Boiler system and boiler system control method

Abstract

To provide a boiler system which can properly perform a blow even if the water quality of makeup water is changed.SOLUTION: A boiler system of one embodiment of the present invention stores a first set value of a condensation magnification of predicted boiler water which is set so as not to be maintained within a range of a management reference value when makeup water has the worst assumed water quality, and to be maintained within the range of the management reference value when the makeup water has the best assumed water quality, and an assumed limit value which is set on the basis of a value obtained by multiplying a second set value of the condensation magnification of the predicted boiler water which is set so as to be maintained within the range of the management reference value when the makeup water has the worst assumed water quality to the worst water-quality main management value, and when it is determined that a current value of the condensation magnification of the boiler water reaches the first set value or larger, and also when it is determined that the main management value which is measured by boiler water quality measurement means reaches the assumed limit value or larger, the boiler system performs a blow by a blow line.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a boiler system and a boiler system control method.

Background Art

[0002] In a boiler system that generates steam by a boiler, only water in the boiler water is discharged as steam, so concentration occurs in which the concentration of dissolved substances such as silica, sulfate ions, chloride ions, etc. in the boiler water increases. If such concentration progresses excessively, there is a risk of causing a phenomenon called "carry-over" in which scale adheres to the inner wall of the water pipe or dissolved substances are mixed into the steam and carried out of the boiler. Therefore, when the boiler water is concentrated, it is common to perform "blowdown" in which a part of the boiler water is discharged to the outside and the remaining boiler water is diluted with makeup water to lower the concentration of dissolved substances. Since such blowdown is a process of discharging heat and water outside the system, it is desirable to perform it at the minimum necessary frequency.

[0003] Regarding the control of such blowdown, Patent Document 1 discloses measuring the value of a water quality management item in makeup water for at least one water quality management item selected from the electric conductivity, chloride ion concentration, sulfate ion concentration, and silica concentration, and preselecting a water quality management item that will deviate from the management standard at the lowest concentration multiple, and performing blowdown control so that the value of this selected water quality management item in the boiler water is within the range of the management standard value. Further, Patent Document 2 discloses a regular drainage mode in which boiler water is blown every time a predetermined combustion time elapses to prevent scale adhesion, and a high-concentration drainage mode in which boiler water is blown when the electric conductivity of the boiler water reaches a predetermined value to suppress the concentration of the boiler water. When a predetermined condition regarding an item of the boiler water or supply water is satisfied, for example, when the temperature of the water pipe is on an upward trend, when it is determined that the regeneration treatment of the ion exchange resin is defective, when the hardness of the supply water exceeds a predetermined value, when the pH value of the boiler water is below a predetermined value, etc., a technique for switching between the regular drainage mode and the high-concentration drainage mode is disclosed.

Prior Art Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2009-30817 [Patent Document 2] Japanese Patent Publication No. 2013-190113 [Overview of the project] [Problems that the invention aims to solve]

[0005] If the quality of the makeup water is constant, the quality of the boiler water can be properly managed by controlling it based on the measured values ​​of specific water quality parameters. However, the quality of the makeup water is not constant and can fluctuate relatively large in different ways depending on the season, the mixing ratio with drain, etc., with different tendencies for each control parameter. While blowdown can be performed based on the measured values ​​of numerous water quality parameters to prevent excessive concentration of the boiler water for each parameter, this increases the complexity of the boiler system configuration, and some control parameters are difficult to measure accurately at high frequency. As a result, the reliability of the boiler system may decrease due to the increase in the number of measurement parameters.

[0006] Therefore, the present invention aims to provide a boiler system and boiler control method that can perform blowdown appropriately even when the quality of the makeup water changes. [Means for solving the problem]

