JP3299344B2 - Overheat prevention device for multi-tube once-through boiler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for preventing overheating in a multi-tube once-through boiler.

[0002]

2. Description of the Related Art An example of a conventional apparatus for preventing overheating in a boiler of this type is disclosed in Japanese Utility Model Laid-Open Publication No. Sho 56-112405. FIG. 9 is a diagram showing the configuration of a conventional multi-tube once-through boiler and its overheating prevention device. As shown in the figure, in the multi-tube once-through boiler, an upper header 1 and a lower header 2 are connected by a number of water tubes 3 to form a water tube wall, and a central portion thereof is a combustion chamber 15. A water feed pump 6 is connected to the lower header 2 by piping, and a burner 7 is disposed above the combustion chamber 15.

In the above-mentioned multi-tube type once-through boiler, a water level control cylinder 4 connected from the upper header 1 and the lower header 2 with connecting pipes 12 and 13 is provided outside as a water level detecting device. Detectors 9, 10, 11 are provided,
Further, a water level detector 8 is provided in the water pipe 3 through the upper canister 1 at a water level in the boiler can which does not generate heat even when combustion is performed, and a signal from these water level detectors 8, 9, 10, and 11 is transmitted through the controller 5 through the controller 5. Thus, the control of the water supply pump 6 and the start and stop of combustion of the burner 7 are controlled.

The water level detectors 9, 10 and 11 are set to different detection water levels, respectively. During normal operation, the water level of the water pipe 3 is maintained within the water levels detected by the water level detectors 10 and 11, and When the water level falls below the water level detected by the water level detector 9, the controller 5 stops the burner 7 from burning.

[0005] In addition, a small amount of chemicals is supplied to the water (water pipe 3).
In the case where the electrical conductivity of the (water in) is low, bubbling of the can water due to boiling in the water pipe 3 becomes slight, and the cooling effect of the pipe wall by the can water is reduced, so that the water level held by the water level detectors 10 and 11 is low. Since there is a case where the water pipe 3 is overheated, the water supply pump 6 is started and stopped and the combustion of the burner 7 is started and stopped by the safe water level in the can set by the water level detector 8. Conventionally, the water level detector 8 is provided in the upstream area of the convection heat transfer surface which does not often come into contact with the flame to prevent the water pipe 3 from being overheated.

[0006]

However, in recent years,
In order to reduce the size and increase the efficiency of the boiler, the local maximum amount of heat received by the heat transfer surface increases, and the difference in the amount of heat received due to the difference in the location of the heat transfer surface also increases. The amount of heat received by each of the water tubes 3 constituting the heat transfer surface of the boiler is different depending on the positional relationship between the combustion flame and the combustion gas, the temperature difference, and the like. Also, the degree of strength is different. That is, in the water pipe 3 receiving a large amount of heat, severe boiling occurs, and the air-water boundary surface shows intense bubbling so that the water-water boundary surface is unclear. In the gas phase, the flow becomes mainly steam, and the cooling effect on the tube wall is reduced.
This tendency is particularly remarkable as boilers become smaller and more efficient.

Under such circumstances, the safety water level in the can is conventionally maintained only at the place where the water level detector 8 is mounted as described above. That is, the water level detector 8
In the water pipe 3 receiving less heat than the water pipe 3 to which the water pipe 3 is attached, there is a concern that the pipe wall cooling action by the can water is weak, and the water pipe 3 is deteriorated due to local overheating and high-temperature oxidation. That is,
When the entire water pipe 3 is viewed, there is a problem that a safe water level is not secured.

The present invention has been made in view of the above points, and provides an overheating prevention apparatus for a multi-tube once-through boiler which can eliminate the above-mentioned problems and prevent deterioration of the water pipe 3 and high-temperature oxidation due to overheating. The purpose is to do.

[0009]

In order to solve the above-mentioned problems, the present invention relates to a space 15 formed by communicating a number of water tubes 3 between an upper header 1 and a lower header 2 as shown in FIG. ,
A control is provided with a burner 7 for injecting fuel into the space 15 for combustion and a water supply pump 6 for supplying water to the water pipe, and for detecting the water level of the water pipe 3 to control the start / stop of the water supply pump 6 and / or the start / stop of the burner 7. In a device for preventing overheating of a multi-tube once-through boiler provided with means, one or more water level detectors 8-1 and 8-2 are provided in an upper header 1 or a water pipe 3 in the boiler to detect one water level. If a water level detector is provided, select the vicinity of the heat transfer surface where the amount of heat received is the least. If a second water level detector is provided, select the vicinity of the heat transfer surface that is in contact with the hottest combustion gas. Select and water level detector 8 from the top
-2, the output signal of the water level detector 8-1 is input to the control means (controller 5) to control the start / stop of the water supply pump 6 and / or the start / stop of the burner 7, and the water level is detected similarly. The output signal of the burner 8-2 is input to the control means to control the start and stop of the burner 7.

