JP2023094928A - Ammonia fuel boiler system - Google Patents

Abstract

To provide an ammonia fuel boiler system capable of suppressing emission of NOx.SOLUTION: An ammonia fuel boiler system includes: a furnace having a burner arrangement region and an addition air input region located downstream of the burner arrangement region; a first burner provided in the burner arrangement region to burn first fuel containing ammonia fuel; a second burner provided in the burner arrangement region to burn second fuel other than ammonia fuel; an air nozzle provided in the burner arrangement region to inject combustion air for burning the first fuel and the second fuel; and a controller configured to control a burner part air ratio that is a ratio of supply amount of combustion air to the burner arrangement region to theoretical air amount required for combustion of the first fuel and the second fuel to a prescribed value or smaller when boiler load is partial load.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to ammonia-fueled boiler systems.

Conventionally, there is known an ammonia-fueled boiler in which ammonia is supplied as fuel into a furnace. For example, in an ammonia-fueled boiler disclosed in Patent Document 1, both pulverized coal and ammonia are supplied to a burner provided in a furnace body. As a result, mixed combustion of ammonia and pulverized coal is performed in the combustion chamber of the furnace body. In the same document, the amount of NOx emissions is reduced by devising an arrangement pattern of burners.

Japanese Patent Application Laid-Open No. 2020-112280

In the ammonia combustion boiler system, regardless of whether or not the configuration disclosed in Patent Literature 1 is employed, it is preferable to take another measure to suppress NOx emissions.

An object of the present disclosure is to provide an ammonia fuel boiler system capable of suppressing NOx emissions.

An ammonia-fueled boiler system according to at least one embodiment of the present disclosure includes:
a furnace having a burner arrangement area and an additional air injection area located downstream of the burner arrangement area;
a first burner provided in the burner arrangement area for burning a first fuel containing ammonia fuel;
a second burner provided in the burner arrangement area for burning a second fuel other than the ammonia fuel;
an air nozzle provided in the burner arrangement area for injecting combustion air for burning the first fuel and the second fuel;
When the boiler load is partial load, the burner section air ratio, which is the ratio of the amount of combustion air supplied to the burner arrangement area, to the theoretical amount of air required for combustion of the first fuel and the second fuel a controller configured to control to a specified value or less;

According to the present disclosure, it is possible to provide an ammonia fuel boiler system capable of suppressing NOx emissions.

1 is a conceptual diagram of an ammonia-fueled boiler system according to one embodiment; FIG. It is a conceptual diagram showing a boiler according to one embodiment. 4 is a graph showing the amount of combustion air supplied and the amount of additional air supplied according to the boiler load according to one embodiment. 4 is a graph showing the relationship between the first burner air ratio and the amount of NOx emissions according to one embodiment. 4 is a graph showing the relationship between the co-firing rate, the burner section air ratio, and the amount of NOx emissions according to one embodiment. 4 is a flowchart showing burner section air ratio control processing according to one embodiment. 4 is a graph showing the relationship between the burner section air ratio and the amount of NOx emissions according to one embodiment.

Preferred embodiments according to the present disclosure will be described below with reference to the drawings. It should be noted that the present invention is not limited by this embodiment, and when there are a plurality of embodiments, the present invention includes a combination of each embodiment. In the following description, "up" and "up" indicate the upper side in the vertical direction, and "down" and "lower side" indicate the lower side in the vertical direction.
In addition, the dimensions, materials, shapes, relative arrangements, etc. of the components described as the embodiment or shown in the drawings are not intended to limit the scope of the present disclosure, but are merely illustrative examples. do not have.
For example, expressions denoting relative or absolute arrangements such as "in a direction", "along a direction", "parallel", "perpendicular", "center", "concentric" or "coaxial" are strictly not only represents such an arrangement, but also represents a state of relative displacement with a tolerance or an angle or distance to the extent that the same function can be obtained.
For example, expressions such as "identical", "equal", and "homogeneous", which express that things are in the same state, not only express the state of being strictly equal, but also have tolerances or differences to the extent that the same function can be obtained. It shall also represent the existing state.
For example, expressions that express shapes such as squares and cylinders do not only represent shapes such as squares and cylinders in a geometrically strict sense, but also include irregularities and chamfers to the extent that the same effect can be obtained. The shape including the part etc. shall also be represented.
On the other hand, the expressions "comprising", "including", or "having" one component are not exclusive expressions excluding the presence of other components.
In addition, the same code|symbol may be attached|subjected about the same structure and description may be abbreviate|omitted.

<Outline of ammonia fuel boiler system 1>
FIG. 1 is a schematic representation of an ammonia-fueled boiler system 1 according to one embodiment of the present disclosure. The ammonia fuel boiler system 1 of this example is incorporated in a thermal power plant. The boiler 10 constituting the ammonia fuel boiler system 1 burns a first fuel containing ammonia fuel and a second fuel other than ammonia fuel, and heats the heat generated by the combustion with feed water and steam to produce superheated steam. It is possible to generate The ammonia fuel can be either liquid ammonia or ammonia gas. The liquid ammonia may be liquid-phase ammonia as a pure substance, or may be a mixture of liquid-phase ammonia and water in a very small proportion. The second fuel may be any fuel other than ammonia fuel, and may be solid fuel, liquid fuel, or gaseous fuel. The following illustrates embodiments in which the second fuel includes coal. Coal as fuel is pulverized coal. In the boiler 10, any of single burning of coal, mixed burning of coal and ammonia fuel, or single burning of ammonia fuel may be performed.

In this embodiment, the boiler 10 has a furnace 11, a combustion device 12, and a combustion gas passage 13, as shown in FIG. The furnace 11 has a hollow rectangular shape and is installed along the vertical direction. The furnace wall 101 that constitutes the furnace 11 is composed of a plurality of heat transfer tubes and fins that connect them. It exchanges heat with steam to suppress the temperature rise of the furnace wall 101 .

