JP7764777B2 - boiler - Google Patents

Description

The present invention relates to a boiler.

Conventionally, there have been systems that calculate the conductivity of the water separated by a separator from the steam coming from the boiler body, and then control the amount of water fed into the boiler body by changing the combustion stage based on that conductivity (for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2020-003094

However, when the boiler's combustion rate is low, the boiler water in the boiler body boils slowly, making it difficult for the boiler water to be transported to the separator. As a result, for example, it becomes difficult for the boiler water to reach the calculation unit that calculates the conductivity, which could lead to problems such as the actual boiler water conductivity not being able to be calculated.

The present invention was devised in light of this situation, and its purpose is to provide a boiler that can extract boiler water and calculate the boiler water's conductivity as accurately as possible even when the boiler's combustion volume is low.

To achieve the above object, a boiler according to one aspect of the present invention comprises a main body that heats boiler water by burning fuel to generate steam; a combustion stage control unit that controls one of multiple combustion stages with different combustion amounts; a feedwater control unit that controls the amount of feedwater supplied to the main body so that the boiler water level becomes a reference water level determined based on the combustion stage controlled by the combustion stage control unit; and a conductivity calculation unit that can calculate the water conductivity according to the boiler water. The feedwater control unit performs water level control to raise the boiler water level above the reference water level determined based on the specified combustion stage when the boiler water level is controlled to a specified combustion stage with a combustion amount equal to or less than a specified amount for a certain period of time.

With the above configuration, if the boiler combustion volume is continuously controlled to a predetermined combustion stage below a predetermined volume for a certain period of time, and the conductivity calculated by the conductivity calculation unit has not changed, and there is a risk that boiler water is not being removed, top-up water level control is performed to raise the water level above the reference water level. This makes it easier for boiler water to be removed, allowing the boiler water conductivity to be calculated as accurately as possible.

Preferably, the water supply control unit cancels the upper water level control when the combustion stage control unit controls the combustion amount to a combustion stage that exceeds the predetermined amount.

With the above configuration, if the combustion volume is controlled to a combustion stage that exceeds a predetermined amount, making it easier for boiler water to be removed, the upper water level control is released. This prevents excessive boiler water from being removed compared to the combustion volume, which could result in the supply of steam with a low dryness level.

Preferably, the water supply control unit cancels the top water level control when the conductivity calculated by the conductivity calculation unit changes.

With the above configuration, if the conductivity calculated by the conductivity calculation unit changes and it is inferred that boiler water has been removed, the top water level control is released. This prevents excessive boiler water from being removed, which could result in an extreme drop in combustion efficiency.

FIG. 1 is a diagram for explaining a schematic configuration of a boiler device. 10 is a flowchart illustrating an example of a water supply control process. 10 is a flowchart illustrating another example of the water supply control process.

<Overview of the configuration>
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, a schematic configuration of a boiler apparatus 1 according to this embodiment will be described with reference to Fig. 1. As shown in Fig. 1, the boiler apparatus 1 includes a boiler main body 2, a blower 3 that sends air into the boiler main body 2, and a fuel supply line 21 that supplies fuel to the boiler main body 2. While an example in which the fuel is oil will be described, the fuel is not limited to a liquid such as oil, and may be a gas such as a gas.

The fuel supply line 21 is provided with a fuel regulating valve 21a that functions as a pressure regulating valve and has a shut-off function, allowing it to adjust the flow rate of fuel supplied to the boiler body 2. The fuel regulating valve 21a is configured, for example, as a motor valve, but is not limited to a motor valve and may also be an air-operated control valve as long as it adjusts the flow rate of fuel. The fuel supplied from the fuel supply line 21 is supplied to the burner 20 in the boiler body 2, where it is mixed with combustion air blown from the blower 3 and burned. The flow rate of the combustion air is adjusted by the opening of a damper provided in the air supply path, or alternatively or additionally by using an inverter to adjust the rotational speed (frequency) of the fan of the blower 3.

