Methods for stabilizing boiler water quality

Abstract

To effectively inject a boiler compound into a can body of a boiler, thereby stabilizing the water quality of boiler water.SOLUTION: A water supply pump for supplying boiler water to a can body of a boiler is intermittently operated. Whenever the water supply pump is intermittently operated, action for injecting a boiler compound to the boiler water is performed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for stabilizing the quality of boiler water. [Background technology]

[0002] The steam generated by boiler water evaporation is mixed with boiler water, and this steam mixed with boiler water, i.e., steam-water mixture, flows into a steam-water separator, where the steam and boiler water are separated. The separated boiler water flows into the bottom of the boiler body through a downcomer that connects the steam-water separator to the boiler body. During boiler operation, these operations are performed continuously, circulating the boiler water and maintaining a stable water quality inside the boiler body (Patent Document 1). To replenish the boiler water lost due to evaporation, a feedwater pump is operated to supply water to the boiler body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-74679 Summary of the Invention [Problem to be solved by the invention]

[0004] Since the boiler is in a state where evaporation and water supply are repeated, it is necessary to inject the required amount of boiler compound into the boiler body along with the water supply in order to stabilize the boiler water quality and prevent corrosion and rust.

[0005] Therefore, an object of the present invention is to stabilize the quality of boiler water by effectively injecting boiler compound into the boiler body. [Means for solving the problem]

[0006] In order to achieve this object, the method of stabilizing the quality of boiler water of the present invention comprises the steps of: A feed water pump for supplying boiler water to the boiler body is operated intermittently, and boiler compound is injected into the boiler water every time the feed water pump is operated intermittently. In this regard, When detecting the electrical conductivity of boiler water and injecting boiler compound into boiler water depending on the level of the detected electrical conductivity, an upper limit and a lower limit are set for the operation time, and when the detected electrical conductivity is a normal electrical conductivity between the electrical conductivity corresponding to the upper limit of the operation time and the electrical conductivity corresponding to the lower limit of the operation time, a certain value of time between the upper limit and the lower limit of the operation time is set as the operation time for injecting boiler compound into boiler water. It is characterized by:

[0007] According to the method for stabilizing the quality of boiler water of the present invention, When the detected electrical conductivity falls below the electrical conductivity corresponding to the upper limit of the operating time, the operating time is set to the upper limit, and when the measured electrical conductivity exceeds the electrical conductivity corresponding to the lower limit of the operating time, the operating time is set to the lower limit. It is preferable that:

[0008] According to the method for stabilizing the quality of boiler water of the present invention, Each time the water supply pump is operated intermittently, a blower is operated to discharge the boiler water from the boiler body. It is preferable that:

[0010] According to the method for stabilizing the boiler water quality of the present invention, when the boiler water in the boiler body is replaced, it is preferable to carry out the operation of injecting boiler compound into the boiler water simultaneously with the operation of the feed water pump, and to continue the operation of injecting boiler compound into the boiler water in the boiler body even after the boiler water in the boiler body reaches a predetermined water level and the feed water pump is stopped. [Effects of the Invention]

[0011] According to the method for stabilizing the quality of boiler water of the present invention, a feed water pump for supplying boiler water to a boiler body of a boiler is operated intermittently, and boiler compound is supplied to the boiler water every time the feed water pump is operated intermittently. Therefore, when new boiler water is intermittently supplied to the boiler body, boiler compound can also be supplied at the same time, and the quality of the boiler water can be reliably stabilized. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram showing the structure of a boiler for carrying out a method for stabilizing the quality of boiler water of a boiler according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram showing an example of an operation sequence of the boiler of FIG. [Figure 3] FIG. 2 is a diagram showing an example of control of the amount of boiler compound injected into the boiler of FIG. 1. [Figure 4] FIG. 10 is a diagram illustrating an example of a sequence of a blowing operation. DETAILED DESCRIPTION OF THE INVENTION

[0013] The principle of the method for stabilizing the boiler water quality of the present invention is to stabilize the concentration of boiler compound in the boiler water, i.e., the water quality, by supplying boiler compound to the boiler water in accordance with the intermittent operation of the feed water pump for supplying boiler water to the boiler body of the boiler.

