Methods for stabilizing boiler water quality

Abstract

To stabilize the water quality of boiler water in a boiler, thereby preventing the generation of carry-over in which a large amount of boiler water is mixed into generated stream, corrosion of each part of a can body, and an overheat state of a heat transfer surface due to the adhesion of scale to a can wall surface.SOLUTION: A method of stabilizing the water quality of boiler water in a boiler is provided. A water supply pump for supplying the boiler water to the boiler is intermittently operated. Whenever the water supply pump is intermittently operated, blow operation for discharging the boiler water to the outside of a can 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] However, because the boiler is in a state where evaporation and water supply are repeated, impurities such as sludge accumulate inside the boiler, and the boiler water becomes more concentrated. This can lead to carryover, in which a large amount of boiler water is mixed into the generated steam, corrosion occurs in various parts of the boiler body, and scale accumulates on the boiler wall, causing overheating on the heat transfer surface. In particular, if corrosion or overheating progresses beyond a certain level, accidents such as the boiler body bursting may occur.

[0005] Therefore, an object of the present invention is to prevent such inconveniences from occurring by stabilizing the quality of boiler water. [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: The feedwater pump for supplying boiler water to the boiler body is operated intermittently, The water supply pump is operated intermittently. During operation, a blowing operation is performed to discharge boiler water from the steam separator, which separates the steam and boiler water contained in the steam-water mixture fluid supplied to the outside from the boiler, Set upper and lower limits for the blowing operation time, Detects the electrical conductivity of boiler water in the steam separator, When the detected electrical conductivity is a normal electrical conductivity between the electrical conductivity corresponding to the upper limit value of the time of the blowing operation and the electrical conductivity corresponding to the lower limit value of the time of the blowing operation, the blowing operation is performed for a time between the upper limit value and the lower limit value of the time of the blowing operation, When the detected electrical conductivity exceeds an electrical conductivity corresponding to an upper limit value of the time for the blowing operation, the time for the blowing operation is set to the upper limit value, and when the measured electrical conductivity falls below an electrical conductivity corresponding to a lower limit value of the time for the blowing operation, the time for the blowing operation is set to the lower limit value. It is characterized by:

[0010] According to the method for stabilizing the boiler water quality of the present invention, when the boiler has been operated at a low load for a certain period of time or more, it is preferable to perform a blowing operation for a predetermined period of time so that the electrical conductivity of the boiler water, the electrical conductivity of which is detected in the steam-water separator, corresponds to the electrical conductivity of the boiler water in the boiler.

[0011] According to the method for stabilizing the boiler water quality of the present invention, when the boiler has been operated at a low load for a certain period of time or more, it is preferable to temporarily put the boiler into a high combustion state, thereby increasing the amount of evaporation and the amount of the steam-water mixture flowing into the steam-water separator. [Effects of the Invention]

[0012] According to the method for stabilizing the quality of boiler water of the present invention, a feed water pump for supplying boiler water to the boiler is intermittently operated, and the feed water pump is intermittently operated. When driving Since a blowing operation is performed to discharge the boiler water outside the boiler, a portion of the boiler water can be continuously and reliably replaced with new feed water, which makes it possible to stabilize the water quality of the boiler water in the boiler and prevent the occurrence of inconveniences such as when the water quality cannot be stabilized. [Brief explanation of the drawings]

[0013] [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 blow rate in the boiler of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] The principle of the method for stabilizing the boiler water quality of a boiler according to the present invention is to stabilize the concentration of the boiler water, i.e., its quality, by discharging the boiler water in small amounts from the boiler every time a feed water pump for supplying boiler water to the boiler is intermittently operated.

[0015] 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 water supply, i.e., boiler water 13, thereby improving thermal efficiency. A water supply pump 17 is provided in the water supply line 12.

[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. As the boiler water 13 becomes concentrated, its electrical conductivity increases, so detecting the electrical conductivity is intended to detect the degree of concentration. The electrical conductivity sensor 23 can be installed at any location where the boiler water 13 is present in the illustrated boiler. However, because the boiler water 13 inside the boiler body 11 is in a boiling state and moving vigorously, it is difficult to measure its stable concentration. In contrast, because the downcomer pipe 19 is installed outside the boiler body 11, it is cooled by outside air, and therefore the boiler water 13 inside the downcomer pipe 19 is not in a boiling state but is in a stable state. Therefore, by installing 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, electrical conductivity sensor 23 is provided in a portion of downcomer pipe 19 where the boiler water 13 has a high electrical conductivity, i.e., in the middle of downcomer pipe 19 along the height direction as shown in the figure. Then, blow pipe 21 is connected to downcomer pipe 19 at a position corresponding to the position where electrical conductivity sensor 23 is provided in downcomer pipe 19.

[0019] A control device 24 controls the operation and stop of the water supply pump 17 and also controls the opening and closing state of the opening and closing 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 illustrated 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 feedwater pump 17 is operated and stopped intermittently by the control device 24 as shown in FIG. 2. The intermittent operation time of the feedwater pump 17 varies for each operation depending on how the level of boiler water 13 drops inside the boiler body 11. In the example of FIG. 2, the first operation time is TA, the second operation time is TB, and the third operation time is TC.

[0022] In the present invention, when the water supply pump 17 is operated to replenish boiler water 13 inside the boiler body 11, the boiler water 13 with a high concentration is simultaneously discharged through the blow pipe 21, thereby lowering the concentration, i.e., the electrical conductivity, of the boiler water 13 inside the boiler body 11. The details are as follows.