The boiler body 2 is formed in a roughly cylindrical shape and contains a burner 20, water pipes 12, an upper header 13, and a lower header 11. The lower header 11 is located at the bottom of the boiler body 2 and is connected to the lower parts of the multiple water pipes 12. The lower header 11 is connected to a water supply pipe 24. The water supply pipe 24 is equipped with a water supply pump 22 and a check valve 23. Water is supplied from the water supply pump 22 to the lower header 11 via the water supply pipe 24, and the supplied water is heated in the water pipes 12. The upper header 13 is located at the top of the boiler body 2 and is connected to the upper parts of the multiple water pipes 12. The upper header 13 collects steam generated in the multiple water pipes 12 and directs it to the separator 5 via the connecting pipe 4.

The boiler apparatus 1 generates steam by burning fuel in the burner 20 in the boiler body 2 to heat and boil boiler water. The generated steam, along with the boiled boiler water, flows from the upper header 13 through the connecting pipe 4 into the separator 5, where it is separated by the separator 5 and extracted from the steam pipe 6. In addition, a downcomer pipe 7 is provided connecting the lower part of the separator 5 to the lower part of the boiler body 2, and the boiler water separated by the separator 5 is returned to the lower header 11 via the downcomer pipe 7. This circulates the boiler water within the boiler body 2.

A conductivity calculation unit 9 is provided in the downcomer pipe 7. The conductivity calculation unit 9 includes, for example, a sensor (electrode) that detects resistance values, and calculates the conductivity of the water in the downcomer pipe 7 from the resistance value. The conductivity calculation unit 9 is electrically connected to the control unit 10, and can input conductivity information to the control unit 10 to identify the calculated conductivity in the downcomer pipe 7.

In addition, a blow pipe 8 is connected to the downcomer pipe 7 midway, which discharges boiler water from the boiler body 2. The blow pipe 8 is equipped with a blow valve 8a. For example, when the conductivity calculated by the conductivity calculation unit 9 exceeds a predetermined value, it is assumed that the boiler water in the boiler body is concentrated, and the boiler water in the boiler body 2 can be discharged (blowed) by opening the blow valve 8a.

The control unit 10 is realized by a computer that includes an internal memory, timer, and arithmetic processing unit, and controls the operation and behavior of the boiler 1, including, for example, operation at ignition and shutdown, multiple combustion stages with different combustion amounts depending on the steam load (e.g., low combustion stage, medium combustion stage, high combustion stage, etc.), and operation of the feedwater pump 22 (feedwater control). The control unit 10 is electrically connected to the blower 3, fuel adjustment valve 21a, blowdown valve 8a, conductivity calculation unit 9, and feedwater pump 22.

The control unit 10 also executes a water supply control process to set a target water level in the water pipe 12 based on the multiple combustion stages and changes in the conductivity of the water in the downcomer pipe 7. The control unit 10 performs a process to control the amount of water supply so that the water level in the water pipe 12 reaches the set target water level. The target water level is set to a reference water level corresponding to the combustion stage being controlled, among the reference water levels defined for each of the multiple combustion stages. For example, in the low combustion stage, the low-fuel reference water level is set as the target water level. In the medium combustion stage, the medium-fuel reference water level is set as the target water level. In the high combustion stage, the high-fuel reference water level is set as the target water level. As shown in Figure 1, the water levels are in the following order: low-fuel reference water level > medium-fuel reference water level > high-fuel reference water level. The reference water levels defined for each of the multiple combustion stages are predetermined to be between the superheat limit water level and the dryness limit water level corresponding to each combustion stage.

Furthermore, in this embodiment, in order to solve problems that may arise in systems that perform predetermined processes, such as draining boiler water, based on the conductivity calculated by the conductivity calculation unit 9, a specific water level that is higher than the low-combustion reference water level is set as the target water level in the low-combustion stage. That is, in systems that perform predetermined processes based on the conductivity calculated by the conductivity calculation unit, for example, in a combustion stage where the amount of combustion is low (e.g., the low-combustion stage), boiling becomes gentle, making it difficult for boiler water to be carried to the separator side by boiling, and making it difficult for boiler water to reach the target location (calculation unit) where the conductivity is calculated. As a result, there is a large discrepancy between the actual conductivity of the boiler water in the main body and the conductivity calculated by the conductivity calculation unit, which could make it impossible to perform the predetermined process appropriately.