[0014] Figure 1 shows the structure of a boiler for carrying out the method of the present invention. Reference numeral 11 denotes a boiler body, which is configured to generate steam 14 by heating boiler water 13 supplied from a water supply line 12 using a burner (not shown). Reference numeral 15 denotes an exhaust gas line extending from the burner. Reference numeral 16 denotes an economizer, which is connected to the exhaust gas line 15 and water supply line 12, thereby recovering the thermal energy contained in the exhaust gas into the feedwater, i.e., the boiler water 13, thereby improving thermal efficiency. A feedwater pump 17 is provided in the water supply line 12.

[0015] A boiler compound supply line 31 is connected to the water supply line 12. An injection pump 33 for boiler compound 32 is provided in this boiler compound supply line 31. Reference numeral 34 denotes a connection point of the boiler compound supply line 31 to the water supply line 12. Check valves 35 and 36 for preventing backflow are provided in the water supply line 12 and the boiler compound supply line 31 upstream of the connection point 34, respectively.

[0016] Steam 14 generated inside the boiler body 11 is extracted from the boiler body 11 in the form of a steam-water mixture fluid containing boiler water 13 that was present inside the boiler body 11, and is taken into a steam-water separator 18. The steam-water separator 18 separates the steam 14 from the boiler water 13 by the action of gravity or the like, and the separated steam 14 is extracted from the upper part of the steam-water separator 18 to the outside of the system and supplied to the destination. The separated boiler water 13 accumulates in the lower part inside the steam-water separator 18, but is circulated to the bottom of the boiler body 11 via a downcomer 19 that connects the steam-water separator 18 and the boiler body 11.

[0017] A blow pipe 21 is connected to the downcomer pipe 19. This blow pipe 21 is used to discharge boiler water 13 accumulated inside the downcomer pipe 19 and the steam separator 18 to the outside of the boiler body 11 by the action of gravity or the action of the pressure of steam 14 present inside the boiler body 11, that is, to blow out the boiler water 13. The blow pipe 21 is provided with an on-off valve 22 for controlling the start and stop of blowing.

[0018] The downcomer pipe 19 is provided with an electrical conductivity sensor 23 for detecting the electrical conductivity of the boiler water 13 inside the downcomer pipe 19. When boiler compound 32 is injected, i.e., supplied, into the boiler water 13, the amount of boiler compound 32 injected increases, and the concentration of the boiler compound 32 in the boiler water 13 increases. As the concentration of the boiler compound 32 in the boiler water 13 increases, the electrical conductivity of the boiler water 13 increases, so the concentration of the boiler compound 32 is detected by detecting the electrical conductivity of the boiler water 13. The electrical conductivity sensor 23 can be installed at any location in the illustrated boiler where the boiler water 13 is present. However, because the boiler water 13 is boiling and moving vigorously inside the boiler body 11, it is difficult to measure the stable electrical conductivity of the boiler water 13, i.e., the stable concentration of the boiler compound 32. In contrast, because the downcomer pipe 19 is installed outside the boiler body 11, it is cooled by outside air. Therefore, the boiler water 13 inside the downcomer pipe 19 is not boiling but is stable. Therefore, by providing the electrical conductivity sensor 23 in the downcomer pipe 19, the electrical conductivity of the boiler water 13 can be detected in a stable state. Furthermore, to prevent an increase in electrical conductivity from being overlooked due to failure to detect it, the electrical conductivity sensor 23 is provided in a portion of the downcomer pipe 19 where the electrical conductivity of the boiler water 13 is high, i.e., in the middle of the downcomer pipe 19 along the height direction as shown in the figure. The blow-off pipe 21 is connected to the downcomer pipe 19 at a position corresponding to the position of the electrical conductivity sensor 23 in the downcomer pipe 19.

[0019] A control device 24 controls the operation and stop of the feed water pump 17 and the injection pump 33 for the boiler compound 32, and also controls the opening and closing state of the on-off valve 22 in the blow pipe 21 based on the detection signal from the electrical conductivity sensor 23.

[0020] Reference numeral 25 denotes a water level gauge, which is connected to the boiler body 11 to detect the level of boiler water 13 inside the boiler body 11. Reference numeral 26 denotes a total blow-out pipe, which is used to drain all of the boiler water 13 inside the boiler body 11 for purposes such as maintenance by opening a valve 27 provided on this total blow-out pipe 26.

[0021] In this configuration, when the boiler is to be operated again after all the boiler water 13 inside the boiler body 11 has been discharged as described above, the valve 27 is closed and the operation of the feedwater pump 17 is started, and the feedwater pump 17 is operated until the boiler water 13 is supplied up to a specified water level inside the boiler body 11. When the specified water level is reached, the operation of the feedwater pump 17 is stopped and the boiler operation is started as necessary.