[0010]

In the water pipe 3 receiving a small amount of heat, the steam-water boundary surface is relatively quiet and stable, and the gas phase becomes a flow mainly composed of steam, and the pipe wall cooling action is reduced. In the present invention, when a water level equal to or lower than the water level set by the water level detector 8-1 provided in the vicinity of the heat transfer surface having the least heat reception amount is detected, the control means starts the water supply pump 6 for a certain period of time. If the water level in the can is kept constant and / or the water level is lower than the set water level for a certain period of time, the combustion of the burner 7 is stopped. Also 2
If more than one water level detector is provided, the water level detector 8-
1 is provided at the same position as described above to provide the same function, and the water level detector 8-2 is provided near the heat transfer surface that contacts the hottest combustion gas, and the water level in the can is adjusted to the water level detector 8-2. When the water level is equal to or less than the water level set by the above, the combustion of the burner 7 is stopped. That is, the water level detector 8-2 is provided in the water pipe 3 which is most likely to be overheated among the many water pipes 3, and by maintaining the water level, the entire water pipe 3 can be protected from overheating.

[0011]

Embodiment 1 An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic view showing a configuration of a multi-tube once-through boiler and a device for preventing overheating thereof according to a first embodiment of the present invention.
FIG. 2 is a sectional view taken along the line AA of FIG. 1, showing a mounting position of the water level detectors 8-1 and 8-2. As shown in the figure, this boiler connects an upper header 1 and a lower header 2 with a number of double concentrically arranged water tubes 3 therebetween to form a concentric water tube wall. Is a combustion chamber 15. A water feed pump 6 is connected to the lower header 2 by piping, and a burner 7 is arranged above the combustion chamber. The fuel injected from the burner 7 burns in the combustion chamber 15, and the combustion exhaust gas passes through the openings 101 of the inner water pipe group 3, and further flows into the inner water pipe 3.
The water is exhausted from the boiler outlet flue 14 between the group and the outer group of water pipes 3, and the water supplied to the water pipes 3 is heated by the water supply pump 6.

In the above-mentioned multi-tube type once-through boiler, a water level control cylinder 4 connected from the upper header 1 and the lower header 2 by connecting pipes 12 and 13 is provided outside as a water level detecting device. Detectors 9, 10, 11 are provided, and controller 5
Is the same as the conventional one in that the detection signals of these detectors 9, 10 and 11 are processed to control the start and stop of the combustion of the water supply pump 6 and the burner 7.

In this embodiment, the water pipe 3 near the heat transfer surface which receives the least amount of heat in the vicinity of the flue 14 of the boiler outlet of the combustion gas.
A first water level detector 8-1 is provided through the upper header 1 through the upper header 1 and the water pipe 3 near the heat transfer surface (the water pipe 3 near the opening 101) in contact with the hottest combustion exhaust gas. A second water level detector 8-2 is provided.

During normal operation, an externally provided water level control cylinder 4
As described above, the controller 5 starts and stops the water supply pump 6 and starts and stops the combustion of the burner 7 in accordance with the signals from the water level detectors 9, 10 and 11.
When the electrical conductivity of the boiler water is low, such as when the boiler is started, or when pure water is used, bubbling due to boiling in the boiler is slight, and is held by the detection signals of the water level detectors 9, 10, and 11. Since the water level becomes lower than the water level held by the signal of the water level detector 8-1 provided in the can, the controller 5 holds the water level in the can by the signal of the water level detector 8-1.

At this time, since the water level detector 8-1 is located in the water pipe 3 near the heat transfer surface receiving the least amount of heat, bubbling due to boiling in the water pipe 3 is the gentlest among all the water pipes 3. That is, in the water pipes 3 other than the water pipe 3, a more intense boiling and bubbling phenomenon occurs than in the water pipe 3 in which the water level detector 8-1 is disposed, so that the pipe wall cooling operation is sufficiently performed. Therefore, if the water pipe 3 constituting the heat transfer surface receiving the least amount of heat receives a safe water level for preventing local overheating, overheating in the other water pipes 3 receiving a large amount of heat can be prevented. That is, a safe water level is secured in all the water pipes 3.

The controller 5 includes the water level detector 8-1.
In addition to the function of keeping the water level constant by receiving the input of the detection signal, the combustion of the burner 7 is stopped when the water level above or below the set water level continues for a certain period of time. Of course, it is possible to have a function of causing the function to be performed.