[0007] A boiler system according to one aspect of the present invention includes a boiler body that stores makeup water internally as boiler water and heats the boiler water to generate steam, a feedwater line that supplies the makeup water to the boiler body, a blowdown line that blows the boiler water to the outside of the boiler body, a boiler water quality measuring means that measures a main control value which is one or more water quality control values ​​for which a management standard value to be maintained in the boiler water is set for each of the boiler water, and at least one of the predicted boiler water quality control values ​​calculated as the value for the predicted boiler water when the makeup water is concentrated from the water quality control value for the makeup water when the makeup water has the worst-case scenario does not stay within the range of the corresponding management standard value, and all of the predicted boiler water quality control values ​​when the makeup water has the best-case scenario are within the range of the management standard value The system includes: a first storage means for storing a first set value of the expected boiler water concentration factor, which is set to maintain within a range of standard values; a second storage means for storing a second set value of the expected boiler water concentration factor, which is set to maintain within a range of the corresponding standard values ​​for all expected boiler water quality management values ​​when the makeup water has the worst-case water quality, and an assumed limit value which is the limit value of the main management value, which is set based on a value obtained by multiplying the main management value in the worst-case water quality; and a blowdown control means for controlling blowdown by the blowdown line, wherein the blowdown control means performs blowdown by the blowdown line when it is determined that the current value of the boiler water concentration factor has become equal to or greater than the first set value, and when it is determined that the main management value measured by the boiler water quality measuring means has become equal to or greater than the assumed limit value.

[0008] The boiler system described above may further include: a means for acquiring the water quality of the makeup water, which acquires one or more water quality management values; and a means for storing multiple data of the water quality management values ​​acquired by the water quality of the makeup water, which indicates the assumed range of water quality for setting the first set value, the second set value, and the assumed limit value.

[0009] In the boiler system described above, the means for acquiring the makeup water quality may acquire the measured value of the water quality management value.

[0010] In the boiler system described above, the feedwater line is configured to produce makeup water by mixing the condensate generated from the steam with feedwater supplied from an external source into a feedwater tank, and the makeup water quality acquisition means may be configured to measure the water quality control value of the feedwater and calculate the water quality control value of the makeup water considering the recovery rate of the condensate.

[0011] Another embodiment of the present invention relates to a boiler system control method comprising: a boiler body that stores makeup water internally as boiler water and heats the boiler water to generate steam; a feedwater line that supplies the makeup water to the boiler body; and a blowdown line that blows the boiler water to the outside of the boiler body. The method comprises the steps of: measuring a main control value for the boiler water, which is one or more water quality control values ​​for which a management standard value to be maintained in the boiler water is set for each of the boiler water; and determining that at least one of the expected boiler water quality control values ​​calculated as the value for the expected boiler water when the makeup water is concentrated from the water quality control value for the makeup water when the makeup water has the worst-case scenario, does not stay within the range of the corresponding management standard value, and the makeup water is expected to The method includes the steps of: setting a first set value for the concentration factor of the expected boiler water so that all of the expected boiler water quality management values ​​when the water has the best possible water quality remain within the range of the management standard value; setting a second set value for the concentration factor of the expected boiler water so that all of the expected boiler water quality management values ​​when the makeup water has the worst possible water quality remain within the range of the corresponding management standard value; setting an assumed limit value, which is the limit value of the main management value, based on the value obtained by multiplying the main management value in the worst possible water quality by the second set value; and performing blowdown using the blow-line when it is determined that the current value of the concentration factor of the boiler water has become equal to or greater than the first set value, and when it is determined that the measured value of the main management value has become equal to or greater than the assumed limit value. [Effects of the Invention]

[0012] According to the present invention, blowdown can be performed appropriately even if the quality of the replenishment water changes. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram showing the configuration of a boiler system relating to one embodiment of the present invention. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a schematic diagram showing the configuration of a boiler system 1 according to one embodiment of the present invention. The boiler system 1 is a system that implements one embodiment of the boiler system control method according to the present invention.

[0015] The boiler system 1 comprises a boiler body 10 that stores makeup water internally as boiler water and heats the boiler water to generate steam, a feedwater line 20 that supplies makeup water to the boiler body 10, a blowdown line 30 that blows the boiler water to the outside of the boiler body 10, a boiler water quality measuring means 40 that measures a main control value which is one or more water quality control values ​​for which a management standard value to be maintained in the boiler water is set, and a control device 50 that controls other components.

[0016] The boiler body 10 includes a boiler 11 for storing boiler water and a burner 12 for burning fuel to heat the boiler 11 and, consequently, the boiler water. The boiler body 10 is also equipped with a steam-water separator 13 for removing water droplets contained in the steam flowing out of the boiler 11, and a steam header 14 for storing the steam from which the water droplets have been removed by the steam-water separator 13.