[0022] However, at that time, it may happen that a sufficient amount of boiler compound 32 has not yet been injected into the boiler water 13. The amount of boiler compound 32 injected into the boiler water 13 can be known by detecting the electrical conductivity of the boiler water 13 inside the downcomer pipe 19 with the sensor 23. If the amount of boiler compound 32 injected into the boiler water 13 is insufficient, the operation of the injection pump 33 for the boiler compound 32 continues even after the feedwater pump 17 is stopped so that the detected electrical conductivity of the boiler water 13 reaches a predetermined value. Alternatively, if it is known how long the injection pump 33 should be operated after the feedwater pump 17 is stopped so that the concentration of the boiler compound 32 in the boiler water 13 reaches a required value, the injection pump 33 is operated for that time and then stopped.

[0023] When the boiler is operated, the level of boiler water 13 inside the boiler body 11 drops due to the generation of steam, so the feedwater pump 17 is operated to replenish the boiler water 13. The operation and stopping of this feedwater pump 17 is performed intermittently by the control device 24 as shown in Figure 2. The intermittent operation time of this feedwater pump 17 varies for each operation depending on how the level of boiler water 13 inside the boiler body 11 drops. In the example of Figure 2, the first operation time is TA, the second operation time is TB, and the third operation time is TC.

[0024] When the water supply pump 17 is operated to replenish the boiler water 13 inside the boiler body 11, the injection pump 33 is simultaneously operated to inject boiler compound 32 into the boiler water 13 supplied to the boiler body 11. The details are as follows.

[0025] That is, the control device 24 sets upper and lower limits for the operating time for injecting boiler compound 32 into boiler water 13, i.e., the operating time of injection pump 33. When the sensor 23 detects the electrical conductivity of boiler water 13, i.e., the detected value of the boiler compound 32 concentration in boiler water 13, within the normal range, the injection pump 32 is operated for a fixed time set between the upper and lower limits. Specifically, as shown in FIG. 2, during the second operation of the feedwater pump 17, the injection pump 33 is simultaneously operated for TA×K, which is calculated by multiplying the first operation time TA of the feedwater pump 17 by a coefficient K. K can be set appropriately depending on the condition of the feedwater and the management status of the boiler water 13, and can be set, for example, in the range of 0.2 to 1.5. Then, the upper limit of the operation time of injection pump 33 is TA×1.5, and the lower limit of the operation time is TA×0.2. A fixed value is set as the value of K under normal conditions so that the operation time remains constant within this range. That is, K has an appropriate value between the upper limit of 1.5 and the lower limit of 0.2.

[0026] Similarly, when the feedwater pump 17 is operated for the third time, the injection pump 33 is simultaneously operated for a time TB×K, which is the time TB obtained by multiplying the second operation time of the feedwater pump 17 by the coefficient K. The value of K at this time is the same as that during the second operation. In this way, by operating the injection pump 33 during the next operation of the feedwater pump 17 in accordance with the previous operation time of the feedwater pump 17, it is possible to inject an appropriate amount of boiler compound 32 that is compatible with the previous operation time of the feedwater pump 17. In this way, the electrical conductivity of the boiler water 13 inside the boiler body 11, i.e., the concentration of the boiler compound 32, can be maintained in a stable state.

[0027] Based on the values ​​of the three coefficients described above, the shortest operation time of the injection pump 33 when the detected boiler water 13 has a high electrical conductivity and a high concentration of boiler compound 32 in the boiler water 13, as shown in FIG. 2, is TA × 0.2. The reason for providing a lower limit is that if the injection time, i.e., the operation time of the injection pump 33, is shortened below the lower limit, the concentration of boiler compound 32 in the boiler water 13 inside the boiler body 11 may fluctuate significantly. If no problem occurs, the shortest operation time of the injection pump 33 can be controlled to TA × 0, i.e., no injection is performed. Furthermore, based on the value of K described above, the longest operation time of the injection pump 33 when the detected boiler water 13 has a low electrical conductivity and a low concentration of boiler compound 32 in the boiler water 13, as shown in FIG. 2, is TA × 1.5. The reason for providing an upper limit is that if the injection time exceeds the upper limit and becomes longer, the injection operation of boiler compound 32 related to the previous intermittent operation may continue during the next intermittent operation of the feedwater pump 17, making control difficult. As long as such problems do not arise, the upper limit can be set to a value exceeding 1.5.