Next, the second water level detector 8-2 will be described. The water level detector 8-2 is provided from the upper header 1 on the water pipe 3 near the heat transfer surface that comes into contact with the hottest flue gas, and the controller 5 uses the detection signal of the water level detector 8-2 to supply a water feed pump. The start and stop of the burner 7 are not performed, and only the start and stop of the combustion of the burner 7 are performed. The water pipe 3 near the heat transfer surface that comes into contact with the hottest combustion gas can reach the superheated temperature in the shortest time when the water level in the water pipe 3 decreases due to a failure of the water supply pump 6 or the like. Therefore, when a water level lower than the water level set by the water level detector 8-2 is detected in the water pipe 3 to which the second water level detector 8-2 is attached, combustion of the burner 7 is stopped and the water pipe is stopped. 3 is to prevent overheating. Further, it is natural that the second water level detector 8-2 may be provided at the position shown in the cross-sectional view of FIG. 3 from the mechanical characteristics of the boiler can body.

FIG. 4 is a view showing an example of an attachment position when one water level detector is provided from the upper header 1 to the inside of the can. In this case, a water level detector 8-1 is provided from the upper header 1 to the water pipe 3 near the heat transfer surface where the amount of received heat is the smallest near the boiler outlet flue 14 of the combustion exhaust gas.

[Embodiment 2] FIG. 5 is a view schematically showing a boiler and a device for preventing overheating of the boiler according to Embodiment 2 of the present invention.
FIG. 6 is a sectional view taken along the line BB of FIG. 5 showing an example of a mounting position of the water level detector. In the figure, the portions denoted by the same reference numerals as those in FIGS. 1 and 2 indicate the same or corresponding portions. As shown in the figure, the boiler is formed in a rectangular shape by a large number of water tubes 3 arranged in parallel in two rows connecting an upper header 1 and a lower header 2, and the water tubes 3 are provided at a predetermined interval in the center thereof. Are arranged. The burner 7 is arranged at one end of the boiler, and the fuel injected from the burner 7 is burned in the boiler, and the combustion exhaust gas is discharged from the other end.

The first water level detector 8-1 is provided on the water pipe 3 serving as a heat transfer surface in the vicinity of the combustion exhaust gas outlet of the combustion chamber 15 receiving the least amount of heat. Further, the second water level detector 8-2 is provided in the water pipe 3 near the heat transfer surface where the amount of heat received by the fuel from the burner 7 in the combustion chamber 15 burns most vigorously. The functions and operations of the water level detectors 8-1 and 8-2 are the same as those in the first embodiment.

In the above embodiment, the first water level detector 8-1 and the second water level detector 8-
Each of the detected water levels 2 may be at the same height or different. Further, since the first water level detector 8-1 is provided on the relatively static air-water boundary surface, chattering and malfunction of the water level detector 8-1 due to the fluctuation of the water surface are reduced, and Stable water supply can be performed while preventing overheating. That is, since the first water level detector 8-1 is provided at the stable air-water boundary surface, the water supply pump 6 is not frequently started and stopped.

[Embodiment 3] FIG. 7 is a diagram showing a schematic configuration of a boiler and an overheat prevention device thereof according to Embodiment 3 of the present invention.
In the figure, the portions denoted by the same reference numerals as those in FIGS. 1 and 2 indicate the same or corresponding portions. As shown in the figure, in the present embodiment, the water level control cylinder 4 is removed from the boiler shown in FIG. In the present embodiment, since the first water level detector 8-1 is provided at the stable air-water boundary surface, the water supply pump can be started and stopped stably, and the first water level detector 8-1 In the water pipe 3 provided with 1, the amount of heat received is the smallest, so that the actual amount of retained water except for bubbles at the retained water level can always be kept constant, so that the water in the can was connected to the outside with the connecting pipe. A normal water level detection device having a water level detector provided in the water level control cylinder can be omitted.

In this case, the water level in the can is always maintained at the water level set by the first water level detector 8-1. Second
The detector 8-2 outputs a signal for starting and stopping the combustion of the burner 7 in the same manner as described above. Naturally, if the state below the water level set in the first water level detector 8-1 provided in the water pipe 3 near the heat transfer surface receiving the least amount of heat continues for a certain period of time, the burner 7 burns. The controller 5 may have a function of stopping the operation.

With such a configuration, the water level control cylinder 4 conventionally provided outside using the connection pipes 12 and 13 can be used.
Becomes unnecessary, and a more simple boiler overheat prevention device for preventing overheating of the water pipe 3 can be configured.

