BOILER CONTROL DEVICE, COMBUSTION SYSTEM, BOILER CONTROL METHOD, AND BOILER CONTROL PROGRAM

Abstract

To suitably control the concentration of NOx in exhaust even when fuel of a different fuel characteristics is used while reducing a burden of adjusting combustion.SOLUTION: The boiler controller generates a NOx master signal according to a difference between a value of NOx concentration detected in exhaust and a target value of NOx concentration. The controller controls a combustion device according to the NOx master signal when there is a sufficient boiler control margin. When there is not a sufficient boiler control margin, the controller controls the combustion device according to a correction signal for adjusting a combustion control parameter selected from a plurality of parameters relating to the combustion device of the boiler so that the control margin is increased.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a boiler control device, a combustion system, a boiler control method, and a boiler control program. [Background technology]

[0002] A large boiler such as a power generation boiler has a hollow furnace that is installed vertically, and a plurality of burners are arranged on the furnace wall along the circumferential direction of the furnace. In addition, a flue is connected to the large boiler vertically above the furnace, and a heat exchanger for generating steam is arranged in the flue. The burner injects a mixture of fuel and air (oxidizing gas) into the furnace to form a flame, and combustion gas is generated and flows into the flue. A heat exchanger is installed in the area where the combustion gas flows, and water or steam flowing inside a heat transfer tube that constitutes the heat exchanger is heated to generate superheated steam.

[0003] Usually, in a boiler, combustion adjustment is performed using several kinds of fuels with different fuel properties during the test run. Then, through this combustion adjustment, the combustion control parameters are adjusted so that the NOx concentration in the exhaust gas and the amount of unburned matter remaining in the ash after combustion (unburned matter in the ash) reach specified values, and the combustion conditions are determined. For example, the combustion control parameters are the damper opening and burner nozzle angle that adjust the combustion air flow rate supplied to the burner for combustion, the damper opening and additional air nozzle angle that adjust the amount of additional air that is supplied to the inside of the boiler for NOx reduction, etc. Then, the setting parameters (combustion control parameters) of the equipment (combustion device) for controlling such combustion conditions are determined so that the NOx concentration is below a standard value that meets, for example, an environmental standard, and the unburned matter in the ash is below a specified value (e.g., 5% or less) required to be used as a valuable resource such as a material for concrete.

[0004] For example, Patent Document 1 proposes that the combustion conditions corresponding to the fuel can be determined accurately and quickly by determining the designated values ​​of the combustion control parameters so that the evaluation target index, which is at least one of the unburned fuel contained in the ash generated by combustion and the NOx concentration in the exhaust gas, satisfies a predetermined criterion. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-108995 A Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, in a boiler, combustion adjustment is performed using a fuel having specific fuel properties selected in advance during a test run, and the combustion conditions (combustion control parameters) appropriate for the fuel properties are determined. Therefore, when a boiler is operated using a fuel for which combustion adjustment has not been performed (e.g., a fuel that has not been used in the past), the combustion control parameters are not necessarily set appropriately, and there is a possibility that, for example, the NOx concentration in the exhaust gas may rise above the standard value. In order to prevent such an increase in NOx concentration, it would be ideal to perform combustion adjustment in advance for many types of fuels expected to be used, but this is not realistic because combustion adjustment requires a lot of time.

[0007] In addition, depending on the type of fuel used, it may be difficult to sufficiently reduce the NOx concentration in the exhaust gas by only adjusting the combustion control parameters. In this case, it is necessary to reduce the NOx concentration in the exhaust gas as much as possible by adjusting the combustion, and furthermore, to use a denitration device that uses ammonia as a reducing agent to reduce the NOx in the exhaust gas. However, if the amount of ammonia used to be supplied to the denitration device increases, the operating costs of the boiler will increase.

[0008] At least one aspect of the present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide a boiler control device, a combustion system, a boiler control method, and a boiler control program that are capable of appropriately controlling the NOx concentration in exhaust gas while reducing the burden of implementing combustion adjustments, even when the boiler is operated using fuels with different fuel properties. [Means for solving the problem]

[0009] In order to solve the above problems, a boiler control device according to at least one aspect of the present disclosure includes: a NOx concentration sensor for detecting a NOx concentration in exhaust gas from a boiler; a NOx master signal generating unit configured to generate a NOx master signal based on a difference between a detection value of the NOx concentration sensor and a NOx concentration target value; a correction signal generating unit configured to generate a correction signal based on a control margin of the boiler; A control unit configured to control a combustion device of the boiler based on the NOx master signal and the correction signal; Equipped with If the correction signal generating unit determines that the control margin of the boiler is not sufficient, the correction signal generating unit provides the control unit with the correction signal for adjusting a combustion control parameter selected from a plurality of parameters related to the combustion device of the boiler so as to increase the control margin.

[0010] In order to solve the above problem, a boiler control method according to at least one aspect of the present disclosure includes: Detecting a NOx concentration in exhaust gas from a boiler; generating a NOx master signal based on a difference between the detected NOx concentration value and a NOx concentration target value; generating a correction signal based on a control margin of the boiler; controlling a combustion device of the boiler based on the NOx master signal and the correction signal; when the correction signal generating unit determines that the control margin of the boiler is not sufficient, the correction signal generating unit controls the combustion device based on the correction signal for adjusting a combustion control parameter selected from a plurality of parameters related to the combustion device of the boiler so that the control margin is increased; Equipped with.

[0011] In order to solve the above problem, a boiler control program according to at least one aspect of the present disclosure includes: Using a computer device, Detecting a NOx concentration in exhaust gas from a boiler; generating a NOx master signal based on a difference between the detected NOx concentration value and a NOx concentration target value; generating a correction signal based on a control margin of the boiler; controlling a combustion device of the boiler based on the NOx master signal and the correction signal; when the correction signal generating unit determines that the control margin of the boiler is not sufficient, the correction signal generating unit controls the combustion device based on the correction signal for adjusting a combustion control parameter selected from a plurality of parameters related to the combustion device of the boiler so that the control margin is increased; It is possible to execute the following. Effect of the Invention

[0012] According to at least one aspect of the present disclosure, it is possible to provide a boiler control device, a combustion system, a boiler control method, and a boiler control program that can appropriately control the NOx concentration in exhaust gas while reducing the burden of implementing combustion adjustments, even when the boiler is operated using fuels with different fuel properties. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic configuration diagram of a combustion system including a boiler according to an embodiment. [Diagram 2] FIG. 2 is a schematic configuration diagram of a control device in FIG. [Diagram 3] 3 is a flowchart showing a method of controlling a boiler by the control device of FIG. 2. [Figure 4] FIG. 3 is a control schematic diagram of a correction signal generating unit in FIG. 2. [Diagram 5] FIG. 3 is a schematic control diagram of the control unit in FIG. 2. [Figure 6A] FIG. 6 is a diagram showing a function Fx1a in FIG. 5. [Figure 6B] FIG. 6 is a diagram showing a function Fx1b in FIG. 5. [Figure 6C] FIG. 6 is a diagram showing a function Fx1c in FIG. 5. [Figure 7A] FIG. 6 is a diagram showing a function FX2a in FIG. 5. [Figure 7B] FIG. 6 is a diagram showing a function FX2b in FIG. 5. [Figure 7C] FIG. 6 is a diagram showing a function FX2c in FIG. 5. [Figure 8] 2 is a schematic cross-sectional view showing a horizontal cross section of the furnace in FIG. 1 in an area where an additional air port is installed. FIG. [Figure 9] FIG. 11 is a control flow diagram according to another aspect of the control unit. [Figure 10] 3 is a control flow diagram of a permission condition determination unit in FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. Note that the present invention is not limited to this embodiment, and when there are multiple embodiments, the present invention also includes a configuration in which each embodiment is combined. In the following description, up and above refer to the upper side in the vertical direction, and down and below refer to the lower side in the vertical direction, and the vertical direction is not precise and includes errors.

[0015] FIG. 1 is a schematic configuration diagram of a combustion system 1 including a boiler 10 that uses coal as a main fuel according to one embodiment.

[0016] The boiler 10 of this embodiment is a coal-fired (pulverized coal-fired) boiler that uses pulverized coal made by crushing coal (carbon-containing solid fuel) as pulverized fuel, burns this pulverized fuel using a burner, and exchanges the heat generated by this combustion with feed water or steam to generate superheated steam.

[0017] In this embodiment, as shown in Fig. 1, a boiler 10 has a furnace 11, a combustion device 12, and a combustion gas passage 13. The furnace 11 has a hollow rectangular cylinder shape and is installed along the vertical direction. The furnace wall 101 constituting the furnace 11 is composed of a plurality of heat transfer tubes and fins connecting them, and exchanges heat generated by the combustion of pulverized fuel with water and steam flowing inside the heat transfer tubes, while suppressing the temperature rise of the furnace wall.

