JP7795767B2 - Methods for stabilizing boiler water quality - Google Patents

Description

The present invention relates to a method for stabilizing the quality of boiler water.

The steam generated by boiler water evaporation, including boiler water, is mixed with the boiler water. This steam mixed with boiler water, i.e., a 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 pipe connecting the steam-water separator to the boiler body. While the boiler is operating, these operations are performed continuously, circulating the boiler water and maintaining a stable, constant 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.

Japanese Patent Application Laid-Open No. 2021-74679

However, because boilers are constantly repeating evaporation and water supply cycles, impurities such as sludge can accumulate inside the boiler, and the boiler water can become more concentrated. This can lead to carryover, where a large amount of boiler water is mixed into the generated steam, corrosion can occur in various parts of the boiler body, and scale can build up on the boiler walls, causing overheating on the heat transfer surfaces. In particular, if corrosion or overheating progresses beyond a certain level, accidents such as the boiler body bursting can occur.

The present invention aims to prevent such inconveniences from occurring by stabilizing the quality of boiler water.

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,
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,
The device is characterized in that when the detected electrical conductivity exceeds the electrical conductivity corresponding to the upper limit value of the blowing operation time, the blowing operation time is set to the upper limit value, and when the measured electrical conductivity falls below the electrical conductivity corresponding to the lower limit value of the blowing operation time, the blowing operation time is set to the lower limit value .

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

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

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 is operated intermittently, and when the feed water pump is operated intermittently, a blowing operation for discharging the boiler water outside the boiler is performed. Therefore, a part of the boiler water can be continuously and reliably replaced with new feed water. As a result, the quality of the boiler water can be stabilized, and inconveniences such as those that would occur if the quality could not be stabilized can be prevented.

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; FIG. 2 is a diagram showing an example of an operation sequence of the boiler of FIG. 1 . FIG. 2 is a diagram illustrating an example of control of the blow rate in the boiler of FIG. 1.

The principle behind the method of stabilizing boiler water quality in this invention is to stabilize the boiler water concentration, i.e., its quality, by discharging boiler water in small amounts from the boiler each time the feedwater pump that supplies boiler water to the boiler is operated intermittently.

Figure 1 shows the structure of a boiler for carrying out the method of the present invention. Reference numeral 11 denotes the 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 from the burner. Reference numeral 16 denotes an economizer, which is connected to the exhaust gas line 15 and water supply line 12 to recover 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.

The 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 taken into the steam-water separator 18. The steam-water separator 18 separates the steam 14 from the boiler water 13 by gravity or other means, and the separated steam 14 is extracted from the top 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.

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 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, i.e., 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.

The downcomer pipe 19 is equipped with an electrical conductivity sensor 23 for detecting the electrical conductivity of the boiler water 13 inside the downcomer pipe 19. Because the electrical conductivity of boiler water 13 increases as it becomes concentrated, detecting electrical conductivity is intended to detect the degree of concentration. The electrical conductivity sensor 23 can be installed anywhere in the illustrated boiler where the boiler water 13 is present. However, because the boiler water 13 inside the boiler body 11 is boiling 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. Therefore, the boiler water 13 inside the downcomer pipe 19 is not boiling but is stable. 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 high electrical conductivity from being overlooked due to failure to detect it, the electrical conductivity sensor 23 is installed in the downcomer pipe 19 in a portion of the boiler water 13 where the electrical conductivity is high, i.e., in the middle of the downcomer pipe 19 along the height direction as shown. The blow pipe 21 is connected to this downcomer pipe 19 at a position corresponding to the position where the electrical conductivity sensor 23 is installed in the downcomer pipe 19.

Reference numeral 24 denotes a control device that controls the operation and stop of the water supply pump 17 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.

25 is a water level gauge that is connected to the boiler body 11 to detect the level of boiler water 13 inside the boiler body 11. 26 is a full blow-off pipe that is used to drain all of the boiler water 13 inside the boiler body 11 for maintenance or other purposes by opening a valve 27 provided on this full blow-off pipe 26.

When the illustrated boiler is operated in this configuration, the boiler water 13 level 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 Figure 2. The intermittent operation time of the feedwater pump 17 varies for each operation depending on how the boiler water 13 level 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.

In the present invention, when the water supply pump 17 is operated to replenish boiler water 13 inside the boiler body 11, the concentrated boiler water 13 is simultaneously discharged through the blow-off pipe 21, thereby reducing the concentration, i.e., the electrical conductivity, of the boiler water 13 inside the boiler body 11. The details are as follows:

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 Figure 2, during the second operation of the feedwater pump 17, the blowing operation is simultaneously performed for TA x 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 condition of the feedwater and the management status of the boiler water 13, for example, in the range of 0.2 to 1.5 (20 to 150%). In this case, the upper limit of the blowing operation time is TA x 1.5, and the lower limit of the blowing operation time is TA x 0.2. A fixed value is set as the value of C under normal conditions so that the blowing operation time remains constant within this range. In other words, C has an appropriate value between the upper limit of 1.5 and the lower limit of 0.2.