[0028] If the concentration of boiler compound 32 in boiler water 13 becomes extremely low and a corresponding low electrical conductivity of boiler water 13 is detected, and in that case a long operation time exceeding the upper limit is required, the operation time of injection pump 33 is limited to 1.5 times the previous operation time of feedwater pump 17, and this length is set as the upper limit of the operation time of injection pump 33. In this case, the operation time of injection pump 33 does not reach the required time and the concentration of boiler compound 32 does not increase sufficiently, so injection operation will be performed at the upper limit for the required number of times from the next time onwards. Then, by repeating such injection operation, the concentration of boiler compound 32 will eventually increase sufficiently and the required operation time of the injection pump will fall below the upper limit, and thereafter control will be performed at the normal time between the above-mentioned upper and lower limits.

[0029] Conversely, if the concentration of boiler compound 32 in the boiler water 13 becomes extremely high and a correspondingly high electrical conductivity is detected, and in that case a short operation time below the lower limit is sufficient, the operation time of the injection pump 33 is shortened only to 0.2 times the previous operation time of the feedwater pump 17, and this length is set as the lower limit of the operation time of the injection pump 33. In this case, the operation time exceeds the required time, and the concentration of the boiler compound 32 does not decrease sufficiently, so the injection pump 33 is operated at the lower limit for the required number of times from the next time onwards. Then, by repeating such an operation, the concentration of the boiler compound 32 eventually decreases to the required level, and the required operation time of the injection pump becomes equal to or exceeds the lower limit, and thereafter, control is performed at the normal time between the above-mentioned upper and lower limits.

[0030] FIG. 3 is a graph illustrating the method for stabilizing boiler water quality from a different perspective than the time axis chart of FIG. 2. This graph plots the electrical conductivity of boiler water 13 detected by sensor 23 on the horizontal axis and the ratio of the water supply time to the boiler compound 32 injection time (i.e., the ratio of the feedwater pump 17 operation time to the injection pump 33 operation time) on the vertical axis. The unit of electrical conductivity is mS / m, or millisiemens per meter. Here, the set value is 300 mS / m, and the allowable or normal range is a range of ±20 percent from this set value, i.e., 240 mS / m to 360 mS / m. The boiler compound 32 concentration is controlled within this range. The value of K is set so that the ratio of the water supply time to the boiler compound 32 injection time is 100%. In other words, K = 1.0. If the value of K can be set to 0, as described above, the amount of boiler compound 32 injected can also be reduced to 0.

[0031] An electrical conductivity of 360 mS / m is set as the upper limit of the detectable concentration of boiler compound 32, and when the detected concentration exceeds this limit, the value of K is set to 0.2. This reduces the operating time of injection pump 33, thereby reducing the amount of boiler compound 32 injected. Also, an electrical conductivity of 240 mS / m is set as the lower limit of the detectable concentration, and when the detected concentration falls below this limit, the value of K is set to 1.5. This increases the operating time of injection pump 33, thereby increasing the amount of boiler compound 32 injected.

[0032] In the above example, during normal operation, the value of K is controlled by setting it to a constant value between the upper and lower limits. However, instead of keeping the value of K constant between the upper and lower limits, the value of K can be varied between the upper and lower limits depending on the detected electrical conductivity. In this case, the graph in Figure 3 will change from the current stepped curve to a curve that slopes downward from the ratio of water supply time to boiler compound injection time at the lower limit of electrical conductivity (240 mS / m) to the ratio of water supply time to boiler compound injection time at the upper limit of electrical conductivity (360 mS / m).

[0033] Since the boiler is in a state where evaporation and water supply are repeated, as the boiler operation time passes, impurities such as sludge accumulate inside the boiler body 11, and the concentration of the boiler water 13 increases. This can cause carryover, in which a large amount of boiler water 13 is mixed into the generated steam 14, corrosion occurs in various parts of the boiler body 11, and scale accumulates on the wall surface of the boiler body 11, causing overheating on the heat transfer surface. In particular, if the corrosion or overheating progresses beyond a certain level, an accident such as the boiler body bursting may occur.

[0034] Therefore, when the feed water pump 17 is operated to replenish the boiler water 13 inside the boiler body 11, it is extremely preferable to simultaneously discharge, i.e., blow out, the boiler water 13, which has become highly concentrated, through the blow pipe 21, thereby reducing the concentration of the boiler water 13 inside the boiler body 11.

