JP2023085588A - Method of stabilizing water quality of boiler water in boiler - Google Patents

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

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

The steam generated by evaporating boiler water in the boiler contains boiler water, and the steam mixed with boiler water, that is, the steam-water mixed fluid flows into the steam separator, where it is separated from the steam. Steam is separated from boiled water. The separated boiler water flows into the bottom of the boiler body through a downcomer pipe that connects the steam separator and the boiler body. During operation of the boiler, these operations are continuously performed to circulate the boiler water, and the quality of the water inside the boiler is stabilized (Patent Document 1). A water supply pump for supplying water to the boiler body is operated to replenish boiler water that has been reduced by evaporation.

JP 2021-74679 A

However, since the boiler is in a state of repeating evaporation and feed water, impurities such as sludge accumulate in the boiler, and the concentration of the boiler water increases. As a result, a large amount of boiler water is mixed into the generated steam, resulting in carry-over, corrosion in various parts of the boiler body, and overheating of the heat transfer surface due to scale build-up on the boiler wall surface. In particular, if the occurrence of corrosion or the occurrence of overheating progresses beyond a certain level, accidents such as bursting of the can body may occur.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to stabilize the quality of boiler boiler water so as to prevent such inconveniences from occurring.

In order to achieve this object, the method for stabilizing the water quality of the boiler boiler according to the present invention comprises intermittently operating a water supply pump for supplying boiler water to the boiler body, and intermittently operating the water supply pump. It is characterized by performing a blowing operation for discharging boiled water to the outside of the boiler each time it is operated.

According to the method for stabilizing the water quality of boiler boiler water of the present invention, the boiler water of the steam separator for separating the steam contained in the steam-water mixed fluid supplied from the boiler to the outside is separated from the boiler water. It is preferred to discharge out of the can.

According to the method for stabilizing the water quality of the boiler boiler of the present invention, the electrical conductivity of the boiler water in the steam separator is detected, and depending on the level of the detected electrical conductivity, the time of the blowing operation is adjusted. An upper limit value and a lower limit value are set, and the detected electrical conductivity is between the electrical conductivity corresponding to the upper limit value of the blowing operation time and the electrical conductivity corresponding to the lower limit value of the blowing operation time. When the electric conductivity is normal, it is preferable to perform the blowing operation for a constant time between the upper limit and the lower limit of the blowing time.

According to the method for stabilizing the water quality of boiler boiler water of the present invention, when the measured electrical conductivity exceeds the electrical conductivity corresponding to the upper limit of the blowing operation time, the upper limit of the blowing operation time and set the blowing time to the lower limit when the measured electrical conductivity falls below the electrical conductivity corresponding to the lower limit of the blowing time.

According to the method for stabilizing the water quality of boiler boiler water of the present invention, the electric conductivity in the steam separator is detected when the boiler is operated at a low load for a certain period of time or longer. The blowing operation is preferably carried out for a predetermined period of time so that the electrical conductivity of the water corresponds to that of the boiler water in the boiler.

According to the method for stabilizing the water quality of the boiler boiler water of the present invention, when the boiler is operated at a low load for a certain period of time or more, the boiler is temporarily placed in a high combustion state to increase the amount of evaporation. It is preferable to increase the amount of the steam-water mixed fluid flowing into the steam-water separator.

According to the method for stabilizing the water quality of boiler water in a boiler of the present invention, the feed water pump for supplying boil water to the boiler is intermittently operated, and each time the feed water pump is intermittently operated, Since the blow operation is performed to discharge the , it is possible to prevent the occurrence of inconvenience such as when it cannot be stabilized.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the structure of the boiler for performing the method of stabilizing the water quality of boiler boiler of embodiment of this invention. FIG. 2 is a diagram showing an example of an operation sequence of the boiler of FIG. 1; FIG. 2 is a diagram showing an example of blow rate control in the boiler of FIG. 1;

The principle of the method for stabilizing the water quality of the boiler water of the boiler of the present invention is to discharge the boiler water to the outside of the boiler in small increments each time the water supply pump for supplying the boiler water to the boiler is intermittently operated. , to stabilize the concentration of the boiler water, that is, its water quality.

