia burners 306 are provided, it is preferred to calculate the ammonia air ratio λ _NH3 for each ammonia burner 306 unit. As described later, since the ammonia air ratio causes a significant change in the amount of NOx generated, it is necessary to strictly calculate the ammonia air ratio for each burner unit, thereby controlling the supply of ammonia fuel and ammonia combustion air. Similarly, the coal burner 302 preferably calculates the air ratio λ _car (coal air ratio) of the carbon-containing fuel for each coal burner 302 unit to control the amount of NOx generated with good accuracy.

The control device 5 (see FIG. 9 ), which is a component of the boiler 2 of one embodiment, calculates the ammonia-air ratio by the amount of air supplied from the ammonia burner 306 (see FIG. 3B and FIG. 3C ) and the amount of air supplied from the auxiliary air nozzles 303 and 305 adjacent to the ammonia burner 306. The amount of air supplied from the auxiliary air nozzles 303 and 305 is calculated as the amount of air for ammonia combustion, which is only the amount of air that contributes to ammonia combustion. For example, as shown in FIG. 3B and FIG. 3C , when the auxiliary air nozzle 303 is adjacent to the ammonia burner 306 and the coal burner 302 and is sandwiched, half of its air amount is calculated as air for the ammonia burner. When the NOx generation amount is higher than the reference value, the ammonia burner air ratio is controlled to be reduced from 0.7 to 0.6, for example. FIG. 5A shows an example of the ammonia burner air ratio and the NOx generation amount. In the test results, the optimal point of the ammonia burner air ratio is 0.6. If the ammonia burner air ratio is reduced to less than 0.6, NOx will increase. Therefore, even if it is reduced to 0.6, the NOx generation amount cannot be reduced. This is because the unburned ammonia reaches the space in the furnace at the same height as the additional air supply area 22, that is, the combustion completion area, and is converted into NOx. Therefore, the air ratio of the ammonia burner is maintained at 0.6, the ratio of the additional air (extra air) to the total air volume fed into the boiler 2 is reduced, and the amount of unburned ammonia reaching the combustion completion area is reduced, thereby attempting to reduce the NOx generated in the combustion completion area.

The ammonia burner 306 is installed to replace (modify) a part of the coal burner 304 as shown in FIG. 3A to FIG. 3C. The coal powder sprayed from the coal burner 304 is adjacent to the ammonia burner 306, and auxiliary air is supplied from the auxiliary air nozzle 303 provided with the start-up fuel burner 307. The auxiliary air nozzle 303 provided with the start-up fuel burner 307 has a damper that can adjust the amount of auxiliary air that can be supplied in the direction of the ammonia burner 306 (the amount of auxiliary air that can be supplied to the ammonia fuel sprayed into the furnace 12). In the case of a structure in which the air nozzle (auxiliary air nozzle) 303 for supplying auxiliary air is sandwiched between the coal burner 302 and the ammonia burner 306, if the amount of air supplied from the nozzle is adjusted to the air amount most suitable for the coal burner 302, the amount of air used to reduce nitrogen oxides of the ammonia burner 306 will become excessive. On the contrary, if the air amount is adjusted to the air amount used to reduce NOx of the ammonia burner, the air amount of the optimal air ratio of the coal burner 302 will be insufficient, resulting in an increase in unburned components in the ash. At this point, in this embodiment, the auxiliary air nozzle 303 sandwiched by the coal burner 302 and the ammonia burner 306 is divided into flow paths 303A and 303B at the top and bottom along with the modification of the boiler 2, and the respective flow rates can be controlled by the damper (refer to Figure 3C and Figure 4). In this way, the amount of air toward the coal burner 302 and the ammonia burner 306 can be adjusted individually. In other words, the amount of air supplied to the coal powder ejected from the coal burner 302 and the amount of air supplied to the ammonia fuel ejected from the ammonia burner 306 can be adjusted individually. The coal burner air ratio is about 0.7~0.9. The air flow rates of the flow paths 303A and 303B from the auxiliary air nozzle 303 can be adjusted individually, thereby suppressing the increase of unburned components in the ash of the coal burner and suppressing the increase of NOx in the ammonia burner. In addition, by converting the coal burner 304 into an ammonia burner 306, the existing boiler 2 dedicated to burning coal can be converted into a boiler 2 burning ammonia fuel. In addition, as shown in FIG. 3, the ammonia burner 306 is arranged adjacent to the coal burner 302, thereby utilizing the heat of coal combustion for ammonia combustion, and stably burning ammonia. Furthermore, the NOx generation amount contained in the combustion gas discharged from the boiler 2 is calculated based on the ammonia supply amount and the combustion air supply amount supplied to the ammonia burner 306, and the first reference range may be set according to the calculation result. Alternatively, the first reference range may be set based on the measurement result of the measuring device installed in the boiler 2 for measuring the NOx concentration.

The boiler 2 of at least one embodiment of the present invention, as shown in FIG. 6A to FIG. 6C, has a startup fuel burner 307 for burning startup fuel, and the aforementioned ammonia burner 306 can be provided by replacing (modifying) a part of the startup fuel burner 307. The ammonia burner 306 includes an ammonia nozzle 306A for injecting ammonia. The ammonia nozzle 306A also functions as a startup fuel nozzle for injecting startup fuel (a specific example is oil). When the boiler 2 is started, the ammonia nozzle 306A injects the startup fuel, and then injects ammonia in response to the satisfaction of the ammonia co-firing condition. In another embodiment, the startup fuel nozzle is configured as a nozzle different from the ammonia nozzle 306A, and may be set in the same section as the ammonia nozzle 306A. When the startup fuel burner 307 is converted into the ammonia burner 306, the air nozzle 303 on one side adjacent to the coal burners 302 and 304 disappears, and the auxiliary air volume toward the coal burner 302 cannot be fully ensured. Therefore, the air volume from the auxiliary air nozzles 301 and 305 on the opposite side of the ammonia burner 306 is increased respectively, thereby making the air ratio of the coal burners 302 and 304 an appropriate value of 0.7 to 0.9. In this embodiment, only the air supplied from the ammonia burner 306 is used for the calculation of the ammonia-air ratio. By optimizing the air ratio of the coal burners 302 and 304, the increase of the unburned components in the ash of the coal burners 302 and 304 can be suppressed.