[0018] The combustion device 12 is provided on the lower side of the furnace wall constituting the furnace 11. In this embodiment, the combustion device 12 has a plurality of burners 21a, 21b, 21c, 21d, 21e, and 21f (hereinafter, collectively referred to as "burners 21") attached to the furnace wall. For example, each of the burners 21a, 21b, 21c, 21d, 21e, and 21f is disposed at equal intervals along the circumferential direction of the furnace 11, and is disposed in a plurality of stages (for example, six stages in FIG. 1) along the vertical direction. However, the shape of the furnace, the number of burner stages, the number and arrangement of burners in one stage, and the like are not limited to this embodiment.

[0019] Burners 21a, 21b, 21c, 21d, 21e, and 21f (hereinafter, when these are collectively referred to, they will be referred to as burners 21 as appropriate) are connected to a plurality of pulverizers (mills) 24a, 24b, 24c, 24d, 24e, and 24f via pulverized coal supply pipes 23a, 23b, 23c, 23d, 23e, and 23f. The pulverizers 24a, 24b, 24c, 24d, 24e, and 24f are configured, for example, such that a pulverizing table (not shown) is supported in a housing of the pulverizer so as to be rotatable and driven, and a plurality of pulverizing rollers (not shown) are supported above the pulverizing table so as to be rotatable in conjunction with the rotation of the pulverizing table. When coal is fed between the multiple crushing rollers and the crushing table, it is crushed and transported by primary air (carrier gas, oxidizing gas) to a classifier (not shown) in the crusher housing, and the pulverized fuel classified within a predetermined particle size range can be supplied to burner 21 via pulverized coal supply pipes 23a, 23b, 23c, 23d, 23e, and 23f.

[0020] Furnace 11 is provided with a wind box 36 at the mounting position of burner 21, and one end of an air duct (airway) 37 is connected to this wind box 36. Air duct 37 is provided with a forced draft fan (FDF: Forced Draft Fan) 38 at the other end.

[0021] Auxiliary burners 22a, 22b, and 22c (hereinafter, collectively referred to as "auxiliary burners 22" as appropriate) are provided near the burner 21. The auxiliary burners 22 are used when igniting the burner 21, or when raising the gas temperature in the furnace 11 to a temperature at which the pulverized fuel can be burned in the burner 21. The fuel used for the auxiliary burners 22 is a fuel with better combustibility than the solid fuel used in the burner 21, and for example, a liquid fuel such as light oil or heavy oil, or a gas fuel such as methane gas is used. When the boiler 10 is started up, the burner 21 is ignited when the gas temperature in the furnace 11 exceeds a predetermined value due to the combustion of the auxiliary burners 22, and the auxiliary burners 22 are extinguished after the combustion state of the burner 21 is stabilized.

[0022] 1, the combustion gas passage 13 is connected to the vertical upper part of the furnace 11. The combustion gas passage 13 is provided with superheaters 102, 103, 104, reheaters 105, 106, and a coal economizer 107 as heat exchangers for recovering heat from the combustion gas, and heat is exchanged between the combustion gas generated in the furnace 11 and the feed water or steam flowing inside each heat exchanger.

[0023] 1, a flue 14 for discharging the combustion gas that has undergone heat exchange is connected to the downstream side of the combustion gas passage 13. An air heater (air preheater) 42 is provided between the flue 14 and an air duct 37, and heat exchange is performed between the air flowing through the air duct 37 and the combustion gas flowing through the flue 14, thereby making it possible to raise the temperature of the combustion air (secondary air, oxidizing gas) supplied to the burner 21.

[0024] Further, a denitration device 43 is provided in the flue 14 at a position upstream of the air heater 42. The denitration device 43 supplies a reducing agent having an effect of reducing nitrogen oxides, such as ammonia or urea water, into the flue 14, and promotes a reaction between the nitrogen oxides in the combustion gas to which the reducing agent has been supplied and the reducing agent by the catalytic action of a denitration catalyst provided in the denitration device 43, thereby removing and reducing the nitrogen oxides in the combustion gas. A 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, and the like at a position downstream of the air heater 42, and a chimney 50 is provided at the downstream end.

[0025] On the other hand, when the multiple pulverizers 24a, 24b, 24c, 24d, 24e, and 24f are driven, the generated pulverized fuel is supplied to the burner 21 together with the primary air through the pulverized coal supply pipes 23a, 23b, 23c, 23d, 23e, and 23f. In addition, the exhaust gas discharged from the flue 14 is heat-exchanged with the air heater 42, and the heated combustion air is supplied to the burner 21 from the air duct 37 through the wind box 36. The burner 21 blows a pulverized fuel mixture, which is a mixture of the pulverized fuel and the primary air, into the furnace 11, and also blows the combustion air into the furnace 11. At this time, the pulverized fuel mixture is ignited to form a flame. A flame is generated at the bottom of the furnace 11, and the high-temperature combustion gas rises in the furnace 11 and is discharged into the combustion gas passage 13. In this embodiment, air is used as the oxidizing gas. The oxygen content may be higher or lower than that of air, and can be used by optimizing the fuel flow rate.

[0026] Each burner 21 is installed at a predetermined angle with respect to the furnace wall 101 and has a burner nozzle that determines the angle of injection of the pulverized fuel mixture into the furnace 11. The burner nozzle angle, which is the angle of the burner nozzle in a vertical cross section with respect to the furnace wall 101, is variable by an actuator (not shown) and is initially set to a preset reference angle (for example, 90 degrees with respect to the furnace wall 101). The actuator can adjust the burner nozzle angle based on a control signal from the control device 100. The burner nozzle angle may also be variable in terms of the angle in a horizontal cross section. By adjusting the angle of the burner nozzle, it is possible to adjust the range of the combustion region A and the reduction region B formed inside the furnace 11, which will be described later, and to adjust the amount of heat exchanged between the combustion gas and the feed water and steam in each heat exchanger.

[0027] Further, the wind box 36 is provided with a wind box damper for adjusting the amount of combustion air supplied to each burner 21. The wind box damper is configured so that the amount of combustion air supplied to each burner 21 can be varied by adjusting the opening degree of the wind box damper. The opening degree of the wind box damper can also be controlled based on a control signal from the control device 100.

[0028] In addition, a plurality of additional air ports 39 are provided in the furnace wall 101 above the mounting position of the burners 21 (only one additional air port 39 is shown as a representative in FIG. 1). The additional air port 39 also constitutes a part of the combustion device 12 of the boiler 10. An end of an additional air duct 40 branched off from the air duct 37 is connected to the additional air port 39. Therefore, the combustion air sent by the forced draft fan 38 can be supplied from the air duct 37 to the wind box 36 and then from this wind box 36 to each burner 21, and the additional combustion air (additional air, hereinafter sometimes referred to as AA) sent by the forced draft fan 38 can be supplied from the additional air duct 40 to the additional air port 39.

[0029] Each of the additional air ports 39 has an additional air nozzle that is installed at a predetermined angle with respect to the furnace wall 101 and determines the angle at which additional air is blown into the furnace 11. The additional air nozzle angle, which is the angle of the additional air nozzle with respect to the furnace wall 101 in a vertical cross section, is variable by an actuator (not shown) and is initially set to a preset reference angle (for example, 90 degrees with respect to the furnace wall 101). The actuator can adjust the additional air nozzle angle based on a control signal from the control device 100. The additional air nozzle angle may also be variable in terms of the angle in a horizontal cross section.

[0030] Further, additional air duct 40 is provided with an additional air damper for adjusting the amount of additional air supplied to each additional air port 39. The opening degree of the additional air damper is adjusted to vary the amount of additional air supplied to each additional air port 39. The opening degree of the additional air damper can also be controlled based on a control signal from control device 100.

[0031] In the furnace 11, a pulverized fuel mixture and combustion air are combusted in the lower region A (combustion region) to generate a flame. Here, the furnace 11 is maintained in a reducing atmosphere inside by setting the amount of air supplied to be less than the theoretical amount of air relative to the amount of pulverized coal supplied. That is, nitrogen oxides (NOx) generated by the combustion of pulverized coal are reduced in region B (reduction region) of the furnace 11, and then additional combustion air is additionally supplied from the additional air port 39 to complete the oxidative combustion of the pulverized coal, thereby reducing the amount of NOx generated by the combustion of pulverized coal.

[0032] Thereafter, as shown in FIG. 1, the combustion gas is heat-exchanged in the second superheater 103, the third superheater 104, the first superheater 102 (hereinafter sometimes simply referred to as the superheater), the second reheater 106, the first reheater 105 (hereinafter sometimes simply referred to as the reheater), and the economizer 107 arranged in the combustion gas passage 13, and then the nitrogen oxides are reduced and removed by the denitrification device 43, the particulate matter is removed by the dust collector 44, and the sulfur oxides are removed by the desulfurization device 46, and then the combustion gas is discharged into the atmosphere from the chimney 50. Note that the heat exchangers do not necessarily need to be arranged in the above-described order with respect to the flow direction of the combustion gas. In addition, the temperature of the steam superheated in each heat exchanger may be controlled, for example, by adjusting the flow rate of spray water to be sprayed on the steam to reduce the steam temperature by a spray valve (not shown) installed in each heat exchanger.

