JP6036244B2 - Boiler control method and boiler control device during suit blower operation - Google Patents

Description

  The present invention relates to a boiler control method and a boiler control device during operation of a suit blower.

  The suit blower is a device that removes deposits by spraying steam or the like toward the heat transfer tube when ash or soot adheres to the heat transfer tube in the boiler and the heat transfer coefficient decreases. When the suit blower is activated, the reduced heat transfer coefficient is rapidly recovered, so that the temperature of the steam generated in the boiler is rapidly increased. In order to suppress this and keep the steam temperature constant, it is generally required to control the boiler by a method different from the normal time when the suit blower is operated.

  Therefore, various technologies relating to boiler control during suit blower operation have been proposed. In such a conventional technique, for example, as described in Patent Documents 1 and 2, in order to cope with a rapid change in steam temperature during the operation of the suit blower, simultaneously with the operation of the suit blower or in advance of the operation. The boiler control settings are changed. Further, as a control method, for example, as described in Patent Document 3, control parameters such as a gain when the suit blower is operated are set independently from the normal time, or as described in Patent Document 4. In addition, it is known that the amount of exhaust gas recirculated and the amount of spray water sprayed by the temperature reducer are changed at an appropriate timing.

JP-A-62-217006 JP-A-1-114611 Japanese Patent Laid-Open No. 62-245209 JP 2001-263606 A

  By the way, as described in the above Patent Documents 1, 3, and 4, high-pressure steam (main steam) generated by the boiler is supplied to the turbine to perform work (power generation) and is discharged from the turbine. A reheat-type power plant that reheats low-pressure steam (reheated steam) in a boiler and supplies the turbine again is widely used for effective use of steam. On the other hand, while supplying main steam to a turbine, it is also common to send it to other plants as needed. In the case of a power plant, in order to stabilize the power generation output, it is necessary to supply a certain amount of main steam to the turbine even when air supply is performed. Therefore, when air supply is performed, the amount of water supplied to the boiler is increased by the amount of steam supplied, and the amount of main steam generated is increased.

  However, it is not easy to combine the above-mentioned two technologies and carry out main steam in a reheat power plant. This is because when the amount of main steam generated is increased, the amount of fuel supplied increases in order to give more heat to the superheater that generates main steam in the boiler. On the other hand, as described above, since a constant amount of main steam is supplied to the turbine regardless of whether or not air is supplied, the amount of reheat steam discharged from the turbine is also constant regardless of whether or not air is supplied. Therefore, when the amount of fuel supplied to the boiler increases due to the air supply, excessive heat is given to the reheater that heats the reheated steam, and the temperature of the reheated steam rises too much.

  Therefore, when supplying main steam in a reheat-type power plant, it is required to control the boiler by a method different from the conventional method. As for boiler control at the time of suit blower operation, if the conventional techniques as described in Patent Documents 1 to 4 are applied as they are, the temperature of the reheat steam cannot be stably controlled, and the plant There is a possibility that the stable operation will be hindered, or the reheat steam temperature may exceed the allowable value set in consideration of the material strength of the pipe.

  Then, this invention is made | formed in view of the said problem, The place made into the objective of this invention is the novel which can operate stably the reheat-type steam plant which supplies the main steam. It is another object of the present invention to provide an improved boiler control method and boiler control device for operating a suit blower.

  In order to solve the above-described problems, according to one aspect of the present invention, a turbine driven by main steam and reheat steam, heating water to generate main steam and heating steam discharged from the turbine And a boiler for generating reheat steam, and a boiler control method at the time of suit blower operation in a plant capable of sending main steam to another plant, the amount of main steam being sent There is provided a boiler control method during operation of a suit blower that sets a control parameter of the boiler during operation of the suit blower.

  By setting the boiler control parameters when the suit blower is operated based on the amount of main steam sent, the amount of main steam generated can be reduced even if the flow ratio of reheated steam to main steam varies due to air supply. The control of the heating based on the standard prevents the temperature of the reheat steam from becoming unstable.

  In order to suppress the temperature rise of the reheat steam during the suit blower operation, the control parameter may be set so that the amount of suppression of the temperature rise becomes smaller as the amount of main steam sent is larger. More specifically, in order to suppress the increase in the temperature of the reheat steam by reducing the recirculation amount of the hot gas discharged from the boiler when the suit blower is operated, the recirculation is performed as the amount of main steam supplied increases. The control parameter may be set so that the amount of decrease is small.