The boiler 2 of at least one embodiment of the present invention has a plurality of auxiliary air nozzles 301, 305 for supplying auxiliary air as shown in Fig. 7A and Fig. 7B, and the ammonia burner 306 is provided by replacing a part of the auxiliary air nozzles 301, 305. In the example of Fig. 7B, the auxiliary air nozzle 305 is replaced with the ammonia burner 306. Similar to the modification of the startup fuel burner 307, the auxiliary air nozzle 305 on one side of the coal burner 304 will disappear, thereby the air volume of the coal burner 304 will be insufficient. Furthermore, when the interval height of the auxiliary air nozzle 305 is low, it is difficult to install the ammonia burner 306 with a flame protector. The nozzle provided with the start-up fuel burner 307 on the opposite side of the ammonia burner 306 adjacent to the coal burner 304 is used as the auxiliary air nozzle 303 to increase the air volume, thereby adjusting to a predetermined air volume. At this time, as shown in FIG. 7B , in the coal burner 304, the auxiliary air nozzle 303 becomes one-sided, but the upper coal burner 302 has auxiliary air nozzles 301 and 303 at the top and bottom, thereby dividing the air flow path of the startup oil burner into flow paths 303A and 303B at the top and bottom, and the air volume can be increased only in the lower flow path 303B, and the respective flow rates can be controlled at the damper, and the air ratio of the coal burner 304 can be optimized, thereby suppressing the increase of unburned components in the ash. In the boiler 2 before the transformation, when the height of the wind box with the auxiliary air nozzle 305 is lower than the height of the coal burner 302 or the start-up fuel burner 307, the ammonia burner 306 with a lower wind box height is installed without a flame protector. For example, the premixing joint nozzle shown in Figure 13 is used.

In at least one embodiment of the present invention, as shown in FIG. 8A and FIG. 8B , the auxiliary air nozzle 301 disposed at the uppermost section of the burner arrangement area 21 is replaced (modified) by an ammonia burner 306. The ammonia burner 306 is disposed adjacent to the coal burner 302. As in the previous example where the ammonia burner 306 is disposed at the auxiliary air nozzle 305, the auxiliary air nozzle 301 on one side of the coal burner 302 disappears, thereby causing insufficient air volume for the coal burner 302. Moreover, when the interval height of the auxiliary air nozzle 301 is low, it is difficult to install the ammonia burner 306 with a flame protector. The air flow path of the startup fuel burner 307 is divided into flow paths 303A and 303B at the top and bottom, and the flow paths 303A and 303B can be controlled individually. In the case of a lower wind box height, an ammonia nozzle with a lower wind box height, i.e., a partial premixing nozzle, is installed without a flame protector (see Figure 13). In this case, ammonia can be used not only as a fuel but also as a denitrifying agent.

The burner used in the above-mentioned embodiment is a diffuse combustion burner or a partially premixed combustion burner (also called a joint burner). In the diffuse combustion burner, a swirler type or a diffuser type can be used as a flame protector. FIG13 shows an example of a structural diagram of a partially premixed joint burner, FIG14 shows an example of a structural diagram of a diffuser burner, and FIG15 shows an example of a structural diagram of a swirl burner. FIG13 shows an example of a joint burner. The joint burner is composed of a nozzle 132 for supplying ammonia to the inside of a wind box 131 and an outer tube 133. The combustion air is supplied from the wind box 131, and a damper for flow adjustment is provided on the upstream side of the wind box 131. Ammonia is injected into the outer tube 133, pre-mixed with the combustion air flowing in from the gap between the nozzle 132 and the outer tube 133, and injected into the furnace. Ammonia will ignite naturally when it is mixed with the air amount suitable for ignition by the high-temperature gas in the furnace. Ammonia and air are partially pre-mixed, so the ignition point is formed at the point where the blowing flow rate of the entire nozzle and the combustion speed of the pre-mixed ammonia and air become consistent. An example of a structural diagram of a diffuser burner is shown in Figure 14. An ammonia nozzle 142 is set inside the wind box 141, and a disc-shaped flame protector 143 (also called a diffuser) is set at the front end of the ammonia nozzle 142. Ammonia is ejected from a plurality of holes 142A provided in the ammonia nozzle 142 (two holes 142A are shown in the figure). Combustion air is supplied from the wind box 141, and a damper for adjusting the flow rate is provided on the upstream side. The combustion air will flow faster around the flame retainer 143, so a vortex is formed on the outer periphery of the circular plate flame retainer 143. The vortex will entrain ammonia to mix with the air and ignite, so the ignition point is formed on the flame retainer 143. An example of a structural diagram of a swirl burner is shown in FIG15. An ammonia nozzle 152 is provided inside the wind box 151, and a flame retainer 153 (also called a swirler) having rotating blades is provided at the front end of the ammonia nozzle 152. Ammonia is sprayed from multiple holes 152A provided in the ammonia nozzle 152 (two holes 152A are shown in the figure). Combustion air is supplied from the wind box 151, and a damper for adjusting the flow rate is provided on the upstream side. When the combustion air passes through the flame retainer 153, it becomes a swirling flow through the swirling blades and flows around the periphery of the ammonia nozzle 152. The swirling flow causes the circulating flow to occur inside the swirling flow, so the ammonia and the circulating flow are mixed and ignited. Therefore, the ignition point of the ammonia flame is formed near the downstream side of the flame retainer 153.

FIG. 16 is a flow chart showing the boiler modification method of the present invention. As described using FIG. 3C , FIG. 6C , FIG. 7B , and FIG. 8B , the boiler 2 before modification is equipped with: a pulverized coal burner 302; and a plurality of injection units that inject pulverized coal, for example, a start-up fuel which may also be oil, or auxiliary air. Each injection unit is a coal burner 304, a start-up fuel burner 307, or an auxiliary air nozzle 301, 303. Then, S11 shown in FIG. 16 represents a process of replacing the injection unit with an ammonia burner 306. By executing S11, for example, an existing boiler 2 that performs exclusive coal combustion can be converted into a boiler 2 that burns ammonia fuel.