The combustion device 12 is provided on the lower side of the furnace wall 101 that constitutes the furnace 11 . In this embodiment, the combustion device 12 has a plurality of burners (eg 21, 22, 23, 24, 25) mounted on the furnace wall 101. FIG. A boiler 10 according to one embodiment is a swirling combustion boiler, and a plurality of burners provided in each stage are arranged at regular intervals along the circumferential direction of the furnace 20 . For example, the burners 21, 22, 23, 24, and 25 are arranged at equal intervals along the circumferential direction of the furnace 11 as one set, and a plurality of stages (for example, five stages in FIG. 1) are arranged along the vertical direction. are placed. However, the shape of the furnace, the number of burners in one stage, the number of stages, the arrangement, etc. are not limited to this embodiment. A boiler 10 according to another embodiment is a facing combustion type boiler. In this case, at least one pair of burners in each stage are provided at positions facing each other.

An ammonia fuel supply unit 60 for supplying ammonia fuel to the boiler 10 is connected to the burners 21 , 22 , 23 via an ammonia supply pipe 69 . As an example, the ammonia supply pipe 69 is connected to a tank that stores ammonia. In the following description, the burners 21, 22, and 23 may be referred to as a first burner 81 in some cases.

In an embodiment employing a liquid ammonia injection method in which the first burner 81 injects liquid ammonia, the ammonia supply pipe 69 supplies high-pressure liquid ammonia to the first burner 81 . In this case, a heat insulating material may be provided in the ammonia supply pipe 69 to prevent vaporization of liquid ammonia. In an embodiment employing an ammonia gas injection method in which the first burner 81 injects ammonia gas, the ammonia supply pipe 69 is provided with at least one ammonia vaporizer for vaporizing liquid ammonia. good too. The ammonia vaporizer may be configured to vaporize liquid ammonia using steam generated in the boiler 10, combustion gas in the boiler 10, or seawater outside the boiler system as a direct or indirect heat source. good. The first burner 81 may be configured to inject another fuel in addition to the ammonia fuel. That is, it is understood that the first burner 81 is a burner configured to burn a first fuel containing ammonia fuel.

The burners 24, 25 are connected to a plurality of pulverizers (mills) 34, 35 via pulverized coal supply pipes 29, 33 (in the following description, the burners 24, 25 are collectively referred to as the second burner 82). In some cases, the pulverizers 34 and 35 may be collectively referred to as the pulverizer 3, and the pulverized coal supply pipes 29 and 33 may be collectively referred to as the pulverized coal supply pipe 38). The second burner 82 is understood to be a burner configured to burn a second fuel other than ammonia fuel (pulverized coal in this example). In the crusher 3, for example, a crushing table (not shown) is rotatably supported in a housing, and a plurality of crushing rollers (not shown) are supported above the crushing table so as to be rotatable in conjunction with the rotation of the crushing table. configured as follows. When the coal is put between the pulverizing rollers and the pulverizing table, it is pulverized. Pulverized coal fuel transported to a classifier (not shown) and classified within a predetermined particle size range is supplied to burners 24 and 25 (second burner 82) from pulverized coal supply pipes 29 and 33 (38). be able to. The carrier gas also plays a role of drying the pulverized coal fuel.

The carrier gas described above is sent to the pulverizer 3 through an air pipe 30 from a primary air fan (PAF) 31 that takes in outside air. The air pipe 30 consists of a hot air guide pipe 30A through which hot air out of the air sent from the primary air fan 31 and heated by the air heater 42 flows, and an air heater 42 out of the air sent out from the primary air fan 31. A cold air guiding pipe 30B through which cold air at room temperature flows without passing through the air, and a carrier gas channel 30C through which the hot air and the cold air flow together. A hot air damper 30D and a cold air damper 30E are provided in the hot air guide tube 30A and the cold air guide tube 30B, respectively. By adjusting the opening of each of these dampers according to the pulverized coal fuel supply conditions, the flow rate and temperature of the carrier gas flowing through the carrier gas flow path 30C are adjusted.

Further, the furnace 11 is provided with a wind box 36 at the mounting position of the burners 21, 22, 23, 24, 25, and one end of an air duct (airway) 37 is connected to the wind box 36. As shown in FIG. The air duct 37 is provided with a forced draft fan (FDF) 32 at the other end. The air duct 37 is also provided with a wind box damper 28 for adjusting the amount of air supplied to the wind box 36 . The degree of opening of the wind box damper 28 is controlled by a controller 90 (see FIG. 2), which will be described later.

Above the installation position of the burner 21 of the furnace 11 (above the wind box 36), there is an additional air (AA: Additional Air) for supplying combustion completion zone 16 (see FIG. 2) in the furnace 11. A plurality of additional air ports (AA ports) 17 are provided. An end of an additional air duct (AA duct) 27 branched from the air duct 37 is connected to the additional air port 17, and part of the air supplied from the forced draft fan 32 is used as additional air for combustion. , can be supplied to the additional air port 17 via the additional air duct 27 . In this embodiment, the additional air port 17 is provided with an additional air adjustment damper 26 . The degree of opening of the additional air adjustment damper 26 is controlled by a later-described controller 90 (see FIG. 2).

The combustion gas passage 13 is connected to the upper portion of the furnace 11 in the vertical direction, as shown in FIG. The combustion gas passage 13 is provided with superheaters 102, 103, 104, reheaters 105, 106, and an economizer 107 as heat exchangers for recovering the heat of the combustion gas. Heat is exchanged between the combustion gas and feed water or steam flowing through each heat exchanger.
Furnace 11 of one embodiment includes a nose 11A projecting into furnace 11 . The nose 11A is designed so that gases (for example, combustion gas and unburned gas) generated in the main combustion zone 15 (see FIG. 2) and the complete combustion zone 16 (see FIG. It is configured to properly flow onto the road 14 . The nose 11A according to one embodiment is provided with a gas thermometer 6 for measuring the nose temperature, which is the temperature of the inner wall surface of the nose 11A. The nose temperature may be treated as the temperature of the combustion gas within the furnace 11 .

As shown in FIG. 1, the combustion gas passage 13 is connected to the downstream side thereof with a flue 14 through which the combustion gas that has undergone heat exchange is discharged. The flue 14 is provided with an air heater 42 for heating air flowing through each of the air duct 37 and the air pipe 30 . In the air heater 42, heat is exchanged between the outside air flowing through the air duct 37 and the combustion gas flowing through the flue 14 to raise the temperature of the combustion air supplied to the burners 21, 22, 23, 24, 25. can be done. Further, in the air heater 42, heat is exchanged between the outside air flowing toward the hot air guide pipe 30A and the combustion gas flowing through the flue 14, so that the outside air can be changed into hot air. Therefore, it is understood that the air heater 42 is configured to use exhaust heat from the boiler 10 to heat the outside air.