[0017] The feedwater line 20 includes a feedwater tank 21 for storing makeup water and a makeup water pump 22 for pressurizing the makeup water and introducing it into the boiler body 10. The feedwater line 20 may also include a water quality sensor 23 for measuring the quality of the makeup water and a chemical injection device 24 for injecting chemicals such as pH adjusters, scale inhibitors, and corrosion inhibitors into the makeup water. The water quality sensor 23 and the chemical injection device 24 may also be located at the outlet of the feedwater tank 21. The water quality sensor 23 may detect the quality of the supply water, the quality of the makeup water before the chemical injection device 24 injects chemicals, or the quality of the makeup water after chemical injection. In other words, the quality of the makeup water supplied to the boiler body 11 may not be measured directly, but may be calculated considering the drain recovery rate, the amount of chemicals injected, etc. Furthermore, as shown in the figure, the feedwater line 20 may be configured to introduce supply water supplied from an external source and drain generated by the condensation of steam into the feedwater tank 21. In other words, makeup water may be produced by mixing the supply water with the drain recovered in the steam trap 25.

[0018] The blow-off line 30 has an openable / closable blow-off valve 31. In other words, the blow-off line 30 blows boiler water out of the boiler body 10 by opening the blow-off valve 31. The blow-off line 30 may be configured to discharge boiler water from the boiler body 11, or, as shown in the figure, it may be configured to discharge boiler water from a pipeline that recirculates boiler water from the steam-water separator 13 to the boiler body 11.

[0019] The boiler water quality measuring means 40 measures a primary control value selected from among several water quality control values ​​for which management standards to be maintained in boiler water are set, such as electrical conductivity (EC), silica concentration, sulfate ion concentration, chloride ion concentration, etc. The primary control value is used as a value that represents the water quality of the boiler water in the boiler body 11. Preferably, the boiler water quality measuring means 40 has a sensor that directly measures the water quality control value of the boiler water inside the boiler body 11. As the primary control value measured by the boiler water quality measuring means 40, electrical conductivity, which can be measured relatively easily for high-temperature, high-pressure boiler water inside the boiler body 11, can be suitably adopted.

[0020] The control device 50 includes a combustion control unit 51, a water supply control unit 52, a makeup water quality acquisition unit 53, a measured value storage unit 54, a first storage unit 55, a second storage unit 56, and a blowdown control unit 57. The control device 50 has a processor, a memory, an input / output interface, etc., and can be realized by one or more computer devices that execute an appropriate control program. Each component of the control device 50 is a classification of the functions of the control device 50, and it does not necessarily have to be strictly distinguishable in terms of physical configuration and program configuration.

[0021] The combustion control unit 51 is combustion control means for controlling the combustion of the burner 12. The combustion control unit 51 can be configured to perform well-known control to change the combustion amount of the burner 12 according to, for example, the pressure of the steam header 14.

[0022] The water supply control unit 52 is water supply control means for controlling the supply of makeup water through the water supply line 20. The water supply control unit 52 can be configured to adjust the makeup water pump 22 so as to keep the water level of the boiler water in the can body 11 constant.

[0023] The makeup water quality acquisition unit 53 is makeup water quality acquisition means for acquiring one or more water quality management values for the makeup water. The makeup water quality acquisition unit 53 may be configured to acquire a detection value such as a water quality sensor 23, that is, an actually measured value of the water quality management value. By specifying the assumed range of the water quality of the makeup water based on the actually measured value, the first setting value, the second setting value, and the assumed limit value described later can be appropriately set, so that the blowdown from the boiler body 10 can be appropriately controlled. Also, the makeup water quality acquisition unit 53 may be configured to receive an input of the analysis result of a sample of the makeup water by the user.

[0024] Furthermore, the makeup water quality acquisition unit 53 may be configured to measure the water quality of the supply water and calculate a water quality management value for the makeup water, taking into account the drain recovery rate. By using the water quality management value for the makeup water calculated taking into account the drain recovery rate, the range of fluctuations in the water quality of the makeup water can be estimated relatively accurately with a small number of measurements, so that blowdown control can be easily and efficiently performed. The makeup water quality acquisition unit 53 may also be configured to calculate a water quality management value for the makeup water supplied to the boiler 11 from various measured values, etc.