A boiler control method according to an embodiment (see FIG. 10B ) is to control the supply amount of ammonia fuel, pulverized coal and combustion air in a boiler 2, wherein the boiler 2 comprises: a furnace 20 comprising a furnace wall 19, an ammonia burner 306 disposed on the furnace wall 19 and burning the ammonia fuel, and pulverized coal burners 302 and 304 disposed at a position different from the ammonia burner 306 on the furnace wall 19 and burning the pulverized coal. The control method comprises: a first calculation step (S10-1), wherein the calculation step is: The first step is to calculate the ratio of the amount of air for ammonia combustion supplied to the ammonia fuel to the theoretical amount of air required for the combustion of the ammonia fuel, i.e., the ammonia-air ratio; the second calculation step (S10-2) is to calculate the ratio of the amount of air for pulverized coal combustion supplied to the pulverized coal to the theoretical amount of air required for the combustion of the pulverized coal, i.e., the pulverized coal-air ratio; and the control step (S10-3) is to control the supply amount so that the ammonia-air ratio satisfies the first standard range and the pulverized coal-air ratio satisfies the second standard range. The upper limit value of the first standard range of the ammonia-air ratio is preferably set to be smaller than the upper limit value of the second standard range of the pulverized coal-air ratio. The optimum value of the air ratio for minimizing NOx emissions is about 0.6 for ammonia fuel, which is smaller than that for pulverized coal (usually about 0.7 to 0.8). By setting the upper limit of the reference range with reference to this optimum value, it is easy to minimize NOx emissions.

FIG9 is a specific structure of a boiler operation system 1 in an implementation form. The boiler operation system 1, in addition to the above-mentioned boiler 2, supply system 15, and measurement system 9, also has a control device 5 for controlling the operation of the boiler 2. The control device 5 in an implementation form includes: a processor 91, ROM 92, RAM 93, and a memory 94. The processor 91 reads the boiler operation program stored in ROM 92 and loads it into RAM 93 to execute the commands contained in the boiler operation program. The processor 91 is a CPU, GPU, MPU, DSP, various computing devices other than these, or a combination of these. The processor 91 can also be implemented by an integrated circuit such as PLD, ASIC, FPGA, and MCU. The memory 94 stores various data related to the execution of the boiler operation program. The memory 94 is, for example, a cache memory. The processor 91 is electrically connected to the supply system 15 and the measurement system 9. In one embodiment, the processor 91 generates the following instructions: other fuel combustion instructions for burning fuels other than ammonia fuel in the furnace 20, ammonia supply start instructions for starting the supply of ammonia fuel to the supply system 15, and ammonia dedicated combustion start instructions for starting dedicated combustion of ammonia in the furnace 20. In one embodiment, these control instructions are sent to the supply system 15. The processor 91 of one embodiment generates an ammonia supply start instruction when it is determined based on the measurement result of the measurement system 9 that the ammonia co-combustion condition for starting ammonia co-combustion is satisfied. Furthermore, the processor 91 of one embodiment starts the ammonia dedicated combustion instruction when it is determined that the ammonia dedicated combustion condition for starting ammonia dedicated combustion is satisfied. The ammonia dedicated combustion condition includes, for example, when the representative temperature in the furnace 20 reaches a specified temperature, when a specified time has passed since the start of ammonia co-combustion, when a predetermined set value is reached after the operator performs a specified input operation, or a combination thereof.

The supply system 15 includes: a primary air supply system 110 for supplying primary air, an additional air supply system 120 for supplying additional air, an ammonia supply system 100 for supplying liquid ammonia, an oil supply system 80 for supplying oil, and a pulverized coal supply system 70 for supplying pulverized coal. The oil supply system 80 and the pulverized coal supply system 70 are each an example of a system for supplying carbon-containing fuel. Primary air, liquid ammonia, pulverized coal, and oil are supplied to the burner unit 30, and additional air is supplied to the additional air supply section 4 provided on the furnace wall 19. The supply system 15 is controlled by the control device 5.

The air supply pipeline 112 of the primary air supply system 110 is connected to the burner unit 30. The air supply pipeline 112 is provided with a flow regulating valve 116 for adjusting the flow of the primary air and a switching valve 118 for switching the connection state of the air supply pipeline 112. The air supply pipeline 122 of the additional air supply system 120 is connected to the additional air supply unit 4. The air supply pipeline 122 is provided with a flow regulating valve 126 for adjusting the flow of the additional air and a switching valve 128 for switching the connection state of the air supply pipeline 122. The flow regulating valves 116, 126 and the switching valves 118, 128 operate in response to the control command sent from the control device 5.

The ammonia supply system 100 includes: the above-mentioned ammonia burner 306, an ammonia tank 101 storing liquid ammonia, an ammonia supply pipeline 102 connecting the ammonia tank 101 and the ammonia burner 306, a pump 103 provided in the ammonia supply pipeline 102, a pressure regulating valve 105 for regulating the pressure of the ammonia supply pipeline 102, a switching valve 107 provided in the ammonia supply pipeline 102 and for switching the connection state between the ammonia tank 101 and the ammonia burner 306, and a flow regulating valve 108 for regulating the flow rate of liquid ammonia flowing in the ammonia supply pipeline 102. The pressure regulating valve 105, the switching valve 107, and the flow regulating valve 108 operate in response to control instructions from the processor 91. Thus, the ammonia supply system 100 can be changed between a supply stop state in which liquid ammonia is not supplied to any ammonia burner 306 and a supply state in which liquid ammonia is supplied to all ammonia burners 306. As described later, when the ammonia supply system 100 is in the supply stop state, oil is supplied from the oil supply system 80 to the ammonia burners 306 of the second burner unit 32 and the third burner unit 33.

An oil supply system 80 of an embodiment includes: an oil supply device 81, an oil supply pipeline 82 connecting the oil supply device 81 and the ammonia burner 306, an oil flow regulating valve 86 for adjusting the flow of oil flowing in the oil supply pipeline 82, and a switching valve 88 for switching the connection state of the oil supply pipeline 82. The oil supply pipeline 82 of this example is connected to each ammonia burner 306 of the second burner unit 32 and the third burner unit 33. In an embodiment, the oil supply device 81, the oil flow regulating valve 86, and the switching valve 88 operate in response to a control command from the control device 5. Thus, the oil supply system 80 can be changed between a supply state of supplying oil to the ammonia burner 306 connected to the oil supply line 82 and a supply stop state of stopping the supply of oil. In other embodiments, the oil supply line 82 may be connected to a start-up fuel burner 37 for spraying oil. Furthermore, the oil supply line 82 may be supplied with atomizing steam. In this case, the oil and the atomizing steam are supplied to the burner unit 30.