Further, the flue 14 is provided with a denitrification device 43 at a position upstream of the air heater 42 . The denitrification device 43 supplies a reducing agent such as ammonia or urea water, which has an effect of reducing nitrogen oxides, into the flue 14, and causes a reaction between the nitrogen oxides in the combustion gas to which the reducing agent is supplied and the reducing agent. is accelerated by the catalytic action of the denitration catalyst installed in the denitration device 43, thereby removing and reducing nitrogen oxides in the combustion gas. The gas duct 41 connected to the flue 14 is provided with a dust collector 44 such as an electric dust collector, an induced draft fan (IDF) 45, a desulfurization device 46, etc., at a position downstream of the air heater 42. A chimney 50 is provided at the end.

On the other hand, when the plurality of pulverizers 34, 35 (3) are driven, the pulverized coal fuel produced together with the carrier gas (primary air, oxidizing gas, combustion air, carrier air) is fed into the pulverized coal supply pipe 29, 33 (38) to burners 24, 25 (second burner 82). In addition, by exchanging heat with the exhaust gas discharged from the flue 14 by the air heater 42, the heated combustion air (primary air, secondary air, oxidizing gas) is transferred from the air duct 37 through the wind box 36. is supplied to the burners 21, 22, 23, 24, 25. The burners 24 and 25 (second burner 82) blow into the furnace 11 a pulverized coal fuel mixture in which pulverized coal fuel and a carrier gas are mixed, and also blow combustion air into the furnace 11. At this time, the pulverized coal fuel is mixed. A flame can be formed by igniting air. A flame is generated in the lower part of the furnace 11 , and high-temperature combustion gas rises inside the furnace 11 and is discharged to the combustion gas passage 13 . Simultaneously with the start of blowing of the pulverized coal fuel mixture (or after the pulverized coal fuel mixture is ignited), the burners 21, 22, 23 (first burner 81) blow the first fuel containing ammonia fuel into the furnace 11. , combustion of the first fuel occurs, and co-firing of pulverized coal and ammonia takes place. Air is used as the oxidizing gas in this embodiment. The oxygen ratio may be higher or lower than that of air, and can be used by optimizing the fuel flow rate.

After that, as shown in FIG. 1, the combustion gas is transferred to the second superheater 103, the third superheater 104, and the first superheater 102 (hereinafter sometimes simply referred to as superheaters) arranged in the combustion gas passage 13. ), the second reheater 106, the first reheater 105 (hereinafter sometimes simply referred to as a reheater), and the economizer 107. After that, nitrogen oxides are reduced and removed by the denitrification device 43. After the particulate matter is removed by the dust collector 44 and the sulfur oxides are removed by the desulfurization device 46, the dust is discharged from the stack 50 into the atmosphere. Note that the heat exchangers do not necessarily have to be arranged in the order described above with respect to the combustion gas flow.

In addition, FIG. 1 does not precisely show the positions of the heat exchangers (superheaters 102, 103, 104, reheaters 105, 106, economizer 107) in the combustion gas passage 13. The arrangement order of the exchangers relative to the burnt gas flow is also not limited to that shown in FIG.

The second fuel injected by the second burner 82 may be solid fuel such as biomass fuel, PC (petroleum coke) fuel generated during petroleum refining, and petroleum residue. In addition, the fuel is not limited to solid fuels, and petroleum oils such as heavy oil, light oil, and heavy oil, and liquid fuels such as factory waste liquids can also be used.Gaseous fuels (natural gas, by-product gas, etc.) ) can also be used. Furthermore, it can also be applied to a mixed firing boiler that uses a combination of these fuels.

<Detailed illustration of the structure of the boiler 10>
FIG. 2 is a schematic diagram showing details of the boiler 10 according to one embodiment of the present disclosure. The furnace 11 of the boiler 10 has a burner arrangement area 4 and an additional air injection area 5 positioned downstream of the burner arrangement area 4 . A first burner 81 and a second burner 82 are provided in the burner arrangement area 4 , and an additional air port 17 is provided in the additional air injection area 5 . Furthermore, the burner arrangement area 4 is provided with an air nozzle 8 configured to inject combustion air supplied from an air duct 37 . The combustion air injected from the air nozzle 8 according to this embodiment is secondary air. 2 or at least one of the air nozzles 8 shown in FIG. 2 may be incorporated in the first burner 81 or the second burner 82. For example, the air nozzle 8 may be arranged to surround a first nozzle (described later) of the first burner 81 or may be arranged to surround a second nozzle (described later) of the second burner 82 . In this case, the combustion air injected by the air nozzle 8 may be primary air or secondary air.

The inventors have found that the burner section air ratio must be kept within an appropriate range in order to suppress the amount of NOx produced by the combustion of the first fuel and the second fuel. The burner section air ratio is the ratio of the amount of combustion air supplied to the burner arrangement area 4 to the theoretical amount of air required for combustion of the first fuel and the second fuel. The amount of air supplied to the burner arrangement region 4 is the total amount of combustion air supplied to the first burner 81 , the second burner 82 and the air nozzle 8 . This burner section air ratio is controlled by a controller 90 as a component of the boiler 10 .

As a more specific example, the controller 90 is configured to control the burner section air ratio to a specified value or less when the boiler load is a partial load. For example, when the boiler 10 is in rated operation, if an operation command to reduce the boiler load below the rated load is input to the controller 90, the boiler load is switched to partial load. As another example, before the freshly started boiler 10 reaches rated operating conditions, the boiler load is at partial load. The boiler load is determined by setting by the operator of the ammonia fuel boiler system 1 , and the set boiler load is input to the controller 90 .

When the boiler load is a partial load, the supply amounts of both the first fuel and the second fuel are relatively small, and the burner section air ratio tends to be excessive. As will be described later in Example 1, when the burner section air ratio exceeds, for example, 1.0, the NOx emissions may increase rapidly. Therefore, when the boiler load becomes a partial load, it is preferable to control the amount of NOx emissions by adjusting the combustion air supplied to the boiler 10 .