[0033] The boiler 10 also has a NOx concentration sensor 60 for detecting the NOx concentration in the exhaust gas flowing through the flue 14. For example, the NOx concentration sensor 60 is disposed downstream of the economizer 107. The detection value of the NOx concentration sensor 60 is transmitted to the control device 100 as an electrical signal, and can be used for various controls performed by the control device 100.

[0034] The control device 100 is a control unit of the boiler 10, and has a hardware configuration including an electronic calculation device such as a computer. Specifically, the hardware configuration includes a CPU (processor) (not shown), memories such as ROM and RAM, a storage device such as an external storage device, and a communication interface. The CPU operates (calculates data, etc.) according to the instructions of a program (control program) loaded into the main storage device, thereby realizing the following functional units.

[0035] Fig. 2 is a schematic configuration diagram of the control device 100 in Fig. 1. The control device 100 includes a NOx concentration detection value acquisition unit 112, a NOx concentration target value setting unit 114, a NOx master signal generation unit 116, a correction signal generation unit 117, a control unit 118, and a permission condition determination unit 120.

[0036] The NOx concentration detection value acquisition unit 112 is configured to acquire a detection value Cm of the NOx concentration in the exhaust gas of the boiler 10. In this embodiment, the NOx concentration in the exhaust gas is detected by a NOx concentration sensor 60 (see FIG. 1) installed in the flue 14 of the boiler 10, and the NOx concentration detection value acquisition unit 112 acquires the detection value Cm of the NOx concentration by receiving a signal including the detection result.

[0037] The NOx concentration target value setting unit 114 sets the NOx concentration target value Cs to, for example, the NOx concentration detection value when fuel having standard fuel properties is used in combustion adjustment as a value indicating the NOx concentration in standard exhaust gas in the boiler 10. The NOx concentration target value Cs is set as a control target value for the detection value Cm of the NOx concentration sensor 60 when adjusting the detection value Cm of the NOx concentration sensor 60 by controlling the combustion device 12 as described below.

[0038] The NOx concentration target value Cs may be a detected NOx concentration value obtained by combustion adjustment using a fuel having a specific combustion property. In this case, the combustion property of the fuel used for the combustion adjustment may be specified by the fuel ratio of the coal fuel (the ratio of fixed carbon to volatile matter in the coal fuel). It is generally known that there is a correlation between the fuel ratio of the coal fuel and the NOx concentration in the exhaust gas, and for example, the higher the fuel ratio, the higher the NOx concentration tends to be. In addition, the NOx concentration target value Cs may be variably set, as described later.

[0039] In this embodiment, the target NOx concentration value Cs is set as the target NOx concentration when medium fuel ratio coal with a medium fuel ratio (typically about 1.3 to 1.6 in a boiler that uses a wide range of coal types) is used. This makes it possible to suitably reduce the NOx concentration by the control described below without performing new combustion adjustments, even when low fuel ratio coal or high fuel ratio coal is used in the boiler 10.

[0040] The fuel ratio range, which is a guideline for classifying the above-mentioned fuel ratios into high / medium / low, is a relative index that depends on the fuel ratio range of multiple coals (candidate coals for use) that are set as combustible at the design stage of the boiler 10. For example, if the fuel ratio range of the candidate coals for use is biased toward the low fuel ratio side, the fuel ratio range defined as medium fuel ratio coal will also shift to the low side.

[0041] The NOx master signal generating unit 116 is configured to generate a NOx master signal Sm1 based on a difference ΔC between the NOx concentration detection value Cm acquired by the NOx concentration detection value acquiring unit 112 and the NOx concentration target value Cs set by the NOx concentration target value setting unit 114. More specifically, as shown in FIG. 2, the NOx master signal generating unit 116 includes a subtractor 116a and a PI controller 116b. The subtractor 116a calculates the difference ΔC from the NOx concentration detection value Cm and the NOx concentration target value Cs input to the NOx master signal generating unit 116. The difference ΔC is further input to the PI controller 116b, whereby a NOx master signal Sm1 corresponding to the difference ΔC input to the NOx master signal generating unit 116 is generated.

[0042] The control unit 118 is configured to control the combustion control parameter Pbc for the combustion device 12 of the boiler 10 based on the NOx master signal Sm1 generated by the NOx master signal generation unit 116. In this way, the combustion device 12 is controlled so that the detection value Cm of the NOx concentration in the exhaust gas approaches the NOx concentration target value Cs set by the NOx concentration target value setting unit 114.

[0043] The correction signal generating unit 117 judges the control margin of the boiler 10. In this embodiment, the control margin for the temperature of main steam (superheated steam) generated in the boiler 10 is judged, and the operation of the correction signal generating unit 117 will be described with reference to Figs. 3 and 4. Fig. 3 is a flowchart showing the operation of the control device 100 in Fig. 2. Fig. 4 is a control flow diagram of the correction signal generating unit 117 in Fig. 2. The control target for determining the control margin of the boiler 10 is not limited to the main steam temperature, and another control target correlated with the concentration of NOx generated by combustion may be selected.

[0044] The control margin for the steam temperature of the boiler 10 can be determined based on each parameter related to the steam temperature control in the boiler 10. The parameter used for such a determination may be, for example, a sensor detection value related to the steam temperature, or a control parameter related to a component that affects the steam temperature. In the former case, for example, when the sensor detection value exceeds (or falls below) a predetermined reference value, it is determined that the control margin for the steam temperature is small (not sufficient for stable operation of the boiler 10). In the latter case, for example, when the control parameter approaches an upper limit value or a lower limit value to some extent and there is not enough margin for control, it is determined that the control margin for the steam temperature is small.

[0045] FIG. 4 exemplarily illustrates, as one aspect of the determination of the control margin for the steam temperature of the boiler 10 in the correction signal generating unit 117, a determination based on the following three conditions. (Condition 1) The detection value Cm of the NOx concentration sensor 60 is less than the standard upper limit value (for example, the detection value Cm of the NOx concentration sensor 60 is less than 140 [ppm] as a value obtained by adding the reduction amount in the denitration device 43 to the environmental emission standard value). (Condition 2) The opening of the spray water flow control valve that controls the main steam temperature of the boiler 10 is near the lower control limit (for example, the opening of the spray valve is 20% or less). (Condition 3) The opening degree of the spray water flow control valve that controls the main steam temperature of the boiler 10 is near the upper control limit (for example, the spray valve opening degree is 80% or more).

[0046] 4, when either Condition 1 and Condition 2, or Condition 3 is satisfied, it is determined that the control margin for the steam temperature of the boiler 10 is small, and in other cases, it is determined that the control margin for the steam temperature of the boiler 10 is sufficient. When it is determined that the control margin for the steam temperature is sufficient, as described above, the difference ΔC between the NOx concentration detection value Cm acquired by the NOx concentration detection value acquisition unit 112 and the NOx concentration target value Cs set by the NOx concentration target value setting unit 114 is input to the PI controller 116b of the NOx master signal generation unit 116, and the NOx master signal Sm1 corresponding to the difference ΔC is output from the PI controller 116b.

[0047] On the other hand, when it is determined that the control margin for the steam temperature of the boiler 10 is small, the correction signal generating unit 117 replaces the NOx concentration target value Cs input to the NOx master signal generating unit 116 with the NOx concentration detection value Cm acquired by the NOx concentration detection value acquiring unit 112 (specifically, this is realized by adding ΔC to Cs on the circuit). As a result, the NOx concentration detection value Cm is input to the PI controller 116b of the NOx master signal generating unit 116 as the NOx concentration target value Cs, so the difference ΔC becomes 0 (zero), and the NOx master signal Sm1 generated based on the difference ΔC is held at the current value. In addition, the correction signal generating unit 117 outputs the correction signal Sm2. (Note that, in more detail, even when the control margin is judged to be sufficient, the current value is held as the correction signal Sm2, but the combustion control parameter Pbc is not changed in the control unit 118.) In this way, when a significant correction signal Sm2 (which changes the combustion control parameter Pbc) is output by the correction signal generating unit 117, the NOx concentration target value Cs is replaced with the NOx concentration detection value Cm, so that the difference ΔC becomes zero, that is, the NOx master signal Sm1 is held, and interference between the control by the NOx master signal Sm1 and the control by the correction signal Sm2 can be avoided. Therefore, when it is judged that the control margin is small, it is possible to essentially control the combustion control parameter Pbc based on the correction signal Sm2.