A pulverized coal supply system 70 of one embodiment comprises: a pulverized coal supply device 71 for supplying pulverized coal using a transport gas, a pulverized coal supply pipeline 72 for connecting the pulverized coal supply device 71 and the burner unit 30, a pulverized coal flow regulating valve 76 for adjusting the flow rate of pulverized coal flowing in the pulverized coal supply pipeline 72, and a switching valve 78 for switching the connection state of the pulverized coal supply pipeline 72. The pulverized coal supply pipeline 72 of this example is connected to the first burner unit 31, the second burner unit 32, and the third burner unit 33. The pulverized coal supply device 71, the pulverized coal flow regulating valve 76, and the switching valve 78 operate in response to a control command from the control device 5. Thus, the pulverized coal supply system 70 can be changed between a supply stop state in which the pulverized coal supply is stopped and a supply state in which the pulverized coal is supplied to the burner unit 30. When the pulverized coal supply system 70 is in the supply state, the pulverized coal supply system 70 supplies pulverized coal to the pulverized coal burners 302 and 304.

The measuring system 9 includes: an air flow meter 114 for measuring the flow rate of primary air supplied by the primary air supply system 110, an air flow meter 124 for measuring the flow rate of additional air supplied by the additional air supply system 120, an ammonia flow meter 109 for measuring the flow rate of ammonia fuel supplied by the ammonia supply system 100, an oil flow meter 84 for measuring the flow rate of oil supplied by the oil supply system 80, a pulverized coal flow meter 74 for measuring the flow rate of pulverized coal supplied by the pulverized coal supply system 70, and the above-mentioned furnace thermometer 6. These flow meters send the measurement results to the processor 91.

The boiler operation system 1 operates, for example, as shown in the flowchart of FIG. 10A , by the control command sent from the processor 91. First, the processor 91 transmits other fuel combustion commands to the supply system 15 (S51). Thereby, the primary air supply system 110 and the additional air supply system 120 each supply air. At this time, the ammonia supply system 100 is in a supply stop state, and the oil supply system 80 and the pulverized coal supply system 70 are also in a supply state. Therefore, oil and pulverized coal are supplied to the burner unit 30. At this time, the ammonia burner 306 of the first burner unit 31 is stopped, and the ammonia burners 306 of the second burner unit 32 and the third burner unit 33 spray oil. Oil and pulverized coal are burned inside the furnace 12. Afterwards, since the ammonia co-combustion condition is satisfied (S53: YES), the processor 91 transmits an ammonia supply start instruction (S55) to the supply system 15. The oil supply system 80 changes to a supply stop state, and the ammonia supply system 100 changes to a supply state. Thereby, the first burner unit 31 sprays liquid ammonia, and the fuel sprayed from the second burner unit 32 and the third burner unit 33 is switched from oil to liquid ammonia. The pulverized coal supply system 70 maintains the supply state. As a result, ammonia and pulverized coal are mixed and burned in the boiler 2. Afterwards, since the ammonia-only combustion condition is satisfied (S57: YES), the control device 5 transmits an ammonia-only combustion instruction to the supply system 15 (S59). The pulverized coal supply system 70 changes to a supply stop state, and the burner operating as a coal burner stops. In addition, the ammonia supply system 100 increases the supply of liquid ammonia. As a result, ammonia is exclusively burned in the boiler 2. In other embodiments, the supply system 15 that receives other fuel combustion instructions from the processor 91 may supply oil to the burner unit 30 first, and then supply oil and pulverized coal to the burner unit 30. Furthermore, after the ammonia supply start instruction is sent to the supply system 15, a mixed combustion of ammonia fuel and oil may be performed, or a mixed combustion of ammonia fuel, pulverized coal, and oil may be performed.

FIG10B is a flow chart showing a NOx control process of an implementation form. The NOx control process is a control method for suppressing the amount of NOx generated when ammonia fuel is mixed with other fuels (in this case, pulverized coal) for combustion. In the NOx control process, first, the processor 91 reads the boiler load and the ammonia mixing ratio (a more specific example is the mixing ratio of ammonia and pulverized coal) (S61). The reading is executed by the processor 91 in response to a request instruction. The processor 91 executes the first calculation (S10-1), which calculates the ratio of the amount of air for ammonia combustion supplied to the ammonia fuel to the amount of air required for combustion of the ammonia fuel, that is, the ammonia-air ratio. The calculation method of the ammonia-air ratio is the same as described above. Next, the processor 91 performs a second calculation (S10-2), which calculates the ratio of the amount of air supplied to the pulverized coal for combustion to the theoretical amount of air required for the pulverized coal combustion, i.e., the pulverized coal-air ratio. An example of the air ratio of a carbon-containing fuel, i.e., the calculation method of the pulverized coal-air ratio (λ _car ), is the same as described above. Next, the processor 91 controls the supply amounts of the ammonia fuel, pulverized coal, and combustion air, respectively (S10-3), so that the ammonia-air ratio calculated in S10-1 satisfies the first reference range, and the pulverized coal-air ratio calculated in S10-2 satisfies the second reference range. As a more detailed example, the processor 91 controls the flow regulating valve 108 of liquid ammonia, the pulverized coal flow regulating valve 76, and the flow regulating valve 116 of primary air, respectively. The processor 91 determines whether the ammonia co-burning is completed (S63). During the execution of the ammonia co-burning (S63: NO), the processor 91 repeatedly executes S10-1, S10-2, and S10-3 in sequence. When it is determined that the ammonia co-burning is completed (S63: YES), the processor 91 ends the NOx control process.

FIG10C shows the control logic of the air quantity of coal and ammonia. The control device 5 multiplies the measured value of the pulverized coal flow meter 74 of the coal burner 302 (pulverized coal burner 302) by the coal burner air ratio (indication value) and the theoretical coal air quantity, thereby calculating the combustion air quantity (Q _{Air_car} ) of the coal burner 302. The control device 5 obtains the difference between the calculated combustion air quantity of the coal burner 302 and the combustion air quantity (measured value) of the coal burner 302, and obtains the combustion air quantity control command value of the coal burner 302. Similarly, the measured value of the ammonia flowmeter 109 is multiplied by the ammonia burner air ratio and the ammonia theoretical air amount, thereby calculating the combustion air amount (Q _{Air_NH3} ) of the ammonia burner 306. The difference between the calculated combustion air amount of the ammonia burner 306 and the combustion air amount (measured value) of the ammonia burner 306 is taken out, and the control device 5 obtains the ammonia burner combustion air amount command value.