According to the above configuration, when the boiler load is a partial load, the controller 90 performs control so that the burner section air ratio becomes equal to or less than the specified value. Therefore, it is possible to suppress the increase in NOx caused by the excessive supply of the first fuel and the second fuel and the excessive burner section air ratio. Therefore, an ammonia fuel boiler system 1 capable of suppressing NOx emissions is realized.

The arrangement pattern of the first burners 81, the second burners 82, and the air nozzles 8 in the burner arrangement area 4 is illustrated below. In the burner arrangement area 4, an air nozzle 8, a second burner 82, an air nozzle 8, a first burner 81, an air nozzle 8, a second burner 82, and an air nozzle 8 are provided in this order from the upper side in the vertical direction. The air nozzles 8 are each connected to an air supply pipe 19 provided with an air damper 18 . Each of the air supply tubes 19 is configured to provide communication between the air duct 37 and the air nozzle 8 . The amount of combustion air supplied to each air nozzle 8 is adjusted by changing the opening degree of the air damper 18 corresponding to each air nozzle 8 . The air damper 18 of this embodiment is connected to the controller 90 via, for example, an IP converter for angle adjustment (not shown). The opening degree of each air damper 18 is adjusted according to a command sent from the controller 90 . In addition, in the embodiment illustrated in FIG. 2 , a plurality of air nozzles 8 are vertically arranged between the first burner 81 and the second burner 82 .

The first burner 81 according to this embodiment includes a first nozzle for injecting a first fuel containing ammonia fuel, and an ammonia supply passage 181 for supplying the ammonia fuel to the first nozzle. The ammonia supply path 181 is connected to the ammonia supply pipe 69 described above. Although not shown in detail, the ammonia supply pipe 69 is provided with an adjustment section for adjusting the amount of ammonia fuel supplied to the first burner 81 . The adjustment unit according to this embodiment is a flow rate adjustment valve for adjusting the flow rate of liquid ammonia. The adjustment unit according to another embodiment may be an ammonia pump for feeding liquid ammonia, and the supply amount of ammonia fuel may be adjusted by changing the driving amount of the ammonia pump. In either embodiment, the regulator is a component of the ammonia fuel supply unit 60 and the controller 90 controls the regulator.

Further, each of the plurality of second burners 82 includes a second nozzle for injecting coal and a coal supply path 182 for supplying coal (pulverized coal) using carrier air. The coal supply path 182 is connected to the pulverized coal supply pipe 38 described above. That is, the coal supply path 182 is configured to supply pulverized coal fuel to the second nozzle using carrier air. The amount of pulverized coal fuel supplied is adjusted by changing the driving amount of the pulverizer 3 . The driving amount of the crusher 3 is controlled by the controller 90 .

In the above configuration, the burner section air ratio (λ) is defined as follows.
λ=( _Qa1 + _Qa2 + _Qa2f )/Qth _... (A)
(Q _a1 : flow rate of combustion air for first fuel (ammonia fuel), Q _a2 : flow rate of secondary air for second fuel (pulverized coal fuel in this example), Q _a2f : flow rate of carrier air for second fuel flow rate, Qth: theoretical air volume of first and second fuel)
When the boiler load is a partial load, the controller 90 performs control to bring the burner section air ratio (λ) to a specified value or less. Further, when the boiler load is a partial load, the controller 90 controls the burner section air ratio to be equal to or higher than the lower limit. This is because if the burner air ratio falls below the lower limit, there is a risk of misfire or the like occurring in the furnace 11 .
The theoretical air amount (Q _th ) in the formula (A) is specified based on the output results of each of the pulverized coal flow meter 39 provided in the pulverized coal supply pipe 38 and the ammonia flow meter 68 provided in the ammonia supply pipe 69. may In addition, the amount of combustion air supplied to the burner arrangement region 4 (Qa1+Qa2+Qa2f) in Equation (A) is determined by the air flow meters (not shown) provided in each of the air duct 37, the additional air duct 27, and the air pipe 30. It may be specified based on the output result and the degree of opening of each air damper 18 . If the air flow meter provided in the air duct 37 is provided at a position closer to the wind box than the upstream end of the additional air duct 27, the output result of the air flow meter of the additional air duct 27 is not referred to. good too.

The arrangement pattern of the first burners 81, the second burners 82, and the air nozzles 8 arranged in the burner arrangement area 4 illustrated in FIG. 2 is merely an example. For example, above the uppermost second burner 82 , a plurality of air nozzles 8 may be arranged in the vertical direction, or the air nozzles 8 may be arranged vertically between the first burner 81 and the second burner 82 . The number of nozzles 8 may be one.

Also, the first fuel according to another embodiment may contain oil, pulverized coal, or the like as fuel other than ammonia fuel. In this case, the first fuel injected by the first nozzle of the first burner 81 may switch between ammonia fuel and oil (or pulverized coal). In embodiments in which the first fuel includes oil, the ammonia supply line 181 is also connected to an oil supply pipe (not shown) for supplying oil as fuel. Similarly, the second fuel according to other embodiments may include oil in addition to coal (pulverized coal). In this case, the coal supply path 182 is also connected to an oil supply pipe for supplying oil as fuel.

<Details of burner section air ratio>
In some embodiments, the specified value for the burner section air ratio (λ) specified by equation (A) is 0.95. That is, when the boiler load is at partial load, the controller 90 is configured to control the burner section air ratio to 0.95 or less. Verification that the amount of NOx generated is suppressed when the burner section air ratio is 0.95 or less will be described later in Example 1. In this embodiment, the controller 90 acquires the boiler load and the ammonia co-firing ratio (hereinafter sometimes simply referred to as co-firing ratio). Then, according to the acquired result, the controller 90 controls the amount of combustion air supplied to the first burner 81 and the amount of combustion air (primary air and secondary air) supplied to the second burner 82, respectively. do. More specifically, the controller 90 adjusts the opening degrees of the air damper 18 and wind box damper 28 to control the burner section air ratio to 0.95 or less. According to the above configuration, the ammonia fuel boiler system 1 that can effectively suppress NOx generation in the boiler 10 is realized by controlling the burner section air ratio to 0.95 or less.