[0048] 2, the control unit 118 is configured to control the combustion control parameter Pbc for the combustion device 12 of the boiler 10, based on the NOx master signal Sm1 generated by the NOx master signal generation unit 116 and the correction signal Sm2 generated by the correction signal generation unit 117. In this way, the combustion device 12 is controlled so that the detection value Cm of the NOx concentration in the exhaust gas approaches the NOx concentration target value Cs set by the NOx concentration target value setting unit 114.

[0049] The combustion control parameter Pbc to be controlled by the control unit 118 is configured to be selected from a plurality of parameters related to the combustion device 12 of the boiler 10. The parameters selected as the combustion parameter Pbc can be selected arbitrarily, but in this embodiment, a case where the burner nozzle angle, additional air nozzle angle, and additional air damper opening degree described above are selected will be described as an example.

[0050] The permission condition determination unit 120 is configured to determine whether or not a permission condition that specifies a condition under which the above control by the NOx master signal Sm1 is permitted is satisfied. When the permission condition determination unit 120 determines that the permission condition is satisfied, a permission signal is sent from the permission condition determination unit 120 to the PI controller 116b of the NOx master signal generation unit 116, and the NOx master signal Sm1 according to the difference ΔC is output. On the other hand, when it is determined that the permission condition is not satisfied, the permission signal is not sent and the NOx master signal Sm1 is not output. Such a command regarding the prohibition of control by the NOx master signal Sm1 can be interrupted at any timing.

[0051] Next, a method for controlling the boiler 10 performed by the control device 100 having the above configuration will be described with reference to FIG.

[0052] In the control device 100, first, the correction signal generating unit 117 determines whether or not the control margin of the boiler 10 is sufficient (step S1). In this embodiment, the determination of whether or not the control margin for the steam temperature of the boiler 10 is sufficient is made based on whether or not the conditions 1 to 3 are satisfied, as described above.

[0053] When it is determined that the control margin of the boiler 10 is sufficient (step S1: YES), the NOx master signal generating unit 116 generates a NOx master signal Sm1 based on the difference ΔC between the NOx concentration detection value Cm acquired by the NOx concentration detection value acquiring unit 112 and the NOx concentration target value Cs set by the NOx concentration target value setting unit 114 (step S2). The correction signal generating unit 117 holds a current value as a correction signal Sm2 (step S3). The control unit 118 controls the combustion control parameter Pbc based on the NOx master signal Sm1 generated in step S2 and the correction signal Sm2 generated in step S3 (more specifically, Sm2 held at the current value) (step S4).

[0054] On the other hand, if it is determined that the control margin of the boiler 10 is not sufficient (step S1: NO), the correction signal generating unit 117 generates a correction signal Sm2 (step S5), and the current value is held as the NOx master signal Sm1 (step S6). Furthermore, the NOx concentration target value Cs set by the NOx concentration target value setting unit 114 is set to be equal to the detection value Cm acquired by the NOx detection value acquiring unit 112 (step S7). In this way, by temporarily rewriting the NOx concentration target value Cs from the original target value so as to be equal to the detection value Cm of the NOx concentration sensor 60, the difference ΔC becomes 0 (zero) in the NOx master signal generating unit 116, and interference between the correction signal Sm2 output from the correction signal generating unit 117 and the NOx master signal Sm1 is avoided.

[0055] In the control unit 118, the combustion control is performed by adjusting the combustion control parameter Pbc arbitrarily selected from among the multiple parameters based on the NOx master signal Sm1 and the correction signal Sm2 generated in each step described above (step S4). For example, even if the NOx concentration target value Cs is set based on the combustion adjustment using a fuel having a specific fuel property, the correction signal generating unit 117 appropriately determines the control margin of the boiler 10, so that the NOx concentration in the exhaust gas can be controlled to be equal to or lower than the reference value that satisfies the environmental standard, without impairing the control stability of the boiler 10, even if a fuel having a fuel property different from that at the time of the combustion adjustment is used.

[0056] Here, in order to explain the effect of control by the correction signal Sm2, a hypothetical case will be considered in which combustion control is performed only by the NOx master signal Sm1 without using the correction signal Sm2 in the above configuration. In this consideration, it is assumed that the NOx concentration target value Cs is set based on the results of using medium fuel ratio coal in the boiler 10, and that the boiler 10 uses high fuel ratio coal.

[0057] When high fuel ratio coal is used, the time required for completion of combustion in the boiler increases due to the fuel property of high fuel ratio coal, which contains less volatile matter, and as a result, the flame length of the pulverized coal flame formed near the burner 21 tends to increase. This causes the combustion region A in the furnace 11 to expand and the reduction region B to shrink. This reduces the effect of reducing NOx in the furnace 11, and the detected NOx concentration Cm increases compared to when medium fuel ratio coal is used. In addition, when considering the amount of heat exchanged (amount of heat absorbed) between the combustion exhaust gas and the water or steam in the heat transfer tube, as the flame length increases, the amount of heat absorbed in the furnace wall 101 relatively decreases, and the amount of heat absorbed in the heat exchangers (e.g., superheaters 102, 103, etc.) in the upper part of the furnace 11 relatively increases. For this reason, the steam temperature of the boiler 10 tends to increase compared to when medium fuel ratio coal is used, and the control margin for the steam temperature may also become smaller (e.g., the opening of the superheater spray valve becomes larger).

[0058] In this state, if control is performed using only the NOx master signal Sm1, the NOx concentration target value Cs becomes smaller than the NOx concentration detection value Cm, the difference ΔC (=NOx concentration detection value Cm-NOx concentration target value Cs) becomes a positive value, and the NOx master signal Sm1 also becomes a positive value. When the NOx master signal Sm1 is positive, as described below, one of the following operations is performed: (i) an operation to decrease the burner nozzle angle, (ii) an operation to increase the additional air nozzle angle, and (iii) an operation to increase the additional air damper opening. Of these operations, (i) and (ii) are both operations to decrease the NOx concentration by expanding the reduction region B, and (iii) is an operation to increase the amount of additional combustion air (relatively reducing the amount of air supplied to the combustion region A) to increase the reduction effect, thereby decreasing the NOx concentration. With respect to the steam temperature, the operation (i) decreases the steam temperature, the operation (ii) increases the steam temperature, and the operation (iii) increases the steam temperature (the effect on the steam temperature is smaller than that of the operation (ii)).

[0059] Here, for example, if the above operations are selected in the order of (i) to (iii) depending on the magnitude of the NOx master signal Sm1, the adjustment will be to decrease the NOx concentration, but to increase the steam temperature. This is because the amount of decrease in steam temperature by operation (i) and the amount of increase in steam temperature by operation (iii) are similar and cancel each other out, but operation (ii) has a large effect on increasing the steam temperature. As described above, when high fuel ratio coal is used, the control margin for steam temperature is already small, and selecting operation (ii), which has a large effect on increasing the steam temperature, may reduce the control stability of the boiler 10. On the other hand, in the control using the correction signal Sm2, as described later, the operation (ii) is not selected, and the control stability of the boiler 10 is suppressed from decreasing.

[0060] In this way, the correction signal generating unit 117 judges whether the control margin of the boiler 10 is sufficient, and the arbitrarily selected combustion control parameter Pbc is controlled by the NOx master signal Sm1 and the correction signal Sm2 set based on the judgment result. In other words, this makes it possible to reduce the NOx concentration in the exhaust gas without impairing the control stability of the boiler 10, and to achieve higher environmental performance. Furthermore, when the NOx concentration discharged to the outside of the system cannot be sufficiently reduced by only the combustion control of the boiler 10, it becomes possible to reduce the amount of ammonia used for denitration in the exhaust gas treatment, and it is possible to reduce the operating cost. Furthermore, it is possible to ensure the control margin of the boiler 10 and stabilize the control state.

[0061] Next, a description will be given of the control of the combustion control parameter Pbc performed in step S4 in Fig. 4. Fig. 5 is a control flow diagram of the control unit 118, Figs. 6A to 6C are diagrams showing functions Fx1a, Fx1b, and Fx1c, respectively, in Fig. 5, and Figs. 7A to 7C are diagrams showing functions Fx2a, Fx2b, and Fx2c, respectively, in Fig. 5.

[0062] The control unit 118 controls the combustion control parameter Pbc based on the NOx master signal Sm1 and the correction signal Sm2. The combustion control parameter Pbc to be controlled by the control unit 118 is selected from a plurality of parameters related to the combustion device 12 of the boiler 10.

[0063] Furthermore, the control unit 118 may select only one of the selected multiple parameters as the combustion control parameter Pbc according to the magnitudes of the NOx master signal Sm1 and the correction signal Sm2. By limiting the number of controlled parameters to one, it is possible to effectively prevent the combustion balance of the coal-fired boiler 10 from being lost due to simultaneous control of multiple parameters.