The configuration of ammonia burners in the case of counter-firing burners is shown in Figures 11A to 11E. In counter-firing, coal powder is supplied from a coal pulverizer to burners arranged horizontally on each wall surface. Therefore, in the case of ammonia co-firing, all horizontally arranged burners are replaced with ammonia-fired burners. Figure 11A shows an example of a total of six burners arranged in three sections on the front and rear walls. One section of the burner is composed of a plurality of burners arranged horizontally. Figure 11A (a) schematically shows the burner configuration of boiler 2 that can burn coal exclusively before modification. One of the six sections of the burner is used as a reserve burner, so it is deactivated during normal operation. The symbol 1104 in (a) indicates a deactivated burner. Since the furnace is heated with oil at startup, the coal burner sections 1101, 1102, and 1105 are coal burners equipped with oil burners. (b) and (c) of FIG. 11A show a modification example (burner configuration example) for making the boiler 2 in (a) a boiler 2 that uses ammonia fuel. (b) shows a case where the coal burners 1103, 1106 and the deactivated burner 1104 are modified into an ammonia burner 1108. In this case, the coal burners 1103 and 1106 are modified into ammonia-only burners 1107 and 1109. (c) shows an example of converting the burners 1101, 1102, 1105 equipped with coal burners and oil burners into burners 1120, 1121, 1123 for both ammonia and oil. At this time, the deactivated burner 1104 is used as the coal burner 1104. Figures 11B and 11D are burner configuration examples and ammonia burner side views respectively showing the A-A section of Figure 11A (b). Figures 11C and 11E are burner configuration examples and oil + ammonia burner side views respectively showing the B-B section of Figure 11A (c). In the counter-firing burner, ammonia (or oil used only at startup) is injected from the center, and flow paths for primary, secondary, and tertiary air as air for ammonia combustion are provided around it. When calculating the ammonia-air ratio of the counter-firing burner unit, only the air supplied to the ammonia burner as air for ammonia combustion (the aforementioned primary to tertiary air) is considered. In the counter-firing, there is no auxiliary air nozzle like in the swirling combustion. Figure 12 schematically shows the state inside the furnace in the case of ammonia co-firing. In the space inside the furnace where additional air (extra air) is supplied, i.e. upstream of the combustion completion zone, a denitrification reduction environment with insufficient air (air ratio of less than 1) is formed due to the combustion of pulverized coal. Therefore, the ammonia burner is fed with an air ratio of less than 1, so that ammonia can be fed into the reduction environment with the high temperature (usually more than 1400°C) formed by the coal burner to produce thermal decomposition and reduction of ammonia. This is also possible in counter-combustion. In Figure 12, the ammonia burner is fed into the high-temperature reduction environment formed by coal with an air ratio of less than 0.8, so the reduction environment of the coal is not damaged, and it can be mixed with the high-temperature coal flame to produce thermal decomposition and reduction. By individually controlling the air ratio of each independent burner, the amount of NOx generated can be controlled by avoiding interference with each other.

(Example) Referring to Fig. 5A to Fig. 5C, the results of the combustion test to determine the relationship between the air ratio of the ammonia burner and the NOx emission when the coal and ammonia are mixed and burned are described. Fig. 5A and Fig. 5B are graphs showing the relationship between the air ratio of the burner and the NOx emission when the ammonia mixing ratio is a predetermined value (Fig. 5B shows the relationship of each burner type). This combustion test is carried out in a horizontal cylindrical combustion furnace, and the mixing ratio of ammonia and coal powder is 25% in terms of heat conversion. The coal burner and the ammonia burner are separated in the vertical direction, with the coal burner at the top and the ammonia burner at the bottom, and auxiliary air nozzles are set at the top and bottom of each burner. Ammonia burners use three types of burners: premix burners, i.e., joint burners, diffuser burners, and diffuser and cyclone burners with different flame protector structures. In this test, the oxygen concentration at the furnace outlet was set to about 4%, and NOx was converted to 6% concentration according to the following (Formula 9) to correct the difference in oxygen concentration at the furnace outlet for comparison. NOx (6% conversion value) = NOx measured value × (21%-6%) ÷ (21%-actual furnace outlet oxygen concentration) ... (Formula 9)

First, the relationship between the air ratio and NOx emission of the ammonia burner is examined when the ammonia burner is a joint type and the co-firing ratio is 33%. FIG5C is a graph showing the relationship between the air ratio of the burner and the NOx emission when the ammonia co-firing ratio is changed. As shown in FIG5C, the NOx is lowest when the air ratio of the ammonia burner is 0.6, and the NOx increases when the air ratio is higher or lower than this. When the air ratio of the ammonia burner is 0.8, the NOx value is about 1.5 times that of 0.6. Generally, in the case of coal combustion, the NOx value is about 150 to 200 ppm, so as long as the air ratio of the ammonia burner is below 0.8, there is not much difference from coal combustion. Moreover, the higher the air ratio of the ammonia burner, the greater the increase in NOx. Even if the air ratio of the ammonia burner is zero, that is, only ammonia is injected from the ammonia burner, NOx will increase, but it can be mixed with coal for combustion. If the air ratio of the ammonia burner is reduced to less than 0.6, NOx will increase instead. Therefore, even if it is reduced to 0.6, the situation where NOx cannot be reduced may be that unburned ammonia reaches the oxidation area (combustion completion area) downstream of the additional air injection part and is converted into NOx. Therefore, it is necessary to keep the air ratio of the ammonia burner at 0.6, reduce the additional air injection rate and increase the air ratio of the coal burner to reduce the amount of unburned ammonia reaching the downstream of the additional air injection part, thereby reducing the NOx generated in the combustion completion area. When the ammonia co-combustion rate is reduced to 25%, 22%, and 11% in the joint burner, the lowest point of NOx generation caused by the air ratio of the ammonia burner cannot be confirmed, but the air ratio that minimizes NOx tends to become lower and lower. In addition, the NOx value tends to increase when the ammonia co-combustion rate is reduced to below 25%. This may be because the auxiliary air of the adjacent coal burner increases, so a part of it is mixed with the ammonia burner side, which actually increases the air ratio of the ammonia burner. In this case, the air ratio of the ammonia burner can be reduced to less than 0.6 to control the NOx value. As shown above, even when the ammonia co-firing rate is changed from 11% to 33%, the NOx value can be suppressed by appropriately controlling the air ratio of the ammonia burner. Even if the primary air ratio (the ratio of the theoretical air ratio of coal to the primary air volume) of the coal burner increases due to the increase in the co-firing rate, the air ratio of the coal burner and the ammonia burner can be individually controlled to control the NOx value below a certain value.