FIG. 3 shows the amount of combustion air supplied to the first burner 81, the amount of combustion air (primary air and secondary air) supplied to the second burner 82, and the amount of combustion air (primary air and secondary air) supplied to the additional air port 17, depending on the boiler load. is a graph showing the amount of additional air supplied to the . On the vertical axis of the graph, 1 corresponds to the theoretical amount of air required for combustion of the first fuel and the second fuel. 100% on the horizontal axis of the graph corresponds to the rated load of the boiler 10 . As shown in the graph, as the boiler load decreases, the amount of air supplied to each of the additional air port 17, the air nozzle 8, the first burner 81, and the second burner 82 tends to decrease. However, the primary air (pulverized coal carrier air) of the second burner 82 is constant irrespective of the boiler load within a range of about 50% or less of the boiler load. This is because it is necessary to secure a certain amount of carrier air for carrying pulverized coal.

Returning to FIG. 2, the second fuel according to some embodiments includes coal (pulverized coal), and the second burner 82 includes a coal feed 182 for feeding the coal with conveying air. The air supplied to the burner arrangement area 4 includes carrier air and secondary air supplied to the air nozzles 8 . The controller 90 of this embodiment is configured to adjust at least the amount of secondary air supplied to the air nozzle 8 to control the burner section air ratio to a specified value or less. The amount of secondary air supplied is adjusted by the controller 90 controlling the opening of the air damper 18 . In another embodiment, the controller 90 may adjust the secondary air supply amount by changing the drive amount of the FDF 38 (see FIG. 1). The advantages of including adjustment of the secondary air supply in the adjustment of the combustion air supply are as follows.

A constant supply amount of air for conveying coal (pulverized coal in this example) in the coal supply path 182 must be ensured in order to prevent the coal from settling during the supply process. As a specific example, when the mill load (coal feed amount) of the pulverizer 3 is equal to or less than a specified value, if the flow rate of the conveying air is reduced in accordance with the decrease in the mill load, the coal settles at the second nozzle or the like. There are risks. Therefore, even if the boiler load is partial load, it may be difficult to reduce the carrier air. In this respect, according to the above configuration, the controller 90 controls at least the supply amount of the secondary air so that the burner section air ratio becomes equal to or less than the specified value. Therefore, even if the boiler load is a partial load during co-firing of coal and ammonia fuel, NOx emissions can be suppressed.

In some embodiments, the burner section air ratio includes a first burner air ratio and a second burner air ratio. The first burner air ratio is the ratio of combustion air for the first fuel to the stoichiometric amount of air for the first fuel. The secondary burner air ratio is the ratio of combustion air for the secondary fuel to the stoichiometric air volume for the secondary fuel. The controller 90 independently controls the air ratios of the first burner 81 and the second burner 82 (the first burner air ratio and the second burner air ratio) so that the burner section air ratio is equal to or less than the specified value. configured to The controller 90 according to the present embodiment controls the opening degrees of the air dampers 18 corresponding to each of the plurality of air nozzles 8, and controls the amount of coal supplied to the pulverizer 3 and the amount of ammonia fuel supplied to the ammonia fuel supply unit 60. Control. According to the above configuration, by independently controlling the first burner air ratio and the second burner air ratio, it is possible to more finely control the burner section air ratio in order to reduce the amount of NOx generated.

In the above embodiment, it is necessary to specify how much the combustion air injected from each air nozzle 8 contributes to the combustion of the first fuel and the combustion of the second fuel. Therefore, in the above-described embodiment, the data indicating the degree of contribution set for each of the plurality of air nozzles 8 may be stored in a memory that constitutes the controller 90, for example. As a more specific example, all of the combustion air injected from the uppermost air nozzle 8 shown in FIG. 2 contributes only to combustion of the second fuel injected from the uppermost second burner 82. is stored. Further, one of the two air nozzles 8 arranged in the vertical direction between the first burner 81 and the second burner 82, the air nozzle 8 close to the first burner 81 is for combustion contributing to the combustion of the first fuel. Data may be stored indicating that only air is to be injected. Further, data may be stored indicating that the other air nozzle 8 injects only combustion air that contributes to combustion of the second fuel. If such data is stored, it is possible to calculate the first burner air ratio and the second burner air ratio through the opening of each air damper 18, and control both air ratios independently. Is possible. Note that the data indicating the degree of contribution is not limited to the examples described above. Data may be stored indicating that a portion of the combustion air injected from a particular air nozzle 8 contributes to combustion of the first fuel and the remaining combustion air contributes to combustion of the second fuel.

The controller 90 according to some embodiments is configured to reduce the combustion air supply to the first burner 81 prior to the first fuel supply when the boiler load switches to partial load. As a more specific example, the controller 90 adjusts the opening degree of the air damper 18 corresponding to the air nozzle 8 that injects the combustion air (secondary air) of the first fuel before reducing the coal supply amount of the pulverizer 3. reduce to The advantages of implementing such control are as follows.

FIG. 4 is a graph showing the result of verifying the relationship between the first burner air ratio and the NOx emission amount through combustion experiments. In this combustion experiment, the first fuel supplied to the first burner 81 contains only ammonia fuel. As can be seen from the graph, when the first burner air ratio increases beyond the specified value (0.6 in the example of FIG. 4), NOx emissions tend to increase. This increasing trend is more severe than the trend of increasing NOx emissions as the first burner air ratio drops below 0.6. Here, when the boiler load is switched to partial load, the supply amount of the first fuel decreases, so the first burner air ratio tends to increase. In this respect, according to the above configuration, when the boiler load is switched to the partial load, the combustion air is supplied to the first burner 81 before the supply amount of the first fuel (that is, the theoretical air amount of the first fuel). Since the amount is reduced, it is possible to suppress the first burner air ratio from increasing beyond the specified value. Therefore, the amount of NOx generated can be reduced.