To address this issue, this embodiment defines a specific water level higher than the low-combustion standard water level. For example, the specific water level is forcibly set as the target water level under the condition that the low-combustion stage has been continuously controlled for a certain period of time or longer, and the conductivity of the water in the downcomer pipe 7 has not changed based on the conductivity calculated by the conductivity calculation unit 9. This allows for a water supply control process that facilitates the transfer of boiler water from the boiler body 2 to the separator side. As a result, it is possible to calculate a conductivity close to the actual conductivity of the boiler water in the body (calculating the boiler water conductivity as accurately as possible), allowing for appropriate processing, such as the discharge of boiler water. The specific water level is defined as, for example, approximately 10 mm higher than the low-combustion standard water level. The water supply control process in this embodiment is described in detail below.

<Water supply control process>
2 is a flowchart illustrating an example of the water supply control process. The control unit 10 starts the water supply control process at regular intervals (for example, every second), and continues the water supply control process until it is terminated.

In step S01, if the operation time (continuous operation time) during the low combustion stage has reached a certain time (e.g., one hour), and the conductivity calculated by the conductivity calculation unit 9 is used to determine whether the conductivity of the water in the downcomer pipe 7 has not changed over the certain time. For example, an example in which the certain time is the same as the fixed time will be described. Therefore, in step S01, it is determined whether the operation time during the low combustion stage is equal to or longer than the certain time, and whether the conductivity has not changed since the change. In step S01, if the operation time during the low combustion stage has not reached the certain time (e.g., during the low combustion stage but before the certain time has elapsed, or during the medium or high combustion stage), and it is not determined based on the conductivity calculated by the conductivity calculation unit 9 that the conductivity of the water in the downcomer pipe 7 has not changed over the certain time (e.g., during the low combustion stage but before the certain time has elapsed or the conductivity has changed, or during the medium or high combustion stage), the process proceeds to step S03. In step S03, it is determined whether a specific water level is set as the target water level. If it is determined in step S03 that a specific water level has not been set as the target water level (for example, if one of the low, medium, or high fuel reference water levels is set), the process proceeds to step S08.

In step S08, it is determined whether the combustion stage has changed in response to the load (steam load). This determination is made regardless of the target water level (for example, even if a specific water level is set, as described below). If it is not determined in step S08 that the combustion stage has changed in response to the load, in step S10, the water supply amount (water supply pump 22) is controlled so that the water level in the water pipe 12 reaches the currently set target water level, and the water supply control process ends. This causes water supply control to be performed so that the water level reaches the reference water level corresponding to the controlled combustion stage.

On the other hand, if it is determined in step S08 that the combustion stage has changed in response to the load, then in step S09, the reference water level determined based on the changed combustion stage is set as the target water level. As a result, in step S10, water supply control is performed so that the reference water level corresponds to the changed combustion stage.

Returning to step S01, if it is determined in step S01 that the operating time in the low combustion stage has reached a certain time and that the conductivity of the water in the downcomer pipe 7 has not changed over the specified time based on the conductivity calculated by the conductivity calculation unit 9, the process proceeds to step S02A, where it is determined whether the low fuel reference water level is set as the target water level. If it is determined in step S02A that the low fuel reference water level is set as the target water level, the process proceeds to step S02B.

If the operating time in the low combustion stage has reached a certain time and the conductivity of the water in the downcomer pipe 7 has not changed over the specified time based on the conductivity calculated by the conductivity calculation unit 9, boiler water has not been removed, and there is a risk of a large discrepancy between the actual conductivity of the boiler water and the conductivity calculated by the conductivity calculation unit 9. Therefore, in step S02B, a specific water level higher than the low combustion reference water level is set as the target water level in the water pipe 12, and the process proceeds to step S08. Thus, when steps S01 and S02A return YES, the specific water level is forcibly set in step S02B regardless of the conductivity value calculated by the conductivity calculation unit 9 (e.g., whether it is high or low). Note that when the specific water level is set, the operating time in the low combustion stage and the time during which the conductivity has not changed are reset. Furthermore, even after the specific water level is set, the combustion stage remains the low combustion stage.

In step S08, immediately after step S02B, it is not determined that the combustion stage has changed, and the process proceeds to step S10, where water supply control is performed so that the water level in the water pipe 12 reaches a specific water level. This makes it easier for boiler water to be carried out of the main body 2, even in a low combustion stage, and allows boiler water to flow into the separator 5. This makes it possible to calculate a conductivity close to the actual conductivity of the boiler water inside the main body, allowing for appropriate discharge of boiler water and other predetermined processes. It also prevents the boiler water from becoming overly concentrated. The water outside the main body 2 that flows into the separator 5 is an example of water corresponding to the boiler water.