  In order to solve the above-mentioned problem, according to another aspect of the present invention, a turbine driven by main steam and reheat steam, and main water is generated by heating feed water and discharged from the turbine. A boiler control device in a plant that is capable of heating steam and generating reheated steam and sending main steam to another plant, based on the amount of main steam sent A boiler control device is provided for setting control parameters of a boiler when a suit blower is operated.

  As described above, according to the present invention, it is possible to stably operate a reheat-type steam plant that performs air supply.

It is a figure which shows the reheat-type power plant to which one Embodiment of this invention is applied. FIG. 2 is a diagram showing an example in the case where there is no air supply to another plant in the reheat power plant shown in FIG. 1. FIG. 2 is a diagram showing an example in the case where there is air supply to another plant in the reheat power plant shown in FIG. 1. It is a graph which shows the relationship between the flow rate ratio with respect to the main steam of the reheat steam in the reheat-type power plant shown in FIG. 1, and power generation output. It is a figure which shows typically control of the amount of GR at the time of the suit blower action | operation in one Embodiment of this invention. It is a figure which shows the example of the control circuit of GR amount which concerns on one Embodiment of this invention.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a diagram showing a reheat power plant to which an embodiment of the present invention is applied. In the reheat-type power plant 1, the boiler 2 heats feed water 3 with a superheater (SH) 2a to generate main steam 4 (superheated steam). Here, in the reheat-type power plant 1, a part of the main steam 4 can be supplied as an air supply 5 to another plant.

  The main steam 4 excluding the air supply 5 is supplied to the turbine 6 (high pressure turbine 6a). When the turbine 6 is driven, the generator 7 connected to the turbine 6 generates electric power. The main steam 4 that has worked in the turbine 6 is discharged from the turbine 6 as low-temperature reheated steam 8a. The boiler 2 heats the low-temperature reheat steam 8a with a reheater (RH: Reheater) 2b to form high-temperature reheat steam 8b, and supplies it again to the turbine 6 (low-pressure turbine 6b). That is, in the reheat power plant 1, the turbine 6 is driven by the main steam 4 and the high-temperature reheat steam 8b. In the following description, when it is not necessary to distinguish between the low-temperature reheat steam 8a and the high-temperature reheat steam 8b, these are collectively referred to as the reheat steam 8.

  In such a reheat-type power plant 1, it is necessary to supply a certain amount of main steam 4 to the turbine 6 regardless of the presence or absence of the air supply 5 in order to stabilize the output (power generation output) of the generator 7. Therefore, when the air supply 5 is performed, the amount of the water supply 3 is increased by that amount, and the amount of main steam 4 generated is also increased. When the production amount of the main steam 4 increases, the amount of fuel supplied to the boiler 2 also increases in order to give more heat to the superheater 2a.

  Further, in order to stabilize the power generation output and maintain equipment such as piping, it is also necessary to keep the temperature and pressure of the main steam 4 and the high-temperature reheat steam 8b supplied to the turbine 6 within a predetermined range. Therefore, the amount of fuel supplied to the boiler 2 is controlled based on feedback of the pressure measurement value of the main steam 4 in addition to being increased or decreased according to the amount of main steam 4 generated as described above. Further, the outlet temperature of the superheater 2a is controlled to be a predetermined temperature by spraying water with a superheat reducer (DeSH: Desuperheater; not shown).

  The boiler 2 is provided with a suit blower 9. As described above, the suit blower 9 is steamed toward the heat transfer tube when ash or soot adheres to the heat transfer tube of the superheater 2a or the reheater 2b in the boiler 2 and the heat transfer coefficient decreases. It is a device that removes deposits by spraying. For example, a plurality of suit blowers 9 are arranged in a region where the superheater 2a and the reheater 2b are arranged, but only one place is shown in the figure for simplicity.