FIG. 1 shows the construction of a boiler for carrying out the method of the invention. Here, reference numeral 11 denotes a boiler, which is configured to generate steam 14 by heating boiler water 13 supplied from a water supply passage 12 by a burner (not shown). 15 is an exhaust gas passage from the burner. An economizer 16 is connected to the exhaust gas line 15 and the water supply line 12 to recover the heat energy of the exhaust gas into the feed water, that is, the boiler water 13, thereby improving the thermal efficiency. . A water supply pump 17 is provided in the water supply path 12 .

The steam 14 generated inside the boiler body 11 is taken out from the boiler body 11 in the form of a steam-water mixed fluid containing the boiler water 13 existing inside the boiler body 11, and is sent to the steam separator 18. It is captured. The steam separator 18 separates the steam 14 and boiler water 13 by the action of gravity or the like, and the separated steam 14 is taken out of the system from the upper part of the steam separator 18 and supplied to the place of use. The separated boiler water 13 accumulates in the lower part inside the steam separator 18 and is circulated to the bottom of the boiler body 11 through the downcomer pipe 19 that connects the steam separator 18 and the boiler body 11 .

A blow pipe 21 is connected to the downcomer pipe 19 . The blow pipe 21 blows the boiler water 13 accumulated inside the downcomer pipe 19 and the steam separator 18 into the boiler body 11 by the action of gravity and the pressure action of the steam 14 existing inside the boiler body 11 . , that is, for blowing the boiled water 13. The blow pipe 21 is provided with an on-off valve 22 for controlling the execution and stop of blowing.

The downcomer 19 is provided with an electrical conductivity sensor 23 for detecting the electrical conductivity of the boiler water 13 inside the downcomer 19 . When the boiler water 13 is concentrated, its electrical conductivity increases, so the degree of concentration is detected by detecting the electrical conductivity. The electrical conductivity sensor 23 can be provided at any location where the boiler water 13 exists in the illustrated boiler. However, since the can water 13 is in a boiling state inside the can body 11 and moves violently, it is difficult to measure its stable concentration. On the other hand, since the downcomer 19 is provided outside the can body 11, it is cooled by the outside air, and therefore the boiler water 13 inside the downcomer 19 is not in a boiling state but in a stable state. 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, in order to prevent the fact that the electrical conductivity is high from being overlooked without being able to detect it, the electrical conductivity sensor 23 detects a portion of the boiler water 13 in the downcomer pipe 19 where the electrical conductivity is high, that is, is provided in the middle portion of the downcomer pipe 19 along the height direction. The blow pipe 21 is communicated with the downcomer 19 in correspondence with the position of the electrical conductivity sensor 23 in the downcomer 19 .

A control device 24 controls the operation and stop of the water supply pump 17 and controls the opening/closing state of the opening/closing valve 22 in the blow pipe 21 based on the detection signal from the electrical conductivity sensor 23 .

A water level gauge 25 communicates with the can body 11 to detect the water level of the can water 13 inside the can body 11 . 26 is a full blow pipe, and by opening a valve 27 provided in this full blow pipe 26, it is used to discharge all the boil water 13 inside the can body 11 for the purpose of maintenance or the like.

In such a configuration, when the illustrated boiler is operated, the level of the boiler water 13 inside the boiler body 11 decreases due to the generation of steam, so the water supply pump 17 is operated to replenish the boiler water 13 . The operation and stoppage of the water supply pump 17 are performed intermittently by the controller 24 as shown in FIG. The intermittent operation time of the water supply pump 17 varies for each operation according to how the level of the boiler water 13 inside the boiler body 11 decreases. 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.

In the present invention, when the water supply pump 17 is operated to replenish the boiler water 13 inside the can body 11, the concentrated boiler water 13 is discharged through the blow pipe 21 at the same time. The concentration of boiled water 13 inside 11, that is, the electrical conductivity is lowered. The details are as follows.

That is, when the control device 24 sets an upper limit value and a lower limit value for the blow operation time, and the detection result of the electric conductivity by the sensor 23, that is, the detection value of the concentration of the boiled water 13 is within the normal range, the upper limit value The blow operation is performed for a certain set time set between and the lower limit. Specifically, as shown in FIG. 2, when the water supply pump 17 is operated for the second time, at the same time, the blow operation is performed for TA×C, which is the time obtained by multiplying the first operation time TA of the water supply pump 17 by the coefficient C. conduct. C can be appropriately set according to the state of water supply and the management state of boiled water 13, and can be set, for example, in the range of 0.2 to 1.5 (20 to 150%). Then, the upper limit of the blow operation time is TA×1.5, and the lower limit of the blow operation time is TA×0.2. Set a constant value to be the value. That is, C has an appropriate value between the upper limit of 1.5 and the lower limit of 0.2.