[0025] The measurement value storage unit 54 is a measurement value storage means that stores multiple data of water quality management values ​​acquired by the supply water quality acquisition unit 53. By storing multiple data of water quality management values, fluctuations in water quality management values ​​according to the time of day, day of the week, season, etc. of the supply water can be predicted more accurately. As a result, the first setting and second setting values ​​and the predicted limit values, which will be described later, can be set appropriately, so that blowdown can be performed appropriately to maintain good boiler water quality without time lag.

[0026] The first storage unit 55 is a first storage means that stores a first set value for the concentration ratio of the expected boiler water, which is set such that at least one of the expected boiler water quality management values ​​calculated from the water quality management value of the makeup water when the makeup water has the worst expected water quality does not remain within the range of the corresponding management standard value, and all of the expected boiler water quality management values ​​when the makeup water has the best expected water quality remain within the range of the management standard value.

[0027] As a specific example, we will explain the case where electrical conductivity, silica concentration, sulfate ion concentration, and chloride ion concentration are used as water quality control values ​​for boiler water. The respective water quality control standard values ​​(upper limits) are assumed to be: electrical conductivity: 300 mS / m, silica concentration: 500 mg / L, sulfate ion concentration: 350 mg / L, and chloride ion concentration: 300 mg / L. Furthermore, as assumed combinations of water quality control values, multiple data of water quality control values ​​stored in the measurement value storage unit 54 will be used. The water quality control values ​​stored in the measurement value storage unit 54 are shown in Table 1.

[0028] [Table 1]

[0029] The expected boiler water quality management values, which are the water quality management values ​​for the expected boiler water obtained by concentrating the makeup water shown in Table 1, are obtained by multiplying each water quality management value in Table 1 by the concentration factor. The maximum concentration factor, which is the concentration factor at which the expected boiler water quality management value reaches the water quality management standard value, is calculated and is shown in Table 2.

[0030] [Table 2]

[0031] Among these, the smallest concentration factor is the chloride ion concentration factor in Data 3 = 6.6. Therefore, in the data in Table 1, Data 3 is used as the assumed value for water quality management when the makeup water has the worst water quality. Furthermore, when the smallest concentration factor among the data is extracted and compared, the data with the largest extracted concentration factor, in this example Data 5 in Table 1, where the silica concentration factor is 12.5 in Table 2, is used as the assumed value for water quality management when the makeup water has the best water quality. Therefore, the first set value for the expected boiler water concentration factor is set to a value greater than 6.6 and less than or equal to 12.5, so that at least one of the expected boiler water quality management values ​​when the makeup water has the worst water quality does not remain within the range of the corresponding management standard value, and all of the expected boiler water quality management values ​​when the makeup water has the best water quality remain within the range of the management standard value. Setting the first set value to a large value reduces the frequency of blowdown, and setting the first set value to a small value more reliably prevents the impurity concentration of the boiler water from becoming excessive. When setting the first setting value automatically, the first setting value can be a value obtained by weighting the lower limit and upper limit values ​​at a predetermined ratio.

[0032] As an example, Table 3 shows the predicted boiler water quality management values ​​for each data point when the first setting value is set to the upper limit of 12.5. In Table 3, predicted boiler water quality management values ​​that exceed the water quality management standard value are indicated with an underline.

[0033] [Table 3]

[0034] As shown in Table 3, all predicted boiler water quality management values ​​for Data 3, where the makeup water has the worst water quality, exceed the management standard value, while all predicted boiler water quality management values ​​for Data 5, where the makeup water has the best water quality, are within the management standard value range. This confirms that the set first setting value satisfies the above conditions.

[0035] The second memory unit 56 is a second memory means that stores an assumed limit value, which is the limit value of the main control value, set based on a value obtained by multiplying the second set value of the expected boiler water concentration factor, which is set so that all expected boiler water quality control values ​​remain within the range of the corresponding control standard value when the makeup water has the worst-case water quality, by the main control value in the worst-case water quality (the assumed worst-case main control value). In other words, the second set value is set so that for all water quality control values ​​where the expected boiler water quality control value at the concentration factor of the first set value deviates from the range of the control standard value, the expected boiler water quality control value at the concentration factor of the second set value remains within the range of the control standard value. The assumed limit value is set as the value obtained by multiplying the worst-case main control value by the second set value, or by multiplying this value by a safety factor.