  Further, the boiler 2 is provided with a gas recirculation (GR) line 10 for introducing high-temperature gas discharged from the top of the furnace through the rear flue to the bottom of the furnace and recirculating it. Yes. The GR line 10 includes a gas recirculation fan (GRF: GR Fan) that guides the high-temperature exhaust gas discharged from the boiler 2 to the bottom of the furnace, and a damper that adjusts the amount of the high-temperature exhaust gas to be recirculated. The temperature of the high-temperature reheated steam 8b is adjusted mainly by the amount of gas recirculation (GR amount) in the GR line 10. As the amount of GR increases, the temperature of the gas flowing through the subsequent stage of the boiler 2 increases, and the temperature of the high-temperature reheat steam 8b heated by the reheater 2b provided in this portion also increases. In addition, the outlet temperature of the reheater 2b is controlled to be a predetermined temperature by spray water injection by a reheat reducer (DeRH: Dereheater) 11.

  As described above, in the reheat power plant 1, the boiler 2 is controlled by adjusting the amount of fuel supplied, the amount of GR, the amount of water injected by the overheat reducer and the reheat reducer 11, and the like. Such control uses, for example, the power generation output, the generation amount and pressure of the main steam 4, the fuel type (coal type if coal), the respective outlet temperatures of the superheater 2a and the reheater 2b as input values, This is realized by appropriately setting control parameters for adjusting the GR amount, the water injection amount, and the like, specifically the parameters of the PID controller and the parameters of the function.

  However, in the reheat-type power plant 1, the amount of main steam 4 generated varies depending on the amount of air supply 5 (air supply amount). Therefore, the boiler with only the input value of control conventionally used as described above. It is difficult to control 2 appropriately. Hereinafter, this point will be further described with reference to FIGS. In addition, numerical values, such as the amount of vapor | steams shown in these figures, are examples, and do not limit the application range of this invention.

  FIG. 2 is a diagram illustrating an example in the case where there is no air supply to another plant in the reheat power plant shown in FIG. 1. In the illustrated example, 120 t / h of feed water 3 is heated by the superheater 2 a of the boiler 2, and main steam 4 of 120 t / h is generated. Since the air supply 5 is not carried out (0 t / h), the main steam 4 of 120 t / h is supplied to the turbine 6 as it is. From the turbine 6, 95t / h low-temperature reheat steam 8a is discharged. In the illustrated example, since 25 t / h of steam is extracted in the turbine 6 for preheating the feed water 3 and the like, the low-temperature reheat steam 8a discharged from the amount of the main steam 4 supplied is reduced. The amount is smaller. The low-temperature reheat steam 8 a is heated by the reheater 2 b of the boiler 2 to become high-temperature reheat steam 8 b of 95 t / h, and is supplied to the turbine 6 again. In addition, the output (power generation output) of the generator 7 at this time is 40 MW.

  FIG. 3 is a diagram illustrating an example of the case where there is air supply to another plant in the reheat power plant shown in FIG. 1. In the illustrated example, 60 t / h of the main steam 4 is supplied as an air supply 5 to another plant. Therefore, in order to maintain the power generation output (40 MW) by supplying the main steam 4 of the same amount (120 t / h) to the turbine 6 as when there is no air supply 5, the 180 t / h feed water 3 is heated by the superheater 2 a The main steam 4 of 180 t / h is generated. As a result, the same main steam 4 of 120 t / h as in the example of FIG. 2 is supplied to the turbine 6, and the low-temperature reheat steam 8 a of 95 t / h is discharged from the turbine 6.

  In the example of FIG. 3 described above, the production amount of the main steam 4 (180 t / h) is increased as compared with the case where there is no air supply 5 (120 t / h). On the other hand, the amount of the reheated steam 8 is the same as in the case where there is no air supply 5 (95 t / h). Therefore, the flow rate ratio of the reheated steam 8 to the main steam 4 (reheated steam flow / main steam flow) is smaller than that without the air supply 5 (95/120 → 95/180). Therefore, when the amount of fuel supplied to the boiler 2 increases based on the amount of main steam 4 generated, the heat given to the reheater 2b becomes excessive with respect to the amount of reheat steam 8. End up. This point will be further described below with reference to FIG.