[0064] Furthermore, the control unit 118 may select the combustion control parameter Pbc from among a plurality of parameters in a predetermined priority order in response to changes in the NOx master signal Sm1 and the steam temperature correction signal Sm2. By selecting the combustion control parameter Pbc in this manner in accordance with a predetermined priority order, it is possible to effectively prevent the combustion balance of the coal-fired boiler 10 from being disturbed. In this case, the priority order may be set based on the sensitivity to the CO concentration in the exhaust gas, which is in a reciprocal relationship with the NOx concentration. By selecting the combustion control parameter in this manner in accordance with the priority order, it is possible to effectively prevent the combustion balance of the coal boiler from being disturbed by suppressing an increase in the CO concentration that occurs in response to a reduction in the NOx concentration.

[0065] Here, the control contents in the control unit 118 will be explained based on a concrete example. In this embodiment, a case where a burner nozzle angle (hereinafter, appropriately referred to as parameter Pa), an additional air nozzle angle (hereinafter, appropriately referred to as parameter Pb), and an additional air damper opening degree (hereinafter, appropriately referred to as parameter Pc) are adopted as parameters related to the combustion device 12 of the boiler 10, which are selection candidates for the combustion control parameter Pbc, will be explained as an example.

[0066] The control unit 118 is configured to select one of these parameters Pa, Pb, and Pc as the combustion control parameter Pbc. In order to realize such a function of the control unit 118, the control unit 118 includes function units 141 to 146 as shown in Fig. 5. The NOx master signal Sm1 is input in parallel to the function units 141, 142, and 143, and the correction signal Sm2 is input in parallel to the function units 144, 145, and 146.

[0067] The function unit 141 has a function Fx1a that defines the relationship between the NOx master signal Sm1 and the bias value ΔPa1 added to the current setting value of the parameter Pa, as shown in Fig. 5. In Fig. 6A, the vertical axis shows the numerical value of the bias value ΔPa1 in percentage, with the operating range of the parameter Pa (burner nozzle angle) (for example, the burner nozzle angle is -25 degrees to 25 degrees with respect to the horizontal direction) being -100% to 100%. As shown in Fig. 6A, the function Fx1a is defined so that ΔPa1 is variable with respect to Sm1 in a specific range of the NOx master signal Sm1 (nx4 ≦ Sm1 ≦ nx3, nx1 ≦ Sm1 ≦ px1, px3 ≦ Sm1 ≦ px4), and ΔPa1 is constant (unchanging) with respect to Sm1 in other ranges.

[0068] The function unit 142 has a function Fx1b that defines the relationship between the NOx master signal Sm1 and the bias value ΔPb1 added to the current setting value of the parameter Pb, as shown in Fig. 5. In Fig. 6B, the vertical axis shows the numerical value of the bias value ΔPb1 in percentage, with the operating range of the parameter Pb (additional air nozzle angle) (for example, the additional air nozzle angle is -25 degrees to 25 degrees with respect to the horizontal direction) being -100% to 100%. As shown in Fig. 6B, the function Fx1b is defined so that ΔPb1 is variable with respect to Sm1 in a specific range of the NOx master signal Sm1 (nx5≦Sm1≦nx4, nx2≦Sm1≦nx1, px1≦Sm1≦px2, px4≦Sm1≦px5), and ΔPb1 is constant (unchanging) with respect to Sm1 in other ranges.

[0069] The function unit 143 has a function Fx1c that defines the relationship between the NOx master signal Sm1 and the bias value ΔPc1 added to the current setting value of the parameter Pc, as shown in Fig. 5. In Fig. 6C, the vertical axis indicates the numerical value of the bias value ΔPc1 in percentage, with the operating range of the parameter Pc (additional air damper opening) being 0% to 100%. As shown in Fig. 6C, the function Fx1c is defined so that ΔPc1 is variable with respect to Sm1 in a specific range of the NOx master signal Sm1 (px2≦Sm1≦px3, px5≦Sm1≦px6), and is constant (unchanging) with respect to Sm1 in other ranges.

[0070] The function unit 144 has a function Fx2a that defines the relationship between the correction signal Sm2 and the bias value ΔPa2 to be added to the bias value ΔPa1, as shown in Fig. 5. In Fig. 7A, the vertical axis shows the numerical value of the bias value ΔPa2 in percentage, with the operating range of the parameter Pa (burner nozzle angle) (for example, the burner nozzle angle is -25 degrees to 25 degrees with respect to the horizontal direction) being -100% to 100%. The function Fx2a is defined so that ΔPa2 is variable with respect to Sm2 in a specific range of the correction signal Sm2 (nz3≦Sm2≦nz2, nz1≦Sm2≦pz1, pz2≦Sm2≦pz3) as shown in Fig. 7A, and ΔPa2 is constant (unchanging) with respect to Sm2 in other ranges.

[0071] Function section 145 has function Fx2b that defines the relationship between correction signal Sm2 and bias value ΔPb2 to be added to bias value ΔPb1, as shown in Fig. 5. In Fig. 7B, the vertical axis shows the numerical value of bias value ΔPb2 in percentage, with the operating range of parameter Pb (additional air nozzle angle) (for example, additional air nozzle angle from -25 degrees to 25 degrees with respect to the horizontal direction) being -100% to 100%. Function Fx2b is defined so that ΔPb2 is constant (unchanging) with respect to Sm2 over the entire range of correction signal Sm2, as shown in Fig. 7B.

[0072] Function section 146 has function Fx2c that defines the relationship between correction signal Sm2 and bias value ΔPc2 added to bias value ΔPc1, as shown in Fig. 5. In Fig. 7C, the vertical axis indicates the numerical value of bias value ΔPc2 in percentage, with the operating range of parameter Pc (additional air damper opening) being 0% to 100%. Function Fx2c is defined so that ΔPc2 is variable with respect to Sm2 in a specific range of correction signal Sm2 (pz1≦Sm2≦pz2, pz3≦Sm2≦pz4), and is constant (unchanging) with respect to Sm2 in other ranges, as shown in Fig. 7C.

[0073] In this way, the functions Fx1a, Fx1b, and Fx1c are set to have different variable ranges for the NOx master signal Sm1, and the functions Fx2a, Fx2b, and Fx2c are set to have different variable ranges for the correction signal Sm2. As a result, the control unit 118 variably controls one of the parameters Pa, Pb, and Pc as the combustion control parameter Pbc in response to changes in the NOx master signal Sm1 or the correction signal Sm2. In other words, the control unit 118 selects one of the parameters Pa, Pb, and Pc as the combustion control parameter Pbc depending on the magnitude of the NOx master signal Sm1 or the correction signal Sm2.

[0074] In addition, the parameters Pa, Pb, and Pc are selected in a predetermined order of priority in the functions Fx1a, Fx1b, and Fx1c when the NOx master signal Sm1 changes, and in the functions Fx2a, Fx2b, and Fx2c when the correction signal Sm2 changes. For example, when the NOx master signal Sm1 increases from 0, the parameters Pa, Pb, and Pc are repeatedly selected one by one in the order of priority. Such an order of priority is set based on the sensitivity (with lower sensitivity being given priority) of each parameter corresponding to the CO concentration in the exhaust gas that has a negative correlation with the NOx concentration (CO concentration increases when NOx concentration decreases). By setting in this way, it is possible to reduce the influence on other operating parameters of the boiler 10 (increase in CO concentration in the exhaust gas in the above example) caused by reducing the NOx concentration.

[0075] In addition, a plurality of variable ranges are prepared for the NOx master signal Sm1 in the functions Fx1a, Fx1b, and Fx1c, and for the correction signal Sm2 in the functions Fx2a, Fx2b, and Fx2c, and the variable ranges of the bias values ​​(ΔPa1, ΔPa2, ΔPb1, ΔPb2, ΔPc1, ΔPc2) for the parameters (Pa, Pb, Pc) in each range are restricted to be relatively small. For example, in the function Fx1a, the bias value ΔPa1 for the parameter Pa is variable in the range of 40 to 20% when nx4≦Sm1≦nx3, is variable in the range of 20 to -20% when nx1≦Sm1≦px1, and is variable in the range of -20 to -40% when px3≦Sm1≦px4. In this way, by setting each variable range relatively small, the combustion control parameter Pbc is prevented from changing suddenly with respect to the NOx master signal Sm1 and the correction signal Sm2. As a result, the combustion balance of the boiler 10 is not disturbed, and it is possible to control the NOx concentration in the exhaust gas while maintaining a stable combustion state.

[0076] Here, a description will be given of a modified example of the above control by the control unit 118. When the opening degrees of the multiple additional air dampers provided in the boiler 10 (i.e., the above-mentioned parameter Pb) are selected as the combustion control parameter Pbc, the control unit 118 may be configured to maintain the opening degrees of the multiple additional air dampers in response to changes in the NOx master signal Sm1 and the correction signal Sm2 when the opening degree of any of the multiple additional air dampers reaches an upper limit value or a lower limit value.