[0035] According to the present invention, if the boiler compound 32 is also injected at that time as described above, the concentration of the boiler compound 32 in the boiler water 13, i.e., the quality of the boiler water 13, can be further stabilized.

[0036] An example of control for discharging the boiler water 13, which has become highly concentrated, through the blow pipe 21 while operating the feed water pump 17 to replenish the boiler water 13 inside the boiler body 11, is as follows. That is, the control of this blow operation can be carried out in the same manner as the control for injecting boiler compound 32 into the boiler water 13. The concentration of the boiler water 13 can be known from the electrical conductivity of the boiler water 13, just like the concentration of the boiler compound 32. That is, the electrical conductivity of the boiler water 13 contains both information on the concentration of the boiler compound 32 and information on the concentration of the boiler water 13.

[0037] That is, the control device 24 sets upper and lower limits for the blowing operation time, and when the electrical conductivity detected by the sensor 23 is within the normal range, the blowing operation is performed for a fixed time set between the upper and lower limits. Specifically, as shown in FIG. 4, during the second operation of the feedwater pump 17, similar to the above, the blowing operation is simultaneously performed for a time TA × C, which is the first operation time TA of the feedwater pump 17 multiplied by a coefficient C. C can be set appropriately depending on the state of the feedwater and the management state of the boiler water 13. For example, as with the coefficient K, it can be set in the range of 0.2 to 1.5. Then, the upper limit of the blowing operation time is TA × 1.5, and the lower limit of the blowing operation time is TA × 0.2. The value of C for normal operation is set so that the blowing operation time is constant within this range. That is, C can have an appropriate value between the upper limit of 1.5 and the lower limit of 0.2.

[0038] Similarly, when the feedwater pump 17 is operated for the third time, a blowing operation is simultaneously performed for a time TB×C, which is the time obtained by multiplying the second operation time TB of the feedwater pump 17 by a coefficient C. The value of C at this time is the same as that during the second operation. In this way, by performing the blowing operation during the next operation of the feedwater pump 17 in accordance with the previous operation time of the feedwater pump 17, the blowing operation can be performed for an appropriate time that matches the previous operation time of the feedwater pump 17. In addition, since the blowing operation is performed simultaneously with the operation of the feedwater pump 17, the amount of boiler water 13 discharged by the blowing operation can be appropriately replenished. In this way, the electrical conductivity of the boiler water 13 inside the boiler body 11, i.e., its concentration, can be maintained in a stable state.

[0039] Based on the values ​​of the three coefficients described above, the minimum blowing time in Figure 4 is TA x 0.2. The reason for setting a lower limit is that if the blowing time is shortened below the lower limit, the concentration of boiler water 13 inside the boiler body 11 may fluctuate significantly. If no problem occurs, the minimum blowing time can be set to TA x 0, i.e., no blowing operation can be performed. Also, in Figure 4, the maximum blowing time is TA x 1.5. The reason for setting an upper limit is that if the blowing time is extended beyond the upper limit, the blowing operation related to the previous intermittent operation may continue during the next intermittent operation of the feedwater pump 17, making control difficult. The upper limit for C can be set above 1.5, provided such problems do not arise.

[0040] Even when the concentration of boiler water 13 inside the boiler body 11 becomes extremely high and a correspondingly high electrical conductivity is detected, requiring a long blowing operation time exceeding the upper limit, the blowing operation time is limited to 1.5 times the previous operating time of the feedwater pump 17, and this length is set as the upper limit of the blowing operation time. In this case, the required blowing operation time does not reach the required time and the concentration of boiler water 13 does not decrease sufficiently, so the blowing operation is performed at the upper limit for the required number of times from the next time onwards. By repeating such an operation, the concentration of boiler water 13 eventually decreases sufficiently and the required blowing operation time falls below the upper limit, and thereafter the operation is controlled to a normal time between the above-mentioned upper and lower limits.

[0041] Conversely, even if the concentration of boiler water 13 inside the boiler body 11 becomes extremely low and a correspondingly low electrical conductivity is detected, and a short blowing operation time below the lower limit is sufficient in that case, the blowing operation time is shortened only to 0.2 times the previous operating time of the feedwater pump 17, and this length is set as the lower limit of the blowing operation time. In this case, the blowing operation time exceeds the required time, and the concentration of boiler water 13 does not increase sufficiently, so the blowing operation is performed at the lower limit for the required number of times from the next time onwards. By repeating such operations, the concentration of boiler water 13 eventually increases to the required level, and the required blowing operation time becomes equal to or exceeds the lower limit, and thereafter, control is performed at the normal time between the above-mentioned upper and lower limits.