[0023] 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, i.e., the detected value of the boiler water 13 concentration, 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. 2, during the second operation of the feedwater pump 17, 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 appropriately set depending on the state of the feedwater and the management state of the boiler water 13, for example, in the range of 0.2 to 1.5 (20 to 150%). 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. A fixed value is set as the value of C for normal operation so that the blowing operation time is constant within this range. That is, C has an appropriate value between the upper limit of 1.5 and the lower limit of 0.2.

[0024] 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, i.e., the concentration, of the boiler water 13 inside the boiler body 11 can be maintained in a stable state.

[0025] Based on the values ​​of the three coefficients, the upper limit, lower limit, and C, as shown in Figure 2, the shortest time for the blowing operation is TA x 0.2. The reason for setting a lower limit is that if the blowing operation 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 shortest time for the blowing operation can be set to TA x 0, i.e., no blowing operation can be performed. Also, in Figure 2, the longest time for the blowing operation is TA x 1.5. The reason for setting an upper limit is that if the blowing operation 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 can also be set above 1.5, provided such problems do not arise.

[0026] 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 the 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 the boiler water 13 eventually decreases sufficiently and the required blowing operation time becomes equal to or less than the upper limit, and thereafter the operation is controlled at the normal time between the above-mentioned upper and lower limits.

[0027] 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 the 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. Then, by repeating such operations, the concentration of the 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.

[0028] FIG. 3 is a graph illustrating a method for stabilizing boiler water quality in a boiler according to the present invention 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 water supply time to blowing 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., from 240 mS / m to 360 mS / m, within which the concentration of boiler water 13 is controlled. In the example of FIG. 3, the value of C is set so that the ratio of water supply time to blowing operation time is 100%. That is, C=1.0.

[0029] An electrical conductivity of 360 mS / m is set as the upper limit of the detection concentration, and even if the detection concentration exceeds this, the coefficient is set to 1.5 (150%). This lengthens the blowing operation time and increases the blowing rate. Also, an electrical conductivity of 240 mS / m is set as the lower limit of the detection concentration, and even if the detection concentration falls below this, the coefficient is set to 0.2 (20%). This shortens the blowing operation time and decreases the blowing rate. Note that if the lower limit can be set to 0 as above, doing so will also keep the blowing rate at 0%.

[0030] As described above, boiler water 13 circulates through the inside of the boiler body 11 and the inside of the steam 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 concentration of boiler water 13, 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.

[0031] Regarding the circulation of boiler water 13 described above, when the boiler is operated at a low load, evaporation is relatively gentle, and therefore the amount of boiler water that splashes up inside 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, increasing the boiler combustion rate under certain conditions activates evaporation and increases the amount of boiler water that splashes up inside boiler body 11, thereby promoting the circulation of boiler water 13, thereby enabling accurate concentration detection. For example, if the low-load operation continues for about 30 minutes to 1 hour, increasing the boiler combustion rate to generate boiled water for about 10 to 20 seconds can cause boiler water 13 to splash inside boiler body 11, thereby ensuring good circulation of boiler water 13. Alternatively, if the feedwater pump 17 is operated intermittently about 20 times while the low-load operation continues, similarly increasing the boiler combustion rate to generate boiled water for about 10 to 20 seconds can ensure good circulation of boiler water 13.

[0032] In the above, the value of C was controlled by setting it to a constant value between the upper and lower limits during normal operation. However, instead of keeping the value of C constant between the upper and lower limits, the value of C can be varied between the upper and lower limits depending on the detected level of electrical conductivity. In this case, the graph in Figure 3 will change from the current stepped curve to a curve that slopes upward from the ratio of water supply time to blow-out time (20%) at the lower limit of electrical conductivity (240 mS / m) to the ratio of water supply time to blow-out time (150%) at the upper limit of electrical conductivity (360 mS / m).

[0033] 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]

[0034] 17 Water supply pump 18 Steam water separator 19 Downpipe 21 Blow piping 22 On-off valve 23 Electrical conductivity sensor 24 Control device

Claims

1. The feedwater pump for supplying boiler water to the boiler body is operated intermittently, When the feedwater pump is intermittently operated, a blowing operation is performed to discharge boiler water from a steam-water separator, which separates the steam and boiler water contained in the steam-water mixture fluid supplied from the boiler to the outside, to the outside of the boiler; Set upper and lower limits for the blowing operation time, Detects the electrical conductivity of boiler water in the steam separator, When the detected electrical conductivity is a normal electrical conductivity between the electrical conductivity corresponding to the upper limit value of the time of the blowing operation and the electrical conductivity corresponding to the lower limit value of the time of the blowing operation, the blowing operation is performed for a time between the upper limit value and the lower limit value of the time of the blowing operation, A method for stabilizing boiler water quality, characterized in that when the detected electrical conductivity exceeds an electrical conductivity corresponding to an upper limit value for the duration of the blowing operation, the duration of the blowing operation is set to the upper limit value, and when the measured electrical conductivity falls below an electrical conductivity corresponding to a lower limit value for the duration of the blowing operation, the duration of the blowing operation is set to the lower limit value.

2. 2. The method for stabilizing the quality of boiler water according to claim 1, wherein, when the boiler has been operated at a low load for a certain period of time or more, a blowing operation is carried out for a predetermined period of time so that the electrical conductivity of the boiler water, the electrical conductivity of which is detected in the steam-water separator, corresponds to the electrical conductivity of the boiler water in the boiler.

3. 3. A method for stabilizing the quality of boiler water according to claim 1, wherein when the boiler has been operated at a low load for a certain period of time or more, the boiler is temporarily put into a high combustion state to increase the amount of evaporation and the amount of steam-water mixture flowing into the steam-water separator.

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