[0077] Fig. 8 is a schematic cross-sectional view showing a horizontal cross section of the installation area of ​​the additional air port 39 in the furnace 11 of Fig. 1. As shown in Fig. 8, the furnace 11 has a rectangular horizontal cross section. The additional air port 39 includes four upper-stage additional air dampers 39a1, 39a2, 39a3, and 39a4 arranged corresponding to four corners C1, C2, C3, and C4, respectively, in the horizontal cross section, and lower-stage additional air dampers 39b1, 39b2, 39b3, and 39b4 arranged vertically below the upper-stage additional air dampers 39a1, 39a2, 39a3, and 39a4. The upper-stage additional air dampers 39a1, 39a2, 39a3, and 39a4 and the lower-stage additional air dampers 39b1, 39b2, 39b3, and 39b4 are arranged to overlap each other when viewed from above in the vertical direction, and have the same configuration as each other.

[0078] One common control in the boiler 10 is to provide differences in the opening degrees of such multiple additional air dampers. For example, in the embodiment shown in Fig. 8, when the opening degrees of the upper-stage additional air dampers 39a1, a3 and the lower-stage additional air dampers 39b1, b3 corresponding to the corner portions C1, C3 are controlled to 50%, the opening degrees of the upper-stage additional air dampers 39a2, a4 and the lower-stage additional air dampers 39b2, b4 corresponding to the corner portions C2, C4 are controlled to 80%, and there is a 30% difference in opening degree between these additional air dampers.

[0079] When the control unit 118 controls the additional air damper opening degree as the combustion control parameter Pbc based on the NOx master signal Sm1 or the correction signal Sm2 as described above, if the opening degree of any of the additional air dampers reaches the upper limit value (100%) or the lower limit value (0%), the control unit 118 controls the opening degrees of all additional air dampers to be maintained at the opening degree at that time in response to changes in the NOx master signal Sm1 or the correction signal Sm2. That is, in the embodiment of Fig. 8, when the opening degree of the upper additional air dampers 39a2, a4 and the lower additional air dampers 39b2, b4 corresponding to the corners C2, C4 reaches the upper limit (100%) due to an increase in the NOx master signal Sm1 or the correction signal Sm2, the opening degree of the upper additional air dampers 39a1, a3 and the lower additional air dampers 39b1, b3 corresponding to the corners C1, C3 is 70% (=100%-30%), so there is still a movable range. In such a case, even if the NOx master signal Sm1 or the correction signal Sm2 further increases, the opening degree of the upper additional air dampers 39a1, a3 and the lower additional air dampers 39b1, b3 corresponding to the corners C1, C3 is also maintained at 70%.

[0080] Such functions in the control unit 118 can be realized by the following configuration: Fig. 9 is a control flow diagram of the control unit 118 according to another aspect.

[0081] In FIG. 9, when parameter Pc (additional air damper opening degree) is selected as the combustion control parameter Pbc, there is provided a first retention judgment unit 152 which judges whether the opening degree of any of the upper-stage additional air dampers 39a1, 39a2, 39a3, 39a4 and the lower-stage additional air dampers 39b1, 39b2, 39b3, 39b4 has reached an upper limit value, and a second retention judgment unit 154 which judges whether the opening degree of any of the upper-stage additional air dampers 39a1, 39a2, 39a3, 39a4 and the lower-stage additional air dampers 39b1, 39b2, 39b3, 39b4 has reached a lower limit value.

[0082] In the first retention judgment unit 152, when either of condition 4, which judges whether the opening degree of any of the upper-stage additional air dampers 39a1, 39a2, 39a3, and 39a4 has reached an upper limit value, and condition 5, which judges whether the opening degree of any of the lower-stage additional air dampers 39b1, 39b2, 39b3, and 39b4 has reached an upper limit value, is satisfied, the combustion control parameter Pbc (in this case, parameter Pc) of the control object is retained, so that the parameter Pc does not change even if the NOx master signal Sm1 or the correction signal Sm2 changes.

[0083] In the second retention judgment unit 154, when either of condition 6, which judges whether the opening degree of any of the upper-stage additional air dampers 39a1, 39a2, 39a3, and 39a4 has reached a lower limit value, and condition 7, which judges whether the opening degree of any of the lower-stage additional air dampers 39b1, 39b2, 39b3, and 39b4 has reached a lower limit value, is satisfied, the combustion control parameter Pbc (in this case, parameter Pc) of the control object is retained, so that the parameter Pc does not change even if the NOx master signal Sm1 or the correction signal Sm2 changes.

[0084] In this way, when the opening degree of any of the multiple additional air dampers of the boiler 10 reaches an upper or lower limit, the respective opening degrees are controlled to be maintained even if the NOx master signal Sm1 or the correction signal Sm2 changes thereafter. As a result, for example, when the opening degrees of the multiple additional air dampers are controlled with a predetermined balance (with an opening degree difference), the balance (opening degree difference) is maintained even when the opening degree of any of the additional air dampers reaches an upper or lower limit, and the combustion balance in the boiler 10 can be suitably prevented from being lost.

[0085] Next, a detailed configuration of the permission condition determination unit 120 will be described with reference to Fig. 10. Fig. 10 is a control flow diagram of the permission condition determination unit 120 in Fig. 2.

[0086] The permission condition determination unit 120 has a function of outputting a permission signal for permitting the implementation of the above control to the NOx master signal generation unit 116 (PI controller 116b). The permission conditions can be defined from various viewpoints, but in this embodiment, as one aspect of the determination control in the permission condition determination unit 120, a determination based on the following six conditions is illustrated as an example. (Condition 8) Is the load of the boiler 10 equal to or greater than a reference value (e.g., 40%)? (Condition 9) Are any of the burners 21 in an ignition state? (Condition 10) Is the auxiliary burner 22 in an extinguished state? (Condition 11) Is the operating state of the boiler 10 undergoing a load change (transient state)? (Condition 12) Is the burner 21 in ignition or extinguishing operation? (Condition 13) Is the system in an emergency operating state (for example, emergency control such as fast cutback (FCB) operation that rapidly reduces the load on the boiler 10) in progress?

[0087] Conditions 8 to 13 are conditions for determining whether the boiler 10 is in a stable operating state where fuel is steadily combusted. When all of the conditions 8 to 10 are satisfied, an ON signal is output, and the ON signal is output after waiting for a predetermined period (e.g., 600 seconds) by the calculator 146.

[0088] Condition 11 is a condition for determining whether or not the boiler 10 is in a transient state accompanied by a load change. Condition 11 is configured such that, when the boiler 10 is not in a transient state, an OFF signal output from condition 11 is continuously confirmed by calculator 147 for a predetermined period (e.g., 300 sec), the OFF signal is inverted by calculator 148 to output an ON signal.

[0089] Condition 12 is a condition for determining whether or not the burner 21 is in an ignition operation or an extinguishing operation when the boiler 10 is started up or stopped. Condition 12 is configured such that, when the burner 21 is not in an ignition operation or an extinguishing operation and an OFF signal output from condition 12 is continuously confirmed by calculator 149 for a predetermined period (e.g., 300 sec), the OFF signal is inverted by calculator 150, thereby outputting an ON signal.

[0090] Condition 13 is a condition for determining whether or not the boiler 10 is in an emergency operation state. In the boiler 10, when the current operating state is measured, emergency operation may be performed to take emergency measures if operation is impaired or there is a possibility of such an impairment. Such emergency operation is performed, for example, manually or automatically by suddenly reducing the boiler load. In condition 13, when the boiler is not in such an emergency operation state, an OFF signal is output, and the OFF signal is inverted by the calculator 151 to output an ON signal.

[0091] In this way, the permission condition determination unit 120 transmits a permission signal to the NOx master signal generation unit 116 (PI controller 116b) on the condition that all of the ON signals resulting from the above-mentioned respective conditions are obtained. As a result, when the permission conditions are established, the NOx master signal Sm1 is generated by giving control permission to the PI controller 116b, and combustion control capable of suitably suppressing the NOx concentration while ensuring a sound operating state of the boiler 10 is possible.

[0092] As described above, in the combustion system 1, by controlling the boiler 10 with the control device 100, it is possible to suitably suppress the NOx concentration in the exhaust gas without performing combustion adjustment for many types of fuel.

[0093] In the above-described embodiment, the boiler of the present invention is a coal-fired boiler, but the boiler may use solid fuels such as biomass fuel, petroleum coke (PC) generated during oil refining, and oil residue. The fuel is not limited to solid fuels, and may be liquid fuels such as petroleum such as heavy oil, light oil, and heavy oil, industrial wastewater, and gaseous fuels such as natural gas and by-product gas, and decarbonized fuels such as hydrogen and ammonia, and may be applied to a mixed-fuel boiler that uses a combination of these fuels.