[0042] The control of the blowing operation time is not limited to the above example, and may be any time as long as the concentration of the boiler compound 32 in the boiler water 13 can be appropriately controlled based on the present invention.

[0043] As described above, boiler water 13 circulates through the boiler body 11 and the steam-water separator 18 and downcomer pipe 19. In this case, when the boiler is operating under low load conditions, the amount of boiler water 13 circulated decreases, which may result in a decrease in the accuracy of detecting the boiler water 13 concentration, i.e., the electrical conductivity. For this reason, when the boiler continues to operate under low load conditions, a blowing operation is performed for a certain period of time after a predetermined time has elapsed or when the feedwater pump has performed intermittent operation a predetermined number of times or more. This increases the amount of boiler water 13 circulated, allowing boiler water 13 with a concentration similar to that of the boiler water 13 inside the boiler body 11 to reach the installation position of the electrical conductivity sensor 23. This allows the electrical conductivity to be detected accurately.

[0044] Regarding the circulation of boiler water 13 described above, when the boiler is operated at a low load, the evaporation state is relatively gentle, and therefore the amount of boiler water that splashes up inside the boiler body 11 due to evaporation is small, which can reduce the degree of circulation of boiler water 13. As a countermeasure, when the boiler is operated at a low load, the boiler combustion rate is increased under certain conditions to activate the evaporation state and increase the amount of boiler water that splashes up inside the boiler body 11, thereby promoting the circulation of boiler water 13, making it possible to accurately detect the concentration of boiler water 13. For example, if the low-load operation state continues for about 30 minutes to 1 hour, increasing the boiler combustion rate to generate boiling water for about 10 to 20 seconds can cause the boiler water 13 to splash inside the boiler body 11, thereby circulating the boiler water 13 well. Alternatively, if the feedwater pump 17 is operated intermittently about 20 times during a sustained low-load operation, the boiler water 13 can be circulated satisfactorily by similarly increasing the boiler combustion utilization and generating boiled water for about 10 to 20 seconds.

[0045] In the above, the blow rate is changed by changing the blow operation time. However, instead of or in addition to this, the valve provided in the blow pipe 21 can be an opening adjustment valve instead of the on-off valve 22 described above, and the blow rate can be changed by controlling the opening of the valve. [Explanation of symbols]

[0046] 17 Water supply pump 18 Steam water separator 19 Downpipe 23 Electrical conductivity sensor 24 Control device 31 Boiler compound supply line 32 Boiler Compound 33 Infusion Pump

Claims

1. A feed water pump for supplying boiler water to a boiler body of a boiler is intermittently operated, and boiler compound is injected into the boiler water every time the feed water pump is intermittently operated, A method for stabilizing boiler water quality, comprising: detecting the electrical conductivity of boiler water; setting upper and lower limit values ​​for operation time when injecting boiler compound into boiler water in accordance with the detected electrical conductivity; and, when the detected electrical conductivity is a normal electrical conductivity between the electrical conductivity corresponding to the upper limit value of said operation time and the electrical conductivity corresponding to the lower limit value of said operation time, setting a fixed value between the upper and lower limit values ​​of said operation time as the operation time for injecting boiler compound into boiler water.

2. A method for stabilizing the water quality of boiler water in a boiler as described in claim 1, characterized in that the operating time is set to the upper limit value when the detected electrical conductivity falls below the electrical conductivity corresponding to the upper limit value of the operating time, and the operating time is set to the lower limit value when the measured electrical conductivity exceeds the electrical conductivity corresponding to the lower limit value of the operating time.

3. A method for stabilizing the water quality of boiler water in a boiler described in claim 1 or 2, characterized in that a blowing operation is performed to discharge the boiler water outside the boiler body each time the feed water pump is operated intermittently.

4. A method for stabilizing the water quality of boiler water in a boiler described in claim 1 or 2, characterized in that when the boiler water in the boiler body is replaced, boiler compound is injected into the boiler water simultaneously with the operation of the feed water pump, and the operation of injecting boiler compound into the boiler water in the boiler body continues even after the boiler water in the boiler body reaches a predetermined water level and the feed water pump stops.

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