Similarly, when the feedwater pump 17 is operated for the third time, a blowing operation is simultaneously performed for TB x C, which is the time TB obtained by multiplying the second operation time of the feedwater pump 17 by a coefficient C. The value of C at this time is the same as 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 period of time that matches the previous operation time of the feedwater pump 17. In addition, because 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.

Based on the three coefficient values (upper limit, lower limit, and C) described above, the minimum blowing time in Figure 2 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 the boiler water 13 inside the boiler body 11 may fluctuate significantly. If no problems arise, the minimum blowing time can be set to TA x 0, i.e., no blowing operation is performed. Also, in Figure 2, 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. As long as such problems do not arise, the upper limit can be set above 1.5.

Even if the concentration of boiler water 13 inside the boiler body 11 becomes extremely high and a correspondingly high electrical conductivity is detected, requiring a longer 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 for the blowing operation time. If this occurs, the required blowing operation time will not be reached and the concentration of the boiler water 13 will not be sufficiently reduced, so the blowing operation will be performed at the upper limit for the required number of times from the next time onwards. By repeating this operation, the concentration of the boiler water 13 will eventually be sufficiently reduced, and the required blowing operation time will fall below the upper limit, and thereafter the operation will be controlled at the normal time between the upper and lower limits described above.

Conversely, 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, the blowing operation time is only shortened 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 will be performed at the lower limit for the required number of times from the next time onwards. By repeating this operation, the concentration of the boiler water 13 will eventually increase to the required level, and the required blowing operation time will exceed the lower limit, and thereafter the operation will be controlled at the normal time between the upper and lower limits described above.

Figure 3 is a graph illustrating the method of stabilizing boiler water quality of the present invention from a different perspective than the time axis chart of Figure 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 blow operation time on the vertical axis. The unit of electrical conductivity is mS/m, or millisiemens per meter. Here, 300 mS/m is set as the set value, and the allowable or normal range is a range of ±20% from this set value, i.e., 240 mS/m to 360 mS/m, within which the concentration of boiler water 13 is controlled. In the example of Figure 3, the value of C described above is set so that the ratio of water supply time to blow operation time is 100%. In other words, C = 1.0.

An electrical conductivity of 360 mS/m is set as the upper limit for detected concentrations, and even if the detected 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 for detected concentrations, and even if the detected concentration falls below this, the coefficient is set to 0.2 (20%). This shortens the blowing operation time and decreases the blowing rate. Furthermore, if the lower limit can be set to 0 as described above, the blowing rate can also be kept at 0% by doing so.

As described above, boiler water 13 circulates between 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 boiler water 13 concentration, i.e., 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 passed or when the feedwater pump has operated intermittently 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 location of the electrical conductivity sensor 23. This allows electrical conductivity to be detected accurately.

Regarding the circulation of boiler water 13 described above, when the boiler is operated at low load, evaporation is relatively gentle, resulting in a small amount of boiler water splashing up inside the boiler body 11 due to evaporation. This can result in a reduced degree of boiler water 13 circulation. As a countermeasure, increasing the boiler combustion rate under certain conditions when the boiler is operated at low load stimulates evaporation and increases the amount of boiler water splashing up inside the boiler body 11, thereby promoting the circulation of boiler water 13, enabling accurate concentration detection. For example, if low-load operation continues for approximately 30 minutes to 1 hour, increasing the boiler combustion rate to generate boiling water for approximately 10 to 20 seconds can cause the boiler water 13 to splash up inside the boiler body 11, thereby ensuring good circulation of the boiler water 13. Alternatively, if the feedwater pump 17 is operated intermittently approximately 20 times during sustained low-load operation, similarly increasing the boiler combustion rate to generate boiling water for approximately 10 to 20 seconds can ensure good circulation of the boiler water 13.

In the above example, during normal operation, the value of C was controlled by setting it to a constant value between the upper and lower limits. 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, instead of the current stepped curve, the graph in Figure 3 will change upward to the right, from the ratio of water supply time to blow-out time at the lower limit of electrical conductivity (240 mS/m) (20%) to the ratio of water supply time to blow-out time at the upper limit of electrical conductivity (360 mS/m) (150%).

In the above example, the blow rate was changed by varying the blow operation time. However, instead of, or in addition to, the valve installed 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 its opening.

17 Feedwater pump 18 Steam-water separator 19 Downstream pipe 21 Blow pipe 22 Opening/closing valve 23 Electrical conductivity sensor 24 Control device

Claims (3)

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. 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. 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.