[0094] In addition, within the scope of the present disclosure, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described embodiments may be combined as appropriate.

[0095] The contents described in each of the above embodiments can be understood, for example, as follows.

[0096] (1) A boiler control device according to one aspect includes: A NOx concentration sensor (e.g., the NOx concentration sensor 60 in the above embodiment) for detecting a NOx concentration in exhaust gas from a boiler (e.g., the boiler 10 in the above embodiment); a NOx master signal generating unit (e.g., the NOx master signal generating unit 116 in the above embodiment) configured to generate a NOx master signal (e.g., the NOx master signal Sm1 in the above embodiment) based on a difference between a detection value of the NOx concentration sensor (e.g., the detection value Cm of the NOx concentration in the above embodiment) and a NOx concentration target value (e.g., the difference ΔC in the above embodiment); A correction signal generating unit (for example, the correction signal generating unit 117 in the above embodiment) configured to generate a correction signal (for example, the correction signal Sm2 in the above embodiment) based on the control margin of the boiler; A control unit (e.g., the control unit 118 in the above embodiment) configured to control a combustion device of the boiler (e.g., the combustion device 12 in the above embodiment) based on the NOx master signal and the correction signal; Equipped with If the correction signal generating unit determines that the control margin of the boiler is not sufficient, the correction signal generating unit provides the control unit with the correction signal for adjusting a combustion control parameter (e.g., the combustion control parameter Pbc in the above embodiment) selected from a plurality of parameters related to the combustion device of the boiler so as to increase the control margin.

[0097] According to the above aspect (1), combustion control of the boiler is performed by adjusting a combustion control parameter selected from a plurality of parameters based on a NOx master signal corresponding to the difference between the detection value of the NOx concentration sensor and the NOx concentration set value, or a correction signal for increasing the control margin, depending on the control margin of the boiler. In particular, when it is determined that the control margin is insufficient, combustion control is performed to increase the control margin based on the correction signal prior to the NOx reduction operation based on the NOx master signal, thereby making it possible to bring the detection value of the NOx concentration sensor closer to the NOx concentration target value without impairing the controllability of the boiler. With this type of combustion control, for example, even if a fuel having different properties from that used during combustion adjustment is used for a NOx concentration set value that is set based on the results of combustion adjustment using fuel with specific properties, the combustion device can be controlled so that the NOx concentration in the exhaust gas approaches the target NOx concentration value without compromising the controllability of the boiler.

[0098] (2) In another embodiment, in the above embodiment (1), When it is determined that the control margin of the boiler is not sufficient, the correction signal generating unit replaces the NOx concentration target value with the detection value of the NOx concentration sensor.

[0099] According to the above aspect (2), when combustion control is performed based on the correction signal, the detection value of the NOx concentration sensor is replaced with the NOx concentration target value, and the difference between the detection value of the NOx concentration sensor and the NOx concentration target value is made substantially 0 (zero), thereby preferably preventing the NOx master signal and the correction signal from competing with each other and causing mutual interference in control.

[0100] (3) In another embodiment, in the above embodiment (1) or (2), The control unit is configured to select one of the plurality of parameters as the combustion control parameter based on the magnitude of the NOx master signal or the correction signal when it is determined that the control margin of the boiler is not sufficient.

[0101] According to the above aspect (3), by limiting the number of parameters selected as the combustion control parameter to one, it is possible to effectively prevent the combustion balance of the boiler from being destroyed by simultaneously controlling a plurality of parameters.

[0102] (4) In another embodiment, in any one of the above (1) to (3), The control unit is configured to select the combustion control parameter from the plurality of parameters in a pre-specified order of priority in response to a change in the NOx master signal or the correction signal.

[0103] According to the above aspect (4), the selection of the combustion control parameters based on the NOx master signal or the correction signal is performed in accordance with a pre-specified priority order, thereby effectively preventing the combustion balance of the boiler from being disturbed.

[0104] (5) In another embodiment, in the above embodiment (4), The priority order is set based on sensitivity to the CO concentration in the exhaust gas.

[0105] According to the above aspect (5), the combustion control parameters are selected in accordance with the priority order set based on the sensitivity to the CO concentration in the exhaust gas, thereby making it possible to suppress an increase in the CO concentration corresponding to a decrease in the NOx concentration, and effectively prevent the combustion balance of the boiler from being disrupted.

[0106] (6) In another embodiment, in any one of the above (1) to (5), When the detection value of the NOx concentration sensor is greater than the target NOx concentration value, the multiple parameters include the boiler's burner nozzle angle (e.g., the nozzle angle of the burner 21 in the above embodiment), the additional air nozzle angle (e.g., the nozzle angle of the additional air port 39 in the above embodiment), and the additional air damper opening (e.g., the damper opening of the additional air port 39 in the above embodiment).

[0107] According to the above aspect (6), when the detection value of the NOx concentration sensor is greater than the target NOx concentration value, by selecting a combustion control parameter from these parameters, it is possible to preferably control the NOx concentration in the exhaust gas by controlling the combustion device while ensuring a balanced combustion state.

[0108] (7) In another embodiment, in any one of the above (1) to (5), When the detection value of the NOx concentration sensor is smaller than the NOx concentration target value, the multiple parameters include the burner nozzle angle of the boiler (e.g., the nozzle angle of the burner 21 in the above embodiment) and the additional air damper opening (e.g., the damper opening of the additional air port 39 in the above embodiment).

[0109] According to the above aspect (7), when the detection value of the NOx concentration sensor is smaller than the target NOx concentration value, by selecting a combustion control parameter from these parameters, it is possible to preferably control the NOx concentration in the exhaust gas by controlling the combustion device while ensuring a balanced combustion state.

[0110] (8) In another embodiment, in any one of the above (1) to (7), When the control unit selects the opening degrees of multiple additional air dampers provided in the boiler as the combustion control parameter, when the opening degree of any of the multiple additional air dampers reaches an upper limit value or a lower limit value, the control unit is configured to maintain the opening degrees of the multiple additional air dampers in response to changes in the NOx master signal.

[0111] According to the above aspect (8), when the opening degree of any of the multiple additional air dampers of the boiler reaches the upper or lower limit, the respective opening degrees are controlled to be maintained against the subsequent change in the NOx master signal. As a result, for example, when the opening degrees of the multiple additional air dampers are controlled with a predetermined balance, the balance is maintained even when the opening degree of any of the additional air dampers reaches the upper or lower limit, and the combustion balance can be suitably prevented from being lost.

[0112] (9) In another embodiment, in any one of the above (1) to (8), The device further includes a permission condition determination unit (for example, the permission condition determination unit 120 in the above embodiment) configured to transmit a permission signal to the control unit when a preset permission condition is met.

[0113] According to the above aspect (9), by implementing the above control when the permission condition is satisfied, it becomes possible to perform combustion control capable of appropriately suppressing the NOx concentration while ensuring a sound operating state of the boiler.

[0114] (10) In another embodiment, in any one of the above (1) to (9), The correction signal is generated based on a control margin for the steam temperature of the boiler.

[0115] According to the above aspect (10), a correction signal is generated based on the control margin for the boiler steam temperature. By using such a correction signal, the detection value of the NOx concentration sensor can be brought closer to the NOx concentration target value without impairing the controllability of the boiler while ensuring the control margin for the boiler steam temperature.

[0116] (11) In another embodiment, in any one of the above (1) to (10), The boiler is primarily fueled by coal.

[0117] According to the above aspect (11), it is possible to perform suitable combustion control in a boiler that uses coal as its main fuel, which is a fuel whose fuel properties fluctuate widely and whose fuel properties have a large effect on the combustion state of the boiler 10, that is, a so-called coal-fired boiler.

[0118] (12) A combustion system according to one aspect of the present invention comprises: A control device according to any one of the above (1) to (11), A boiler configured to be controlled by the control device; Equipped with.

[0119] According to the above aspect (12), it is possible to realize a combustion system capable of suitably suppressing the NOx concentration in the exhaust gas from the boiler without performing combustion adjustment for many types of fuel.

[0120] (13) A method for controlling a boiler according to one aspect includes the steps of: Detecting a NOx concentration in exhaust gas from a boiler; generating a NOx master signal (e.g., the NOx master signal Sm1 in the above embodiment) based on a difference (e.g., the difference ΔC in the above embodiment) between the detected value of the NOx concentration (e.g., the detected value Cm of the NOx concentration in the above embodiment) and a NOx concentration target value (e.g., the NOx concentration target value Cs in the above embodiment); generating a correction signal (for example, the correction signal Sm2 in the above embodiment) based on the control margin of the boiler; A step of controlling a combustion device of the boiler (for example, the combustion device 12 of the above embodiment) based on the NOx master signal and the correction signal; When the correction signal generating unit determines that the control margin of the boiler is not sufficient, the correction signal generating unit controls the combustion device based on the correction signal for adjusting a combustion control parameter (e.g., the combustion control parameter Pbc in the above embodiment) selected from a plurality of parameters related to the combustion device of the boiler so as to increase the control margin; Equipped with.