[0036] In the example in Table 1, the second setting value for the concentration factor is set to a value that does not exceed the minimum value among the maximum concentration factors in Table 2, i.e., the concentration factor for chloride ions in data 3 = 6.6. The difference between the second setting value and the minimum value among the maximum concentration factors is a margin in case the supplemental water used is of a much worse quality than assumed. When setting the second setting value automatically, the second setting value can be obtained by multiplying the minimum value among the maximum concentration factors by a predetermined coefficient of 1 or less.

[0037] The assumed limit value may be set as the primary control value of any water quality data (data 1-4, 6 underlined in Table 3) or all data (data 1-6) where any water quality management value deviates from the range of the management standard value when the concentration ratio is set as the first setting value, or as the maximum value among the primary control values ​​(maximum value of electrical conductivity in Table 1: data 3), or as the primary control value in the worst water quality data (data 3 with the minimum value in Table 2) multiplied by the second setting value, and may also be set as the value obtained by multiplying this value by a safety coefficient. When the assumed limit value is rounded, it is preferable to truncate the fractional part of the value obtained by multiplying the primary control value in the worst water quality by the second setting value.

[0038] In the example in Table 1, if the second concentration factor is set to 6.25, the value obtained by multiplying the electrical conductivity of data 3 (43.4), which is the worst value among the main control values ​​of the water quality data where any of the water quality control values ​​deviate from the range of the control standard when the concentration factor is set to the first value, is 271.25. In this case, the assumed limit value can be set to, for example, 270.

[0039] The blowdown control unit 57 is a blowdown control means that controls blowdown by the blowdown line 30. The blowdown control unit 57 performs blowdown by the blowdown line 30 when it is determined that the current value of the concentration factor of the boiler water has reached or exceeded a first set value, and when it is determined that the main control value measured by the boiler water quality measuring means 40 has reached or exceeded an assumed limit value. The current value of the concentration factor of the boiler water can be calculated based on the evaporation rate of the boiler body 10, the amount of water retained, the combustion time, and the amount of boiler water discharged in past blowdowns.

[0040] As is clear from the above explanation, the boiler system control method according to one embodiment of the present invention implemented in boiler system 1 includes the steps of measuring a main control value, which is one of one or more water quality control values ​​for which a management standard value to be maintained in the boiler water is set, and checking that at least one of the expected boiler water quality control values ​​calculated as the value in the expected boiler water where the makeup water is concentrated from the water quality control value of the makeup water when the makeup water has the worst expected water quality does not stay within the range of the corresponding management standard value, and all of the expected boiler water quality control values ​​when the makeup water has the best expected water quality are within the management standard value The system includes the steps of: setting a first set value for the expected boiler water concentration factor so as to maintain it within a certain range; setting a second set value for the expected boiler water concentration factor so as to maintain all expected boiler water quality control values ​​within the range of their respective corresponding control standards when the makeup water has the worst-case water quality; setting an assumed limit value, which is the limit value of the main control value, based on the value obtained by multiplying the main control value in the worst-case water quality by the second set value; and performing blowdown by the blow-off line 30 when it is determined that the current value of the boiler water concentration factor has become equal to or greater than the first set value, and when it is determined that the measured value of the main control value has become equal to or greater than the assumed limit value.

[0041] In boiler system 1, blowdown is performed at the optimal timing when the current concentration ratio is determined to be equal to or greater than the first set value, that is, when makeup water with normal water quality is concentrated. Furthermore, boiler system 1 also performs blowdown without delay when the main control value measured by the boiler water quality measuring means exceeds the assumed limit value, that is, when the quality of the boiler water deteriorates prematurely due to fluctuations in the quality of the makeup water. As a result, boiler system 1 can maintain good boiler water quality so that the expected boiler water quality control value remains within the control standard value range. In addition, since the assumed limit value is set taking into account water quality control values ​​other than the main control value, boiler system 1 can perform appropriate blowdown so that all water quality control values ​​in the boiler water remain within the control standard value range, provided that the variation in water quality control values ​​is within the assumed range. Moreover, since the boiler water quality is measured only by the main control value, boiler system 1 can have a simple and reliable device configuration.