When the specific water level is set, the operating time in the low combustion stage and the time during which the conductivity remains unchanged are reset as described above. Therefore, step S01 returns NO, and step S03 returns YES, resulting in the flow proceeding to step S04. In step S04, the conductivity calculated by the conductivity calculation unit 9 is used to determine whether the conductivity of the water in the downcomer pipe 7 has changed (e.g., compared to the conductivity before the specific water level was set). In step S04, the flow indirectly determines whether boiler water has actually been delivered to the separator 5 side based on whether the conductivity of the water in the downcomer pipe 7 has changed. If it is determined in step S04 that the conductivity in the downcomer pipe 7 has changed, it is assumed that boiler water has actually been delivered to the separator 5 side, and in step S05, the low-fuel reference water level is set as the target water level in the water pipe 12. The flow then proceeds to step S08, where the water feed rate is controlled in step S10 according to the flow described above, and the water feed control process ends. In this way, if the conductivity calculated by the conductivity calculation unit 9 changes and it is inferred that boiler water has been taken out of the boiler main body 2, the setting of the specific water level as the target water level is canceled. This makes it possible to prevent steam with a low dryness level from being supplied as much as possible.

On the other hand, if it is not determined in step S04 that the conductivity of the water in the downcomer pipe 7 has changed, the process proceeds to step S08, and the water supply amount is controlled in step S10 according to the flow described above, terminating the water supply control process. Note that in step S08, even when a specific water level is set, it is determined whether the combustion stage has changed depending on the load. Therefore, even when a specific water level is set, if the combustion stage changes to a medium combustion stage or the like depending on the load, a reference water level corresponding to the changed combustion stage is set in step S09, and the setting of the specific water level is canceled.

Furthermore, if, in step S01, the operating time in the low combustion stage has reached a certain time, and it is determined that the conductivity of the water in the downcomer pipe 7 has not changed over the specified time based on the conductivity calculated by the conductivity calculation unit 9, and it is not determined in step S02A that the low combustion reference water level has been set as the target water level, then the specific water level has already been set, and the process proceeds directly to step S08, and the water feed rate is controlled in step S10 according to the flow described above, terminating the water feed control process. In other words, if the specific water level has already been set as the target water level, the specific water level will remain set as the target water level until the conductivity calculated by the conductivity calculation unit 9 changes or the combustion stage changes.

In this embodiment, as shown in steps S01, S02A, and S02B of FIG. 2 , if the boiler has been operating in a low combustion stage (low combustion rate) for a certain period of time or longer, and the conductivity of the water in the downcomer pipe 7 based on the conductivity calculated by the conductivity calculation unit 9 has not changed over a predetermined period of time, and there is a risk that boiler water has not been transported to the separator 5, the target water level in the water pipe 12 is set to a specific water level higher than the reference water level, regardless of the conductivity value (e.g., high or low) calculated by the conductivity calculation unit 9. This makes it easier for boiler water to be transported outside the boiler body 2. As a result, for example, the conductivity calculation unit 9 can more easily calculate the actual boiler water conductivity (calculating the actual boiler water conductivity as accurately as possible), and predetermined processes such as boiler water discharge can be appropriately performed based on that conductivity. Furthermore, it is possible to prevent the boiler water from becoming overly concentrated.

Furthermore, as shown in steps S08 and S09 of Figure 2, even if a specific water level has been set, if the low combustion stage changes to the medium combustion stage or the high combustion stage depending on the load, and boiler water is more likely to be taken out of the boiler body 2 than when it was in the low combustion stage, the reference water level based on the post-change combustion stage is set as the target water level, regardless of the conductivity value calculated by the conductivity calculation unit 9, and the setting of the specific water level is canceled. This makes it possible to prevent excessive boiler water from being taken out and steam with low dryness being supplied as much as possible.

Furthermore, as shown in steps S04 and S05 of Figure 2, if the conductivity of the water in the downcomer pipe 7 changes when a specific water level is set, the specific water level setting is canceled and the reference water level based on the low combustion stage is set as the target water level. This makes it possible to prevent as much boiler water as possible from being taken out of the boiler body 2, which would drastically reduce combustion efficiency.

The present invention is not limited to the above-described embodiment, and various modifications and applications are possible. Below, we will explain modifications of the above-described embodiment that can be applied to the present invention.