Next, as shown in FIG5B, in a diffuser burner, when the flame protector is a diffuser type or a swirler type, the NOx generation amount tends to be lower in the diffuser type than in the swirler type. The diffuser type is a disc-shaped diffuser installed at the front end of the burner, and the air is circulated around it to protect the flame, and the ignition point is very close to the burner. On the other hand, the swirler type generates a swirling flow with the burner as the center by swirl flow, and protects the flame by the circulating flow, and forms an ignition point on the downstream side of the front end of the burner. The reduction environment formed by the ammonia burner is from the ignition point to the additional air injection point. Therefore, the closer the ignition point is to the front end of the burner, the longer the distance to the reduction environment is, and the retention time of the reduction environment will also be longer, which is believed to promote the reduction of NOx. Even in the diffusion type burner, it is impossible to obtain the air ratio of the ammonia burner that minimizes NOx, but there is a tendency to become a lower value than the joint type. It can be said that the air ratio of the ammonia burner can be controlled to minimize NOx in each burner form.

Although the embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, but also includes embodiments in which the embodiments described above are modified or in which these embodiments are appropriately combined.

In this specification, expressions of relative or absolute configurations such as "in a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric" or "coaxial" do not strictly indicate only such configurations, but also include tolerances, or states of relative displacement with an angle or distance to the extent that the same function can be obtained. For example, expressions indicating the state of equality of things such as "same", "equal" and "homogeneous" do not strictly indicate only the state of equality, but also include tolerances, or states of differences to the extent that the same function can be obtained. Furthermore, in this specification, the expressions indicating shapes such as a quadrangular shape or a cylindrical shape do not only indicate shapes such as a quadrangular shape or a cylindrical shape in the strict geometric sense, but also include shapes such as concave and convex parts or chamfered parts within the range that can obtain the same effect.

Furthermore, in this specification, expressions such as "having", "containing", or "having" a constituent element do not constitute exclusive expressions that exclude the existence of other constituent elements.

<Others>

The contents described in the above-mentioned implementation forms can be summarized as follows.

1) A boiler (20) of at least one embodiment of the present invention comprises: a furnace (20) comprising a furnace wall (19), an ammonia burner (50) disposed on the furnace wall (19) and burning ammonia fuel, and a pulverized coal burner (302, 304) disposed at a position of the furnace wall (19) different from the ammonia burner (50) and burning pulverized coal.

2) In some embodiments, the boiler (20) described in 1) above is provided with a control device (5) for controlling the supply amount of the aforementioned ammonia fuel, the aforementioned pulverized coal, and the combustion air, and the control device (5) comprises: a first calculation unit for calculating the ratio of the amount of ammonia combustion air supplied to the aforementioned ammonia fuel to the theoretical amount of air required for the combustion of the aforementioned ammonia fuel, i.e., the ammonia-air ratio; a second calculation unit for calculating the ratio of the amount of pulverized coal combustion air supplied to the aforementioned pulverized coal to the theoretical amount of air required for the combustion of the aforementioned pulverized coal, i.e., the pulverized coal-air ratio; and a control unit for controlling the aforementioned supply amount so that the aforementioned ammonia-air ratio satisfies the first reference range and the aforementioned pulverized coal-air ratio satisfies the second reference range.

3) In some embodiments, the boiler (20) described in 2) above, the first calculation unit calculates the ammonia-air ratio for each of the plurality of ammonia burners (50), and the control unit controls the supply amount so that each ammonia-air ratio satisfies the first reference range.

4) In some embodiments, the boiler (20) described in 2) or 3) above is provided with an air nozzle (303) disposed adjacent to the ammonia burner (50) on the furnace wall (19), and the first calculation unit calculates the ammonia-air ratio using the amount of air for ammonia combustion including the amount of air supplied to the ammonia fuel, among the amount of air injected from the air nozzle (303).

5) In some embodiments, the boiler (20) described in any one of 2) to 4) above, the upper limit value of the aforementioned first reference range is lower than the upper limit value of the aforementioned second reference range.

6) In some embodiments, the boiler (20) described in any one of 2) to 5) above, the first reference range is below 0.8.

7) In some embodiments, the boiler (20) described in any one of 2) to 5) above, the aforementioned first reference range is below 0.7.

8) In some embodiments, the boiler (20) described in any one of 2) to 7) above, the first reference range is set based on the value of nitrogen oxides in the combustion gas discharged from the furnace (20).

9) In some embodiments, the boiler (20) described in any one of 1) to 8) above is provided with an auxiliary air nozzle (303) adjacent to the aforementioned ammonia burner (50) for supplying auxiliary air, and the aforementioned auxiliary air nozzle (303) is provided with a damper capable of adjusting the amount of auxiliary air, and the auxiliary air can be supplied in the direction of the aforementioned ammonia burner (50).

10) In some embodiments, the boiler (20) described in any one of 1) to 9) above, the aforementioned ammonia burner (50) comprises: an ammonia nozzle (142, 152) for spraying the aforementioned ammonia fuel, and a startup fuel nozzle (ammonia nozzle 306A) for spraying startup fuel.

11) In some embodiments, the boiler (20) described in any one of 1) to 10) above, the aforementioned ammonia burner (50) and the aforementioned pulverized coal burner (302, 304) are arranged adjacent to each other.

12) In some embodiments, the boiler (20) described in 8) above, the furnace wall (19) comprises: a burner arrangement area, which is provided with the ammonia burner (50) and the pulverized coal burners (302, 304); and an additional air supply area, which is provided with an additional air supply section for supplying additional air at a position downstream of the burner arrangement area, and the ammonia burner (50) is located at the uppermost section of the burner arrangement area.

13) In some embodiments, the boiler (20) described in any one of 1) to 12) above, the aforementioned ammonia burner (50) is a diffusion burner or a partially premixed burner.

14) In some embodiments, the boiler (20) described in 13) above, the aforementioned diffusion burner or the aforementioned partial premixing burner is any one of a partially premixing joint type, a diffusion type and a swirler type or a diffuser type burner having a different flame retainer structure.