When the boiler load is switched to partial load, the controller 90 according to some embodiments sets the supply amount of the second fuel (in this example, the coal supply amount) before the supply amount of the combustion air to the second burner 82. is configured to lower the According to the above configuration, when the boiler load is switched to the partial load, it is possible to suppress the shortage of the combustion air for the second fuel, so misfires in the furnace 11 can be suppressed. Moreover, since the air ratio in the second burner 82 can be prevented from becoming excessively low, the amount of NOx generated can also be reduced. Therefore, an increase in NOx can be suppressed while maintaining stable ignition.

In some embodiments, the allowable burner section air ratio is higher when the boiler load is at partial load than when the boiler load is not at partial load. That is, in some embodiments, the controller 90 controls the burner section air ratio to be equal to or lower than the steady-state value when the boiler load is not partial load, and controls the burner section air ratio to the steady-state value when the boiler load is partial load. It is configured to control to be below a specified value higher than. As an example, the steady-state value of the burner section air ratio is 0.9. A specified value of the burner section air ratio is, for example, 0.95. Regardless of whether the boiler load is partial load or not, the burner section air ratio is preferably 0.6 or more in order to avoid misfires in the furnace 11 . According to the above configuration, when the boiler load is a partial load, it is possible to allow the burner section air ratio to temporarily become higher than the steady-state value. Therefore, NOx emissions can be continuously suppressed while allowing temporary large fluctuations in the burner section air ratio.

As a more specific example, in an embodiment in which coal (pulverized coal) is employed as the second fuel, the second burner air ratio is 0.9 or less when the boiler load is not partial load, and the boiler load may be 1.0 or less when is a partial load. This is because the sensitivity of NOx production to second burner air ratio is relatively low during boiler load fluctuations.

In some embodiments, the supply of each of the first and second fuels is reduced when the boiler load is at partial load. The relative relationship between the start timing for decreasing the first supply amount, which is the supply amount of the first fuel, and the start timing for decreasing the second supply amount, which is the supply amount of the second fuel, changes according to the co-firing ratio. . A more specific example will be described below.

When the boiler load is partial load, the controller 90 according to some embodiments sets the start timing of the control for decreasing the first supply amount to the second supply amount when the co-firing rate is lower than the specified co-firing rate. It is configured to be earlier than the start timing of the control for lowering. FIG. 5 is a graph showing the relationship between the co-firing rate, the burner section air ratio, and the amount of NOx emissions. As can be seen from the graph, regardless of the burner air ratio, in a range where the co-firing ratio is lower than the specified co-firing ratio R, the lower the co-firing ratio, the lower the amount of NOx generated. In this respect, according to the above configuration, when the co-firing rate is lower than the specified co-firing rate, the first supply amount decreases before the second supply rate, so the ammonia co-firing rate is positively lowered, suppressing the amount of NOx generated. can.

Further, when the boiler load is partial load, the controller 90 according to some embodiments sets the start timing of the control for decreasing the second supply amount to the first It is configured to be earlier than the start timing of the control for reducing the supply amount. As can be seen from the graph shown in FIG. 5, in the range where the co-firing ratio is equal to or higher than the specified co-firing ratio R, the higher the co-firing ratio, the lower the NOx generation amount. In this regard, according to the above configuration, when the co-firing ratio is equal to or higher than the specified co-firing ratio, the second supply amount decreases before the first supply amount, so the co-firing ratio tends to increase, suppressing the amount of NOx generated. can.

Note that the controller 90 according to some embodiments includes a processor, ROM, RAM, and memory. The processor is configured to read a boiler operating program stored in ROM, load it into RAM, and execute the instructions contained in the boiler operating program. The boiler operation program includes a burner section air ratio control program for executing burner section air ratio control processing (see FIG. 6), which will be described later. A processor is a CPU, GPU, MPU, DSP, various arithmetic devices other than these, or a combination thereof. Processors may be implemented by integrated circuits such as PLDs, ASICs, FPGAs, and MCUs. Various data are stored in the memory as the boiler operation program is executed. The memory is flash memory as an example.

<Example of Burner Air Ratio Control Processing>
Referring to FIG. 6, the burner section air ratio control process executed by the controller 90 of the ammonia fuel boiler system 1 is illustrated. The following description describes the control process for an embodiment in which the first fuel contains only ammonia fuel and the second fuel is coal.

First, the controller 90 acquires combustion conditions in the furnace 11 of the boiler 10 (S11). Combustion conditions include boiler load, co-firing rate, and burner section air ratio. At least some of these combustion conditions may be input by an operator, for example. For example, when the operator inputs the boiler load, the controller 90 may acquire the co-firing rate and the burner section air ratio according to the input result based on prescribed processing. The controller 90 may also obtain the first burner air ratio and the second burner air ratio in addition to the burner section air ratio defined by equation (A).

Next, the controller 90 acquires the supply amounts of the ammonia fuel and the coal, for example, by computation based on the combustion conditions acquired in S11 (S13). Further, the controller 90 acquires the supply amounts of combustion air and additional air, for example, by computation (S15). This combustion air is the combustion air supplied to the first burner 81 , the second burner 82 and the air nozzle 8 . Further, the controller 90 acquires the opening degrees of various dampers based on the supply amounts of the combustion air and the additional air acquired in S15 (S17). Various dampers include a plurality of air dampers 18 and wind chest dampers 28 .

Next, the controller 90 adjusts the various dampers, the pulverizer 3, and the ammonia fuel supply unit 60 based on the opening degrees of the various dampers acquired in S17 and the supply amounts of the ammonia fuel and coal acquired in S13. section is controlled (S19). The controller 90 ends the burner section air ratio control process.

(Example 1)
With reference to FIG. 7, the result of specifying the relationship between the burner section air ratio and the NOx emission amount by a combustion test will be described. FIG. 7 is a graph showing the relationship between the burner section air ratio and the amount of NOx emissions. A vertically extending drop tube furnace (DTF) and a single burner test furnace were used in the combustion tests. Combustion tests performed at DTF were mono-combustion of ammonia, co-combustion of ammonia and pulverized coal, and mono-combustion of pulverized coal. The co-firing rate of ammonia co-firing is 25% or 50% in terms of heat quantity. Also, the combustion test conducted in the single burner test furnace was for pulverized coal mono-firing.