In the above embodiment, an example was described in which the specific water level was set as a water level higher than the low-combustion standard water level. However, as shown in Figure 1, a special water level higher than the specific water level may be set in addition to the specific water level. For example, during the low-combustion stage in which the specific water level is set, if a predetermined time has passed without the conductivity of the water in the downcomer pipe 7 changing, the special water level is forcibly set as the target water level, thereby performing water supply control processing that makes it even easier for boiler water to be transported from the boiler body 2 to the separator side. Note that the special water level is set, for example, to a water level approximately 10 mm higher than the specific water level.

Figure 3 is a flowchart illustrating an example of water supply control processing when a special water level is set in addition to the above embodiment. Note that the same parts as in the above embodiment are designated by the same reference numerals and will not be described again. In step S01, if the system is in the low combustion stage and the operating time in the low combustion stage has not reached a certain time, and if it is not determined that the conductivity of the water in the downcomer pipe 7 has not changed over a predetermined time period based on the conductivity calculated by the conductivity calculation unit 9, the process proceeds to step S03A. In step S03A, it is determined whether a special water level or special water level has been set. If it is not determined in step S03A that a special water level or special water level has been set as the target water level, the process proceeds to step S08A.

In step S08A, it is determined whether the combustion stage has changed in response to the load (steam load). This determination is made regardless of the water level set as the target water level (for example, even if a special water level is set in addition to a specific water level). If it is not determined in step S08A that the combustion stage has changed in response to the load, the water feed rate is controlled in step S10, and the water feed control process ends. On the other hand, if it is determined in step S08A that the combustion stage has changed in response to the load, the process proceeds to step S09, the water feed rate is controlled in step S10, and the water feed control process ends.

Also, if a specific water level has already been set, and step S01 determines that the system is in the low combustion stage and the operating time in that stage has reached a certain time, and that the conductivity of the water in the downcomer pipe 7 has not changed over a predetermined time period based on the conductivity calculated by the conductivity calculation unit 9, and proceeds to step S02A, it is determined that the low combustion reference water level has not been set as the target water level, so step S02C is proceeded to, where a special water level higher than the specific water level is set as the target water level. Then, step S08A is proceeded to, and in step S10, water supply control is performed according to the flow described above so that the water level in the water pipe 12 reaches the special water level, and the water supply control process ends. In this way, even after setting the target water level to the specific water level, if the operating time in the low combustion stage reaches a certain time, the conductivity calculated by the conductivity calculation unit 9 remains unchanged for a predetermined time (when the same conditions as those for setting the specific water level in Figure 3 are met), and it is estimated that boiler water has not yet been removed from the boiler body 2, a special water level higher than the specific water level is set. This more reliably ensures that boiler water is removed from the boiler body 2. As a result, the conductivity calculation unit 9 can more easily calculate the actual boiler water conductivity, preventing the boiler water from becoming overly concentrated. Note that when the special water level is set, the operating time in the low combustion stage and the time during which the conductivity remains unchanged are reset. Furthermore, even after the special water level is set, the combustion stage remains the low combustion stage.

On the other hand, if it is determined in step S03A that a specific water level or special water level has been set as the target water level, the process proceeds to step S04. If it is not determined in step S04 that the conductivity of the water in the downcomer pipe 7 has changed, the process proceeds to step S08A, and the water supply amount is controlled in step S10 according to the process described above, and the water supply control process ends. In other words, if the special water level has already been set as the target water level, the special water level will remain set as the target water level until the conductivity calculated by the conductivity calculation unit 9 changes or the combustion stage changes.

On the other hand, if it is determined in step S04 that the conductivity of the water in the downcomer pipe 7 has changed, the process proceeds to step S05A. In step S05A, it is determined whether a specific water level has been set as the target water level. If it is not determined in step S05A that a specific water level has been set as the target water level, i.e., if a special water level has been set as the target water level, the process proceeds to S05C, where the specific water level is set as the target water level in the water pipe 12. The process then proceeds to step S08A, where the water supply amount is controlled in step S10 according to the flow described above, and the water supply control process ends.