15) A boiler control method according to at least one embodiment of the present invention, the boiler comprising: a furnace (20) comprising a furnace wall (19), an ammonia burner (50) disposed on the furnace wall (19) and burning ammonia fuel, and a pulverized coal burner (302, 304) disposed at a position of the furnace wall (19) different from the ammonia burner (50) and burning pulverized coal, wherein the boiler controls the supply amount of the ammonia fuel, the pulverized coal and combustion air, and the boiler control method comprises: a first calculation step (S10-1 ), which calculates the ratio of the amount of air supplied to the aforementioned ammonia fuel for combustion to the theoretical amount of air required for the aforementioned ammonia fuel combustion, i.e., the ammonia-air ratio; the second calculation step (S10-2), which calculates the ratio of the amount of air supplied to the aforementioned pulverized coal for combustion to the theoretical amount of air required for the aforementioned pulverized coal combustion, i.e., the pulverized coal-air ratio; and the control step (S10-3), which controls the aforementioned supply amount to make the aforementioned ammonia-air ratio meet the first reference range, and the aforementioned pulverized coal-air ratio meet the second reference range.

16) A boiler modification method according to at least one embodiment of the present invention, the boiler comprising: a furnace (20) comprising a furnace wall (19), a pulverized coal burner (302, 304) disposed on the furnace wall (19) and burning pulverized coal, a plurality of injection units disposed at positions of the furnace wall (19) different from the pulverized coal burner (302, 304) and used to inject pulverized coal or start-up fuel or auxiliary air, and a control device (5), the boiler modification method comprising a replacement step, wherein at least one of the plurality of injection units is replaced with an ammonia burner (50) burning ammonia fuel, for controlling The control device (5) for controlling the supply amount of the ammonia fuel, the pulverized coal, and the combustion air comprises: a first calculation unit for calculating the ratio of the amount of ammonia combustion air supplied to the ammonia fuel to the theoretical amount of air required for the combustion of the ammonia fuel, i.e., the ammonia-air ratio; a second calculation unit for calculating the ratio of the amount of pulverized coal combustion air supplied to the pulverized coal to the theoretical amount of air required for the combustion of the pulverized coal, i.e., the pulverized coal-air ratio; and a control unit for controlling the supply amount so that the ammonia-air ratio satisfies the first reference range and the pulverized coal-air ratio satisfies the second reference range.

2: Boiler

4:Add air supply unit

5: Control device

8: Rear flue

9: Measurement system

11: Nose

12: Fireplace

15: Supply system

19: Fireplace wall

20: Fireplace

21: Burner configuration area

22: Additional air supply area

30: Burner unit

31: 1st burner unit

32: Second burner unit

33: The third burner unit

37: Starting fuel burner

50: Ammonia burner

70: Pulverized coal supply system

71: Coal powder supply device

72: Pulverized coal supply pipeline

74: Pulverized coal flow meter

76: Pulverized coal flow regulating valve

78: Switching valve

80: Oil supply system

81: Oil supply device

82: Oil supply pipeline

84: Oil flow meter

86: Oil flow regulating valve

88: Switching valve

91: Processor

92:ROM

93:RAM

94:Memory

100: Ammonia supply system

101: Ammonia tank

102: Ammonia supply pipeline

103: Pump

105: Pressure regulating valve

107: Switching valve

108: Flow regulating valve

109: Ammonia flow meter

110:1 air supply system

114:1 air flow meter

116: Flow regulating valve

118: Switching valve

120:Additional air supply system

124:Add air flow meter

126:Add air flow regulating valve

128: Switching valve

131: Bellows

132: Ammonia supply nozzle

133: Outer tube

141: Bellows

142: Ammonia nozzle

143: Inflammation protector (diffuser)

151: Bellows

152: Ammonia nozzle

153: Flame protector (cyclone)

301: Auxiliary air nozzle

302: Pulverized coal burner

303: Auxiliary air nozzle

303: Air nozzle

304: Pulverized coal burner 305: Auxiliary air nozzle 306: Ammonia burner 306A: Ammonia nozzle 1101: Coal burner with start-up oil burner 1102: Coal burner with start-up oil burner 1103: Coal burner 1104: Coal burner 1105: Coal burner with start-up oil burner 1106: Coal burner 1107: Ammonia burner 1108: Ammonia burner 1109: Ammonia burner 1120: Start-up oil burner/ammonia dual-purpose burner 1121: Starting oil burner/Ammonia dual-purpose burner 1123: Starting oil burner/Ammonia dual-purpose burner

[Figure 1] A conceptual diagram of a boiler operation system in an embodiment. [Figure 2] A conceptual diagram showing a burner in a previous example. [Figure 3A] A cross-sectional diagram showing the configuration of a boiler burner before modification in an embodiment (a modification example of a coal burner). [Figure 3B] A cross-sectional diagram showing the configuration of a boiler burner after modification in an embodiment (a modification example of a coal burner). [Figure 3C] A conceptual diagram showing the correspondence between the configuration of a burner before and after modification in an embodiment (a modification example of a coal burner). [Figure 4] An explanatory diagram showing the air flow associated with combustion in an ammonia burner in an embodiment. [FIG. 5A] is an explanatory diagram showing the relationship between the ammonia burner-air ratio and the amount of nitrogen oxides generated in a burner of an embodiment. [FIG. 5B] is an explanatory diagram showing the relationship between the shape of the burner, the ammonia burner-air ratio, and the amount of nitrogen oxides generated in an embodiment. [FIG. 5C] is an explanatory diagram showing the relationship between the ammonia co-combustion rate, the ammonia burner-air ratio, and the amount of nitrogen oxides generated in an embodiment. [FIG. 6A] is a cross-sectional diagram showing the configuration of the burner of a boiler before modification of an embodiment (modification example of a start-up fuel burner). [FIG. 6B] is a cross-sectional diagram showing the configuration of the burner of a boiler after modification of an embodiment (modification example of a start-up fuel burner). [Fig. 6C] is a conceptual diagram showing the correspondence between the configuration of the burners before and after the modification of a boiler of an embodiment (modification example of the start-up fuel burner). [Fig. 7A] is a cross-sectional diagram showing the configuration of the burners of a boiler after the modification of an embodiment (modification example of the air nozzle). [Fig. 7B] is a conceptual diagram showing the correspondence between the configuration of the burners before and after the modification of a boiler of an embodiment (modification example of the air nozzle). [Fig. 8A] is a cross-sectional diagram showing the configuration of the burners of a boiler after the modification of an embodiment (modification example of the top air nozzle). [Fig. 8B] is a conceptual diagram showing the correspondence between the configuration of the burners before and after the modification of a boiler of an embodiment (modification example of the top air nozzle). [Figure 9] A control system diagram of a boiler in an embodiment. [Figure 10A] A flow chart of a control method of a boiler in an embodiment. [Figure 10B] A flow chart of a NOx control process in an embodiment. [Figure 10C] A control logic diagram for calculating a control command value of a combustion air volume in an embodiment. [Figure 11A] Ammonia burner configuration of an opposing combustion burner in an embodiment. [Figure 11B] A cross-sectional view in the direction of the arrow of line A-A of Figure 11A. [Figure 11C] A cross-sectional view in the direction of the arrow of line B-B of Figure 11A. [Figure 11D] A side view of an ammonia burner in an embodiment. [Figure 11E] A side view of an oil-ammonia burner in an embodiment. [Figure 12] A conceptual diagram showing the oxidation-reduction state in a boiler of an embodiment. [Figure 13] A diagram showing the structure of a joint burner. [Figure 14] A diagram showing the structure of a diffuser burner. [Figure 15] A diagram showing the structure of a swirl burner. [Figure 16] A flow chart of a boiler modification method.