Similarly, when the water supply pump 17 is operated for the third time, the blow operation is simultaneously performed for TB×C, which is the time obtained by multiplying the second operation time TB of the water supply pump 17 by the coefficient C. The value of C at this time is the same value as in the second operation. In this way, by performing the blow operation during the next operation of the water supply pump 17 corresponding to the previous operation time of the water supply pump 17, the blow operation can be performed for an appropriate time suitable for the previous operation time of the water supply pump 17. It can be carried out. In addition, since the blowing operation is performed simultaneously with the operation of the water supply pump 17, the amount of boiled water 13 discharged by the blowing operation can be properly replenished. In this way, the electric conductivity, ie the concentration, of the boiler water 13 inside the can body 11 can be maintained in a stable state.

According to the values of the three coefficients, ie, the upper limit value, the lower limit value, and the C value, the shortest time for the blow operation in FIG. 2 is TA×0.2. The reason why the lower limit is set in this way is that if the blow operation time is shortened by falling below the lower limit, the concentration of the boiler water 13 inside the can body 11 may fluctuate greatly. If there is no problem, it is possible to set the shortest time of the blow operation to TA×0, that is, control the blow operation not to be performed. Also, in FIG. 2, the maximum blowing time is TA×1.5. The reason for setting the upper limit value is that if the blow operation time becomes longer than the upper limit value, the blow operation related to the previous intermittent operation will continue to be performed at the next intermittent operation of the water supply pump 17, making it difficult to control. This is because there is a risk that As long as such a problem does not arise, it is also possible to set the upper limit above 1.5.

The concentration of the boiler water 13 inside the can body 11 becomes extremely high, and a correspondingly high electric conductivity is detected. The operation time is up to 1.5 times the previous operation time of the water supply pump 17, and this length is the upper limit of the blow operation time. Then, since the blowing operation time does not reach the required time and the concentration of the boiler water 13 does not decrease sufficiently, the blowing operation will be performed at the upper limit value for the required number of times after the next time. By repeating such operations, eventually the concentration of the boiler water 13 will be sufficiently reduced, and the required blowing operation time will be below the upper limit. will be controlled in the normal time.

On the contrary, even when the concentration of the boil water 13 inside the can body 11 becomes extremely low and a correspondingly low electrical conductivity is detected, in which case a short blow operation time below the lower limit value is sufficient, the blowing The operation time is shortened to only 0.2 times the previous operation time of the water supply pump 17, and this length is taken as the lower limit of the blow operation time. Then, the blowing operation time exceeds the required time, and the concentration of the boiler water 13 does not rise sufficiently, so that the blowing operation is performed at the lower limit for the required number of times after the next time. By repeating such operations, the concentration of the boiler water 13 eventually rises to the required level, and the required blowing operation time exceeds the lower limit. Control will be performed in the normal time between

FIG. 3 is a graph showing the method of stabilizing the boiler boiler water quality of the present invention from a different point of view than the time axis chart of FIG. In this graph, the horizontal axis represents the electric conductivity of the boiler water 13 detected by the sensor 23, and the vertical axis represents the ratio (%) between the water supply time and the blow operation time. The unit of electrical conductivity is mS/m, or millisiemens per meter. Here, the set value is 300 mS/m, and the range of this set value ±20%, that is, the range from 240 mS/m to 360 mS/m is set as the allowable range, that is, the normal range, and the concentration of the boiler water 13 is controlled. ing. 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.

The electric conductivity of 360 mS/m is set as the upper limit of the detected concentration, and even if the detected concentration exceeds this, the coefficient is set to 1.5 (150%). This lengthens the blow operation time and increases the blow rate. Further, the electric conductivity of 240 mS/m is set as the lower limit of the detected concentration, and even if the detected concentration is below this, the coefficient is set to 0.2 (20%). As a result, the blow operation time is shortened and the blow rate is lowered. If the lower limit value can be set to 0 as described above, the blow rate can also be suppressed to 0%.