Furthermore, if it is determined in step S05A that a specific water level has been set as the target water level, the process proceeds to S05B, where the low fuel reference water level is set as the target water level, and the process proceeds to step S08A. The water supply amount is controlled in step S10 according to the flow described above, and the water supply control process ends. In this way, even if a specific water level is set and it is determined in step S04 that the conductivity has changed, the specific water level is set first, and then a water level is set that is gradually lower in accordance with the change in conductivity, so that the low fuel reference water level is set when the conductivity changes further after the specific water level is set. However, this is not limited to this, and if it is determined in step S04 that the conductivity has changed when a special water level is set, the low fuel reference water level may be set without going through stages.

In step S08A, even if a special water level or the like is set, if the load changes to a medium combustion stage or the like, the standard water level corresponding to the changed combustion stage is set in step S09, and the setting of the special water level or the like is canceled.

In the above embodiment, the example was given in which the predetermined time during which the conductivity of the water in the downcomer pipe 7 remains unchanged (S01), one of the conditions for setting a specific water level, is the same as the fixed time during operation in the low combustion stage. However, the predetermined time during which the conductivity of the water in the downcomer pipe 7 remains unchanged, one of the conditions for setting a specific water level, may be different from the fixed time during operation in the low combustion stage. For example, the fixed time during which the conductivity of the water in the downcomer pipe 7 remains unchanged, which is determined to be the condition met, may be set to be shorter than the fixed time (1 hour) during operation in the low combustion stage. In this case, for example, the condition for setting a specific water level may be met if the conductivity of the water in the downcomer pipe 7 changes during the initial transition to the low combustion stage, but the conductivity of the water in the downcomer pipe 7 remains unchanged for the most recent fixed time (e.g., 10 minutes) after the fixed time during operation in the low combustion stage has elapsed.

Furthermore, while an example has been described in which the fixed time, which is the operating time in the low combustion stage among the conditions for setting the specific water level, and the fixed time, which is the operating time in the low combustion stage among the conditions for setting the special water level, are the same, this is not limited to this, and different times may be set for both. For example, the fixed time, which is the operating time in the low combustion stage among the conditions for setting the special water level, may be set to a time shorter than the fixed time (1 hour) that is longer than the average time required, under normal circumstances, for the water level in the water pipe 12 to reach the specific water level and for the boiler water to be removed from the boiler.

Furthermore, as with the fixed time in step S01 described above, the predetermined time during which the conductivity of the water in the downcomer pipe 7 does not change, which is one of the conditions for setting a specific water level, and the predetermined time during which the conductivity of the water in the downcomer pipe 7 does not change, which is one of the conditions for setting a special water level, are the same time. However, this is not limited to this, and different times may be set for both. For example, the predetermined time during which the conductivity of the water in the downcomer pipe 7 does not change, which is one of the conditions for setting a special water level, may be set to be shorter than the predetermined time during which the conductivity of the water in the downcomer pipe 7 does not change, which is one of the conditions for setting a specific water level.

In the above embodiment, the "low combustion stage" with the lowest combustion amount, as shown in step S01 of FIG. 2, was used as an example of a "predetermined combustion stage" where a water level higher than the reference water level can be set by satisfying the conditions for setting a specific water level, etc. However, this is not limited to this, and other examples include a "low combustion stage" and a "medium combustion stage" as long as the combustion amount is below a level where boiler water boils slowly and therefore does not easily flow into, for example, separator 5. In this case, if the operating time in the medium combustion stage reaches a certain time or more and the conductivity does not change, a water level higher than the medium combustion reference water level is set as the target water level in step S02B. Note that in the above embodiment, the "medium combustion stage" and "high combustion stage" were used as examples of a "combustion stage where the combustion amount exceeds a predetermined amount." However, as described above, if the "predetermined combustion stage where the combustion amount is below a predetermined amount" is the "low combustion stage" or "medium combustion stage," the "combustion stage where the combustion amount exceeds a predetermined amount" becomes the "high combustion stage."

In the above embodiment, an example was described in which the boiler apparatus 1 is configured as a so-called four-position control boiler that can be controlled to one of the low combustion stage, medium combustion stage, high combustion stage, and combustion stop stage. However, the boiler that makes up the boiler apparatus 1 is not limited to this, and for example, in addition to a four-position control boiler, it may also be a so-called three-position control boiler that can be controlled to one of the low combustion stage, high combustion stage, and combustion stop stage. In the case of a three-position control boiler, the combustion stage in which the combustion amount is below a predetermined amount is the low combustion stage, and the combustion stage in which the combustion amount is above the predetermined amount is the high combustion stage.