  FIG. 4 is a graph showing the relationship between the flow rate ratio of reheated steam to main steam and the power generation output in the reheat power plant shown in FIG. The numerical value given to each series shows the air supply amount. When the air supply rate is 0 t / h (when there is no air supply 5), all the main steam 4 generated by the boiler 2 is supplied to the turbine 6, so that the flow rate of the main steam 4 and the flow rate of the main steam 4 can be reduced. The flow rate of the hot steam 8 changes at the same rate. Therefore, the flow ratio of the reheated steam 8 to the main steam 4 is substantially constant regardless of the power generation output. Therefore, when there is no air supply 5, the temperature of both the main steam 4 and the reheated steam 8 is set to an appropriate range by controlling the amount of fuel supplied to the boiler 2 based on the power generation output. I was able to keep it.

  However, in the case of an air supply amount of 20 t / h to 100 t / h (when there is an air supply 5), as described above with reference to FIG. 3, a part of the main steam 4 generated in the boiler 2 is supplied. Since the gas 5 is supplied to another plant, the flow rate ratio of the reheated steam 8 to the main steam 4 is smaller than that in the case of the air supply amount 0 t / h. Further, in the case of an air supply amount of 20 t / h to 100 t / h, when the power generation output increases, the amount of main steam 4 supplied to the turbine 6 increases and the amount of reheat steam 8 also increases. The flow ratio of the hot steam 8 to the main steam 4 is increased.

  Thus, in the reheat-type power plant 1, the amount of air supply 5 (air supply amount) greatly affects the temperature of the high-temperature reheat steam 8b heated by the reheater 2b. Therefore, the control parameters for adjusting the amount related to the temperature of the high-temperature reheat steam 8b such as the amount of GR and the amount of water injected in the reheat reducer 11 are the conventional input conditions such as the power generation output and the outlet temperature of the reheater 2b. In addition to this, it is desirable to set based on the air supply amount.

  Embodiment of this invention is related with the control at the time of a suit blower operation | movement especially among control of such a boiler 2. FIG. Below, with reference to FIG. 5 and FIG. 6, control of the boiler 2 at the time of the suit blower operation | movement which concerns on embodiment of this invention is further demonstrated.

  FIG. 5 is a diagram schematically showing the control of the GR amount when the suit blower is operated in one embodiment of the present invention. In the figure, the GR amounts in “initial state”, “before suit blower operation” and “after suit blower operation” are shown. The amount of GR is adjusted by, for example, the opening of a damper in the GR line 10. In the illustrated example, it is assumed that the power generation output is constant.

  The “initial state” is a state when the reheat power plant 1 starts operation, for example. At this time, since ash and soot are hardly attached to the surface of the heat transfer tubes of the superheater 2a and the reheater 2b in the boiler 2, the heat transfer rate is high. Thereafter, as the plant is operated, ash and soot adhere to the surface of the heat transfer tube, and the heat transfer rate gradually decreases. Then, the state is “before the suit blower is activated”.

  “Before the operation of the suit blower” is a state in which it is determined that the suit blower is to be operated on the condition that a predetermined time has elapsed since the heat transfer rate is reduced or the operation is started, or by the operation of the operator. . In the state before “suit blower operation”, the adhesion of ash and soot on the surface of the heat transfer tube is the highest in the three states shown in the figure, and the heat transfer coefficient is the lowest. Here, since the boiler 2 is automatically controlled so as to maintain the temperature of the reheat steam 8, the GR amount is the largest among the three states in the “before the suit blower operation”, and the rear stage of the boiler 2. The temperature of the gas flowing through is the highest.

  “After the suit blower is activated” is a state when the suit blower is activated to remove deposits on the heat transfer tube and the heat transfer coefficient is recovered. Therefore, at this time, the heat transfer coefficient of the heat transfer tube is rapidly increased as compared with the state before “operation of the suit blower”. Since the heat transfer coefficient of the heat transfer tube of the reheater 2b also rapidly increases, if the normal feedback control based on the temperature measurement value is performed, the rapid temperature increase of the reheat steam 8 cannot be prevented. Therefore, when the suit blower is in operation, for example, the feedback control is performed by setting a value such as a gain that is different from the normal value, or the GR amount is forcibly changed by the preceding control, so that the reheat steam 8 A sudden temperature rise is prevented.