[Embodiment 4] FIG. 8 is a diagram showing a schematic configuration of a boiler and an overheating prevention device thereof according to Embodiment 4 of the present invention.
In the figure, the portions denoted by the same reference numerals as those in FIGS. 1 and 2 indicate the same or corresponding portions. In this embodiment, the water level control cylinder 4 is removed from the boiler shown in FIG. 5 for the same reason as described above.

Although not shown in FIGS. 1 to 8, a third water level detector is provided from the upper header 1 to another part inside the boiler to have a function of controlling the combustion of the burner 7. Further, a triple safety function against overheating of the water pipe 3 can be provided.

[0027]

As described above, according to the present invention, the following excellent effects are expected. (1) A water level detector is provided in the vicinity of the heat transfer surface receiving the least amount of heat, and control of starting and stopping of the feedwater pump and / or starting and stopping of the burner is performed by a detection signal of the water level detector. This has the effect of preventing overheating of the water pipe.

(2) Further, a water level detector is provided in the vicinity of the heat transfer surface in contact with the hottest combustion gas, and the start and stop of the burner are controlled by the detection signal of the water level detector. This has the effect of protecting the water tubes that are easily overheated and preventing overheating.

(3) Further, a water level detecting device constructed by providing a water level detector in a water level control cylinder provided outside a water can using a connecting pipe becomes unnecessary, and a simple overheat prevention device is realized. I can do it.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a multi-tube once-through boiler of the present invention and a device for preventing overheating thereof.

FIG. 2A is a diagram illustrating an example of a mounting position of a water level detector.
It is an A sectional arrow view.

FIG. 3 is a diagram illustrating an example of a mounting position of a water level detector.
It is an A sectional arrow view.

FIG. 4 is a sectional view taken along the line AA of FIG. 1 showing an example of an attachment position when one water level detector is provided.

FIG. 5 is a diagram showing a schematic configuration of another multi-tube once-through boiler of the present invention and a device for preventing overheating thereof.

FIG. 6B shows an example of a mounting position of the water level detector in FIG.
FIG.

FIG. 7 is a view showing a schematic configuration of another multi-tube once-through boiler of the present invention and a device for preventing overheating thereof.

FIG. 8 is a diagram showing a schematic configuration of another multi-tube once-through boiler of the present invention and a device for preventing overheating thereof.

FIG. 9 is a schematic sectional view of a conventional multi-tube once-through boiler and its overheating prevention device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper header 2 Lower header 3 Water pipe 4 Water level control cylinder 5 Controller 6 Water supply pump 7 Burner 8 Water level detector 8-1 Water level detector 8-2 Water level detector 9 Water level detector 10 Water level detector 11 Water level Detector 12 Connection pipe 13 Connection pipe 14 Boiler outlet flue 15 Space

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-306002 (JP, A) JP-A-1-179804 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F22D 5/00 F22B 21/06 F22B 37/42

Claims (4)

(57) [Claims] 1. A control means for communicating between an upper header and a lower header with a number of water pipes and detecting a water level in a boiler can to control start / stop of a water supply pump and / or start / stop of a burner. An overheat prevention device for a multi-tube once-through boiler, wherein one water level detector is provided near a heat transfer surface receiving the least amount of heat, an output signal of the water level detector is input to the control means, and An apparatus for preventing overheating of a multi-tube once-through boiler, which starts and / or stops the burner. 2. The method according to claim 1, wherein the number of water level detectors is two or more, and a first water level detector is provided near a heat transfer surface receiving the least amount of heat, and an output signal of the first water level detector is sent to the control means. The apparatus for preventing overheating of a multi-tube once-through boiler according to claim 1, wherein an input is made to start and stop the feed water pump and / or start and stop the burner. 3. The method according to claim 1, wherein the number of the water level detectors is two or more, the first water level detector is provided near the heat transfer surface having the least heat reception, and the second water level detector is provided with the combustion gas having the highest heat reception. The second water level detection is provided in the vicinity of a heat transfer surface that is in contact with the first water level detector. The output signal of the first water level detector is input to the control means to start and stop the water supply pump and / or the burner. 2. The overheat prevention device for a multi-tube once -through boiler according to claim 1 , wherein an output signal of a vessel is input to said control means to start and stop said burner. 4. The apparatus according to claim 1, wherein the number of the water level detectors is two or more, and a first water level detector is provided near a heat transfer surface receiving the least amount of heat, and an output signal of the first water level detector is sent to the control means. claims, characterized in that to the activation of the input by the water supply pump stop and / or to perform the start and stop of the burner, the output signal of another level detector to the control means perform the start and stop of the burner 2. The overheat prevention device for a multi-tube once -through boiler according to 1 .