301: Auxiliary air nozzle

302: Pulverized coal burner

303: Auxiliary air nozzle

303A: Flow path

303B: Flow path

304: Pulverized coal burner

305: Auxiliary air nozzle

306: Ammonia burner

Claims (15)

A boiler comprises: a furnace including a furnace wall, an ammonia burner provided on the furnace wall and burning ammonia fuel, a pulverized coal burner provided at a position of the furnace wall different from the ammonia burner and burning pulverized coal, and a control device for controlling the supply amount of the ammonia fuel, the pulverized coal, and combustion air, the control device comprising: a first calculation unit for calculating the ammonia combustion air supplied to the ammonia fuel; The ratio of the amount of air supplied to the pulverized coal to the theoretical amount of air required for the combustion of the ammonia fuel, i.e., the ammonia-air ratio; a second calculation unit, which calculates the ratio of the amount of air supplied to the pulverized coal for combustion to the theoretical amount of air required for the combustion of the pulverized coal, i.e., the pulverized coal-air ratio; and a control unit, which controls the supply amount so that the ammonia-air ratio satisfies the first reference range and the pulverized coal-air ratio satisfies the second reference range. The boiler as described in claim 1, wherein the first calculation unit calculates the ammonia-air ratio for each of the plurality of ammonia burners, and the control unit controls the supply amount so that each ammonia-air ratio satisfies the first reference range. The boiler as described in claim 2, wherein an air nozzle is provided on the furnace wall adjacent to the ammonia burner, and the first calculation unit calculates the ammonia-air ratio using the amount of air for ammonia combustion including the amount of air supplied to the ammonia fuel, among the amount of air ejected from the air nozzle. A boiler as described in claim 2, wherein the upper limit value of the aforementioned first reference range is lower than the upper limit value of the aforementioned second reference range. The boiler as described in claim 2, wherein the first reference range is below 0.8. The boiler as described in claim 2, wherein the first reference range is below 0.7. A boiler as described in claim 2, wherein the first reference range is set based on the value of nitrogen oxides in the combustion gas discharged from the furnace. The boiler as described in claim 1 or 2, wherein an auxiliary air nozzle is provided adjacent to the aforementioned ammonia burner to supply auxiliary air, and the aforementioned auxiliary air nozzle has a damper capable of adjusting the amount of auxiliary air, and the auxiliary air can be supplied in the direction of the aforementioned ammonia burner. The boiler as described in claim 1 or 2, wherein the aforementioned ammonia burner comprises: an ammonia nozzle for spraying the aforementioned ammonia fuel, and a starting fuel nozzle for spraying the starting fuel. The boiler as described in claim 1 or 2, wherein the aforementioned ammonia burner is installed adjacent to the aforementioned pulverized coal burner. The boiler as described in claim 7, wherein the furnace wall comprises: a burner arrangement area, which is provided with the ammonia burner and the pulverized coal burner; and an additional air supply area, which is provided with an additional air supply section for supplying additional air at a position downstream of the burner arrangement area, and the ammonia burner is located at the uppermost section of the burner arrangement area. A boiler as described in claim 1 or 2, wherein the aforementioned ammonia burner is a diffusion burner or a partially premixed burner. The boiler as described in claim 12, wherein the aforementioned diffusion burner or the aforementioned partial premixing burner is any one of a partially premixing joint type, a diffusion type and a swirler type or a diffuser type burner with a different flame retainer structure. A boiler control method, the boiler comprising: a furnace including a furnace wall, an ammonia burner disposed on the furnace wall and burning ammonia fuel, a pulverized coal burner disposed at a position of the furnace wall different from the ammonia burner and burning pulverized coal, the boiler controlling the supply amounts of the ammonia fuel, the pulverized coal, and combustion air, the boiler control method comprising: a first calculation step of calculating the ammonia combustion air supplied to the ammonia fuel; a first calculation step, which calculates the ratio of the amount of air supplied to the pulverized coal for combustion to the theoretical amount of air required for combustion of the pulverized coal, i.e., the pulverized coal-air ratio; and a control step, which controls the supply amount to make the ammonia-air ratio meet the first standard range and the pulverized coal-air ratio meet the second standard range. A boiler modification method, the boiler comprising: a furnace including a furnace wall, a pulverized coal burner disposed on the furnace wall and burning pulverized coal, a plurality of injection units disposed at a position of the furnace wall different from the pulverized coal burner and used to inject pulverized coal or start-up fuel or auxiliary air, and a control device, the boiler modification method comprising a replacement step, in which at least one of the plurality of injection units is replaced with an ammonia burner that burns ammonia fuel, and the control device is used to control the supply amount of the ammonia fuel, the pulverized coal, and the combustion air. The control device comprises: a first calculation unit, which calculates the ratio of the amount of air for ammonia combustion supplied to the ammonia fuel to the theoretical amount of air required for the combustion of the ammonia fuel, i.e., the ammonia-air ratio; a second calculation unit, which calculates the ratio of the amount of air for pulverized coal combustion supplied to the pulverized coal to the theoretical amount of air required for the combustion of the pulverized coal, i.e., the pulverized coal-air ratio; and a control unit, which controls the supply amount so that the ammonia-air ratio satisfies the first reference range and the pulverized coal-air ratio satisfies the second reference range.

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