As described above, the boiler water 13 circulates through the inside of the boiler body 11 , the steam separator 18 and the downcomer pipe 19 . In this case, when the boiler is operated in a low-load state, the amount of circulation of the boiler water 13 decreases, which may reduce the detection accuracy of the concentration of the boiler water 13, that is, the electrical conductivity. . Therefore, when the boiler continues to operate in a low-load state, the blowing operation is performed for a certain amount of time after a predetermined period of time has passed or when the water supply pump has been intermittently operated more than a predetermined number of times. By doing so, the amount of circulation of the boiler water 13 increases, and the boiler water 13 having the same concentration as the concentration of the boiler water 13 inside the can body 11 can reach the installation position of the electrical conductivity sensor 23. can. This allows the electrical conductivity to be detected accurately.

Regarding the circulation of the boiler water 13 described above, when the boiler is operated at a low load, the evaporation state is relatively mild. Therefore, the degree of circulation of boiler water 13 may decrease. As a countermeasure, when the boiler is operated at a low load, the amount of combustion in the boiler is increased under certain conditions to activate the evaporation state and reduce the amount of boiler water splashing up inside the boiler body 11. Accurate concentration detection can be made possible by increasing the concentration and thereby promoting the circulation of the boiler water 13 . For example, when the low-load operation continues for about 30 minutes to 1 hour, the combustion amount of the boiler is increased to generate boiling water for about 10 to 20 seconds. can be splashed and the boiler water 13 can be well circulated. Alternatively, if the water supply pump 17 is intermittently operated about 20 times while the low-load operation continues, similarly increasing the combustion amount of the boiler to generate boiling water for about 10 to 20 seconds, Boiler water 13 can be circulated well.

In the above, during normal operation, the value of C is set to a constant value between the upper limit and the lower limit for control. However, instead of this, the value of C is not constant between the upper limit and the lower limit, and the value of C is changed between the upper limit and the lower limit according to the level of the detected electrical conductivity. can also In the case of warping, instead of the current stepped graph, the graph in FIG. It changes upward to the ratio (150%) of water supply time and blow time at the upper limit of electrical conductivity (360 mS/m).

In the above description, when the blow rate is changed, the blow operation time is changed. Alternatively, or together with this, the valve provided in the blow pipe 21 may be an opening control valve instead of the opening/closing valve 22 described above, and the blow rate may be changed by controlling the opening.

17 water supply pump 18 steam separator 19 downcomer pipe 21 blow pipe 22 on-off valve 23 electrical conductivity sensor 24 control device

Claims (6)

A water supply pump for supplying boiler water to the boiler body is intermittently operated, and each time the water supply pump is intermittently operated, a blow operation is performed to discharge the boiler water to the outside of the boiler. A method of stabilizing the water quality of boiler boiler water. 2. The can of the boiler according to claim 1, wherein boil water is discharged from a steam separator for separating boil water and steam contained in the steam-water mixed fluid supplied from the boiler to the outside. A method for stabilizing water quality. The electrical conductivity of the boiler water in the steam separator is detected, and the upper and lower limits are set for the blow operation time according to the level of the detected electrical conductivity. If the electrical conductivity is normal between the electrical conductivity corresponding to the upper limit of the time of the blowing operation and the electrical conductivity corresponding to the lower limit of the time of the blowing operation, the time of the blowing operation 3. The method for stabilizing the quality of boiler boiler water according to claim 2, wherein the blowing operation is performed for a constant time between the upper limit and the lower limit of . When the detected electrical conductivity exceeds the electrical conductivity corresponding to the upper limit of the blowing operation time, the upper limit of the blowing operation time is set, and the measured electrical conductivity is the lower limit of the blowing operation time. 4. The method for stabilizing the water quality of boiler boiler water according to claim 3, wherein the blow operation time is set to the lower limit when the electric conductivity corresponding to the value falls below. When the boiler is operated at low load for a certain period of time or more, the electrical conductivity of the boiler water detected in the steam separator is used as the electrical conductivity of the boiler water in the boiler. 5. The method for stabilizing the water quality of boiler boiler water according to claim 3 or 4, characterized in that the blowing operation is carried out for a predetermined period of time so as to correspond. When the boiler is operated at a low load for a certain period of time or longer, the boiler is temporarily placed in a high combustion state to increase the amount of evaporation and increase the amount of steam-water mixed fluid flowing into the steam separator. The method for stabilizing the water quality of boiler boiler water according to any one of claims 1 to 4, characterized in that:

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