The boiler constituting the boiler system 1 may be, for example, a boiler whose load rate can be proportionally controlled between 10% and 100%. In this case, the predetermined combustion amount serving as the judgment criterion in step S01 of FIG. 2 may be, for example, the combustion amount resulting in a load rate of 20%, and the process may proceed to step S02A when a certain period of time has passed since the load rate reached 20% or less. In this case, when the certain period of time has passed since the load rate reached 10% (and the conductivity has not changed over the certain period of time), the process corresponding to step S02B sets the target water level to a level higher than the reference water level based on 10%. When the certain period of time has passed since the load rate reached 20% (and the conductivity has not changed over the certain period of time), the process corresponding to step S02B sets the target water level to a level higher than the reference water level based on 20%.

In the above embodiment, the difference between the reference water level and the specific water level, and the difference between the specific water level and the special water level described in the modified example, are both 10 mm. However, the difference between the reference water level and the specific water level, and the difference between the specific water level and the special water level, are not limited to this, as long as they are water level differences that make it easier for boiler water to be removed from the boiler body 2 by raising the target water level, and may be, for example, any level difference between 5 mm and 15 mm. Furthermore, both the specific water level and the special water level may be water levels that are below the dryness limit water level corresponding to the combustion stage (e.g., the low combustion stage). Alternatively, only the specific water level may be below the dryness limit water level, and the special water level may be a water level that is lower than the dryness limit water level, while the special water level may be a water level higher than the dryness limit water level.

In the above embodiment, one hour was used as an example of the fixed time in step S01 used to determine whether the operating time in the low combustion stage has reached the fixed time, but it may be two hours, etc. The fixed time in step S01 may be, for example, shorter than the average time required for boiler water to become highly concentrated in the low combustion stage. In a boiler that issues an alarm to notify of a possible malfunction of the conductivity calculation unit 9 and prompt inspection when the conductivity calculated by the conductivity calculation unit 9 has not changed (remained constant) for a specific time (e.g., one hour), it is preferable that the fixed time in step S01 be set to a time shorter than the specific time (e.g., 50 minutes). As a result, when it is determined in step S01 that a certain time has been reached and the specific water level is set in step S02, boiler water becomes more likely to be taken out of the boiler main body 2, and if the conductivity calculation unit 9 is not malfunctioning, the conductivity will change and an alarm can be avoided. However, if the conductivity does not change even after the specific water level is set, there is a higher possibility that the conductivity calculation unit 9 is malfunctioning, which increases the accuracy of the alarm notification.

In addition, in a boiler that issues an alarm to warn of the possibility of a malfunction of the conductivity calculation unit 9 and to prompt inspection, if the conductivity calculated by the conductivity calculation unit 9 does not change even after a predetermined time has elapsed since the specific water level was set in Figure 2 (e.g., a predetermined time that is longer than the average time required under normal circumstances for the water level in the water pipe 12 to reach the specific water level and for the boiler water to be removed outside), the conductivity calculation unit 9 may be malfunctioning, and an alert to that effect may be issued. Similarly, in the case of Figure 3, if the conductivity calculated by the conductivity calculation unit 9 does not change even after a predetermined special time has elapsed since the special water level was set (e.g., a predetermined time that is longer than the average time required under normal circumstances for the water level in the water pipe 12 to reach the special water level and for the boiler water to be removed outside), the conductivity calculation unit 9 may be malfunctioning, and an alert to that effect may be issued. As a result, when it is determined in step S01 that a certain time has been reached and a specific water level, etc. is set in step S02B in Figure 2 and step S02C in Figure 3, an alarm is sounded if the conductivity does not change despite the situation being such that boiler water is more likely to be taken out of the boiler main body 2, thereby suggesting at the appropriate time that the conductivity calculation unit 9 may be malfunctioning.

In the above embodiment, an example was described in which the conditions for setting a specific water level include the conductivity not changing over a predetermined period of time, regardless of the value of the conductivity calculated by the conductivity calculation unit 9. However, the conditions are not limited to this, and may include the range of change in conductivity being limited to a predetermined range based on the conductivity history over a predetermined period of time (the conductivity not changing beyond the predetermined range).