The relationship between the burner air ratio and the amount of NOx emissions in ammonia mono-firing will be examined. As shown in FIG. 7, the NOx emissions from ammonia mono-firing with a burner air ratio of 1.0 are more than twice the NOx emissions from pulverized coal mono-firing in the DTF or single burner test furnace. On the other hand, it was found that the amount of NOx emissions in ammonia mono-firing where the burner air ratio is 0.9 or less is lower than that in pulverized coal mono-firing. In particular, it was found that the amount of NOx emissions in the ammonia-only combustion with a burner air ratio of 0.8 was the lowest in this combustion test. Furthermore, the amount of NOx emissions in the ammonia-only combustion where the burner section air ratio is less than 0.8 is less than or equal to the emission amount when the burner section air ratio is 0.8 (see FIG. 5). Therefore, it is understood that the burner section air ratio is preferably set to 0.9 or less when ammonia mono-firing is performed in rated operation of the boiler 10 .

The amount of NOx emissions in co-firing of ammonia and pulverized coal is greater than the amount of NOx emissions in ammonia-only firing (see FIG. 5). In ammonia mono-firing, there is a risk that NOx will rapidly increase when the burner air ratio is around 1.0, and it is predicted that the same tendency will appear in ammonia co-firing. This is because oxygen in the inner space of the furnace 11 becomes excessive. Therefore, it can be seen that the burner air ratio is preferably 0.9 or less when the boiler 10 is operated at rated operation, regardless of whether ammonia mono-firing or ammonia co-firing occurs.

However, when the boiler load fluctuates, the burner section air ratio may also fluctuate significantly compared to during rated operation. Therefore, it is preferable that a certain degree of margin is reflected in the upper limit value of the burner section air ratio. As can be seen from the graph of ammonia mono-firing in FIG. 7, the increasing trend of NOx emissions corresponding to burner air ratios of 0.9 to 0.95 corresponds to burner air ratios of 0.95 to 1.0. It is slower than the increasing trend of NOx emissions. Therefore, it is understood that the limitation condition of the burner section air ratio can be relaxed from 0.9 or less to 0.95 or less only when the boiler load is a partial load. Similar conclusions are drawn when ammonia co-firing is carried out.

Note that when a boiler 10 having a general size used for thermal power generation is operated, it is not realistic for the burner section air ratio to be less than 0.6. (also applies when Therefore, the lower limit of the burner section air ratio is 0.6 or more. The controller 90 preferably performs control so that the burner section air ratio is 0.6 or higher.

<Summary>
The contents described in the several embodiments described above are understood as follows, for example.

1) An ammonia-fueled boiler system (1) according to at least one embodiment of the present invention,
a furnace (11) having a burner placement area (4) and an additional air injection area (5) located downstream of the burner placement area;
a first burner (81) provided in the burner arrangement area for burning a first fuel containing ammonia fuel;
a second burner (82) provided in the burner arrangement area for burning a second fuel other than the ammonia fuel;
an air nozzle (8) provided in the burner arrangement area for injecting combustion air for burning the first fuel and the second fuel;
When the boiler load is partial load, the burner section air ratio, which is the ratio of the amount of combustion air supplied to the burner arrangement area, to the theoretical amount of air required for combustion of the first fuel and the second fuel a controller (90) configured to control below a specified value.

The inventors have found that the amount of NOx emissions from a boiler using ammonia fuel as fuel depends on the burner section air ratio. According to the configuration 1) above, when the boiler load is a partial load, the controller performs control so that the burner section air ratio is equal to or less than the specified value. Therefore, it is possible to suppress the increase in NOx caused by the excessive supply of the first fuel and the second fuel and the excessive burner section air ratio. Therefore, an ammonia fuel boiler system capable of suppressing NOx emissions is realized.

2) In some embodiments, the ammonia-fueled boiler system of 1) above, comprising:
The prescribed value of the burner section air ratio is a value of 0.95 or less.

According to the findings of the inventors, the generation of NOx in the boiler can be effectively suppressed by setting the burner section air ratio to 0.95 or less. Therefore, according to the above configuration 2), an ammonia fuel boiler system capable of effectively suppressing NOx emissions is realized.

3) In some embodiments, the ammonia-fueled boiler system of 1) or 2) above, wherein
the second fuel includes coal;
said second burner includes a coal feed passage (182) for feeding said coal with conveying air;
The combustion air supplied to the burner arrangement area includes the carrier air and secondary air supplied to the air nozzle,
The controller is configured to adjust at least the supply amount of the secondary air to control the burner section air ratio to the specified value or less.

A constant supply of air for transporting coal in the coal supply path must be ensured in order to prevent the coal from settling during the supply process. Therefore, when the boiler load for mixed combustion of coal and ammonia fuel is a partial load, it may be difficult to reduce the carrier air. In this respect, according to the configuration 3) above, the controller controls at least the supply amount of the secondary air so that the burner section air ratio becomes equal to or less than the specified value. Therefore, even if the boiler load is a partial load during co-firing of coal and ammonia fuel, NOx emissions can be suppressed.

4) In some embodiments, the ammonia-fueled boiler system of any one of 1) to 3) above,
The burner section air ratio is
a first burner air ratio, which is the ratio of the combustion air of the first fuel to the theoretical air amount of the first fuel;
a second burner air ratio, which is the ratio of the combustion air of the second fuel to the stoichiometric amount of air of the second fuel;
The controller is
The first burner air ratio and the second burner air ratio are independently controlled so that the burner section air ratio becomes equal to or less than the specified value when the boiler load is switched to partial load.

According to the above configuration 4), by independently controlling the first burner air ratio and the second burner air ratio, the burner section air ratio can be more finely controlled in order to reduce the amount of NOx generated. can be done.

5) In some embodiments, the ammonia-fueled boiler system of any one of 1) to 4) above,
The controller is
When the boiler load is switched to partial load, the amount of combustion air supplied to the first burner is reduced before the amount of supply of the first fuel.

According to the knowledge of the inventors, when the air ratio in the first burner exceeds the specified value and further increases, the amount of NOx produced tends to increase rapidly. Further, when the boiler load is switched to partial load, the supply amount of the first fuel decreases, so the air ratio in the first burner tends to increase. In this respect, according to the configuration of 5) above, when the boiler load is switched to partial load, the amount of combustion air supplied to the first burner decreases before the amount of first fuel supplied. It is possible to suppress the air ratio from increasing beyond the specified value, and to reduce the amount of NOx generated.