[0042] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications and variations are possible. For example, the boiler system according to the present invention may not include means for acquiring makeup water quality and means for storing measured values, and may be configured such that it is essential for the user to calculate a first set value and an assumed limit value and input the calculated values ​​into the first storage means and the second storage means. [Explanation of symbols]

[0043] 1. Boiler System 10 Boiler body 11 Can body 12 burners 13 Steam water separator 14 Steam Header 20 Water supply lines 21 Water tank 22. Water supply pump 23 Water quality sensors 24 Chemical dosing device 25 Steam Traps 30 Browline 31 Blow-off valve 40 Boiler water quality measurement method 50 Control device 51 Combustion control unit 52 Water supply control unit 53 Makeup water quality acquisition department 54 Measurement Value Storage Unit 55 1st memory section 56 2nd memory section 57 Blow control unit

Claims

1. A boiler body that stores makeup water internally as boiler water and heats the boiler water to generate steam, A water supply line for supplying the makeup water to the boiler body, A blow line for blowing the boiler water out of the boiler body, A boiler water quality measuring means for measuring a main control value, which is one or more water quality control values ​​for which a management standard value to be maintained in the boiler water is set for each of the boiler water, A first storage means for storing a first set value for the concentration ratio of the expected boiler water, which is set such that at least one of the expected boiler water quality management values ​​calculated from the water quality management value of the makeup water when the makeup water has the worst expected water quality does not stay within the range of the corresponding management standard value, and all of the expected boiler water quality management values ​​when the makeup water has the best expected water quality stay within the range of the management standard value, A second storage means for storing a second setting value for the concentration factor of the expected boiler water, which is set based on the value obtained by multiplying the main control value in the worst-case water quality by the second setting value for the concentration factor of the expected boiler water, which is set based on the value obtained by multiplying the main control value in the worst-case water quality, so that all the expected boiler water quality control values ​​remain within the range of the corresponding control standard value when the makeup water has the worst-case water quality; A blow control means for controlling blowing by the blow line, Equipped with, The blowdown control means determines that the current value of the concentration factor of the boiler water has become equal to or greater than the first set value, and determines that the main control value measured by the boiler water quality measuring means has become equal to or greater than the assumed limit value, and performs blowdown using the blowdown line. Boiler system.

2. Regarding the aforementioned supplemental water, a means for obtaining the supplemental water quality to obtain one or more water quality management values, A measurement value storage means that stores multiple data of the water quality management values ​​acquired by the water quality acquisition means, which indicates the assumed range of the water quality of the supplement water for setting the first set value, the second set value, and the assumed limit value, The boiler system according to claim 1, further comprising the above.

3. The boiler system according to claim 2, wherein the means for obtaining the supply water quality obtains the measured value of the water quality management value.

4. The water supply line is configured to produce the makeup water by mixing the drain generated by the condensation of the steam with a water supply tank that stores supply water supplied from an external source. The boiler system according to claim 3, wherein the means for obtaining the quality of the supply water is configured to measure the water quality management value of the supply water and to calculate the water quality management value of the supply water taking into consideration the recovery rate of the drain.

5. A boiler body that stores makeup water internally as boiler water and heats the boiler water to generate steam, A water supply line for supplying the makeup water to the boiler body, A blow line for blowing the boiler water out of the boiler body, A control method for a boiler system comprising: The process of measuring the main control value, which is one or more water quality control values ​​for which a management standard value to be maintained in the boiler water is set for each of the boiler water, A step of setting a first set value for the concentration factor of the expected boiler water such that at least one of the expected boiler water quality management values ​​calculated from the water quality management value of the makeup water when the makeup water has the worst-case expected water quality does not remain within the range of the corresponding management standard value, and all of the expected boiler water quality management values ​​when the makeup water has the best-case expected water quality remain within the range of the management standard value, A step of setting a second set value for the concentration factor of the expected boiler water so that all of the expected boiler water quality control values ​​remain within the range of the corresponding control standard values ​​when the makeup water has the worst-case water quality expected, A step of setting an assumed limit value, which is the limit value of the main control value, based on the value obtained by multiplying the main control value in the worst water quality by the second set value, The process of blowing down using the blow-line when it is determined that the current value of the concentration factor of the boiler water has become equal to or greater than the first set value, and when it is determined that the measured value of the main control value has become equal to or greater than the assumed limit value, A boiler system control method comprising the following:

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