  In one embodiment of the present invention, the control parameter in the feedback control or the preceding control is set so that the reduction amount of the GR amount by the control at the time of the suit blower operation is changed according to the amount of the air supply 5 (air supply amount). Is set. As a result, for example, as shown in the drawing, the reduction width when the air supply amount is 0 t / h is d1, the reduction width when the air supply amount is 30 t / h, d2, and the reduction amount when the air supply amount is 60 t / h. D1> d2> d3> d4 when the width is d3 and the decrease width is 100 t / h. That is, in this embodiment, the amount of decrease in the amount of GR when the suit blower is activated decreases as the amount of air supply increases.

  This is because when the amount of air supplied is large, the amount of main steam 4 produced is larger than the amount (constant) of reheat steam 8, so the amount of fuel supplied to the boiler 2 is also large, and therefore the reheat steam 8. This is because the temperature of the is easy to rise. Reflecting this state, in the feedback control based on the temperature measurement value before the operation of the suit blower (normal time), the GR amount is set to be smaller as the air supply amount is larger.

  Here, if the same control parameter is set regardless of the presence or absence of air supply and the control at the time of the suit blower operation is performed, for example, the change amount of the GR amount by the advance control is too large, or the reheat steam 8 is controlled by feedback control. There is a possibility that the GR amount when the suit blower is operated becomes a value significantly different from the appropriate GR amount because the gain related to the temperature change of the suit blower is too large. For example, as shown in the figure, when the air supply amount is 60 t / h, the GR amount is changed by the same change amount d1 as when the air supply amount is 0 t / h when the suit blower is operated (in the case of a general reheat power plant). If it decreases, it will be far below the appropriate amount of GR. In this case, the amount of GR is too small, and the temperature of the reheat steam 8 is too low.

  Thus, if the amount of GR is significantly different from the appropriate amount of GR, it takes time until the appropriate amount of GR is reached in the subsequent control. As a result, the power generation output becomes unstable or the high-temperature reheat steam 8b. Temperature may deviate from the allowable value. Therefore, in the present embodiment, the above-described problem is solved by adjusting the reduction amount of the GR amount by the control during the operation of the suit blower according to the air supply amount and setting a more appropriate GR amount.

  FIG. 5 is a diagram schematically showing a boiler control method when the suit blower is operated, and the GR amount is not necessarily controlled as shown in the actual operation. For example, although the amount of GR after the suit blower is activated at each air supply amount is shown to be approximately the same as that in the initial state, it is often different in practice. This is because, generally, a plurality of suit blowers are installed in the vicinity of the superheater 2a and the reheater 2b and operate sequentially, so that the heat transfer coefficient in the heat transfer tube does not recover to a value close to the initial state at a time. .

  Although the control of the amount of GR when the suit blower is operated has been described here, the control when the suit blower is activated also for other amounts of control such as the control of the amount of water injected by the reheat reducer 11 when the suit blower is activated. By setting the parameter based on the amount of air supplied, it is possible to prevent the temperature of the reheat steam from becoming unstable. More specifically, when suppressing the temperature rise of the reheat steam when the suit blower is activated, the temperature of the reheat steam is set by setting a control parameter so that the suppression range of the temperature rise becomes smaller as the air supply amount increases. Can be prevented from falling too much.

  FIG. 6 is a diagram illustrating an example of the GR amount control circuit 100 according to an embodiment of the present invention. The control circuit 100 is provided to adjust the amount of GR by controlling the opening of a damper provided in the GR line 10 in, for example, the reheat power plant 1 as shown in FIG. In this case, the control circuit 100 is provided with measuring means or input for acquiring various values such as the output of the generator 7 (power generation output), the amount of the air supply 5, the outlet temperature of the reheater 2b, and the fuel type. Means are connected.

  In the figure, “Fx” represents a function (calculation), and “T” represents a switch. A solid line represents a circuit at normal time, a broken line represents a circuit selected when the suit blower (SB) is operated, and a thick line represents a circuit for reflecting the air supply amount on the setting of the control parameter when the suit blower is operated. .

  Here, in the control circuit 100, the control parameters when the suit blower is activated are set based on the air supply amount. More specifically, for example, an air supply amount may be given as one of input values for determining a parameter of the PID controller, and an input value of the PID controller based on a power generation output or a fuel type is calculated. The air supply amount may be reflected in the parameter of the function. Thereby, for example, the control of the GR amount as shown in FIG. 5 is realized.