6) In some embodiments, the ammonia-fueled boiler system of any one of 1) to 5) above,
The controller is
When the boiler load is switched to partial load, the amount of supply of the second fuel is reduced prior to the amount of supply of the combustion air to the second burner.

According to the above configuration 6), when the boiler load is switched to the partial load, it is possible to suppress the shortage of the combustion air for the second fuel, so it is possible to suppress misfires in the furnace. Moreover, since the air ratio in the second burner can be prevented from becoming excessively low, the amount of NOx generated can also be reduced. Therefore, an increase in NOx can be suppressed while maintaining stable ignition.

7) In some embodiments, the ammonia-fueled boiler system of any one of 1) through 6) above,
The controller is
when the boiler load is not a partial load, controlling the burner section air ratio to be below a steady-state value;
When the boiler load is a partial load, the burner section air ratio is controlled to be equal to or less than the specified value higher than the steady-state value.

According to the above configuration 7), when the boiler load is a partial load, it is possible to allow the burner section air ratio to temporarily become higher than the steady-state value. Therefore, NOx emissions can be continuously suppressed while allowing temporary large fluctuations in the burner section air ratio.

8) In some embodiments, the ammonia-fueled boiler system of any one of 1) through 7) above,
The controller is
When the boiler load is partial load, when the co-firing rate of the first fuel and the coal is lower than the prescribed co-firing rate, the start timing of the control for reducing the supply amount of the first fuel is changed to the second It is configured to be earlier than the start timing of the control for reducing the fuel supply amount.

According to the findings of the inventors, in a range where the co-firing ratio is lower than the prescribed co-firing ratio, the lower the co-firing ratio, the lower the amount of NOx generated. In this respect, according to the configuration of 8) above, when the co-firing rate is lower than the specified co-firing rate, the supply amount of the first fuel decreases before the supply amount of the second fuel, so the ammonia co-firing rate decreases positively. , the amount of NOx generated can be suppressed.

9) In some embodiments, the ammonia-fueled boiler system of any one of 1) through 8) above, comprising:
The controller is
When the boiler load is partial load, when the co-firing rate of the ammonia fuel and the second fuel is equal to or higher than a prescribed co-firing rate, the start timing of the control for reducing the supply amount of the second fuel is set to the above-mentioned It is configured to be earlier than the start timing of the control for reducing the supply amount of the first fuel.

According to the knowledge of the inventors, in a range where the co-firing ratio is equal to or higher than the prescribed co-firing ratio, the higher the co-firing ratio, the lower the NOx generation amount. In this respect, according to the above configuration 9), when the co-firing rate is equal to or higher than the specified co-firing rate, the supply amount of the second fuel decreases before the supply amount of the first fuel, so the co-firing rate tends to increase. , the amount of NOx generated can be suppressed.

1: Ammonia-fueled boiler system 4: Burner arrangement area 5: Additional air injection area 8: Air nozzle 10: Boiler 11: Furnace 81: First burner 82: Second burner 90: Controller R: Specified co-firing rate

Claims (9)

a furnace having a burner arrangement area and an additional air injection area located downstream of the burner arrangement area;
a first burner provided in the burner arrangement area for burning a first fuel containing ammonia fuel;
a second burner provided in the burner arrangement area for burning a second fuel other than the ammonia fuel;
an air nozzle provided in the burner arrangement area for injecting combustion air for burning the first fuel and the second fuel;
When the boiler load is partial load, the burner section air ratio, which is the ratio of the amount of combustion air supplied to the burner arrangement area, to the theoretical amount of air required for combustion of the first fuel and the second fuel Ammonia fueled boiler system, comprising: a controller configured to control below a specified value. 2. The ammonia fuel boiler system according to claim 1, wherein said specified value of said burner section air ratio is a value of 0.95 or less. the second fuel includes coal;
the second burner includes a coal feed passage for feeding the coal using conveying air;
The combustion air supplied to the burner arrangement area includes the carrier air and secondary air supplied to the air nozzle,
3. The ammonia fuel boiler system according to claim 1, wherein said controller is configured to adjust at least the supply amount of said secondary air to control said burner section air ratio to be equal to or less than said prescribed value. The burner section air ratio is
a first burner air ratio, which is the ratio of the combustion air of the first fuel to the theoretical air amount of the first fuel;
a second burner air ratio, which is the ratio of the combustion air of the second fuel to the stoichiometric amount of air of the second fuel;
The controller is
wherein the first burner air ratio and the second burner air ratio are independently controlled so that the burner section air ratio becomes equal to or less than the specified value when the boiler load is switched to partial load. Item 4. The ammonia fuel boiler system according to any one of Items 1 to 3. The controller is
5. Any one of claims 1 to 4, wherein the amount of combustion air supplied to the first burner is reduced prior to the amount of supply of the first fuel when the boiler load is switched to partial load. Ammonia fueled boiler system according to paragraph. The controller is
6. Any one of claims 1 to 5, wherein when the boiler load is switched to partial load, the amount of supply of the second fuel is reduced prior to the amount of supply of the combustion air to the second burner. Ammonia fueled boiler system according to paragraph. The controller is
when the boiler load is not a partial load, controlling the burner section air ratio to be below a steady-state value;
7. The ammonia according to any one of claims 1 to 6, wherein when the boiler load is a partial load, the burner section air ratio is controlled to be equal to or lower than the specified value higher than the steady-state value. fuel boiler system. The controller is
When the boiler load is a partial load, when the co-firing rate of the first fuel and the second fuel is lower than the prescribed co-firing rate, the start timing of the control for reducing the supply amount of the first fuel is set to the above-mentioned 8. The ammonia fuel boiler system according to any one of claims 1 to 7, wherein the start timing of the control for reducing the supply amount of the second fuel is earlier than the start timing. The controller is
When the boiler load is partial load, when the co-firing rate of the first fuel and the second fuel is equal to or higher than a specified co-firing rate, the start timing of the control for reducing the supply amount of the second fuel is 9. The ammonia fuel boiler system according to any one of claims 1 to 8, wherein the start timing of the control for reducing the supply amount of the first fuel is earlier than the start timing.

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