In the above embodiment, an example was described in which step S04 in Figure 2 determines whether the conductivity of the water in the downcomer pipe 7 has changed, but this is not limiting. For example, it may be determined whether the conductivity of the water in the downcomer pipe 7 has changed by a predetermined value (e.g., 50 S/m) or more.

In the above embodiment, as shown in steps S01 and S02B of Figure 2, an example was described in which the target water level is set to a water level higher than the reference water level when operation in the low combustion stage, where the boiler combustion amount is low, has continued for a certain period of time or more and the conductivity of the water in the downcomer pipe 7 based on the conductivity calculated by the conductivity calculation unit 9 has not changed for a certain period of time. However, this is not limited to this. When operation in the low combustion stage, where the boiler combustion amount is low, has continued for a certain period of time or more, the target water level may be set to a water level higher than the reference water level even if the conductivity of the water in the downcomer pipe 7 has changed. Furthermore, when the conductivity of the water in the downcomer pipe 7 based on the conductivity calculated by the conductivity calculation unit 9 has not changed for a certain period of time in the low combustion stage, the target water level may be set to a water level higher than the reference water level even if operation in the low combustion stage has not continued for a certain period of time.

In the above embodiment, the conductivity sensor (a sensor that detects resistance) included in the conductivity calculation unit 9 is provided in the downcomer pipe 7, enabling calculation of the conductivity of the water in the downcomer pipe 7. However, the conductivity sensor included in the conductivity calculation unit 9 may also be provided in the lower header 11, enabling calculation of the conductivity of the water in the lower header 11. Water that is taken outside the main body 2 and flows into the lower header 11 via the separator 5 is an example of boiler water. In this case, the conductivity sensor included in the conductivity calculation unit 9 may be provided adjacent to the connection between the lower header 11 and the downcomer pipe 7, for example. This makes it less likely that freshly supplied water will be confused with water that has flowed through the downcomer pipe 7, making it possible to calculate the conductivity of the water that has flowed from the downcomer pipe 7 into the lower header 11. As a result, the actual boiler water conductivity can be calculated as accurately as possible.

In the above embodiment, an example of a boiler apparatus 1 having a single boiler body 2 has been described. However, the present invention can also be applied to a multi-boiler installation system in which multiple boiler bodies are installed. In a multi-boiler installation system, a number control method is used to control the number of operating boilers depending on the load situation. In this number control method, an operating priority is preset for each boiler body. While a boiler body with a higher priority is operating in a high combustion phase, a boiler body with a lower priority may continue to wait in a low combustion phase. In such a case, for a boiler body that continues to wait in the low combustion phase, the boiler water may boil slowly, as shown in the above embodiment, and the conductivity may not be accurately determined. By applying the present invention to such a boiler body, it becomes possible to accurately determine whether the boiler water in the boiler body is concentrated.

The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications that are equivalent in meaning to and within the scope of the claims.

REFERENCE SIGNS LIST 1 Boiler device 2 Boiler body 3 Blower 4 Connecting pipe 5 Separator 6 Steam pipe 7 Downcomer pipe 8 Blow pipe 8a Blow valve 9 Conductivity calculation unit 10 Control unit 11 Lower header 12 Water pipe 13 Upper header 20 Burner 21 Fuel supply line 21a Fuel adjustment valve 22 Feedwater pump 23 Check valve 24 Feedwater pipe

Claims (3)

a main body that heats boiler water by burning fuel to generate steam;
a combustion stage control unit that controls the combustion amount to one of a plurality of combustion stages having different combustion amounts;
a water supply control unit that controls the amount of water supplied to the main body so that the boiler water level becomes a reference water level determined based on the combustion stage controlled by the combustion stage control unit;
a conductivity calculation unit that can calculate the conductivity of water according to the boiler water,
The water supply control unit performs an upper water level control to raise the boiler water level to a level higher than a reference water level determined based on the predetermined combustion stage when the combustion amount is controlled to a predetermined amount or less among the plurality of combustion stages continuously for a certain period of time or more and the conductivity calculated by the conductivity calculation unit does not change. The boiler described in claim 1, wherein the water supply control unit cancels the upper water level control when the combustion stage control unit controls the combustion amount to a combustion stage that exceeds the predetermined amount. 3. The boiler according to claim 1, wherein the water supply control unit cancels the upper water level control when the conductivity calculated by the conductivity calculation unit changes.