  First, a normal control circuit will be described. In the illustrated example, a power generation output 101, an air supply amount 103, a reheater outlet temperature measurement value 107, and a fuel type 111 are used as input conditions for control. The value calculated by the function 102 from the power generation output 101 and the value calculated by the function 104 from the air supply amount 103 are added by the adder 105 to calculate the target value 106 of the reheater outlet temperature. A difference between the target value 106 and the measured value 107 of the reheater outlet temperature 107 is calculated by the subtractor 108, and this difference is input to the PID controller 109.

  On the other hand, the value calculated by the function 110 from the power generation output 101 is also input to the PID controller 109. Similarly, a value calculated from the fuel type 111 by the function 112 is also input to the PID 109. These values are used for setting parameters such as a gain when the PID controller 109 outputs the GR damper opening by inputting the difference between the target value 106 and the measured value 107 of the reheater outlet temperature.

  Further, separately from the control based on the reheater outlet temperature, the value determined by the preceding control signal 113 is added to the value output by the PID controller 109 by the adder 114, and the GR damper opening 115 is determined. Is done.

  When the suit blower is activated, the heat conductivity of the heat transfer tube changes abruptly, so that at least a part of the above functions and the PID controller are replaced with ones that execute different calculations and different controls. For example, the function 110 having the power generation output 101 as an input can be replaced with the function 117 by the switch 116. Further, the function 112 having the fuel type 111 as an input can be replaced with the function 119 by the switch 118. Further, the input by the preceding control signal 113 can be input to the adder 114 through the calculation by the function 121 by the switch 120. The PID controller 109 can also be replaced with the PID controller 123 by the switch 122. For example, the PID controller 123 may have a higher gain than that of the PID controller 109 and can respond quickly to changes in the reheater outlet temperature.

  In one embodiment of the present invention, the air supply amount 103 is given as an input to at least one of the function 117, the function 119, the function 121, or the PID controller 123 selected when the suit blower is operated, thereby supplying the air. Setting of control parameters based on the air volume is realized. Which function or PID controller is supplied with the air supply amount 103 as an input can be appropriately designed according to the specific configuration of the control circuit.

  Although the control circuit for adjusting the GR amount has been described here, the control circuit for adjusting other amounts such as the amount of water injected in the reheat reducer 11 is similarly set to the air supply amount 103. It is possible to realize the setting of control parameters based on it. Further, the above example is only an example of the control circuit for the GR amount, and various other control circuit configurations are possible.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Reheat type power plant 2 Boiler 3 Water supply 4 Main steam 5 Air supply 6 Turbine 7 Generator 8a Low temperature reheat steam 8b High temperature reheat steam 9 Suit blower 10 GR line 11 Reheat reducer

Claims (4)

A turbine driven by main steam and reheat steam; and a boiler that heats feed water to generate the main steam and heats steam discharged from the turbine to generate the reheat steam, A boiler control method during operation of a suit blower in a plant capable of sending main steam to another plant,
In order to suppress the temperature rise of the reheat steam when the suit blower is operated, the control parameter of the boiler is set so that the amount of suppression of the temperature rise becomes smaller as the amount of the main steam sent increases. wherein, boiler control method at the time of scan Tsuburowa operation. In suppressing the temperature rise of the reheat steam by reducing the recirculation amount of the hot gas discharged from the boiler during the operation of the suit blower, the recirculation amount increases as the amount of main steam supplied increases. the decline and sets the control parameter so smaller, the boiler control method at the time of suit blower operation according to claim 1. A turbine driven by main steam and reheat steam; and a boiler that heats feed water to generate the main steam and heats steam discharged from the turbine to generate the reheat steam, A boiler control device in a plant capable of sending main steam to another plant,
In order to suppress the temperature rise of the reheat steam when the suit blower is operated, the control parameter of the boiler is set so that the suppression range of the temperature rise becomes smaller as the amount of the main steam sent increases. to the boiler controller. In suppressing the temperature rise of the reheat steam by reducing the recirculation amount of the hot gas discharged from the boiler during the operation of the suit blower, the recirculation amount increases as the amount of main steam supplied increases. The boiler control device according to claim 3, wherein the control parameter is set so that a decrease width of the boiler decreases.

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