[0121] According to the above aspect (13), combustion control of the boiler is performed by adjusting a combustion control parameter selected from a plurality of parameters based on a NOx master signal corresponding to the difference between the detection value of the NOx concentration sensor and the NOx concentration set value, or a correction signal for increasing the control margin, in accordance with the control margin of the boiler. In particular, when it is determined that the control margin is insufficient, combustion control is performed to increase the control margin based on the correction signal prior to the NOx reduction operation based on the NOx master signal, so that the detection value of the NOx concentration sensor can be brought closer to the NOx concentration target value without impairing the controllability of the boiler. With this type of combustion control, for example, even if a fuel having different properties from that used during combustion adjustment is used for a NOx concentration set value that is set based on the results of combustion adjustment using fuel with specific properties, the combustion device can be controlled so that the NOx concentration in the exhaust gas approaches the target NOx concentration value without compromising the controllability of the boiler.

[0122] (14) A boiler control program according to one embodiment of the present invention comprises: Using a computer device, Detecting a NOx concentration in exhaust gas from a boiler; generating a NOx master signal (e.g., the NOx master signal Sm1 in the above embodiment) based on a difference (e.g., the difference ΔC in the above embodiment) between the detected value of the NOx concentration (e.g., the detected value Cm of the NOx concentration in the above embodiment) and the NOx concentration target value (e.g., the NOx concentration target value Cs in the above embodiment); generating a correction signal (for example, the correction signal Sm2 in the above embodiment) based on the control margin of the boiler; A step of controlling a combustion device of the boiler (for example, the combustion device 12 of the above embodiment) based on the NOx master signal and the correction signal; When the correction signal generating unit determines that the control margin of the boiler is not sufficient, the correction signal generating unit controls the combustion device based on the correction signal for adjusting a combustion control parameter (e.g., the combustion control parameter Pbc in the above embodiment) selected from a plurality of parameters related to the combustion device of the boiler so as to increase the control margin; It is possible to execute the following.

[0123] According to the above aspect (14), the combustion control of the boiler is performed by adjusting a combustion control parameter selected from a plurality of parameters based on a NOx master signal corresponding to the difference between the detection value of the NOx concentration sensor and the NOx concentration set value, or a correction signal for increasing the control margin, according to the control margin of the boiler. In particular, when it is determined that the control margin is insufficient, the detection value of the NOx concentration sensor can be brought closer to the NOx concentration target value without impairing the controllability of the boiler by performing combustion control for increasing the control margin based on the correction signal prior to the NOx reduction operation by the NOx master signal. According to this type of combustion control, for example, even when a fuel having different properties from that at the time of combustion adjustment is used for a NOx concentration set value set based on the result of combustion adjustment using a fuel having specific properties, the combustion device can be controlled so that the NOx concentration in the exhaust gas approaches the NOx concentration target value without impairing the controllability of the boiler. [Explanation of symbols]

[0124] 1 Combustion system (boiler system) 10. Boiler 11 Furnace 12 Combustion equipment 13 Combustion gas passage 14 Flue 21a~21f Burner 22a~22c Auxiliary burner 23a~23f Pulverized coal supply pipe 24a~24f Crusher (Mill) 36 Wind box 37 Air duct (airway) 38 Forced draft fan (FDF) 39 Additional air port 40 Additional Air Duct 41 Gas Duct 42 Air heater (air preheater) 43 Denitration equipment 44 Dust collector 45 Induced Draft Fan (IDF) 46 Desulfurization equipment 60 Concentration Sensor 100 Control device 101 Furnace wall 102 1st superheater (heat exchanger) 103 Second superheater (heat exchanger) 104 Third superheater (heat exchanger) 105 1st reheater (heat exchanger) 106 Second reheater (heat exchanger) 107 Energy saver (heat exchanger) 112 NOx concentration detection value acquisition unit 114 NOx concentration target value setting unit 116 NOx master signal generator 117 Correction signal generator 118 Control Unit 120 Permission condition determination section 141~146 Function section 152 1st retention judgment section 154 2nd retention judgment section

Claims

1. A burner that is attached to a furnace wall constituting a furnace and has a burner nozzle whose angle with respect to the furnace wall is variable; an additional air port provided on the furnace wall above the burner and having an additional air nozzle whose angle with respect to the furnace wall is variable; an additional air duct provided with an additional air damper capable of varying the amount of additional air supplied to the additional air port by adjusting an opening degree of the additional air duct; A boiler control device comprising: a NOx concentration sensor for detecting a NOx concentration in exhaust gas from the boiler; a NOx master signal generating unit configured to generate a NOx master signal for controlling a combustion control parameter related to a combustion device of the boiler so that the detection value of the NOx concentration sensor approaches a NOx concentration target value; a correction signal generating unit configured to generate a correction signal for selecting the combustion control parameter from a plurality of parameters related to the combustion device so as to increase a control margin, which is a margin in a control range of an operating element related to control of the main steam temperature of the boiler, when the control margin is determined to be insufficient; a control unit configured to control a combustion device of the boiler based on the NOx master signal and the correction signal, A boiler control device, wherein the plurality of parameters include an angle of the burner nozzle, an angle of the additional air nozzle, and an opening degree of the additional air damper.

2. A boiler control device as described in claim 1, wherein when it is determined that the control margin is insufficient, the NOx master signal is maintained at a current value by replacing the NOx concentration target value with the detection value of the NOx concentration sensor.

3. A boiler control device as described in claim 1 or 2, configured so that when it is determined that the control margin is insufficient, the combustion control parameter is selected from the multiple parameters in a pre-specified order of priority.

4. The boiler control device according to claim 3 , wherein the priority order is set based on sensitivity to a CO concentration in the flue gas.

5. A control device for a boiler as described in any one of claims 1 to 4, configured such that when the opening degree of a plurality of additional air dampers provided in the boiler is selected as the combustion control parameter, when the opening degree of any of the plurality of additional air dampers reaches an upper limit or lower limit, the opening degree of the plurality of additional air dampers is maintained in response to changes in the NOx master signal.

6. The boiler control device according to claim 1 , further comprising: a permission condition determination unit configured to transmit a permission signal to the NOx master signal generation unit when a preset permission condition is satisfied.

7. The boiler control device according to claim 1 , wherein the boiler uses coal as a main fuel.

8. A control device according to any one of claims 1 to 7; A boiler configured to be controlled by the control device; A combustion system comprising:

9. A burner attached to a furnace wall constituting a furnace and having a burner nozzle whose angle with respect to the furnace wall is variable; an additional air port provided on the furnace wall above the burner and having an additional air nozzle whose angle with respect to the furnace wall is variable; an additional air duct provided with an additional air damper capable of varying the amount of additional air supplied to the additional air port by adjusting an opening degree of the additional air duct; A method for controlling a boiler comprising: Detecting a NOx concentration in exhaust gas from the boiler; generating a NOx master signal for controlling a combustion control parameter related to a combustion device of the boiler so that the detected value of the NOx concentration approaches a target value of the NOx concentration; generating a correction signal for selecting the combustion control parameter from a plurality of parameters related to the combustion device so as to increase a control margin, which is a margin in a control range of an operating element related to control of the main steam temperature of the boiler, when the control margin is determined to be insufficient; controlling a combustion device of the boiler based on the NOx master signal and the correction signal; Equipped with The method for controlling a boiler, wherein the plurality of parameters include an angle of the burner nozzle, an angle of the additional air nozzle, and an opening degree of the additional air damper.

10. A burner attached to a furnace wall constituting a furnace and having a burner nozzle whose angle with respect to the furnace wall is variable; an additional air port provided on the furnace wall above the burner and having an additional air nozzle whose angle with respect to the furnace wall is variable; an additional air duct provided with an additional air damper capable of varying the amount of additional air supplied to the additional air port by adjusting an opening degree of the additional air duct; A boiler control program comprising: Using a computer device, Detecting a NOx concentration in exhaust gas from the boiler; generating a NOx master signal for controlling a combustion control parameter related to a combustion device of the boiler so that the detected value of the NOx concentration approaches a target value of the NOx concentration; generating a correction signal for selecting the combustion control parameter from a plurality of parameters related to the combustion device so as to increase a control margin, which is a margin in a control range of an operating element related to control of the main steam temperature of the boiler, when the control margin is determined to be insufficient; controlling a combustion device of the boiler based on the NOx master signal and the correction signal; It is possible to execute A boiler control program, wherein the plurality of parameters include an angle of the burner nozzle, an angle of the additional air nozzle, and an opening degree of the additional air damper.

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